Grafting RGD containing peptides onto hydroxyapatite to promote osteoblastic cells adhesion.

Ceramics possess osteoconductive properties but exhibit no intrinsic osteoinductive capacity. Consequently, they are unable to induce new bone formation in extra osseous sites. In order to develop bone substitutes with osteogenic properties, one promising approach consists of creating hybrid materials by associating in vitro biomaterials with osteoprogenitor cells. With this aim, we have developed a novel strategy of biomimetic modification to enhance osseointegration of hydroxyapatite (HA) implants. RGD-containing peptides displaying different conformations (linear GRGDSPC and cyclo-DfKRG) were grafted onto HA surface by means of a three-step reaction procedure: silanisation with APTES, cross-linking with N-succinimidyl-3-maleimidopropionate and finally immobilisation of peptides thanks to thiol bonding. Whole process was performed in anhydrous conditions to ensure the reproducibility of the chemical functionalisation. The three-step reaction procedure was characterised by high resolution X-ray photoelectron spectroscopy. Efficiency of this biomimetic modification was finally demonstrated by measuring the adhesion of osteoprogenitor cells isolated from HBMSC onto HA surface.

Physical and biological characteristics of the main biomaterials used in pelvic surgery.

Our study compared mechanical and biological properties of four materials classically used in surgery: polyethylene terephtalate (Mersilene), polypropylene (Marlex), polytetrafluoroethylene (Teflon) and expanded one (Gore-Tex) and polyaramide (Kevlar). No deterioration for polytetrafluoroethylene and polypropylene under irradiation was observed when materials were treated by physical means. Mechanical tests showed that all these materials could bear more than 50 N. Such a high tensile strength is never reached in visceral physiology. Results of graft elongation during tensile strength test shows two classes: a first one that includes high elongation grafts (Gore-Tex and Marlex) and a second one that includes low elongation grafts (Mersilene and Kevlar). As these materials have many potential uses in surgery, we have performed cytotoxicity tests. Material extracts were obtained under standardized conditions, and we have looked at a potentially toxic effect of substances eventually leached from the materials towards cells cultured in vitro. None of the material extracts listed above were cytotoxic except for untreated Kevlar. Toxicity disappeared when Kevlar was treated with methanol. As suspected, untreated Kevlar contains toxic additives introduced during the manufacture of this textile. Thus, in spite of good mechanical properties, Kevlar should not be used in pelvic surgery on account of its lower bicompatibility. These results shows that the choice of the grafts by surgeons must be relevant in a given application.

Lack of responsiveness to glucose of microencapsulated islets of Langerhans after three weeks' implantation in the rat--influence of the complement.

Microencapsulated islets of Langerhans retrieved from peritoneal cavity of rats three weeks after implantation had a reduced hormonal secretion and were no longer responsive to alterations in glucose levels. Activation of complement could not completely account for the observed fibrosis which was thought to be responsible for the loss of responsiveness of the encapsulated cells.