Widely distributable and retainable in-situ gelling material for treating myocardial infarction.

Intramyocardial hydrogel injection is a promising therapy to prevent negative remodeling following myocardial infarction (MI). In this study, we report a mechanism for in-situ gel formation without external stimulation, resulting in an injectable and tissue-retainable hydrogel for MI treatment, and investigate its therapeutic outcomes. A liquid-like polymeric solution comprising poly(3-acrylamidophenylboronic acid-co-acrylamide) (BAAm), polyvinyl alcohol (PVA), and sorbitol (S) increases the viscous modulus by reducing the pre-added sorbitol concentration is developed. This solution achieves a sol-gel transition in-vitro in heart tissue by spontaneously diffusing the sorbitol. After intramyocardial injection, the BAAm/PVA/S with lower initial viscous modulus widely spreads in the myocardium and gelate compared to a viscoelastic alginate (ALG) hydrogel and is retained longer than the BAAm/S solution. Serial echocardiogram analyses prove that injecting the BAAm/PVA/S into the hearts of subacute MI rats significantly increases the fraction shortening and ejection shortening and attenuates the expansion of systolic LV diameter for up to 21 d after injection compared to the saline injection as a control, but the ALG injection does not. In addition, histological evaluation shows that only the BAAm/PVA/S decreases the infarct size and increases the wall thickness 21 d after injection. The BAAm/PVA/S intramyocardial injection is better at restraining systolic ventricular dilatation and cardiac failure in the rat MI model than in the control groups. Our findings highlight an effective injectable hydrogel therapy for MI by optimizing injectability-dependent distribution and retention of injected material. STATEMENT OF SIGNIFICANCE: In-situ gelling material is a promising strategy for intramyocardial hydrogel injection therapy for myocardial infarction (MI). Since the sol-gel transition of reported materials is driven by external stimulation such as temperature, pH, or ultraviolet, their application in vivo remains challenging. In this study, we first reported a synthetic in-situ gelling material (BAAm/PVA/S) whose gelation is stimulated by spontaneously reducing pre-added sorbitol after contacting the heart tissue. The BAAm/PVA/S solution spreads evenly, and is retained for at least 21 d in the heart tissue. Our study demonstrated that intramyocardial injection of the BAAm/PVA/S with more extensive distribution and longer retention had better effects on preventing LV dilation and improving cardiac function after MI than that of viscoelastic ALG and saline solution. We expect that these findings provide fundamental information for the optimum design of injectable biomaterials for treating MI.