In the search for more ideal bone graft materials for clinical application, the investigation into ceramic bone cements or bone void filler is ongoing. Calcium phosphate-based materials have been widely explored and implemented for medical use in bone defect repair. Such materials are an excellent choice because the implant mimics the natural chemistry of mineralized bone matrix and in injectable cement form, can be implemented with relative ease. However, of the available calcium phosphate cements, none fully meet the ideal standard, displaying low strengths and acidic setting reactions or slow setting times, and are often very slow to resorb in vivo. The study of magnesium phosphates for bone cements is a relatively new field compared to traditional calcium phosphate bone cements. Although reports are more limited, preliminary studies have shown that magnesium phosphate cements (MPC) may be a strong alternative to calcium phosphates for certain applications. The goal of the present publication is to review the history and achievements of magnesium phosphate-based cements or bone void fillers to date, assess how these cements compare with calcium phosphate competitors and to analyze the future directions and outlook for the research, development, and clinical implementation of these cements.

Bone grafting is widely used for the treatment of cranio-maxillofacial bone injuries. 3D printing of biodegradable Fe alloy is anticipated to be advantageous over current bone grafting techniques. 3D printing offers the fabrication of precise and tailored bone grafts to fit the patient specific bone defect needs. Biodegradable Fe alloy is a good candidate for 3D printing synthetic grafts to regenerate bone tissue without eliciting complications. CALPHAD theoretical models were used to develop new Fe-Mn-Ca/Mg alloys to enhance the degradation rates of traditional Fe-Mn alloys. In vitro experimental results also showed enhanced degradation rates and good cytocompatibility of sintered Fe-Mn-Ca/Mg compacts. 3D printing of Fe-Mn and Fe-Mn-1Ca alloys further demonstrated their feasibility as potentially viable bone grafts for the future.

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Polymeric film coatings were applied by dip coating on two magnesium alloy systems, AZ31 and Mg4Y, in an attempt to slow the degradation of these alloys under in vitro conditions. Poly(lactic-co-glycolic acid) polymer in solution was explored at various concentrations, yielding coatings of varying thicknesses on the alloy substrates. Electrochemical corrosion studies indicate that the coatings initially provide some corrosion protection. Degradation studies showed reduced degradation over 3 days, but beyond this time point however, do not maintain a reduction in corrosion rate. Scanning electron microscopy indicates inhomogeneous coating durability, with gas pocket formation in the polymer coating, resulting in eventual detachment from the alloy surface. In vitro studies of cell viability utilizing mouse osteoblast cells showed improved biocompatibility of polymer coated substrates over the bare AZ31 and Mg4Y substrates. Results demonstrate that while challenges remain for long term degradation control, the developed polymeric coatings nevertheless provide short term corrosion protection and improved biocompatibility of magnesium alloys for possible use in orthopedic applications.

Magnesium phosphate implants may be used for bone void filling applications, potentially replacing traditionally studied bioceramics, which suffer from limited resorption and inferior mechanical properties compared to natural bone. In this study, amorphous and crystalline trimagnesium phosphates were synthesized and characterized utilizing a variety of analytical methods. In vitro solubility and cytotoxicity of the corresponding amorphous and crystalline phosphates were also analyzed. Amorphous magnesium phosphate was shown to be more soluble than the crystalline counterpart in vitro while inducing mineralization of an amorphous phosphate phase mimicking hydroxyapatite-type characteristic morphology on the substrate surface. The rapid mineralization of the amorphous magnesium phosphate was found to promote the proliferation and differentiation of osteoblast-like cells in comparison to the crystalline phase. Both magnesium phosphates hindered the differentiation of monocytes into osteoclasts. The combined effects of the spontaneous serum-mediated apatite-like mineralization, increased osteoblast differentiation and suspended osteoclast formation indicate that the amorphous magnesium phosphates may be promising bioactive materials for bone void repair applications.