# Crosslinker-Free, Printable Alginate–Boronic Acid Hydrogel Adhesive with Enhanced Mechanical Performance for Soft Tissue Fixation

## TL;DR

This paper introduces a new printable hydrogel adhesive made from alginate and boronic acid that is strong, biocompatible, and suitable for soft tissue repair without needing harmful crosslinkers.

## Contribution

The novel contribution is a crosslinker-free, printable hydrogel adhesive with enhanced mechanical performance for soft tissue fixation.

## Key findings

- The Alg-APBA hydrogel adhesive achieved a shear strength of 19.0 ± 0.5 kPa and interfacial toughness of 58.0 ± 2.11 J/m².
- The adhesive remained stable in acidic environments and showed good biocompatibility with keratinocytes and fibroblast cells.
- The material exhibited shear-thinning and self-healing properties suitable for bioprinting with high print fidelity.

## Abstract

Tissue adhesives offer a promising alternative to traditional sutures and staples, particularly in situations requiring rapid, minimally invasive wound closure. To address the limitations of commercially available cyanoacrylate-based adhesives, numerous hydrogel adhesives have been developed. This study presents the synthesis and characterisation of an alginate–aminophenylboronic acid (Alg-APBA) hydrogel adhesive, optimised for bioprinting as a method allowing us to control the thickness of the adhesive layer. The adhesive combines the biocompatibility of alginate with the pH-responsive bonding ability of boronic acid groups, eliminating the need for oxidative crosslinkers. Successful conjugation of APBA to alginate was confirmed via 1H NMR, FTIR and UV-VIS spectroscopy, with a degree of substitution reaching approximately 46% or ~0.22 mol%. Rheological analysis demonstrated shear-thinning and self-healing properties suitable for bioprinting, achieving a high print fidelity (Pr ratio = 0.99 ± 0.08) and repeatability. Mechanical testing showed a shear strength of 19.0 ± 0.5 kPa and an interfacial toughness of 58.0 ± 2.11 J/m2, exceeding those of commercial fibrin adhesives. Additionally, the adhesive joint remained stable after one week of incubation in an acidic environment. The material demonstrated biocompatibility during in vitro testing with keratinocytes and fibroblast cells. These results indicate that Alg-APBA is a strong, biocompatible and printable hydrogel adhesive with potential applications in soft tissue implant fixation.