WO2019045646A1

WO2019045646A1 - Method and apparatus for mechanical testing of an orthosis

Info

Publication number: WO2019045646A1
Application number: PCT/SG2018/050434
Authority: WO
Inventors: Tsurayuki MURAKAMI; See Lin CHEUNG
Original assignee: Forefront Additive Manufacturing Pte Ltd; Tan Tock Seng Hospital Pte Ltd
Priority date: 2017-08-31
Filing date: 2018-08-28
Publication date: 2019-03-07
Also published as: SG11202001649QA

Abstract

Disclosed is a method and apparatus (10) for testing material properties of an orthosis (27). The orthosis (27) is secured, preferably by a clamping mechanism, so that the orthosis (27) may bend through a predetermined portion of the orthosis. Force is applied, preferably by an actuator, in a first direction and transmitted to enable the orthosis (27) to bend through the predetermined portion in a manner which mimics forces applied to the orthosis (27) in use. Preferably, the actuator is in operative association with connector rods and joints such as slider-and-pin joints and ball joints.

Description

METHOD AND APPARATUS FOR MECHANICAL TESTING OF AN ORTHOSIS

Technical Field

This invention relates to a method and apparatus for bench-testing an orthosis. The invention is particularly concerned with the testing of additive manufactured orthoses, and may also be used for the testing of conventional orthoses. More particularly, it provides a systematic method and parameters for analysing the properties of the materials used in additive manufactured orthoses in terms of material stiffness and fatigue resistance.

Background

The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

An orthosis is a customised external medical device to aid in the support, correction and/or alignment of the human body. It is used to counteract the effect of an actual or developing deformity. One such device takes the form of a spinal brace for patients with spinal scoliosis. It may also aid in improving functions of movable parts for patients with physical impairments. For example, an ankle foot orthosis can be used to counteract the effects of a foot drop in stroke patients as they walk.

An ankle foot orthosis is an assistive device commonly prescribed to patients with lower extremity neuromuscular or musculoskeletal impairments to address biomechanical gait abnormalities. It is a supportive brace that corrects a patient's lower limb alignment. The device is commonly custom fabricated by an orthotist.

The conventional process of fabricating an ankle foot orthosis involves a complex moulding process. In a typical process, an orthotist will use Plaster of Paris bandages to encircle a patient's lower limb, and will manually manipulate the joint to maintain the desired joint alignment until the plaster sets. Once the plaster hardens, the plaster cast will be cut and removed. This resultant negative plaster cast will be filled up with further plaster mixtures to create a positive plaster mould. This positive plaster mould is a replica of the patient's lower limb. It is then physically rectified and modified by the orthotist using a hand file and sand screen. Rectification is based on biomechanical concepts and the desired alignment. The rectified positive plaster mould is then used as a reference for the fabrication of the ankle foot orthosis. In the next stage of the fabrication process, a large thermoplastic polypropylene sheet is heated in a conventional or infra-red oven set at 185 °C / 365 °F. Depending on the thickness (3 to 8 millimetres) and the size of the polypropylene sheet required, it is heated up for 3 to 8 minutes in an infrared oven but longer in a conventional oven, typically for 15 to 20 minutes. Once the thermoplastic polypropylene sheet is soft and malleable, it is removed from the oven and immediately placed over the rectified positive plaster mould. The malleable polypropylene sheet is then vacuum draped over the rectified positive plaster mould, and left to cool. After allowing the draped plastic to cool for 24 hours, the orthotist traces the outline of the ankle foot orthosis with a marker pen. A cast saw is used to cut away the excess plastic. This is followed by the grinding of all edges using a belt sander, and then polishing and buffing to smooth the orthosis. The final step is to drill holes to place rivets for securing Velcro straps to the orthosis. In use, these straps fasten the ankle foot orthosis securely on the patient.

The conventional subtractive manufacturing process is labour intensive. It also requires a large amount of space for various equipment and machinery. It is time consuming as it requires 24 hours for the polypropylene sheet to cool before the next phase of the fabrication process can commence. The casting, rectification, fabrication and finishing processes are also dependent on the individual skills and workmanship of the orthotists and their technicians. Furthermore, the manufacturing process cannot be repeated for the same patient using the same plaster mould cast because the plaster mould cast is often broken during the fabrication process. Even if not broken, the plaster mould will dry out and slightly shrink in size, causing volumetric changes should another mould be done on the same cast. Hence, patients are required to repeat the whole process should they require a similar ankle foot orthosis.

Additionally, the conventional subtractive manufacturing method of fabricating an ankle foot orthosis does not allow any room for further customisation or optimisation of the design. For instance, certain portions of the orthosis may require a thicker or thinner depth for strength, durability, elasticity or comfort. The ability to create complex inner cavities for comfort or optimised function is limited with the conventional subtractive manufacturing method. In general, this requires further steps in which additional components are fabricated separately.

Additive manufacturing, commonly known as "3D printing", is used in many industries, especially in the field of healthcare and medical technology. Additive manufacturing allows the fabrication process for an orthosis to be shortened. The process involves less material wastage and allows for design of the orthosis to be optimised for function and adjusted to incorporate additional components for comfort.

The first step in an additive manufacturing process for fabricating an ankle foot orthosis is to use a handheld optical 3D scanner to electronically capture a high- resolution 3D model of the patient's lower limb. The captured 3D model is uploaded into Computer Aided Design (CAD) software. The scanning process is safe and clean for both the patient and the orthotist. Rectification of the 3D model can be done by the orthotist using the CAD software. Rectification or adjustment can thus be performed to have the ideal joint alignment based on biomechanical concepts with the aid of a library of modification templates. Rectification with CAD software allows greater precision and, since a library of rectification templates is used, the process is more consistent and repeatable among orthotists. The 3D model of the ankle foot orthosis goes through further design optimisation before it is printed. A Finite Element Analysis (FEA) process is undertaken and may result in customising of the thickness of the ankle foot orthosis at locations anticipated to be subjected to substantial force during use. The final electronic design of the ankle foot orthosis is then exported to a sheer program for processing before being 3D printed through fused deposition modelling. This is a 4-stage process involving orientation determination, support generation, slicing and tool-path generation. The 3D printed ankle foot orthosis will then be fitted with the necessary straps in a final finishing phase. This additive manufacturing process requires less labour, time, workshop space, equipment and machinery.

There are already various companies and institutions using additive manufacturing to create orthotic products or devices for patients. However, material properties and functional integrity of these customised orthotic devices are generally not reliably tested and assessed prior to use. Additively manufactured orthoses have materials with properties significantly different from those of orthoses made using the conventional subtractive method. Without properly testing and assessing material properties of the orthoses prior to use, patient safety and care may be compromised.

It is desirable to provide a method and an apparatus for testing material properties of an orthosis, which address at least one of the drawbacks of the prior art and/or to provide the public with a useful choice.

Summary

According to a first aspect, there is provided a method for testing material properties of an orthosis, comprising: securing the orthosis to allow the orthosis to bend through a predetermined portion; applying force in a first direction; and transmitting the applied force to the orthosis to enable the orthosis to bend through the predetermined portion in a manner which mimics forces applied to the orthosis in use. Preferably, the applied force may be translated into a rotational movement to bend the orthosis through the predetermined portion. It is envisaged that a lateral movement may be allowed so that the bending movement of the orthosis may be deflected. The rotational and lateral movements may be designed or intended to substantially or sufficiently resemble movements or forces experienced by the orthosis upon movement of a user wearing the orthosis. With such a configuration, material properties of the orthosis, such as stiffness and fatigue resistance, may be reliably tested, with the results being more descriptive of an actual use scenario of the orthosis.

According to a second aspect, there is provided an apparatus for testing material properties of an orthosis, comprising: a clamping mechanism operable to secure the orthosis to allow the orthosis to bend through a predetermined portion; an actuator operable to apply force in a first direction; and a linking mechanism arranged to connect the actuator to the orthosis to enable the applied force to be transmitted to bend the orthosis through the predetermined portion in a manner which mimics forces applied to the orthosis in use. In a specific embodiment, the actuator may comprise an actuator rod extending in the first direction. The apparatus may further comprise a force measurement device for measuring the force applied by the actuator. The measured force can be used to calculated stiffness and fatigue resistance of the orthosis according to static equations of motion. Preferably, the apparatus may further comprise a computing device for calculating the force applied to the orthosis.

It is possible that the actuator may be in operative association with a first connector rod. In such a configuration, the operative association of the actuator and the first connector rod may be through a first joint which translates the applied force into a rotational movement to bend the orthosis. In a specific example, the first joint may include a slider-and-pin joint. It is also possible that the first connector rod may be in operative association with a second connector rod. In such a configuration, the operative association of the first connector rod and the second connector rod may be through a second joint which allows lateral movement. In a specific example, the second joint may include a ball joint.

Preferably, the orthosis may be secured to the second connector rod. Advantageously, the second connector rod may be anchored through a third joint which allows lateral movement. Specifically, the third joint may be a ball joint.

According to a third aspect, there is provided a method for testing material properties of an orthosis, comprising: securing the orthosis to allow the orthosis to bend through a predetermined portion; generating a force by an actuator; and in response to the generated force, generating rotational and lateral movements to cause the orthosis to bend through the predetermined portion.

The described embodiment is particularly advantageous. The generated rotational and lateral movements are applied to the orthosis to cause the orthosis to bend in a manner that resembles the bending or deflection of the orthosis by a user in use. The rotational and lateral movements may be designed or intended to substantially or sufficiently resemble movements or forces experienced by the orthosis upon movement of a user wearing the orthosis. With such a configuration, material properties such as stiffness and fatigue resistance of the orthosis may be reliably tested, with the results being more descriptive of an actual use scenario of the orthosis.

According to a fourth aspect, there is provided an apparatus for testing material properties of an orthosis, comprising: a clamping mechanism operable to secure the orthosis to allow the orthosis to bend through a predetermined portion; an actuator operable to generate a force; and a linking mechanism arranged to generate rotational and lateral movements, in response to the generated force, for causing the orthosis to bend through the predetermined portion. It should be appreciated that features relating to one aspect may be applicable to another aspect. Brief Description of the Drawings

In order that the disclosure may be readily understood and put into practical effect, reference will now be made to at least one embodiment as illustrated with reference to the accompanying figures and examples. The figures together with the description serve to further illustrate the at least one embodiment of the invention and explain various principles and advantages. Among the figures:

Figure 1 is an isometric view of a testing apparatus with an ankle foot orthosis (AFO), according to one embodiment of the present invention;

Figure 2 is an enlarged partial view of a heel clamping jig and a metatarsophalangeal jig of the apparatus of Figure 1 ;

Figure 3 is an enlarged partial view of a portion of Figure 1 , showing the jigs from another angle;

Figure 4 is an enlarged partial view of an upper section of the apparatus of Figure 1 ;

Figure 5A is an enlarged partial view of an upper intermediate section of the apparatus of Figure 1 ; and

Figure 5B is an enlarged partial view of a lower intermediate section of the apparatus of Figure 1.

Detailed Description

Some materials used in additive manufacturing may not have suitable properties for orthoses or certain orthosis designs. Such materials, if used in the making of orthoses, may result in susceptibility of the orthoses to deformation or even breakage, which compromise functionality and safety. This invention seeks in one aspect to reduce the risk of inadvertent patient use of orthoses with unsuitable material properties, where the orthoses may be additively or conventionally manufactured. Stiffness and fatigue resistance are two material properties critical to ensuring the functional performance of an orthosis. Accordingly, the present invention provides a method of testing material properties of an orthosis by mimicking forces applied when the orthosis is worn by a patient. The method is applicable, for example, to orthoses including upper limb orthoses, lower limb orthoses and spinal orthoses. Upper limb orthoses may include clavicular and shoulder orthoses, arm orthoses, elbow orthoses, forearm-wrist orthoses, forearm-wrist- thumb orthoses, forearm-wrist-hand orthoses and hand orthoses. Lower limb orthoses may include foot orthoses, ankle-foot orthoses, knee-ankle-foot orthoses and knee orthoses.

By way of example, for an ankle foot orthosis (AFO), stiffness of the ankle joint and that of the metatarsophalangeal joint determine the rate of progression of the lower limb during the stance phase of gait. Control of the rate of progression of the lower limb is essential for alignment control for a patient with a lower limb physical impairment. Hence, material stiffness is measured for these two specific joints. The ankle deflects through approximately 12^° of motion, and the metatarsophalangeal joint through 20° of motion within a gait cycle. The stiffness of the AFO is thus defined as the moment around the joints exerted by the AFO per degree of ankle/metatarsophalangeal joint rotation (Newton-meters/degree). The stiffness of a 3D printed ankle foot orthosis should be close to that of a conventionally manufactured ankle foot orthosis, and must meet the minimum stiffness requirement of 1.56 Nm/degree as indicated in the scientific literature (Kobayashi, T., Leung, A.K. and Hutchins, S.W., 2011. Techniques to measure rigidity of ankle-foot orthosis: a review. Journal of Rehabilitation Research & Development; D.J.J. Bregman, A. Rozumalski, D. Koops, V. de Groot, M. Schwartz, J. Harlaar, "A new method for evaluating ankle foot orthosis characteristics: BRUCE" Journal of Gait & Posture 30 (2009) 144-149). The amount of mediolateral splaying of the device is also measured over the ankle joint from 0° - 12° of deflection, and when recovered back or returned to 0° of deflection. The 3D printed ankle foot orthosis must be able to recover back or return to its original dimensions or shape when the ankle foot orthosis returns to 0° of deflection. If the mediolateral splaying of the ankle joint fails to recover back or return to its original dimensions or shape, permanent deformation has occurred. Splaying refers to an increased distance between the medial and lateral borders at the point of the ankle axis, compared to its original position. Measurements are made for the ankle joint using vernier caliper at every degree of deflection from 0° to 12°, and when recovered back or returned to 0°. The measurement results are compared with those of the traditionally manufactured AFO. The fatigue resistance of an ankle foot orthosis is a measurement of the ability of the orthosis to resist deformation under repeated loading over a period of time, and is critical for ensuring long-term safety and functionality. A user with a pathological gait pattern would typically go through 500,000 gait cycles in a period of 6 months. Hence, in one application, a thorough cyclic loading test of 500,000 cycles mimicking a human gait pattern is carried out to test for any signs of material breakage or deformation. This will provide an indication of the fatigue resistance of the material. A 3D printed ankle foot orthosis must survive 500,000 cycles of the cyclic loading fatigue resistance testing without any signs of material deformation. A bench-testing apparatus 10 in accordance with one embodiment of the present invention is shown in Figure 1. The apparatus 10 includes a testing rig 12 and a frame 11 (which includes upright member 18) supporting the testing rig 12. An ankle-foot orthosis (AFO) 27 is secured within the frame 11 and with respect to the testing rig 12. The testing rig 12 can be divided into three main sections of interest, including an upper section 13, an intermediate section 14 and a lower section 15. The top section 13 is where force is applied by an actuator 16 of the apparatus 10 to the testing rig 12. The intermediate section 14 is where force applied by the actuator 16 is transferred or transmitted to the AFO 27. The lower section 15 is where the AFO 27 is secured.

A detailed view of the upper section 13 is provided in Figure 4. The actuator 16 may be any type of linear actuator, for example one including a motor and a ball screw. The actuator 16 is operable to reciprocatingly drive an actuator rod 17 of the apparatus 10 to alternatingly move in downward and upward motions along a vertical direction (i.e., along the z-axis, labelled in Figure 1 ). The actuator rod 17 is connected to a load cell 19 of the apparatus 10 operable to measure the force applied by the actuator 16. For instance, the measurement may be made by the load cell 19 along the downward motion, e.g., at the lowest point where transition from the downward movement to the upward movement occurs. The applied force may be conveyed to a computer (not shown) or the like in operative association with the load cell 19. The corresponding force applied to the AFO 27 can be calculated using static equations of motion. Such a calculation is well understood by a person skilled in the art and is not discussed herein for the sake of brevity.

The load cell 19 includes a holder 20 configured to receive an upper connector rod 24 through a slider-and-pin joint. Specifically, the slider-and-pin joint includes a pin 22 extending through an aperture formed in an upper end of the upper connector rod 24. Such a configuration allows for sliding movement of the upper connector rod 24 along the pin 22 in the direction of the y-axis, and for rotational movement of the upper connector rod 24 about the pin 22 along the x-z plane perpendicular to the y-axis. Such a rotational movement contributes to the bending of the AFO 27. Sliding movement of the upper connecting rod 24 along the pin 22 is bounded such that the AFO 27 does not move uncontrollably. In particular, the holder 20 is shown to define a U-shaped recess receiving the pin 22. The sliding movement is restricted by opposing inner surfaces of the holder 20 coinciding with the pin 22 and partially defining the U-shaped recess.

The intermediate section 14 is shown in more detail in Figures 5A and 5B. In the intermediate section 14, the upper connector rod 24 connects to a lower connector rod 25 via a ball joint 26. Accordingly, a limited range of movement of the lower connector rod 25 in any direction, including a lateral direction along the y-axis, relative to the upper connector rod 24 is permitted by the ball joint 26. The lower connector rod 25 is also connected to an AFO holder 28, to which an upper portion of the AFO 27 is secured. The AFO holder 28 may be any suitable means for connecting the lower connector rod 25 to the AFO 27. In one form the AFO holder 28 is a block fitted within an upper opening of the AFO 27. The AFO holder 28 is secured to the AFO 27 by way of at least one integrally formed clip that extends around a wall portion of the AFO 27 defining the upper opening. The AFO holder 28 also has a strap which, when secured around or with respect to the AFO 27, pulls or moves the AFO 27 in response to movement (e.g., rotation) of the lower connector rod 25. This allows force to be transferred from the lower connector rod 25 to the AFO 27. Since the AFO 27 is secured to via the holder 28 with respect to the lower connector rod 25, the AFO 27 will deflect to the angle of the lower connector rod 25, and will rotate with the lower connector rod 25. The connector rods 24, 25, the ball joint 26, the AFO holder 28, and the slider-and- pin joint of the holder 20 together serve as a linking mechanism connecting the actuator 16 via the actuator rod 17 to the AFO 27 to bend the AFO 27 through the predetermined portion.

The lower section 15 is shown in detail in Figure 2 and Figure 3. Figure 3 is an enlarged partial representation of Figure 1 , marked by "A". These figures show a heel clamping jig 15a and a metatarsophalangeal (MTP) clamping jig 15b. Together, the heel and MTP clamping jigs 15a, 15b define a clamping mechanism for securing the AFO 27 to allow the AFO 27 to bend through a predetermined portion in response to movement of the lower connector rod 25. In this embodiment, the predetermined portion of the AFO 27 includes a heel portion and an MTP portion corresponding to the jigs 15a, 15b, respectively. The heel clamping jig 15a includes a heel holder 30 shaped to fit inside the AFO 27 and arranged corresponding to the heel portion. The heel holder 30 is held firmly and downwardly within the AFO 27 at the heel portion by a locking bar 31 to hold the AFO 27 against a base of the frame 11. The locking bar 31 is supported by locking bar supports 32, 33. The locking bar 31 is formed with slots for threaded engagement with the respective locking bar supports 32, 33. In particular, a threaded portion of each of the locking bar supports 32, 33 extends into a respective one of the slots for threaded engagement with a respective nut for securing the locking bar supports 32, 33 with respect to the locking bar 31. The locking bar 31 may be removed or released from the locking bar supports 32, 33 by loosening and removing the nuts. The MTP clamping jig 15b includes an MTP holder 34 held against the AFO 27 at the MTP portion by a locking bar 35.

The heel holder 30 is secured in place with the locking bar 31 when testing stiffness at the ankle joint (or the heel portion) of the AFO 27 ("the stiffness test") and also when testing fatigue resistance. The locking bar 31 is removed when testing stiffness of the MTP joint (or the MTP portion) of the AFO 27 ("the MTP test"). With the locking bar 31 removed, the AFO 27 is held down only at the MTP joint by the MTP clamping jig 15b, allowing the AFO 27 to bend through the MTP portion for stiffness of the MTP joint to be measured. The heel holder 30 is provided with a ball joint 31 a serving as an anchor point for anchoring the lower connecting rod 25. The ball joint 31a, which allows lateral movement, may form part of the linking mechanism.

In use, during the stiffness test, the actuator 16 applies force in a downward direction to the actuator rod 17 to cause displacement of the actuator rod 17 by a certain amount. Such a movement of the actuator rod 17 causes force to be applied to the AFO 27 via the connector rods 24, 25 and the ball joint 26, thereby bending the AFO 27 around the ankle joint (if testing the ankle joint) or the MTP joint (if testing the MTP joint). A particular amount of displacement of the actuator rod 17 corresponds to a certain bend angle at the joint. The load cell 19 captures the force applied by the actuator 16 at each bend angle. For the stiffness test of the ankle joint, the reading is measured at 0°, 1 °, 2° and at each degree of movement to 12°, and then at each degree of movement back to 0°. That is, the force applied by the actuator 16 is captured by the load cell 19 at each step of 1 ° from 0° to 12° and then back to 0°. By applying the static equations as described previously, the actual force acting on the AFO 27 at each bend angle and hence the stiffness of the joint can be calculated. The process may be repeated (e.g., for 5 times) to verify the result or to obtain an average stiffness. The MTP test is conducted in a similar way, with the heel clamping jig 15a removed or released and with readings taken at each degree of deflection from 0° to 20° and back to 0°. The stiffness of the MTP joint can be calculated using the static equations.

For the fatigue test, similar to the stiffness test, the actuator 6 moves the actuator rod 17 downwardly to a certain extent, bending the AFO 27. The actuator 16 then removes the applied force, whereupon the AFO 27, if not deformed or otherwise broken, resiliently straightens. The AFO 27 is deflected from 0° to 6° for 50,000 cycles, and stiffness tests are conducted to observe any change in behaviour or properties of the material. In other words, the actuator 16 reciprocatingly moves in the downward and upward motions for 50,000 cycles, repeatedly applying force to the AFO 27 via the testing rig 12 with a deflection angle of 6° during the downward motion, and allowing the AFO 27 to return from deflection during the upward motion. A comparison of results of stiffness tests obtained before and after (or at the first and last ones) the 50,000 cycles provides an indication or measurement of fatigue resistance. In particular, the ankle joint opening is measured to detect the occurrence of any significant plastic deformation. Due to the design of the joints, the testing apparatus 10 allows the AFO 27 to deflect in the x-z plane and also to some extent in the x-y plane. As the AFO 27 is asymmetric in design, this freedom of deflection allows the AFO 27 to rotate along its neutral axis for the tests, so that the forces applied to the AFO 27 are similar to forces that would be applied by the natural gait of a person wearing the AFO 27 in use. In other words, the forces applied to the AFO 27 are representative of a natural gait of a user. In one example, a conventionally-made polypropylene ankle foot orthosis was tested using a bench-testing apparatus in a configuration similar to that shown in Figure 1. The conventional orthosis was clamped to the base of the apparatus by the heel clamping jig (as depicted in Figure 2) and the MTP clamping jig (as depicted in Figure 3). The conventional orthosis was induced to go through the intended deflections at the ankle and metatarsophalangeal joints as described above with reference to Figures 4 and 5. The load cell captured the force applied by the actuator during the deflection of the conventional orthosis for each deflection angle. Material stiffness of the conventional orthosis was computed in the manner set forth above. With the computed material stiffness of the conventional orthosis, baseline or reference parameters can be accordingly set for additively manufactured orthoses. The material stiffness of the conventional polypropylene ankle foot orthosis was calculated to be 4.40 Nm/degree for the ankle joint at 12° of deflection and 0.09 Nm/degree for the metatarsophalangeal joint at 20° of deflection. Mediolateral splaying of the conventional orthosis was measured to be 21 millimetres at 12° of ankle deflection and 0 millimetres when returned to 0° of ankle deflection. These tests and their readings were taken 5 times to ensure reliability of the measurements. During cyclic loading for fatigue resistance testing, the conventional orthosis demonstrated increased strained hardening based on its material stiffness up to the 150,000^th cycle before returning to original stiffness values at 500,000 cycles. The test results showed that no significant failure was experienced by the conventional orthosis at the end of the 500,000 cycles.

In another example, orthoses made respectively from two commonly used materials in additive manufacturing were put through the same testing protocol described in relation to Example 1. These materials were polycarbonate and nylon-12. The polycarbonate orthosis exhibited material stiffness of 5.31 Nm/degree, which is higher than the material stiffness of the conventional polypropylene orthosis tested in Example 1. However, the polycarbonate orthosis failed the cyclic loading fatigue resistance testing, showing signs of deformation and cracking at the 18,000^th cycle. The 3D printed nylon-12 orthosis exhibited material stiffness of 4.18 Nm/degree at the ankle joint. It survived the 500,000 cycles of the cyclic loading fatigue resistance testing without showing any signs of material deformation. Both 3D printed polycarbonate and nylon-12 orthoses displayed mediolateral splaying magnitudes similar to that displayed by the conventional polypropylene orthosis.

The method and apparatus of the present invention make it possible to test whether a material is suitable for use in the 3D printing of orthoses. The examples demonstrate that, although the 3D printed polycarbonate orthosis has the highest ankle joint stiffness, it has decreased fatigue resistance after repeated loading. Therefore the use of 3D printed polycarbonate is not advisable in a clinical setting unless the design is enhanced to account for the difference in mechanical properties. The 3D printed nylon-12 orthosis was less stiff than the conventional polypropylene orthosis, but it exceeds the minimum stiffness requirement. It has fatigue resistance comparable to that of the conventional polypropylene orthosis and is mechanically sound for use in the clinical setting. The method and apparatus of the present invention also allows clinicians and engineers to methodically assess the material properties of additive manufactured orthoses to determine if they meet the biomechanical requirements of patients. This may be done, when designing new types of orthoses with new features, to consider safety and functionality for that design before individual orthoses with the features in that new design are prepared. The assessment may also be performed for quality control by sampling orthoses of the same design, prepared for a patient using standard or common design parameters. Unlike the conventional subtractive process in which casting and moulding would have to be repeated in order to prepare another orthosis, the design for a 3D printed orthosis is stored in a computer so another orthosis can be printed to replace the one destroyed in fatigue testing. Moreover, if it is desirable to test only flexibility, in order to ensure that a specific design does suit an individual patient, this could be done for the actual orthosis. If it proved, for example, that flexibility was not as anticipated, the design could be revised for a new orthosis to be printed accordingly. This rigorous process will ensure that patients are safeguarded whilst at the same time counterbalancing the timely introduction of new technology to daily clinical care.

Other alternative embodiments are described below.

The clamping mechanism defined by the jigs 15a, 15b may include other types of fastening mechanism or fastener. For example, the clamping mechanism may include a fastener having at least one of a clasp and a strap for fastening the orthosis to facilitate bending of the orthosis at a predetermined portion.

Any other force measurement device or arrangement may be used in place of or in conjunction with the load cell 19.

Claims

Claims:

1. A method for testing material properties of an orthosis, comprising:

securing the orthosis to allow the orthosis to bend through a predetermined portion;

applying force in a first direction; and

transmitting the applied force to the orthosis to enable the orthosis to bend through the predetermined portion in a manner which mimics forces applied to the orthosis in use.

2. A method according to claim 1 wherein the applied force is translated into a rotational movement to bend the orthosis through the predetermined portion.

3. A method according to either one of claim 1 or 2 wherein a lateral movement is allowed so that the bending movement of the orthosis may be deflected.

4. An apparatus for testing material properties of an orthosis, comprising: a clamping mechanism operable to secure the orthosis to allow the orthosis to bend through a predetermined portion;

an actuator operable to apply force in a first direction; and

a linking mechanism arranged to connect the actuator to the orthosis to enable the applied force to be transmitted to bend the orthosis through the predetermined portion in a manner which mimics forces applied to the orthosis in use.

5. An apparatus according to claim 4 wherein the actuator comprises an actuator rod extending in the first direction.

6. An apparatus according to either one of claims 4 and 5 further comprising a force measurement device for measuring the force applied by the actuator.

7. An apparatus according to any one of claims 4 to 6 further comprising a computing device for calculating the force applied to the orthosis.

8. An apparatus according to any one of claims 4 to 7 wherein the actuator is in operative association with a first connector rod.

9. An apparatus according to claim 8 wherein the operative association of the actuator and the first connector rod is through a first joint which translates the applied force into a rotational movement to bend the orthosis.

10. An apparatus according to claim 9 wherein the first joint includes a slider- and-pin joint.

11. An apparatus according to any one of claims 8 to 10 wherein the first connector rod is in operative association with a second connector rod.

12. An apparatus according to claim 11 wherein the operative association of the first connector rod and the second connector rod is through a second joint which allows lateral movement.

13. An apparatus according to claim 12 wherein the second joint includes a ball joint.

14. An apparatus according to any one of claims 11 to 13 wherein the orthosis is secured to the second connector rod.

15. An apparatus according to any one of claims 12 to 14 wherein the second connector rod is anchored through a third joint which allows lateral movement.

16. An apparatus according to claim 15 wherein the third joint is a ball joint.

17. A method for testing material properties of an orthosis, comprising: securing the orthosis to allow the orthosis to bend through a predetermined portion;

generating a force by an actuator; and

in response to the generated force, generating rotational and lateral movements to cause the orthosis to bend through the predetermined portion.

18. An apparatus for testing material properties of an orthosis, comprising: a clamping mechanism operable to secure the orthosis to allow the orthosis to bend through a predetermined portion;

an actuator operable to generate a force; and

a linking mechanism arranged to generate rotational and lateral movements, in response to the generated force, for causing the orthosis to bend through the predetermined portion.