Martin Buggy

Bone cements and fillers: a review.

Charnley [1] developed the first bone cement in the 1960s using poly(methyl methacrylate) (PMMA), which remains the most widely used material for fixation of orthopaedic joint replacements. In the field of dentistry, zinc polycarboxylate and glass polyalkenoate cements received major research interest from the 1970s to the present day. The discovery of a well-integrated intermediate layer between bone and many bioactive ceramic phases from the calcium–phosphate system, such as hydroxyapatite (HA), resulted in the development of new cements incorporating such phases. These investigations ranged from the development of castable bioactive materials to modified bioactive composites. This paper attempts to give a broad overview of the many different types of cements that have being developed in the past and those which are being researched at the present time. It has lead to a set of fundamental design criteria that should be considered prior to the development of a cement for use as a bone cement or in applications requiring a bone substitute.

Recycling of composite materials

Abstract An economic survey of composite manufacturing was carried out to help to identify suitable fibre/resin systems for recycling trials. Three separate recycling strategies were also adopted. The first of these was the re-use of in-process polyester/glass prepreg offcuts, which were quantified and then reprocessed using a simple pressing technique. Three different panel types were pressed and subjected to comparative physical and mechanical testing. Solvent recycling trials were carried out on carbon fibre/PEEK APC-2. Initially methylene chloride proved successful, so concentrated sulphuric acid was used. Polymer recovered using the acid was checked for purity against 380-P moulding compound. The final process investigated was recovery of aramid fibre (Twaron™) from an epoxy matrix by solvent swelling, the solvent system used being 50% DMSO and 50% Toluene at 105°C. The recovered fibre was tested against virgin fibre to ascertain what degradation of the properties resulted from the process.

Irradiation of poly-d,l-lactide

Compression-moulded samples of poly-d,l-lactide have been γ-irradiated in air to give received doses up to 10 Mrad. Molecular weight and mechanical property changes have been established and are consistent with a random scission process. Substantial embrittlement occurs at the higher dose levels. The radiochemical yield for scission G(s) has been calculated to be 2·9 over the dose range examined. The properties of irradiated materials have been monitored over a 504-day period and show no evidence of post-irradiation aging. Moisture uptake has been measured by immersion in pH 7·4 buffer at 37°C and indicates that the irradiated material absorbs water at a slightly slower rate than the unirradiated material. The primary effect of irradiation on hydrolytic degradation is associated with the initial reduction of molecular weight and there are no subsequent changes in degradation mechanism.

A comparison of the effects of ?-irradiation and ethylene oxide sterilization on the properties of compression moulded poly-d,l-lactide

Compression moulded specimens from two batches of poly-d,l-lactide, of different molecular weights, have been subjected to γ-radiation and to ethylene oxide (ETO) exposure to establish the effects of sterilizing procedures on potential orthopaedic implants. Materials were exposed to between zero and 10 Mrad, and up to three standard ETO cycles. Tensile properties, dynamic mechanical behaviour, fracture toughness and hydrolytic degradation rates were measured. Molecular weight change was determined by size exclusion chromatography and solution viscosity. Calculated radiochemical yields suggest that the primary effects of irradiation are random chain scission. A clear relationship between properties and molecular weight was established and is used to interpret the relative effects of the two sterilization procedures. With γ-irradiation scission processes cause a fall in molecular weight in both batches whereas ETO only significantly affected the lower molecular weight batch. It is thought that the ETO effects are determined by moisture diffusion rates which are molecular weight dependent, and therefore property changes with the higher molecular weight material are more limited.

Curing of carbon fibre reinforced epoxy matrix composites

Abstract The curing kinetics and viscosity of two carbon fibre reinforced epoxy systems, Fibredux 914C and Fiberite HYE 1248M2F, were measured using differential scanning calorimetry (DSC) and torsion rheometry. Fibredux 914C is a high temperature (175°C) cure system and Fiberite is a low temperature (120°C) cure system. Values of kinetic parameters were obtained from dynamic and isothermal DSC scans using an nth order reaction model. Viscosity measurements as a function of time were made for both systems and fitted to an expression relating viscosity to degree of cure.

Thermal stability of a ureidopyrimidinone model compound

Abstract A dimer of N-[(butylamino)carbonyl]-6-methylisocytosine was prepared as a model compound in order to study the thermal stability of ureidopyrimidinone supramolecular polymers during heat/cool cycles. The dimer did not self-heal (i.e. disintegrate and reform reversibly) as expected; it underwent thermal degradation in three stages once heated to its melting point of 225 °C. Infrared spectra and optical micrographs were taken before and after these cycles, and the gases evolved at each stage of the degradation process were identified by gas chromatography-mass spectroscopy. A degradation mechanism is proposed whereby the dimers butane-1-isocyanate ‘tail’ cleaves first, followed by the isocytosine ‘head’ breaking down above 244 °C. The kinetics of the degradation process were also determined, from which the activation energy was calculated to be 71.5 kJ/mol. In conclusion, the implications for processing related supramolecular polymers are discussed.

The influence of hydroxyapatite: Zinc oxide ratio on the setting behavior and mechanical properties of polyalkenoate cements

The influence of hydroxyapatite (HA) content on the setting behavior and mechanical properties of hydroxyapatite–zinc oxide–poly(acrylic acid) (HA–ZnO–PAA) composite cements were investigated as a function of HA content. The working time increased with HA content up to 45 wt % HA and then decreased whilst the setting time increased with increasing HA content. Mechanical properties were determined after storage in water at 37 °C for 1, 7 and 28 days. Youngs moduli and compressive strength go through a maximum at approximately 30 and 45 wt % HA. Youngs modulus increases with time, which is consistent with an ongoing crosslinking reaction.© 2001 Kluwer Academic Publishers

A comparison of in-vitro and in-vivo degradation of poly(D, L-lactide) bio-absorbable intra-medullary plugs

Poly(D,L-lactide) has been evaluated as a material for the manufacture of intra-medullary plugs to be used in total hip arthopalsty. Plugs were manufactured by compression moulding and subjected to in-vitro and in -vito degradation. In-vitro hydrolysis was carried out by immersion in phosphate buffered saline (Ringers solution) at 37°C and rates of degradation were relatively rapid with molecular weight halving after 30 days. In-vitro degradation was assessed by implantation into dogs followed by retrieval at intervals up to 24 months. Molecular weight was gound to reduce to half the original value in about 190 days. It is thought that this difference in degradation rate is because of diffusional control of the overall process. Histology showed that the implanted plugs were resorbed over 24 months.

An evaluation of poly-d,l-lactide bio-absorbable intramedullary plugs

Poly-d,l-lactide has been evaluated as a material for the manufacture of intramedullary plugs to be used in total hip arthoplasty. Raw materials with weight-average molecular weights between 207 000 and 105 000 were used to compression mould plugs and plaques for the production of standard test specimens, and the effects of drying, compression moulding and sterilisation by γ irradiation on molecular weight were determined. The cumulative effect of the manufacturing and sterilising processes is a reduction in molecular weight of between a third and a half depending upon irradiation dose. The mechanical strength of the plugs was assessed by a specially developed test designed to produce stresses similar to those experienced in insertion and the failure load was found to depend on molecular weight. In vitro hydrolysis was carried out by immersion in phosphate-buffered saline at 37 °C and rates of degradation also showed a dependence upon molecular weight; this is considered to arise from the easier diffusion of small molecules into and out of lower-molecular-weight matrices. Although material taken from the centre of plaque mouldings exposed to saline buffer shows evidence of the development of a bimodal molecular weight distribution, indicating some trapping of oligomers, material sampled from different parts of the plugs showed more uniform degradation. The long-term stability of the products was assessed by storing plugs in standard packaging under conditions of controlled humidity and temperature, and monitoring mechanical strength and molecular weight over a period of 3 years. Storage temperature was found to be more important than humidity.

Continuous and discontinuous fatigue crack growth of irradiated ultrahigh molecular mass polyethylene in saline solution at 37C

To provide data for prosthesis design, the fatigue crack growth resistance of irradiated ultrahigh molecular mass polyethylene (UHMMPE) in saline solution at 37°C was determined from tests performed on compact tension specimens, comparable in size to the components in knee prostheses. The specimens were cyclically loaded by using a sinusoidal wave form at 1 Hz with a minimum-to-maximum load ratio of 0.1. Scanning electron microscopic fractography was used to examine the fracture surfaces. At higher stress levels, the Pariss Law was used to analyse the data, and a striation pattern with each striation corresponding to multi-cycles was observed. At lower stress levels, discontinuous fatigue crack growth was found, a phenomenon which dominated the fatigue life of the material and had not been reported previously in this material. A craze zone ahead of the crack tip was observed, which formed the discontinuous crack growth band with a length relevant to the Dugdale plastic zone length.