Thoraco-lumbar traumatic vertebral fractures augmentation by osteo-conductive and osteo-inductive bone substitute containing strontium–hydroxyapatite: our experience

Cytotoxicity and cell response of preosteoblast in calcium sulfate-augmented PMMA bone cement

Poly(methyl methacrylate) (PMMA) has been widely used in orthopedic applications, but bone ingrowth and toxic monomer release are drawback of this material. Particle reinforcement with osteoconductive substitute, such as calcium sulfate (CaSO₄), is one of the solutions used to modify PMMA bone cement. The current study investigated the mechanical, chemical and biological properties of CaSO₄-augmented bone cement. Mechanical strength was measured by a material testing machine. The concentration of methyl methacrylate (MMA) monomer from the various formulations of PMMA mixed with CaSO₄was measured by ultra-performance liquid chromatography (UPLC). CCK-8 assay and ALP assay were performed to evaluate cytotoxicity of released MMA monomer and cell differentiation. The attachment of cells to CaSO₄-augmented bone cement discs was observed by confocal and scanning electron microscopy, and surface topography was also evaluated by atomic force microscopy. The results revealed that increased CaSO₄weight ratios led to compromised mechanical strength and increased MMA monomer release. Cell density and cell differentiation on CaSO₄-augmented bone cement discs were decreased at CaSO₄weight ratios above 10%. In addition, the presence of micropores on the surface and surface roughness were both increased for PMMA composite discs containing higher levels of CaSO₄. These results demonstrated that fewer MC3T3-E1 cells on the surface of CaSO₄-PMMA composites was correlated to increased MMA monomer release, micropore number and surface roughness. In summary, the augmentation of a higher proportion of CaSO₄(>10 wt. %) to PMMA did not promote the biological properties of traditional PMMA bone cement.

A novel and injectable strontium-containing hydroxyapatite bone cement for bone substitution: A systematic evaluation

Reconstruction of bone defects is still a challenge. In this study, we developed and systematically evaluated a novel injectable strontium-containing hydroxyapatite (Sr-HA) bone cement in which Sr-HA powder included 5% Sr and was mixed with a setting liquid that included 5% potassium citrate. This Sr-HA cement was mainly composed of HA and α-tricalcium phosphate (TCP) and exhibited favorable injectability (100%), setting times (the initial setting time was 240 s and the final setting time was 420 s), compressive strength (73.4 MPa), maximal load and maximum bending stress, and excellent radiopacity. In addition, the Sr-HA cement also had excellent biocompatibility that exhibited low cytotoxicity for cell proliferation and no obvious disturbing effect on the osteogenic differentiation of periodontal ligament stem cells (DLSCs) and dental pulp stem cells (DPSCs). However, the Sr-HA cement could slightly promote the osteogenic differentiation of MC3T3 cells, which also implied that it would promote osseointegration between the cement and surrounding bone but would not obviously disturb the biological behavior of DLSCs and DPSCs. An in vivo study further confirmed that Sr-HA cement exhibited favorable osseointegration with the maxilla and tibia. All these findings implied that the novel Sr-HA cement was a suitable bone substitution for bone defects.

Bone morphogenetic proteins: a powerful osteoinductive compound with non-negligible side effects and limitations

Healing and regeneration of large bone defects leading to non-unions is a great concern in orthopedic surgery. Since auto- and allografts have limitations, bone tissue engineering and regenerative medicine (TERM) has attempted to solve this issue. In TERM, healing promotive factors are necessary to regulate the several important events during healing. An ideal treatment strategy should provide osteoconduction, osteoinduction, osteogenesis, and osteointegration of the graft or biomaterials within the healing bone. Since many materials have osteoconductive properties, only a few biomaterials have osteoinductive properties which are important for osteogenesis and osteointegration. Bone morphogenetic proteins (BMPs) are potent inductors of the osteogenic and angiogenic activities during bone repair. The BMPs can regulate the production and activity of some growth factors which are necessary for the osteogenesis. Since the introduction of BMP, it has added a valuable tool to the surgeon's possibilities and is most commonly used in bone defects. Despite significant evidences suggesting their potential benefit on bone healing, there are some evidences showing their side effects such as ectopic bone formation, osteolysis and problems related to cost effectiveness. Bone tissue engineering may create a local environment, using the delivery systems, which enables BMPs to carry out their activities and to lower cost and complication rate associated with BMPs. This review represented the most important concepts and evidences regarding the role of BMPs on bone healing and regeneration from basic to clinical application. The major advantages and disadvantages of such biologic compounds together with the BMPs substitutes are also discussed.