Fabrication of pH‐Responsive Acryloyl Phenylalanine‐Grafted Chondroitin Sulfate Hydrogels With Tunable Swelling Potential

This work reports the first hydrogel of its kind, based on phenylalanine amino acid‐grafted chondroitin sulfate, exhibiting high and variable swelling without rupture. Grafting of N‐Acryloyl‐L‐phenylalanine (APA) on chondroitin sulfate enhances the strength of the hydrogel without compromising the swelling ratio. In this study, N‐Acryloyl‐L‐phenylalanine was first prepared by reacting L‐phenylalanine with acryloyl chloride. Chondroitin sulfate was then grafted with APA via free radical polymerization using ammonium persulfate (APS) as the initiator. Key grafting parameters (Percentages of grafting, efficiency, conversion, yield, rate, and homopolymer content) were optimized to get the Poly(Acryloyl Phenylalanine‐chondroitin sulfate) [CS‐g‐PAPA] graft copolymer. CS‐g‐PAPA, 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS), and acrylamide (AAm) were cross‐linked with N, N′‐methylenebisacrylamide (NN‐MBA) to form CS‐APA‐co‐(AMPS‐co‐AAm) (CAAM) hydrogels. N‐Acryloyl‐L‐phenylalanine (APA) structure was confirmed by Fourier Transform Infrared (FTIR) and Nuclear magnetic resonance (NMR) spectroscopic techniques. The highest grafting yield (82.3%) was achieved at 50°C, 180 min, and optimal APA (11.42 × 10 −2 mol/dm 3 ) and APS (14.62 × 10 −2 mol/dm 3 ) concentrations. The properties of CAAM hydrogel were analyzed, including mesh size, crosslink density, Flory–Huggins parameter, molecular weight between crosslinks, and swelling behavior. The CAAM hydrogels were characterized by FTIR, X‐RD, NMR, SEM, DTA, and DTG techniques. CAAM hydrogels have been tested for equilibrium and dynamic swelling in water and buffer solutions with pH values of 1.2, 4.6, 7.4, 8.2, 9.6, and 10.4. CAAM hydrogels have a broad variable swelling nature of 35.38–56.22 g/g by varying the cross‐linker and exhibiting pH responsiveness.