Light-Regulated Angiogenesis via a Phototriggerable VEGF Peptidomimetic

Hydrogel-Based Growth Factor Delivery Platforms: Strategies and Recent Advances

Growth factors play a crucial role in regulating a broad variety of biological processes and are regarded as powerful therapeutic agents in tissue engineering and regenerative medicine in the past decades. However, their application is limited by their short half-lives and potential side effects in physiological environments. Hydrogels are identified as having the promising potential to prolong the half-lives of growth factors and mitigate their adverse effects by restricting them within the matrix to reduce their rapid proteolysis, burst release, and unwanted diffusion. This review discusses recent progress in the development of growth factor-containing hydrogels for various biomedical applications, including wound healing, brain tissue repair, cartilage and bone regeneration, and spinal cord injury repair. In addition, the review introduces strategies for optimizing growth factor release including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cellular system-based delivery. Finally, the review presents current limitations and future research directions for growth factor-delivering hydrogels.

4D Biochemical Photocustomization of Hydrogel Scaffolds for Biomimetic Tissue Engineering

Programmable engineered tissues and the materials that support them are instrumental to the development of next-generation therapeutics and gaining new understanding of human biology. Toward these ends, recent years have brought a growing emphasis on the creation of "4D" hydrogel culture platforms-those that can be customized in 3D space and on demand over time. Many of the most powerful 4D-tunable biomaterials are photochemically regulated, affording users unmatched spatiotemporal modulation through high-yielding, synthetically tractable, and cytocompatible reactions. Precise physicochemical manipulation of gel networks has given us the ability to drive critical changes in cell fate across a diverse range of distance and time scales, including proliferation, migration, and differentiation through user-directed intracellular and intercellular signaling. This Account provides a survey of the numerous creative approaches taken by our lab and others to recapitulate the dynamically heterogeneous biochemistry underpinning in vivo extracellular matrix (ECM)-cell interactions via light-based network (de)decoration with biomolecules (e.g., peptides, proteins) and in situ protein activation/generation. We believe the insights gained from these studies can motivate disruptive improvements to emerging technologies, including low-variability organoid generation and culture, high-throughput drug screening, and personalized medicine. As photolithography and chemical modification strategies continue to mature, access to and control over new and increasingly complex biological pathways are being unlocked. The earliest hydrogel photopatterning efforts selectively encapsulated bioactive peptides and drugs into rudimentary gel volumes. Through continued exploration and refinement, next-generation materials now boast reversible, multiplexed, and/or Boolean logic-based biomolecule presentation, as well as functional activation at subcellular resolutions throughout 3D space. Lithographic hardware and software technologies, particularly those enabling image-guided patterning, allow researchers to precisely replicate complex biological structures within engineered tissue environments. The advent of bioorthogonal click chemistries has expanded 4D tissue engineering toolkits, permitting diverse constructs to be independently customized in the vicinity of any cell that is amenable to hydrogel-based culture. Additionally, the adoption of modern protein engineering techniques including genetic code expansion and chemoenzymatic alteration provides a roadmap toward site-specific modification of nearly any recombinant or isolated protein, affording installation of photoreactive and click handles without sacrificing their bioactivity. While the established bind, release, (de)activate paradigm in hydrogel photolithography continues to thrive alongside these modern engineering techniques, new studies are also demonstrating photocontrol of more complex or nonclassical operations, including engineered material-microorganism interfaces and functional protein photoassembly. Such creative approaches offer exciting new avenues for the field, including spatial control of on-demand biomolecule production from cellular depots and patterned bioactivity using a growing array of split protein pairs. Taken together, these technologies provide the foundation for truly biomimetic photopatterning of engineered tissues.

Vascularized polypeptide hydrogel modulates macrophage polarization for wound healing

Wound repair involves a sophisticated process that includes angiogenesis, immunoregulation and collagen deposition. However, weak revascularization performance and the lack of biochemical cues to trigger immunomodulatory function currently limit biomaterial applications for skin regeneration and tissue engineering. Herein, we fabricate a new bioactive polypeptide hydrogel (QK-SF) constituted by silk fibroin (SF) and a vascular endothelial growth factor mimetic peptide KLTWQELYQLKYKGI (QK) for tissue regeneration by simultaneously promoting vascularization and macrophage polarization. Our results showed that this QK-SF hydrogel can be prepared via an easy manufacturing process, and exhibited good gel stability and low cytotoxicity to cultured human umbilical vein endothelial cells (HUVECs) via both live/dead and cell counting kit-8 assays. Importantly, this QK-SF hydrogel triggered macrophage polarization from M1 into M2, as exemplified by the enhanced expression of the M2 marker and decreased expression of the M1 marker in RAW264.7 cells. Furthermore, the QK-SF hydrogel showed high capacity for inducing endothelial growth, migration and angiogenesis, which were proved by increased expression of angiogenesis-related genes in HUVECs. Consistent with in vitro findings, in vivo data show that the QK-SF hydrogel promoted M2 polarization, keratinocyte differentiation, and collagen deposition in the mouse skin wound model in immunohistochemistry assay. Furthermore, this QK-SF hydrogel can reduce inflammation, induce angiogenesis and promote wound healing as exemplified by the increased vessel formation and decreased wound area in the mouse skin wound model. Altogether, these results indicate that the bioactive QK-SF hydrogel plays dual functional roles in promoting angiogenesis and immunoregulation for tissue regeneration. STATEMENT OF SIGNIFICANCE: The QK-SF hydrogel plays dual functional roles in promoting angiogenesis and immunoregulation for tissue repair and wound healing. The QK-SF hydrogel can be prepared via an easy manufacturing process, and exhibited good gel stability and low cytotoxicity to cultured HUVECs. The QK-SF hydrogel triggered macrophage polarization from M1 into M2. The QK-SF hydrogel showed high capacity for inducing endothelial growth, migration and angiogenesis. The QK-SF hydrogel promoted M2 polarization, keratinocyte differentiation, and collagen deposition.

Soft nano and microstructures for the photomodulation of cellular signaling and behavior

Photoresponsive soft materials are everywhere in the nature, from human's retina tissues to plants, and have been the inspiration for engineers in the development of modern biomedical materials. Light as an external stimulus is particularly attractive because it is relatively cheap, noninvasive to superficial biological tissues, can be delivered contactless and offers high spatiotemporal control. In the biomedical field, soft materials that respond to long wavelength or that incorporate a photon upconversion mechanism are desired to overcome the limited UV-visible light penetration into biological tissues. Upon light exposure, photosensitive soft materials respond through mechanisms of isomerization, crosslinking or cleavage, hyperthermia, photoreactions, electrical current generation, among others. In this review, we discuss the most recent applications of photosensitive soft materials in the modulation of cellular behavior, for tissue engineering and regenerative medicine, in drug delivery and for phototherapies.