Liquid-Liquid Phase-Separated Hydrogel with Tunable Sol-Gel Transition Behavior as a Hotmelt-Adhesive Postoperative Barrier

Injectable microcapillary network hydrogels engineered by liquid-liquid phase separation for stem cell transplantation

Injectable hydrogels are promising carriers for cell delivery in regenerative medicine. However, injectable hydrogels composed of crosslinked polymer networks are often non-microporous and prevent biological communication with host tissues through signals, nutrients, oxygen, and cells, thereby limiting graft survival and tissue integration. Here we report injectable hydrogels with liquid-liquid phase separation-induced microcapillary networks (μCN) as stem cell-delivering scaffolds. The molecular modification of gelatin with hydrogen bonding moieties induced liquid-liquid phase separation when mixed with unmodified gelatin to form μCN structures in the hydrogels. Through spatiotemporally controlled covalent crosslinking and dissolution processes, porous μCN structures were formed in the hydrogels, which can enhance mass transport and cellular activity. The encapsulation of cells with injectable μCN hydrogels improved cellular spreading, migration, and proliferation. Transplantation of mesenchymal stem cells with injectable μCN hydrogels enhanced graft survival and recovered hindlimb ischemia by enhancing material-tissue communication with biological signals and cells through μCN. This facile approach may serve as an advanced scaffold for improving stem cell transplantation therapies in regenerative medicine.

Miscibility and ternary diagram of aqueous polyvinyl alcohols with different degrees of saponification

Liquid-liquid phase separation (LLPS), an important phenomenon in the field of polymer science and material design, plays an essential role in cells and living bodies. Poly(vinyl alcohol) (PVA) is a popular semicrystalline polymer utilized in the synthesis of artificial biomaterials. The aqueous solutions of its derivatives with tuned degrees of saponification (DS) exhibit LLPS. However, the miscibility and LLPS behavior of PVA aqueous solution are still unclear. This study describes the miscibility diagram of the ternary mixture, where water and two types of poly(vinyl alcohol) (PVA) with different DSs [98 (PVA98), 88 (PVA88), 82 (PVA82), and 74 mol% (PVA74)] were blended. UV-Vis measurement was conducted to evaluate the miscibility. Immiscibility was more pronounced at elevated temperatures, exhibiting LLPS. The ternary immiscibility diagram, displaying miscible-immiscible behaviors in the aqueous mixtures of PVA74:PVA98, PVA82:PVA98, and PVA88:PVA98 (blended at a constant volume ratio), indicated that increasing the concentration, temperature, and blend ratio of PVAs at a lower DS increased immiscibility, suggesting that the free energy of mixing increases with increasing these parameters. The miscible-immiscible behaviors of PVAs/water systems provide fundamental knowledge about LLPS and the design of PVA-based materials.

Engineering thixotropic supramolecular gelatin-based hydrogel as an injectable scaffold for cell transplantation

Despite many efforts focusing on regenerative medicine, there are few clinically-available cell-delivery carriers to improve the efficacy of cell transplantation due to the lack of adequate scaffolds. Herein, we report an injectable scaffold composed of functionalized gelatin for application in cell transplantation. Injectable functionalized gelatin-based hydrogels crosslinked with reversible hydrogen bonding based on supramolecular chemistry were designed. The hydrogel exhibited thixotropy, enabling single syringe injection of cell-encapsulating hydrogels. Highly biocompatible and cell-adhesive hydrogels provide cellular scaffolds that promote cellular adhesion, spreading, and migration. Thein vivodegradation study revealed that the hydrogel gradually degraded for seven days, which may lead to prolonged retention of transplanted cells and efficient integration into host tissues. In volumetric muscle loss models of mice, cells were transplanted using hydrogels and proliferated in injured muscle tissues. Thixotropic and injectable hydrogels may serve as cell delivery scaffolds to improve graft survival in regenerative medicine.