domingo, 22 de abril de 2012

Polysaccharide-Coated Thermosets For Orthopaedic Applications: From Material Characterization To In Vivo Tests

The development of tissue engineering and regenerative medicine techniques has introduced the new concept of “bioactive” biomaterial, able to induce specific biological responses by engaging interactions with the surrounding living tissue at  the molecular level.In particular, for applications in orthopaedics and dentistry the ideal biomaterial surface should be able to induce osteogenesis and ensure a stable biological/chemical bond between implant and bone.

Various materials are clinically used for orthopaedic implants, in particular titanium, CoCrMo and  stainless steel alloys. In spite of their good biocompatibility, such metallic materials have some drawbacks, mostly related to high stiffness, possible wear of surface oxide and lack of bioactivity.  Alternative materials are being sought to overcome such limitations.

The long term stability and success of orthopaedic implants depend on the osseointegration process  which is strongly influenced by the biomaterial surface. A promising approach to enhance implant  integration involves the modification of the surface of the implant by means of polymers which mimic the natural components of the extracellular matrix,  e.g. polysaccharides. In this study methacrylate thermosets (bisphenol A glycidylmethacrylate/triethyleneglycol dimethacrylate), a widely used composition for orthopaedic and dental applications, have been coated by electrostatic deposition of a bioactive chitosan-derivative. This polysaccharide was shown to induce osteoblasts aggregation in vitro, to stimulate cell proliferation and to enhance alkaline phosphatase activity. 
The coating deposition was studied by analyzing the effect of pH and ionic strength on the grafting of the polysaccharide. Contact angle studies show that the functionalized material displays a higher hydrophilic character owing to the increase of surface polar groups. The mechanical properties of the coating were evaluated by nanoindentation studies which point to higher values of indentation 
hardness and modulus (E) of the polysaccharide surface layer, while the influence of cyclic stress on the construct was assessed by fatigue tests. Finally, in vivo tests in minipigs showed that the polysaccharide-based implant showed a good biocompatibility and an ability for osseointegration at least similar to that of the titanium Ti6Al4V alloy with roughened surface.  

Polysaccharide-Coated Thermosets for Orthopaedic Applications: from Material 
Characterization to In Vivo Tests 
Andrea Travan*, Eleonora Marsich*, Ivan Donati*, Marie-Pierre Foulc, Niko Moritz,
Hannu T. Aro, Sergio Paoletti* 
*Department of Life Sciences, University of Trieste, Via Giorgieri 1, Trieste I-34127, Italy 
Rescoll, Société de Recherche, 8 Allée Geoffroy Saint-Hilaire, 33615 Pessac, France 
Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology,               
University of Turku, Kiinamyllynkatu 10, 20520, Turku, Finland

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