In situ tissue engineering with synthetic self-assembling peptide nanofiber scaffolds, PuraMatrix, for mucosal regeneration in the rat middle-ear

Application of the Self-Assembling Peptide Hydrogel RADA16 for Hemostasis during Tonsillectomy: A Feasibility Study

Tonsillectomy is a common surgical procedure but carries a high risk of readmission for secondary bleeding and pain. This study evaluated the feasibility and effectiveness of using the hemostatic self-assembling peptide hydrogel RADA16 (PuraBond, 3-D Matrix SAS; Caluire et Cuire, France) to control bleeding from the tonsillectomy wound bed. Readmission/re-operation rates were compared between a prospective case series of 21 primarily adult tonsillectomy patients treated with topical RADA16 and an untreated historical Control group of 164 patients who underwent tonsillectomy by 10 surgeons at a single tertiary hospital in the UK between March 2019 and June 2022. Cumulative readmission rates for any reason were 2-fold elevated in Control subjects (18.9%; n = 31/164 subjects) compared to patients treated intra-operatively with RADA16 hemostatic hydrogel (9.5%; n = 2/21) (p = 0.378). Readmission rates for postoperative bleeding were 3-fold higher in Controls (14.6%; n = 24/164 subjects) than in the RADA16-treated group (4.8%; n = 1/21) (p = 0.317). A similar rate of retreatment for pain was recorded in the Control (4.3%; n = 7/164) and RADA16 (4.8%; n = 1/21) groups (p = 0.999). Two Control subjects (1.2%) required re-operation for recalcitrant bleeding; no RADA16 subject (0.0%) required re-operation for any reason. No device-related adverse events occurred in the RADA16 group. Surgeons were pleased with the easy learning curve and technical feasibility associated with intra-operatively administering RADA16 hemostatic hydrogel. Intra-operative hemostasis using RADA16 peptide hydrogel was straightforward and was associated with a trend of 3-fold lower rates of readmission for postoperative bleeding events than untreated Control subjects.

Histochemistry for Molecular Imaging in Nanomedicine

All the nanotechnological devices designed for medical purposes have to deal with the common requirement of facing the complexity of a living organism. Therefore, the development of these nanoconstructs must involve the study of their structural and functional interactions and the effects on cells, tissues, and organs, to ensure both effectiveness and safety. To this aim, imaging techniques proved to be extremely valuable not only to visualize the nanoparticles in the biological environment but also to detect the morphological and molecular modifications they have induced. In particular, histochemistry is a long-established science able to provide molecular information on cell and tissue components in situ, bringing together the potential of biomolecular analysis and imaging. The present review article aims at offering an overview of the various histochemical techniques used to explore the impact of novel nanoproducts as therapeutic, reconstructive and diagnostic tools on biological systems. It is evident that histochemistry has been playing a leading role in nanomedical research, being largely applied to single cells, tissue slices and even living animals.

A new strategy for the treatment of middle ear infection using ciprofloxacin/amoxicillin-loaded ethyl cellulose/polyhydroxybutyrate nanofibers

A middle ear infection occurs due to the presence of several microorganisms behind the eardrum (tympanic membrane) and is very challenging to treat due to its unique location and requires a well-designed treatment. If not treated properly, the infection can result in severe symptoms and unavoidable side effects. In this study, excellent biocompatible ethyl cellulose (EC) and biodegradable polyhydroxybutyrate (PHB) biopolymer were used to fabricate drug-loaded nanofiber scaffolds using an electrospinning technique to overcome antibiotic overdose and insufficient efficacy of drug release during treatment. PHB polymer was produced from Halomonas sp., and the purity of PHB was found to around be 90 %. Additionally, ciprofloxacin (CIP) and amoxicillin (AMX) are highly preferable since both drugs are highly effective against gram-negative and gram-positive bacteria to treat several infections. Obtained smooth nanofibers were between 116.24 and 171.82 nm in diameter and the addition of PHB polymer and antibiotics improved the morphology of the nanofiber scaffolds. Thermal properties of the nanofiber scaffolds were tested and the highest Tg temperature resulted at 229 °C. The mechanical properties of the scaffolds were tested, and the highest tensile strength resulted in 4.65 ± 6.33 MPa. Also, drug-loaded scaffolds were treated against the most common microorganisms that cause the infection, such as S.aureus, E.coli, and P.aeruginosa, and resulted in inhibition zones between 10 and 21 mm. MTT assay was performed by culturing human adipose-derived mesenchymal stem cells (hAD MSCs) on the scaffolds. The morphology of the hAD MSCs' attachment was tested with SEM analysis and hAD MSCs were able to attach, spread, and live on each scaffold even on the day of 7. The cumulative drug release kinetics of CIP and AMX from drug-loaded scaffolds were analysed in phosphate-buffered saline (pH: 7.4) within different time intervals of up to 14 days using a UV spectrophotometer. Furthermore, the drug release showed that the First-Order and Korsmeyer-Peppas models were the most suitable kinetic models. Animal testing was performed on SD rats, matrix and collagen deposition occurred on days 5 and 10, which were observed using Hematoxylin-eosin and Masson's trichrome staining. At the highest drug concentration, a better repair effect was observed. Results were promising and showed potential for novel treatment.

Tissue engineering in otology: a review of achievements

Tissue engineering application in otology spans a distance from the pinna to auditory nerve covered with specialized tissues and functions such as sense of hearing and aesthetics. It holds the potential to address the barriers of lack of donor tissue, poor tissue match, and transplant rejection through provision of new and healthy tissues similar to the host and possesses the capacity to renew, to regenerate, and to repair in-vivo and was shown to be a bypasses for any need to immunosuppression. This review aims to investigate the application of tissue engineering in otology and to evaluate the achievements and challenges in external, middle and inner ear sections. Since gaining the recent knowledge and training on use of different scaffolds is essential for otology specialists and who look for the recovery of ear function and aesthetics of patients, it is shown in this review how utilizing tissue engineering and cell transplantation, regenerative medicine can provide advancements in hearing and ear aesthetics to fit different patients' needs.

Self-assembling peptide RADA16: a promising scaffold for tissue engineering and regenerative medicine

RADA16 is a peptide-based biomaterial whose acidic aqueous solution spontaneously forms an extracellular matrix-like 3D structure within seconds upon contact with physiological pH body fluids. Meanwhile, its good biocompatibility, low immunogenicity, nontoxic degradation products and ease of modification make it an ideal scaffold for tissue engineering. RADA16 is a good delivery vehicle for cells, drugs and factors. Its shear thinning and thixotropic properties allow it to fill tissue voids by injection and not to swell. However, the weaker mechanical properties and poor hydrophilicity are troubling limitations of RADA16. To compensate for this limitation, various functional groups and polymers have been designed to modify RADA16, thus contributing to its scope and progress in the field of tissue engineering.

Self-assembling RADA16 peptide hydrogel supports hemostasis, synechiae reduction, and wound healing in a sheep model of endoscopic nasal surgery

OBJECTIVES

Complications of endoscopic sinus/nasal turbinate surgery include postoperative hemorrhage, synechiae formation, and poor wound healing. Our primary objectives were to evaluate whether a topical hydrogel based on self-assembling RADA16 peptides: i) reduces bleeding and synechiae formation, and ii) supports wound healing, using a sheep nasal surgery model.

METHODS

Thirty sheep received endoscopic surgery-created bilateral nasal mucosal injuries on the middle turbinate/opposing septum. Injuries were randomly assigned RADA16, Gelatin-thrombin, or no treatment. Outcomes included intra-operative hemostasis, scar tissue/synechiae formation and wound healing at 2 weeks and the 6-week study terminus, and histopathology.

RESULTS

Intra-operative hemostasis time improved with RADA16 and Gelatin-thrombin versus Control wounds (139.7±56.2 s, 145.4±58.1 s, and 224.0±69.9 s, respectively; p < 0.0001 for both comparisons). Two-week synechiae scores (maximum 4 points) were similar in Controls (2.9±1.8 points) and Gelatin-thrombin (3.1±1.6 points) wounds (p > 0.05), but were reduced in RADA16 sites by 91% versus Controls and 92% versus Gelatin-thrombin treatment (0.3±0.6 points; p < 0.0001 for both comparisons). Six-week synechiae scores were similar in Control (1.1±1.7 points) and Gelatin-thrombin (1.7±2.0 points) wounds (p > 0.05), but reduced 100% in RADA16-treated wounds. Synechiae occurred in fewer RADA16-treated sites at 2 weeks (20%) versus Gelatin-thrombin (80%) and Controls (75%; p < 0.01) and at 6 weeks (0%, 50% and 35%, respectively; p < 0.01). RADA16 was associated with significantly lower 6-week histopathology scores, driven by reduced submucosal fibrosis and angiogenesis.

CONCLUSION

Although RADA16 and Gelatin-thrombin similarly accelerated hemostasis in this sheep endoscopic sinus surgery model, only RADA16 reduced postoperative synechiae formation at 2 weeks with an absence of synechiae at 6 weeks. Histology suggested RADA16 enhanced mucosal regeneration.

Release systems based on self-assembling RADA16-I hydrogels with a signal sequence which improves wound healing processes

Self-assembling peptides can be used for the regeneration of severely damaged skin. They can act as scaffolds for skin cells and as a reservoir of active compounds, to accelerate scarless wound healing. To overcome repeated administration of peptides which accelerate healing, we report development of three new peptide biomaterials based on the RADA16-I hydrogel functionalized with a sequence (AAPV) cleaved by human neutrophil elastase and short biologically active peptide motifs, namely GHK, KGHK and RDKVYR. The peptide hybrids were investigated for their structural aspects using circular dichroism, thioflavin T assay, transmission electron microscopy, and atomic force microscopy, as well as their rheological properties and stability in different fluids such as water or plasma, and their susceptibility to digestion by enzymes present in the wound environment. In addition, the morphology of the RADA-peptide hydrogels was examined with a unique technique called scanning electron cryomicroscopy. These experiments enabled us to verify if the designed peptides increased the bioactivity of the gel without disturbing its gelling processes. We demonstrate that the physicochemical properties of the designed hybrids were similar to those of the original RADA16-I. The materials behaved as expected, leaving the active motif free when treated with elastase. XTT and LDH tests on fibroblasts and keratinocytes were performed to assess the cytotoxicity of the RADA16-I hybrids, while the viability of cells treated with RADA16-I hybrids was evaluated in a model of human dermal fibroblasts. The hybrid peptides revealed no cytotoxicity; the cells grew and proliferated better than after treatment with RADA16-I alone. Improved wound healing following topical delivery of RADA-GHK and RADA-KGHK was demonstrated using a model of dorsal skin injury in mice and histological analyses. The presented results indicate further research is warranted into the engineered peptides as scaffolds for wound healing and tissue engineering.

Inhibition of TGF-β signaling enables long-term proliferation of mouse primary epithelial stem/progenitor cells of the tympanic membrane and the middle ear mucosa

The surface of the middle ear is composed of the tympanic membrane (TM) and the middle ear mucosa (MEM). A number of diseases and conditions such as otitis media, middle ear cholesteatoma, and perforation of the TM have been reported to cause dysfunction of the middle ear, ultimately leading to high-frequency hearing loss. Despite its importance in repairing the damaged tissues, the stem/progenitor cells of the TM and the MEM epithelia remains largely uncharacterized due, in part, to the lack of an optimal methodology to expand and maintain stem/progenitor cells long-term. Here, we show that suppression of TGF-β signaling in a low Ca²⁺ condition enables long-term proliferation of p63-positive epithelial stem/progenitor cells of the TM and the MEM while avoiding their malignant transformation. Indeed, our data show that the expanded TM and MEM stem/progenitor cells respond to Ca²⁺ stimulation and differentiate into the mature epithelial cell lineages marked by cytokeratin (CK) 1/8/18 or Bpifa1, respectively. These results will allow us to expand epithelial stem/progenitor cells of the TM and MEM in quantity for large-scale analyses and will enhance the use of mouse models in developing stem cell-mediated therapeutic strategies for the treatment of middle ear diseases and conditions.

Biomaterials and Extracellular Vesicle Delivery: Current Status, Applications and Challenges

In this review, we will discuss the current status of extracellular vesicle (EV) delivery via biopolymeric scaffolds for therapeutic applications and the challenges associated with the development of these functionalized scaffolds. EVs are cell-derived membranous structures and are involved in many physiological processes. Naïve and engineered EVs have much therapeutic potential, but proper delivery systems are required to prevent non-specific and off-target effects. Targeted and site-specific delivery using polymeric scaffolds can address these limitations. EV delivery with scaffolds has shown improvements in tissue remodeling, wound healing, bone healing, immunomodulation, and vascular performance. Thus, EV delivery via biopolymeric scaffolds is becoming an increasingly popular approach to tissue engineering. Although there are many types of natural and synthetic biopolymers, the overarching goal for many tissue engineers is to utilize biopolymers to restore defects and function as well as support host regeneration. Functionalizing biopolymers by incorporating EVs works toward this goal. Throughout this review, we will characterize extracellular vesicles, examine various biopolymers as a vehicle for EV delivery for therapeutic purposes, potential mechanisms by which EVs exert their effects, EV delivery for tissue repair and immunomodulation, and the challenges associated with the use of EVs in scaffolds.

Evaluating the role of the self-assembling topical haemostat PuraBond® in Transoral Robotic Surgery (TORS) for oropharyngeal cancer: A case series

Background

Methods

Results

Conclusion

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Major haemorrhage is a key concern following transoral robotic surgery (TORS).

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Purabond® is a synthetic haemostatic agent used in other surgical settings.

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Our series is the first to evaluate the role of Purabond® in TORS.

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We demonstrate excellent outcomes in terms of bleeding and swallowing complications.

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Larger, prospective controlled studies are needed to further assess these outcomes.

Bringing hydrogel-based craniofacial therapies to the clinic

This review explores the evolution of the use of hydrogels for craniofacial soft tissue engineering, ranging in complexity from acellular injectable fillers to fabricated, cell-laden constructs with complex compositions and architectures. Addressing both in situ and ex vivo approaches, tissue restoration secondary to trauma or tumor resection is discussed. Beginning with relatively simple epithelia of oral mucosa and gingiva, then moving to more functional units like vocal cords or soft tissues with multilayer branched structures, such as salivary glands, various approaches are presented toward the design of function-driven architectures, inspired by native tissue organization. Multiple tissue replacement paradigms are presented here, including the application of hydrogels as structural materials and as delivery platforms for cells and/or therapeutics. A practical hierarchy is proposed for hydrogel systems in craniofacial applications, based on their material and cellular complexity, spatial order, and biological cargo(s). This hierarchy reflects the regulatory complexity dictated by the Food and Drug Administration (FDA) in the United States prior to commercialization of these systems for use in humans. The wide array of available biofabrication methods, ranging from simple syringe extrusion of a biomaterial to light-based spatial patterning for complex architectures, is considered within the history of FDA-approved commercial therapies. Lastly, the review assesses the impact of these regulatory pathways on the translational potential of promising pre-clinical technologies for craniofacial applications. STATEMENT OF SIGNIFICANCE: While many commercially available hydrogel-based products are in use for the craniofacial region, most are simple formulations that either are applied topically or injected into tissue for aesthetic purposes. The academic literature previews many exciting applications that harness the versatility of hydrogels for craniofacial soft tissue engineering. One of the most exciting developments in the field is the emergence of advanced biofabrication methods to design complex hydrogel systems that can promote the functional or structural repair of tissues. To date, no clinically available hydrogel-based therapy takes full advantage of current pre-clinical advances. This review surveys the increasing complexity of the current landscape of available clinical therapies and presents a framework for future expanded use of hydrogels with an eye toward translatability and U.S. regulatory approval for craniofacial applications.

PuraStat RADA16 Self-Assembling Peptide Reduces Postoperative Abdominal Adhesion Formation in a Rabbit Cecal Sidewall Injury Model

Objective: To evaluate the effect of PuraStat (2.5% RADA16) administration on postoperative abdominal adhesion formation in an in vivo model.

Methods: Anesthetized New Zealand white rabbits underwent cecal sidewall abrasion surgery in which the cecal serosa and juxtaposed parietal peritoneum were abraded after access through an abdominal midline incision. Eight animals were randomized to receive PuraStat administration at the interface of the injured tissues before incision closure, and five animals served as untreated controls. Treated animals received 3–12 ml PuraStat solution per lesion. Animals were sacrificed 14 days after surgery and examined for adhesion formation at the wound site.

Results: At study terminus, adhesions were identified in 90% (9/10) of abraded cecum/peritoneal wound sites in untreated controls versus 25% (4/16) of PuraStat-treated sites (p = 0.004). Mean ± SD Total Adhesion Score (average of the values for extent + strength of the adhesion in both defects per animal; maximum score = 14 points) was significantly 76% lower in PuraStat-treated animals (2.0 ± 3.0 points) compared to untreated controls (8.2 ± 1.9 points) (p = 0.029). Mean adhesion coverage area of wound sites was 79% lower in PuraStat-treated animals than controls (p < 0.001), and mean adhesion durability was 72% lower in PuraStat-treated animals versus controls (p = 0.005). Remnant hydrogel was observed at the wound sites of 75% of treated animals at postoperative Day 14.

Conclusion: PuraStat treatment has a positive protective effect in the cecal sidewall injury model, and significantly reduces abdominal adhesion formation at the interface of the injured cecum and overlying peritoneal sidewall defect.

Multicellular Ovarian Cancer Model for Evaluation of Nanovector Delivery in Ascites and Metastatic Environments

A novel multicellular model composed of epithelial ovarian cancer and fibroblast cells was developed as an in vitro platform to evaluate nanovector delivery and ultimately aid the development of targeted therapies. We hypothesized that the inclusion of peptide-based scaffold (PuraMatrix) in the spheroid matrix, to represent in vivo tumor microenvironment alterations along with metastatic site conditions, would enhance spheroid cell growth and migration and alter nanovector transport. The model was evaluated by comparing the growth and migration of ovarian cancer cells exposed to stromal cell activation and tissue hypoxia. Fibroblast activation was achieved via the TGF-β1 mediated pathway and tissue hypoxia via 3D spheroids incubated in hypoxia. Surface-modified nanovector transport was assessed via fluorescence and confocal microscopy. Consistent with previous in vivo observations in ascites and at distal metastases, spheroids exposed to activated stromal microenvironment were denser, more contractile and with more migratory cells than nonactivated counterparts. The hypoxic conditions resulted in negative radial spheroid growth over 5 d compared to a radial increase in normoxia. Nanovector penetration attenuated in PuraMatrix regardless of surface modification due to a denser environment. This platform may serve to evaluate nanovector transport based on ovarian ascites and metastatic environments, and longer term, it provide a means to evaluate nanotherapeutic efficacy.

Therapeutic Potential of a Self-Assembling Peptide Hydrogel to Treat Colonic Injuries Associated with Inflammatory Bowel Disease

BACKGROUND AND AIMS

The Self-assembling Peptide Hydrogel [SAPH, PuraMatrix], a fully synthetic peptide solution designed to replace collagen, has recently been used to promote mucosal regeneration in iatrogenic ulcers following endoscopic submucosal dissection. Herein, we evaluated its utility in ulcer repair using a rat model of topical trinitrobenzene sulphonic acid [TNBS]-induced colonic injuries.

METHODS

Colonic injuries were generated in 7-week-old rats by injecting an ethanol solution [35%, 0.2 mL] containing 0.15 M TNBS into the colonic lumen. At 2 and 4 days post-injury, the rats were subjected to endoscopy, and SAPH [or vehicle] was topically applied to the ulcerative lesion. Time-of-flight secondary ion mass spectrometry [TOF-SIMS] was used to detect SAPH. Colonic expression of cytokines and wound healing-related factors were assessed using real-time polymerase chain reaction or immunohistochemistry.

RESULTS

SAPH treatment significantly reduced ulcer length [p = 0.0014] and area [p = 0.045], while decreasing colonic weight [p = 0.0375] and histological score [p = 0.0005] 7 days after injury. SAPH treatment also decreased colonic expression of interleukin [IL]-1α [p = 0.0233] and IL-6[p = 0.0343] and increased that of claudin-1 [p = 0.0486] and villin [p = 0.0183], and β-catenin staining [p = 0.0237]. TOF-SIMS revealed lesional retention of SAPH on day 7 post-injury. Furthermore, SAPH significantly promoted healing in in vivo mechanical intestinal wound models.

CONCLUSIONS

SAPH application effectively suppressed colonic injury, downregulated inflammatory cytokine expression, and upregulated wound healing-related factor expression in the rat model; thus, it may represent a promising therapeutic strategy for IBD-related colonic ulcers.

Clinical Use of the Self-Assembling Peptide RADA16: A Review of Current and Future Trends in Biomedicine

RADA16 is a synthetic peptide that exists as a viscous solution in an acidic formulation. In an acidic aqueous environment, the peptides spontaneously self-assemble into β-sheet nanofibers. Upon exposure and buffering of RADA16 solution to the physiological pH of biological fluids such as blood, interstitial fluid and lymph, the nanofibers begin physically crosslinking within seconds into a stable interwoven transparent hydrogel 3-D matrix. The RADA16 nanofiber hydrogel structure closely resembles the 3-dimensional architecture of native extracellular matrices. These properties make RADA16 formulations ideal topical hemostatic agents for controlling bleeding during surgery and to prevent post-operative rebleeding. A commercial RADA16 formulation is currently used for hemostasis in cardiovascular, gastrointestinal, and otorhinolaryngological surgical procedures, and studies are underway to investigate its use in wound healing and adhesion reduction. Straightforward application of viscous RADA16 into areas that are not easily accessible circumvents technical challenges in difficult-to-reach bleeding sites. The transparent hydrogel allows clear visualization of the surgical field and facilitates suture line assessment and revision. The shear-thinning and thixotropic properties of RADA16 allow its easy application through a narrow nozzle such as an endoscopic catheter. RADA16 hydrogels can fill tissue voids and do not swell so can be safely used in close proximity to pressure-sensitive tissues and in enclosed non-expandable regions. By definition, the synthetic peptide avoids potential microbiological contamination and immune responses that may occur with animal-, plant-, or mineral-derived topical hemostats. In vitro experiments, animal studies, and recent clinical experiences suggest that RADA16 nanofibrous hydrogels can act as surrogate extracellular matrices that support cellular behavior and interactions essential for wound healing and for tissue regenerative applications. In the future, the unique nature of RADA16 may also allow us to use it as a depot for precisely regulated drug and biopharmaceutical delivery.

Human Cerebrospinal Fluid Modulates Pathways Promoting Glioblastoma Malignancy

Glioblastoma (GBM) is the most common and devastating primary cancer of the central nervous system in adults. High grade gliomas are able to modify and respond to the brain microenvironment. When GBM tumors infiltrate the Subventricular zone (SVZ) they have a more aggressive clinical presentation than SVZ-distal tumors. We suggest that cerebrospinal fluid (CSF) contact contributes to enhance GBM malignant characteristics in these tumors. We evaluated the impact of human CSF on GBM, performing a transcriptome analysis on human primary GBM cells exposed to CSF to measure changes in gene expression profile and their clinical relevance on disease outcome. In addition we evaluated the proliferation and migration changes of CSF-exposed GBM cells in vitro and in vivo. CSF induced transcriptomic changes in pathways promoting cell malignancy, such as apoptosis, survival, cell motility, angiogenesis, inflammation, and glucose metabolism. A genetic signature extracted from the identified transcriptional changes in response to CSF proved to be predictive of GBM patient survival using the TCGA database. Furthermore, CSF induced an increase in viability, proliferation rate, and self-renewing capacity, as well as the migratory capabilities of GBM cells in vitro. In vivo, GBM cells co-injected with human CSF generated larger and more proliferative tumors compared to controls. Taken together, these results provide direct evidence that CSF is a key player in determining tumor growth and invasion through the activation of complex gene expression patterns characteristic of a malignant phenotype. These findings have diagnostic and therapeutic implications for GBM patients. The changes induced by CSF contact might play a role in the increased malignancy of SVZ-proximal GBM.

Creating Structured Hydrogel Microenvironments for Regulating Stem Cell Differentiation

The development of distinct biomimetic microenvironments for regulating stem cell behavior and bioengineering human tissues and disease models requires a solid understanding of cell-substrate interactions, adhesion, and its role in directing cell behavior, and other physico-chemical cues that drive cell behavior. In the past decade, innovative developments in chemistry, materials science, microfabrication, and associated technologies have given us the ability to manipulate the stem cell microenvironment with greater precision and, further, to monitor effector impacts on stem cells, both spatially and temporally. The influence of biomaterials and the 3D microenvironment's physical and biochemical properties on mesenchymal stem cell proliferation, differentiation, and matrix production are the focus of this review chapter. Mechanisms and materials, principally hydrogel and hydrogel composites for bone and cartilage repair that create "cell-supportive" and "instructive" biomaterials, are emphasized. We begin by providing an overview of stem cells, their unique properties, and their challenges in regenerative medicine. An overview of current fabrication strategies for creating instructive substrates is then reviewed with a focused discussion of selected fabrication methods with an emphasis on bioprinting as a critical tool in creating novel stem cell-based biomaterials. We conclude with a critical assessment of the current state of the field and offer our view on the promises and potential pitfalls of the approaches discussed.

Synthetic peptide hydrogels as 3D scaffolds for tissue engineering

The regeneration of tissues and organs poses an immense challenge due to the extreme complexity in the research work involved. Despite the tissue engineering approach being considered as a promising strategy for more than two decades, a key issue impeding its progress is the lack of ideal scaffold materials. Nature-inspired synthetic peptide hydrogels are inherently biocompatible, and its high resemblance to extracellular matrix makes peptide hydrogels suitable 3D scaffold materials. This review covers the important aspects of peptide hydrogels as 3D scaffolds, including mechanical properties, biodegradability and bioactivity, and the current approaches in creating matrices with optimized features. Many of these scaffolds contain peptide sequences that are widely reported for tissue repair and regeneration and these peptide sequences will also be discussed. Furthermore, 3D biofabrication strategies of synthetic peptide hydrogels and the recent advances of peptide hydrogels in tissue engineering will also be described to reflect the current trend in the field. In the final section, we will present the future outlook in the design and development of peptide-based hydrogels for translational tissue engineering applications.

L1CAM-ILK-YAP Mechanotransduction Drives Proliferative Activity of Epithelial Cells in Middle Ear Cholesteatoma

Middle-ear cholesteatoma (cholesteatoma) is a chronic otitis media with an enhanced proliferation of epithelial cells. Negative pressure in the middle ear is thought to be important for the etiology of cholesteatoma. However, the mechanism of cholesteatoma formation remains unclear. Integrin-linked protein kinase (ILK), an important modulator of actin cytoskeletal dynamics, interacts with extracellular matrix and results in the up-regulation of mechanotransduction effector Yes-associated protein (YAP). The L1 cell adhesion molecule (L1CAM) has recently been reported as an activator of the mechanotransduction effectors related to cell proliferation and migration. In this study, we demonstrated a stretch assay for middle-ear cultured cells and performed immunohistochemistry using antibodies against Ilk, Yap, and L1cam. The tympanic membrane was also analyzed within a new middle-ear negative-pressure animal model and human cholesteatoma tissues, using immunohistochemistry with antibodies against ILK, YAP, Ki-67, and L1CAM. The expression of cytoplasmic ILK and nuclear shift of YAP increased in the thickened epithelium of the tympanic membrane under a negative-pressure load and the cholesteatoma. The expression of L1CAM was detected in the stromal cells, which enhanced epithelial cell proliferation depending on ILK signaling events. In conclusion, we demonstrated the possibility that the stromal L1CAM and epithelial ILK-YAP signaling played an important role in epithelial growth under mechanotransduction in cholesteatoma formation.

Environmentally responsive hydrogels for repair of cardiovascular tissue

Cardiovascular diseases (CVDs) pose a serious threat to human health, which are characterized by high disability and mortality rate globally such as myocardial infarction (MI), atherosclerosis, and heart failure. Although stem cells transplantation and growth factors therapy are promising, their low survival rate and loss at the site of injury are major obstacles to this therapy. Recently, the development of hydrogel scaffold materials provides a new way to solve this problem, which have shown the potential to treat CVD. Among these scaffold materials, environmentally responsive hydrogels have great prospects in repairing the microenvironment of cardiovascular tissues and vascular regeneration. They provide a new method for the treatment of cardiovascular tissue repair and space-time control for the release of various therapeutic drugs, including small-molecule drugs, growth factors, and stem cells. Herein, this article reviews the occurrence and current treatment of CVD, as well as the repair of cardiovascular injury by several environmental responsive hydrogels systems currently used, mainly focusing on the delivery of growth factors or the application of cell therapy to revascularization. In addition, we will also discuss the enormous potential and personal perspectives of environmentally responsive hydrogels in cardiovascular repair.

A Cell-Free SDKP-Conjugated Self-Assembling Peptide Hydrogel Sufficient for Improvement of Myocardial Infarction

Biomaterials in conjunction with stem cell therapy have recently attracted attention as a new therapeutic approach for myocardial infarction (MI), with the aim to solve the delivery challenges that exist with transplanted cells. Self-assembling peptide (SAP) hydrogels comprise a promising class of synthetic biomaterials with cardiac-compatible properties such as mild gelation, injectability, rehealing ability, and potential for sequence modification. Herein, we developed an SAP hydrogel composed of a self-assembling gel-forming core sequence (RADA) modified with SDKP motif with pro-angiogenic and anti-fibrotic activity to be used as a cardioprotective scaffold. The RADA-SDKP hydrogel was intramyocardially injected into the infarct border zone of a rat model of MI induced by left anterior descending artery (LAD) ligation as a cell-free or a cell-delivering scaffold for bone marrow mesenchymal stem cells (BM-MSCs). The left ventricular ejection fraction (LVEF) was markedly improved after transplantation of either free hydrogel or cell-laden hydrogel. This cardiac functional repair coincided very well with substantially lower fibrotic tissue formation, expanded microvasculature, and lower inflammatory response in the infarct area. Interestingly, BM-MSCs alone or in combination with hydrogel could not surpass the cardiac repair effects of the SDKP-modified SAP hydrogel. Taken together, we suggest that the RADA-SDKP hydrogel can be a promising cell-free construct that has the capability for functional restoration in the instances of acute myocardial infarction (AMI) that might minimize the safety concerns of cardiac cell therapy and facilitate clinical extrapolation.

A Simple Injectable Moldable Hydrogel Assembled from Natural Glycyrrhizic Acid with Inherent Antibacterial Activity

Injectable low-molecular-weight hydrogels (LMWHs) from biocompatible materials have attracted much attention in biomedical applications because they can adapt any desired sizes and cavity shapes. Searching for simple, biocompatible injectable LMWHs owning inherent antibacterial activity without complicated chemical modification remains an open question to avoid the tedious synthesis/purification process and the easy bacterial infection of hydrogels in a moist environment. In this work, glycyrrhizic acid (GL), a naturally occurring compound, was found to form a stable transparent LMWH at 37 °C in physiological phosphate buffered saline (PBS) with nanoclusters as the microstructures. Moreover, this hydrogel exhibited great injectable and moldable properties. The antibacterial study showed that the growth of Gram-positive Staphylococcus aureus (S. aureus) could be completely inhibited by GL, whereas noneffect on Gram-negative Escherichia coli (E. coli) was observed. In addition, cell viability and hemolysis assay revealed that GL had good biocompatibility and hemocompatibility to mammalian cells because of its natural origin. Our simple biocompatible injectable moldable LMWH with inherent antibacterial ability has potential in the area of biomaterials and 3D bioprinting.

Regulation of DNA methylation levels in the process of oral mucosal regeneration in a rat oral ulcer model

DNA methylation is an important epigenetic mechanism for cellular maintenance. However, the methylation pattern and the key molecule regulated epigenetically in oral mucosal regeneration is unclear. In this study, we generated a rat oral ulcer model and investigated the cell proliferative activities and DNA methylation patterns immunohistochemically. We also performed immunohistochemical analysis of a regulator of epithelial stem/progenitor cell differentiation in the rat model. We demonstrated immunohistochemistry using antibodies for the molecules as follows: Ki-67, a marker of cellular proliferation; 5-methylcytosine (5-mC), a marker of DNA methylation; 5-hydroxymethylcytosine (5-hmC), a marker of DNA demethylation; Dnmt1, a maintenance DNA methyltransferase; Dnmt3a and Dnmt3b, de novo DNA methyltransferases; and Wnt5a, a regulator of stem/progenitor cell differentiation. In this model, re-epithelialization was completed at Day 4 after ulceration. Regenerating mucosal hypertrophy reached a peak at Day 5 and appeared normal at Day 14. Ki-67-positive cells increased at Day 2 and returned to normal at Day 6 after ulceration. The ratio of the expression level of 5-mC to 5-hmC declined at Day 5 and returned to normal at Day 6. The expression level of Dnmt1 had not changed compared to the normal control at every time point. On the other hand, the expression levels of Dnmt3a and Dnmt3b had decreased significantly at Day 5 and returned to normal at Day 6. Moreover, Wnt5a-positive cells increased at Day 5. In conclusion, oral mucosal regeneration was strictly regulated by DNA methylation. Moreover, Wnt5a might play a critical role in oral mucosal regeneration.

Enzyme-responsive progelator cyclic peptides for minimally invasive delivery to the heart post-myocardial infarction

Injectable biopolymer hydrogels have gained attention for use as scaffolds to promote cardiac function and prevent negative left ventricular (LV) remodeling post-myocardial infarction (MI). However, most hydrogels tested in preclinical studies are not candidates for minimally invasive catheter delivery due to excess material viscosity, rapid gelation times, and/or concerns regarding hemocompatibility and potential for embolism. We describe a platform technology for progelator materials formulated as sterically constrained cyclic peptides which flow freely for low resistance injection, and rapidly assemble into hydrogels when linearized by disease-associated enzymes. Their utility in vivo is demonstrated by their ability to flow through a syringe and gel at the site of MI in rat models. Additionally, synthetic functionalization enables these materials to flow through a cardiac injection catheter without clogging, without compromising hemocompatibility or cytotoxicity. These studies set the stage for the development of structurally dynamic biomaterials for therapeutic hydrogel delivery to the MI.

Microfluidic assembly of hydrogel-based immunogenic tumor spheroids for evaluation of anticancer therapies and biomarker release

Diffuse large B cell lymphoma (DLBCL), the most common subtype of Non-Hodgkin lymphoma, exhibits pathologic heterogeneity and a dynamic immunogenic tumor microenvironment (TME). However, the lack of preclinical in vitro models of DLBCL TME hinders optimal therapeutic screening. This study describes the development of an integrated droplet microfluidics-based platform for high-throughput generation of immunogenic DLBCL spheroids. The spheroids consist of three cell types (cancer, fibroblast and lymphocytes) in a novel hydrogel combination of alginate and puramatrix, which promoted cell adhesion and aggregation. This system facilitates dynamic analysis of cellular interaction, proliferation and therapeutic efficacy via spatiotemporal monitoring and secretome profiling. The immunomodulatory drug lenalidomide had direct anti-proliferative effect on activated B-cell like DLBCL spheroids and reduced several cytokines and other markers (e.g., CCL2, CCL3, CCL4, CD137 and ANG-1 levels) compared with untreated spheroids. Collectively, this novel spheroid platform will enable high-throughput anti-cancer therapeutic screening in a semi-automated manner.

Evaluation of YAP signaling in a rat tympanic membrane under a continuous negative pressure load and in human middle ear cholesteatoma

OBJECTIVES

Mechanotransduction plays an important role in cell-proliferative activities. Negative pressure in the middle ear is thought to be an important factor related to the etiology of acquired middle ear cholesteatoma. However, the correlation between negative pressure in the middle ear and the mechanism of middle ear cholesteatoma formation remains unclear. In this study, we investigated the expression of key molecules for mechanotransduction immunohistochemically.

METHODS

An immunohistochemical analysis was performed using anti-Wnt5a (a marker of alternative Wnt signaling), -Yes-associated protein (YAP) (a marker of mechanosensing) and -pYAP (phosphorylated YAP at Ser 127: inactivated YAP) antibody in the tympanic membrane (TM) under a negative pressure load and in human middle ear cholesteatoma tissues.

RESULTS

The number of Wnt5a-positive cells had increased and YAP nuclear translocation was observed in epithelial and mesenchymal cells in the pars flaccida (PF) of the TM under a negative-pressure load and in human middle ear cholesteatoma tissues.

CONCLUSIONS

We demonstrated that negative pressure in the middle ear might possibly induce cell proliferation PF of TM in response to mechanical force (mechanotransduction) through YAP nuclear translocation mediated by alternative Wnt signaling, thus affecting human middle ear cholesteatoma formation.

Panel 2: Anatomy (Eustachian Tube, Middle Ear, and Mastoid-Anatomy, Physiology, Pathophysiology, and Pathogenesis)

Objective In this report, we review the recent literature (ie, past 4 years) to identify advances in our understanding of the middle ear-mastoid-eustachian tube system. We use this review to determine whether the short-term goals elaborated in the last report were achieved, and we propose updated goals to guide future otitis media research. Data Sources PubMed, Web of Science, Medline. Review Methods The panel topic was subdivided, and each contributor performed a literature search within the given time frame. The keywords searched included middle ear, eustachian tube, and mastoid for their intersection with anatomy, physiology, pathophysiology, and pathology. Preliminary reports from each panel member were consolidated and discussed when the panel met on June 11, 2015. At that meeting, the progress was evaluated and new short-term goals proposed. Conclusions Progress was made on 13 of the 20 short-term goals proposed in 2011. Significant advances were made in the characterization of middle ear gas exchange pathways, modeling eustachian tube function, and preliminary testing of treatments for eustachian tube dysfunction. Implications for Practice In the future, imaging technologies should be developed to noninvasively assess middle ear/eustachian tube structure and physiology with respect to their role in otitis media pathogenesis. The new data derived from these structure/function experiments should be integrated into computational models that can then be used to develop specific hypotheses concerning otitis media pathogenesis and persistence. Finally, rigorous studies on medical or surgical treatments for eustachian tube dysfunction should be undertaken.

Supramolecular biofunctional materials

This review discusses supramolecular biofunctional materials, a novel class of biomaterials formed by small molecules that are held together via noncovalent interactions. The complexity of biology and relevant biomedical problems not only inspire, but also demand effective molecular design for functional materials. Supramolecular biofunctional materials offer (almost) unlimited possibilities and opportunities to address challenging biomedical problems. Rational molecular design of supramolecular biofunctional materials exploit powerful and versatile noncovalent interactions, which offer many advantages, such as responsiveness, reversibility, tunability, biomimicry, modularity, predictability, and, most importantly, adaptiveness. In this review, besides elaborating on the merits of supramolecular biofunctional materials (mainly in the form of hydrogels and/or nanoscale assemblies) resulting from noncovalent interactions, we also discuss the advantages of small peptides as a prevalent molecular platform to generate a wide range of supramolecular biofunctional materials for the applications in drug delivery, tissue engineering, immunology, cancer therapy, fluorescent imaging, and stem cell regulation. This review aims to provide a brief synopsis of recent achievements at the intersection of supramolecular chemistry and biomedical science in hope of contributing to the multidisciplinary research on supramolecular biofunctional materials for a wide range of applications. We envision that supramolecular biofunctional materials will contribute to the development of new therapies that will ultimately lead to a paradigm shift for developing next generation biomaterials for medicine.

Engineering β-sheet peptide assemblies for biomedical applications

Hydrogels have been widely studied in various biomedical applications, such as tissue engineering, cell culture, immunotherapy and vaccines, and drug delivery. Peptide-based nanofibers represent a promising new strategy for current drug delivery approaches and cell carriers for tissue engineering. This review focuses on the recent advances in the use of self-assembling engineered β-sheet peptide assemblies for biomedical applications. The applications of peptide nanofibers in biomedical fields, such as drug delivery, tissue engineering, immunotherapy, and vaccines, are highlighted. The current challenges and future perspectives for self-assembling peptide nanofibers in biomedical applications are discussed.

Growth of Self-Assembled Bio-Organic Nanomatrices for Skin Tissue Engineering — An in vitro Study

In this paper, we have developed self-assembled nanoscale assemblies that were prepared by conjugating furan-2-carboxylic acid-3-aminopropyl amide with the short peptide sequence Gly-His (abbreviated Gly-His-FCAP). To mimic the extracellular matrix of mammalian fibroblasts and keratinocytes, the assemblies were then conjugated with Type I collagen. We then integrated the collagen bound Gly-His-FCAP assemblies with a short peptide sequence derived from salamander skin into the nanoscale assemblies for the first time to impart regenerative and wound healing properties to the composites. The antioxidant, antimicrobial and biodegradable properties were examined and results indicate that the nanocomposites displayed antioxidant properties as displayed by 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The biodegradability was found to be gradual. The nanocomposites were also found to inhibit the growth of the fungus Rhizopus sporangia over an 18[Formula: see text]h growth period. As proof of concept, to demonstrate the development of three-dimensional (3D) engineered skin in vitro, 3D printed PLA scaffolds of 2.5[Formula: see text]mm thickness were submerged in media containing nanocomposites and co-cultures of dermal fibroblasts with epidermal keratinocytes mimicking three dimensional skin substitute was examined. Our results indicated that the nanocomposites adhered to and supported cell proliferation and mimicked the components of skin and may have potential applications in skin tissue regeneration.

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping address fundamental questions about the mechanisms or the consequences of the self-assembly of molecules, including low molecular weight ones. Finally, we provide a perspective on supramolecular hydrogelators. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring supramolecular hydrogelators as molecular biomaterials for addressing the societal needs at various frontiers.

Self-Assembling Peptide Nanofibrous Hydrogel on Immediate Hemostasis and Accelerative Osteosis

The use of local agents to achieve hemostasis of bone that does not interfere with repair and recovery is a complex and emergency subject in surgery. In this study, the dual functional biodegradable self-assembling nanopeptide (SAP) RADA16-I was synthesized by solid phase synthesis and was shown to exhibit immediate hemostasis and accelerative osteosis. The RADA16-I showed good performance as a hemostatic agent, which was investigated by comparison with the effects of bone wax in the ilium bone defect model of New Zealand rabbits. The RADA16-I exhibited efficient function of bone regeneration in both radiographic analysis and histological examination, while the bone wax inhibited osteogenesis. Moreover, in in vivo experiment, the RADA16-I was shown to exhibit excellent biocompatibility, while the group with bone wax showed a severe inflammatory response at the interface with bone. Thus, the RADA16-I is proven to be an excellent biocompatible material with effective dual function of hemostasis and osteosis.

Peptide gel in a scaffold as a composite matrix for endothelial cells

The performance of a composite environment with human umbilical vein endothelial cells (HUVECs) has been studied to provide an in vitro proof of concept of their potential of being easily vascularized. These cells were seeded in 1 mm thick scaffolds whose pores had been filled with a self-assembling peptide gel, seeking to improve cell adhesion, and viability of these very sensitive cells. The combination of the synthetic elastomer poly(ethyl acrylate), PEA, scaffold and the RAD16-I peptide gel provides cells with a friendly ECM-like environment inside a mechanically resistant structure. Immunocytochemistry, flow cytometry and scanning electron microscopy were used to evaluate the cell cultures. The presence of the self-assembling peptide filling the pores of the scaffolds resulted in a truly 3D nanoscale context mimicking the extracellular matrix environment, and led to increased cells survival, proliferation as well as developed cell-cell contacts. The combined system consisting of PEA scaffolds and RAD16-I, is a very interesting approach as seems to enhance endothelization, which is the first milestone to achieve vascularized constructs.

Peptide-directed self-assembly of functionalized polymeric nanoparticles. Part II: effects of nanoparticle composition on assembly behavior and multiple drug loading ability

Peptide-functionalized polymeric nanoparticles were designed and self-assembled into continuous nanoparticle fibers and three-dimensional scaffolds via ionic complementary peptide interaction. Different nanoparticle compositions can be designed to be appropriate for each desired drug, so that the release of each drug is individually controlled and the simultaneous sustainable release of multiple drugs is achieved in a single scaffold. A self-assembled scaffold membrane was incubated with NIH3T3 fibroblast cells in a culture dish that demonstrated non-toxicity and non-inhibition on cell proliferation. This type of nanoparticle scaffold combines the advantages of peptide self-assembly and the versatility of polymeric nanoparticle controlled release systems for tissue engineering.

Applications of self-assembling peptide scaffolds in regenerative medicine: the way to the clinic

Peptides that self-assemble into well-defined nanofibrous networks provide a prominent alternative to traditional biomaterials for fabricating scaffolds for use in regenerative medicine and other biomedical applications. Such scaffolds can be generated by decorating a peptide backbone with other bioactives such as cell specific adhesion peptides, growth factors and enzyme cleavable sequences. They can be designed to mimic the three-dimensional (3D) structural features of native ECM and can therefore also provide insight into the ECM-cell interactions needed for development of scaffolds that can serve as regeneration templates for specific target tissues or organs. This review highlights the potential application of self-assembling peptides in regenerative medicine.

The neutral self-assembling peptide hydrogel SPG-178 as a topical hemostatic agent

Conventional self-assembling peptide hydrogels are effective as topical hemostatic agents. However, there is a possibility to harm living tissues due to their low pH. The aim of the present study was to demonstrate the efficacy of SPG-178, a neutral self-assembling peptide hydrogel, as a topical hemostatic agent. First, we measured the bleeding duration of incisions made on rat livers after application of SPG-178 (1.0% w/v), SPG-178 (1.5% w/v), RADA16 (1.0% w/v), and saline (n = 12/group). Second, we observed the bleeding surfaces by transmission electron microscopy immediately after hemostasis. Third, we measured the elastic and viscous responses (G' and G″, respectively) of the hydrogels using a rheometer. Our results showed that bleeding duration was significantly shorter in the SPG-178 group than in the RADA16 group and that there were no significant differences in transmission electron microscopy findings between the groups. The greater the G' value of a hydrogel, the shorter was the bleeding duration. We concluded that SPG-178 is more effective and has several advantages: it is non-biological, transparent, nonadherent, and neutral and can be sterilized by autoclaving.

Influence of continuous negative pressure in the rat middle ear

OBJECTIVES/HYPOTHESIS

High negative pressure in the middle ear was thought to be closely related to the etiology of retraction-type cholesteatoma. Recently, it has been detected that mechanical forces are important factors in epithelial turnover and affect cytoskeletal remodeling. Continuous negative pressure in the middle ear may possibly accelerate the proliferation and differentiation of epithelial cells of the tympanic membrane.

STUDY DESIGN

Animal experimental study.

METHODS

Eleven adult male Sprague-Dawley rats were used, and continuous negative pressure was loaded by connecting a catheter from the rat's middle ear to the supply route of an implantable microinfusion pump, iPRECIO. At 7 days after implantation of the device, an otoendoscopic examination and micro-computed tomography (CT) analysis of the temporal bone were performed; the temporal bones were then collected for histological and immunohistochemical analysis. The degree of proliferation and differentiation of epithelial cells of the tympanic membrane was investigated immunohistochemically using the anti-cytokeratin-5 and anti-cytokeratin-10 antibodies.

RESULTS

Otoendoscopic examination revealed retraction of the pars flaccida in all of the ears under negative pressure. In the micro-CT analysis, soft tissue density area in the hypotympanum was observed in all ears under negative pressure. Histological analysis revealed thickened epithelium of the pars flaccida. In this region, the thickness of layers with cytokeratin-5-positive cells and cytokeratin-10-positive cells were increased.

CONCLUSIONS

Continuous negative pressure in the middle ear can lead to thickening of the epithelium of the pars flaccida, and may accelerate the proliferation and differentiation of epithelial cells.

Self-assembling peptide of D-amino acids boosts selectivity and antitumor efficacy of 10-hydroxycamptothecin

D-peptides, which consist of D-amino acids and can resist the hydrolysis catalyzed by endogenous peptidases, are one of the promising candidates for construction of peptide materials with enhanced biostability in vivo. In this paper, we report on a self-assembling supramolecular nanostructure of D-amino acid-based peptide Nap-G(D)F(D)F(D)YGRGD (D-fiber, (D)F meant D-phenylalanine, (D)Y meant D-tyrosine), which were used as carriers for 10-hydroxycamptothecin (HCPT). Transmission electron microscopy observations demonstrated the filamentous morphology of the HCPT-loaded peptides (d-fiber-HCPT). The better selectivity and antitumor activity of D-fiber-HCPT than L-fiber-HCPT were found in the in vitro and in vivo antitumor studies. These results highlight that this model D-fiber system holds great promise as vehicles of hydrophobic drugs for cancer therapy.