Cell-instructive biomaterials in tissue engineering and regenerative medicine.

The field of biomaterials aims to improve regenerative outcomes or scientific understanding for a wide range of tissue types and ailments. Biomaterials can be fabricated from natural or synthetic sources and display a plethora of mechanical, electrical, and geometrical properties dependent on their desired application. To date, most biomaterial systems designed for eventual translation to the clinic rely on soluble signaling moieties, such as growth factors, to elicit a specific cellular response. However, these soluble factors are often limited by high cost, convoluted synthesis, low stability, and difficulty in regulation, making the translation of these biomaterials systems to clinical or commercial applications a long and arduous process. In response to this, significant effort has been dedicated to researching cell-directive biomaterials which can signal for specific cell behavior in the absence of soluble factors. Cells of all tissue types have been shown to be innately in tune with their microenvironment, which is a biological phenomenon that can be exploited by researchers to design materials that direct cell behavior based on their intrinsic characteristics. This review will focus on recent developments in biomaterials that direct cell behavior using biomaterial properties such as charge, peptide presentation, and micro- or nano-geometry. These next generation biomaterials could offer significant strides in the development of clinically relevant medical devices which improve our understanding of the cellular microenvironment and enhance patient care in a variety of ailments.

Self-Initiated Photopolymerization of Anti-Inflammatory Zwitterionic Hydrogels with Sustained Release.

Hydrogels are three-dimensional networks of hydrophilic polymers that have garnered significant attention as wound-healing materials. Many synthetic hydrogels are fabricated using a radical polymerization approach that requires an initiator molecule that is often photo- or thermosensitive. Initiator-free hydrogels are an emerging area of research that focuses on hydrogel fabrication that occurs in the absence of an initiator or cross-linker molecule, making these hydrogels highly relevant in tissue engineering and regenerative medicine due to their excellent cytocompatibility and ease of scale-up. Here we present on the development of initiator-free zwitterionic hydrogels that photopolymerize without any initiator or cross-linker while under cytocompatible conditions. The hydrogels exhibit a wide range of mechanical characteristics that are dependent on their polymer composition. They resist nonspecific protein adsorption and exhibit a sustained release of proteins and small molecules. Additionally, these self-initiated hydrogels significantly mitigate inflammatory macrophage activation in vitro. Overall, the development of self-initiated photopolymerized zwitterionic hydrogels offers significant progress in the fields of biomaterials and materials science.

Fabrication of Size-Controlled and Emulsion-Free Chitosan-Genipin Microgels for Tissue Engineering Applications.

Chitosan microgels are of significant interest in tissue engineering due to their wide range of applications, low cost, and immunogenicity. However, chitosan microgels are commonly fabricated using emulsion methods that require organic solvent rinses, which are toxic and harmful to the environment. The present protocol presents a rapid, non-cytotoxic, non-emulsion-based method for fabricating chitosan-genipin microgels without the need for organic solvent rinses. The microgels described herein can be fabricated with precise size control. They exhibit sustained release of biomolecules, making them highly relevant for tissue engineering, biomaterials, and regenerative medicine. Chitosan is crosslinked with genipin to form a hydrogel network, then passed through a syringe filter to produce the microgels. The microgels can be filtered to create a range of sizes, and they show pH-dependent swelling and degrade over time enzymatically. These microgels have been employed in a rat growth plate injury model and were demonstrated to promote increased cartilage tissue repair and to show complete degradation at 28 days in vivo. Due to their low cost, high convenience, and ease of fabrication with cytocompatible materials, these chitosan microgels present an exciting and unique technology in tissue engineering.

Polyelectrolyte Complex Hydrogels with Controlled Mechanics Affect Mesenchymal Stem Cell Differentiation Relevant to Growth Plate Injuries.

The growth plate is a complex cartilage structure in long bones that mediates growth in children. When injured, the formation of a "bony bar" can occur which impedes normal growth and can cause angular deformities or growth arrest. Current treatments for growth plate injuries are limited and result in poor patient outcomes, necessitating research toward novel treatments that can prevent bony bar formation and stimulate cartilage regeneration. This study investigates alginate-chitosan polyelectrolyte complex (PEC) hydrogels as an injectable biomaterial system to prevent bony bar formation. Biomaterial properties including stiffness and degradation are quantified, and the effect that material properties have on mesenchymal stem cell (MSC) fate is quantified in vitro. Specifically, this study aims to elucidate the effectiveness of biomaterial-based control over the differentiation behavior of MSCs toward osteogenic or chondrogenic lineages using biochemical metabolite assays and quantitative real time PCR. Further, the PEC hydrogels are employed in a rat growth plate injury model to determine their effectiveness in preventing bony bar formation in vivo. Results indicate that hydrogel composition and material properties affect the differentiation tendency of MSCs in vitro, and the PEC hydrogels show promise as an injectable biomaterial for growth plate injuries.

Topical gel-based biomaterials for the treatment of diabetic foot ulcers.

Diabetic foot ulcers (DFUs) are a devastating ailment for many diabetic patients with increasing prevalence and morbidity. The complex pathophysiology of DFU wound environments has made finding effective treatments difficult. Standard wound care treatments have limited efficacy in healing these types of chronic wounds. Topical biomaterial gels have been developed to implement novel treatment approaches to improve therapeutic effects and are advantageous due to their ease of application, tunability, and ability to improve therapeutic release characteristics. Here, we provide an updated, comprehensive review of novel topical biomaterial gels developed for treating chronic DFUs. This review will examine preclinical data for topical gel treatments in diabetic animal models and clinical applications, focusing on gels with protein/peptides, drug, cellular, herbal/antioxidant, and nano/microparticle approaches. STATEMENT OF SIGNIFICANCE: By 2050, 1 in 3 Americans will develop diabetes, and up to 34% of diabetic patients will develop a diabetic foot ulcer (DFU) in their lifetime. Current treatments for DFUs include debridement, infection control, maintaining a moist wound environment, and pressure offloading. Despite these interventions, a large number of DFUs fail to heal and are associated with a cost that exceeds $31 billion annually. Topical biomaterials have been developed to help target specific impairments associated with DFU with the goal to improve healing. A summary of these approaches is needed to help better understand the current state of the research. This review summarizes recent research and advances in topical biomaterials treatments for DFUs.

Photopolymerized Zwitterionic Hydrogels with a Sustained Delivery of Cerium Oxide Nanoparticle-miR146a Conjugate Accelerate Diabetic Wound Healing.

In the United States, $87 billion per year is spent on the care of diabetic ulcers alone. Although the pathophysiology of diabetic wound healing is multifaceted, high systemic levels of inflammation and increased reactive oxygen species are often implicated in the wound healing impairment. Zwitterionic materials have been demonstrated to reduce inflammation and increase extracellular matrix deposition in wound beds, and here, we demonstrate a fabrication method for photopolymerized zwitterionic hydrogels that also enables sustained drug delivery over time. A therapeutic molecule of interest that is examined in this work is cerium oxide nanoparticle tagged with microRNA-146a (CNP-miR146a) to combat both oxidative stress and inflammation. The hydrogels are composed of zwitterionic and nonzwitterionic monomers, and the hydrogel formation occurs in the absence of a crosslinker. The hydrogels exhibit a wide range of stiffness and mechanical properties depending on their monomer content. Additionally, these hydrogels exhibit sustained release of nanoparticles and proteins. Finally, when employed in an in vivo diabetic mouse wound healing model, the zwitterionic hydrogels alone and laden with the CNP-miR146a conjugate significantly improved the rate of diabetic wound healing. Overall, these materials have excellent potential to be used as a topical treatment for chronic diabetic wounds.

Emulsion-free chitosan-genipin microgels for growth plate cartilage regeneration.

The growth plate is a cartilage tissue near the ends of children's long bones and is responsible for bone growth. Injury to the growth plate can result in the formation of a 'bony bar' which can span the growth plate and result in bone growth abnormalities in children. Biomaterials such as chitosan microgels could be a potential treatment for growth plate injuries due to their chondrogenic properties, which can be enhanced through loading with biologics. They are commonly fabricated via an emulsion method, which involves solvent rinses that are cytotoxic. Here, we present a high throughput, non-cytotoxic, non-emulsion-based method to fabricate chitosan-genipin microgels. Chitosan was crosslinked with genipin to form a hydrogel network, and then pressed through a syringe filter using mesh with various pore sizes to produce a range of microgel particle sizes. The microgels were then loaded with chemokines and growth factors and their release was studied in vitro. To assess the applicability of the microgels for growth plate cartilage regeneration, they were injected into a rat growth plate injury. They led to increased cartilage repair tissue and were fully degraded by 28 days in vivo. This work demonstrates that chitosan microgels can be fabricated without solvent rinses and demonstrates their potential for the treatment of growth plate injuries.