Abstract
A series of semi-interpenetrating polymer network (semi-IPN) hydrogels were synthesized and investigated in this study. Linear copolymer poly(N-isopropylacrylamide-co-itaconamic acid) p(NIPAM-co-IAM), which is formed by copolymerization of N-isopropylacrylamide (NIPAM) and itaconamic acid (IAM, 4-amino-2-ethylene-4-oxobutanoic acid), was introduced into a solution of NIPAM to form a series of pH and thermo dual-responsive p(NIPAM-co-IAM)/pNIPAM semi-IPN hydrogels by free radical polymerization. The structural, morphological, chemical, and physical properties of the linear copolymer and semi-IPN hydrogels were investigated. The semi-IPN hydrogel showed high thermal stability according to thermal gravimetric analyzer (TGA). Scanning electronic microscopy (SEM) images showed that the pore size was in the range of 119~297 µm and could be controlled by the addition ratio of the linear copolymer in the semi-IPN structure. The addition of linear copolymer increased the fracture strain from 57.5 ± 2.9% to 91.1 ± 4.9% depending on the added amount, while the compressive modulus decreased as the addition increased. Moreover, the pH and thermo dual-responsive properties were investigated using differential scanning calorimetry (DSC) and monitoring the swelling behavior of the hydrogels. In deionized (DI) water, the equilibrium swelling ratio of the hydrogels decreased as the temperature increased from 20 °C to 50 °C, while it varied in various pH buffer solutions. In addition, the swelling and deswelling rates of the hydrogels also significantly increased. The results indicate that the novel pH-thermo dual-responsive semi-IPN hydrogels were synthesized successfully and may be a potential material for biomedical, drug delivery, or absorption application.
Highlights
Hydrogel is a type of polymer material with a three-dimensional network capable of absorbing water without dissolving
The pNIPAM network was formed in the presence of the linear copolymer and a semi-IPN hydrogel was obtained
The results demonstrate that linear copolymer p(NIPAM-co-itaconamic acid (IAM)) increases the results demonstrate that linear copolymer p(NIPAM-co-IAM) increases the fracture strain of semi-IPN
Summary
Hydrogel is a type of polymer material with a three-dimensional network capable of absorbing water without dissolving. At temperatures below its LCST, the cross-linked pNIPAM is hydrophilic and absorbs water to a swollen state On the contrary, it is hydrophobic and water is removed from the network to a shrunken state with decreased volume material [13,14]. LCST, it possesses strong hydrogen bonds between pNIPAM and water, causing the swollen state, while above LCST, the interaction with pNIPAM is stronger than the hydrogen bonds, leading to the shrunken state Having this special feature, pNIPAM hydrogel can be used as a thermo-responsive carrier in many fields, such as in drug release [17,18], for bioactive molecule separation [19], as a catalyst [20], for cell harvesting [21], as a seal-healing hydrogel [22], etc. Conventional pNIPAM hydrogels have some disadvantages: they are brittle at room temperature and have poor mechanical properties, a low swelling ratio, and a slow response rate [23,24,25]
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