Hee Seok Yang

Next-generation implantable neural interfaces require highly flexible, biocompatible, and transient material platforms to minimize mechanical mismatch with neural tissues and avoid secondary retrieval surgeries. This study developed a soft and biodegradable neural interfacing platform fabricated from milk-derived protein (MDP) and polyvinyl alcohol functionalized with 3,4-dihydroxyphenylalanine (DOPA) as an immunomodulatory nerve guidance conduit. The fabricated MDP-DOPA hydrogel conduits exhibited favorable protein-release kinetics, compliant mechanical stability that matched native neural tissues, and controlled biodegradation profiles. In vitro, the MDP-DOPA substrate significantly attenuated pro-inflammatory M1 macrophage polarization while selectively promoting the pro-regenerative M2 phenotype in RAW 264.7 cells, subsequently enhancing PC12 neuritogenesis through the bioactivity of released cascade peptides. In vivo, a rat 10-mm sciatic nerve defect model demonstrated that the implantation of soft MDP-DOPA conduits drastically improved structural and functional neural integration. This was evidenced by an enhanced sciatic functional index, elevated nerve conduction velocity, and robust axonal remyelination in the distal segments, closely approaching the recovery level of clinical gold-standard autografts. Furthermore, early-stage in vivo analysis verified that the platform successfully orchestrated a pro-regenerative immunomodulatory microenvironment at the interface site within 1 week. These findings highlight the potential of MDP-DOPA hydrogels as bioinstructive, soft, and stable electronic encapsulation or scaffolding platforms for next-generation implantable neural technologies for clinical translation.

Effective bone regeneration requires biomaterials that exhibit appropriate bioactive functions, particularly osteoconductive and osteoinductive properties. Here, we engineered a cell-derived, decellularized extracellular matrix (cdECM) into a novel mineralized ECM scaffold by harnessing the polymer-induced liquid precursor (PILP) process, an effective strategy for generating calcium phosphate (CaP) mineralized constructs. Mineral deposition within cdECM was successfully achieved through the PILP mineralization, which stabilizes the amorphous precursor phase and promotes matrix-associated mineralization. The resulting mineralized ECM (mECM) exhibited osteoconductive properties, as evidenced by excellent cytocompatibility and enhanced cell proliferation of osteogenic cells. The mECM also demonstrated osteoinductive potential, as confirmed by enhanced alkaline phosphatase activity, increased calcification, and up-regulated osteogenic gene expression in mouse preosteoblasts and human mesenchymal stem cells. Moreover, mECM promoted M2-like macrophage polarization and enhanced tubular formation of endothelial cells. To enable localized in vivo delivery of both ECM-derived biological cues and minerals, a sheet-type mECM scaffold was fabricated using hyaluronic acid as a supporting matrix and further stabilized by glutaraldehyde vapor crosslinking. In a mouse calvarial defect model, the mECM sheet facilitated new bone formation and supported advanced bone maturation, accompanied by enhanced angiogenesis and an M2-dominant anti-inflammatory milieu at an early time point. Collectively, our findings demonstrate that PILP mineralization can be successfully applied to cdECM for generating a bioactive mECM scaffold with enhanced regenerative capacity, representing a promising biomaterial platform for bone tissue regeneration.

A scaffold design for tendon regeneration has been proposed, which mimics the microstructural features of tendons and provides appropriate mechanical properties. We synthesized a temperature-triggered shape-memory polymer (SMP) using the ring-opening polymerization of polycaprolactone (PCL) with polyethylene glycol (PEG) as a macroinitiator. We fabricated a micropatterned patch using SMP via capillary force lithography, which mimicked a native tendon, for providing physical cues and guiding effects. The SMP patches (the SMP-flat patch is referred to as SMP-F, and the SMP-patterned patch is referred to as SMP-P) were surface-modified with 3,4-dihydroxy-L-phenylalanine (L-DOPA, referred to as D) for improving cell adhesion. We hypothesized that SMP patches could be applied in minimally invasive surgery and the micropatterned structure would improve tendon regeneration by providing geometrical cues. The SMP patches exhibited excellent shape-memory properties, mechanical performance, and biocompatibility in vitro and in vivo. Especially, SMP-DP demonstrated enhanced cell behaviors in vitro, including cell orientation, elongation, migration, and tenogenic differentiation potential. The in vivo data showed notable biomechanical functionality and histological morphometric findings in various analyses of SMP-DP in the ruptured Achilles tendon model.

In this research, we introduced a novel strategy for fabricating cell sheets (CSs) prepared by simply adding a fibrinogen solution to growth medium without using any synthetic polymers or chemical agents. We confirmed that the fibrinogen-based CS could be modified for target tissue regardless of size, shape, and cell types. Also, fibrinogen-based CSs were versatile and could be used to form three-dimensional (3D) CSs such as multi-layered CSs and those mimicking native blood vessels. We also prepared fibrinogen-based spheroid sheets for the treatment of ischemic disease. The fibrinogen-based spheroid sheets had much higher in vitro tubule formation and released more angiogenic factors compared to other types of platform in this research. We transplanted fibrinogen-based spheroid sheets into a mouse hindlimb ischemia model and found that fibrinogen-based spheroid sheets showed significantly improved physiological function and blood perfusion rates compared to the other types of platform in this research.

Recently, a number of studies reported that casein was composed of various multifunctional bioactive peptides such as casein phosphopeptide and β-casochemotide-1 that bind calcium ions and induce macrophage chemotaxis, which is crucial for bone homeostasis and bone fracture repair by cytokines secreted in the process. We hypothesized that the effects of the multifunctional biopeptides in casein would contribute to improving bone regeneration. Thus, we designed a tissue engineering platform that consisted of casein and polyvinyl alcohol, which was a physical-crosslinked scaffold (milk-derived protein; MDP), via simple freeze-thaw cycles and performed surface modification using 3,4-dihydroxy-l-phenylalanine (DOPA), a mussel adhesive protein, for immobilizing adhesive proteins and cytokines for recruiting cells in vivo (MDP-DOPA). Both the MDP and MDP-DOPA groups proved indirectly contribution of macrophages migration as RAW 264.7 cells were highly migrated toward materials by contained bioactive peptides. We implanted MDP and MDP-DOPA in a mouse calvarial defect orthotopic model and evaluated whether MDP-DOPA showed much faster mineral deposition and higher bone density than that of the no-treatment and MDP groups. The MDP-DOPA group showed the accumulation of host M2 macrophages and mesenchymal stem cells (MSCs) around the scaffold, whereas MDP presented mostly M1 macrophages in the early stage.