Polymers in contact lens applications VI. The ‘dissolved’ oxygen permeability of hydrogels and the design of materials for use in continuous-wear lenses

Ng, Chiong O.; Tighe, Brian

doi:10.1002/pi.4980080403

Cited by 28 publications

(4 citation statements)

References 15 publications

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“…It is well documented that both water content and matrix composition affect the transport of simple molecules, such as oxygen permeation through hydrogel membranes. 37–39 The diffusion of hydrated species (e.g. ophthalmic dyes or drugs) is subject to similar influences, with both size and structural features of the hydrated species together with hydration pathways and molecular structures of the matrix playing a part.…”

Section: Resultsmentioning

confidence: 99%

The design of contact lens based ocular drug delivery systems for single-day use: Part (I) Structural factors, surrogate ophthalmic dyes and passive diffusion studies

Mahomed

Tighe

2014

J Biomater Appl

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The poor retention and efficacy of instilled drops as a means of delivering drugs to the ophthalmic environment is well-recognised. The potential value of contact lenses as a means of ophthalmic drug delivery and consequent improvement of pre-corneal retention is one obvious route to the development of a more effective ocular delivery system. Furthermore, the increasing availability and clinical use of daily disposable contact lenses provides the platform for the development of viable single-day use drug delivery devices based on existing materials and lenses. In order to provide a basis for the effective design of such devices, a systematic understanding of the factors affecting the interaction of individual drugs with the lens matrix is required. Because a large number of potential structural variables are involved it is necessary to achieve some rationalisation of the parameters and physicochemical properties (such as molecular weight, charge, partition coefficients) that influence drug interactions. Ophthalmic dyes and structurally related compounds based on the same core structure were used to investigate these various factors and the way in which they can be used in concert to design effective release systems for structurally different drugs. Initial studies of passive diffusional release form a necessary precursor to the investigation of the features of the ocular environment that over-ride this simple behaviour. Commercially available contact lenses of differing structural classifications were used to study factors affecting the uptake of the surrogate actives and their release under "passive" conditions. The interaction between active and lens material shows considerable and complex structure dependence which is not simply related to equilibrium water content (EWC). The structure of the polymer matrix itself was found to have the dominant controlling influence on active uptake; hydrophobic interaction with the ophthalmic dye playing a major role.3

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Section: Resultsmentioning

confidence: 99%

The design of contact lens based ocular drug delivery systems for single-day use: Part (I) Structural factors, surrogate ophthalmic dyes and passive diffusion studies

Mahomed

Tighe

2014

J Biomater Appl

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“…Bruch's membrane exists in an enclosed environment with no air interface. Early fundamental studies of hydrogel oxygen permeability were also carried out in stirred cells that maintained full hydration [63]. As the importance of oxygen permeability for corneal health became more widely understood and the commercial application of hydrogels as contact lenses grew, however, so did the need for convenient techniques to measure lens permeability.…”

Section: Discussionmentioning

confidence: 99%

A study of the permeation and water-structuring behavioural properties of PEG modified hydrated silk fibroin membranes

Mann

Lydon

Tighe

et al. 2021

Biomed. Phys. Eng. Express

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The potential of naturally occurring substances as a source of biomedical materials is well-recognised and is being increasingly exploited. Silk fibroin membranes derived from Bombyx mori silk cocoons exemplify this, for example as substrata for the growth of ocular cells with the aim of generating biomaterial-cell constructs for tissue engineering. This study investigated the transport properties of selected silk fibroin membranes under conditions that allowed equilibrium hydration of the membranes to be maintained. The behaviour of natural fibroin membranes was compared with fibroin membranes that have been chemically modified with poly(ethylene glycol). The permeation of the smaller hydrated sodium ion was higher than that of the hydrated calcium ion for all three ethanol treated membranes investigated. The PEG and HRP-modified C membrane, which had the highest water content at 59.6±1.5% exhibited the highest permeation of the three membranes at 95.7±2.8×10 -8 cm 2 s −1 compared with 17.9±0.9×10 -8 cm 2 s −1 and 8.7±1.7×10 -8 cm 2 s −1 for membranes A and B respectively for the NaCl permeant. Poly(ethylene glycol) was used to increase permeability while exploiting the crosslinking capabilities of horseradish peroxidase to increase the compressive strength of the membrane. Importantly, we have established that the permeation behaviour of water-soluble permeants with hydrated radii in the sub-nanometer range is analogous to that of conventional hydrogel polymers.

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“…Results presented here concur with that observation. In several earlier studies the nature of water in conventional hydrogels lenses was not observed to have any significant effect on oxygen permeabilities; total water content was repeatedly shown to have the dominant influence . However, in terms of ion permeation—where both the size and extent of hydration of the permeating species can vary considerably, water structuring effects of the hydrogel matrix had not been extensively studied.…”

Section: Discussionmentioning

confidence: 97%

Investigating the permeation properties of contact lenses and its influence on tear electrolyte composition

et al. 2018

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The health of the cornea is paramount; the aim of this study was to assess the permeation of essential tear electrolytes through a range of commercial contact lenses. Donor/ receiver conductivity measurements were recorded using a dual-chamber diffusion system which allowed material permeability profiles and coefficients to be calculated. Water structuring properties of the contact lenses were measured by differential scanning calorimetry. Freezing water was subdivided into "ice-like" water (free, non-bound and has a melting point close to that of pure water) and polymer-associated water (free but loosely bound to the polymer matrix). Each material interacts differently with each of the three salts, for example; lotrafilcon B (34% equilibrium water content [EWC]) shows a higher and larger range of receiver concentrations post KCl, NaCl, CaCl 2 permeation (76, 59 and 42 mM, respectively) compared with the lower and tighter range exhibited by lotrafilcon A (22% EWC) (36, 22, and 18 mM, respectively). Additionally, in terms of the relationship between permeation and water structure, balafilcon A (34% EWC) has a high KCl permeation (P 60 258 × 10 −8 cm 2 /s) and ice-like water (14%), but narafilcon A (44% EWC) has a low ion permeation (P 60 3.9 × 10 −8 cm 2 /s) and significantly less ice-like water (4%). The permeation trends for the silicone hydrogel materials could not be fully explained by water content and structuring. Composition and, in particular, the microstructure and morphology of these materials must impart a greater influence on permeation capability.

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Polymers in contact lens applications VI. The ‘dissolved’ oxygen permeability of hydrogels and the design of materials for use in continuous-wear lenses

Cited by 28 publications

References 15 publications

The design of contact lens based ocular drug delivery systems for single-day use: Part (I) Structural factors, surrogate ophthalmic dyes and passive diffusion studies

The design of contact lens based ocular drug delivery systems for single-day use: Part (I) Structural factors, surrogate ophthalmic dyes and passive diffusion studies

A study of the permeation and water-structuring behavioural properties of PEG modified hydrated silk fibroin membranes

Investigating the permeation properties of contact lenses and its influence on tear electrolyte composition

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