Abstract
Hydrogels are highly attractive delivery vehicles for therapeutic proteins. Their innate biocompatibility, hydrophilicity and aqueous permeability allow stable encapsulation and release of proteins. The release rates also can be controlled simply by altering the crosslinking density of the polymeric network. However, the crosslinking density also influences the mechanical properties of hydrogels, generally opposite to the permeability. In addition, the release of larger proteins may be hindered below critically diminished porosity determined by the crosslinking density. Herein, the physical properties of the hydrogels are tuned by presenting functional pendant chains, independent of crosslinking density. Heterobifunctional poly(ethylene glycol) monomethacrylate (PEGMA) with various end functional groups is synthesized and copolymerized with PEG dimethacrylate (PEGDA) to engineer PEG hydrogels with pendant PEG chains. The pendant chains of the PEG hydrogels consisting of sulfonate, trimethylammonium chloride, and phenyl groups are utilized to provide negative charge, positive charge and hydrophobicity, respectively, to the hydrogels. The release rates of proteins with different isoelectric points are controlled in a wide range by the type and the density of functional pendant chains via electrostatic and hydrophobic interactions.
Highlights
Hydrogels are a popular class of carriers for various biological molecules, such as proteins and DNA, as well as cells and tissues for biomedical applications[1,2,3,4]
The moduli of TMAC-PEG hydrogels decreased with Φ only by 40% and 50% for hydrogels with 8% Poly(ethylene glycol) dimethacrylate (PEGDA) and 4% PEG monomethacrylate (PEGMA) and 6% PEGDA and 6% PEGMA, respectively. These results indicated that (1) the increased charge density within the Sulfo-PEG hydrogels and TMAC-PEG hydrogels with increasing Φ likely pushed the polymer chains further apart via repulsion during swelling and resulted in greater chain relaxation, and (2) the larger decrease in moduli for Sulfo-PEG hydrogels compared to TMAC-hydrogels is likely due to the greater charge density of the Sulfo group compared to TMAC groups, as evidenced by their zeta potentials[26,27]
Various physical properties of PEG hydrogels were controlled independent of the crosslinking density by presenting pendant PEG chains with characteristic end functional groups in order to control the release of proteins having different isoelectric points
Summary
Hydrogels are a popular class of carriers for various biological molecules, such as proteins and DNA, as well as cells and tissues for biomedical applications[1,2,3,4]. The release rates of encapsulated biomolecules from hydrogels are often controlled in an efficient manner by varying the crosslinking density of the polymeric network, which in effect controls the porosity of the hydrogel[7,8,9] This approach is often encountered with a few critical drawbacks. The release may be severely hindered for the hydrogel having significantly reduced pores, which is especially critical for the release of larger macromolecules such as large proteins and DNA8,12 To overcome these issues, it would be ideal to control the release rates of encapsulated species in a wide range while minimally affecting the crosslinking density of the hydrogels. Since proteins have varying degrees of hydrophobicity based on amino acid compositions, the release from PEG hydrogels with hydrophobic phenyl pendant chains was explored
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