Mike J. Jenkins

Effect of sterilisation by gamma irradiation on the ability of polycaprolactone (PCL) to act as a scaffold material

This paper investigates the effect of sterilisation by gamma irradiation (dose 2.5Mrad) on the following properties of polycaprolactone (PCL): (1) degradation rate (catalysed by lipase), (2) mechanical properties, (3) the ability of cells to attach and subsequently grow on its surface. Gel permeation chromatography (GPC) was used to determine the effects of gamma irradiation of weight average (M(w)) and number average (M(n)) molecular weights. Gamma irradiation significantly decreased the rate of degradation, although the rates depended on the initial mass of polymer; it also affected the appearance of the degraded specimens when they were examined by scanning electron microscopy. Irradiation also significantly increased the mechanical yield stress but not the failure stress of PCL. It caused a significant increase in M(w) and decrease in M(n) that could be attributed to chain scission and cross-linking. Chondrocyte attachment and growth on PCL was not significantly affected by gamma irradiation.

Evaluation of liposomes coated with a pH responsive polymer

Liposomes have been coated with the pH responsive polymer, Eudragit S100, and the formulations potential for lower gastrointestinal (GI) targeting following oral administration assessed. Cationic liposomes were coated with the anionic polymer through simple mixing. The evolution of a polymer coat was studied using zeta potential measurements and laser diffraction size analysis. Further evidence of an association between polymer and liposome was obtained using light and cryo scanning electron microscopy. Drug release studies were carried out at pH 1.4, pH 6.3 and pH 7.8, representing the pH conditions of the stomach, small intestine and ileocaecal junction, respectively. The polymer significantly reduced liposomal drug release at pH 1.4 and pH 6.3 but drug release was equivalent to the uncoated control at pH 7.8, indicating that the formulation displayed appropriate pH responsive release characteristics. While the coating layer was not able to withstand the additional challenge of bile salts this reinforces the importance of evaluating these types of formulations in more complex media.

Enthalpic relaxation in semi-crystalline PEEK

Abstract The effect of crystallisation on the glass transition temperature and enthalpic relaxation in poly(ether ether ketone) (PEEK) has been investigated. The increase in glass transition temperature and the activation enthalpy of ageing is explained in terms of the amorphous phase being constrained by the crystallites. The extent of enthalpic relaxation with time has been analysed in terms of the Cowie–Ferguson model and the β value was found to be dependent on both temperature and the crystalline morphology, changes in the co-operativity of the relaxations are used to explain this observation.

Polyhydroxybutyrate accumulation by a Serratia sp.

A strain of Serratia sp. showed intracellular electron-transparent inclusion bodies when incubated in the presence of citrate and glycerol 2-phosphate without nitrogen source following pre-growth under carbon-limitation in continuous culture. About 1.3xa0mmol citrate were consumed per 450xa0mg biomass, giving a calculated yield of maximally 55% of stored material per g of biomass dry wt. The inclusion bodies were stained with Sudan Black and Nile Red (NR), suggesting a lipid material, which was confirmed as polyhydroxybutyrate (PHB) by analysis of molecular fragments by GC and by FTIR spectroscopy of isolated bio-PHB in comparison with reference material. Multi-parameter flow cytometry in conjunction with NR fluorescence, and electron microscopy, showed that not all cells contained heavy PHB bodies, suggesting the potential for increasing the overall yield. The economic attractiveness is enhanced by the co-production of nanoscale hydroxyapatite (HA), a possible high-value precursor for bone replacement materials.

Crystallisation in miscible blends of PEEK and PEI

The crystallisation of PEEK from miscible blends of PEEK and PEI has been measured and the results analysed in terms of the Avrami equation and the Hoffman and Lauritzen crystallisation theory. The melting of the crystals was analysed in terms of the Hoffman and Weeks theory and it was found that the β values were in excess of unity. The product of the surface free energies was found and discussed in terms of the variation in blend composition.

A Comparison of the use of FTIR spectroscopy with DSC in the characterisation of melting and crystallisation in polycaprolactone

The infrared spectrum of polycaprolactone has been recorded as a function of temperature in the range where melting and crystallisation of the polymer can occur. Examination of the carbonyl band of the spectra reveals a clear morphological sensitivity; heating the semi-crystalline polymer through the melting region results in a decrease in the intensity of the crystalline component of the carbonyl band. Accordingly, there was a subsequent increase in intensity of the crystalline carbonyl band on cooling. To enable comparison of these findings with a more conventional method of thermal analysis, similar experiments were conducted using a differential scanning calorimeter. The heated ATR accessory adopted for use in the FTIR spectrometer imposed significant limitations in the range of possible heating and cooling rates, but when these rates were carefully matched between FTIR and DSC, close correlation between the melting point and onset of re-crystallisation was observed. The results confirm that FTIR can be used as an alternative, if more laborious, way of investigating melting and re-crystallisation.

Relaxation behaviour in blends of PEEK and PEI

Abstract Blends of poly(ether ether ketone) and poly(ether imide) have been produced in the composition range 2–20xa0wt% poly(ether ether ketone) and dynamic mechanical and dielectric behaviour of these materials have been investigated. A composition dependent α process was observed using both techniques, the temperature of which increased with increasing poly(ether imide) content. The low temperature relaxation behaviour of poly(ether imide) and the dielectric relaxation time in the glass transition region was found to be affected by the addition of poly(ether ether ketone). The variation of loss and storage permittivities showed that the asymmetric broadening was strongly dependent on the blend composition, indicating a high degree of interaction between the components.

Active screen plasma surface modification of polycaprolactone to improve cell attachment

To tailor polycaprolactone (PCL) surface properties for biomedical applications, film samples of PCL were surface modified by the active screen plasma nitriding (ASPN) technique. The chemical composition and structure were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The wettability of the surface modified polymers was investigated by contact angle and surface energy methods. Biocompatibility of the prepared PCL samples was evaluated in vitro using MC3T3-E1 osteoblast-like cells. The degradability was assessed by determining the self-degradation rate (catalyzed by lipase). The results show that ASPN surface modification can effectively improve osteoblast cell adhesion and spreading on the surface of PCL. The main change in chemical composition is the exchange of some carboxyl groups on the surface for hydroxyl groups. The active-screen plasma nitriding technique has been found to be an effective and practical method to effectively improve osteoblast cell adhesion and spreading on the PCL surface. Such changes have been attributed to the increase in wettablity and generation of new hydroxyl groups by plasma treatment. After active-screen plasma treatment, the PCL film is still degradable, but the enzymatic degradation rate is slower compared with untreated PCL film.

The effect of the environment on the mechanical properties of medical grade silicones.

Silicone spacers have been in use as replacement joints in the human hand for over 30 years. Since they were first used there has been a number of designs all of which have had problems with fracture. This may be due to a defect in the material caused during implantation, or by bony intrusions within the arthritic hand after implantation. The aim of this research was to investigate the effect of the environment on the mechanical properties of medical grade silicones used for human implantation. The materials were subjected to static tensile testing after various forms of ageing. The environmental conditions included temperatures of 37 and 80 degrees C and the environments of Ringers solution, distilled water, and air. The environmental conditions employed resulted in reduced mechanical strength with ageing time of the silicones. This research supports the view that failure of silicone implants in the hand could be partly attributed to the effects of environmental ageing of the material.

The kinetics of crystallization of poly(ε-caprolactone) measured by FTIR spectroscopy

The kinetics of crystallization of poly(ε-caprolactone), PCL, have been measured by FTIR spectroscopy using the absorbance of the crystalline and amorphous phase carbonyl bands at 1725 and 1735xa0cm−1, respectively, to determine the fractional crystallinity as a function of time and over the temperature range 43–47xa0°C. A comparison was also made with DSC which was found to have limited sensitivity such that it could only measure the primary stage of the crystallization and not the secondary. Both primary and secondary crystallization could be measured by FTIR spectroscopy with sufficient accuracy to measure the kinetics of each and limited only by the length of time over which the measurements were made.