Abstract
The controlled release of therapeutic inorganic ions from biomaterials is an emerging area of international research. One of the foci for this research is the development of materials, which spatially and temporally modulate therapeutic release, via controlled degradation in the intended physiological environment. Crucially however, our understanding of the release kinetics for such systems remains limited, particularly with respect to the influence of physiological loading. Consequently, this study was designed to investigate the effect of dynamic mechanical loading on a composite material intended to stabilize, reinforce and strengthen vertebral bodies. The composite material contains a borate glass engineered to release strontium as a therapeutic inorganic ion at clinically relevant levels over extended time periods. It was observed that both cyclic (6 MPa 2 Hz) and static (4.3 MPa) compressive loading significantly increased the release of strontium ions in comparison to the static unloaded case. The observed alterations in ion release kinetics suggest that the mechanical loading of the implantation environment should be considered when evaluating the ion release kinetics.
Highlights
Percutaneous vertebroplasty (PVP), is a minimally invasive technique through which bone cement is injected directly into a fractured vertebral body, providing mechanical support and immobilization without the need for invasive orthopedic surgery
A highly hydrophilic Bis glycydil dimethacrylate (Bis GMA), hydroxyl ethyl methacrylate (HEMA) polymer blend was chosen as the resin phase of the composite; with the particular ratios of glass and HEMA content being based on previous investigations by MacDonald et al to maximize ion release efficiency over 60 days[15]
No significant changes were observed in the calcium concentration of the simulated body fluid (SBF) over the 48 h experiment (Fig. 3)
Summary
Percutaneous vertebroplasty (PVP), is a minimally invasive technique through which bone cement is injected directly into a fractured vertebral body, providing mechanical support and immobilization without the need for invasive orthopedic surgery. For composite resin cements, intended for both dental and orthopedic applications, hydrophilic modifications have been used to alter ion release kinetics Such modifications increase water sorption and degradation of the inorganic filler phase; frequently a bioactive glass[16,17]. While vertebroplasty materials are much less compliant than hydrogel materials, the addition of small hydrophilic mono-functional monomers, such as poly- hydroxyl ethyl methacrylate (HEMA) to composite resins has been shown to alter water sorption behavior and to reduce the modulus of elasticity of composite resins by up to 40%24 As such hydrophilic modifications of composite resin cements may result in loading dependent alterations of bioactive glass filler degradation kinetics. Ion release into solution was assessed using inductively coupled plasma optical emission spectroscopy (ICP-OES)
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