This study was designed to assess the duration of hyaluronic acid (HA) release from model contact... more This study was designed to assess the duration of hyaluronic acid (HA) release from model contact lens materials when HA was physically incorporated into the hydrogel during synthesis and to assess the effects of the HA release on lysozyme sorption. Model conventional and silicone hydrogel contact lens materials containing HA of various molecular weights as a releasable wetting agent were prepared. The HA was released into phosphate-buffered saline and MilliQ water, and the release was monitored using ultraviolet spectroscopy. Hyaluronic acid release was quantified by enzyme-linked immunosorbent assay. The effect of the releasable HA on lysozyme sorption to the materials was also analyzed using 125-I-labeled protein. Hyaluronic acid loaded into the materials using this method could be released from conventional hydrogel materials for 21 days; the model silicone hydrogels showed release of more than 7 weeks. With one exception, the releasable HA decreased lysozyme sorption. Hyaluronic acid physically incorporated into contact lens materials during synthesis may therefore be released for extended periods of time of up to 7 weeks. Hyaluronic acid release leads to decreased protein adsorption in general. This method has potential for modification of conventional and silicone hydrogel lenses with releasable HA as a wetting agent.
The potential of hydrophobically-modified poly(vinyl pyrrolidone) as a shear-responsive, self-ass... more The potential of hydrophobically-modified poly(vinyl pyrrolidone) as a shear-responsive, self-associative hydrogel for ophthalmic applications is demonstrated. Hydrophobic modification was achieved via random copolymerization of N-vinylpyrrolidone with N-vinylformamide, the latter of which can be hydrolyzed to expose a desired degree of reactive amine groups permitting grafting of alkyl chlorides of varying alkyl chain lengths. The resulting materials formed highly shear-responsive physical hydrogels, exhibiting tunable shear thinning over 4-5 decades of viscosity from infinite shear to zero shear conditions that facilitates lubrication upon blinking and/or facile injection or drop-based delivery to the anterior or posterior segments of the eye. Viscosity changes due to self-association over time can also be tuned by changing the length of the hydrophobe, with C18-grafted materials exhibiting prolonged thickening over several weeks to form extremely stiff hydrogels and shorter grafts equilibrating significantly faster but forming weaker gels. The hydrogels remained transparent even at very high polymer concentrations (20 wt%) and are demonstrated to facilitate controlled release of a model drug (doxorubicin). The polymers exhibit minimal cytotoxicity in vitro to human corneal epithelial cells and retinal pigment epithelial cells, particularly when lower molecular weight backbone polymers were used. In vivo assessments in rabbits indicated no significant conjunctival edema or redness, secretion, corneal opacity, or iris involvement upon anterior application. Following intravitreal injection in rat eyes, no opacification of the lens, cornea or vitreous, nor any morphological or functional change to the posterior segment was observed. Examination of wholemount tissues and histology demonstrated no adverse effect from the injection or deposition of material. As such, these shear-thinning materials offer potential for drug delivery in both the anterior and posterior segments or as a vitreal replacement that can be easily administered or removed.
Numerous biologically active growth factors are secreted by the lacrimal gland and distributed vi... more Numerous biologically active growth factors are secreted by the lacrimal gland and distributed via the tears over the ocular surface, where they affect cellular proliferation, migration, differentiation, and survival. The role of growth factors and their receptors in maintenance of tissue homeostasis and wound healing continues to be elucidated, and the effect of growth factor imbalances in ocular surface diseases is just beginning to be understood. For instance, in eyes with ocular surface diseases, including conjunctivitis, corneal erosion, keratitis, and corneal ulcers, epidermal growth factor release rates have been shown to be significantly lower than in normal eyes during reflex tearing. Future research into the mechanisms of dry eye disease will focus on reasons for decreased tear and growth factor production in the neuronal reflex loop or the acinar lacrimal gland cells. Animal models to test therapeutic approaches must be developed.
Poly (dimethyl siloxane) (PDMS) has been widely used as a biomaterial in ophthalmic and other app... more Poly (dimethyl siloxane) (PDMS) has been widely used as a biomaterial in ophthalmic and other applications due to its good compatibility, high mechanical strength, excellent oxygen permeability and transparency. However, for use as an artificial cornea, contact lens and in other applications, modifications with hydrophilic functional groups or polymers are necessary to improve wettability for tear protein and mucin interactions and to improve glucose permeability for cellular health. Poly (N-isopropyl acrylamide) (PNIPAAM) is a biocompatible and hydrophilic polymer that has been extensively studied on controlled drug release applications due to its lower critical solution temperature (LCST) phenomenon. In the current work, a composite interpenetrating network (IPN) of PDMS and PNIPAAM was formed to generate polymers with oxygen and glucose permeability as well as improved wettability compared to PDMS homopolymers and greater mechanical strength than PNIPAAM homopolymers. Transparent vinyl and hydroxyl terminated PDMS/PNIPAAM IPNs (PDMS-V and PDMS-OH IPNs, respectively) were successfully synthesized. Transmission electron microscopy images verified the structure of the IPNs. Surface analysis suggested that PNIPAAM was present on the surface as well as in the bulk material. PDMS-OH IPNs generated from a PDMS-OH matrix cured in the presence of solvent had the highest glucose permeability at 10(-7)cm2/s, comparable to that of the native cornea. The LCST phenomenon remained in these materials, although changes were not as abrupt as with pure PNIPAAM. These results suggest that these materials may be further developed as ophthalmic biomaterials or for controlled drug-release applications.
Proceedings of The National Academy of Sciences, 2003
Our objective was to determine whether key properties of extracellular matrix (ECM) macromolecule... more Our objective was to determine whether key properties of extracellular matrix (ECM) macromolecules can be replicated within tissue-engineered biosynthetic matrices to influence cellular properties and behavior. To achieve this, hydrated collagen and N-isopropylacrylamide copolymer-based ECMs were fabricated and tested on a corneal model. The structural and immunological simplicity of the cornea and importance of its extensive innervation for optimal functioning
Proteoglycan 4 (PRG4, or lubricin) is a lubricating mucin-like glycoprotein recently discovered a... more Proteoglycan 4 (PRG4, or lubricin) is a lubricating mucin-like glycoprotein recently discovered at the ocular surface, where it functions as a boundary lubricant and appears to play a protective role. Recent technological advances have enabled abundant expression of full-length recombinant human PRG4 (rhPRG4). The objectives of this study were to 1) biochemically characterize the gross structure and glycosylations of full-length rhPRG4, and 2) assess the ocular surface boundary lubricating ability of rhPRG4 at both human cornea-eyelid and human cornea-polydimethylsiloxane (PDMS) biointerfaces. rhPRG4 expressed by a Chinese hamster ovary cell line was characterized and compared to native bovine PRG4 by SDS-PAGE western blotting, and protein identity was assessed by tandem mass spectrometry (MS/MS). Human corneas were articulated against PDMS or human eyelids, at effective sliding velocities of 0.3-30 mm/s under physiological loads of ∼15 kPa, to assess and compare the ocular lubricat...
Nonspecific protein adsorption generally occurs at the biomaterial-tissue interface and usually h... more Nonspecific protein adsorption generally occurs at the biomaterial-tissue interface and usually has adverse consequences. Thus, surfaces that are protein-resistant are eagerly sought with the expectation that these materials will exhibit improved biocompatibility. Surfaces modified with end-tethered poly(ethylene oxide) (PEO) have been shown to be protein-resistant to some degree. Although the mechanisms are unclear, it has been suggested that chain length, chain density, and chain conformation are important factors. To investigate the effects of PEO chain density, we selected a model system based on the chemisorption of chain-end thiolated PEO to a gold substrate. Chain density was varied by varying PEO solubility (proximity to cloud point) and incubation time in the chemisorption solution. The adsorption of fibrinogen and lysozyme to these surfaces was investigated. It was found that for 750 and 2000 MW PEO layers, resistance to fibrinogen increased with chain density and was maximal at a density of approximately 0.5 chains/nm(2) (80% decrease in adsorption compared to unmodified gold). As PEO chain density increased beyond 0.5/nm(2) adsorption increased. For PEO of 5000 MW the optimal chain density was 0.27/nm(2) and gave only a 60% reduction in fibrinogen adsorption. It is suggested that, at high chain density, the chemisorbed PEO is dehydrated giving a surface that is no longer protein resistant. The PEO-modified surfaces were found also to be resistant to lysozyme adsorption with reductions similar to, if somewhat less than, those for fibrinogen. The fibrinogen to lysozyme molar ratios were within the expected range for close-packed layers of these proteins in their native conformation and were relatively insensitive to PEO chain density and MW. This may suggest that such adsorption as did occur, even at chain densities giving minimum adsorption, may have been on patches of unmodified gold.
Tissue-engineering techniques are being used to build in vitro models of organs as substitutes fo... more Tissue-engineering techniques are being used to build in vitro models of organs as substitutes for human donor organs for transplantation as well as in vitro toxicology testing (as alternatives to use of animals). Tissue engineering involves the fabrication of scaffolds from materials that are biologically compatible to serve as cellular supports and microhabitats in order to reconstitute a desired tissue or organ. Three organ systems that are currently the foci of tissue engineering efforts for both transplantation and in vitro toxicology testing purposes are discussed. These are models of the cornea, nerves (peripheral nerves specifically), and cardiovascular components. In each of these organ systems, a variety of techniques and materials are being used to achieve the same end results. In general, models that are designed with consideration of the developmental and cellular biology of the target tissues or organs have tended to result in morphologically and physiologically accurate models. Many of the models, with further development and refinement, have the potential to be useful as functional substitute tissues and organs for transplantation or for in vitro toxicology testing.
Light-responsive polymers with controllable, reversible crosslink mechanisms have the potential t... more Light-responsive polymers with controllable, reversible crosslink mechanisms have the potential to create unique biomaterials with stimulus-controlled swelling, degradation and diffusion properties useful in tissue engineering and drug delivery applications. Generic photodimerizing polyethylene glycol-anthracene macromolecules that may be grafted to various polymers to effectively control their crosslinking via a photodimerization mechanism have been developed. These generic crosslinkers were shown to effectively introduce photoresponsive properties into hyaluronate and alginate as model hydrophilic polymers. In vitro testing using human corneal epithelial cells was used to demonstrate cytocompatibility of the resulting photogels. The effective crosslinking density of the photogels could be increased resulting in a decrease in the release rate of small and large molecules from the photogels following exposure to 365 nm light. This tuneable crosslinking has the potential to manipulate the delivery rates of therapeutics resulting in control over treatment profiles and may lend itself to various applications, which may benefit from light induced changes in crosslinking.
A clear understanding of the mechanisms responsible for the protein-resistant nature of end-tethe... more A clear understanding of the mechanisms responsible for the protein-resistant nature of end-tethered poly(ethylene oxide) (PEO) surfaces remains elusive. A barrier to improved understanding is the fact that many of the factors involved (chain length, chain density, hydration, conformation, and distal chemistry) are inherently correlated. We hypothesize that, by comparing systems of variable but precisely known chain density, it should be possible to gain additional insight into the effects of the other factors. To evaluate this hypothesis, chain-end-thiolated PEOs were chemisorbed to gold-coated silicon wafers such that a range of chain densities was obtained. Three different PEOs were investigated: hydroxy-terminated chains of molecular weight 600 (600-OH), methoxy-terminated chains of molecular weight 750 (750-OCH3), and methoxy-terminated chains of molecular weight 2000 (2000-OCH3). In situ null ellipsometry was used to determine PEO chemisorption kinetics, ultimate PEO chain densities, protein adsorption kinetics, and ultimate protein adsorbed quantities. With this approach, it was possible to ascertain the effects of PEO distal chemistry (-OH, -OCH3), chain length, and layer hydration on protein adsorption. The data obtained suggested that properties related to chain density (conformational freedom, hydration) were the main determinants of protein resistance at chain densities up to a critical value of approximately 0.5 chain/nm2; at this value, protein adsorption was a minimum for the methoxy-terminated PEOs. For the hydroxyl-terminated PEO, adsorption leveled off at the critical value. Thus distal chemistry appears to be a major determinant of protein resistance at chain densities greater than the critical value.
Journal of Ocular Pharmacology and Therapeutics, 1996
The effect of corneal epithelial wound creation on epidermal growth factor (EGF) concentration in... more The effect of corneal epithelial wound creation on epidermal growth factor (EGF) concentration in tears was evaluated in order to better understand the effects of EGF on the wound healing process. The tears of New Zealand white rabbits were sampled by micropipette one day prior to wounding, immediately prior to the creation of a 7.5 mm diameter anterior keratectomy wound, immediately following wound creation, and at 1, 2, 3, 7, and 14 days following wounding. A volume of 50 microL was taken at each sampling time, and all tear samples were assayed for EGF by an enzyme linked immunosorbent assay (ELISA). The results demonstrated that the concentration of EGF in the tear layer rises dramatically immediately following wound creation. The basal measured EGF concentration was approximately 600 pg/mL; immediately following wound creation, this rose to approximately 1600 pg/mL. By 1 day following creation of the wound, the concentration of EGF in the tears had returned to the basal level. A second, marginally significant increase in the tear concentration was noted at 3 days post wounding. The EGF concentration in the tears were not significantly different at any other time. The measured dramatic rise in EGF concentration in the tears in response to the creation of a corneal epithelial wound provides further evidence of the importance of tear EGF in the wound healing process. The concentrations in all cases were on the order of ng/mL, suggesting that the intercellular concentrations in this range result in optimal cell stimulation.
This study was designed to assess the duration of hyaluronic acid (HA) release from model contact... more This study was designed to assess the duration of hyaluronic acid (HA) release from model contact lens materials when HA was physically incorporated into the hydrogel during synthesis and to assess the effects of the HA release on lysozyme sorption. Model conventional and silicone hydrogel contact lens materials containing HA of various molecular weights as a releasable wetting agent were prepared. The HA was released into phosphate-buffered saline and MilliQ water, and the release was monitored using ultraviolet spectroscopy. Hyaluronic acid release was quantified by enzyme-linked immunosorbent assay. The effect of the releasable HA on lysozyme sorption to the materials was also analyzed using 125-I-labeled protein. Hyaluronic acid loaded into the materials using this method could be released from conventional hydrogel materials for 21 days; the model silicone hydrogels showed release of more than 7 weeks. With one exception, the releasable HA decreased lysozyme sorption. Hyaluronic acid physically incorporated into contact lens materials during synthesis may therefore be released for extended periods of time of up to 7 weeks. Hyaluronic acid release leads to decreased protein adsorption in general. This method has potential for modification of conventional and silicone hydrogel lenses with releasable HA as a wetting agent.
The potential of hydrophobically-modified poly(vinyl pyrrolidone) as a shear-responsive, self-ass... more The potential of hydrophobically-modified poly(vinyl pyrrolidone) as a shear-responsive, self-associative hydrogel for ophthalmic applications is demonstrated. Hydrophobic modification was achieved via random copolymerization of N-vinylpyrrolidone with N-vinylformamide, the latter of which can be hydrolyzed to expose a desired degree of reactive amine groups permitting grafting of alkyl chlorides of varying alkyl chain lengths. The resulting materials formed highly shear-responsive physical hydrogels, exhibiting tunable shear thinning over 4-5 decades of viscosity from infinite shear to zero shear conditions that facilitates lubrication upon blinking and/or facile injection or drop-based delivery to the anterior or posterior segments of the eye. Viscosity changes due to self-association over time can also be tuned by changing the length of the hydrophobe, with C18-grafted materials exhibiting prolonged thickening over several weeks to form extremely stiff hydrogels and shorter grafts equilibrating significantly faster but forming weaker gels. The hydrogels remained transparent even at very high polymer concentrations (20 wt%) and are demonstrated to facilitate controlled release of a model drug (doxorubicin). The polymers exhibit minimal cytotoxicity in vitro to human corneal epithelial cells and retinal pigment epithelial cells, particularly when lower molecular weight backbone polymers were used. In vivo assessments in rabbits indicated no significant conjunctival edema or redness, secretion, corneal opacity, or iris involvement upon anterior application. Following intravitreal injection in rat eyes, no opacification of the lens, cornea or vitreous, nor any morphological or functional change to the posterior segment was observed. Examination of wholemount tissues and histology demonstrated no adverse effect from the injection or deposition of material. As such, these shear-thinning materials offer potential for drug delivery in both the anterior and posterior segments or as a vitreal replacement that can be easily administered or removed.
Numerous biologically active growth factors are secreted by the lacrimal gland and distributed vi... more Numerous biologically active growth factors are secreted by the lacrimal gland and distributed via the tears over the ocular surface, where they affect cellular proliferation, migration, differentiation, and survival. The role of growth factors and their receptors in maintenance of tissue homeostasis and wound healing continues to be elucidated, and the effect of growth factor imbalances in ocular surface diseases is just beginning to be understood. For instance, in eyes with ocular surface diseases, including conjunctivitis, corneal erosion, keratitis, and corneal ulcers, epidermal growth factor release rates have been shown to be significantly lower than in normal eyes during reflex tearing. Future research into the mechanisms of dry eye disease will focus on reasons for decreased tear and growth factor production in the neuronal reflex loop or the acinar lacrimal gland cells. Animal models to test therapeutic approaches must be developed.
Poly (dimethyl siloxane) (PDMS) has been widely used as a biomaterial in ophthalmic and other app... more Poly (dimethyl siloxane) (PDMS) has been widely used as a biomaterial in ophthalmic and other applications due to its good compatibility, high mechanical strength, excellent oxygen permeability and transparency. However, for use as an artificial cornea, contact lens and in other applications, modifications with hydrophilic functional groups or polymers are necessary to improve wettability for tear protein and mucin interactions and to improve glucose permeability for cellular health. Poly (N-isopropyl acrylamide) (PNIPAAM) is a biocompatible and hydrophilic polymer that has been extensively studied on controlled drug release applications due to its lower critical solution temperature (LCST) phenomenon. In the current work, a composite interpenetrating network (IPN) of PDMS and PNIPAAM was formed to generate polymers with oxygen and glucose permeability as well as improved wettability compared to PDMS homopolymers and greater mechanical strength than PNIPAAM homopolymers. Transparent vinyl and hydroxyl terminated PDMS/PNIPAAM IPNs (PDMS-V and PDMS-OH IPNs, respectively) were successfully synthesized. Transmission electron microscopy images verified the structure of the IPNs. Surface analysis suggested that PNIPAAM was present on the surface as well as in the bulk material. PDMS-OH IPNs generated from a PDMS-OH matrix cured in the presence of solvent had the highest glucose permeability at 10(-7)cm2/s, comparable to that of the native cornea. The LCST phenomenon remained in these materials, although changes were not as abrupt as with pure PNIPAAM. These results suggest that these materials may be further developed as ophthalmic biomaterials or for controlled drug-release applications.
Proceedings of The National Academy of Sciences, 2003
Our objective was to determine whether key properties of extracellular matrix (ECM) macromolecule... more Our objective was to determine whether key properties of extracellular matrix (ECM) macromolecules can be replicated within tissue-engineered biosynthetic matrices to influence cellular properties and behavior. To achieve this, hydrated collagen and N-isopropylacrylamide copolymer-based ECMs were fabricated and tested on a corneal model. The structural and immunological simplicity of the cornea and importance of its extensive innervation for optimal functioning
Proteoglycan 4 (PRG4, or lubricin) is a lubricating mucin-like glycoprotein recently discovered a... more Proteoglycan 4 (PRG4, or lubricin) is a lubricating mucin-like glycoprotein recently discovered at the ocular surface, where it functions as a boundary lubricant and appears to play a protective role. Recent technological advances have enabled abundant expression of full-length recombinant human PRG4 (rhPRG4). The objectives of this study were to 1) biochemically characterize the gross structure and glycosylations of full-length rhPRG4, and 2) assess the ocular surface boundary lubricating ability of rhPRG4 at both human cornea-eyelid and human cornea-polydimethylsiloxane (PDMS) biointerfaces. rhPRG4 expressed by a Chinese hamster ovary cell line was characterized and compared to native bovine PRG4 by SDS-PAGE western blotting, and protein identity was assessed by tandem mass spectrometry (MS/MS). Human corneas were articulated against PDMS or human eyelids, at effective sliding velocities of 0.3-30 mm/s under physiological loads of ∼15 kPa, to assess and compare the ocular lubricat...
Nonspecific protein adsorption generally occurs at the biomaterial-tissue interface and usually h... more Nonspecific protein adsorption generally occurs at the biomaterial-tissue interface and usually has adverse consequences. Thus, surfaces that are protein-resistant are eagerly sought with the expectation that these materials will exhibit improved biocompatibility. Surfaces modified with end-tethered poly(ethylene oxide) (PEO) have been shown to be protein-resistant to some degree. Although the mechanisms are unclear, it has been suggested that chain length, chain density, and chain conformation are important factors. To investigate the effects of PEO chain density, we selected a model system based on the chemisorption of chain-end thiolated PEO to a gold substrate. Chain density was varied by varying PEO solubility (proximity to cloud point) and incubation time in the chemisorption solution. The adsorption of fibrinogen and lysozyme to these surfaces was investigated. It was found that for 750 and 2000 MW PEO layers, resistance to fibrinogen increased with chain density and was maximal at a density of approximately 0.5 chains/nm(2) (80% decrease in adsorption compared to unmodified gold). As PEO chain density increased beyond 0.5/nm(2) adsorption increased. For PEO of 5000 MW the optimal chain density was 0.27/nm(2) and gave only a 60% reduction in fibrinogen adsorption. It is suggested that, at high chain density, the chemisorbed PEO is dehydrated giving a surface that is no longer protein resistant. The PEO-modified surfaces were found also to be resistant to lysozyme adsorption with reductions similar to, if somewhat less than, those for fibrinogen. The fibrinogen to lysozyme molar ratios were within the expected range for close-packed layers of these proteins in their native conformation and were relatively insensitive to PEO chain density and MW. This may suggest that such adsorption as did occur, even at chain densities giving minimum adsorption, may have been on patches of unmodified gold.
Tissue-engineering techniques are being used to build in vitro models of organs as substitutes fo... more Tissue-engineering techniques are being used to build in vitro models of organs as substitutes for human donor organs for transplantation as well as in vitro toxicology testing (as alternatives to use of animals). Tissue engineering involves the fabrication of scaffolds from materials that are biologically compatible to serve as cellular supports and microhabitats in order to reconstitute a desired tissue or organ. Three organ systems that are currently the foci of tissue engineering efforts for both transplantation and in vitro toxicology testing purposes are discussed. These are models of the cornea, nerves (peripheral nerves specifically), and cardiovascular components. In each of these organ systems, a variety of techniques and materials are being used to achieve the same end results. In general, models that are designed with consideration of the developmental and cellular biology of the target tissues or organs have tended to result in morphologically and physiologically accurate models. Many of the models, with further development and refinement, have the potential to be useful as functional substitute tissues and organs for transplantation or for in vitro toxicology testing.
Light-responsive polymers with controllable, reversible crosslink mechanisms have the potential t... more Light-responsive polymers with controllable, reversible crosslink mechanisms have the potential to create unique biomaterials with stimulus-controlled swelling, degradation and diffusion properties useful in tissue engineering and drug delivery applications. Generic photodimerizing polyethylene glycol-anthracene macromolecules that may be grafted to various polymers to effectively control their crosslinking via a photodimerization mechanism have been developed. These generic crosslinkers were shown to effectively introduce photoresponsive properties into hyaluronate and alginate as model hydrophilic polymers. In vitro testing using human corneal epithelial cells was used to demonstrate cytocompatibility of the resulting photogels. The effective crosslinking density of the photogels could be increased resulting in a decrease in the release rate of small and large molecules from the photogels following exposure to 365 nm light. This tuneable crosslinking has the potential to manipulate the delivery rates of therapeutics resulting in control over treatment profiles and may lend itself to various applications, which may benefit from light induced changes in crosslinking.
A clear understanding of the mechanisms responsible for the protein-resistant nature of end-tethe... more A clear understanding of the mechanisms responsible for the protein-resistant nature of end-tethered poly(ethylene oxide) (PEO) surfaces remains elusive. A barrier to improved understanding is the fact that many of the factors involved (chain length, chain density, hydration, conformation, and distal chemistry) are inherently correlated. We hypothesize that, by comparing systems of variable but precisely known chain density, it should be possible to gain additional insight into the effects of the other factors. To evaluate this hypothesis, chain-end-thiolated PEOs were chemisorbed to gold-coated silicon wafers such that a range of chain densities was obtained. Three different PEOs were investigated: hydroxy-terminated chains of molecular weight 600 (600-OH), methoxy-terminated chains of molecular weight 750 (750-OCH3), and methoxy-terminated chains of molecular weight 2000 (2000-OCH3). In situ null ellipsometry was used to determine PEO chemisorption kinetics, ultimate PEO chain densities, protein adsorption kinetics, and ultimate protein adsorbed quantities. With this approach, it was possible to ascertain the effects of PEO distal chemistry (-OH, -OCH3), chain length, and layer hydration on protein adsorption. The data obtained suggested that properties related to chain density (conformational freedom, hydration) were the main determinants of protein resistance at chain densities up to a critical value of approximately 0.5 chain/nm2; at this value, protein adsorption was a minimum for the methoxy-terminated PEOs. For the hydroxyl-terminated PEO, adsorption leveled off at the critical value. Thus distal chemistry appears to be a major determinant of protein resistance at chain densities greater than the critical value.
Journal of Ocular Pharmacology and Therapeutics, 1996
The effect of corneal epithelial wound creation on epidermal growth factor (EGF) concentration in... more The effect of corneal epithelial wound creation on epidermal growth factor (EGF) concentration in tears was evaluated in order to better understand the effects of EGF on the wound healing process. The tears of New Zealand white rabbits were sampled by micropipette one day prior to wounding, immediately prior to the creation of a 7.5 mm diameter anterior keratectomy wound, immediately following wound creation, and at 1, 2, 3, 7, and 14 days following wounding. A volume of 50 microL was taken at each sampling time, and all tear samples were assayed for EGF by an enzyme linked immunosorbent assay (ELISA). The results demonstrated that the concentration of EGF in the tear layer rises dramatically immediately following wound creation. The basal measured EGF concentration was approximately 600 pg/mL; immediately following wound creation, this rose to approximately 1600 pg/mL. By 1 day following creation of the wound, the concentration of EGF in the tears had returned to the basal level. A second, marginally significant increase in the tear concentration was noted at 3 days post wounding. The EGF concentration in the tears were not significantly different at any other time. The measured dramatic rise in EGF concentration in the tears in response to the creation of a corneal epithelial wound provides further evidence of the importance of tear EGF in the wound healing process. The concentrations in all cases were on the order of ng/mL, suggesting that the intercellular concentrations in this range result in optimal cell stimulation.
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