Synthesis of Poly(acrylic acid)-Cysteine-Based Hydrogels with Highly Customizable Mechanical Properties for Advanced Cell Culture Applications

Abstract

The fabrication of highly customizable scaffolds is a key enabling technology in the development of predictive in vitro cell models for applications in drug discovery, cancer research, and regenerative medicine. Naturally derived and synthetic hydrogels are good candidates for in vitro cell growth studies, owing to their soft and biocompatible nature; however, they are often hindered by limited ranges of stiffness and the requirement to modify the gel with additional extracellular matrix (ECM) proteins for cell adherence. Here, we report on the synthesis of a printable synthetic hydrogel based on cysteine-modified poly(acrylic acid) (PAA-Cys) with tuneable mechanical and swelling properties by incorporating acrylic acid into the PAA-Cys network and subsequent photoinitiated thiol-acrylate cross-linking. Control of the acrylic acid concentration and UV curing time produces a series of hydrogels with swelling ratios in excess of 100% and Young’s modulus values ranging from ∼2 to ∼35 kPa, of which most soft tissues fall within. Biocompatibility studies with RPE1 cells showed excellent cell adhesion and cell viability without the need for further modification with ECM proteins, but still can be modified as needed. The versatility of the hydrogel tuneable properties is demonstrated by culturing with RPE1 cells, which in vivo perform an important function in the visual process and the dysfunction of which may lead to various retinal abnormalities, such as glaucoma.

Green Hydrogel Synthesis: Emphasis on Proteomics and Polymer Particle-Protein Interaction

“…Wei et al used VPM as a peptide crosslinker to synthesize PEG maleimide-based hydrogels with PBS as the solvent to serve as a cell scaffold for bone defect repair; the crosslinks could be degraded by a metalloprotease produced by the cells [ 173 ]. Though synthetic polymers may support additional tunability and improved mechanical properties, biocompatibility and biodegradability are key advantages of using natural polymers for hydrogel preparation [ 174 , 175 ]. Smith et al used a dual-oxyamine-modified tobacco etch virus (TEV) peptide to form protease-degradable crosslinks between ketone-modified hyaluron and aldehyde-modified methylcellulose in PBS and media [ 176 ].…”

“…Demonstrating the tunability of mechanical properties, Bolanta et al employed an aqueous photoinitiated thiol-acrylate crosslinking of acrylic acid and cysteine-functionalized polyacrylic acid. Varying degrees of swelling and stiffness were achieved based on acrylic acid content and irradiation time, an important feature for versatile in vitro cell growth applications where optimal stiffness depends on cell type [ 174 ]. Slawinski et al utilized photopolymerization with the photoactivation of ruthenium in phosphate buffer to crosslink BSA via the linkage of tyrosine hydroxyl groups in the presence of acetic acid.…”

Self‐Healable and 4D Printable Hydrogel for Stretchable Electronics

“…[ 21 , 22 ] Poly (acrylic acid) (AAC) has been widely used for preparing hydrogels. However, the previously reported works focus on investigating the effects of contents of chemicals (i.e., AAC, crosslinker, and metal ions) on the mechanical properties of hydrogels, [ 23 , 24 ] modifying the mechanical and conductive properties of AAC‐based hydrogels with additional polymers (i.e., cysteine, [ 25 ] graphene oxide, [ 26 ] polyacrylamide [ 27 ] ), investigating the self‐healing properties of AAC‐based hydrogel reinforced by additives, [ 28 , 29 ] and preparing 3D printable AAC‐based hydrogel with carbon nanotube fillers [ 30 ] and poly(ethylene glycol). [31 ] A single material that combines stretchability, conductivity, self‐healing ability and 4D printability has not been reported as it is an ongoing challenge of designing such multifunctional materials.…”