Charge balance transition enabled Janus hydrogel for robust wet-tissue adhesion and anti-postoperative adhesion

<i>Janus</i> hydrogels have recently emerged as promising bioadhesives for efficient wet-tissue adhesion and anti-postoperative adhesion. However, existing <i>Janus</i> hydrogel adhesives normally need varied chemical designs of different layers to achieve asymmetric adhesive/anti-adhesive properties on either side. Here, we present a new strategy to construct an adhesive/anti-adhesive <i>Janus</i> hydrogel tissue patch accomplished by switching the charge-balance of the hydrogel layers with similar compositions (anionic carboxyl polymer and cationic ε-polylysine, EPL). The bottom layer (AL) is formed under acidic condition (pH 2.85), featuring abundant -COOH and -NH₃ ⁺ residues, which provide rapid & robust adhesion to diverse wet tissues (up to 100.4 kPa) with high bursting pressure (362.5 mmHg), while the top layer (MLT) is formed under neutral condition, achieving a balanced charge between -COOH/-NH₂ and -COO^-/-NH₃ ⁺ groups, which mimic the overall electroneutral structure of zwitterionic materials for efficient anti-postoperative tissue adhesion (up to 6 weeks). Further <i>in vivo</i> studies validated that the integrated AL/MLT hydrogel patch is biodegradable (within 10 weeks), exhibits broad-spectrum antibacterial activity (up to 99.8 %), and outperforms the commercial fibrin gel in sutureless wound sealing, rat gastric tissue repair, and anti-postoperative adhesion. This strategy may open a new avenue to develop adhesive/anti-adhesive <i>Janus</i> bioadhesives for efficient non-invasive internal tissue sealing and promoted wound healing.