A transparent, moisturizing, antibacterial and mechanically flexible hydrogel for emergency conservation of unearthed bone relics

Abstract

The excavation of bone relics holds significant implications for studying the origins, evolution, and decline of cultures. However, effectively protecting fragile unearthed bone relics like ivory remains challenging due to environmental changes from burial to exposure, which can cause dehydration and microorganism proliferation, leading to deterioration. Herein, a moisturizing and antibacterial polyacrylamide (PAM) hydrogel containing glycerol (Gly) and betaine hydrochloride (Bh) is designed for emergency conservation of unearthed bone relics. Gly forms strong hydrogen bonds with the water molecules in the hydrogel, which not only inhibits the diffusion of water molecules into the air, thereby extending their moisturizing duration, but also prevents the diffusion of water molecules into bone relics, avoiding reverse osmosis damage to the relics. Consequently, this allows the relics to maintain their initial moisture content for a prolonged period. Additionally, Gly forms hydrogen bonds with PAM, which imparts high flexibility, strength, elongation, and toughness to the hydrogel, enabling it to conform closely to curved ivory surfaces and resist external forces. In addition, the introduction of Bh significantly enhances the hydrogel’s antibacterial properties, achieving antibacterial rates of 97.96 % against Salmonella and 100 % against Escherichia coli. Based on these advantages, we have applied the hydrogel to the emergency conservation of unearthed bone relics at Sanxingdui. After applying the hydrogel to the ivory surface, the results are significant. 1 day after application, the ivory’s weight retention rate is maintained at over 95 %. Even after 7 days of protection, the appearance of the ivory remains almost unchanged, its mechanical properties are still preserved at more than 90 % of the original levels, and the growth of bacteria on the ivory surface is effectively inhibited. Therefore, this research offers a new approach to the preservation of unearthed bone relics.