C A. Khatri

Synthesis, characterization and evaluation of urethane derivatives of Bis-GMA.

OBJECTIVES The aims of the study were to synthesize derivatives of Bis-GMA having pendant n-alkyl urethane substituents and to characterize and evaluate their physicochemical properties. METHODS Stoichiometric amounts of Bis-GMA and n-alkyl isocyanates were reacted in dichloromethane with dibutyltin dilaurate as a catalyst. Volumetric shrinkage, water uptake, degree of vinyl conversion, refractive index and viscosity of resulting urethane monomers and those of Bis-GMA were measured. The flexural strengths of their corresponding homopolymers and that of Bis-GMA were also measured. RESULTS These types of urethane derivatives of Bis-GMA exhibited lower viscosities and were more hydrophobic than Bis-GMA. Generally, the viscosity of these experimental monomers decreased with increasing chain length of the alkyl urethane substituent. Photopolymerization of the new monomers gave high degrees of vinyl conversion compared to Bis-GMA. The experimental monomers also yielded polymers with lower polymerization shrinkages at equivalent degrees of vinyl conversion, than Bis-GMA. The refractive indices of these urethane derivatives were similar to Bis-GMA, but the flexural strengths of their polymers were lower than that of the Bis-GMA homopolymer, decreasing with increasing chain length of the alkyl urethane substituent. SIGNIFICANCE Because of their excellent overall properties, these new derivatives of Bis-GMA have potential as dental monomers that can improve many properties of resin based dental materials that utilize methacrylate monomer systems.

Preliminary report on the biocompatibility of a moldable, resorbable, composite bone graft consisting of calcium phosphate cement and poly(lactide-co-glycolide) microspheres ☆

We have assessed the biocompatibility of a new composite bone graft consisting of calcium phosphate cement (CPC) and poly(lactide‐co‐glycolide) (PLGA) microspheres (approximate diameter of 0.18–0.36 mm) using cell culture techniques. CPC powder is mixed with PLGA microspheres and water to yield a workable paste that could be sculpted to fit the contours of a wound. The cement then hardens into a matrix of hydroxyapatite microcrystals containing PLGA microspheres. The rationale for this design is that the microspheres will initially stabilize the graft but can then degrade to leave behind macropores for colonization by osteoblasts. The CPC matrix could then be resorbed and replaced with new bone. In the present study, osteoblast‐like cells (MC3T3‐E1 cells) were seeded onto graft specimens and evaluated with fluorescence microscopy, environmental scanning electron microscopy and the Wst‐1 assay (an enzymatic assay for mitochondrial dehydrogenase activity). Cells were able to adhere, attain a normal morphology, proliferate and remain viable when cultured on the new composite graft (CPC–PLGA) or on a control graft (CPC alone). These results suggest that our new cement consisting of CPC and PLGA microspheres is biocompatible. This is the first time that a ‘polymer‐in‐mineral’ (PLGA microspheres dispersed in a CPC matrix) cement has been formulated that is moldable, resorbable and that can form macropores after the cement has set.

Polymer-Filled Calcium Phosphate Cement: Mechanical Properties and Controlled Release of Growth Factor

Novel calcium phosphate cement (CPC) was developed by incorporating pore-forming particulates (porogens) to induce macropores and proteins to stimulate bone growth. A paste was made from CPC powder (0.15 g, equimolar mixture of tetracalcium phosphate and dicalcium phosphate), biodegradable polymer microspheres [0.1 g, volume fraction of 0.6, (0.17 to 0.36) mm in diameter], and 0.062 g of water. Disks for determining diametral tensile strength (DTS) and mass loss were prepared from the paste in a mold at 37 °C. Disks for the release of a protein were similarly prepared using a solution of the protein, and biodegradable polymer microspheres or water-soluble crystals (mannitol or salicylic acid) as porogens. The disks were immersed at 37 °C in an aqueous solution in order to quantify the effects of the solution on DTS and mass loss, as well as the release of the protein into the solution. The initial DTS value for the disks was (6.4 ± 0.9) MPa. The release of the protein from the CPC/porogen disks persisted for at least 300 h. The release rate of Protein A from the CPC/mannitol disks increased with the volume fraction of mannitol crystals. At a fixed volume fraction of porogens, the release rate of TGF-β1 from the CPC/porogen disks increased with the dissolution rate of the porogens. Thus, the release of a protein from composite grafts consisting of CPC and porogens can be modulated by the volume fraction and the dissolution rate of the porogens.Copyright