Abstract
This study introduces an original concept in the development of hydrogel materials for controlled release of charged organic compounds based on semi-interpenetrating polymer networks composed by an inert gel-forming polymer component and interpenetrating linear polyelectrolyte with specific binding affinity towards the carried active compound. As it is experimentally illustrated on the prototype hydrogels prepared from agarose interpenetrated by poly(styrene sulfonate) (PSS) and alginate (ALG), respectively, the main benefit brought by this concept is represented by the ability to tune the mechanical and transport performance of the material independently via manipulating the relative content of the two structural components. A unique analytical methodology is proposed to provide complex insight into composition–structure–performance relationships in the hydrogel material combining methods of analysis on the macroscopic scale, but also in the specific microcosms of the gel network. Rheological analysis has confirmed that the complex modulus of the gels can be adjusted in a wide range by the gelling component (agarose) with negligible effect of the interpenetrating component (PSS or ALG). On the other hand, the content of PSS as low as 0.01 wt.% of the gel resulted in a more than 10-fold decrease of diffusivity of model-charged organic solute (Rhodamine 6G).
Highlights
Hydrogel represents a three-dimensional, water-swollen network assembled from cross-linked chains of either polymer molecules or partially coagulated colloidal particles
Results of the frequency sweeps are shown for agarose gels and selected semiIPN gels in Figure 1a,b
The value of complex modulus (calculated using Equation (1)) is almost frequency-independent for all analyzed hydrogels. This represents a characteristic rheological feature of densely cross-linked gel networks where the deformation response in the linear viscoelastic region is not significantly affected by the timescale of the deformation [60,61,62]. It can be seen in the same figure that the overall stiffness of semiIPN gels can be adjusted over a wide range of values by alternating the concentration of the network-making component
Summary
Hydrogel represents a three-dimensional, water-swollen network assembled from cross-linked chains of either polymer molecules or partially coagulated colloidal particles. Since the first pioneer works on covalently cross-linked poly(2-hydroxyethyl methacrylate) gels published by Wichterle and Lim in 1960 [3], significant progress has been made in the field of hydrogel design for biomaterial use, in particular in improving the physical form of the hydrogel delivery (including micro- or nanoparticulate gels [5,6], gel films [7,8], etc.), in providing a specific response to a change in the external conditions (such as temperature [9,10], pH [11,12] or concentration of a particular biomolecule [13,14]), or in obtaining materials with precisely designed internal architecture such as the superporous gels [15,16], hydrogels self-assembled from biopolymers produced by genetically engineered microorganisms [17,18], dual network gels [19,20] and many others. Until now, hydrogel materials have gained a prominent position in the field of medical research but have been put into common practice in tissue engineering [21,22], regenerative medicine [23,24], diagnostic [25,26] or separation techniques [27,28], cell immobilization and cultivation and, perhaps most exclusively, in drug-delivery applications [29]
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