Stimulation of in vivo angiogenesis by cytokine-loaded hyaluronic acid hydrogel implants

In situ photo-crosslinkable hyaluronic acid-based hydrogel embedded with GHK peptide nanofibers for bioactive wound healing

A versatile hydrogel was developed for enhancing bioactive wound healing by introducing the amphiphilic GHK peptide (GHK-C16) into a photo-crosslinkable tyramine-modified hyaluronic acid (HA-Ty). GHK-C16 self-assembled into GHK nanofibers (GHK NF) in HA-Ty solution, which underwent in situ gelation after the wound area was filled with precursor solution. Blue light irradiation (460-490 nm), with riboflavin phosphate as a photoinitiator, was used to trigger crosslinking, which enhanced the stability of the highly degradable hyaluronic acid and enabled sustained release of the nanostructured GHK derivatives. The hydrogels provided a microenvironment that promoted the proliferation of dermal fibroblasts and the activation of cytokines, leading to reduced inflammation and increased collagen expression during wound healing. The complexation of Cu2+ into GHK nanofibers resulted in superior wound healing capabilities compared with non-lipidated GHK peptide with a comparable level of growth factor (EGF). Additionally, nanostructured Cu-GHK improved angiogenesis through vascular endothelial growth factor (VEGF) activation, which exerted a synergistic therapeutic effect. Furthermore, in vivo wound healing experiments revealed that the Cu-GHK NF/HA-Ty hydrogel accelerated wound healing through densely packed remodeled collagen in the dermis and promoting the growth of denser fibroblasts. HA-Ty hydrogels incorporating GHK NF also possessed improved mechanical properties and a faster wound healing rate, making them suitable for advanced bioactive wound healing applications. STATEMENT OF SIGNIFICANCE: By combining photo-crosslinkable tyramine-modified hyaluronic acid with self-assembled Cu-GHK-C16 peptide nanofibers (Cu-GHK NF), the Cu-GHK NF/HA-Ty hydrogel offers remarkable advantages over conventional non-structured Cu-GHK for wound healing. It enhances cell proliferation, migration, and collagen remodeling-critical factors in tissue regeneration. The incorporation of GHK nanofibers complexed with copper ions imparts potent anti-inflammatory effects, promoting cytokine activation and angiogenesis during wound healing. The Cu-GHK NF/hydrogel's unique properties, including in situ photo-crosslinking, ensure high customization and potency in tissue regeneration, providing a cost-effective alternative to growth factors. In vivo experiments further validate its efficacy, demonstrating significant wound closure, collagen remodeling, and increased fibroblast density. Overall, the Cu-GHK NF/HA-Ty hydrogel represents an advanced therapeutic option for wound healing applications.

Bioinspired Collagen/Hyaluronic Acid/Fibrin-Based Hydrogels for Soft Tissue Engineering: Design, Synthesis, and In Vitro Characterization

A major challenge for future drug development comprises finding alternative models for drug screening. The use of animal models in research is highly controversial, with an ongoing debate on their ethical acceptability. Also, animal models are often poorly predictive of therapeutic outcomes due to the differences between animal and human physiological environments. In this study, we aimed to develop a biomimetic hydrogel that replicates the composition of skin for potential use in in vitro modeling within tissue engineering. The hydrogel was fabricated through the crosslinking of collagen type I, hyaluronic acid, four-arm PEG succinimidyl glutarate (4S-StarPEG), and fibrinogen. Various ratios of these components were systematically optimized to achieve a well-interconnected porosity and desirable rheological properties. To evaluate the hydrogel's cytocompatibility, fibroblasts were embedded within the matrix. The resulting hydrogel exhibited promising properties as a scaffold, also facilitating the growth of and proliferation of the cells. This biomimetic hydrogel holds great potential for tissue engineering applications, particularly in skin regeneration and cancer research. The study used melanoma spheroids fabricated using the 96-round bottom well plate method as a potential application. The results demonstrate that the developed hydrogels allowed the maintenance of spheroid integrity and viability, meaning it has a promising use as a three-dimensional in vitro model of melanoma for both tissue engineering and drug screening applications.

Angiogenesis induction as a key step in cardiac tissue Regeneration: From angiogenic agents to biomaterials

Cardiovascular diseases are the leading cause of death worldwide. After myocardial infarction, the vascular supply of the heart is damaged or blocked, leading to the formation of scar tissue, followed by several cardiac dysfunctions or even death. In this regard, induction of angiogenesis is considered as a vital process for supplying nutrients and oxygen to the cells in cardiac tissue engineering. The current review aims to summarize different approaches of angiogenesis induction for effective cardiac tissue repair. Accordingly, a comprehensive classification of induction of pro-angiogenic signaling pathways through using engineered biomaterials, drugs, angiogenic factors, as well as combinatorial approaches is introduced as a potential platform for cardiac regeneration application. The angiogenic induction for cardiac repair can enhance patient treatment outcomes and generate economic prospects for the biomedical industry. The development and commercialization of angiogenesis methods often involves collaboration between academic institutions, research organizations, and biomedical companies.

hapln1a+ cells guide coronary growth during heart morphogenesis and regeneration

Although several tissues and chemokines orchestrate coronary formation, the guidance cues for coronary growth remain unclear. Here, we profile the juvenile zebrafish epicardium during coronary vascularization and identify hapln1a+ cells enriched with vascular-regulating genes. hapln1a+ cells not only envelop vessels but also form linear structures ahead of coronary sprouts. Live-imaging demonstrates that coronary growth occurs along these pre-formed structures, with depletion of hapln1a+ cells blocking this growth. hapln1a+ cells also pre-lead coronary sprouts during regeneration and hapln1a+ cell loss inhibits revascularization. Further, we identify serpine1 expression in hapln1a+ cells adjacent to coronary sprouts, and serpine1 inhibition blocks vascularization and revascularization. Moreover, we observe the hapln1a substrate, hyaluronan, forming linear structures along and preceding coronary vessels. Depletion of hapln1a+ cells or serpine1 activity inhibition disrupts hyaluronan structure. Our studies reveal that hapln1a+ cells and serpine1 are required for coronary production by establishing a microenvironment to facilitate guided coronary growth.

Functionalization of biomimetic mineralized collagen for bone tissue engineering

Mineralized collagen (MC) is the basic unit of bone structure and function and is the main component of the extracellular matrix (ECM) in bone tissue. In the biomimetic method, MC with different nanostructures of neo-bone have been constructed. Among these, extra-fibrous MC has been approved by regulatory agencies and applied in clinical practice to play an active role in bone defect repair. However, in the complex microenvironment of bone defects, such as in blood supply disorders and infections, MC is unable to effectively perform its pro-osteogenic activities and needs to be functionalized to include osteogenesis and the enhancement of angiogenesis, anti-infection, and immunomodulation. This article aimed to discuss the preparation and biological performance of MC with different nanostructures in detail, and summarize its functionalization strategy. Then we describe the recent advances in the osteo-inductive properties and multifunctional coordination of MC. Finally, the latest research progress of functionalized biomimetic MC, along with the development challenges and future trends, are discussed. This paper provides a theoretical basis and advanced design philosophy for bone tissue engineering in different bone microenvironments.

Therapeutic angiogenesis based on injectable hydrogel for protein delivery in ischemic heart disease

Ischemic heart disease (IHD) remains the leading cause of death and disability worldwide and leads to myocardial necrosis and negative myocardial remodeling, ultimately leading to heart failure. Current treatments include drug therapy, interventional therapy, and surgery. However, some patients with severe diffuse coronary artery disease, complex coronary artery anatomy, and other reasons are unsuitable for these treatments. Therapeutic angiogenesis stimulates the growth of the original blood vessels by using exogenous growth factors to generate more new blood vessels, which provides a new treatment for IHD. However, direct injection of these growth factors can cause a short half-life and serious side effects owing to systemic spread. Therefore, to overcome this problem, hydrogels have been developed for temporally and spatially controlled delivery of single or multiple growth factors to mimic the process of angiogenesis in vivo. This paper reviews the mechanism of angiogenesis, some important bioactive molecules, and natural and synthetic hydrogels currently being applied for bioactive molecule delivery to treat IHD. Furthermore, the current challenges of therapeutic angiogenesis in IHD and its potential solutions are discussed to facilitate real translation into clinical applications in the future.

VEGF-Encoding, Gene-Activated Collagen-Based Matrices Promote Blood Vessel Formation and Improved Wound Repair

Disruption in vascularization during wound repair can severely impair healing. Proangiogenic growth factor therapies have shown great healing potential; however, controlling growth factor activity and cellular behavior over desired healing time scales remains challenging. In this study, we evaluated collagen-mimetic peptide (CMP) tethers for their capacity to control growth factor gene transfer and growth factor activity using our recently developed gene-activated hyaluronic acid-collagen matrix (GAHCM). GAHCM was comprised of DNA/polyethyleneimine (PEI) polyplexes that were retained on hyaluronic acid (HA)-collagen hydrogels using CMPs. We hypothesized that using CMP-collagen tethers to control vascular endothelial growth factor-A (VEGF-A) gene delivery in fibroblasts would provide a powerful strategy to modulate the proangiogenic behaviors of endothelial cells (ECs) for blood vessel formation, resulting in enhanced wound repair. In co-culture experiments, we observed that CMP-modified GAHCM induced tunable gene delivery in fibroblasts as predicted, and correspondingly, VEGF-A produced by the fibroblasts led to increased growth and persistent migration of ECs for at least 7 days, as compared to non-CMP-modified GAHCM. Moreover, when ECs were exposed to fibroblast-containing VEGF-GAHCM with higher levels of CMP modification (50% CMP-PEI, or 50 CP), high CD31 expression was stimulated, resulting in the formation of an interconnected EC network with a significantly higher network volume and a larger diameter network structure than controls. Application of VEGF-GAHCM with 50 CP in murine splinted excisional wounds facilitated prolonged prohealing and proangiogenic responses resulting in increased blood vessel formation, improved granulation tissue formation, faster re-epithelialization, and overall enhanced repair. These findings suggest the benefits of CMP-collagen tethers as useful tools to control gene transfer and growth factor activity for improved treatment of wounds.

Magnetic-responsive Covalent Adaptable Networks

Covalent adaptable networks (CANs) are reprocessable polymers whose structural arrangement is based on the recombination of dynamic covalent bonds. Composite materials prepared by incorporating magnetic particles into CANs attract much attention due to their remote and precise control, fast response speed, high biological safety and strong penetration of magnetic stimuli. These properties often involve magnetothermal effect and direct magnetic-field guidance. Besides, some of them can also respond to light, electricity or pH values. Thus, they are favorable for soft actuators since various functions are achieved such as magnetic-assisted self-healing (heating or at ambient temperature), welding (on land or under water), shape-morphing, and so on. Although magnetic CANs just start to be studied in recent two years, their advances are promised to expand the practical applications in both cutting-edge academic and engineering fields. This review aims to summarize recent progress in magnetic-responsive CANs, including their design, synthesis and application.

Efficacy of stem cell secretome loaded in hyaluronate sponge for topical treatment of psoriasis

Psoriasis vulgaris is an inflammatory disease characterized by distinctive skin lesions and dysregulated angiogenesis. Recent research uses stem cell secretion products (CM); a set of bioactive factors with therapeutic properties that regulate several cellular processes, including tissue repair and angiogenesis. The aim of this work was to evaluate the effect of CM of Wharton's gelatin MSC (hWJCM) in a treatment based on the bioactivation of a hyaluronic acid matrix (HA hWJCM) in a psoriasiform-like dermatitis (PD) mouse model. A preclinical study was conducted on PD mice. The effect of hWJCM, Clobetasol (Clob) gold standard, HA Ctrl, and HA hWJCM was tested topically evaluating severity of PD, mice weight as well as skin, liver, and spleen appearance. Treatment with either hWJCM, HA Ctrl or HA hWJCM, resulted in significant improvement of the PD phenotype. Moreover, treatment with HA hWJCM reduced the Psoriasis Area Severity Index (PASI), aberrant angiogenesis, and discomfort associated with the disease, leading to total recovery of body weight. We suggest that the topical application of HA hWJCM can be an effective noninvasive therapeutic solution for psoriasis, in addition to other skin diseases, laying the groundwork for future studies in human patients.

Natural Presentation of Glycosaminoglycans in Synthetic Matrices for 3D Angiogenesis Models

Glycosaminoglycans (GAGs) are long, linear polysaccharides that occur in the extracellular matrix of higher organisms and are either covalently attached to protein cores, as proteoglycans or in free form. Dependent on their chemical composition and structure, GAGs orchestrate a wide range of essential functions in tissue homeostasis. Accordingly, GAG-based biomaterials play a major role in tissue engineering. Current biomaterials exploit crosslinks between chemically modified GAG chains. Due to modifications along the GAG chains, they are limited in their GAG-protein interactions and accessibility to dissect the biochemical and biophysical properties that govern GAG functions. Herein, a natural presentation of GAGs is achieved by a terminal immobilization of GAGs to a polyethylene glycol (PEG) hydrogel. A physicochemical characterization showed that different end-thiolated GAGs can be incorporated within physiological concentration ranges, while the mechanical properties of the hydrogel are exclusively tunable by the PEG polymer concentration. The functional utility of this approach was illustrated in a 3D cell culture application. Immobilization of end-thiolated hyaluronan enhanced the formation of capillary-like sprouts originating from embedded endothelial cell spheroids. Taken together, the presented PEG/GAG hydrogels create a native microenvironment with fine-tunable mechanobiochemical properties and are an effective tool for studying and employing the bioactivity of GAGs.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

Therapeutic angiogenesis in coronary artery disease: a review of mechanisms and current approaches

INTRODUCTION

Despite tremendous advances, the shortcomings of current therapies for coronary disease are evidenced by the fact that it remains the leading cause of death in many parts of the world. There is hence a drive to develop novel therapies to tackle this disease. Therapeutic approaches to coronary angiogenesis have long been an area of interest in lieu of its incredible, albeit unrealized potential.

AREAS COVERED

This paper offers an overview of mechanisms of native angiogenesis and a description of angiogenic growth factors. It progresses to outline the advances in gene and stem cell therapy and provides a brief description of other investigational approaches to promote angiogenesis. Finally, the hurdles and limitations unique to this particular area of study are discussed.

EXPERT OPINION

An effective, sustained, and safe therapeutic option for angiogenesis truly could be the paradigm shift for cardiovascular medicine. Unfortunately, clinically meaningful therapeutic options remain elusive because promising animal studies have not been replicated in human trials. The sheer complexity of this process means that numerous major hurdles remain before therapeutic angiogenesis truly makes its way from the bench to the bedside.

Interventions Preventing Vaginitis, Vaginal Atrophy after Brachytherapy or Radiotherapy Due to Malignant Tumors of the Female Reproductive Organs-A Systematic Review

BACKGROUND

Radiotherapy, as a method of treatment of cervical and uterine cancers, may induce severe late-onset vaginal side effects. Unfortunately, little evidence on the management of adverse effects has been presented. This study aimed to evaluate the available interventions which reduce symptoms of vaginitis and vaginal atrophy by improving dyspareunia, mucosal inflammation, vaginal pH and vaginal dryness in women who have undergone brachytherapy or radiotherapy due to uterine or cervical malignancies.

MATERIALS AND METHODS

A comprehensive literature search was performed following PRISMA guidelines. The systematic search was conducted using electronic databases, namely Scopus, Web of Science and PubMed, between October and November 2020 to identify randomized controlled trials (RCT) and, prospective randomized studies (PRS).

RESULTS

The analyzed population consists of 376 patients with uterine or cervical cancer, treated with hyaluronic acid, vitamin A, vitamin E, alpha-tocopherol acetate and dienestrol. Intervention with HA along with vitamin A and vitamin E revealed advantage in endpoints such as reduced dyspareunia, vaginal mucosal inflammation, vaginal dryness, bleeding, fibrosis and cellular atypia. Administration of alpha-tocopherol acetate reduced vaginal mucosal inflammation and improved vaginal acanthosis, whereas dienestrol resulted in reduced dyspareunia, vaginal caliber and bleeding.

CONCLUSIONS

Vaginal suppositories were found to be clinically effective at the management of late-onset vulvovaginal side effects after radiotherapy.

Histologic evaluation of therapeutic responses in ischemic myocardium elicited by dual growth factor delivery from composite glycosaminoglycan hydrogels

In this project, the ability of dual growth factor-preloaded, silk-reinforced, composite hyaluronic acid-based hydrogels to elicit advantageous histologic responses when secured to ischemic myocardium was evaluated in vivo. Reinforced hydrogels containing both Vascular Endothelial Growth Factor (VEGF) and Platelet-derived Growth Factor (PDGF) were prepared by crosslinking chemically modified hyaluronic acid and heparin with poly(ethylene glycol)-diacrylate around a reinforcing silk mesh. Composite patches were sutured to the ventricular surface of ischemic myocardium in Sprague-Dawley rats, and the resulting angiogenic response was followed for 28 days. The gross appearance of treated hearts showed significantly reduced ischemic area and fibrous deposition compared to untreated control hearts. Histologic evaluation showed growth factor delivery to restore myofiber orientation to pre-surgical levels and to significantly increase elicited microvessel density and maturity by day 28 in infarcted myocardial tissue (p < 0.05). In addition, growth factor delivery reduced cell apoptosis and decreased the density of elicited mast cells and both CD68+ and anti-inflammatory CD163+ macrophages. These findings suggest that HA-based, dual growth factor-loaded hydrogels can successfully induce a series of beneficial responses in ischemic myocardium, and offer the potential for therapeutic improvement of ischemic myocardial remodeling.

Pulp Regeneration in an Immature Maxillary Central Incisor Using Hyaluronic Acid Hydrogel

Pulp regenerative procedure is one of the treatment options for endodontically involved immature permanent teeth. The regenerative endodontic procedure was performed in a child of 9 years. After thorough canal disinfection using triple antibiotic paste for 21 days, bleeding was induced from the apex to provide for the stem cells. After that hyaluronic acid (HA) hydrogel was introduced into the canal space to act as injectable scaffold for pulp regeneration. This was followed by mineral trioxide aggregate placement to provide tight seal from the coronal aspect. Later, the tooth was restored with composite restoration. This approach offers the clinicians great opportunity to physiologically strengthen the immature root walls. The present report presents a regenerative endodontic procedure with HA hydrogel for a traumatized central incisor with arrested root development. The continued root development in the present case suggests that this treatment option may be able to resume the root maturation process in immature teeth with open apices.

Orf Virus IL-10 and VEGF-E Act Synergistically to Enhance Healing of Cutaneous Wounds in Mice

Orf virus (OV) is a zoonotic parapoxvirus that causes highly proliferative skin lesions which resolve with minimal inflammation and scarring. OV encodes two immunomodulators, vascular endothelial growth factor (VEGF)-E and interleukin-10 (ovIL-10), which individually modulate skin repair and inflammation. This study examined the effects of the VEGF-E and ovIL-10 combination on healing processes in a murine wound model. Treatments with viral proteins, individually and in combination, were compared to a mammalian VEGF-A and IL-10 combination. Wound biopsies were harvested to measure re-epithelialisation and scarring (histology), inflammation, fibrosis and angiogenesis (immunofluorescence), and gene expression (quantitative polymerase chain reaction). VEGF-E and ovIL-10 showed additive effects on wound closure and re-epithelialisation, and suppressed M1 macrophage and myofibroblast infiltration, while allowing M2 macrophage recruitment. The viral combination also increased endothelial cell density and pericyte coverage, and improved collagen deposition while reducing the scar area. The mammalian combination showed equivalent effects on wound closure, re-epithelialisation and fibrosis, but did not promote blood vessel stabilisation or collagen remodeling. The combination treatments also differentially altered the expression of transforming growth factor beta isoforms, Tgfβ1 and Tgfβ3. These findings show that the OV proteins synergistically enhance skin repair, and act in a complimentary fashion to improve scar quality.

Hyaluronic Acid Macromer Molecular Weight Dictates the Biophysical Properties and in Vitro Cellular Response to Semisynthetic Hydrogels

In situ-forming hydrogels present a promising approach for minimally invasive cell transplantation and tissue regeneration. Among prospective materials, hyaluronic acid (HyA) has displayed great potential, owing to its inherent biocompatibility, biodegradation, and ease of chemical modification. However, current studies in the literature use a broad range of HyA macromer molecular weights (MWs) from <100 kDa to 1 MDa with no consensus regarding an optimal MW for a specific application. We investigated the effects of different HyA macromer MWs on key biophysical properties of semisynthetic hydrogels, such as viscosity, gelation time, shear storage modulus, molecular diffusion, and degradation. Using higher-MW HyA macromers leads to quicker gelation times and stiffer, more stable hydrogels with smaller mesh sizes. Assessment of the potential for HyA hydrogels to support network formation by encapsulated vascular cells derived from human-induced pluripotent stem cells reveals key differences between HyA hydrogels dependent on macromer MW. These effects must be considered holistically to address the multifaceted, nonmonotonic nature of HyA MW on hydrogel behavior. Our study identified an intermediate HyA macromer MW of 500 kDa as providing optimal conditions for a readily injectable, in situ-forming hydrogel with appropriate biophysical properties to promote vascular cell spreading and sustain vascular network formation in vitro.

Comparison of the Effect of Two Hyaluronic Acid Preparations on Fibroblast and Endothelial Cell Functions Related to Angiogenesis

Hyaluronic acid (HA) is used in substitutive and aesthetic medicine with various applications. Ultrapure absorbable HA (Bioregen^®) and a mix of reticulated and free low molecular weight HA (Regenyal Idea Bioexpander®) (both provided by Regenyal Laboratories Srl, San Benedetto del Tronto (AP), Italy) represent a reliable hydrating device and skin filler, useful for skin blemishes, lines and wrinkles, and lip widening, respectively. The commercial products are known for their safety, but data on the molecular, cellular, and tissue responses are lacking. We aimed to evaluate the bioavailability and the pro-angiogenic features of the products Bioregen^® and Bioexpander^® in vitro on cultured endothelial cells (ECs) and dermal fibroblasts in vivo when injected into experimental animals. When added to fibroblasts and ECs, Bioexpander^® induced cell migration. The two HA preparations were well tolerated, while a transient proangiogenic behavior of Bioexpander^®, when implanted subcutaneously in mice, was found. The neovascular response was evident in the first week with higher levels of VEGF and FGF-2 before undergoing regression. In conclusion, our data strengthen the safety of HA synthetic preparations both in vitro and in vivo. Even if a proangiogenic response is documented, it is modest and transient, leading to tissue recovery and absence of an inflammatory infiltrate.

Hydrogel vehicles for sequential delivery of protein drugs to promote vascular regeneration

In recent years, as the mechanisms of vasculogenesis and angiogenesis have been uncovered, the functions of various pro-angiogenic growth factors (GFs) and cytokines have been identified. Therefore, therapeutic angiogenesis, by delivery of GFs, has been sought as a treatment for many vascular diseases. However, direct injection of these protein drugs has proven to have limited clinical success due to their short half-lives and systemic off-target effects. To overcome this, hydrogel carriers have been developed to conjugate single or multiple GFs with controllable, sustained, and localized delivery. However, these attempts have failed to account for the temporal complexity of natural angiogenic pathways, resulting in limited therapeutic effects. Recently, the emerging ideas of optimal sequential delivery of multiple GFs have been suggested to better mimic the biological processes and to enhance therapeutic angiogenesis. Incorporating sequential release into drug delivery platforms will likely promote the formation of neovasculature and generate vast therapeutic potential.

Enhanced angiogenesis by the hyaluronic acid hydrogels immobilized with a VEGF mimetic peptide in a traumatic brain injury model in rats

Angiogenesis plays an important role in brain injury repair, which contributes to the reconstruction of regenerative neurovascular niche for promoting axonal regeneration in the lesion area. As a major component of developing brain extracellular matrix, hyaluronic acid (HA) has attracted more attention as a supporting matrix for brain repair. In the present study, HA-KLT hydrogel was developed via modifying HA with a VEGF mimetic peptide of KLT (KLTWQELYQLKYKGI). The characterization of the hydrogel shows that it could provide a porous, three-dimensional scaffold structure, which has a large specific surface area available for cell adhesion and interaction. Compared with the unmodified HA hydrogel, the HA-KLT hydrogel could effectively promote the attachment, spreading and proliferation of endothelial cells in vitro. Furthermore, the pro-angiogenic ability of hydrogels in vivo was evaluated by implanting them into the lesion cavities in the injured rat brain. Our results showed that the hydrogels could form a permissive interface with the host tissues at 4 weeks after implantation. Moreover, they could efficiently inhibit the formation of glial scars at the injured sites. The HA-KLT hydrogel could significantly increase the expression of endoglin/CD105 and promote the formation of blood vessels, suggesting that HA-KLT hydrogel promoted angiogenesis in vivo. Collectively, the HA-KLT hydrogel has the potential to repair brain defects by promoting angiogenesis and inhibiting the formation of glial-derived scar tissue.

Engineering an Artificial T-Cell Stimulating Matrix for Immunotherapy

T cell therapies require the removal and culture of T cells ex vivo to expand several thousand-fold. However, these cells often lose the phenotype and cytotoxic functionality for mediating effective therapeutic responses. The extracellular matrix (ECM) has been used to preserve and augment cell phenotype; however, it has not been applied to cellular immunotherapies. Here, a hyaluronic acid (HA)-based hydrogel is engineered to present the two stimulatory signals required for T-cell activation-termed an artificial T-cell stimulating matrix (aTM). It is found that biophysical properties of the aTM-stimulatory ligand density, stiffness, and ECM proteins-potentiate T cell signaling and skew phenotype of both murine and human T cells. Importantly, the combination of the ECM environment and mechanically sensitive TCR signaling from the aTM results in a rapid and robust expansion of rare, antigen-specific CD8+ T cells. Adoptive transfer of these tumor-specific cells significantly suppresses tumor growth and improves animal survival compared with T cells stimulated by traditional methods. Beyond immediate immunotherapeutic applications, demonstrating the environment influences the cellular therapeutic product delineates the importance of the ECM and provides a case study of how to engineer ECM-mimetic materials for therapeutic immune stimulation in the future.

Dual Aptamer-Functionalized in Situ Injectable Fibrin Hydrogel for Promotion of Angiogenesis via Codelivery of Vascular Endothelial Growth Factor and Platelet-Derived Growth Factor-BB

In situ injectable hydrogels hold great potential for in vivo applications such as drug delivery and regenerative medicine. However, it is challenging to ensure stable sequestration and sustained release of loaded biomolecules in these hydrogels. As aptamers have high binding affinities and specificities against target biomolecules, we studied the capability of aptamers in functionalizing in situ injectable fibrin (Fn) hydrogels for in vivo delivery of two growth factors including vascular endothelial growth factor (VEGF) and platelet-derived growth factor-BB (PDGF-BB). The results show that aptamer-functionalized fibrinogen (Fg) could form in situ injectable Fn hydrogels with porous structures. The aptamer-functionalized Fn hydrogels could sequester more VEGF and PDGF-BB than the native Fn and release these growth factors in a sustained manner with high bioactivity. After the aptamer-functionalized Fn hydrogels were subcutaneously injected into mice, the codelivery of VEGF and PDGF-BB could promote the growth of mature blood vessels. Therefore, this study has successfully demonstrated that aptamer-functionalized in situ injectable hydrogels hold great potential for in vivo codelivery of multiple growth factors and promotion of angiogenesis .

Development of Biocompatible HA Hydrogels Embedded with a New Synthetic Peptide Promoting Cellular Migration for Advanced Wound Care Management

In the past few years, there have been many efforts underway to develop effective wound healing treatments for traumatic injuries. In particular, wound-healing peptides (WHPs) and peptide-grafted dressings hold great promise for novel therapeutic strategies for wound management. This study reports a topical formulation of a new synthetic WHP (REGRT, REG) embedded in a hyaluronic acid (HA)-based hydrogel dressing for the enhancement of acute excisional wound repair. The copper-free click chemistry is utilized to form biocompatible HA hydrogels by cross-linking dibenzocyclooctyl-functionalized HA with 4-arm poly(ethylene glycol) (PEG) azide. The HA hydrogels are grafted with the REG peptide, a functional derivative of erythroid differentiation regulator1, displaying potent cell motility-stimulating ability, thus sustainably releasing physiologically active peptides for a prolonged period. Combined with the traditional wound healing benefits of HA, the HA hydrogel embedded REG (REG-HAgel) accelerates re-epithelialization in skin wound healing, particularly by promoting migration of fibroblasts, keratinocytes, and endothelial cells. REG-HAgels improve not only rate, but quality of wound healing with higher collagen deposition and more microvascular formation while being nontoxic. The peptide-grafted HA hydrogel system can be considered as a promising new wound dressing formulation strategy for the treatment of different types of wounds with combinations of various natural and synthetic WHPs.

Current and future options for dental pulp therapy

Dental pulp is a connective tissue and has functions that include initiative, formative, protective, nutritive, and reparative activities. However, it has relatively low compliance, because it is enclosed in hard tissue. Its low compliance against damage, such as dental caries, results in the frequent removal of dental pulp during endodontic therapy. Loss of dental pulp frequently leads to fragility of the tooth, and eventually, a deterioration in the patient’s quality of life. With the development of biomaterials such as bioceramics and advances in pulp biology such as the identification of dental pulp stem cells, novel ideas for the preservation of dental pulp, the regenerative therapy of dental pulp, and new biomaterials for direct pulp capping have now been proposed. Therapies for dental pulp are classified into three categories; direct pulp capping, vital pulp amputation, and treatment for non-vital teeth. In this review, we discuss current and future treatment options in these therapies.

The soluble nectin-4 ecto-domain promotes breast cancer induced angiogenesis via endothelial Integrin-β4

Cancer stem cells secrete diffusible factors into the microenvironment that bind to specific endothelial cell receptors and initiate an angiogenesis cascade. Tumor-induced angiogenesis is an important parameter of tumorigenesis and is critical for tumor growth and metastasis. A pvrl-4 encoded gene, NECTIN-4, has potential roles in cancer cell growth and aggressiveness, and it is only expressed in cancer cells. There is evidence that nectin-4 plays a role in tumorigenesis, but the function of nectin-4 in tumor angiogenesis has lacked thorough evidence of mechanism. Using highly metastatic breast cancer cells and human umbilical vein endothelial cells (HUVECs), we have developed an excellent angiogenesis model and systematically studied the contribution of nectin-4 to angiogenesis. We also provide in-depth in ovo, in vivo and in vivo evidence that nectin-4 causes angiogenesis. Following hypoxia, metastatic breast cancer stem cells (mBCSCs) driven ADAM-17 expression causes the shedding of the ecto-domain of nectin-4 into the microenvironment, which physically interacts with integrin-β4 specifically on endothelial cells. This interaction promotes angiogenesis via the Src, PI3K, AKT, iNOS pathway and not by Phospho-Erk or NF-κβ pathways. In vitro, in ovo and in vivo induction and abrogation of an angiogenesis cascade in the presence and absence of the nectin-4 ecto-domain, respectively, confirms its role in angiogenesis. Thus, disrupting the interaction between nectin-4 ecto-domain and integrin-β4 may provide a means of targeting mBCSC-induced angiogenesis.

Effects of locally applied adipose tissue-derived microvascular fragments by thermoresponsive hydrogel on bone healing

Insufficient vascularization is a major cause for the development of non-unions. To overcome this problem, adipose tissue-derived microvascular fragments (MVF) may serve as vascularization units. However, their application into bone defects needs a carrier system. Herein, we analyzed whether this is achieved by a thermoresponsive hydrogel (TRH). MVF were isolated from CD-1 mice and cultivated after incorporation into TRH, while non-incorporated MVF served as controls. Viability of MVF was assessed immunohistochemically over a 7-day period. Moreover, osteotomies were induced in femurs of CD-1 mice. The osteotomy gaps were filled with MVF-loaded TRH (TRH + MVF), unloaded TRH (TRH) or no material (control). Bone healing was evaluated 14 and 35 days postoperatively. MVF incorporated into TRH exhibited less apoptotic cells and showed a stable vessel morphology compared to controls. Micro-computed tomography revealed a reduced bone volume in TRH + MVF femurs. Histomorphometry showed less bone and more fibrous tissue after 35 days in TRH + MVF femurs compared to controls. Accordingly, TRH + MVF femurs exhibited a lower osseous bridging score and a reduced bending stiffness. Histology and Western blot analysis revealed an increased vascularization and CD31 expression, whereas vascular endothelial growth factor (VEGF) expression was reduced in TRH + MVF femurs. Furthermore, the callus of TRH + MVF femurs showed increased receptor activator of NF-κB ligand expression and higher numbers of osteoclasts. These findings indicate that TRH is an appropriate carrier system for MVF. Application of TRH + MVF increases the vascularization of bone defects. However, this impairs bone healing, most likely due to lower VEGF expression during the early course of bone healing.

STATEMENT OF SIGNIFICANCE

In the present study we analyzed for the first time the in vivo performance of a thermoresponsive hydrogel (TRH) as a delivery system for bioactive microvascular fragments (MVF). We found that TRH represents an appropriate carrier for MVF as vascularization units and maintains their viability. Application of MVF-loaded TRH impaired bone formation in an established murine model of bone healing, although vascularization was improved. This unexpected outcome was most likely due to a reduced VEGF expression in the early phase bone healing.

Human neural stem cells dispersed in artificial ECM form cerebral organoids when grafted in vivo

Human neural stem cells (hNSC) derived from induced pluripotent stem cells can be differentiated into neurons that could be used for transplantation to repair brain injury. In this study we dispersed such hNSC in a three-dimensional artificial extracellular matrix (aECM) and compared their differentiation in vitro and following grafting into the sensorimotor cortex (SMC) of postnatal day (P)14 rat pups lesioned by localised injection of endothelin-1 at P12. After 10-43 days of in vitro differentiation, a few cells remained as PAX6⁺ neuroprogenitors but many more resembled post-mitotic neurons expressing doublecortin, β-tubulin and MAP2. These cells remained dispersed throughout the ECM, but with extended long processes for over 50 μm. In vivo, by 1 month post grafting, cells expressing human specific markers instead organised into cerebral organoids: columns of tightly packed PAX6 co-expressing progenitor cells arranged around small tubular lumen in rosettes, with a looser network of cells with processes around the outside co-expressing markers of immature neurons including doublecortin, and CTIP2 characteristic of corticofugal neurons. Host cells also invaded the graft including microglia, astrocytes and endothelial cells forming blood vessels. By 10 weeks post-grafting, the organoids had disappeared and the aECM had started to break down with fewer transplanted cells remaining. In vitro, cerebral organoids form in rotating incubators that force oxygen and nutrients to the centre of the structures. We have shown that cerebral organoids can form in vivo; intrinsic factors may direct their organisation including infiltration by host blood vessels.

* Central Growth Factor Loaded Depots in Bone Tissue Engineering Scaffolds for Enhanced Cell Attraction

Tissue engineering, the application of stem and progenitor cells in combination with an engineered extracellular matrix, is a promising strategy for bone regeneration. However, its success is limited by the lack of vascularization after implantation. The concept of in situ tissue engineering envisages the recruitment of cells necessary for tissue regeneration from the host environment foregoing ex vivo cell seeding of the scaffold. In this study, we developed a novel scaffold system for enhanced cell attraction, which is based on biomimetic mineralized collagen scaffolds equipped with a central biopolymer depot loaded with chemotactic agents. In humid milieu, as after implantation, the signaling factors are expected to slowly diffuse out of the central depot forming a gradient that stimulates directed cell migration toward the scaffold center. Heparin, hyaluronic acid, and alginate have been shown to be capable of depot formation. By using vascular endothelial growth factor (VEGF) as model factor, it was demonstrated that the release kinetics can be adjusted by varying the depot composition. While alginate and hyaluronic acid are able to reduce the initial burst and prolong the release of VEGF, the addition of heparin led to a much stronger retention that resulted in an almost linear release over 28 days. The biological activity of released VEGF was proven for all variants using an endothelial cell proliferation assay. Furthermore, migration experiments with endothelial cells revealed a relationship between the degree of VEGF retention and migration distance: cells invaded deepest in scaffolds containing a heparin-based depot indicating that the formation of a steep gradient is crucial for cell attraction. In conclusion, this novel in situ tissue engineering approach, specifically designed to recruit and accommodate endogenous cells upon implantation, appeared highly promising to stimulate cell invasion, which in turn would promote vascularization and finally new bone formation.

Improved vascularization of porous scaffolds through growth factor delivery from heparinized polyethylene glycol hydrogels

Surface modification with heparin has previously been shown to increase vascularization of porous scaffolds. In order to determine its efficacy with sustained release, heparin (Hep) was covalently incorporated into degradable (Type D) and non-degradable (Type N) polyethylene glycol (PEG) hydrogels. After in vitro characterization of their physicochemical properties, growth factor (GF) loaded, heparinised Type D gels were formed within the pores of porous polyurethane disks, which were then implanted and evaluated in a subcutaneous model. Type N gels formed faster (3.1±0.1 vs. 7.2±0.2min), were stiffer (10.0±0.5kPa vs. 7.1±1.2kPa) and more stable than degradable gels (>6month stability vs. disintegration ⩽22d in vitro; all p<0.001). Sustained release of covalently incorporated (CI) heparin from Type N (56days; first order kinetics) and Type D (21days; zero order kinetics) was achieved, as opposed to non-covalently incorporated (NI) heparin that eluted in a burst release within the first 2days. While Type D gels initially impeded tissue ingrowth into the porous scaffolds, they were completely degraded and replaced by ingrown tissue after 28days in vivo. At the latter timepoint disks containing gels without Hep or with non-covalently incorporated Hep were less vascularized than empty (no gel) controls. In contrast, the incorporation of covalently heparinized (no GF) and GF containing gels (no Hep) resulted in a 50% and 42% (p<0.05) improvement in vascularization, while an increase of 119% (p<0.001) was achieved with a combination of covalently attached Hep and GF. These gels thus provide a sustained release system for heparin and GF that extends the duration of their action to local tissue ingrowth.

STATEMENT OF SIGNIFICANCE

The paper describes the modification and covalent incorporation of heparin into degradable and non-degradable polyethylene glycol hydrogels in a way that provides for the hydrolytic cleavage of the linker for the release of the heparin in original and active form, and in an extended (21-56d) controlled (zero and first order respectively) manner. The successful use of these gels as growth-factor containing and releasing matrices for the improvement of in vivo vascularization holds promise for many potential uses in tissue engineering and regenerative medicine applications, such as vascular grafts and myocardial infarction therapy, where the antithrombotic and/or growth factor binding/potentiating properties are required.

Tissue Engineering Strategies for Myocardial Regeneration: Acellular Versus Cellular Scaffolds?

Heart disease remains one of the leading causes of death in industrialized nations with myocardial infarction (MI) contributing to at least one fifth of the reported deaths. The hypoxic environment eventually leads to cellular death and scar tissue formation. The scar tissue that forms is not mechanically functional and often leads to myocardial remodeling and eventual heart failure. Tissue engineering and regenerative medicine principles provide an alternative approach to restoring myocardial function by designing constructs that will restore the mechanical function of the heart. In this review, we will describe the cellular events that take place after an MI and describe current treatments. We will also describe how biomaterials, alone or in combination with a cellular component, have been used to engineer suitable myocardium replacement constructs and how new advanced culture systems will be required to achieve clinical success.

Hyaluronic acid-based hydrogel scaffold without angiogenic growth factors enhances ovarian tissue function after autotransplantation in rats

One of the problems encountered during ovarian transplantation is that the number of primordial follicles in the grafts is considerably reduced 2 d after transplantation due to post-transplantation ischemia. This study investigates if the use of hyaluronic acid-based hydrogel (HABH) with and without vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) could prevent or minimize ischemia-induced follicle loss during ovarian autotransplantation and thereby restore ovarian tissue function in the rat model. In this study, twenty four female rats were subjected to bilateral ovariectomy and were randomly divided into 3 groups for ovarian tissue autotransplantation. Group A included rats with ovarian tissue without HABH, VEGF and bFGF, group B comprised rats with ovarian tissue encapsulated with HABH and group C had rats with ovarian tissue encapsulated with HABH containing VEGF and bFGF. Three days after transplantation, the grafts were assessed through histological and hormonal analyses. Apoptotic, angiogenic and maturation genes expressions were also analyzed. The mean number of follicles in all developmental stages increased in group B (P  <  0.05). The level of FSH decreased in group B (P  <  0.05) whereas, the expression level of VEGF gene increased in group B (P  <  0.05). No significant changes were observed in the expression levels of maturation and apoptotic genes in all groups. In conclusion, ovarian encapsulation with HABH alone can prevent or minimize ischemia-induced follicle loss, preserve the follicular pool, promote follicular survival, facilitate angiogenesis, and restore hormone levels. However, its efficiency in a clinical setting and in comparison with other hydrogels needs further investigation.

Glycosaminoglycan-Based Biohybrid Hydrogels: A Sweet and Smart Choice for Multifunctional Biomaterials

Glycosaminoglycans (GAGs) govern important functional characteristics of the extracellular matrix (ECM) in living tissues. Incorporation of GAGs into biomaterials opens up new routes for the presentation of signaling molecules, providing control over development, homeostasis, inflammation, and tumor formation and progression. Recent approaches to GAG-based materials are reviewed, highlighting the formation of modular, tunable biohybrid hydrogels by covalent and non-covalent conjugation schemes, including both theory-driven design concepts and advanced processing technologies. Examples of the application of the resulting materials in biomedical studies are provided. For perspective, solid-phase and chemoenzymatic oligosaccharide synthesis methods for GAG-derived motifs, rational and high-throughput design strategies for GAG-based materials, and the utilization of the factor-scavenging characteristics of GAGs are highlighted.

Perspectives On: Local and Sustained Delivery of Angiogenic Growth Factors

This review emphasizes the role of angiogenesis in tissue engineering, introduces various angiogenic growth factors, and highlights current status of delivery systems for angiogenic growth factors using natural and synthetic biomaterials. A short overview of angiogenic growth factors is presented, followed by the introduction of emerging strategies for designing smart delivery carriers.

A tunable hydrogel system for long-term release of cell-secreted cytokines and bioprinted in situ wound cell delivery

For many cellular therapies being evaluated in preclinical and clinical trials, the mechanisms behind their therapeutic effects appear to be the secretion of growth factors and cytokines, also known as paracrine activity. Often, delivered cells are transient, and half-lives of the growth factors that they secrete are short, limiting their long-term effectiveness. The goal of this study was to optimize a hydrogel system capable of in situ cell delivery that could sequester and release growth factors secreted from those cells after the cells were no longer present. Here, we demonstrate the use of a fast photocross-linkable heparin-conjugated hyaluronic acid (HA-HP) hydrogel as a cell delivery vehicle for sustained growth factor release, which extends paracrine activity. The hydrogel could be modulated through cross-linking geometries and heparinization to support sustained release proteins and heparin-binding growth factors. To test the hydrogel in vivo, we used it to deliver amniotic fluid-derived stem (AFS) cells, which are known to secrete cytokines and growth factors, in full thickness skin wounds in a nu/nu murine model. Despite transience of the AFS cells in vivo, the HA-HP hydrogel with AFS cells improved wound closure and reepithelialization and increased vascularization and production of extracellular matrix in vivo. These results suggest that HA-HP hydrogel has the potential to prolong the paracrine activity of cells, thereby increasing their therapeutic effectiveness in wound healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1986-2000, 2017.

Bioprinting Cellularized Constructs Using a Tissue-specific Hydrogel Bioink

Bioprinting has emerged as a versatile biofabrication approach for creating tissue engineered organ constructs. These constructs have potential use as organ replacements for implantation in patients, and also, when created on a smaller size scale as model "organoids" that can be used in in vitro systems for drug and toxicology screening. Despite development of a wide variety of bioprinting devices, application of bioprinting technology can be limited by the availability of materials that both expedite bioprinting procedures and support cell viability and function by providing tissue-specific cues. Here we describe a versatile hyaluronic acid (HA) and gelatin-based hydrogel system comprised of a multi-crosslinker, 2-stage crosslinking protocol, which can provide tissue specific biochemical signals and mimic the mechanical properties of in vivo tissues. Biochemical factors are provided by incorporating tissue-derived extracellular matrix materials, which include potent growth factors. Tissue mechanical properties are controlled combinations of PEG-based crosslinkers with varying molecular weights, geometries (linear or multi-arm), and functional groups to yield extrudable bioinks and final construct shear stiffness values over a wide range (100 Pa to 20 kPa). Using these parameters, hydrogel bioinks were used to bioprint primary liver spheroids in a liver-specific bioink to create in vitro liver constructs with high cell viability and measurable functional albumin and urea output. This methodology provides a general framework that can be adapted for future customization of hydrogels for biofabrication of a wide range of tissue construct types.

Hyaluronan Is Crucial for Stem Cell Differentiation into Smooth Muscle Lineage

Deciphering the extracellular signals that regulate SMC differentiation from stem cells is vital to further our understanding of the pathogenesis of vascular disease and for development of cell-based therapies and tissue engineering. Hyaluronan (HA) has emerged as an important component of the stem cell niche, however its role during stem cell differentiation is a complicated and inadequately defined process. This study aimed to investigate the role of HA in embryonic stem cell (ESC) differentiation toward a SMC lineage. ESCs were seeded on collagen-IV in differentiation medium to generate ESC-derived SMCs (esSMCs). Differentiation coincided with increased HA synthase (HAS) 2 expression, accumulation of extracellular HA and its assembly into pericellular matrices. Inhibition of HA synthesis by 4-methylumbelliferone (4MU), removal of the HA coat by hyaluronidase (HYAL) or HAS2 knockdown led to abrogation of SMC gene expression. HA activates ERK1/2 and suppresses EGFR signaling pathways via its principle receptor, CD44. EGFR inactivation coincided with increased binding to CD44, which was further augmented by addition of high molecular weight (HMW)-HA either exogenously or via HAS2 overexpression through adenoviral gene transfer. HMW-HA-stimulated esSMCs displayed a functional role in vascular tissue engineering ex vivo, vasculogenesis in a matrigel plug model and SMC accumulation in neointimal lesions of vein grafts in mice. These findings demonstrate that HAS2-induced HA synthesis and organization drives ESC-SMC differentiation. Thus, remodeling of the HA microenvironment is a critical step in directing stem cell differentiation toward a vascular lineage, highlighting HA as a potential target for treatment of vascular diseases. Stem Cells 2016;34:1225-1238.

Encapsulation of PEGylated low-molecular-weight PEI polyplexes in hyaluronic acid hydrogels reduces aggregation

The effective delivery of DNA locally could increase the applicability of gene therapy in tissue regeneration and therapeutic angiogenesis. One promising approach is through use of porous hydrogel scaffolds that incorporate and deliver DNA in the form of nanoparticles to the affected sites. While we have previously reported on caged nanoparticle encapsulation (CnE) to load DNA polyplexes within hydrogels at high concentrations without aggregation, frequent issues with limited polyplex release following CnE have been encountered. In this study, we report two alternative approaches to polyplex presentation for decreasing aggregation in porous hydrogels. The first approach reduces polyplex aggregation by utilizing polyethylene glycol modification of the gene carrier polymer polyethyleneimine (sPEG-PEI) to mitigate charge-charge interactions between polyplexes and the scaffold during gelation. The second approach electrostatically presents polyplexes on the surfaces of scaffold pores as opposed to an encapsulated presentation. The sPEG-PEI polymer formed a smaller, less toxic, and more stable polyplex that exhibited less aggregation within HA gels when compared to the traditionally used linear PEI (LPEI) polymer. Surface-coated polyplexes also resulted in a more homogenous distribution of polyplexes in hydrogels. Furthermore, sPEG-PEI polyplexes retained transfection abilities comparable to LPEI in 3D surface-coated transfections. These results demonstrate a significant improvement in scaffold-mediated gene delivery and show promise in applications to multi-gene delivery systems.

STATEMENT OF SIGNIFICANCE

A promising gene delivery approach for regenerative medicine is implanting porous hydrogel scaffolds loaded with DNA nanoparticles for delivery to affected sites. However, loading DNA polyplexes at high concentrations within hydrogels results in significant aggregation. Here, we describe two methods for decreasing aggregation of DNA polyplexes in porous gels. First, the gene carrier polymer polyethyleneimine (PEI) was modified with polyethylene glycol (sPEG-PEI) to mitigate the electrostatic interactions between polyplexes and scaffold polymer to in turn decrease aggregation. Second, polyplexes were presented along the surfaces of the pores of the hydrogel instead of being encapsulated within the gel. These methods allow for highly tunable and sustained transgene expression from scaffold-mediated gene delivery while avoiding polyplex aggregation.

A hydrogel bioink toolkit for mimicking native tissue biochemical and mechanical properties in bioprinted tissue constructs

Advancement of bioprinting technology is limited by the availability of materials that both facilitate bioprinting logistics as well as support cell viability and function by providing tissue-specific cues. Herein we describe a modular hyaluronic acid (HA) and gelatin-based hydrogel toolbox comprised of a 2-crosslinker, 2-stage polymerization technique, and the capability to provide tissue specific biochemically and mechanically accurate signals to cells within biofabricated tissue constructs. First, we prepared and characterized several tissue-derived decellularized extracellular matrix-based solutions, which contain complex combinations of growth factors, collagens, glycosaminoglycans, and elastin. These solutions can be incorporated into bioinks to provide the important biochemical cues of different tissue types. Second, we employed combinations of PEG-based crosslinkers with varying molecular weights, geometries (linear, 4-arm, and 8-arm), and functional groups to yield hydrogel bioinks that supported extrusion bioprinting and the capability to achieve final construct shear stiffness values ranging from approximately 100 Pa to 20 kPa. Lastly, we integrated these hydrogel bioinks with a 3-D bioprinting platform, and validated their use by bioprinting primary liver spheroids in a liver-specific bioink to create in vitro liver constructs with high cell viability and measurable functional albumin and urea output. This hydrogel bioink system has the potential to be a versatile tool for biofabrication of a wide range of tissue construct types.

STATEMENT OF SIGNIFICANCE

Biochemical and mechanical factors both have important implications in guiding the behavior of cells in vivo, yet both realms are rarely considered together in the context of biofabrication in vitro tissue construct models. We describe a modular hydrogel system that (1) facilitates extrusion bioprinting of cell-laden hydrogels, (2) incorporates tissue-specific factors derived from decellularized tissue extracellular matrix, thus mimicking biochemical tissue profile, and (3) allows control over mechanical properties to mimic the tissue stiffness. We believe that employing this technology to attend to both the biochemical and mechanical profiles of tissues, will allow us to more accurately recapitulate the in vivo environment of tissues while creating functional 3-D in vitro tissue constructs that can be used as disease models, personalized medicine, and in vitro drug and toxicology screening systems.

Designer Hydrogels for Precision Control of Oxygen Tension and Mechanical Properties

Oxygen levels and mechanical properties provide vital cues to regulate myriad cellular functions and stem cell fate decisions. Here, we present a hybrid hydrogel system in which we can control independently oxygen levels and mechanical properties. We designed, synthesized and analyzed a hybrid hydrogel system comprised of two polymer backbones, gelatin and dextran. Both polymers were crosslinked via a laccase-mediated, oxygen consuming reaction. By specifically controlling the concentration of phenolic molecules available to react in our hydrogel, we could precisely control the time in which the hydrogel remained hypoxic (TH). We were able to achieve a range of TH from the order of minutes to greater than 10 hours. Additionally, by incorporating a secondary crosslinker, transglutaminase, mechanical properties could be adjusted in a user-defined fashion, with dynamic elastic modulus (G') values ranging from <20 Pa to >1 kPa. Importantly, oxygen levels and substrate mechanical properties could be individually tuned and decoupled in our hybrid hydrogels, while retaining the potential to study possible synergistic effects between the two parameters. By precisely controlling oxygen tension and mechanical properties, we expect that research utilizing the new hybrid hydrogels will enhance our understanding of the complex 3D cellular processes mediated by each parameter individually and may also hold clinical interest as acellular therapies.

Depot-Based Delivery Systems for Pro-Angiogenic Peptides: A Review

Insufficient vascularization currently limits the size and complexity for all tissue engineering approaches. Additionally, increasing or re-initiating blood flow is the first step toward restoration of ischemic tissue homeostasis. However, no FDA-approved pro-angiogenic treatments exist, despite the many pre-clinical approaches that have been developed. The relatively small size of peptides gives advantages over protein-based treatments, specifically with respect to synthesis and stability. While many pro-angiogenic peptides have been identified and shown promising results in vitro and in vivo, the majority of biomaterials developed for pro-angiogenic drug delivery focus on protein delivery. This narrow focus limits pro-angiogenic therapeutics as peptides, similar to proteins, suffer from poor pharmacokinetics in vivo, necessitating the development of controlled release systems. This review discusses pro-angiogenic peptides and the biomaterials delivery systems that have been developed, or that could easily be adapted for peptide delivery, with a particular focus on depot-based delivery systems.

The effects of hyaluronic acid vaginal gel on the vaginal epithelium of ovariectomized rats

OBJECTIVE

Hyaluronic acid is one of the best materials of water retention which can be used in vaginal atrophy. This study is to evaluate the role and mechanism of the hyaluronic acid vaginal gel (Hyalofemme) in the vaginal epithelium of ovariectomized rats.

MATERIALS AND METHODS

Sixty SD rats were randomly divided into control group (Sham ovariectomy, Sham-OVX), tendency group (ovariectomy, OVX), and experiment group (ovariectomy+Hyalofemme, OVX+Hyalofemme). The hyaluronic acid vaginal gel was administered local vaginal therapy to the experiment group with cytologicaly confirmed vaginal atrophy. The doses were adjusted by animal weight according to human dosage. After daily treatment for 14 days, VEGF and P-AKT activations were detected by Western blot in the experiment group.

RESULTS

The hyaluronic acid vaginal gel proved to be very effective in the cytological reversal of vaginal atrophy but did not increase uterine weight. Vaginal microecosystem indicators were negative in the control group and the experiment group. By contrast, the indicators were positive in the tendency group.

CONCLUSION

Hyaluronic acid vaginal gel is effective in the reversal of vaginal atrophy and is beneficial for improving vaginal microecosystem in the postmenopausal rat model. The hyaluronic acid vaginal gel can also improve the repair capacity of the vaginal epithelium.

Cell and tissue engineering for liver disease

Despite the tremendous hurdles presented by the complexity of the liver's structure and function, advances in liver physiology, stem cell biology and reprogramming, and the engineering of tissues and devices are accelerating the development of cell-based therapies for treating liver disease and liver failure. This State of the Art Review discusses both the near- and long-term prospects for such cell-based therapies and the unique challenges for clinical translation.