Abstract
The transport properties of hydrogels largely affect their performance in biomedical applications ranging from cell culture scaffolds to drug delivery systems. Solutes can move through the polymer mesh as a result of concentration gradients in the interstitial fluid or pressure gradients that move the fluid and solutes simultaneously. The relationship between the two modalities of transport in hydrogels can provide insight for the design of materials that can function effectively in the dynamic conditions experienced in vitro and in vivo, yet this correlation has not been previously elucidated. Here, fluorescence recovery after photobleaching (FRAP) is used to measure the diffusivity of dextran molecules of different size within polyethylene glycol hydrogels. Spherical indentation analyzed in a poroelastic framework is used to measure the permeability to fluid flow of the same hydrogels. It is found that while the diffusivity varies with exp(ξ-2), where ξ is the mesh size of the hydrogels, it also varies with exp(k-1), where k is the intrinsic permeability. For the same hydrogel structure, diffusive transport is affected by the solute size, while convective transport is unaffected. As spherical indentation is a reliable, quick and non-destructive testing method for hydrated soft materials, the relationship provides the means to faster assessment of the transport properties of hydrogels and, ultimately, of their effective use in biomedical applications.
Highlights
Control of solute transport within hydrogels, polymer networks incorporating large quantities of water, determines the successful use of these materials in biomedical applications
Convection of the interstitial fluid may increase the transport of cell nutrients or drugs: solutes can travel inside hydrogels through diffusion within the fluid, by action of a concentration gradient, as well as by convection with the fluid, driven by a pressure gradient
The mobility of solutes by diffusion within the pores is quantified by the diffusion coefficient, DS, which is some fraction of the diffusion coefficient of the solute in pure liquid, D0.4 The mobility of fluids by convection, in turn, is expressed by the hydraulic permeability, K, defined as the ratio between the intrinsic permeability of the material, k, and the dynamic viscosity of the fluid, η
Summary
Control of solute transport within hydrogels, polymer networks incorporating large quantities of water, determines the successful use of these materials in biomedical applications. Mathews Avenue, Urbana, Illinois 61801, United States (Received 20 April 2018; accepted 10 September 2018; published online 4 October 2018)
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