Biomimetic approach to tunable adhesion of polyurethane adhesives through Fe3+ crosslinking and hydrophobic tween units with balance of adhesion/cohesion forces

Biocompatible adhesives have some limitations such as weak adhesion and low flexibility. To overcome these limitations, we described multiple strategies to provide strong adhesion and high flexibility through Tweens, chlorogenic acid (CLA) and polyethylene glycol (PEG) by reducing excessive interaction between tissue and the adhesive. We synthesized polyurethane-based adhesives using aliphatic 4,4′-methylenebis(cyclohexyl isocyanate) (HMDI), PEG, CLA and Tween units. Hydrophobic side chains in polymer resulted in lower Tg (−36.95-30.36 °C) which indicated more flexibility. The highest adhesion strengths were found as almost 346 kPa for bare polyurethane and 492 kPa for chelated polymer (PU-T40-CLA-15% (5% Tween 40, 15% chlorogenic acid and 80% PEG 200 containing polymer)) with FeCl3. The addition of Tween units provided more stable structure to polymers which proved with in vitro erosion studies. Relatively low erosion values were seen as 5.7, 5.6 and 8.2% in PU-T40-CLA-5% (15% Tween 40, 5% chlorogenic acid and 80% PEG 200 containing polymer), PU-T40-CLA-10% (10% Tween 40, 10% chlorogenic acid and 80% PEG 200 containing polymer), and PU-T40-CLA-15% (5% Tween 40, 15% chlorogenic acid and 80% PEG 200 containing polymer), respectively. In vitro biocompatibility results showed high cell viability in PU-T40-15% as more than 100%. Overall, our findings indicated that these material designs (PU-T-CLAs) provided to overcome the significant challenges of tissue adhesives by improving the flexible character and adhesive strength of the adhesives.