Biomimmetic Phenolic Hydrogels

Hydrogels with versatile properties have undergone extensive research for applications in surgical adhesives, soft robotics, and wearable device development. These materials must be biocompatible, non-toxic, and have minimal foreign body reactions. However, several challenges such as poor adhesion, excessive swelling, undesirable degradation rate, and extensive preparation before application persist.<br/><br/>PEG (polyethylene glycol)- based hydrogels stand out as promising candidates for these applications. Nevertheless, many commercially available PEG-based adhesives or gels demand extensive on-site preparation and special storage conditions prior to use. The adhesion is often inadequate, and swelling rate cannot be controlled.<br/><br/>To that effect, here we report a non-toxic biomimetic hydrogel based on PEG polymer chains functionalized with phenolic functional groups (Gallol and Catechol) developed for robust adhesion and with customizable properties (for example, modulus, degradation and swelling rate). Our two-part device simplifies on-site preparation prior to administration, making it also suitable for use as a surgical adhesive. The hydrogel network consists of 4-arm PEG chains grafted with either catechol or gallol units, crosslinked using Ferric ions or sodium periodate as agents. Other polymer backbones like Polyethyleneimine (PEI) have also been investigated. The concentration of crosslinking agents with respect to that of phenolic groups' dictate the dominant mode of interaction, either coordination or covalent crosslinking. Furthermore, the overall self-healing ability, adhesive strength, and cohesive strength are tunable by the crosslinker’s concentration relative to the PEG chains. Likewise, various findings have suggested that incorporating nanocomposite clay into the network can enhance the gel’s cohesive strength.<br/><br/>In a comparative adhesion study, our optimal formulations, when tested alongside commercial PEG based adhesives on leather, exhibited shear strength of up to 253kPa, which was almost 12 times higher than Coseal^TM's shear strength of 22kPa after two hours of application. No delamination from the substrates (e.g., pig skin, leather, or collagen) was observed.