EP0700331A1

EP0700331A1 - Process for forming thermoplastic materials, in particular absorbable thermoplastics

Info

Publication number: EP0700331A1
Application number: EP94916189A
Authority: EP
Inventors: Dieter Bendix; Randolf Von Oepen; Stefan Seibt
Original assignee: Boehringer Ingelheim International GmbH; Boehringer Ingelheim GmbH
Current assignee: Boehringer Ingelheim International GmbH; Boehringer Ingelheim GmbH
Priority date: 1993-05-05
Filing date: 1994-05-04
Publication date: 1996-03-13
Also published as: DE4314869A1; JPH09500151A; WO1994025242A1; FI955280A0; FI955280A

Abstract

The present invention pertains to a new process for forming thermoplastic materials - in particular bioabsorbable thermoplastics - at temperatures below the melting temperature range, using gases under critical conditions.

Description

Process for shaping thermoplastics, in particular resorbable thermoplastics

The present invention relates to a new process for shaping thermoplastics - in particular bioabsorbable plastics - at temperatures below the melting temperature range using gases or substances in the liquid state under high pressure.

According to the state of the art, thermoplastic moldings and semi-finished products are mainly produced by machining, reshaping, from solution or using the so-called primary molding process. In particular for the processing of resorbable plastics for the medical field and other technical thermoplastics, the above-mentioned methods have, in principle, z. T. very serious disadvantages.

For example, during machining, semi-finished products are machined to the final geometry by machining. Due to the high material waste, the long processing times, the risk of micro-notches on the processing surfaces, which can lead to premature failure of the molded part, as well as the limited shaping options, this process can only be used to a very limited extent in plastic molding.

In the case of resorbable plastics, the high material waste and the purity (in particular for medical applications) that are difficult to guarantee (use of lubricants and coolants) represent serious disadvantages.

In the forming process, semi-finished products are shaped to the final geometry below the melting temperature. However, with

ORIGINAL DOCUMENTS this method, only the simplest geometries can be realized. The macromolecules are oriented in the forming direction; this leads to an anisotropic property profile with increased mechanical properties in the stretching direction, but weakening in the transverse direction.

On the other hand, only very thin layers can be applied to appropriate supports using methods in which the solution is usually shaped in organic solvents. Especially when applying several layers to create larger wall thicknesses, there is a risk of residual solvent remaining in the molded part. This is particularly unacceptable in the case of resorbable plastics, since the solvents undesirably get into the organism in the course of degradation.

In the primary molding process - such as Extrusion and injection molding - the thermoplastic must be melted in order to be able to mold it. The high temperature required above the melting range in the case of thermally unstable plastics - in particular in the case of resorbable polymers and some engineering plastics - leads to molecular weight reduction, which in turn has a disadvantageous influence on the mechanical properties.

Extrusion also only allows the production of semi-finished products of simple geometry. - On the other hand, molded parts with complex geometries - as they are required for medical applications - cannot be produced by extrusion.

On the other hand, moldings of complex geometries can be produced by injection molding. The thermoplastic melt is introduced into the cooled tool, the melt solidifying during the filling phase. However, this usually inevitably leads to undesired orientations in the molded part, which, particularly in the case of amorphous resorbable plastics, can lead to uncontrollable shrinkage when used medically as an implant material.

The inhomogeneous cooling of the molding compound also freezes tensions which lead to undesired distortion after removal from the mold. Furthermore, it is not possible with this method to produce molded parts with a large flow length / wall thickness ratio.

Particularly for thermally labile resorbable polymers, careful processing into complex molded part geometries at low temperatures below the melting range is desirable. This is with the above

Processing methods - if at all - can only be implemented inadequately.

The object of the present invention is accordingly to provide a method for shaping thermoplastic materials - in particular resorbable thermoplastics - which avoids the disadvantages known from the prior art. According to the invention this object is achieved in that the viscosity of a thermoplastic - such. B. a resorbable plastic - by fumigation with one or more - possibly liquefied - gases under high pressure - preferably in the supercritical range - so far reduced that the thermoplastic material can be molded. - The low viscosity is an essential prerequisite for the formation of complex geometries.

Suitable thermoplastic polymers for the process according to the invention are, in particular, amorphous polyesters, for resorbable objects - ie objects that can be broken down by the human or animal body - polyesters based on α-hydroxycarboxylic acids are particularly preferred.

Among other things, particular preference is given to amorphous poly-D, L-lactide,

Copoly ere from D, L-lactide and glycolide as well

Poly- (L-lactide-co-D, L-lactide), wherein the ratio of

L-lactide to D, L-lactide can be up to 90 to 10 - preferably 70 to 30 -, poly-meso-lactide,

Poly (D, L-lactide-co-trimethylene carbonate),

Poly (meso-lactide-co-trimethylene carbonate) and amorphous

Poly (L-lactide-co-trimethylene carbonate).

Fumigation according to the invention at low temperatures and under high pressure presupposes that the gas has good solubility in the respective polymer. - The solubility of gases or liquids in polymers is a function of pressure and temperature. Particularly good solubility parameters are achieved when the gas changes into the so-called supercritical state.

Supercritical liquids or gases are known from the prior art. Examples here include carbon dioxide, ethylene, propane, ammonia, nitrous oxide, water and toluene. Depending on the supercritical substance used in each case, the process according to the invention can be carried out at a pressure in a range from 50 to 800 bar - preferably 50 to 400 bar and particularly preferably 50 to 200 bar.

Surprisingly, it was found that carbon dioxide is particularly suitable for lowering the viscosity of polymers. Carbon dioxide goes into the at a temperature of 31 ° C and a pressure of just over 73.76 bar supercritical state and has a 25 times larger diffusion coefficient in polymers than, for example, nitrogen.

However, other gases or liquids under high pressure or in the supercritical range can also be used in the method according to the invention.

Three variants of the method according to the invention are presented below:

a) Rieselfδrmiger plastic is introduced into a mold cavity and gassed under high pressure. If the viscosity is reduced to such an extent that the plastic can be deformed, the mold cavity is reduced and a compact molded part is produced.

b) Rieselfδrmiger plastic is introduced into a mold antechamber and gassed under high pressure. As soon as the viscosity lowers so much that the plastic can be deformed, the mold cavity is reduced - preferably by the penetration of an injection plunger - and the plastic is pressed into the mold cavity. The pressures for filling a previously manufactured mold are only determined by the pressure losses caused by the geometry and are therefore considerably lower than in a comparable molded part production in the injection molding process, since the viscosity in this case is not a function of time. This means that even very thin-walled molded parts with long flow paths can be manufactured.

c) A precisely dosed preform - preferably in the form of a tablet - can also be processed analogously using the two methods mentioned above. Due to the almost constant viscosity of the "polymer melt" during the filling time, the molded part can be filled very slowly in order to counteract degradation of the molecular weight by shear. Internal stresses due to temperature gradients across the cross section of the molded part can also be avoided. Shaped bodies which are produced with this process are free of orientations, since molecules which have been aligned by the filling process have a sufficiently long time to relax after the mold has been filled.

The mold itself must have sufficient ventilation options so that the gas can escape from the polymer again. It is therefore necessary to use sintering tools or tools with ventilation slots. - As tools, silicone tools are to be mentioned here as examples, which are suitable for the production of individual implants as well as for small series and prototypes. - Silicone is particularly suitable due to its special diffusion properties, its high dimensional stability and its uncomplicated processability.

For the production - for example - of small series but also large series are among others Tools made of PUR soft foam. Polyurethane also has excellent diffusion properties and also has excellent dimensional stability.

Sintered metal tools with a barrier layer made of "a gas-permeable membrane (e.g. silicone paint) are also suitable for the production of small and large series.

A vacuum can be applied to the tool to accelerate the degassing. The shaped body can be removed from the mold when the viscosity has risen to such an extent that it is dimensionally stable. To illustrate the manufacturing process, reference is made to the drawings:

1 shows the diagram of a gassing system suitable for the method according to the invention. - This consists essentially of the gas supply 1 with pressure indicator 2, the filters 3 and 4, the coolers 5 and 6, the adjustable diaphragm pump 7, the pulsation damper 8 and the shut-off valves 9 and 10, the safety valve 11 and the pressure indicator 12 and the autoclave 13 with the temperature display 14 and the pressure display 15 as well as the shut-off valve 16 and the silencer 17.

Fig. 2 shows the process autoclave 20, in which the devices required for the shaping such as press or injection unit are introduced.

3 shows the injection unit 28 with the release mechanism 21, the spring pretensioning device 22, the spring 23, the piston rod 24, the piston 25 and the piston antechamber 26 as well as the tool 29 with the closing mechanism 27.

The injection unit 28 serves to inject polymer plasticized by CO2 into a tool.

First, the polymer granules are filled into the piston vestibule 26 of the injection unit 28. The spring 23 is then preloaded, the injection pressure being able to be set, for example, between 1 and 10 bar. The injection unit together with the flanged tool 29 is inserted into the process autoclave 13 (FIG. 1). Fumigation follows, which is characterized by the parameters of pressure, temperature and time. After reaching the desired state of fumigation, a trigger mechanism 21 is actuated from the outside and the injection is thus triggered. The plasticized polymer is injected into the mold cavity (see FIG. 4). This is followed by the pressure release, which can take place at different speeds depending on the desired molded part structure and the tool material used.

The tool 29 consists of clamping plates made of perforated sheet metal and shaped plates which contain the cavity to be molded. A wide variety of materials can be used as mold plate materials. Silicone and polycarbonate are used in the application examples. Tools made of sintered metal or polyurethane foams are also possible.

4 shows a tool holding device 30 with a flange and a retaining valve (for example made of polycarbonate) 31, sprue nozzle 32, check valve (with ball) 33, shaped plates 34, clamping plates made of perforated plate 35 and the cavity 36.

5 shows the result of an application example for the shaping with the aid of the gassing process

The production of a resorbable vascular clip is described schematically below.

Procedure:

- Construction of the molded part using a CAD system

- Production of a prototype using stereolithography

- Casting of the prototype tool with silicone rubber

(KE-1300T from HEK

- Production of the molded part using the silicone tool in the gassing process

Material: 50:50 blend of PDLLA (poly-D, L-lactide) and P (DLLA-co-TMC) poly (D, L-lactide-co-trimethylene carbonate 50-50) Process parameters:

Fumigation time 2 h Fumigation temperature: 38 ° C Fumigation pressure: 100 bar Injection pressure: 5 bar Pressure relief: 6 h

Result: microcellular clip, see photos, in Fig. 5.

As already mentioned, it is a further object of the present invention to produce compact moldings which can be loaded with active substances as required. Press technology, which is described here as an example for a tension rod, offers one possibility of producing the molded parts described.

Tool technology:

The tool (in the present case a plunge edge tool for producing a compact tension rod) consists of a shaped plate 40 on which the contour of the plunger is raised (see FIG. 6). The form aperture 41 has exactly the negative contour of the press ram. A sintered metal 43 serves as the cover plate, which facilitates gas entry and exit. A special - gas-permeable - foil 42 prevents the material, whose viscosity is greatly reduced, from penetrating into the sintered pores. The bulk material (resorbable polymer, addition of active ingredients) is compressed by bracing the molded plate with the sintered metal plate by means of disc springs 44.

In addition, the fitting bolt 45 is shown in FIG. 6. The mold plate, mold panel and sintered metal are made of stainless steel. Procedure:

Pour the polymer in powder, granule or flake form into the mold. If loading with active ingredients is desired, the polymer is first mixed with the active ingredient. The press ram (mold plate 40) is inserted into the mold panel 41 and clamped over the screws by means of disc springs. The entire tool is placed in the autoclave 13 (Fig. 1).

Process parameters:

The autoclave is filled with CO2, which is compressed by means of a piston diaphragm pump, the process pressure is between 20 and 2000 bar, preferably between 60 and 200 bar. The process temperature is less than 37 ° C when loaded with temperature-sensitive active ingredients. However, the temperature can be freely selected between -70 ° C and 400 ° C by tempering the autoclave.

Material:

Absorbable polymers, preferably amorphous absorbable

Polymers. Active ingredients: no restriction.

Results:

A mixture of 50 volume percent resorbable material (eg Resomer® R 207, a poly-D, L-lactide with an inherent viscosity of approx. 1.5) and 50 volume percent active ingredient (model substance powdered sugar) was added to the tool. 7 shows two scanning electron micrographs of the sample. The sample was cold broken. The molded body obtained is compact and the active substance particles (sugar) are very well bound in the matrix. In the present case, FIG. 7 discloses the morphology of a body made of Resomer® R 207 loaded with 50% by weight of cane sugar.

Another object of the present invention is to foam foamed articles with a given geometry. The foam structure should be as integral as possible in order to increase the bending stiffness of the samples compared to a molded part with the same mass.

Tool technology:

A tension rod was selected as the part geometry. 8 shows a modular foaming tool; this tool consists of 2 support plates, 51, 52, 2 gas-permeable plastic plates 53, 54 (for example made of polycarbonate) and intermediate plates 55 with a special grinding for gas and degassing. The intermediate plates are centered by means of dowel bolts 45. The tool is clamped with screws and nuts 46, 47. The number of intermediate plates specifies the height of the foamed component.

Procedure:

Input of a preform, manufactured e.g. in injection molding or pressing. Lock the tool. Inserting the filled tool in the autoclave and pressurizing it with CO2 •

Litigation:

A variation of the process parameters showed that a relatively low gassing pressure (100 bar) and a low gassing temperature of 30 ° C show good properties with regard to an integral foam formation. Higher pressures (200 bar) and a higher process temperature (65 ° C) lead to a foam structure with an even pore distribution. The time was kept constant at 60 minutes. Material:

An injection molded tension rod made of Resomer® R was used as the material

207 used.

Results:

With a degree of foaming of 150% (factor 2.5), the foam structure shown in FIG. 9 resulted for a pressure of 100 bar, a temperature of 30 ° C. and a fumigation time of 60 minutes. A comparison of the bending stiffness shows an increase by a factor of 4 for keline deflections (<2 mm) compared to the unfoamed tension rod of the same mass.

Figs. 10 and 11 show the homogeneous foam formation at a pressure of 200 bar, a temperature of 65 ° C. and a gassing time of 60 minutes.

With this method it is also possible to achieve partially foamed structures by "jacking out" the parts that are not to be foamed by an insert. The process management must be adjusted in this case.

10 shows the internal structure of the foamed material.

11 shows the foam structure of poly (D, L-lactide-L-lactide) / poly-L-lactide at 65 ° C., 200 bar and a degree of foaming of 150.

Production of a resorbable tube

Procedure:

Machining of a polycarbonate tool Production of the molded part using the polycarbonate tool in the gassing process

Material: 50:50 blend of PDLLA and P (DLLA-co-TMC) (50-50)

Process parameters:

Fumigation time: 2 h Fumigation temperature: 45 ° C Fumigation pressure: 100 bar Injection pressure: 10 bar Pressure relief: 2 h

Result: almost compact tube, outer diameter 6 mm, inner diameter 4 mm, length: 18 mm

FIG. 12 shows the systematic process sequence when producing a self-expanding foam: step 1 relates to filling; the dry ice tablet 60 and the - loaded - polymer 61 are introduced into an appropriately designed reaction vessel. Step 2 includes closing the reaction vessel 62 with a subsequent increase in temperature. Finally, step 3 relates to the deep-cold removal of the sample body 63 with subsequent warming up to the expanding foam 64.

Another object of the present invention relates ^• selbstexpantierende foams. In particular, the object of the present invention is to produce a component which is dimensionally stable at low temperature and foams at body temperature. Tool technology:

A small lockable stainless steel container.

Procedure:

Filling a certain amount of dry ice (solid CO2) and a resorbable body, optionally loaded with active ingredients. Enter dry ice and shaped bodies in the cooled stainless steel chamber and close them. Warm the stainless steel chamber to room temperature. Before removing the body, the small pressure chamber and its contents must be cooled (depending on the amount of dry ice weighed in and the resulting gas pressure), a temperature of approx. 0 ° C is sufficient. Opening the small pressure container, taking the sample and positioning it at the desired indication point, for example to list a bone defect or to close a medullary cavity. The process chain is shown in Fig. 12.

Material: Amorphous resorbable polymer, e.g. Resomer® R 207.

Results:

Depending on the input of dry ice, the foaming temperature and the resulting removal temperature of the molded body can be specified. Depending on the amount of gas dissolved, the body expands isotropically by a factor of 2, which corresponds to an eightfold increase in its volume.

In addition, it should be noted that small (for example within the scope of 1% by weight) addition of solvents - such as acetone - to the gas - for example carbon dioxide - increases the solubility in the polymer - for example poly-L-lactide - by approximately 500% increase. In summary, it can be said that the methods presented are characterized by the following properties:

Production of moldings of complex geometry without thermal damage,

Production of stress-free molded bodies,

Possibility to manufacture molded bodies with thin walls and possibly long flow paths,

Avoiding molecular weight loss due to shear.

Depending on the enthermoplastic material used and depending on the limits set by the supercritical material, the gassing can be in a temperature range from 20 to 400 ° C. - preferably 20 to 120 ° C. and for resorbable polyesters based on lactide and Glycolide particularly preferably in a range from 20 to 80 ° C.

However, only low temperatures are required to lower the viscosity of the biodegradable polyesters mentioned. In particular when using carbon dioxide, temperatures of approximately 30 ° C. are sufficient to reduce the viscosity of thermoplastic polymers - in particular absorbable polymers - to such an extent that they can be shaped. Because of these low temperatures, it is possible to add fillers to the polymer which are sensitive to temperature and therefore cannot otherwise be used in the usual processing methods. In particular for resorbable polymers, it is advisable to insert pharmaceutical active ingredients into an implant, for example an osteosynthesis device, such as a bone plate, for example. mix in before processing. The active ingredient can then be absorbed by the polymer or by

Diffusion mechanisms are slowly released to the neighboring body tissue.

The shaping takes place in the case of polymers which are loaded with fillers, analogously to the production of shaped bodies in accordance with the abovementioned methods. In order to guarantee the finest possible distribution of the fillers in the molded body, the filler must be mixed well with the polymer. One possibility is to mix the polymer and filler before gassing and to reduce the viscosity of the mixture (compound) by subsequent gassing to such an extent that it can be shaped into its shaped body.

Another variant consists in first reducing the viscosity of the polymer by gassing and then mixing in a filler. In this method the filler can also be a liquid component. After mixing, the compound can in turn be shaped into a shaped body in the manner described above.

The lowering of the viscosity due to the fumigation also makes it possible to foam a preform. First, a compact preform - preferably in the injection molding process - is produced and inserted into a corresponding tool, which has the contour of the foamed end product. According to the method described above, the tool must have sufficient ventilation options or be made of a sintered metal. The inserted molded part is gassed with the tool under a high pressure, so that the gas or the supercritical fluid is dissolved in the polymer. After the pressure has been released, the molded part can expand in the mold by expansion of the gas dissolved in the molded part. The foaming can be influenced by heating be, the temperature is significantly lower than the melting temperature. Due to the predetermined contour of the mold cavity, the molding foams in a defined manner. The degree of foaming can be specified precisely on the basis of the free volume made available.

This development is particularly useful for resorbable polymers. For example, resorbable bone plates are currently being tested for splinting fractures. However, the strength of the resorbable polymers is often not sufficient to fully substitute metallic implants in a similar dimension. To the weaker

To compensate for material properties, the plates often have to be dimensioned comparatively much larger. An associated mass accumulation of resorbable plastics in the body is, on the other hand, not very desirable. On the one hand, the resorption time increases with increasing implant size, which is undesirable in many cases - on the other hand, an increased use of material during the resorption can lead to undesirable reactions of the body. A bone plate which is only foamed in height and which is produced by the method described above, however, has an essentially increased flexural rigidity with an integral density distribution and the same mass used. Because of the foam structure, such an implant can be absorbed faster than a comparably stiff implant, which is of compact construction.

According to the foaming process described above, it is also possible to foam in two stages, to partially foam a previously produced molded part. For this purpose, the molded part is again placed in a tool which corresponds to the end contour of the foamed component. The places that should be compact in the later molded part will tightly enclosed by the tool. The areas to be foamed had the space around which the molded part should foam at this point. The production of partially foamed components proceeds analogously to the process for producing foamed molded parts described above.

Partial foaming is particularly desirable for resorbable implants. Although the foamed bone plates described above have a significantly increased flexural strength with the same use of material as a compact shaped plate, it is hardly possible to adapt such a plate to the bone. However, it is necessary to be able to adapt bone plates to the respective geometry of the bone. Due to the thermoplastic material behavior of resorbable polymers, partial heating at the desired bending point - e.g. B. with a warm object or with a hot air blower - the plate can be adjusted. However, a foamed structure has a very poor thermal conductivity due to the porosity, so that a foamed plate is very difficult to bend. The places where the possibility of bending should be provided should therefore be switched off compactly.

The above-mentioned tasks are solved by the methods described in the above examples. Different, different refinements of the method will become apparent to the person skilled in the art from the present description. However, it is expressly pointed out that the example and the description associated with it are provided only for the purpose of explanation and description and should not be regarded as a limitation of the invention.

Claims

1. A process for the molding of thermoplastics, characterized in that the thermoplastic is introduced in a free-flowing form or in the form of a preform into a mold cavity and the viscosity of the plastic is reduced with supercritical compounds to such an extent that it can be deformed and by reducing the mold cavity creates a compact shaped body.

2. A process for shaping thermoplastics, characterized in that it comprises the following steps

introducing a compact preform into a shaping tool which has the contour of the desired molded part.

Fumigation of the preform with one or more gases at a pressure in the range from 50 to 800 bar or with one or more liquefied gases under high pressure in the range from 50 to 800 bar under supercritical conditions.

expand the preform within the molding tool.

3. The method according to claim 2, characterized in that the preform is partially foamed, the resulting molded part having a compact or a foamed structure at the desired locations.

4. The method according to any one of claims 1 to 3, characterized in that the gas or liquid is in a supercritical state.

5. The method according to claim 4, characterized in that the supercritical compound is selected from the group of carbon dioxide, ethylene, propane, ammonia, nitrous oxide, water or toluene.

6. The method according to any one of claims 1 to 5, characterized in that the method is carried out at a temperature in a range from 20 to 400 ° C.

7. The method according to any one of claims 1 to 5, characterized in that the method is carried out at a temperature in a range from 20 to 120 ° C.

8. The method according to any one of claims 1 to 5, characterized in that the method is carried out at a temperature in a range of 20 to 80 ° C.

9. The method according to any one of claims 1 to 5, characterized in that the method is carried out at a pressure in the range from 50 to 400 bar.

10. The method according to any one of claims 1 to 5, characterized in that the method is carried out at a pressure in the range from 50 to 200 bar.

11. The method according to any one of claims 1 to 10, characterized in that an amorphous thermoplastic material - in particular an amorphous polyester - is used as the thermoplastic material.

12. The method according to claim 11, characterized in that the polyester used is a polyester which is derived from one or more α-hydroxycarboxylic acids.

13. The method according to claim 12, characterized in that the α-hydroxycarboxylic acid is represented by glucolic acid, D- or L-lactic acid.

14. The method according to any one of claims 11 to 12, characterized in that a copolymer is used as the thermoplastic material.

15. The method according to claim 16, characterized in that a copolymer is used as a copolymer based on an α-hydroxycarboxylic acid and another physiologically compatible comonomer.

16. The method according to claim 15, characterized in that the copolymer is poly-D, L-lactide, copolymers of D, L-lactide and glycolide, poly (L-lactide-co-D, L-lactide), poly (D , L-lactide-co-trimethylene carbonate,

Poly (meso-lactide-co-trimethylene carbonate or poly (L-lactide-co-trimethylene carbonate) is used.

17. The method according to claim 16, characterized in that a poly (L-lactide-co-D, L-lactide) is used in which the ratio of L-lactide to D, L-lactide is up to 90:10.

18. The method according to claim 17, characterized in that the ratio of L-lactide to D, L-lactide is up to 70 to 30.

19. The method according to any one of claims 1 to 18, characterized in that free-flowing plastic is preferably filled as a powder or granules in a mold cavity is, the plastic flowable under critical conditions then compacted by reducing the mold cavity of the plastic and molded into a molded part.

20. The method according to any one of claims 1 to 19, characterized in that free-flowing plastic is preferably filled as a powder or granules in a vestibule and the flowable plastic is then pressed into a mold cavity by reducing the size of the vestibule and molded into a molded part.

21. The method according to any one of claims 1 to 19, characterized in that a preform is used in tablet form.

22. The method according to any one of claims 1 to 19, characterized in that a preform is introduced into a mold cavity which is larger in its dimensions and is then gassed and then foamed in the mold cavity to the final geometry.

23. The method according to any one of claims 1 to 22, characterized in that the foaming process taking place after the gassing is controlled by heating.

24. The method according to any one of claims 21 or 22, characterized in that the preform is partially foamed by a suitable choice of the dimensions of the mold cavity.

25. The method according to any one of claims 1 to 24, characterized in that solid additives - for example pharmaceutically active additives - are mixed into the free-flowing plastic.

26. The method according to any one of claims 1 to 24, characterized in that pharmaceutical additives are added in liquid form after the flowability of the plastic has been reached.

27. The method according to claim 25 or 26, characterized in that pharmaceuticals - in particular antibiotics or growth proteins or X-ray contrast agents - are used as additives.

28. The method according to any one of claims 1 to 27, characterized in that a silicone tool, a tool made of flexible polyurethane foam or polycarbonate or a sintered metal tool with a barrier layer made of a gas-permeable membrane is used as the shaping tool.

29. Shaped part, produced by a method according to one of claims 1 to 28, characterized in that it is a compact shaped part.

30. Molding produced by a method according to one of claims 1 to 28, characterized in that it is a foamed molding.