Untersuchungen zur Modifikation der Oberfläche und des Porensystems eines porösen Knochenersatzwerkstoffes aus TiO 2/Glas-Kompositkeramik

The basic structural and chemical properties of the porous TiO2/glass composite Ecopore suggest that this novel material could be used as bone replacement. Ecopore is non-toxic and permits a limited cellular adhesion and growth on its surface. In order to optimize ingrowth of bone tissue in vivo, the aim of the work was to enhance adhesion and growth of bone forming cells on the composite via surface modification as well as the implementation of an osteoinductive system.The biochemical modification comprised acid and alkaline etching of the surface, respectively, and functionalization with aminosilane. Alkaline etching was most effective for the subsequent binding of silane. Silanized Ecopore was covalently coated with the cell adhesion mediator fibronectin and the osteoinductive factor BMP-2, respectively, using a homobifunctional crosslinker with a polyethylene glycol spacer. A fraction of 60% of the totally bound protein was adsorbed on Ecopore in both cases. In vitro studies revealed that human osteoblasts showed a better spreading and proliferation on fibronectin-coated compared to unmodified Ecopore. BMP-2-responsive embryonal fibroblasts proliferated on BMP-2-coated Ecopore, but only displayed a minor induction of alkaline phosphatase. This indicated that most of the BMP-2 was inactivated after immobilization.Fibronectin-, BMP-2-coated, etched and unmodified Ecopore was implanted into rabbit femora. The animals received a weekly injection of fluorescent bone markers to quantify ingrowth of bone. After 6 weeks, cross sections of preparations of the implants were investigated via microscopy. Histology revealed no indication for inflammation in the vicinity of the implants. Ecopore and bone tissue established direct contact to each other without remaining gaps. In case of both protein-coated implant groups, bone apposition rates were significantly higher compared to the unmodified and etched controls, according to the distances of fluorescence-marked growth zones. Quantification of the totally ingrown bone via energy dispersive X-ray analysis showed that bone was significantly most abundant in the fibronectin-coated group, whereas there was no significantly higher bone fraction in the BMP-2-coated group.According to the limited effectiveness of the BMP-2 coating, an alternative strategy was pursued in the next part of the study. Ecopore was filled with heparinized collagen sponge to realize a surface-independent release system for BMP-2. The surface was blocked with serum albumin prior filling to prevent adsorption of the osteoinductive factor. The release of BMP-2 was retarded in the case of heparinized compared to unmodified collagen filling. The released factor induced alkaline phosphatase in embryonal fibroblasts, indicating unimpaired biological functionality.In the described animal model, unfilled, collagen filled as well as additionally heparinized Ecopore was compared, with the filled versions optionally loaded with BMP-2. After 6 weeks, bridging of the defect gap and partial ingrowth only occured in the BMP-2-loaded heparinized group. Throughout this experiment, osteoconduction was less compared to the results of the surface modification study, indicating passivation of the surface after blocking with albumin.As a summary, Ecopore is a material which can be easily manufactured using highly available components and which shows basic biocompatibility. Its surface could be effectively functionalized with fibronectin, whereas BMP-2 coating was almost ineffective. The combination with collagen matrix allowed a reversible binding and release of biologically functional BMP-2.The suitability of Ecopore as bone replacement is restricted according to the limited mechanical strength, the heterogeneous structure of the pore system and the irreversible adsorption of proteins. In the field of hard tissue replacement, the gained experience nevertheless can be used in projects based on alternative carrier materials.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• von Walter, Matthias

Contributors dc:contributor

• Jahnen-Dechent, Wilhelm

• info:eu-repo/classification/ddc/610
• Medizin
• Knochen
• Biomaterial
• Modifizierung
• Fibronectin
• Knochen-Morphogenese-Proteine
• Osteoblast
• bone
• modification
• bone morphogenetic protein

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122513%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:60825