Influence of gold nanoparticles on collagen fibril morphology quantified using transmission electron microscopy and image analysis

Background: Development of implantable biosensors for disease detection is challenging because of poor biocompatibility of synthetic materials. A possible solution involves engineering interface materials that promote selfassembly and adhesion of autologous cells on sensor surfaces. Crosslinked type-1 collagen is an acceptable material for developing engineered basement membranes. In this study, we used functionalized gold nanoparticles as the crosslinking agent. Functionalized nanoparticles provide sites for crosslinking collagen as well as sites to deliver signaling compounds that direct selfassembly and reduce inflammation. The goal of this study was to obtain a quantitative parameter to objectively determine the presence of crosslinks. Methods: We analyzed TEM images of collagen fibrils by two methods: Run length analysis and topology analysis after medial axis transform. Results: Run length analysis showed a significant reduction of the interfibril spaces in the presence of nanoparticles (change of 40%, P < 0.05), whereas the fibril thickness remained unchanged. In the topological network, the number of elements, number of branches and number of sides increased significantly in the presence of nanoparticles (P < 0.05). Other parameters, especially the number of loops showed only a minimal and nonsignificant change. We chose a ratiometric parameter of the number of branches normalized by the number of loops to achieve independence from gross fibril density. This parameter is lower by a factor of 2.8 in the presence of nanoparticles (P < 0.05). Conclusion: The numerical parameters presented herein allow not only to quantify fibril mesh complexity and crosslinking, but also to help quantitatively compare cell growth and adhesion on collagen matrices of different degree of crosslinking in further studies. © 2006 Haidekker et al; licensee BioMed Central Ltd.