Computational modeling of Protein based super-absorbents from waste

Hydrogels are used for various applications, for example as transporters in drug delivery, incontrol lenses, and as superabsorbent material in diapers.[1] Most synthetic produced hydrogelsare based on synthetic polymers. Even though they are efficient and cheap, they are notbiodegradable and sometimes even toxic.To produce more environmental friendly and biodegradable superabsorbent polymers (Bio-SAPs), other building blocks can be used, such as polysaccharides[2] and various proteinstructures, for example fish shells[3], collagen[4], soy protein[5] and egg protein[6]. Experimentalstudies at the University of Boras show that it is possible to produce Bio-SAPs from by-productsof ethanol production from ligno-cellulose.[2, 6, 7]2. MethodWe have studied the absorption properties of protein structures in silico as a comparison toexperimental studies. The NPT Gibbs Ensemble Monte Carlo (GEMC) simulation scheme withtwo phases is used in order to calculate the absorption capacity of the protein. Pure water wassimulated in the first GEMC-phase and the peptide in the second phase. The simulations weremade with SPC/E water model [8] and the AMBER99 atomistic force field for the peptides [9].Furthermore, mesoscopic studies with coarse grained force fields have been done.To facilitate faster computations, we used cell lists for the atom-atom interactions,configurational bias algorithm to build the water molecules and the peptide side-chains, and thecavity bias algorithm [10] for molecule insertions.Model peptides have been studied with varying secondary structure, temperature andprotonation (pH). We also plan to study how cross-links affect the absorption. One of the peptideswe study is a 20 amino acid long peptide called SSP1.[11] This peptide is designed to form afibrous structure a hydrogel, and its structure is well defined. We have also studied a peptidewhich changes secondary structure when changing the pH, and concentration.[12] This makes itpossible to compare absorption properties with respect to the secondary structure.3. ConclusionWe have simulated peptides with the Gibbs Ensemble Monte Carlo scheme in order to studythe water absorption rate dependent of structure, charge, pH and temperature. This information isuseful when developing new biodegradable superabsorbent materials