Innovativer Regionaler Wachstumskern "Molecular designed biological coating (MBC)": Verbundprojekt 3: Biofunktionalisierte Metallschäume als Knochenimplantate - POROMES. Schlussbericht. Förderkennzeichen BMBF 03WKBH3 A-C

Almost all currently available implants for bone defect reconstruction in load bearing applications are made of metals, polymeric materials, and sintered ceramics. Though these materials are considered sufficiently biocompatible, they generally do not form stable interfaces with surrounding bone tissue so that after individually different periods implant failures may occur and revisions may become necessary. A further important reason for implant failure is mechanical mismatch between implant and bone structure. This is especially true for large implants designed for bone reconstruction. An ideal material for substitution and regeneration of extended bone defects should combine high initial mechanical stability and degradability. The aim was to utilise biocompatible metal foams for their structural and mechanical similarity with cancellous bone (structural biocompatibility) and combine these with appropriate modifications of the metal surface to confer bioactivity (surface biocompatibility). In the authors' approach to create bioactive metal structures, metal foam surfaces were coated with nanostructured calcium phosphates or by filling the pores of metal foams with biomimetic bone like calcium phosphates (mineral bone cement). The authors developed cellular metal foams based on different metals (stainless steel 316L, steel alloys) with appropriate properties (mechanics, open cellularity, homogeneity). Subsequently, bioactivation processes result in suitable implant materials: open cellular bioactive coated metal foams composite materials existing of i) cellular (and bioactivated) metal foam and ii) mineral bone cement, entailing a material with outstanding statical and dynamical mechanics. In cell culture experiments with human mesenchymal stem cells bioactivated metal foams showed high biocompatibility and bioactivity. A substantial stop towards a fully resorbable and degradable implant was achieved by a new bioactive coating which initially protects iron metal foams from corrosion. Degradation of these metal foams will not start before active resorption of this coating has occurred. Hence the implant may be integrated first and then fully degrade over time and finally become substituted completely by own bone tissue. The authors conclude that development of bioactivated metal foams and metal foam/mineral bone cement composites for application as bone implant materials deserves further efforts. Based on the achieved results implantation studies are justified and should be predictive for performance in clinical application