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Posted: April 14, 2009
Biocompatible materials for rapid prototyping of prosthetic implants
(Nanowerk News) The implantation of integrated biomedical devices to the human body provides challenges to engineering materials science and biology. The demand for metallic and polymeric biomaterials is greatly increasing because of the rapid growth of the world’s population, the increasing proportion of older people and the high functional requirements of younger people.
Rapid prototyping (RP) of medical devices and custom-made prosthetic implants is also an area of growing interest and subject to intensive research during the last decades. The unique advantages of layer additive manufacturing open the way for design and development of multi-tasking functional tools with a wide range of applications from dentistry to regenerative medicine and tissue engineering.
The current materials of choice for RP are metals, ceramics and limited range of biocompatible polymers. Photopolymers are most attractive for biomedical applications offering mechanical properties versatility and unlimited options in functionalization.
Soft lithography process
The Custom-fit project has been developing during the last 4 years new bio-compatible materials which can be used in its machines. As the machines developed into the project framework have achieved the rapid manufacturing of Multi-Materials Graded Structures, one of the project’s partners, DSM from the Netherlands, has been developing new bio-compatible materials which can be printed with these techniques.
They have achieved the development of photo-curable resins, based on either bio-stable or biodegradable oligomers. These materials are readily processable on commercial RP machines, yielding high quality, biocompatible polymers and demonstrating the versatility and prospective of RP as method of choice for fabrication of biomedical devices. The biostable resins comprised polyester/polyether oligomers bearing acrylate or methacrylate functions while the biodegradable composites have been prepared from methacrylate-functionalized, biocompatible polyesters.
The chemical composition, purity and molecular weight distribution of the synthesized oligomers were proven by means of 1H NMR, IR spectroscopy and gel permeation chromatography. The conversion of (meth)acrylate functions after the photo-curing process was estimated by FT-IR. Standard mechanical tests were performed on 40 mm long tensile bars produced by Envisiontec perfactory machine.
Applying polyester/polyether backbone oligomers and reactive diluents DSM adapted composites to the optimal viscosity requirements of the Envisiontec machine. This made it possible to use the full machine capacity and to obtain precise RP-parts as small as 50 microns. Such accuracy was essentially important when targeting a custom-fitting artificial implant. Furthermore the RP processing afforded a high (meth)acrylate conversion of the cured polymers and resulted in materials with a broad range of mechanical properties. The results demonstrated the flexibility of both the composite materials and the production method in fabrication of parts of desired mechanical properties.
In order to obtain biodegradable RP-parts, DSM prepared also methacrylate functionalized biodegradable oligomers and incorporated them in RP-processable composites. Applying different biodegradable polyesters they fine tuned the degradation rate of the final, photo-cured material.
The production method ensured a high conversion of the methacrylate functions. This finding is supported also by the toxicological studies on the cured material where no harmful extractables were found. The tested material meets the requirements of the Intracutaneous Test according ISO 10993-10 guidelines.