In vivo biocompatibility of SrO and MgO doped brushite cements

The addition of dopants in biomaterials has emerged as a critical regulator of bone formation and regeneration due to their imminent role in the biological process. The present work evaluated the role of strontium (Sr) and magnesium (Mg) dopants in brushite cement (BrC) on in vivo bone healing performance in a rabbit model. Pure, 1 wt% SrO (Sr-BrC), 1 wt% MgO (Mg-BrC), and a binary composition of 1.0 wt% SrO + 1.0 wt% MgO (Sr + Mg-BrC) BrCs were implanted into critical-sized tibial defects in rabbits for up to 4 months. The in vivo bone healing of three doped and pure BrC samples was examined and compared using sequential radiological examination, histological evaluations, and fluorochrome labeling studies. The results indicated excellent osseous tissue formation for Sr-BrC and Sr + Mg-BrC and moderate bone regeneration for Mg-BrC compared to pure BrC. Our findings indicated that adding small amounts of SrO, MgO, and binary dopants to the BrC can significantly influence new bone formation for bone tissue engineering.

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

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.

In Situ Synchrotron X-ray Diffraction Analysis of the Setting Process of Brushite Cement: Reaction and Crystal Growth

Brushite cements are fast self-setting materials that can be used as bone substitute materials. Although tracing their fast setting process is a challenge, it is important for the understanding of the same, which in turn is important for the material's further development and use in the clinics. In this study, the setting rate, phase formation, and crystal growth of brushite cements were quantitatively studied by in situ synchrotron powder X-ray diffraction (SXRD) on a time scale of seconds. The influence of reactant ratios and a retardant (citric acid) on the setting reaction were analyzed. To complement the in situ investigations, scanning electron microscopy was carried out for ex situ morphological evolution of crystals. The initial reaction followed a four-step process, including a fast nucleation induction period, nucleation, crystal growth, and completion of the setting. The brushite crystal size grew up to the micro scale within 1 min, and the brushite content increased linearly after the nucleation until all monocalcium phosphate monohydrate (MCPM; Ca(H₂PO₄)₂·H₂O) had dissolved within minutes, followed by a slow increase until the end of the monitoring. By adjusting the MCPM to the β-tricalcium phosphate (β-TCP, β-Ca₃(PO4)₂) ratio in the starting powders, the brushite/monetite ratio in the cements could be modified. In the presence of citric acid, the formation of brushite nuclei was not significantly retarded, whereas the increase in brushite content and the growth of crystal size were effectively hindered. The amount of monetite also increased by adding citric acid. This is the first time that the brushite setting process has been characterized in the first seconds and minutes of the reaction by SXRD.

Mechanical and In Vitro Biocompatibility of Brushite Cement Modified by Polyethylene Glycol

Brushite (dicalcium phosphate dihydrate, DCPD) cement, owing to its high solubility in physiological condition and ability to guide new bone formation, is widely used to treat bone defects. In the present study, we have evaluated the effects of poly ethylene glycol (PEG) addition on the setting time, compressive strength and in vitro biocompatibility of brushite cement. The brushite cements were prepared by mixing β-tricalcium phosphate [β-TCP, Ca(3)(PO(4))(2)] and monocalcium phosphate monohydrate [MCPM, Ca(H(2)PO(4))(2). H(2)O]. PEG was introduced at 2.0 and 5.0 wt% with the liquid. Introduction of PEG resulted in marginal increase in both initial and final setting time; however, significantly affected the compressive strength. Effects of PEG incorporation on in vitro biocompatibility of brushite cements were studied by using human fetal osteoblast cells (hFOB) cells. Field emission scanning electron microscope (FESEM) images and immunohistochemical analysis indicated that pure and PEG incorporated brushite cement facilitates cell adhesion, proliferation and differentiation. Fewer cells expressed vinculin protein with increased PEG content in the cement. Cell proliferation was found to decrease with increased PEG concentration while the cell differentiation increased with PEG content. Our results provide a better understanding of in vitro biocompatibility of PEG added brushite cements that can be used to customize the cement compositions based on application need.