Mechanical Properties of Double Network Poly (Acrylic Acid) Based Hydrogels for Potential Use as a Biomaterial.

Load-bearing applications of hydrogels include soft robots, tissue engineering, and stretchable electronics. This paper presents an extensive study of double network poly (acrylic acid) based hydrogel on stress relaxation, compression fatigue, shear stress, and shock absorption properties as a potential load-bearing soft tissue replacement biomaterial. Double network poly (acrylic acid) hydrogel was selected due to simple processing and availability. The optimized formulation of poly (acrylic acid) hydrogel was used for samples preparation. The compression modulus varied with hydrogel formulation, crosshead speed and swelled amount of the hydrogel. Stress relaxation and shock absorption properties of hydrogel were compared with polyurethane gel used in soft insoles (Shore 5A). Developed hydrogel displayed good fatigue properties up to 10,000 loading cycle at maximum stress of 390±30 kPa and at 84±4% strain. Further, maximum average shear stress and shear modulus of 80 kPa and 140 kPa respectively were observed at 84% strain before fracture.

Photochromic superabsorbent polymers.

Photochromic superabsorbent polymers (PSAPs) with a hydrophilic core and a photochromic shell were prepared by inverse suspension polymerization using acrylic acid (AA) and acrylamide (AM) as monomers, potassium persulfate as the initiator, N,N'-methylene bisacrylamide (BIS) as a cross-linker, sorbitan monostearate (Span60) as the dispersant, cyclohexane as the solvent and bis(methacryloylamino)azobenzene (AC) as the photochromic surface cross-linker. The polymer was characterized by NMR, infrared spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Water absorption (Q) and the photoresponse of the PSAPs was investigated. The PSAPs prepared have excellent water absorption (2800 g g-1). When the sample is irradiated at 350 nm water expulsion from the swollen PSAPs was observed.