Osteoblasts cultured on three-dimensional synthetic hydroxyapatite implanted on a chick allantochorial membrane induce ectopic bone marrow differentiation

Significance of nano- and microtopography for cell-surface interactions in orthopaedic implants

Cell-surface interactions play a crucial role for biomaterial application in orthopaedics. It is evident that not only the chemical composition of solid substances influence cellular adherence, migration, proliferation and differentiation but also the surface topography of a biomaterial. The progressive application of nanostructured surfaces in medicine has gained increasing interest to improve the cytocompatibility and osteointegration of orthopaedic implants. Therefore, the understanding of cell-surface interactions is of major interest for these substances. In this review, we elucidate the principle mechanisms of nano- and microscale cell-surface interactions in vitro for different cell types onto typical orthopaedic biomaterials such as titanium (Ti), cobalt-chrome-molybdenum (CoCrMo) alloys, stainless steel (SS), as well as synthetic polymers (UHMWPE, XLPE, PEEK, PLLA). In addition, effects of nano- and microscaled particles and their significance in orthopaedics were reviewed. The significance for the cytocompatibility of nanobiomaterials is discussed critically.

Novel mineral contrast agent for magnetic resonance studies of bone implants grown on a chick chorioallantoic membrane

Magnetic resonance imaging (MRI) studies of tissue engineered constructs prior to implantation clearly demonstrate the utility of the MRI technique for studying the bone formation process. To test the utility of our MRI protocols for explant studies, we present a novel test platform in which osteoblast-seeded scaffolds were implanted on the chorioallantoic membrane of a chick embryo. Scaffolds from the following experimental groups were examined by high-resolution MRI: (a) cell-seeded implanted scaffolds (CIM), (b) unseeded implanted scaffolds (UCIM), (c) cell-seeded scaffolds in static culture (CIV) and (d) unseeded scaffolds in static culture (UCIV). The reduction in water proton transverse relaxation times and the concomitant increase in water proton magnetization transfer ratios for CIM and CIV scaffolds, compared to UCIV scaffolds, were consistent with the formation of a bone-like tissue within the polymer scaffold, which was confirmed by immunohistochemistry and fluorescence microscopy. However, the presence of angiogenic vessels and fibrotic adhesions around UCIM scaffolds can confound MRI findings of bone deposition. Consequently, to improve the specificity of the MRI technique for detecting mineralized deposits within explanted tissue engineered bone constructs, we introduce a novel contrast agent that uses alendronate to target a Food and Drug Administration-approved MRI contrast agent (Gd-DOTA) to bone mineral. Our contrast agent termed GdALN was used to uniquely identify mineralized deposits in representative samples from our four experimental groups. After GdALN treatment, both CIM and CIV scaffolds, containing mineralized deposits, showed marked signal enhancement on longitudinal relaxation time-weighted (T1W) images compared to UCIV scaffolds. Relative to UCIV scaffolds, some enhancement was observed in T1W images of GdALN-treated UCIM scaffolds, subjacent to the dark adhesions at the scaffold surface, possibly from dystrophic mineral formed in the fibrotic adhesions. Notably, residual dark areas on T1W images of CIM and UCIM scaffolds were attributable to blood inside infiltrating vessels. In summary, we present the efficacy of GdALN for sensitizing the MRI technique to the deposition of mineralized deposits in explanted polymeric scaffolds.