Summary:This work focuses on the characterisation of ascorbic acid/persulphate initiating system.... more Summary:This work focuses on the characterisation of ascorbic acid/persulphate initiating system. Three different persulphates were used (ammonium, potassium and sodium), and a range of initiator concentrations were tested. Gel time, gel quality, initiator toxicity, and cell survival upon encapsulation were measured. No significant differences were observed between the three types of persulphates. Higher concentrations of the initiators resulted in faster gel times (5min for 0.05wt% initiator) and higher quality gels (less than 20% sol fraction), although the lower initiator concentrations were better in terms of cell growth inhibition and survival upon encapsulation. Overall, this system shows great promise for use in biomedical applications, however there is a need to minimise the initiator concentration to increase cell compatibility while maintaining a high enough concentration for adequate gel formation.
Synthetic scaffolds show great promise for use in tissue engineering due to their ability to mimi... more Synthetic scaffolds show great promise for use in tissue engineering due to their ability to mimic some aspects of the extracellular matrix, however, their use has been hindered by the lack of inherent recognition sites that are required for protein and cell interactions. Heparan sulfate (HS), a glycosaminoglycan polysaccharide present in the basement membrane and on the cell surface, binds growth factors and cytokines and enhances the signalling of these ligands by forming complexes with their receptors. This study focuses on the formation of photopolymerised hydrogels derived from methacrylated macromers of poly(vinyl alcohol) (PVA) and heparin, with the aim of imparting the growth factor activation property of heparin to the synthetic scaffolds. It was shown that the methacrylate group attachment on heparin did not result in the fragmentation of heparin molecules, and that the biological activity of the methacrylated heparin was preserved as determined by tests on its anticoagulation properties and ability to signal fibroblast growth factor-2 (FGF-2). The addition of heparin into the PVA hydrogels resulted in an increase in mass swelling ratio from 5.8 for pure PVA to 6.5 and 6.6 for PVA/heparin co-hydrogels of 19/1 and 17.5/2.5 (w/w) compositions, respectively. It is believed that heparin molecules can be added into a synthetic PVA scaffold without adversely affecting the structural and mechanical stability of the PVA scaffold. The tensile moduli of the co-hydrogels remained close to that of PVA hydrogels (61 kPa), even up to 2.5% heparin composition (PVA/hep 17.5/2.5). Finally, the co-hydrogels were found to retain the growth factor signalling activity of heparin at equilibrium.
Increasing demands on neuroprosthetic bioelectrodes have created a need for electrode materials t... more Increasing demands on neuroprosthetic bioelectrodes have created a need for electrode materials that can support the safe and sustainable delivery of electrical stimulation to excitable tissues. Conducting polymers have become a focal point of research into next-generation electrode materials due to their superior electrical properties for charge transfer in biological environments. Perhaps the greatest potential of conducting polymers within neural applications is their ability to accommodate biofunctionality through the incorporation and controlled release of bioactive molecules. Incorporation of neurotrophic factors, cell adhesion molecules and various drug compounds within conducting polymers has been shown to assist in the development of higher quality tissue–electrode interfaces. However, limitations associated with drug loading and the impact of adding biological molecules on mechanical and electrical properties of biofunctionalised conducting polymers restrict their use in medical device applications. This chapter assesses the role of conducting polymers as bioelectrode materials, means of biofunctionalisation and the resultant challenges and limitations. Furthermore, this chapter evaluates the strategies developed to overcome these limitations in the pursuit of the development of high quality neural interfaces.
Journal of the Mechanical Behavior of Biomedical Materials, 2022
Water is a crucial component of bone, affecting the interplay of collagen and minerals and contri... more Water is a crucial component of bone, affecting the interplay of collagen and minerals and contributing to bone's high strength and ductility. Dehydration has been shown to significantly effect osseous mechanical properties; however, studies comparing the effects of various dehydrating environments on fracture toughness of bone are scarce. Accordingly, the crack resistance curve (R-curve) behavior of human and sheep cortical bone was characterized in a bio-bath, in ambient pressure air, and in scanning electron microscopes (SEMs) under three different environmental conditions (water vapor pressure, air pressure, and high-vacuum). The aim of this work was to better understand the impact of test environment on both intrinsic and extrinsic toughening and hence crack initiation toughness, K0 and crack growth resistance, dK/dΔa. Results show significantly lower K0 values for samples that were tested inside SEMs combined with pronounced extrinsic toughening through microcracking and crack path deflections out of the mode I plane. Importantly, all three SEM test environments gave similar results, and thus it does not matter which type of SEM is used. Ex situ testing of hydrated samples revealed similar K0 for both environments but elevated crack growth resistance for testing in ambient air relative to the bio-bath. Our data reveals the experimental difficulties to directly observe microscale crack propagation in cortical bone that resembles the in vivo situation. Ex situ testing immersed in Hanks' Balanced Salt Solution (HBSS) with subsequent crack path analysis, while tedious, is thought to presents the most realistic picture of the in vivo structure-fracture property relations in biological tissue.
Since the permeation of the inflammatory cytokines into hydrogel scaffolds has been shown to caus... more Since the permeation of the inflammatory cytokines into hydrogel scaffolds has been shown to cause dysfunction of encapsulated cells, appropriate design strategies to circumvent this are essential. In the present work, it was hypothesized that highly crosslinked PVA-fucoidan and PVA-carrageenan hydrogels can control permeation of the trefoil-shaped inflammatory cytokine IL-1β while allowing the permeation of the globular protein albumin. PVA, fucoidan, and carrageenans were functionalized with methacrylate groups and the functionalized polymers were co-crosslinked by UV photopolymerization. The resultant hydrogels were characterized physicochemically and the release of fucoidan and carrageenans was quantified by developing a colorimetric assay, which was validated by XPS analysis. The permeability characteristics of the hydrogels were evaluated using bovine serum albumin (BSA), IgG, and IL-1β. The results demonstrated an increase in hydrogel swelling through the incorporation of the polysaccharides with minimal overall mass loss. The release studies showed hydrogel stability, where the formulations exhibited ~43% retention of fucoidan and ~60-80% retention of carrageenans consistently up to 7 days. The permeation data revealed very low permeation of IgG and IL-1β through the hydrogels, with <1% permeation after 24 h, while allowing >6% permeation of BSA. These data indicate that such hydrogels can be used as the basis for cytokine-protective implantable devices for clinical applications.
Jackfruit mucilage (JM) obtained from the fruit, Artocarpus heterophyllus was melt blended with p... more Jackfruit mucilage (JM) obtained from the fruit, Artocarpus heterophyllus was melt blended with poly(ε‐caprolactone) (PCL). The physical properties of the blends with more than 60 wt% PCL were investigated. Depression in the equilibrium melting temperature () and the presence of extinction rings in the spherulites of PCL in the blends confirmed miscibility of the two components. The carbonyl and the COC groups of PCL and JM were responsible for the interactions as identified by Fourier transform infrared spectroscopy. The thermal stability of PCL decreased marginally in the blends with increasing JM content. The scanning electron microscopy (SEM) images indicated that no phase separation occurred. Porosity and the mechanical strength of the blends decreased with increasing JM content. Blends exposed to porcine pancreatic lipase showed enzymatic degradation of JM but not PCL and SEM images showed holes in the sample indicative of selective degradation of JM. Cell growth inhibition ...
Summary:This work focuses on the characterisation of ascorbic acid/persulphate initiating system.... more Summary:This work focuses on the characterisation of ascorbic acid/persulphate initiating system. Three different persulphates were used (ammonium, potassium and sodium), and a range of initiator concentrations were tested. Gel time, gel quality, initiator toxicity, and cell survival upon encapsulation were measured. No significant differences were observed between the three types of persulphates. Higher concentrations of the initiators resulted in faster gel times (5min for 0.05wt% initiator) and higher quality gels (less than 20% sol fraction), although the lower initiator concentrations were better in terms of cell growth inhibition and survival upon encapsulation. Overall, this system shows great promise for use in biomedical applications, however there is a need to minimise the initiator concentration to increase cell compatibility while maintaining a high enough concentration for adequate gel formation.
Synthetic scaffolds show great promise for use in tissue engineering due to their ability to mimi... more Synthetic scaffolds show great promise for use in tissue engineering due to their ability to mimic some aspects of the extracellular matrix, however, their use has been hindered by the lack of inherent recognition sites that are required for protein and cell interactions. Heparan sulfate (HS), a glycosaminoglycan polysaccharide present in the basement membrane and on the cell surface, binds growth factors and cytokines and enhances the signalling of these ligands by forming complexes with their receptors. This study focuses on the formation of photopolymerised hydrogels derived from methacrylated macromers of poly(vinyl alcohol) (PVA) and heparin, with the aim of imparting the growth factor activation property of heparin to the synthetic scaffolds. It was shown that the methacrylate group attachment on heparin did not result in the fragmentation of heparin molecules, and that the biological activity of the methacrylated heparin was preserved as determined by tests on its anticoagulation properties and ability to signal fibroblast growth factor-2 (FGF-2). The addition of heparin into the PVA hydrogels resulted in an increase in mass swelling ratio from 5.8 for pure PVA to 6.5 and 6.6 for PVA/heparin co-hydrogels of 19/1 and 17.5/2.5 (w/w) compositions, respectively. It is believed that heparin molecules can be added into a synthetic PVA scaffold without adversely affecting the structural and mechanical stability of the PVA scaffold. The tensile moduli of the co-hydrogels remained close to that of PVA hydrogels (61 kPa), even up to 2.5% heparin composition (PVA/hep 17.5/2.5). Finally, the co-hydrogels were found to retain the growth factor signalling activity of heparin at equilibrium.
Increasing demands on neuroprosthetic bioelectrodes have created a need for electrode materials t... more Increasing demands on neuroprosthetic bioelectrodes have created a need for electrode materials that can support the safe and sustainable delivery of electrical stimulation to excitable tissues. Conducting polymers have become a focal point of research into next-generation electrode materials due to their superior electrical properties for charge transfer in biological environments. Perhaps the greatest potential of conducting polymers within neural applications is their ability to accommodate biofunctionality through the incorporation and controlled release of bioactive molecules. Incorporation of neurotrophic factors, cell adhesion molecules and various drug compounds within conducting polymers has been shown to assist in the development of higher quality tissue–electrode interfaces. However, limitations associated with drug loading and the impact of adding biological molecules on mechanical and electrical properties of biofunctionalised conducting polymers restrict their use in medical device applications. This chapter assesses the role of conducting polymers as bioelectrode materials, means of biofunctionalisation and the resultant challenges and limitations. Furthermore, this chapter evaluates the strategies developed to overcome these limitations in the pursuit of the development of high quality neural interfaces.
Journal of the Mechanical Behavior of Biomedical Materials, 2022
Water is a crucial component of bone, affecting the interplay of collagen and minerals and contri... more Water is a crucial component of bone, affecting the interplay of collagen and minerals and contributing to bone's high strength and ductility. Dehydration has been shown to significantly effect osseous mechanical properties; however, studies comparing the effects of various dehydrating environments on fracture toughness of bone are scarce. Accordingly, the crack resistance curve (R-curve) behavior of human and sheep cortical bone was characterized in a bio-bath, in ambient pressure air, and in scanning electron microscopes (SEMs) under three different environmental conditions (water vapor pressure, air pressure, and high-vacuum). The aim of this work was to better understand the impact of test environment on both intrinsic and extrinsic toughening and hence crack initiation toughness, K0 and crack growth resistance, dK/dΔa. Results show significantly lower K0 values for samples that were tested inside SEMs combined with pronounced extrinsic toughening through microcracking and crack path deflections out of the mode I plane. Importantly, all three SEM test environments gave similar results, and thus it does not matter which type of SEM is used. Ex situ testing of hydrated samples revealed similar K0 for both environments but elevated crack growth resistance for testing in ambient air relative to the bio-bath. Our data reveals the experimental difficulties to directly observe microscale crack propagation in cortical bone that resembles the in vivo situation. Ex situ testing immersed in Hanks' Balanced Salt Solution (HBSS) with subsequent crack path analysis, while tedious, is thought to presents the most realistic picture of the in vivo structure-fracture property relations in biological tissue.
Since the permeation of the inflammatory cytokines into hydrogel scaffolds has been shown to caus... more Since the permeation of the inflammatory cytokines into hydrogel scaffolds has been shown to cause dysfunction of encapsulated cells, appropriate design strategies to circumvent this are essential. In the present work, it was hypothesized that highly crosslinked PVA-fucoidan and PVA-carrageenan hydrogels can control permeation of the trefoil-shaped inflammatory cytokine IL-1β while allowing the permeation of the globular protein albumin. PVA, fucoidan, and carrageenans were functionalized with methacrylate groups and the functionalized polymers were co-crosslinked by UV photopolymerization. The resultant hydrogels were characterized physicochemically and the release of fucoidan and carrageenans was quantified by developing a colorimetric assay, which was validated by XPS analysis. The permeability characteristics of the hydrogels were evaluated using bovine serum albumin (BSA), IgG, and IL-1β. The results demonstrated an increase in hydrogel swelling through the incorporation of the polysaccharides with minimal overall mass loss. The release studies showed hydrogel stability, where the formulations exhibited ~43% retention of fucoidan and ~60-80% retention of carrageenans consistently up to 7 days. The permeation data revealed very low permeation of IgG and IL-1β through the hydrogels, with <1% permeation after 24 h, while allowing >6% permeation of BSA. These data indicate that such hydrogels can be used as the basis for cytokine-protective implantable devices for clinical applications.
Jackfruit mucilage (JM) obtained from the fruit, Artocarpus heterophyllus was melt blended with p... more Jackfruit mucilage (JM) obtained from the fruit, Artocarpus heterophyllus was melt blended with poly(ε‐caprolactone) (PCL). The physical properties of the blends with more than 60 wt% PCL were investigated. Depression in the equilibrium melting temperature () and the presence of extinction rings in the spherulites of PCL in the blends confirmed miscibility of the two components. The carbonyl and the COC groups of PCL and JM were responsible for the interactions as identified by Fourier transform infrared spectroscopy. The thermal stability of PCL decreased marginally in the blends with increasing JM content. The scanning electron microscopy (SEM) images indicated that no phase separation occurred. Porosity and the mechanical strength of the blends decreased with increasing JM content. Blends exposed to porcine pancreatic lipase showed enzymatic degradation of JM but not PCL and SEM images showed holes in the sample indicative of selective degradation of JM. Cell growth inhibition ...
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