PurposeThe aim was to determine effects of diluent monomer and monocalcium phosphate monohydrate (MCPM) on polymerization kinetics and volumetric stability, apatite precipitation, strontium release and fatigue of novel dual-paste composites for vertebroplasty.Materials and methodsPolypropylene (PPGDMA) or triethylene (TEGDMA) glycol dimethacrylates (25 wt%) diluents were combined with urethane dimethacrylate (70 wt%) and hydroxyethyl methacrylate (5 wt%). 70 wt% filler containing glass particles, glass fibers (20 wt%) and polylysine (5 wt%) was added. Benzoyl peroxide and MCPM (10 or 20 wt%) or N-tolyglycine glycidyl methacrylate and tristrontium phosphate (15 wt%) were included to give initiator or activator pastes. Commercial PMMA (Simplex) and bone composite (Cortoss) were used for comparison. ATR-FTIR was used to determine thermal activated polymerization kinetics of initiator pastes at 50–80°C. Paste stability, following storage at 4–37°C, was assessed visually or through mixed paste polymerization kinetics at 25°C. Polymerization shrinkage and heat generation were calculated from final monomer conversions. Subsequent expansion and surface apatite precipitation in simulated body fluid (SBF) were assessed gravimetrically and via SEM. Strontium release into water was assessed using ICP-MS. Biaxial flexural strength (BFS) and fatigue properties were determined at 37°C after 4 weeks in SBF.ResultsPolymerization profiles all exhibited an inhibition time before polymerization as predicted by free radical polymerization mechanisms. Initiator paste inhibition times and maximum reaction rates were described well by Arrhenius plots. Plot extrapolation, however, underestimated lower temperature paste stability. Replacement of TEGDMA by PPGDMA, enhanced paste stability, final monomer conversion, water-sorption induced expansion and strontium release but reduced polymerization shrinkage and heat generation. Increasing MCPM level enhanced volume expansion, surface apatite precipitation and strontium release. Although the experimental composite flexural strengths were lower compared to those of commercially available Simplex, the extrapolated low load fatigue lives of all materials were comparable.ConclusionsIncreased inhibition times at high temperature give longer predicted shelf-life whilst stability of mixed paste inhibition times is important for consistent clinical application. Increased volumetric stability, strontium release and apatite formation should encourage bone integration. Replacing TEGDMA by PPGDMA and increasing MCPM could therefore increase suitability of the above novel bone composites for vertebroplasty. Long fatigue lives of the composites may also ensure long-term durability of the materials.

14 Purpose: The aim was to determine effects of diluent monomer and monocalcium 15 phosphate monohydrate (MCPM) on polymerization kinetics and volumetric stability, 16 apatite precipitation, strontium release and fatigue of novel dual-paste composites for 17 vertebroplasty. 18 Materials and methods: Polypropylene (PPGDMA) or triethylene (TEGDMA) glycol 19 dimethacrylates (25 wt%) diluents were combined with urethane dimethacrylate (70 20 wt%) and hydroxyethyl methacrylate (5 wt%). 70 wt% filler containing glass particles, 21 glass fibers (20 wt%) and polylysine (5 wt%) was added. Benzoyl peroxide and MCPM 22 (10 or 20 wt%) or N-tolyglycine glycidyl methacrylate and tristrontium phosphate (15 23 wt%) were included to give initiator or activator pastes. Commercial PMMA (Simplex) 24 and bone composite (Cortoss) were used for comparison.

The study aim was development of composite bone cements with lower monomer content, viscosity and modulus but a higher conversion and strength than the commercial composite Cortoss TM. Urethane dimethacrylate (UDMA), Triethylene glycoldimethacrylate (TEGDMA) and Hydroxyethyl methacrylate (HEMA) were combined with 0.5 or 1 wt% initiator / activator. This monomer was subsequently combined with 70-80 wt% glass filler. FTIR was used to assess reaction inhibition time and half-life in addition to final monomer conversion at 26 and 37 °C. Biaxial flexural strength and modulus were measured after 24 hours in water or simulated body fluid at 37 °C and compared with that of Cortoss (Commercial Composite bone cement). Results showed that even with 1/3 rd less monomer content, the experimental composites could be mixed through a finer syringe tip than Cortoss. Cure rate and final conversion were increased by raising temperature, initiator and activator concentration. Strength and modulus were raised by increasing initiator concentration. All experimental formulations had greater monomer conversion and strength than Cortoss and those with low initiators also had lower modulus. The experimental materials show promise as an alternative bone cements.

Conventional PMMA bone cement, and more lately BisGMA (bisphenol A-glycidyl methacrylate) composite bone cement, are employed in various bone augmentation procedures such as vertebroplasty. Problems with these materials include high curing exotherm and shrinkage, leakage of toxic components after insertion, and exhibition of a modulus mismatch between bone cement and weak bone. A novel high molecular weight dimethacrylate, polypropylene glycol dimethacrylate (PPG), was used in combination with urethane dimethacrylate (UDMA), hydroxy-ethyl-methacrylate (HEMA), silica glass particles and fibres to create PPG fibre composite (PFC) dual paste materials. This study was designed to ascertain whether PFCs are a viable alternative to Cortoss™ composite bone void filler and Simplex P™ PMMA bone cement for osteoporotic vertebroplasty and fracture fixation applications. The degree of monomer conversion and curing kinetics of the PFCs and commercial bone cements were found using FTIR whilst the mechanical properties were found through biaxial flexural testing. An equation was derived to describe the curing profiles of the PFCs and commercial bone cements. The curing profiles and equations, and mechanical properties of the PFCs, Cortoss™ and Simplex P™ bone cements were compared. It was found that PFC materials had more complete monomer conversion, and faster cure than Cortoss™ and Simplex P. The flexural strength of some of the experimental materials was comparable to Cortoss™ and Simplex P. Incorporating fibres into the PFC materials prevented brittle fracture exhibited by Cortoss™ and mimicking the fracture behaviour of Simplex P.