Synergistic Effects of Silicon/Zinc Doped Brushite and Silk Scaffolding in Augmenting the Osteogenic and Angiogenic Potential of Composite Biomimetic Bone Grafts

Abstract

Cell instructive scaffolding platforms displaying synergistic effects by virtue of their chemical and physical cues have tremendous scope in modulating cell phenotype and thus improving the success of any graft. In this regard, we report here the development of Si- and Zn-doped brushite cement composited with silk scaffolding that hierarchically emulated the cancellous bone. The composite scaffolds fabricated exhibited an open porous network capable of enhanced osteoblast survival as attested by increased alkaline phosphatase activity and also sustaining osteoclast activity affirmed by tartrate resistant acid phosphatase staining. Moreover, the chemical cues presented by dissolutions products from the composite scaffold enabled the osteoblasts to secrete proangiogenic factors which favored better endothelial cell survival, confirmed through in vitro experiments. Moreover, the efficacy of these composite biomimetic scaffolds was validated in vivo in volumetric femur defects in rabbits, which revealed that these matrices influenced vascular cell infiltration and favored the formation of matured bony plate. Fluorochrome labeling studies and microtomography analysis revealed that at the end of three months, the implanted composite scaffolds had completely resorbed, leaving behind neo-osseous tissue and vouching for clinical translation of these composite matrices as viable and affordable bone-graft substitutes.

Inorganic Agents for Enhanced Angiogenesis of Orthopedic Biomaterials

“…Simple; it does not indicate the ratio of live/dead cells. [68] DNA synthesis quantification through mitotic divisions Radioactive; slow.…”

“…Simple; ambiguous interpretation of data-need for an additional assay to validate the results. [ 73,74] Alamar Blue/ PrestoBlue [ 68,75] Migration Migration along a gradient (chemotaxis)…”

“…It is usually incubated with the cells for about 1-2 h (could be more in case of slowly dividing cells), and the intensity can then be analyzed on an absorbance-or a fluorescent-based plate reader. The most commonly used colorimetric assays are MTT [73,74] (reduction of yellow tetrazolium salt to purple formazan), Alamar Blue, and PrestoBlue [68,75] (reduction of blue resazurin to red resorufin). [53,54,72]…”

“…The findings show that Zn can be incorporated in coatings on metallic substrates [69,104,107,133] as well as in bioglass and other ceramic materials. [14,67,68] Similar to magnesium and copper, the angiogenic ability of zinc is strongly dependent on its concentration and high doses can have adverse effects on the viability of ECs. An investigation of the effect of pure metal zinc on ECs showed that low concentrations of zinc of up to 3.92 mg L −1 (60 µm) promoted the angiogenic behavior of ECs, while higher doses inhibited their activity.…”

“…[104] Owing to its high corrosion rate, supplementary surface modification was often adopted to control the ion release and improve the cytocompatibility of zinc. [133] Zinc was often found as a codoped agent in combination with other bioactive elements such as copper, [67] magnesium, [69,107] phosphorus/calcium, [67,133,134] or silicon, [14,68] which also reported improved viability of ECs in vitro [14,135] and formation of blood vessels in vivo. [134] However, the positive effects were often attributed to the synergistic effect of zinc and the other element.…”