Water as the often neglected medium at the interface between materials and biology

Abstract

Despite its apparent simplicity, water behaves in a complex manner and is fundamental in controlling many physical, chemical and biological processes. The molecular mechanisms underlying interaction of water with materials, particularly polymer networks such as hydrogels, have received much attention in the research community. Despite this, a large gulf still exists in applying what is known to rationalize how the molecular organization of water on and within these materials impacts biological processes. In this perspective, we outline the importance of water in biomaterials science as a whole and give indications for future research directions towards emergence of a complete picture of water, materials and biology.

Fig. 1. Graphic illustration of water content in PEGDA hydrogels.

a Water content under different swelling conditions. b Comparison of water content in hydrogels with different PEGDA molecular weight. c Comparison of water content in hydrogels with different PEGDA weight fraction. (Figure reproduced from Yang et al, Polymers, 2021, 13 (6), 845, 10.3390/polym13060845).

Fig. 2. Examples of ‘synthesis to application’ of hydrogels.

a Design of poly-dl-serine (PSer) from l-serine and d-serine. The high l-serine content in silk sericin and the high level of d-serine in the human body as an important neurotransmitter altogether inspired the design of anti-FBR material PSer. b Water solubility of poly-β-homoserine (β-HS) (about 10 mg/mL), poly-l-serine (P-l-Ser) (<0.1 mg/mL due to its β-sheet folding) and PSer (>500 mg/mL). c Circular dichroism spectrum of PSer. d Synthesis of β-HS and PSer. LiHMDS Lithium hexamethyldisilazide, DMAc dimethylacetamide. e Photographs of poly-dl-serine diacrylamide (PSerDA) that was well dissolved at a concentration of 20 wt% and was used to prepare PSer hydrogels by photo-crosslinking in the presence of 0.1% photoinitiator (Irgacure 2959). f PSer hydrogels and PEG hydrogels implanted subcutaneously into C57/BL6 mice induced low FBR and obvious FBR respectively (Figure reproduced from Zhang et al. Nat. Commun. 12, 5327 (2021), 10.1038/s41467-021-25581-9).

Fig. 3. Number of biomedically-relevant journal articles published on hydrogel swelling since 2000 (blue bars) compared to the number of those same papers that mention PBS (orange bars).

Inset: The same data presented on a logarithmic scale to enable easier visualization. Source of data: Web of Science. See Supplementary Information for details of the method used to conduct the search.