WO2009090682A1 - Stimulation device - Google Patents

Abstract

An array of multi-functional transducers or multi-functional elements, with arbitrary spatial distribution, includes stimulating elements able to apply electrical, thermal, mechanical chemical, magnetic, or electromagnetic stimulations which, by means of a proper electronic interface, can be determined even by taking into account signals and local parameter obtained by one or more respective electrodes or sensors, with the application of the stimulation and the measurement of signals or local parameters following any desired timing

Description

STIMULATION DEVICE

Description BACKGROUND

1. Field of the invention This invention refers to a stimulation device which contains stimulating elements able to apply stimuli of various types, e.g. electrical, thermal, mechanical or chemical.

Such stimuli can be emitted depending on the measurement of a number of considerations and parameters, such as, for instance, temperatures and electric potentials, chemical compositions and so on, measured, for instance, by sensors, microsensors, or other devices. An example of stimulating device included in the present invention is an array of electrodes implanted in the brain, with the goal to apply electrical and/or thermal stimuli.

Another example can be a system able to apply a desired temperature distribution and a desired voltage distribution to a tissue or other chemical or biological substances, in order to favor chemical or biological processes or in order to permit a fast cellular regeneration, or to a physical substrate, in order to permit the growth of new or improved nanostructures.

2.1 State of the art (technological problems)

Transducers are devices which transduce signals belonging to one energy domain into signals belonging to another energy domain; for instance, a temperature dependent resistor transduces temperature (thermal energy domain) into a resistance (electrical energy domain) [Middelhoeck et al . 2000] .

Transducers which transduce signals from other energy domains into signals in the electrical domain are called sensors; transducers which transduce signals from the electrical domain into other energy domains are called actuators. Sensors and actuators are therefore necessary for interfacing electronic systems with the environment. We will refer to a single device performing many different functions, including at least one (and, eventually, more than one) transduction processes, as to a multi-functional transducer. For instance, figure 3 shows quartz microbalance whose top metal electrode is a multifunctional transducer as it can simultaneously act as temperature sensor, heater, electrode for the resonator, and flow sensor [Falconi et al. 2006]. Clearly, mutli-functional transducers can be extremely important in those applications which require very compact systems (e.g. in vivo medical applications).

Figure 4 shows a planar array of multi-functional transducers.

Voltages can be measured and/or controlled with rather high accuracy and precision; moreover, the voltages of an array of electrodes can also be measured/controlled with high accuracy and precision. For instance, micro-electrode arrays for neuronal tissue cultures [Gross et al. 1985] usually comprise about 60 uniformly distributed, 2-D electrodes with diameters ranging between 10 and 100 micrometers (various application-specific configurations are also available, e.g. 3-D shaped Pt electrodes may penetrate dead cell layers); commercially available interfacing systems allow to measure/control the voltages of these micro-electrodes (i.e. for each electrode the user can decide if he wants to measure the voltage of the electrode or if he wants to apply to that electrode a desired electrical stimulation) so that, for instance, both stimulation and recording of electrical activities of electrogenic cells are possible. The electrode density can be very important for investigating electrophysiological processes with sufficient spatial resolution or for effective stimulations ([Wise et al. 2004]). Clearly, the design of the measurement/control system is more and more complex as the number of elements in the array increases; moreover, the density of electrodes is generally limited by technological considerations (e.g. the number of contacts). These difficulties may be significantly alleviated if "system-on-chip" solutions are adopted, as demonstrated by the recently reported 128x128 [Eversmann et al. 2003] and 256x256 [Lei et al. 2008] CMOS arrays of electrodes. The potential of microelectrode arrays for material science has not yet been sufficiently investigated.

Temperature can also be measured and/or controlled with rather high accuracy and precision. However, in some cases, existing transduction strategies are not sufficiently compact if they must be integrated with other functionalities. Moreover, measuring/controlling the temperatures of an array of elements is not straightforward; this difficulty is, for instance, an obstacle to the comprehension of many sophisticated, temperature dependent processes in cells (apoptosis, thermotaxis, temperature sensing, heat shock proteins,...) and the fabrication of innovative systems. As a first problem, a good thermal insulation between the elements is critical if different temperatures must be independently set (with reasonable amounts of power); for this reason, since typical substrate materials have rather high thermal conductivities, minimizing the substrate thickness (e.g. etching) is necessary; clearly, the thermal conductivity of substances/samples on the substrate can also degrade the thermal insulation. This problem, obviously, is exacerbated by high-density requirements. Moreover, temperature measurement requires to transduce temperature into an electrical quantity; temperature control also requires thermal actuators (heating and/or cooling). Single point temperature control may take advantage of two different devices used as, respectively, temperature sensor and actuator; however, a single device (resistor, transistor,...) can be simultaneously (or quasi-simultaneously) used as a temperature sensor and as an heater; in this case, as in hot-wire anemometers, we have a multi-functional transducer.

Even a single metallic junction can act both as a thermal actuator (Peltier effect) and as a temperature sensor (Seebeck effect) by adopting some form of time multiplexing [Wijngards 2003] or by using appropriate interfacing techniques [Yun et al. 2006]; this approach allows both the temperature measurement and an extremely localized heating/cooling. The localized cooling allowed by Peltier devices can have very important applications (e.g. interrupting epileptic seizures). Clearly, especially for in-vivo medical applications, where high density is a priority, the development of novel, even more compact transducers with high degrees of functionalities to interface with cells and tissues can be crucial.

Remarkable examples include the use of a single metallic junction for performing both electrical stimulation and/or recording, together with high-accuracy, high-precision temperature measurement [Cosman 1990, Webster 1999], as discussed below; even more functional transducers could be important in some cases.

Recently, arrays of temperature controllable microelements have been integrated; in [Shu et al. 2005] it has been shown that a non-uniform temperature distribution can pattern cells on the substrate or accelerate neural development within the heated regions; according to the authors, this was the first investigation on the effects of micrometer-scale temperature fields in cell cultures.

The reported arrays of elements whose temperatures can be independently controlled are characterized by poor temperature accuracy due to the rudimentary interface (the voltage applied to the heaters was adjusted manually); moreover, the elements were rather large and did not have electrical functionalities. Similar considerations apply to [Yang et al. 2004, Cheng et al. 2004, Goncalves et al. 2008]. Though the simultaneous, high-density, high accuracy, high precision measurement/control of both the voltages and temperatures of an array of elements has never been reported, it could have many important applications, both from a theoretical (e.g. insight into fundamental biological processes) and from a practical (e.g. therapeutic procedures) point of view.

Temperature controlled electrodes are widely used in (hot-wire) electrochemistry and allows the selective heating of small volumes of a solution while leaving the "bulk solution" relatively unaffected [Beckmann et al. 1998]; an array of temperature-controllable microelectrodes has also been described [Yang et al. 2004]; moreover, in principle, previously reported arrays of temperature controllable microelements could be somehow modified in order to include electrical functionalities.

However, as a first problem, in many applications both high density and a small number of contacts (except for CMOS solutions) are critical and, therefore, suitable transducers are needed; for instance, if resistors are used for temperature sensing, 4-wires techniques would be necessary if high-accuracy and high-precision are important (particularly because of temperature gradients), thus severely limiting the density. Moreover, the integration of high- accuracy, high-precision circuitry able to measure/control both the temperatures and the voltages of all the elements is also a challenge and requires the combination of high- accuracy, high-precision interfacing techniques [Enz et al. 1996, Falconi et al. 2007] with "high-density" capabilities. Besides, mismatch between different temperature sensing devices must be taken into account and efficient calibration strategies must be adopted.

2.2 State of the art (part II: applications)

As to intracellular measurements, patch-clamp or sharp-electrode techniques routinely allow to measure intracellular electrical activities; however, there is a lack of simple methods for intra-cellular temperature recordings. Systems for applying rapid thermal (heating or cooling) stimuli to cells during patch clamp recording or ion imaging have also been reported [Reid et al. 2001]. Moreover, microtechnology offer great opportunities for ion- channel research [Sigworth et al. 2005] and, in particular, permits the fabrication of integrated patch-clamps. However, existing patch-clamps are not enough functional, with special reference to the absence of sufficient thermal (e.g. high accuracy, high precision temperature recording) and chemical (e.g. high-accuracy, spatio-temporally controlled release of significant proteins and factors) functionalities.

As to extracellular measurements, standard [Gross et al. 1985] and CMOS [Eversmann et al. 2003, Lei et al. 2008] microelectrode arrays routinely allow to measure extracellular electrical activities in cell cultures; however, the high-accuracy, high-precision, high-density measurement of temperature distributions inside cell cultures and tissues is, practically, unexplored. Moreover, drugs can be delivered to the culture or tissue with poor spatio- temporal control. The growth of cells and tissues (e.g. neuro-degeneration, neuro-regeneration, neuroprotection, and neuro-pharmaco-kinetics) is also affected by combinations of chemical, electrical, thermal, mechanical, and electromagnetic stimulations; however, existing in-vitro and in-vivo (e.g. for tissue repair) systems are not enough flexible to allow the efficient generation of arbitrary combinations of these stimulations, with special reference to the generation of high-accuracy, high-precision, distributions of temperatures and voltages and to the localized, spatio-temporal Iy controlled release of drugs or relevant substances.

In order to analyze biosamples (e.g. cells) it is possible to measure the functional response of a cell (Ca2+ transient, membrane ruffling...) to a given stimulus (electrical, chemical,...); existing systems do not allow the application of sufficiently arbitrary stimulations. In needles and micro-needles for injection and in surgical and minimally invasive surgical tools (including implantable tools), various improvements are needed. For instance, in contrast with orally-administered drugs, needles for drug delivery often lead to better drug absorption and do not suffer for enzymatic degradation in the intestine and liver; however, existing needles are painful and unsatisfactory for frequently repeated drug delivery; even if microneedles potentially avoid contacting nerves (painless) and capillaries (bloodless), existing microneedles are not yet completely satisfactory. As an alternative to traditional methods for drug delivery, trans-dermal drug delivery [Prausnitz et al. 2008], beside avoiding interactions with intestine and liver, can be better tolerated by patients and permit a gradual release, eventually with complex release profiles, determined by microcontrollers [Subramony et al. 2006]. On the other hand, the possibility to trans-dermally deliver drugs is very limited because, mainly, of the barrier properties of the outer layer of the skin (stratum corneum); in order to allow to trans-dermally deliver a higher number of drugs, many approaches have been proposed, including iontophoresis, electroporation, ultra-sounds, chemical "enhancers", micro-needles [Prausnitz 2004], thermal ablation,... (different methods can also be combined, as discussed for instance in [Prausnitz et al. 2008] and in [Wang et al. 2005]).

In particular, heat can significantly change skin permeability [Park et al. 2008]. For instance, the local application of heat pulses can result in local thermal ablation (e.g. by using radio- frequency signals of resistive micro-heaters) which can be well tolerated by the patient as the ablation is limited to extremely small regions.

On the other hand, existing systems for trans-dermal drug delivery which take advantage of heat for improving skin permeability (with respect to the drug or substance to be delivered) have limited performance because of the lack of transducers with a sufficient degree of functionalities. Besides, micro-needles for trans-dermal delivery (which, according to the classification in [Prausnitz 2004], take advantage of the approaches "poke with patch", "coat and poke" or "dip and scrape") also have limited performance because of the insufficient thermal functionalities of micro-needles. Existing systems which use electroporation (or electropermeabilization), that is variations of the electrical conductivity and of the permeabilita of the cell membranes due to electrical fields, have limited performance because of the lack of thermal functionalities. Moreover, existing surgical and minimally invasive surgical tools (including implantable tools) are not easy to be positioned, do not automatically recognize the surrounding tissues, can not satisfactorily evaluate the properties of the surrounding tissues, can not satisfactorily release relevant substances to the surrounding tissues. As an additional difficulty, all the required functionalities should be integrated in sufficiently compact instruments.

Existing high density interfaces for neural tissue can only record or apply electrical signals. This insufficient degree of functionalities may limit the therapeutic effectiveness of current deep brain stimulation (DBS) protocols.

Le interfacce esistenti ad alta densita per il tessuto nervoso possono solo registrare o applicare stimoli elettrici. Questo insufficiente grado di funzionalita puό limitare l'efficacia terapeutica degli attuali protocolli di deep brain stimulation (DBS).

In fact, with reference to epilepsy, though Peltier-cooling can block rat hippocampal neurotransmission mechanisms and interrupt epileptic seizures [Yang et al. 2005], existing DBS systems are not able to locally cool the brain; moreover, existing DBS systems do not monitor temperature in proximity of the electrodes, which could also be very important: first, since DBS locally heats the brain [Elwassif et al. 2006, Kim et al. 2007], continuous temperature monitoring could allow the design of more effective DBS protocols. In fact, obviously, the application of electrical stimuli results in local variations of the brain temperature and, though these variations are quite small (less than 0,8⁰C according to the only available model [Elwassif et al. 2006]), many brain functions are extremely sensitive to temperature. It would then be useful to monitor temperature during electrical stimulation in order to maximize the efficiency of the therapy. Besides, temperature monitoring could reduce the risks induced by some diagnostic procedures which can lethally heat the DBS leads. Moreover, DBS leads with temperature sensing capabilities could be easier to be placed. DBS leads allowing the spatio-temporally controlled release of substances would also, obviously, be very important and could improve the effectiveness of this therapy or significantly increase the battery lifetime or the leads durability.

Finally, existing microelectrode arrays do not allow the study of the effects of localized cooling on epileptic seizures, of the effects of thermal stimuli on cell cultures, of the thermal signals generated by the cells. Electrical stimulators for medical applications (e.g. deep brain stimulations, RF lesion generators for pain relief, electrosurgical generators, bladder stimulators, tibial nerve stimulators,...) always induce heating of tissues; in some systems, in order to avoid excessive heating a temperature sensor is used (e.g. RFG-3C RF Lesion Generator available from Radionics, Inc., Burlington), while in other systems (deep brain stimulation, commercially available from Medtronic, Inc., Minneapolis, Minnesota) it would be not easy to add a temperature sensor as the lead must be very compact.

The inclusion of a temperature sensor, as in [Staunton et al. 2005] however results in a more complex fabrication/assembling and/or in larger volume. The thermopile approach adopted in [Brucker et al. 2002] can significantly reduce the number of wires for ablation catheters, as each stimulation site only requires one wire for the electrode two different devices and temperature monitoring of all the stimulation sites only requires two additional wires. However, first, thermal stimulation is not possible; second, the simultaneous, high-accuracy, high-precision measurement of the temperatures of all the electrodes is also not possible (as the thermopile does not allow to distinguish among the temperatures of the different electrodes).

The latter capability would also be important, for instance, if thermo-responsive coatings coat the electrodes and one wants to selectively activate substances release at only one (or some) of the electrodes.

Moreover, high-accuracy, high-precision measurement of all the temperatures of the electrodes could be important for correct positioning of the catheter.

The galvanic cell approach adopted in [Taylor et al. 2001] also allows to control the tissue temperature during ablation; however, the accuracy of the measurement may be insufficient and necessarily involves two electrodes. In many applications, the ability to locally cool the tissue can be very important; for instance, in electrosurgical generators the tissue may be heated to such high temperatures that local or general anaesthesia is necessary [Sluijter et al. 2001]); in other cases heat can produce a high-resistance coagulum that limits current delivery; in other cases, heat can produce undesired tissue damage. In [Cosman 1990, Webster 1999] the same metal used for applying the electrical stimulation is used, in combination with another metal, to form a metallic junction which can be used to sense the temperature; in [Webster 1999] the two wires are, respectively, a wire designed for carrying the large stimulation currents, and a small wire for implementing the temperature sensing metallic junction which is as small as possible in order to result in a compact catheter; when compared with previous catheters using internal, distinct temperature sensors, the important advantages of such a solution include that temperature is measured, in practice, exactly at the electrode, without delay, and in excellent thermal contact with tissue; moreover, the probe can be smaller and cheaper, also because of the reduced number of wires, when compared with traditional strategies for sensing the temperatures of the electrodes; though the approach in [Cosman 1990, Webster 1999] also allows both electrical recording and electrical stimulation by means of the same electrode, it is not enough functional with reference to thermal stimulation (rather than simply recording); in fact, due to the lack of suitable solutions, "global" and slow cooling solutions are generally used and, though the thermoelectric effect [Rittman et al. 2003] has been proposed for avoiding excessive heating in ablation systems, the application of localized, high-accuracy, high-precision, fast thermal stimulations is, in practice, not feasible, despite its potential applications (e.g. the so called brain pace maker has been proposed for interrupting epileptic seizures); for these reasons, novel, multi-functional transducers and novel arrays of multi-functional elements are needed. Finally, for all these systems, the addition of spatio-temporally controlled release of substances could also be very important in some applications.

Skin perfusion evaluation systems [Ozarowski et al. 2002] diagnose the vascular sufficiency of the skin by measuring the thermal properties of the skin, with applications in early detection and/or prevention of localized tissue necrosis (i.e. pressure ulcers, bed sores, decubitus ulcers). Similarly, in the Marstock stimulator the metal probe is heated until the patient feels it warm and, consequently, reverses the flow of the current in the Peltier device, resulting in cooling (and/or viceversa). However, the absence of additional functionalities, with special reference to electrical, chemical, and mechanical functionalities limit the accuracy of these systems and their ability to diagnose other pathologic conditions of the skin. Systems for early detection of the diabetic foot also include a smart insole [Shoureshi et al. 2008] comprising an array of temperature sensors, with the possible inclusion of pressure and humidity sensors, an algorithm which detects the presence of an anomalous temperature profile, and, eventually, can warn the patient. However, the absence of additional functionalities, with special reference to electrical, chemical (other than humidity measurement), and mechanical (other than pressure measurement) functionalities limit the accuracy of the system and its ability to diagnose other pathologic conditions of the skin.

Thermoelectric therapy devices [Deutsch R, 1992] can apply cold or heat and stimulate the skin both electrically and mechanically (massage). However, the absence of additional functionalities, with special reference to chemical functionalities limit the therapeutic potentialities of the system; moreover, the absence of on-demand stimulation protocols, automatically determined by a diagnostic skin analysis, performed by using interfaces with a combination of chemical, thermal, electrical, or mechanical functionalities, also limit the utility of the systems; finally, different devices are needed for electrical (electrode) and thermal stimulation (thermocouple) and these different devices are only used for stimulation, but not for recording.

Temperature and electric fields strongly affect the properties of devices, materials, microsystems, and nanostructures. For instance, the techniques for the growth of self assembled nanostructures require that temperature be within a certain range; as another example, in [Sunden 2006] it has been shown that, though the rest of the system is at room temperature, it is possible to grow, by means of chemical vapor deposition, nanotubes on the top of a heated cantilever. On the other hand, the fabrication of integrated electronic devices, microsystems, nanostructures, and materials is generally done with "passive" substrates, thus limiting the possibility to fabricate integrated electronic devices, microsystems, nanostructures, and materials with better performance and thus forbidding to define patterns without using proper masks.

ABSTRACT OF THE INVENTION

The technical problem solved by the present invention is to allow the fabrication of a stimulation device overcoming the problems described in the description of the state of the art.

This problem is solved by a device containing one or more multi-functional transducers or multi-functional elements, according to the detailed description below, able to measure one or more local parameters and to apply stimulations of various types (electrical, thermal, chemical, mechanical, magnetic, electromagnetic), where the stimulation can, eventually, be determined also taking into account the measured local parameters, and where the detection phase and the stimulation phase are sequential, simultaneous, or are performed according to a desired timing.

In a preferred embodiment of this invention, the device comprises at least one stimulating element containing a component for temperature measurement and for energy transfer.

In a preferred embodiment of this invention, this component is a bi-metallic component able to perform one or more of the following tasks: measure the temperature by taking advantage of the Seebeck effect; perform an energy transfer, with addition or subtraction of heat, by taking advantage of the Peltier effect; measure an electric potential and/or apply an electric potential.

By using this device, it is possible to perform a smart stimulation, which takes into account, in the determination of the stimulations to be applied, of parameters, e.g. temperature of local electric potentials, measured by means of electrodes, sensors, or micro-sensors.

In medicine, these systems will allow to improve the effectiveness of systems for electrical and/or thermal stimulations and, in technology, these systems will permit the fabrication of new materials, microstructures, and nanostructures or of improved materials, microstructures, and nanostructures.

In the following, this invention will be described with reference to some examples of applications and to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a simplified block scheme of a device according to the present invention.

Figure 2 schematically shows systems for measurement and control of temperature distributions according to the present invention.

Figure 3 shows a modified quartz microbalance; the two-terminals top metal may simultaneously act as the electrode, temperature sensor, flow sensor, and heater.

Figure 4 shows an array of elements according to the present invention.

Figure 5 shows the circuit-diagram of the proposed interface for the AB electrode-sensor- heater shown in figure 1.

Figure 6 shows an electro-thermo-couple (basic principle) and a proposed interface. Figure 7 shows a substrate after the deposition of the first material for the fabrication of an array of junctions and of their connections; the contacts and the junctions outside the "active" area (black square) are shown only for some elements.

Figure 8 shows a substrate with an array of junctions and their connections; the contacts and the junctions outside the "active" area (black square) are shown only for some elements; for proper operations, the temperature in the gold area must be uniform and must be accurately set/measured, so that the temperatures of the junctions in the active area can be accurately determined.

Figure 9 schematically shows an array of elements constituting a device according to the present invention.

Figures 10, 11, and 12 show the circuit schemes of additional examples of implementation of stimulation devices according to the present invention.

DETAILED DESCRIPTION

In general, a possible implementation of a device according to the present invention is schematically shown in figure 1.

In the device, the stimulating element is able to detect thermal information (temperature) and/or electrical information (potential difference) and is properly connected to an electronic digital interface, comprising a microcontroller, a microprocessor, a PC which includes a proper software or algorithm, predetermined or modifiable by the user or determined taking into account physical, chemical, or biological parameters measured by the system of by an auxiliary system.

The digital interface, taking into account the input data, will be able to apply a stimulation, for instance heating, cooling, voltage, drug delivery, and so on, and to monitor the effects by means of a proper feedback, regulated by the software. In a first example, the stimulation device is suitable for the application of a deep brain electrical stimulation, where the electrical signals to be applied are automatically determined by taking into account the temperatures of the electrodes, which can be determined by using the electrodes themselves as temperature sensors (or micro-sensors) or by using transducers (or micro-transducers) placed in proximity of the electrodes themselves. In a possible implementation, the electrical stimulations are activated only if the temperatures of the electrodes are below a certain threshold. In another possible implementation, the electrical stimulations are applied only if the electrical and/or thermal signals measured by the system satisfy certain activation criteria.

The electrodes implanted in the brain must, obviously, be extremely small, thus making it difficult the accurate and precise measurement of the temperature of the microelectrode in correspondence of the brain region where the electrical stimulation is applied.

Such function can be performer by taking advantage of the Seebeck effect, i.e. by placing metallic junctions at the points where the temperature must be measured (or very close to these points).

In such manner, it will be possible to fabricate a thermocouple, or a thermopile, where one of the junctions is in the point where the temperature must be measured, and the other junction can be fabricated in a point where the absolute temperature is known, or can be measured, or can be controlled.

Depending on the implementations, the junction between the two metals coincides with the electrode used for the electrical stimulation, or can be very closet o such electrode. It must be pointed out that, by taking advantage of high-accuracy, high-precision techniques, this device allows the analyses of thermal signals in the brain and, more in general, in biological tissues with very high precision and with spatial resolution in the order of micrometers.

A second example is a system for brain electrothermal stimulation, where the electrical and/or thermal stimulation is activated only when the electrical and/or thermal signals measured by the system satisfy certain activation criteria.

In this general definition it is included the systems for the therapy of various neurodegenerative diseases and of epilepsy (epileptic seizures can be interrupted by local cooling), where these systems, as soon as some electrical or thermal signals reveal that treatment is necessary or useful, can activate the electrical and/or thermal stimulation, eventually permitting (simultaneously or sequentially or with any desired timing) the measurement of the temperature and/or of the electrical signals generated by the adjacent tissue.

Beside the above-mentioned Seebeck effect, it is possible to take advantage of the Joule effect, with the use of resistors which can locally transfer a controlled quantity of heat and can be used for the measurement of temperature by inspection of their electrical resistances.

A third example is given by a substrate where the temperature distribution can be controller with high spatial resolution. With reference to figure 2, with A it is labeled an array of 4 "sensor-actuator" couples TN, TS, TW, TE (temperature sensor and heater/cooler), each identified by its own character (N, S, W, E).

Assuming that it is possible to perfectly control the temperature of each "sensor-actuator" couple, figures 2B and 2C show the simulations of temperature distributions on a substrate, and it is obviously possible to use more "sensor-actuator" couples, as schematically shown in figures 2D and 2E.

In this context, it can be convenient to use simple heaters as actuators; though this approach does not permit cooling, it can be very convenient from a technological point of view. The sensor-actuator couplet can be placed in a very accurate way and at distances variable from centimeters (macroscopic systems or substrates constituted by entire wafers) to fractions of micrometers. Etching techniques can reduce the thermal constants to very low values and permit very fast thermal variations. The same type of technique can be applied in solution of in a generic container. In this example, as sensors-actuators it is possible to use transistors fabricated within a semiconductor substrate.

A fourth example is a system similar to that described in the third example, where it is controlled the distribution of the electric potential instead of the distribution of temperature.

A fifth example is a system similar to that described in the fourth example, where both the distributions of temperature and electric potential are simultaneously controlled.

A sixth example is a medical system where the stimulations to be applied are determined by taking into account the signals measured by electrodes, sensors, or microsensors.

In this category are included pacemakers where the temperature of the electrodes is used to determine the electrical stimulation. In other words, the temperatures of the electrodes are measured by means of the electrodes themselves, as the electrodes are made of a junction of two different metals, or by means of a temperature sensor very close to the electrode.

In this category it is included the automatic systems for performing injections with needles or micro-needles where mechanical (insertion of the needle) and/or chemical (drug delivery) and/or thermal (heating/cooling) stimulations are optimized depending on the signals measured by electrodes, sensors, or microsensors connected to the needles or micro-needles themselves, such as temperature, electric potential, chemical or biochemical parameters. For instance, the measurement of temperature and the heating/cooling can be performed by integrating in the needles or micro-needles the junction of two different metals and taking advantage of the Seebeck (temperature measurement) and/or Peltier (heating/cooling) effects or by means of a temperature sensor and/or thermal actuator in good thermal contact with the needle of micro-needle.

A seventh example is a smart incubator with the application of electrical thermal, mechanical, or chemical stimulations for a faster cellular growth and for neuroregeneration where the stimulations take into account temperatures, electrical potentials and other local parameters measured by means of electrodes, sensors, or microsensors. A possible implementation includes a smart incubator able to generate a desired distribution of temperature and electric potential, dynamically controllable, with the goal to enable a faster cellular regeneration.

In the above described examples and in the next examples, it will be described: new multifunctional transducers (i.e. devices able to perform two or more functions, including at least one, and eventually more than one, transduction processes), new arrays of multi-functional elements (i.e. arrays of elements, each element performing two or more functions, including one, and eventually more than one, transduction processes), and their applications, including electronic circuits for interfacing the described transducers and multi-functional elements.

In the following, the expression "array" must be interpreted in the broadest sense, as an ordered set of elements (i.e. not limited to the simple planar array shown in figure 4). An array of elements can, in fact, include elements on different planes (3D array), can have nonuniform spatial distributions for the elements, can be made of two or more different types of elements, each element with its own spatial distribution.

With reference to figure 3, showing a two-terminal metal used as temperature sensor, heater, flow sensor, and electrode, we observe that a two-terminal resistor, made of any material, can be used as resistive temperature sensor, resistive heater, thermal resistance sensor, and electrode for the application or measurement of electrical voltages. This multi-functional transducer will be referred to as electro-thermo-resistor.

If an electro-thermo-resistor is in good thermal contact with a thermo-responsive polymer or with any type of material which, in response to a suitable thermal stimulation or to a suitable electrical stimulation, releases proteins, trophic factors, or other relevant substances, this multi-functional device will be referred to as chemo-electro-thermo-resistor. For instance, heating-resistors used in ink-jets can be seen as a rudimentary chemo-electro- thermo-resistors; however, in comparison with those heating-resistors, more functional chemo-electro-thermo-resistors may have higher electrical, thermal, or chemical functionalities (e.g. recording electrical signals or applying electrical stimulations). For both electro-thermo-resistors and chemo-electro-thermo-resistors, the two-terminal resistor material can be fabricated in many other geometrical configurations (i.e. with different layouts), can be fabricated on different substrates (i.e. not only on a quartz microbalance), and can be in physical contact with different types of materials.

These transducers are not only useful for measuring the speed of a flow, as in [Falconi et al. 2006], but can be used to measure the thermal resistance between the transducer and the environment; this functionality can be important for monitoring, for instance, the properties of materials during various fabrication procedures, as described below.

The electrical functionalities are not restricted to providing the electrode for a resonator, as in [Falconi et al. 2006], but can also be used for many other purposes, including electrical stimulation of tissues, recording of the electrical activities of electrogenic cells, deflection of ions during some ion deposition techniques, and others, as described below. Electro-thermo- resistors with the above described additional functionalities (when compared with [Falconi et al. 2006] and chemo-electro-thermo-resistors performing electrical recording and/or stimulation are objects of this invention. With reference to the possible application of electrical stimulation, we also describe a novel electronic interface shown in figure 5, which is also an object of the present invention.

In the interface shown in figure 5 the resistor R_AB is the electrical model for the electro- thermo-resistor or chemo-electro-thermo-resistor, of which the modified quartz microbalance shown in figure 3 [Falconi et al. 2006] is only one possible implementation. As in the previously reported correspondent interface [Falconi et al. 2006], the feedback loop equates the ratios R/R₂ and R/R_AB and the D flip flop avoids stability issues. In the interface shown in figure 5, CH clock controls the chopper switches (which enable the straight connections during one phase and the cross connections during the other phase) so that the average current, in a given direction, through the resistor R_AB is zero and, therefore, at low frequency, ideally, the voltage is constant along all the resistor AB (this property may be important, for instance, for applications in tissue stimulation and material sciences if the stimulated tissues/materials only respond to low frequency electrical fields). Eventually, some dummy switches can be added in series with the resistor R₂ in order to compensate the parasitic resistances of the chopper switches, as obvious for the skilled in the art.

Second, even during heating, the average current, in a given direction, through R_AB is zero, thus allowing higher current densities without degradation (e.g. electromigration). Various methods can be adopted for generating a proper CH clock signal, including a simple clock signal or, more accurately, using two auxiliary 2-counters (one for the heating cycles and one for the non-heating cycles), where for each heating or non-heating cycle the correspondent counter is increased.

The proposed interface, shown in figure 5, which is an object of this invention may be important, for instance, for applications in tissue stimulation and material sciences if the stimulated areas only respond to low frequency electrical fields.

Clearly, the supply voltages for the comparator and the flip-flop are v_OD and v_ss, i.e. the voltage V_AB._B sets the reference potential for the interface. As described in [Falconi et al. 2006], the resistance R_AUX allows both a reliable start up and a reliable comparison (between the input voltages of the comparator) when M₀ is off.

However, an important trade-off exists: on one hand a non-zero current will flow through the top electrode even when M₀ is off and no heating is desired; in order to keep this current small R_Aux must be enough large; on the other hand, when M₀ is off, an accurate comparison requires a small R_AUX- If very high accuracy is important, this trade-off may be totally eliminated by using two different resistors for the temperature sensor and the heater; the temperature sensor will then be interfaced with standard techniques known to those skilled in the art.

Figure 6 shows another multi-functional transducer, which will be referred to as electro- thermo-couple, which is an object of the present invention apart its less functional, previously known, implementations ([Cosman 1990, Webster 1999], see later for a discussion).

Figure 6 also shows a possible electronic interface for an electro-thermo-couple, which is also an object of the present invention; M₁ and M₂ represent different metals, whileas M₃ is an arbitrary metal, corresponding to the wires of the circuit. The dotted boxes represent regions at the same temperature T_JA, T_JB e T_x (in practice, often both the junction B and the junctions C will generally be at the same temperature). The multi-functional transducer is in contact with the environment at the junction A, which can also perform electrical activities (voltage measurement, as explicitly shown in figure 6, by means of the instrumentation amplifier IAi and/or voltage control by means of a driving circuit to be connected to the DRIVE node). The instrumentation amplifier IA₂ amplifies the Seebeck voltage which is related to the difference between the temperatures of the junctions A and B. The switched capacitor equivalent of a resistor (i.e. the 4 switches connected to the flying capacitor C₀) enables heating/cooling (Peltier effect). The switched capacitor interface easily allows to control heating/cooling without the need to bias the thermocouple, which would be incompatible with recording of electrical activities of, for instance, electrogenic cells or tissues; other techniques well known by the skilled in the art can be used for cooling/heating the junction A.

If needed, before connecting the pre-charged capacitor Co to the electro-thermo-couple, the switch connected to the BIAS node can pre-bias the top armature of the capacitor Co in order to minimize the current iiuij which is injected into the environment in electrical contact with the junction A because of the switched capacitor circuit which should, ideally, only activate the Peltier effect (the junction A, acting as the electrode, is the single point of the electro- thermo-couple in electrical contact with the environment).

In a preferred implementation, the pre-biasing voltage is generated by an auxiliary instrumentation amplifier having the same input voltages as IAi.

In another preferred implementation the pre-biasing voltage is generated by a voltage buffer having the same input as the positive input terminal of IA₁.

In both these preferred implementations, in practice, the Thevenin voltage seen by the electrode is used for bootstrapping the impedance seen by the electrode A.

In another preferred implementation, the pre-biasing voltage is generated by a digital to analogical converter driven by a digital system containing a look-up table obtained in calibration, in order to apply, for a measured output of IA₁, the voltage which minimizes the error current injected into the environment in electrical contact with the junction A due to the switched capacitor circuit which should, ideally, only activate the Peltier effect.

Other electronic interfaces are possible. In [Cosman 1990, Webster 1999] a single metallic junction has been used as a multi-functional transducer which, according to the proposed nomenclature, is an electro-thermo-couple as it can perform electrical activities (stimulation and/or recording) together with high-accuracy, high-precision temperature measurement; however, even those multi-functional transducers did not allow thermal stimulation, which is also possible with the proposed electro-thermo-couple, as described above. Additionally, since the spatio-temporally controlled release of substances could also be very important in some applications, we suggest that if an electro-thermo-couple is in good thermal contact with a thermo-responsive polymer or any type of material which, in response to a suitable thermal stimulation or to a suitable electrical stimulation, releases proteins, trophic factors, or other relevant substances, the multi-functional device will be referred to as chemo- electro-thermo-couple, with potential applications in, for instance, chemo-electro-thermal stimulation of tissues or in material sciences.

With reference to figure 6, it is clear that other electronic interfaces can be designed, as known by those skilled in the art. ****

In the following, we refer to an element of an array as a multi-functional element if the element of the array performs two or more different functions, including at least one, and eventually more than one, transduction process.

For instance, standard microelectrode arrays [Gross et al. 1985] (currently commercially available, e.g. Multichannel Systems) and CMOS microelectrode arrays are arrays of elements.

According to the previous definition, each element in an array of multi-functional elements may be constituted by a single or by more devices. As an example, which is also an object of this invention, an array of elements which can contemporarily measure the temperature distribution and the voltage distribution on a substrate may be fabricated in different manner; for instance, it could be constituted by an array of electro-thermo-couples (i.e. each element is constituted by a single device, i.e. by one electro-thermo-couple) or it could be constituted by an array of multi-functional elements, being each element constituted by a temperature sensing device (e.g. a temperature dependent resistor) and by a distinct electrode (for measuring the electrical activity).

It is another object of the present invention an array of elements where for some or all the elements it is possible to measure their temperatures and for some or all the elements it is possible to measure their voltages and where, eventually, the groups of elements subject to a certain operation can be dynamically changed. A similar array where some or all the elements of the array can also release on-demand proteins or significant substances is another object of the present invention. As another object of the present invention, similar arrays may also be exposed to proper combinations of electromagnetic (e.g. taking advantage of lasers, leds, antennas,...) and mechanical stimulations (e.g. taking advantage of ultra-sounds, high intensity focused ultra-sounds, vibrations, rotations,...). In all cases, each element can be constituted by a single device or by more devices.

It is another object of the present invention an array of elements where for some or all the elements it is possible to measure their temperatures and for some or all the elements it is possible to set their voltages to desired values and where, eventually, the groups of elements subject to a certain operation can be dynamically changed.

A similar array where some or all the elements of the array can also release on-demand proteins or significant substances is another object of the present invention. The above referred arrays of multi-functional elements for cell cultures, electrogenic cell cultures, neuronal cell cultures, lab-on-chip, tissue engineering, pharmacology, analysis of biological samples, material science, and more, constitute other objects of the present invention. In all cases, each element can be constituted by a single device or by more devices. The above described arrays may provide insight into fundamental biological processes and/or have important practical applications: though many cells (e.g. electrogenic cells) are very sensitive to temperature, the simultaneous measurement of both the extracellular electrical activity and temperature distribution in cell cultures is not currently possible (though extracellular thermal signals can be small and can be further attenuated by the non- ideal thermal contact between the cell and the temperature sensor, high-accuracy, high- resolution temperature measurement techniques are available).

Localized temperature variations can be important for the study of heat-schock-proteins (HSP) at cellular level; the combination of thermoresponsive polymers and of thermal stimulations can allow the spatio-temporally controlled release of proteins or trophic factors or relevant substances with high spatial resolution (e.g. for tissue engineering); stem cells could be affected by thermal and/or electrical and/or chemical stimulations; thermal osmosis [Spanner 1954] has not yet been satisfactorily investigated despite its potentially critical role (e.g. for photobiomodulation); smart systems able to simultaneously apply controlled (thermal, electrical, mechanical, chemical,...) stimulations and to record appropriate (electrical, optical,...) signals could improve our ability to perform low cost, on chip analysis of biological samples, could affect the drug absorption properties, could improve our tissue engineering capabilities; in-vitro study of epilepsy (mechanisms and therapy). Said arrays may also allow a better understanding of various mechanisms (neuro- degeneration, neuro-regeneration, neuro-protection, and neuro-pharmaco-kinetics) and an improved ability to facilitate tissue growth or tissue repair by means of more flexible combinations of stimuli. In particular, other objects of this inventions are systems for the application of thermal stimuli, eventually in combination with electrical, magnetic, mechanical, and chemical stimulations (including the release of drugs or other relevant substances), in order to modify the properties of cells (in particular stem cells), both in cell cultures, and in living beings and, in particular, within the human body. In particular, it is an object of this invention a device able to contain a cell culture, containing, for instance, stem cell cultures, and to apply proper thermal stimulations in order to keep the entire culture at an almost constant temperature and to dynamically change the temperature according to a certain protocol, eventually, but not necessarily, determined even by means of signals measured with sensors or other systems, e.g. microscopes. In particular, it is another object of this invention a device able to contain a cell culture, containing for instance stem cells, and to apply a non uniform temperature distribution to the cell culture and to dynamically change the temperature distribution according to a certain protocol, eventually, but not necessarily, determined even by means of signals measured with sensors or other systems, e.g. microscopes. For cell cultures the thermal stimulations can be applied by taking advantage of proper transducers (bipolar transistor, resistors, thermocouples,...) whose temperatures can be accurately controlled and which are close to the cell or cells of interest, or even by placing (eventually with use of microscopes or other instruments for cells monitoring) structures or microstructures whose temperatures can be accurately set and also by means of the application of electromagnetic or acoustic stimulations.

The applications of interest include tissue engineering, analysis of cell cultures and of various temperature dependent mechanisms, pharmacology.

Within the human body, the thermal stimulations can be applied by means of implantable microsystems or even by means of wireless nanoheaters (e.g. similar to gold nanoshells for thermal ablation of tumors). The applications also include the diagnosis and therapy of diseases.

Other objects of the present invention are systems (to be used for the fabrication of devices, materials, microsystems, and nanostructures) which take advantage of "active" substrates, able to generate a desired distribution of the electrical potential on the substrate and/or a desired distribution of temperature on the substrate, in order to modify the properties of what is fabricated on the substrate, where transducers can be fabricated as previously described (e.g. by means of electro-thermo-resistors) or are generic transducers or electrodes (for instance, a single pnp transistor can, in CMOS systems, be particularly advantageous for the measurement of temperature [Bakker 2000, Falconi et al. 2008]).

Obviously, the distributions of electric potential and/or temperature can be dynamically changed in order to dynamically change the growth conditions, thus permitting the formation of new structures.

In particular, arrays of multi-functional elements can be used in material science and in the deposition of materials for the fabrication of new materials, new devices, new nanostructures or for mask-free patterning procedures which can, eventually, be combined with traditional fabrication procedures, even with masks. Many different substrates can be used, depending on the final application.

These systems for material science are also objects of this invention. In a preferred implementation, the multi-functional elements are used for the growth of materials; in another preferred implementation, these systems are used for the characterization of materials after the growth.

In another preferred implementation, these systems are used both for the growth and for the characterization of materials, including a growth which is, at least partially, controlled by signals obtained with a simultaneous or preceding characterization obtained by means of the multi-functional elements, eventually also in combination with other characterization techniques.

Obviously, other standard techniques (lithography, etching, micromachining, thin film deposition,...) for the growth and/or characterization of materials can be used in any desired combination with the proposed methodology, both sequentially or simultaneously or with any desired timing.

In fact, if the voltages of all the electrodes can be independently set by an interface (external or on-chip) which can, in a preferred implementation, be arbitrarily programmed (e.g. by a user friendly software or by a memory), the properties of the grown materials or structures can be modified.

For instance, in all the techniques which use ions sent toward the substrate (e.g. ionic implantation, pulsed laser deposition,...), the application of proper electric fields can deflect ions, so that desired patterns can be created without masks or so that the properties of the patterns can be modified if this approach is used in combination with masks.

Moreover, electrodes external to the substrate can also be used, in combination with the electrodes on the substrate, in order to define the desired patters. Similarly, the applications of electric fields can facilitate or slow down various growth reactions (e.g. vapor-liquid-solid processes, VLS, or vapor-solid, VS). Similarly, the application of temperature gradients dynamically controlled can permit, in combination with standard techniques, the creation of desired doping profiles for the fabrication of improved electronic devices or for the improvement of the characteristics of the fabricated devices; similarly, the application of dynamically controlled temperature gradients can permit the growth of nanostructures only in the desired regions or the growth of new types of nanostructures. Similarly, the simultaneous application of dynamically controlled, proper electric fields and temperature gradients can permit the fabrication of improved electronic devices or the growth of new types of nanostructures. For instance, such substrates could be used in many standard fabrication processes (e.g. ion implantation, pulsed-laser-deposition,...) or in other processes for the growth of new materials, meta-materials, and nanostructures with controlled properties.

The elements of the proposed arrays would, according to the previous definitions, be multifunctional elements, as among their functions we may identify transduction functions: in fact, each element transduces an electrical signal, its voltage, into, for instance, thermal signals (e.g. the electrode voltage modifies the fabricated structures/materials and therefore, in general, affects the thermal resistance between different points) or into, as another example, mechanical signals (e.g. the electrode voltage modifies the fabricated structures/materials and therefore, in general, affects some mechanical signals). As an additional possibility, which is also an object of the proposed invention, each element of the array could be a multi-functional transducer. In particular, beside electrical stimulation, it could be possible, by using suitable transducers and electronic interfaces, to measure electrical and/or thermal signals at some selected or all the electrodes (recording) in order to on-line monitor the properties of the grown materials/structures, with the possibility to accordingly modify some fabrication parameter (including the voltages of the electrodes).

As an additional possibility, which is also an object of this invention, it is also possible, by using suitable transducers and electronic interfaces, to apply thermal stimulations and also thermally triggered chemical stimulations. For instance, electro-thermo-resistors, electro-thermo-couples, chemo-electro-thermo- resistors, chemo-electro-thermo-couples could be elements of the array; the array can be made of uniformly distributed, identical multi-functional elements or can be made of any combination of arbitrarily distributed multi-functional elements. The multi-functional elements may all belong to the same "layer" or may be fabricated on different layers of a substrate.

The separate or combined application of electric fields, thermal stimulation, and release of suitable substances can modify the grown structures/materials in a controllable manner. In principle, the proposed arrays of multi-functional transducers and suitable electronic interfaces allow the high-accuracy, high-precision, programmable application of chemical, thermal, and electrical stimulations during material/structures growth, with the additional possibility to on-line measure thermal and electrical signals which can be used as feedback signals to control the properties of the grown materials/structures.

As an object of the present invention, the proposed arrays of multi-functional elements may allow low-cost mask-free patterning and the growth of novel types of structures/materials. As another object of the present invention, the proposed arrays of multi-functional elements may also be combined with traditional masks for modifying the properties of the grown materials/structures as well as for combining both the methodologies for an improved or substantially different control on the geometries of the grown material/structures. In particular, the proposed invention may find application in nanotechnology and in the fabrication of new types of materials, including new types of meta-materials.

It should be noted that the proposed invention may also be used for the low-cost mask-free patterning of appropriate materials and structures; in fact, the cost of each array of multifunctional elements can be very low (mass-production) and a single interface can drive many substrates (sequentially and/or in parallel).

As obvious to those skilled in the art, the electronic interface for driving the array of multifunctional elements may be realized with different technological strategies, including but not limited to full integration on the same substrate, full integration on a separate substrate, partial integration on the same or different substrate and use of discrete devices. Obviously, for high-density and high number of elements, it is convenient to integrate, at least, all the analog circuits, including analog-to-digital converters and digital-to-analog converters, on chip (similar to what happens for traditional microelectrode arrays, [Eversmann et al. 2003, Lei et al. 2008]), with the chip eventually connected to an external, programmable, digital interface.

On the other hand, if all the electronics devices are external to the substrate containing the array of multi-functional elements, there will be severe limits on the number of contacts, so that, if an high number of elements is desired, all other things being equal (e.g. for a given degree of functionality), it is better to choose the multi-functional element which requires the minimum number of connections from the substrate containing the array to external (to the substrate) devices. In a preferred implementation, the complete interface comprises a PC and a user-friendly software, so that the user can easily program the various stimulations and can also specify how those stimulations should be changed depending on the various measurements.

Other objects of this invention include "active" substrates containing transducers or microsystems which can be activated during the fabrication of materials or devices or microsystems or nanostructures on the substrate. For instance, it is an object of this invention a substrate with a mechanical actuator or any set of mechanical actuators, even different and even non-uniformly distributed, integrated on the same substrate or on other substrates or anyway anchored to other structures, where the mechanical actuators dynamically permit or forbid, depending on proper control signals, the exposition of parts of the substrate, constituting a sort of "active mask". As another example, it i san object of this invention, an "active" substrate containing a set of electrodes and/or multi-functional transducers for the control of the distributions of temperature and of electrical potential along the substrate and a set of mechanical actuators (e.g. piezoelectric actuators,...) which dynamically permit or forbid, depending on proper control signals, the exposition of parts of different parts of the substrate or anyway can modify the properties of what is fabricated on the substrate.

As another example, other objects of this invention are "active" substrates, as above described, used in combination with traditional techniques (in particular, also in combination with standard lithographic techniques and masks) in order to fabricated electronic devices, microsystems, materials, and nanostructures. With reference to the active substrates here proposed, it is evident that, for a given functionality of the active substrate, the structures which perform this functionality, must properly operate until the last step of the fabrication process which require that particular functionality. For instance, if the electronic circuits for the control of the temperature distribution on the substrate are completely integrated on the active substrate, the temperatures of the part of the active substrate containing these electronic circuits must be such that proper operation is guaranteed until, at least, the last step of the fabrication procedure where it is desired to control the temperature distribution along the substrate.

Micromachining (etching) can significantly reduce the thermal coupling between the parts of the active substrate which must be heated up to high temperatures and the parts of the substrate which contain structures which can not tolerate too high temperatures (e.g. control electronics). Moreover, the "active substrate" can be constituted by more (mechanically and electrically) inter-connected substrates, where the different substrates, depending on the needs, can be fabricated with different technologies.

It must be observed that an enitre substrate, for instance silicon substrate, containing integrated circuits for the control electronics can be used as active substrate or, alternatively, the substrate can be divided into more parts, each implementing an autonomous active substrate.

It is another object of this invention an electrical stimulator using a single electro-thermocouple or a single electro-thermo-resistor for temperature measurement and electrical stimulation.

In [Cosman 1990, Webster 1999] the same metal used for applying the electrical stimulation is used, in combination with another metal, to form a metallic junction which can be used to sense the temperature; a similar solution has not been applied in deep brain stimulation systems.

It is another object of the present invention an electrical stimulator using an array of electro- thermo-couples and/or an array of electro-thermo-resistors, where some or all the multi- functional transducers of the array can perform (simultaneously, sequentially, or with any desired timing) temperature measurement and electrical stimulation.

The present invention can, for instance, be used for fabricating temperature-aware deep brain stimulation systems where the electrical stimulation is adapted depending on the temperatures of the different electrodes; clearly, a more efficient electrical stimulation can have various benefits (more benefits and/or less discomfort for the patient, increased battery lifetime, reduced degradation of the quality of the electrical contact between the electrodes and the surrounding neural tissue...). Temperature monitoring may also reduce the risks induced by some diagnostic procedures which can lethally heat the DBS leads or may help in positioning the DBS leads during implantation.

Similar benefits can also be obtained for other (than DBS) electrical stimulators using the same multi-functional transducers, which are also objects of this invention.

It is another object of the present invention an electrical stimulator using a single electro- thermo-couple or a single electro-thermo-resistor for temperature measurement, electrical stimulation, and thermal stimulation.

It is another object of the present invention an electrical stimulator using an array of electro- thermo-couples and/or an array of electro-thermo-resistors, where some or all the multifunctional transducers of the array can perform (simultaneously, sequentially, or with any desired timing) temperature measurement, electrical stimulation, and thermal stimulation.

The present invention can therefore be used for fabricating electro-thermal deep brain stimulation systems where electro-thermo-couples can locally cool, by means of Peltier cooling, specific regions of the brain in order to interrupt epileptic seizures, in order to deliver a more effective deep brain electrical stimulation, or in order to impede excessive heating of the brain.

Similar benefits can also be obtained for fabricating novel, innovative, different (i.e. other than DBS) electrical stimulators using the same multi-functional transducers, which are also objects of this invention.

As an example of implementation, the arrays of electro-thermo-couples or electro-thermo- resistors needed for temperature-aware or electro-thermal deep brain stimulation can be fabricated using an approach similar to [Cheung KC et al. 2007].

At least two different metals must be used in case of electro-thermo-couples; in this case, high performance thermoelectric materials can also be deposited on flexible polyimide substrate by co-evaporation [Goncalves LM et al. 2007] or by using other techniques.

Arrays of multi-functional elements can also find other important biological and medical applications. As an example, chemo-electro-thermo-resistors, chemo-electro-thermo-couples, or their arrays could be very convenient devices for the thermally-triggered, spatio- temporally controlled release of drugs, proteins, and relevant substances [Huber et al. 2003]. In fact, the addition of chemical functionalities could be important for many electrical stimulators for in-vivo medical applications; since in those applications compactness is critical, multi-functional transducers with an high degree of functionalities are required.

It is an object of the present invention an electrical stimulator using a single chemo-electro- thermo-couple or a single chemo-electro-thermo-resistor for temperature measurement, electrical stimulation, and triggered release of relevant substances by means of an electrically or thermally responsive coating.

It is another object of the present invention an electrical stimulator which has an array of chemo-electro-thermo-couples and/or an array of chemo-electro-thermo-resistors, where some or all the multi-functional transducers of the array can perform (simultaneously, sequentially, or with any desired timing) temperature measurement, electrical stimulation, and triggered release of relevant substances by means of an electrically or thermally responsive coating.

As a possible example of application of this invention, since the quality of the electrical contact between microelectrode arrays implanted in the brain and the surrounding neural tissue is generally subject to degradation, the spatio-temporal Iy controlled release of relevant substances may help to keep good electrical contacts between the microelectrode arrays and the surrounding neural tissues.

Such a system could be, for instance, important for deep brain stimulation and for different brain-computer interfaces.

It is also an object of the present invention a DBS system using chemo-electro-thermo- resistors or chemo-electro-thermo-couples so that, beside electrical stimulation, electrical recording, temperature monitoring, and, eventually, thermal stimulation, the multi-functional transducers also allow the spatio-temporally controlled release of substances in order to, for instance, improve the effectiveness of this therapy or significantly increase the battery lifetime or the leads durability or the quality of the electrical contact between the electrode and the surrounding neural tissue. Similar benefits can also be obtained for innovative, different (i.e. other than DBS) electrical stimulators using the same multi-functional transducers, which are also objects of this invention. It is another object of the present invention a thermo-patch-clamp device made of a patch- clamp and of a temperature sensor and/or of a thermal actuator in order to allow intracellular temperature measurement and/or to apply extremely fast, localized thermal stimuli (as the thermal stimuli in [Reid et al. 2001] may not be enough fast nor have sufficiently high spatial resolution).

As a preferred implementation, a patch-clamp will contain a junction between two materials which will be part of a thermocouple, thus allowing high-precision, high-accuracy intra- cellular temperature measurements and/or thermal stimulation (obviously, for absolute temperature measurement, the temperature of the auxiliary junction of the thermocouple must be accurately set or measured).

It is another object of the present invention an array of the above described thermo-patch- clamps which, in a preferred implementation, can be fabricated using microtechnology on a single substrate and may have an on-chip or off-chip electronic interface.

It is another object of the present invention a chemo-thermo-patch-clamp which, beside the addition of a temperature sensor and/or of a thermal actuator also allows the spatio- temporally controlled release of proteins and significant substances by taking advantage of coatings which can be thermally or electrically triggered. Other objects of this invention include arrays of chemical sensors integrated on one or more substrates where the dynamic control of the distributions of temperature and/or electric potential allows to obtain information on the chemical environment.

Other objects of the present invention include a needle, a micro-needle, an array of needles, and an array of micro-needles for drug delivery, surgical tools and minimally invasive surgical tools using multi-functional transducers or arrays of multi-functional elements in order to perform one or more of the following functionalities (simultaneously, sequentially, or with any desired timing): measure the temperatures of surrounding tissues; apply thermal stimulations; measure the electrical signals generated by the surrounding tissues; apply electrical stimulations; release relevant substances (in the case of needles and micro-needles, these additional substances may be released before the drug delivery and/or during the drug delivery and/or after the drug delivery).

In fact, in needles and micro-needles for drug delivery and in surgical and minimally invasive surgical tools the addition of a temperature sensor and/or the ability to heat/cool the tissue, could be advantageous for various reasons. First, recording the temperature and/or other thermal signals (e.g. thermal impedance) and/or other electrical signals can help to evaluate the distance between the needle/tool and the body or a specific tissue or the position of the needle/tool with respect to regions of the body of interest, thus allowing a correct placement and/or a correct timing of the drug delivery. Eventually, the temperature and/or other thermal signals (e.g. thermal impedance) and/or other electrical signals measured by the needle of by the tool could be elaborated by a digital system and compared with other signals previously measured or also in a previous calibration phase in order to compensate the normal variability of temperature of the human body. Second, the thermal actuation capability could help to reduce the patient discomfort and/or locally increase/reduce blood flow or drug adsorption or facilitate cicatrisation. Third, by measuring the temperature variations induced by a known heating/cooling power, the thermal resistance between the needle/tool can be measured, thus helping, in principle, to discriminate between different tissues or to evaluate the properties of tissues. Moreover, the proposed needles/tools could also apply electrical stimulations and/or record signals and/or measure the impedance seen by the needle/tool.

The addition of spatio-temporal Iy controlled release of substances could also be very important in particular applications. By using multi-functional transducers or arrays of multifunctional elements, the proposed needles/tools can obtain an high degree of functionalities and, at the same time, can be sufficiently compact.

As a preferred implementation, a needle/tool can be designed in such a way that the tip is constituted by two different metals, so that its temperature can be measured with high- accuracy and high-precision.

As another preferred implementation, the metallic junction at the tip of the needle/tool can also allow electrical stimulation. As another preferred implementation, the metallic junction at the tip of the needle/tool can also allow the measurement of electrical signals. Moreover, the metallic junction at the tip of the needle/tool can also allow the application of thermal stimulations and can also allow the delivery of relevant substances.

Other preferred implementations include needles/tools which use a metallic junction or an array of metallic junctions or a resistor or an array of resistors in order to perform any combination of the following functionalities (simultaneously, sequentially, or with any desired timing): the temperatures of the metallic junctions/resistors can be measured with high-accuracy and high-precision; the metallic junction/resistor can be used for electrical stimulation; the metallic junctions/resistors can be used for measuring electrical signals (including voltages generated by the tissues or impedances of the surroundings); the metallic junctions/resistors can apply thermal stimulations; the metallic junctions/resistors, in good thermal contact with a thermo-responsive coating, can trigger the delivery of relevant substances; the metallic junctions/resistors can be utilized for fabricating micro-needles for trans-dermal drug delivery with thermal functionalities, to be integrated with traditional approaches (according to the classification given in [Prausnitz 2004] "poke with patch", "coat and poke" o "dip and scrape"); systems with micro-needles with thermal functionalities (measurement of the skin temperature as control signal and/or application of thermal stimulations) for trans-dermal drug delivery are objects of this invention, if the thermal functionalities are performed by miniaturized multi-functional transducers in direct contact with the skin at the moment of drug delivery, or if the thermal functionalities are performed by transducers whose thermal contact with the skin is guaranteed by the microneedles themselves.

Other objects of this invention are systems with micro-needles for trans-dermal drug delivery with the micro-needles having thermal functionalities, with these thermal functionalities combined with other methods for the release of drugs or substances (iontophoresis, electroporation, ultrasounds, chemical "enhancers", thermal ablation by means of radio- frequency signals or ohmic heaters or by means of water vapor or by other methods).

In particular, objects of this invention are systems for trans-dermal drug delivery assisted by thermal ablation with the thermal functionalities of the micro-needles limited to the measurement of the temperature in order to permit the application of thermal ablation controlled by means of the skin temperature measurements performed by transducers integrated in the micro-needle or in good thermal contact with the micro-needle.

As an example, the same metallic junction/resistor (integrated in the micro-needle or in good thermal contact with the skin by means of the micro-needle) used for skin temperature measurement and/or for the application of thermal stimuli or also additional electrodes can allow the simultaneous or sequential application of electrical stimuli (iontophoresis and/or

Electroporation) and of thermal stimuli in order to improve the skin permeability. The gradual release can be obtained by driving the multi-functional transducers with an electronic interface connected to a microcontroller or to another appropriate electronic system.

Other objects of this invention are systems for trans-dermal drug delivery which take advantage of multi-functional transducers of the electro-thermo-resistor type or electro- thermo-couple in order to improve the skin permeability by means of the simultaneous and/or sequential application of temperature and/or electrical pulses, by taking advantage of the dependence of skin permeability on temperature (e.g. [Park 2008]) and on electric fields (electroporation) and/or the action of injection associated to temperature gradients and to electric fields (iontophoresis). Additional objects of this invention are, in particular, thermo-electro-poration systems which take advantage of the simultaneous application of thermal and electrical stimuli in order to improve the permeability of skin or cell membranes.

Additional objects of this invention are, in particular, arrays of multi-functional transducers made on flexible substrates that can be applied on the body and can apply stimulations of various types (electrical, thermal, magnetic, electromagnetic, mechanical or chemical) for applications of rehabilitation, training, exercise, healing of tissues, animals, or humans.

For the sake of clarity, we here describe some possible implementations of some of the objects of the present invention. Other implementations which will be obvious to those skilled in the art are also included as objects of the present invention.

For simplicity, the figures 7 and 8 illustrating arrays of multi-functional elements refer to 4x4 arrays; it is obvious that any dimension of the array is possible.

For all the arrays we identify an "active" area (black square in figures 7 and 8). With reference to the "active" area, the substrate (e.g. a glass substrate) can be etched in order to improve the thermal insulation between different elements of the array. With reference to the areas of the contacts and of the junctions outside the "active" area (gray area in figure 8), the substrate should not be etched and, if necessary, various methods can be used for improving the thermal contact (e.g. depositing in this area a thick layer of electrically insulating, thermally conductive material or by using appropriate thermally conductive, electrically insulating paste or by depositing a thin layer of an electrical insulator and covering the region with high-thermal-conductivity paste, etc.).

The temperatures of the auxiliary junctions (all contained in the gold area shown in figure 6) must be, ideally, identical; this temperature of the auxiliary junctions must be measured or set with high accuracy and high precision, so that the temperatures of the junctions in the active area can also be measured and/or set with high accuracy and high precision. For this purpose various methods, well known to those skilled in the art, can be used. However, as preferred implementation, a high accuracy high precision temperature sensor (e.g. platinum resistor) can be placed in good thermal contact with the region containing the auxiliary junctions. As another preferred implementation, the region containing the auxiliary junctions could be in good thermal contact (but not in electrical contact) with a solution whose temperature can be set or measured with high accuracy and high precision. With reference to figure 8, beside the electrodes and the contacts (small squares), all the other metal parts must generally be passivated, as in standard microelectrode arrays.

Among many possible substrates (including appropriate substrates required for the growth of various materials in material science), for biomedical applications standard flexible printed circuit technology may be used; this technology has, for instance, been used for integrating the microelectrode arrays in [Giovangrandi et al. 2006].

As significant advantages, the technology is very simple and the microarray can be easily designed; as an example, polyimide films are very interesting as they are very thin, have a good thermal resistivity, and can be easily metalized (e.g. DuPont™ Kapton). Traditional Tellurium compounds (BΪ₂Tβ₃ and Sb₂Tβ3) are the most widely used materials in conventional thermoelectric generators and in Peltier coolers. Recently, the successful thin- film deposition of these high-performance thermoelectric materials has been reported; it is interesting to observe that the deposition is compatible with both traditional IC technologies [Goncalves LM et al. 2008] and with flexible polyimide substrates [Goncalves LM et al. 2007].

As a preferred implementation, a single multi-functional transducer can perform (simultaneously, sequentially, or with any desired timing) electrical, thermal, and, eventually, chemical functionalities; clearly, in the fabrication process of these transducers various layers of different materials can be used. Figure 7 shows a substrate after the deposition of the first material. Figure 8 shows the same substrate after the deposition of the second material. For simplicity, in both figures 7 and 8 the contacts and the junctions outside the "active" area (square) are shown only for some elements; the temperature in the gray area must be uniform and must be accurately measured or set, so that the temperatures of the junctions in the active area can be accurately determined. With reference to the "active" area, the substrate (e.g. a glass substrate) can be etched in order to improve the thermal insulation between different elements of the array; with reference to the areas of the contacts and of the junctions outside the "active" area (gray area in figure 8), the substrate should not be etched and, if necessary, various methods can be used for improving the thermal contact (e.g. depositing in this area a thick layer of electrically insulating, thermally conductive material or by using proper electrically- insulating thermally-conductive paste or by depositing a thin layer of electrical insulator and covering the region with high thermal conductivity paste etc.). If an electrically insulating layer is deposited on top of the thermocouples everywhere but in correspondence of the contacts, the junctions in the "active" area can also perform electrical activities (recording or stimulation).

If desired, beside for temperature measurement, each junction in the "active" area can also be used as a thermal actuator (Peltier effect). In this way, an array of electro-thermo-couples is easily fabricated.

If, in proximity of the junctions in the "active" area thermo-responsive coatings are placed, each one being in good thermal contact with a correspondent junction, an array of chemo- electro-thermo-couples is easily fabricated. It must be observed that, if the same junction must simultaneously or quasi-simultaneously perform both electrical and chemical activities, the thermo-responsive coatings must not degrade the electrical contact between the junction of the chemo-electro-thermo-couple and the substance/sample/material which must be in electrical contact with the junction (in practice it may be necessary that only a part of the junction is coated by the thermo-responsive coating or even that the thermo-responsive coating is not placed exactly on top of the junction).

In particular, arrays of electro-thermo-couples and arrays of chemo-electro-thermo-couples can be used for cell cultures and neuronal cell cultures. As another preferred implementation, arrays of chemo-electro-thermo-resistors or of electro-thermo-resistors can also be used so that a single multi-functional transducer can perform electrical, thermal, and, eventually, chemical functionalities, as above described.

As another preferred implementation, the array of multi-functional elements will comprise an array of thermally active elements and an array of electrically active elements. The array of thermally active elements and the array of electrically active elements may be stacked vertically or may be on the same layer; may have the same or different numbers of elements and the same or a different spatial distribution of elements.

An advantage of this preferred implementation, since different, electrically insulated devices are used for performing the electrical and the thermal functionalities, the interface for measuring and/or controlling the electrical signals can be identical to those usually employed with standard microelectrode arrays. For instance, in cell cultures or neuronal cell cultures, the top layer, in contact with the culture, must necessarily perform the electrical activities and can be similar to traditional microelectrodes arrays (in particular, the materials in contact with the cultures should be biocompatible). However, on the same top layer or on a bottom layer, electrically insulated from the top electrically active layer, it is possible to fabricate an array of metallic junctions for temperature sensing (similar to those shown in figures 7 and 8) or an array of resistors for temperature sensing and thermal actuation or, anyway, it is possible to integrate an array of transducers with thermal functionalities (e.g. an array of transistor in an integrated circuit process).

In a preferred implementation, the contacts for the electrical activities could be on the top layer and the contacts for the thermal activities could be on the bottom layer; in another preferred implementation, all the contacts for the external interface could be on the top layer; in another preferred implementation, all the contacts for the external interface could be on the bottom layer.

Since in similar arrays to be interfaced with off-substrate electronics, the number of contacts is generally severely limited, we also describe a method for reducing the number of the required contacts for a given number of elements, which is another object of the present invention; in practice, the thermally active elements may be realized by an array of junctions, where all the junctions share an electrically continuous metal film as the first material, so that only one contact is sufficient for this material, and the second material is patterned in order to provide a contact for each junction.

It is necessary to observe that this solution is not possible when the same metallic junction must also perform electrical activities, as all the different junctions share an electrically continuous metal film (however, the Seebeck voltages of every junction can still be measured). Therefore, provided that a contact can be made to the continuous metal film which is shared by all the junctions, only a single contact is required for each junction.

The metal film may actually be patterned with a design and lay-out in such a way that it does not act as a thermal short circuit for the different junctions. Moreover, either the first material is passivated before depositing the second material, either two different metal layers

(connected by vias) can be used. As another preferred implementation of the thermally active elements, an array of identical resistors can be used both as heaters and as temperature sensors (similar to [Falconi et al. 2006]). Moreover, two different arrays of resistors (made of the same or different materials, deposited on the same or different insulated layers) can be used as, respectively, heaters and temperature sensors.

Since the electrically active devices (i.e. the electrodes) must necessarily be integrated on the top side of the substrate (i.e. for cell cultures, the side which is in contact with the culture), the thermally active devices may be integrated on the same top side of the substrate or on the bottom side. However, if the thermally active devices are on the bottom side of the substrate, the thermal resistance between a thermally active device and the correspondent (to that specific device) region of the culture must be as small as possible; on the contrary, the thermal resistance between different thermally active devices must be as large as possible. It is an object of the present invention an array of multi-functional elements which is realized on a substrate, having on the top side an array of bio-compatible electrodes which allow to record the electrical activities of cells and/or to apply electrical stimulations and on the bottom side an array of thermally active elements which can be used for measuring the temperature distribution along the cell culture and/or applying thermal stimulations to the cell cultures with high accuracy, high precision, and high spatial resolution, and having appropriate electronic interfaces comprising a user-friendly software.

The present invention also concerns an on-chip array of multi-functional elements, similar to the systems described above, comprising an on-chip electronic interfaces. The multifunctional elements and the interface will be integrated in a CMOS or other standard integrated-circuits process with the addition of, eventually, non standard process steps for the integration of the multi-functional elements or of some parts of the multi-functional elements or for etching or for deposition or for passivation or for other procedures. In CMOS or other standard integrated-circuits processes it may be convenient to use, for temperature sensing and/or for heating, transistors or other devices (e.g. the pnp parasitic vertical bipolar transistors in standard CMOS processes have good characteristics for temperature sensing [Bakker 2000, Falconi et al. 2008]).

Moreover this invention concerns a smart incubator able to apply proper combinations of electrical and/or thermal and/or mechanical and/or chemical and/or electromagnetic stimuli by using multi-functional transducers or an array of multi-functional elements, according to the previous descriptions, so that a faster cell growth or tissue repair or cell regeneration can take place or so that some important cellular mechanisms are modified.

Moreover the invention concerns a lab-on-chip able to apply proper combinations of electrical and/or thermal and/or mechanical and/or chemical and/or electromagnetic stimuli by using multi-functional transducers or an array of multi-functional elements, according to the previous descriptions, so that a biological sample of interest may be characterized, eventually in combination with other standard techniques.

Other objects of this invention are systems for the evaluation of skin perfusion which beside thermal functionalities, also have, by means of proper transducers, electrical and/or chemical and/or mechanical functionalities in order to improve the accuracy of these systems and their ability to diagnose other pathological conditions of the skin.

Other objects of this invention are systems for the early diagnosis of the diabetic foot and of other similar pathologies which, beside thermal functionalities, by means of proper transducers, also have additional functionalities, with particular reference to the electrical and/or chemical (not limited to humidity measurement) and/or mechanical (not limited to pressure measurement) functionalities in order to improve the accuracy of the system and the ability to diagnose other pathological conditions of the skin.

Other objects of this invention are thermoelectric therapeutic devices which, beside applying cold or hot and stimulating the skin electrically and mechanically (massage), also have chemical functionalities and can apply stimulations determined also taking into account the skin analysis performed by using interfaces having a combinations of chemical, thermal, electrical or mechanical functionalities.

Other objects of this invention are thermoelectric therapeutic devices which take advantage of a single multi-functional transducer in order to perform (simultaneously, sequentially, or with any desired timing) both the electrical and thermal functionalities (instead of using a thermocouple for the thermal stimulation and an electrode for the electrical stimulation).

It is another object of this invention a system which combines one of the above described arrays of multi-functional transducers with thermal images taken by a thermographic camera in order to complement the very-high-number-of-pixel image of the thermographic camera (less accurate and less precise) with the high precision and high accuracy measurements of the on-the-substrate temperature sensors, thus potentially resulting in a very-high-number-of- pixel, high accuracy, high precision thermal images.

Moreover, this invention concerns a system combining one of the arrays of multi-functional transducers previously described with systems of finite element simulations and, eventually, with thermal images taken by a thermographic camera in order to obtain thermal images characterized by high accuracy and high precision and by a very high number of pixels.

The proposed invention will, in particular, be useful for high density interfaces, required, in particular, in biomedical sciences (lab-on-chip, cell cultures, pharmacology, tissue engineering, neural engineering, surgery, etc.) and in material sciences (nanotechnology, definition of structures on smart substrates without using masks, various techniques of deposition, meta-materials, etc.). For instance, the applications of the proposed inventions include: smart systems able to measure and/or control the temperatures and voltages of high density arrays of elements in an accurate, precise, fast, and programmable manner; chemo-electro-thermal interfaces which, beside various electrical and thermal functionalities, permit the thermally triggered release, in controlled instants and positions, of proteins, trophic factors, and other substances of interest; electro-thermo-couples; chemo-electro-thermo-couples; electro-thermo-resistor; chemo-electro-thermo-resistor; thermo-patch-clamp; chemo-thermo-patch-clamp; arrays of elements for heat shock and stimulation of temperature gradients; flexible therapeutic chemo-electro-thermal, electro-thermal, or thermal tools; smart chemo-electro-thermal, electro-thermal, or thermal bed; chemo-electro-thermal or electro-thermal minimally invasive surgical tools; chemo-electro-thermal or electro-thermal ablative systems; surgical tools, needles, and micro-needles with thermal functionalities; deep-brain-stimulation systems with temperature measurement and/or application of thermal stimulations.

Figure 9 schematically shows how, within an array of elements, by dynamically controlling the temperatures of the elements A and B it is possible to generate dynamically variable temperature gradients between the elements A and B. The velocity of variation of the temperatures of the elements A and B are limited by the thermal time constants of the system which can, in many cases, be made very small (e.g. in the order of milliseconds) by applying to the substrate etching procedures. Obviously, similarly to what is shown in figure 9, it is possible, by dynamically controlling the voltages of the elements A and B, to generate dynamically variable electric fields between the elements A and B. In the same way, by dynamically controlling both the temperatures of the elements A and B, and the voltages of the elements A and B, it is possible to simultaneously generate dynamically variable temperature gradients and electric fields between the elements A and B.

Figure 10 shows a circuit, also an object of this invention, also shown for the case of a resistor with positive temperature coefficient, for the temperature control by means of a resistor, R_x, which is at the same time temperature sensor and heater (and can even be used as electrode, flow sensor and for other purposes). In comparison with the previous interface, the circuit allows to remove the auxiliary resistor which was placed between the drain and source of Mo (thus solving the trade-offs associated with that resistor), by means of the introduction of the logic gate OR whose output drives the gate of M_n and whose inputs are the signal Measure and the output of the D flip-flop, Q. In practice, during the measurement phase the signal Measure is high and, therefore, the output of the gate OR, which drives the gate of M₀ is high, so that M₀ is off; in this measurement phase the circuit uses two current sources I_A and I_B in order to bias R_x and the reference resistor R_RI;_F- The current sources I_A and I_B, in an integrated implementation, can be realized by current mirrors of various types or with other techniques, which are well known to those skilled in the art, with the goal to obtain a good accuracy of the ratio between the currents I_A and I_B. The regulation of the desired temperature can be done by regulating the reference resistor (e.g. if this reference resistor is made with a digital potentiometer) or by varying the ratio between the currents I_A and h (a similar approach has been used in [Falconi et al. 2008]). During normal operations, assuming for the resistor R_x a positive temperature coefficient (only in this case the feedback is negative), the circuit allows to equate, by means of the loop, the resistance of the resistor R_x and the quantity (which, in general, will be known with good accuracy) R_!{EF * (I_A /I_B) .

In an integrated implementation (e.g. CMOS), the input offset voltage and the input 1/f noise of the comparator can easily be compensated with various techniques well known to those skilled in the art (e.g. auto zero).

As an evolution of the circuit shown in figure 10, figure 1 1 shows a circuit, also object of this invention, also shown for the case of a positive temperature coefficient, which, in order to allow a 4 wires measurement, takes advantage of a high gain DDA (differential difference amplifier) , used as comparator of the difference between the differences V_rV₂ and V₃-V₄, where the terminals 1,2,3 and 4 of the DDA are shown in the figure.

In an integrated implementation (e.g. CMOS), the input offset voltage and the input 1/f noise of the DDA can easily be compensated with various techniques well known to those skilled in the art (e.g. auto zero). As an evolution of the circuit shown in figure 1 1, figure 12 shows a circuit, also object of this invention, also shown for the case of a positive temperature coefficient, which permits to use higher currents in the heater due to the two blocks of chopper switches (both driven by the same control signals), in a manner similar to what has been previously described for the circuit which uses the auxiliary resistor in order to avoid degradation of R_x (e.g. electromigration).

In some cases it can be advantageous to remove the block of chopper switches connected to the DDA (the other chopper block must in this case be used always with the straight connections enabled during the measurement phases, when the signal Measure is high). Beside the circuits explicitly shown in this description, other circuits which use the same ideas here described and can be obtained from the described circuits by introducing variations well known to those skilled in the art are also objects of this invention.

To the above described stimulation device a man skilled in the art, in order to meet further and specific needs, can add several further changes and variants, all included in the protection scope of the present invention, a defined by the annexed claims.

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Claims

Claims

1. Stimulation device including stimulating elements, with arbitrary spatial distribution, able to apply electrical, thermal, mechanical, magnetic, electromagnetic, or chemical stimulations, where one or more stimulating elements are locally associated to one or more respective sensor elements, so that the stimulation phase substantially clashes with the detection of one or more local parameters by means of an electronic interface.

2. Device as in claim 1, in which one or more stimulating elements, beside applying stimulations, perform the function of sensor elements thus allowing the detection of a process parameter.

3. Device as in claim 2, in which said stimulating elements comprise a component for the measurement of temperature and for energy transfer.

4. Device as in claim 3, in which said component is an electro-thermo-couple, i.e. a bimetallic component which, driven by a proper circuit, is able to perform one or more of the following operations: measuring the temperature by means of the Seebeck effect, transferring energy, with addition or subtraction of heat, by means of the Peltier effect, measuring the electric potential and/or applying an electrical potential.

5. Device as in claim 3, in which said component is an electro-thermo-resistor, i.e. a resistor which, driven by a proper circuit, is able to perform one or more of the following operations: measuring the temperature, transferring energy, with addition of heat, by means of the Joule effect, measuring the electric potential and/or applying an electric potential.

6. Device as in claim 3, in which said component is a transistor which, driven by a proper circuit, is able to perform one or more of the following operations: measuring the temperature, transferring energy, with addition of heat, measuring the electric potential and/or applying an electric potential.

7. Device as in any of the previous claims, in which said electronic interface comprises a microcontroller or a microprocessor or a PC including a proper software or algorithm.

8. Device as in any of the previous claims, in which the stimulating element is an electrode.

9. Device as in claim 8, which comprises an array of elements, each element allowing the application of an electric voltage and/or a quantity of energy to a substrate according to any algorithm and eventually taking into account the measurement of electrical and/or thermal signals performed by each element.

10. Device as in claim 9, in which in some or in all the elements it is fabricated a junction of two different metals in the points where it is desired to measure the temperature.

1 1. Device as in any of the claims from 1 to 7, in which the stimulating element is an element able to deliver drugs, proteins, trophic factors, or other substances of interest.

12. Device as in claim 1 1 , in which the stimulating element comprises a junction of two different metals and takes advantage of the Seebeck effect for the measurement of the temperature and of the Peltier effect for energy transfer with addition or subtraction of heat.

13. Device as in any of the previous claims, which comprises an array of multifunctional elements, with arbitrary spatial distribution, which perform two or more different functions, with at least one transduction process, in which each multi-functional element is constituted by a single device or by more devices, so that the array can simultaneously measure the temperature distribution and the voltage distribution, eventually including among the elements electro-thermo-couples or electro-thermo-resistors which can measure the electrical activity and/or measure electrical potentials.

14. Device as in claim 13, in which some or all the elements of the array can release in a controlled manner drugs, proteins or other substances of interest.

15. Device as in claims 13 and 14, in which some or all the elements of the array can also apply mechanical stimulations.

16. Device as in any of the previous claims, in which for a group of elements A it is possible to measure their temperatures, for another group of elements B it is possible to measure their voltages, for another group of elements C it is possible to set their temperatures at desired values and for another group of elements D it is possible to set their voltages at desired values, being eventually possible to dynamically change the groups A, B, C, and D.

17. Device as in claim 16, in which there are also mechanical actuators which dynamically permit or forbid the exposition of parts of substrate depending on proper control signals, thus constituting "active masks" for various types of processes, such as doping, thin film deposition, and others.

18. Device as in claims 16 and 17, in which there are also materials able to release substances of interest in consequence of a proper stimulation.

19. Devices as in claims 16, 17, and 18, in which there are also sensors of mechanical and/or chemical and/or electromagnetic and/or magnetic quantities.

20. Device as in any of the previous claims, in which some stimulating elements and some sensors elements are integrated on a substrate whereas other stimulating elements and other sensors elements are external to the substrate.

21. Device as in claim 3, arranged for performing a patch-clamp function, eventually with the possibility to release drugs, proteins or other substances of interest.