I.A. Jones

Physical and biocompatibility properties of poly-ε-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.

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.

Automatically generated geometric descriptions of textile and composite unit cells

This paper presents an algorithm that generates geometric descriptions of unit cells of textiles and composite materials. The purpose of these geometric descriptions is to act as domains for calculations preformed at the scale of the unit cell, where the heterogeneity of the material must be considered. The algorithm defines both the volumes of the tows and the empty volumes that extend between the tows within the calculation domain, for general textiles. Resulting geometric descriptions are provided as assemblies of topologically simple volumes that encompass either part of a tow or part of an empty volume. Typical applications of the geometric definitions include the calculation of local permeability values for textile preforms and the investigation of local stress distributions in textile composites.

A summary review of mechanical properties prediction methods for textile reinforced polymer composites

Abstract The use of textile reinforcements for polymer composite components has become a common practice due to the favourable material costs and labour requirements compared with traditional unidirectional prepreg composites, and the high stiffness and strength compared with the use of randomly orientated reinforcements. As a result, determination of both elastic properties and failure behaviour of textile composites has been the subject of substantial research in recent years. This paper presents a review of some of the analytical and numerical models pertaining to the mechanics of textile composites which have been published in the literature. Particular consideration is given to the suitability of models for the analysis of non-orthogonal weave structures such as those which have been deformed in shear during component manufacture. The intention of the paper is not to provide a detailed analysis of the underlying mathematics of the models discussed, but rather to provide an overview of the work conducted in order to direct further reading.

Polymerisation and stabilisation of polycaprolactone using a borontrifluoride-glycerol catalyst system

This paper describes a new synthetic route to poly-e-caprolactone. A new cationic polymerisation has been developed which uses a borontrifluoride catalyst to open the caprolactone monomer, and glycerol to increase the molecular weights of the products. A post-treatment method has also been developed to reduce the amount of residual catalyst in the final product. This reduces the extent of borontrifluoride catalysed hydrolysis and therefore allows variation of the degradation rate of the material.

Initial development into a novel technique for manufacturing a long fibre thermoplastic bioabsorbable composite: in-situ polymerisation of poly-ϵ-caprolactone

Abstract A novel process has been developed for producing a bioabsorbable composite for use as a bone repair material. A variant of resin transfer moulding (RTM), a technique normally associated with thermosetting matrices, has been used with a thermoplastic matrix (poly-ϵ-caprolactone) to produce a long fibre composite which is intended to be completely degradable within the human body. The in-situ polymerisation technique is being developed for producing implants for reconstructive facial surgery. The combination of the specialist thermoplastic matrix, the long fibre reinforcement required and the complex three-dimensional geometry of these components has led to the development of an alternative processing route from those used for conventional long fibre thermoplastic composites. The chemical and mechanical properties of the poly-ϵ-caprolactone produced using this technique have been investigated and are comparable to commercially available material produced using a conventional bulk polymerisation process. Long fibre composites have been manufactured using both woven and knitted absorbable suture material.

Preparation and Characterization of Phosphate Glass Fibers and Fabrication of Poly(caprolactone) Matrix Resorbable Composites

Phosphate glass fibers (20Na2O—24CaO—16MgO—40P 2O5) were prepared with varying pulling speeds from 50 to 2000 m/min. Fiber diameters ranging from 48 ± 6 μm to 12 ± 4 μm were obtained at pulling speeds of 50 and 2000 m/min respectively. Degradation tests of the fibers (up to 7 days) were carried out in aqueous medium at 37°C and indicated that phosphate glass fibers experience a higher mass loss initially before reaching a plateau. Before composite fabrication, fibers were treated using 3-aminopropyltriethoxysilane. Phosphate glass fiber reinforced poly(ε-caprolactone) matrix unidirectional composites were prepared by using both in-situ polymerization and compression molding techniques. For in-situ polymerized composites (25% fiber by volume), flexural strength (FS), flexural modulus (FM), tensile strength (TS), tensile modulus (TM), and impact strength (IS) were found to be 105 MPa, 5.9 GPa, 88 MPa, 6.8 GPa, and 27 kJ/m2, respectively. For compression molded composites (10% fiber by volume), FS, FM, TS, TM, and IS were found to be 55 MPa, 2.1 GPa, 46 MPa, 1.6 GPa, and 14 kJ/m2 respectively. After 6 weeks of immersion in aqueous media (37°C), the fibers inside the composite had degraded as determined by scanning electron microscope.

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.

Development of new inverse boundary element techniques in photoelasticity

This paper presents a number of possible algorithms for inverse boundary element (BE) techniques applied to photoelastic analysis. The BE technique is shown to be an ideal companion to photoelastic analysis since, unlike the finite element (FE) method, the interior solutions can be represented by unconnected points rather than by discretized elements. From the photoelastic principal stress information obtained at a sufficient number of internal points, the unknown boundary conditions can be reconstructed using the inverse boundary element method (BEM). The inverse BE theory and numerical formulation are presented for problems involving Cartesian stress components and are then extended to photoelastic stress analysis. The inverse BE approach follows two stages. In stage 1, the photoelastic stress measurements of the differences in principal stresses and their directions at the interior points are used to compute the unknown boundary conditions on the surface. In stage 2, the individual stress components are calculated by the forward BEM using the computed boundary conditions from stage 1. The effect of scatter of the experimental results is also included in the analysis. A number of examples are presented in this paper and are shown to be in excellent agreement with other solutions.

Monomer transfer moulding and rapid prototyping methods for fibre reinforced thermoplastics for medical applications

Abstract The development of biodegradable materials for surgical applications is a growing area, especially in the area of fracture repair. A fully biodegradable composite has been developed for the manufacture of surgical implants tailored to the patients injury. This composite consists of a poly-ϵ-caprolactone matrix and a biodegradable glass fibre reinforcement. This paper describes two approaches to the manufacture of such implants using geometries derived from patient scan data: a variant of structural reaction injection moulding or resin transfer moulding, and a rapid prototyping method based upon material deposition modelling.