Colin Birkinshaw - Academia.edu (original) (raw)

Papers by Colin Birkinshaw

Adsorption Science & Technology, 2009

Manganese oxide-coated sand (MOCS) and manganese oxidecoated crushed brick (MOCB) were characteri... more Manganese oxide-coated sand (MOCS) and manganese oxidecoated crushed brick (MOCB) were characterized and employed for the removal of Pb(II) ions from aqueous solution. Scanning electron microscopy (SEM), FT-IR, X-ray diffraction (XRD) methods and BET analyses were used to study the surface properties of the adsorbents. Adsorption of Pb(II) ions from aqueous solutions was investigated by batch experiments. The estimated optimum pH for Pb(II) ion retention by the considered adsorbents was 5. Both the Freundlich and Langmuir isotherms provided a reasonable fit to the experimental data for the adsorption of Pb(II) ions. The adsorption capacities of the coated adsorbents at a pH value of 5 and a temperature of 20 ºC were 0.029 mmol/g and 0.030 mmol/g for MOCS and MOCB, respectively. The adsorption kinetics were tested using the pseudo-first-order and pseudo-second-order equations as well as the intraparticle diffusion model, with the rate constants from the three kinetic models being calculated. The best correlation coefficients were obtained using the pseudo-second-order kinetic model. Results from this study suggest that the manganese oxide-coated sorbent is potentially suitable for the removal of Pb(II) ions from aqueous solutions.

Journal of Applied Polymer Science, 1997

The mechanism of thermally induced elongation in poly(ethylene terephthalate) fiber spun at 3500 ... more The mechanism of thermally induced elongation in poly(ethylene terephthalate) fiber spun at 3500 m min−1 has been examined. This partially oriented fiber has a crystalline content of about 25% and a high degree of orientation. The effect of time and tension during heat treatment was examined, and it was found that yarns that were allowed to relax during an initial brief heat treatment at 130°C subsequently elongated by up to 5% during a long heat treatment at the same temperature. Yarns that were not allowed to relax during the brief heat treatment did not elongate on subsequent heating. The morphological and mechanical changes associated with these processes have been studied using differential scanning calorimetry, X-ray diffraction (XRD), birefringence measurement, microscopy, and tensile testing. A large increase in crystallinity was observed during the brief heat treatment, but a much smaller increase took place during the long heat treatment. XRD indicated that substantial crystal reorganization occurred during both heat treatments, but c-axis growth was most significant in those materials that elongated during long heat treatment. It is proposed that it is this c-axis growth, in conjunction with conversion of disordered amorphous material into oriented crystalline material, that is responsible for the observed elongation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 989–995, 1997

Journal of Materials Science: Materials in Medicine, 2008

Two polycarbonate polyurethanes, Bionate 75D and Bionate 80A, have been characterized for applica... more Two polycarbonate polyurethanes, Bionate 75D and Bionate 80A, have been characterized for application in biomimetic joint replacement systems. Procedures involved measurement of the effects of compounding and moulding on molecular weight, melt rheometry, and mechanical testing using conditioned and aged specimens. The effects of compounding with hydroxyapatite and carbon fibres were also evaluated. With Bionate 75D moulding reduces the molecular weight by 30%. Passing the material through a twin screw extruder without filler has similar molecular weight reduction effects to injection moulding. Inclusion of carbon fibre has little additional effect on molecular weight, although moulding of the fibre filled compound causes some further degradation, and Mw is almost halved compared with the original value. Inclusion of hydroxyapatite reduces Mw in a moulded component to less than a quarter of the original value and some form of chemical interaction between the polymer and filler is presumed. The apparent melt viscosity of the Bionate 75D was reduced by the addition of both carbon fibres and hydroxyapatite and this is thought to arise from reduction in molecular weight during the compounding process and the development of shear planes at the polymer-filler interface. The polymer glass transition temperatures are shifted to slightly higher values by the inclusion of filler. The tensile test results show the reinforcing effect of the carbon fibres, but poor wetting and pull out of the fibres was evident. Water absorption results suggest that the materials stabilise after 2 weeks, but the tensile results indicate that property change occurred between 1 month and 5 months of exposure. However the shape of the stress-strain curves is not altered, but with extended water exposure is translated to lower stress levels.

Polymer Degradation and Stability, 1992

Compression-moulded samples of poly-D,L-lactide have been y-irradiated in air to give received do... more Compression-moulded samples of poly-D,L-lactide have been y-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.

Polymer Testing, 2012

Simultaneous tensile testing and wide and small angle X-ray diffraction (WAX and SAX) have been u... more Simultaneous tensile testing and wide and small angle X-ray diffraction (WAX and SAX) have been used to compare three different ultra high molecular weight polyethylenes (UHMWPE), two linear and one crosslinked, with low density polyethylene (LDPE) and high density polyethylene (HDPE), with the intention of identifying any behavioural characteristics displayed uniquely by the ultra high molecular weight materials. Two strain rates were used, 0.025/s and 0.125/s. The results demonstrate that the original morphology of the polymer has a controlling influence on the tensile behaviour. With spherulitic HDPE, increasing strain causes the development of a monoclinic crystal population and cavitation occurs at a strain of around 0.1, whereas LDPE shows little morphological change up to fracture. In comparison, the two linear UHMWPEs and the cross-linked UHMWPE, which are not spherulitic, show the development of a monoclinic structure with strain, which is similar to HDPE, but with no cavitation, which is a notable difference with HDPE. Crosslinking appears to have no significant effect on the stress-strain response of these materials. With UHMWPEs, a crystal perfection process, rather than cavitation, is associated with yielding. The WAX data for all of the linear polymers, HDPE and UHMWPE, shows that the loss of the orthorhombic phase and the creation of the monoclinic phase are approximately linear with strain. Lamellae and lattice alignment, judged by the degree of ovality of the SAX plot, is shown to be a useful discriminator of morphological change at low strain.

Journal of Materials Science: Materials in Medicine, 2007

Medical grade ultra high molecular weight polyethylene (UHMWPE) of two molecular weights has been... more Medical grade ultra high molecular weight polyethylene (UHMWPE) of two molecular weights has been gamma irradiated in air to give received doses of 3.5 and 10 Mrad and aged in air for 25 months. Differential scanning calorimetry and wide and small angle X-ray diffraction (WAX and SAX) techniques and transmission electron microscopy have been used to characterize the materials. Polymer from an orthopaedic component, retrieved 10 years after implantation, has been subjected to the same analytical programme. The X-ray diffraction data shows that following irradiation two events occur with time, first a crystal refinement process, indicated by pronounced sharpening of the SAX peak, and secondly growth of a new crystal population of reduced lamellae thickness compared to the original crystal structures, shown by the development of a bimodal SAX pattern. Following irradiation crystallinity increases with time and this second crystal population makes a significant contribution to that increase. The retrieved component shows full development of these processes. It is considered that these crystallographic changes with time are responsible for the observed time dependent changes in the mechanical properties of air irradiated UHMWPE.

Journal of Materials Science: Materials in Medicine, 2008

In order to improve the mechanical properties and control the degradation rate of hyaluronic acid... more In order to improve the mechanical properties and control the degradation rate of hyaluronic acid (HA) an investigation of the structural and mechanical properties of the hydrogels crosslinked using divinyl sulfone (DVS), glutaraldehyde (GTA) and freeze-thawing, or autocrosslinking has been carried out. The thermal and mechanical properties of the gels were characterised by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and compression tests. The solution degradation products of each system have been analysed using size exclusion chromatography (SEC) and the Zimm-Stockmayer theory applied. Autocrosslinked gels swell the most quickly, whereas the GTA crosslinked gels swell most slowly. The stability of the autocrosslinked gels improves with a reduction in solution pH, but is still poor. GTA and DVS crosslinked gels are robust and elastic when water swollen, with glass transition values around 20 degrees C. SEC results show that the water soluble degradation products of the gels show a reduction in the radius of gyration at any particular molecular weight and this is interpreted as indicating increased hydrophobicity arising from chemical modification.

Journal of Applied Polymer Science, 2010

ABSTRACT Hydrogels, based on hyaluronic acid or hyaluronan (HA), are gaining attention as possibl... more ABSTRACT Hydrogels, based on hyaluronic acid or hyaluronan (HA), are gaining attention as possible cell-scaffolding materials for the regeneration of a variety of tissues. This article describes how HA, a naturally occurring polymer, has been crosslinked to reduce its degradation rate and freeze dried to produce porous materials suitable for tissue engineering. The resulting pore architecture has been assessed as a function of freezing temperature and freezing rate, type of crosslinkers, and methods used in the crosslinking process. On comparing the average densities of crosslinked and uncrosslinked scaffolds, it is apparent that the chemical modification increases sponge density and wall thickness of the pores while decreasing the pore size. The mechanical response of the modified materials has been investigated by equilibrium-swelling measurements and compression tests. These materials have an average pore size ranging from 167 to 215 μm, which suggests that they would be a suitable temporary site for cell proliferation. The materials exhibit moderate mechanical integrity and are expected to be capable of withstanding physiological stresses in vivo. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Journal of Applied Polymer Science, 2008

Hyaluronic acid (HA) has been crosslinked in solution with glutaraldehyde (GTA), 1-ethyl-3-(3-dim... more Hyaluronic acid (HA) has been crosslinked in solution with glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), poly(ethylene glycol) diglycidylether (EX 810), and divinyl sulfone (DVS) to form hydrogels. Flory-Rehner calculations were used to determine molecular weight between crosslinks (M c), the crosslink density (V e), and mesh size (e) of crosslinked hydrogels after 24-h swelling in distilled water. Generally, lower molecular weight films gave rise to decreased molecular weights between crosslinks as well as increased effective crosslink densities and decreased mesh size. The effects of pH and salt concentration were evaluated. Use of lower molecular weight HA gave rise to decreased molecular weights between crosslinks as well as increased effective crosslink densities and decreased mesh size. Water diffusion coefficients were measured for DVS and GTA hydrogels and were found to be 1.4 3 10 210 and 1.8 3 10 210 m 2 s 21. Autocrosslinked and HA polyethyleneimine gels were also produced but had very limited stabilities compared with the covalently crosslinked materials.

Journal of Applied Polymer Science, 2007

The effectiveness of four different reagents, glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopro... more The effectiveness of four different reagents, glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), poly(ethyelene glycol) diglycidyl ether (EX 810), and divinyl sulfone (DVS) as crosslinkers for cast hyaluronic acid (HA) films has been evaluated. Films were prepared by casting from solution and exposed to solutions of the crosslinkers in acetone-water solution. Swelling in water and in phosphate buffered saline (PBS) was then used to assess the effectiveness of the crosslinkers. GTA-crosslinked films were found to be of low stability compared with those treated with EDC, EX 810, and DVS. Results suggest that instability in GTA-crosslinked materials arises in part from residual acid catalyst. The effects of polymer molecular weight are not uniform. With GTA-crosslinked film produced from higher molecular weight HA swells more, and this is attributed to reduced diffusion of the crosslinker, but with EDC, the opposite effect is observed, implying some additional molecular weight dependent mechanism. Differential scanning calorimetry and dynamic mechanical thermal analysis results suggest that there are no significant structural difference between the gels for each crosslinker system and only the crosslink density and moisture content alters the transitions.

Carbohydrate Polymers, 2013

This review focuses on hyaluronic acid (HA) tissue scaffolding materials. Scaffolds are defined i... more This review focuses on hyaluronic acid (HA) tissue scaffolding materials. Scaffolds are defined in terms of formation mechanisms and mode of action. Solution properties are discussed as an understanding of the hydrodynamics of HA is fundamental in optimising the subsequent modification and the chemistries behind important tissue engineering applications that are emerging from recent research on this increasingly valuable carbohydrate polymer are described. Key scaffold characteristics such as mechanical, biological function and degradation are discussed. The latest technologies behind scaffold processing are assessed and the applications of HA based scaffolds are discussed.

Macromolecular Rapid Communications, 2001

Currently, significant metal-laden waste streams are produced from a number of industries with ob... more Currently, significant metal-laden waste streams are produced from a number of industries with obvious consequences for the environment. A variety of techniques are being used to treat these wastewaters. One such technique is adsorption and recent focus in this area has been around the preparation of selective adsorbents based on naturally occurring support materials. In our work, a regenerated cellulose wood pulp was grafted with the vinyl monomer glycidyl methacrylate (GMA) and was further functionalised with imidazole to produce a novel adsorbent material, cellulose-g-GMA-imidazole. A series of adsorption studies were carried out on the cellulose-g-GMA-imidazole to assess its capacity in the separate removal of lead and nickel ions (Pb(II), Ni(II)) from aqueous solution. Cellulose-g-GMA-imidazole sorbent showed an uptake of approximately 72 mg g of Pb(II) and 45 mg g of Ni(II) from aqueous solution. The adsorption process in both cases followed the Langmuir model of adsorption an...

Small samples of Sitka spruce (Picea sitchensis), lodgepole pine (Pinus contorta) and Japanese la... more Small samples of Sitka spruce (Picea sitchensis), lodgepole pine (Pinus contorta) and Japanese larch (Larix leptolepis) selected from normal commercial stock have been acetylated using the facilities of Stichting Hout Research in the Netherlands. The weight percent gains (WPG) used were 14% and 17% with the spruce, 16% and 19% with the pine and 17% with the larch. The acetylated materials were subject to three point bending to evaluate mechanical property change, three cycle anti-shrink efficiency (ASE) testing, equilibrium moisture content measurement and fungal resistance assessment using Coniophora puteana. Mechanical properties showed no significant change following acetylation. Equilibrium moisture contents were much reduced, although there was little difference between the pine at 16WPG and 19WPG. The repeated wetting and drying cycles of the ASE tests indicated that the chemical modification was permanent and the fungal tests showed very significant improvement in durability....

Ultra high molecular weight polyethylene, UHMWPE, is used as an articulating surface in prostheti... more Ultra high molecular weight polyethylene, UHMWPE, is used as an articulating surface in prosthetic surgery and is sterilised by γ-irradiation. This causes both immediate and time dependent chain scission processes to occur, releasing material for further crystal growth, leading to an increase in stiffness and predisposing the surface to wear.

Key Engineering Materials, 1991

Compliant layer technology, in which a soft polymer mimics the performance of natural cartilage, ... more Compliant layer technology, in which a soft polymer mimics the performance of natural cartilage, potentially represents a resolution to the wear and associated longevity coupled with conventional metalon-plastic joints. In this two-part study, the friction and wear of compliant layer polyurethane (PU) tibial inserts articulating against metal femoral components were investigated as part of a preliminary in vitro screening. In Part I the friction and lubrication regimes were evaluated both experimentally using Stribeck analysis and theoretically using the theory of Hamrock and Dowson to investigate the joints ability to operate within a fluid film lubrication regime. Using aqueous carboxymethyl cellulose (CMC) fluids as the lubricant the joints were shown to operate with low friction and specifically, in some individual joints, with friction factors equivalent to ceramic-on-ceramic bearings as observed in hip bearings. Protein containing lubricants caused an increase in friction relative to the CMC solutions and it is proposed that this results from the shearing of interfacial protein layers adsorbed onto the articulating surfaces. Overall, the friction and lubrication results demonstrated the ability of compliant layer joints to operate with fluid film lubrication and consequential lower frictional torque during the walking cycle. In Part II of this study the wear performance of this articulation system will be investigated.

Polymer Degradation and Stability, 1999

γ irradiation of ultra-high molecular weight polyethylene (UHMWPE) results in both immediate and ... more γ irradiation of ultra-high molecular weight polyethylene (UHMWPE) results in both immediate and time dependent property changes. The time dependent changes are believed to arise from long lived free radicals reacting with oxygen and causing chain scission. Samples of UHMWPE have been irradiated in air and in vacuum at ambient temperatures to various dose levels, and subjected to a series

Adsorption Science & Technology, 2009

Manganese oxide-coated sand (MOCS) and manganese oxidecoated crushed brick (MOCB) were characteri... more Manganese oxide-coated sand (MOCS) and manganese oxidecoated crushed brick (MOCB) were characterized and employed for the removal of Pb(II) ions from aqueous solution. Scanning electron microscopy (SEM), FT-IR, X-ray diffraction (XRD) methods and BET analyses were used to study the surface properties of the adsorbents. Adsorption of Pb(II) ions from aqueous solutions was investigated by batch experiments. The estimated optimum pH for Pb(II) ion retention by the considered adsorbents was 5. Both the Freundlich and Langmuir isotherms provided a reasonable fit to the experimental data for the adsorption of Pb(II) ions. The adsorption capacities of the coated adsorbents at a pH value of 5 and a temperature of 20 ºC were 0.029 mmol/g and 0.030 mmol/g for MOCS and MOCB, respectively. The adsorption kinetics were tested using the pseudo-first-order and pseudo-second-order equations as well as the intraparticle diffusion model, with the rate constants from the three kinetic models being calculated. The best correlation coefficients were obtained using the pseudo-second-order kinetic model. Results from this study suggest that the manganese oxide-coated sorbent is potentially suitable for the removal of Pb(II) ions from aqueous solutions.

Journal of Applied Polymer Science, 1997

The mechanism of thermally induced elongation in poly(ethylene terephthalate) fiber spun at 3500 ... more The mechanism of thermally induced elongation in poly(ethylene terephthalate) fiber spun at 3500 m min−1 has been examined. This partially oriented fiber has a crystalline content of about 25% and a high degree of orientation. The effect of time and tension during heat treatment was examined, and it was found that yarns that were allowed to relax during an initial brief heat treatment at 130°C subsequently elongated by up to 5% during a long heat treatment at the same temperature. Yarns that were not allowed to relax during the brief heat treatment did not elongate on subsequent heating. The morphological and mechanical changes associated with these processes have been studied using differential scanning calorimetry, X-ray diffraction (XRD), birefringence measurement, microscopy, and tensile testing. A large increase in crystallinity was observed during the brief heat treatment, but a much smaller increase took place during the long heat treatment. XRD indicated that substantial crystal reorganization occurred during both heat treatments, but c-axis growth was most significant in those materials that elongated during long heat treatment. It is proposed that it is this c-axis growth, in conjunction with conversion of disordered amorphous material into oriented crystalline material, that is responsible for the observed elongation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 989–995, 1997

Journal of Materials Science: Materials in Medicine, 2008

Two polycarbonate polyurethanes, Bionate 75D and Bionate 80A, have been characterized for applica... more Two polycarbonate polyurethanes, Bionate 75D and Bionate 80A, have been characterized for application in biomimetic joint replacement systems. Procedures involved measurement of the effects of compounding and moulding on molecular weight, melt rheometry, and mechanical testing using conditioned and aged specimens. The effects of compounding with hydroxyapatite and carbon fibres were also evaluated. With Bionate 75D moulding reduces the molecular weight by 30%. Passing the material through a twin screw extruder without filler has similar molecular weight reduction effects to injection moulding. Inclusion of carbon fibre has little additional effect on molecular weight, although moulding of the fibre filled compound causes some further degradation, and Mw is almost halved compared with the original value. Inclusion of hydroxyapatite reduces Mw in a moulded component to less than a quarter of the original value and some form of chemical interaction between the polymer and filler is presumed. The apparent melt viscosity of the Bionate 75D was reduced by the addition of both carbon fibres and hydroxyapatite and this is thought to arise from reduction in molecular weight during the compounding process and the development of shear planes at the polymer-filler interface. The polymer glass transition temperatures are shifted to slightly higher values by the inclusion of filler. The tensile test results show the reinforcing effect of the carbon fibres, but poor wetting and pull out of the fibres was evident. Water absorption results suggest that the materials stabilise after 2 weeks, but the tensile results indicate that property change occurred between 1 month and 5 months of exposure. However the shape of the stress-strain curves is not altered, but with extended water exposure is translated to lower stress levels.

Polymer Degradation and Stability, 1992

Compression-moulded samples of poly-D,L-lactide have been y-irradiated in air to give received do... more Compression-moulded samples of poly-D,L-lactide have been y-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.

Polymer Testing, 2012

Simultaneous tensile testing and wide and small angle X-ray diffraction (WAX and SAX) have been u... more Simultaneous tensile testing and wide and small angle X-ray diffraction (WAX and SAX) have been used to compare three different ultra high molecular weight polyethylenes (UHMWPE), two linear and one crosslinked, with low density polyethylene (LDPE) and high density polyethylene (HDPE), with the intention of identifying any behavioural characteristics displayed uniquely by the ultra high molecular weight materials. Two strain rates were used, 0.025/s and 0.125/s. The results demonstrate that the original morphology of the polymer has a controlling influence on the tensile behaviour. With spherulitic HDPE, increasing strain causes the development of a monoclinic crystal population and cavitation occurs at a strain of around 0.1, whereas LDPE shows little morphological change up to fracture. In comparison, the two linear UHMWPEs and the cross-linked UHMWPE, which are not spherulitic, show the development of a monoclinic structure with strain, which is similar to HDPE, but with no cavitation, which is a notable difference with HDPE. Crosslinking appears to have no significant effect on the stress-strain response of these materials. With UHMWPEs, a crystal perfection process, rather than cavitation, is associated with yielding. The WAX data for all of the linear polymers, HDPE and UHMWPE, shows that the loss of the orthorhombic phase and the creation of the monoclinic phase are approximately linear with strain. Lamellae and lattice alignment, judged by the degree of ovality of the SAX plot, is shown to be a useful discriminator of morphological change at low strain.

Journal of Materials Science: Materials in Medicine, 2007

Medical grade ultra high molecular weight polyethylene (UHMWPE) of two molecular weights has been... more Medical grade ultra high molecular weight polyethylene (UHMWPE) of two molecular weights has been gamma irradiated in air to give received doses of 3.5 and 10 Mrad and aged in air for 25 months. Differential scanning calorimetry and wide and small angle X-ray diffraction (WAX and SAX) techniques and transmission electron microscopy have been used to characterize the materials. Polymer from an orthopaedic component, retrieved 10 years after implantation, has been subjected to the same analytical programme. The X-ray diffraction data shows that following irradiation two events occur with time, first a crystal refinement process, indicated by pronounced sharpening of the SAX peak, and secondly growth of a new crystal population of reduced lamellae thickness compared to the original crystal structures, shown by the development of a bimodal SAX pattern. Following irradiation crystallinity increases with time and this second crystal population makes a significant contribution to that increase. The retrieved component shows full development of these processes. It is considered that these crystallographic changes with time are responsible for the observed time dependent changes in the mechanical properties of air irradiated UHMWPE.

Journal of Materials Science: Materials in Medicine, 2008

In order to improve the mechanical properties and control the degradation rate of hyaluronic acid... more In order to improve the mechanical properties and control the degradation rate of hyaluronic acid (HA) an investigation of the structural and mechanical properties of the hydrogels crosslinked using divinyl sulfone (DVS), glutaraldehyde (GTA) and freeze-thawing, or autocrosslinking has been carried out. The thermal and mechanical properties of the gels were characterised by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and compression tests. The solution degradation products of each system have been analysed using size exclusion chromatography (SEC) and the Zimm-Stockmayer theory applied. Autocrosslinked gels swell the most quickly, whereas the GTA crosslinked gels swell most slowly. The stability of the autocrosslinked gels improves with a reduction in solution pH, but is still poor. GTA and DVS crosslinked gels are robust and elastic when water swollen, with glass transition values around 20 degrees C. SEC results show that the water soluble degradation products of the gels show a reduction in the radius of gyration at any particular molecular weight and this is interpreted as indicating increased hydrophobicity arising from chemical modification.

Journal of Applied Polymer Science, 2010

ABSTRACT Hydrogels, based on hyaluronic acid or hyaluronan (HA), are gaining attention as possibl... more ABSTRACT Hydrogels, based on hyaluronic acid or hyaluronan (HA), are gaining attention as possible cell-scaffolding materials for the regeneration of a variety of tissues. This article describes how HA, a naturally occurring polymer, has been crosslinked to reduce its degradation rate and freeze dried to produce porous materials suitable for tissue engineering. The resulting pore architecture has been assessed as a function of freezing temperature and freezing rate, type of crosslinkers, and methods used in the crosslinking process. On comparing the average densities of crosslinked and uncrosslinked scaffolds, it is apparent that the chemical modification increases sponge density and wall thickness of the pores while decreasing the pore size. The mechanical response of the modified materials has been investigated by equilibrium-swelling measurements and compression tests. These materials have an average pore size ranging from 167 to 215 μm, which suggests that they would be a suitable temporary site for cell proliferation. The materials exhibit moderate mechanical integrity and are expected to be capable of withstanding physiological stresses in vivo. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Journal of Applied Polymer Science, 2008

Hyaluronic acid (HA) has been crosslinked in solution with glutaraldehyde (GTA), 1-ethyl-3-(3-dim... more Hyaluronic acid (HA) has been crosslinked in solution with glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), poly(ethylene glycol) diglycidylether (EX 810), and divinyl sulfone (DVS) to form hydrogels. Flory-Rehner calculations were used to determine molecular weight between crosslinks (M c), the crosslink density (V e), and mesh size (e) of crosslinked hydrogels after 24-h swelling in distilled water. Generally, lower molecular weight films gave rise to decreased molecular weights between crosslinks as well as increased effective crosslink densities and decreased mesh size. The effects of pH and salt concentration were evaluated. Use of lower molecular weight HA gave rise to decreased molecular weights between crosslinks as well as increased effective crosslink densities and decreased mesh size. Water diffusion coefficients were measured for DVS and GTA hydrogels and were found to be 1.4 3 10 210 and 1.8 3 10 210 m 2 s 21. Autocrosslinked and HA polyethyleneimine gels were also produced but had very limited stabilities compared with the covalently crosslinked materials.

Journal of Applied Polymer Science, 2007

The effectiveness of four different reagents, glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopro... more The effectiveness of four different reagents, glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), poly(ethyelene glycol) diglycidyl ether (EX 810), and divinyl sulfone (DVS) as crosslinkers for cast hyaluronic acid (HA) films has been evaluated. Films were prepared by casting from solution and exposed to solutions of the crosslinkers in acetone-water solution. Swelling in water and in phosphate buffered saline (PBS) was then used to assess the effectiveness of the crosslinkers. GTA-crosslinked films were found to be of low stability compared with those treated with EDC, EX 810, and DVS. Results suggest that instability in GTA-crosslinked materials arises in part from residual acid catalyst. The effects of polymer molecular weight are not uniform. With GTA-crosslinked film produced from higher molecular weight HA swells more, and this is attributed to reduced diffusion of the crosslinker, but with EDC, the opposite effect is observed, implying some additional molecular weight dependent mechanism. Differential scanning calorimetry and dynamic mechanical thermal analysis results suggest that there are no significant structural difference between the gels for each crosslinker system and only the crosslink density and moisture content alters the transitions.

Carbohydrate Polymers, 2013

This review focuses on hyaluronic acid (HA) tissue scaffolding materials. Scaffolds are defined i... more This review focuses on hyaluronic acid (HA) tissue scaffolding materials. Scaffolds are defined in terms of formation mechanisms and mode of action. Solution properties are discussed as an understanding of the hydrodynamics of HA is fundamental in optimising the subsequent modification and the chemistries behind important tissue engineering applications that are emerging from recent research on this increasingly valuable carbohydrate polymer are described. Key scaffold characteristics such as mechanical, biological function and degradation are discussed. The latest technologies behind scaffold processing are assessed and the applications of HA based scaffolds are discussed.

Macromolecular Rapid Communications, 2001

Currently, significant metal-laden waste streams are produced from a number of industries with ob... more Currently, significant metal-laden waste streams are produced from a number of industries with obvious consequences for the environment. A variety of techniques are being used to treat these wastewaters. One such technique is adsorption and recent focus in this area has been around the preparation of selective adsorbents based on naturally occurring support materials. In our work, a regenerated cellulose wood pulp was grafted with the vinyl monomer glycidyl methacrylate (GMA) and was further functionalised with imidazole to produce a novel adsorbent material, cellulose-g-GMA-imidazole. A series of adsorption studies were carried out on the cellulose-g-GMA-imidazole to assess its capacity in the separate removal of lead and nickel ions (Pb(II), Ni(II)) from aqueous solution. Cellulose-g-GMA-imidazole sorbent showed an uptake of approximately 72 mg g of Pb(II) and 45 mg g of Ni(II) from aqueous solution. The adsorption process in both cases followed the Langmuir model of adsorption an...

Small samples of Sitka spruce (Picea sitchensis), lodgepole pine (Pinus contorta) and Japanese la... more Small samples of Sitka spruce (Picea sitchensis), lodgepole pine (Pinus contorta) and Japanese larch (Larix leptolepis) selected from normal commercial stock have been acetylated using the facilities of Stichting Hout Research in the Netherlands. The weight percent gains (WPG) used were 14% and 17% with the spruce, 16% and 19% with the pine and 17% with the larch. The acetylated materials were subject to three point bending to evaluate mechanical property change, three cycle anti-shrink efficiency (ASE) testing, equilibrium moisture content measurement and fungal resistance assessment using Coniophora puteana. Mechanical properties showed no significant change following acetylation. Equilibrium moisture contents were much reduced, although there was little difference between the pine at 16WPG and 19WPG. The repeated wetting and drying cycles of the ASE tests indicated that the chemical modification was permanent and the fungal tests showed very significant improvement in durability....

Ultra high molecular weight polyethylene, UHMWPE, is used as an articulating surface in prostheti... more Ultra high molecular weight polyethylene, UHMWPE, is used as an articulating surface in prosthetic surgery and is sterilised by γ-irradiation. This causes both immediate and time dependent chain scission processes to occur, releasing material for further crystal growth, leading to an increase in stiffness and predisposing the surface to wear.

Key Engineering Materials, 1991

Compliant layer technology, in which a soft polymer mimics the performance of natural cartilage, ... more Compliant layer technology, in which a soft polymer mimics the performance of natural cartilage, potentially represents a resolution to the wear and associated longevity coupled with conventional metalon-plastic joints. In this two-part study, the friction and wear of compliant layer polyurethane (PU) tibial inserts articulating against metal femoral components were investigated as part of a preliminary in vitro screening. In Part I the friction and lubrication regimes were evaluated both experimentally using Stribeck analysis and theoretically using the theory of Hamrock and Dowson to investigate the joints ability to operate within a fluid film lubrication regime. Using aqueous carboxymethyl cellulose (CMC) fluids as the lubricant the joints were shown to operate with low friction and specifically, in some individual joints, with friction factors equivalent to ceramic-on-ceramic bearings as observed in hip bearings. Protein containing lubricants caused an increase in friction relative to the CMC solutions and it is proposed that this results from the shearing of interfacial protein layers adsorbed onto the articulating surfaces. Overall, the friction and lubrication results demonstrated the ability of compliant layer joints to operate with fluid film lubrication and consequential lower frictional torque during the walking cycle. In Part II of this study the wear performance of this articulation system will be investigated.

Polymer Degradation and Stability, 1999

γ irradiation of ultra-high molecular weight polyethylene (UHMWPE) results in both immediate and ... more γ irradiation of ultra-high molecular weight polyethylene (UHMWPE) results in both immediate and time dependent property changes. The time dependent changes are believed to arise from long lived free radicals reacting with oxygen and causing chain scission. Samples of UHMWPE have been irradiated in air and in vacuum at ambient temperatures to various dose levels, and subjected to a series