Composites for bone repair: phosphate glass fibre reinforced PLA with varying fibre architecture.

Internal fixation for bone fractures with rigid metallic plates, screws and pins is a proven operative technique. However, refracture's have been observed after rigid internal fixation with metal plates and plate fixation has been known to cause localised osteopenia under and near the plate. In the present study, resorbable composites comprising a PLA matrix reinforced with iron doped phosphate glass fibres were investigated. Non-woven random mat laminates of approximately 30% and 45% fibre volume fraction (V(f)) were produced, along with unidirectional and 0°-90° samples of approximately 20% V(f). The non-woven composite laminates achieved maximum values of 10 GPa modulus and 120 MPa strength. The 0-90º samples showed unexpectedly low strengths close to matrix value (~50 MPa) although with a modulus of 7 GPa. The UD specimens exhibited values of 130 MPa and 11.5 GPa for strength and modulus respectively. All the modulus values observed were close to that expected from the rule of mixtures. Samples immersed in deionised water at 37°C revealed rapid mechanical property loss, more so for the UD and 0-90º samples. It was suggested that continuous fibres wicked the degradation media into the composite plates which sped up the deterioration of the fibre-matrix interface. The effect was less pronounced in the non-woven random mat laminates due to the discontinuous arrangement of fibres within the composite, making it less prone to wicking. Random mat composites revealed a higher mass loss than the UD and 0°-90° specimens, it was suggested this was due to the higher fibre volume fractions of these composites and SEM studies revealed voidage around the fibres by day 3. Studies of pH of the degradation media showed similar profiles for all the composites investigated. An initial decrease in pH was attributed to the release of phosphate ions into solution followed by a gradual return back to neutral.

A virtual reality surgery simulation of cutting and retraction in neurosurgery with force-feedback.

A virtual-reality surgical simulator aimed at neurosurgery is presented. The simulator utilises boundary element (BE) technology to develop real-time realistic deformable models of the brain. The simulator incorporates the simulation of surgical prodding, pulling and cutting. Advanced features include the separation the cut surfaces by retractors and post-cutting deformations. The experience of virtual surgery is enhanced by implementing 3D stereo-vision and the use of two hand-held force-feedback devices.

Preparation of poly(epsilon-caprolactone)/continuous bioglass fibre composite using monomer transfer moulding for bone implant.

Poly(epsilon-caprolactone) (PCL)/continuous bioglass fibre composite was prepared using the monomer transfer moulding technique coupled with a surface initiated polymerisation. The bioglass fibres were surface treated with an amine ended silane in order to initiate polymerisation of epsilon-caprolactone from the fibre surface. Surface initiated polymerisation significantly improved the Young's modulus and flexural strength and water resistance of the composite. Initial in vitro biocompatibility assessment suggests that amine ended silane treatment of bioglass fibres before their inclusion in the composite does not have a negative effect on the biological responses in terms of macrophage activation as measured by IL-1beta release and craniofacial osteoblast attachment.

Controlled degradation and macrophage responses of a fluoride-treated polycaprolactone.

We have developed a new bone replacement material based on polycaprolactone (PCL), which can act as a suitable matrix for monomer transfer molding of degradable composites. A boron trifluoride catalyst with glycerol additive was used to produce PCL with a degradation rate that can be altered by treatment with fluoride ions. The effect of cations on the degradation of the polymer and macrophage cell responses are discussed. We found that treatment with fluoride ions reduced the degradation rate. No significant difference between these three fluorides was observed although a general trend was seen where KF-treated PCL appeared to degrade slower than NaF-treated PCL which was slower than NH(4)F-treated PCL. Variation in solubilities of the salts was observed where the K(+) cation had the highest solubility and the Na(+) cation had the lowest solubility, which suggests that NaF was able to degrade the polymer more efficiently than the other fluorides. No significant macrophage activation was observed after culture on the polymer surfaces as determined by peroxide and IL-1 beta release, whereas some activation occurred after culture in degradation products.

Craniofacial osteoblast responses to polycaprolactone produced using a novel boron polymerisation technique and potassium fluoride post-treatment.

There is no ideal material for craniofacial bone repair at present. The aim of this study was to test the biocompatibility of polycaprolactone (PCL) synthesised by a novel method allowing control of molecular weight and degradation rate, with regard to it being used as matrix for a biodegradable composite for craniofacial bone repair. Human primary craniofacial cells were used, isolated from paediatric skull after surgery. Cell responses were analysed using various assays and antibody staining. Cells attached and spread on the PCL in a similar manner to the Thermanox controls as shown by phalloidin staining of F-actin. Cells maintained the osteoblast phenotype as demonstrated by alkaline phosphatase assay and antibody staining throughout the time points studied, up to 28 days. Cells proliferated on the PCL as shown by a DNA assay. Collagen-1 staining showed extensive production of a collagen-1 containing extracellular matrix, which was also shown to be mineralised by alizarin red staining. Short-term (up to 48 h) attachment studies and long-term (up to 28 days) expression of markers of the osteoblast phenotype have been demonstrated on the PCL. This new method of synthesising PCL shows biocompatibility characteristics that give it potential to be used for craniofacial bone repair.

Long-term craniofacial osteoblast culture on a sodium phosphate and a calcium/sodium phosphate glass.

The aim of this study was to determine the characteristics of human craniofacial osteoblasts cultured on sodium phosphate glass and calcium-sodium phosphate glass in a long-term culture of up to 28 days. The characteristics studied were attachment, proliferation, alkaline phosphatase activity, collagen-1 production, and mineralization. A comparison of the degradation rate, measured by mass loss of the glasses, which are intended for use as a component of a novel degradable composite for craniofacial bone repair, was also performed. It was our hypothesis that the glass would be degradable with a change in degradation rate observed by calcium addition and support osteoblast proliferation and expression of the above characteristics. The inclusion of calcium into the reaction mixture significantly decreased the degradation rate, and it is suggested that the slower degradation is the result of pseudo crosslinking (ionic crosslinks rather than covalent bonding) of the polyphosphate chains by the calcium ions. Therefore, twice as many P-O bonds will need to be hydrolyzed for dissolution of the metal phosphate to occur, therefore greatly reducing the rate of hydrolysis. Osteoblasts were able to attach, spread, and proliferate in a manner comparable with the positive control, as shown by analysis of variance. Formation of a collagen-rich mineralized matrix was also observed. The results presented here suggest that a biocompatible soluble glass has been produced, which has potential to be included in a novel biodegradable craniofacial implant.

Techniques for laser welding polymeric devices.

Recent advances in laser techniques mean that lasers are now being considered as an alternative to vibration, ultrasonic, dielectric, hot plate or hot bar welding, and adhesive bonding of plastics. The techniques required to put laser welding methods into practice are described for medical devices, tubular systems, films and synthetic fabrics.

Synthesis, degradation, and in vitro cell responses of sodium phosphate glasses for craniofacial bone repair.

This report outlines the initial synthesis, degradation, and short-term biocompatibility of sodium phosphate glasses, for use in the drawing of fibers and manufacture of biodegradable composites. Biocompatibility studies were performed using a macrophage cell line and primary human craniofacial osteoblasts. Sodium hydrogen phosphate and sodium dihydrogen phosphate glass synthesized for less than 1 h, resulted in a higher degradation rate than glass synthesized for 3 h or more (0.015 mg cm(-2) h(-1)). Glasses with high and low ratios of hydrogen phosphate to dihydrogen phosphate had very similar degradation rates. A condensation route for the formation of the glass should give rise to varying degradation rates with varying ratios of starting materials. It is suggested that the degradation rate of the glass is independent of the concentrations of the initial reagents and that ring-opening polymerization, which reaches an equilibrium state, occurs. Biocompatibility studies suggest minimal macrophage activation (low levels of peroxide and interleukin-1beta release and rounded morphology) and high osteoblast biocompatibility. The ultimate aim of our studies is to produce a biocompatible soluble phosphate glass that can be drawn into fibers for incorporation into a polycaprolactone matrix for craniofacial bone repair. This report demonstrates the successful production of a soluble glass, which is biocompatible with regard to osteoblasts and macrophages. Recent data from our laboratory have demonstrated successful fiber drawing and production of a novel polycaprolactone.

Laser welding of thermoplastic materials.

The capabilities of the three main types of laser are compared and a new technique is introduced, which laser welds plastics using an infrared absorber to create a joint that is almost invisible to the human eye.

Physical and biocompatibility properties of poly-epsilon-caprolactone produced using in situ polymerisation: a novel manufacturing technique for long-fibre composite materials.

Preliminary investigations into a novel process for the production of poly-epsilon-caprolactone (PCL) to be used as a matrix material in a bioabsorbable composite material are detailed. This material is primarily being developed as a bone substitute for use in maxillofacial reconstructive surgery, however, the technique described could be adapted to other areas where bioabsorbable composite materials may be used. The development of a totally bioabsorbable long-fibre composite material would allow a two-stage degradation to occur with the matrix material degrading first leaving a scaffold structure of degradable fibres which would be absorbed at a later stage. Caprolactone monomer was polymerised in situ within a tool cavity to produce a net shape moulding. Inclusion of a fibre preform within the tool cavity which was impregnated by the liquid monomer produces a long-fibre composite material. PCL with a range of molecular weights has been produced using this liquid moulding technique to assess the physical and biocompatibility properties compared to commercially available PCL. Osteoblast-like cells derived from human craniofacial bone (CFC) have been used to assess the in vitro biocompatibility of the PCL. The results show that high-quality PCL with a narrow molecular weight distribution and properties similar to commercially available PCL can be produced using this technique. Polymerisation of the monomer around a woven fibre preform made of a poly(lactic acid) (PLA)/poly(glycolic acid) (PGA) copolymer (vicryl mesh) produced a bioabsorbable long-fibre composite material. Further work is ongoing to develop this system towards a method for improving craniofacial bone reconstruction.