Vascularization strategies in tissue engineering approaches for soft tissue repair

The role of extracellular matrix hydrogels and adipose-derived stromal cells in soft tissue vascularization - A systematic review

Decellularized extracellular matrix (dECM) hydrogels loaded with adipose-derived stromal cells (ASC) or their conditioned medium (ASC CM) present a promising and versatile treatment approach for tissue vascularization and regeneration. These hydrogels are easy to produce, store, personalize, manipulate, and deliver to the target tissue. This literature review aimed to investigate the applications of dECM hydrogels with ASC or ASC CM for in vivo tissue vascularization. Fourteen experimental studies have been reviewed using vessel density as the primary outcome parameter for in vivo vascularization. The studies consistently reported an increased efficacy in augmenting angiogenesis by the ASC or ASC CM-loaded hydrogels compared to untreated controls. However, this systematic review shows the need to standardize procedures and characterization, particularly of the final administered product(s). The findings from these experimental studies highlight the potential of dECM hydrogel with ASC or ASC CM in novel tissue regeneration and regenerative medicine applications.

Enhancing bone repair through improved angiogenesis and osteogenesis using mesoporous silica nanoparticle-loaded Konjac glucomannan-based interpenetrating network scaffolds

We have fabricated and characterized novel bioactive nanocomposite interpenetrating polymer network (IPN) scaffolds to treat bone defects by loading mesoporous silica nanoparticles (MSNs) into blends of Konjac glucomannan, polyvinyl alcohol, and polycaprolactone. By loading MSNs, we developed a porous nanocomposite scaffold with mechanical strengths comparable to cancellous bone. In vitro cell culture studies proved the cytocompatibility of the nanocomposite scaffolds. RT-PCR studies confirmed that these scaffolds significantly upregulated major osteogenic markers. The in vivo chick chorioallantoic membrane (CAM) assay confirmed the proangiogenic activity of the nanocomposite IPN scaffolds. In vivo studies were performed using Wistar rats to evaluate the scaffolds' compatibility, osteogenic activity, and proangiogenic properties. Liver and renal function tests confirmed that these scaffolds were nontoxic. X-ray and μ-CT results show that the bone defects treated with the nanocomposite scaffolds healed at a much faster rate compared to the untreated control and those treated with IPN scaffolds. H&E and Masson's trichrome staining showed angiogenesis near the newly formed bone and the presence of early-stage connective tissues, fibroblasts, and osteoblasts in the defect region at 8 weeks after surgery. Hence, these advantageous physicochemical and biological properties confirm that the nanocomposite IPN scaffolds are ideal for treating bone defects.

Uncovering the Embryonic Origins of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a severe degenerative muscle disease caused by mutations in the DMD gene, which encodes dystrophin. Despite its initial description in the late 19th century by French neurologist Guillaume Duchenne de Boulogne, and identification of causal DMD genetic mutations in the 1980s, therapeutics remain challenging. The current standard of care is corticosteroid treatment, which delays the progression of muscle dysfunction but is associated with significant adverse effects. Emerging therapeutic approaches, including AAV-mediated gene transfer, CRISPR gene editing, and small molecule interventions, are under development but face considerable obstacles. Although DMD is viewed as a progressive muscle disease, muscle damage and abnormal molecular signatures are already evident during fetal myogenesis. This early onset of pathology suggests that the limited success of current therapies may partly be due to their administration after aberrant embryonic myogenesis has occurred in the absence of dystrophin. Consequently, identifying optimal therapeutic strategies and intervention windows for DMD may depend on a better understanding of the earliest DMD disease mechanisms. As newer techniques are applied, the field is gaining increasingly detailed insights into the early muscle developmental abnormalities in DMD. A comprehensive understanding of the initial events in DMD pathogenesis and progression will facilitate the generation and testing of effective therapeutic interventions.

Ultrasound-Mediated Antibiotic Delivery to In Vivo Biofilm Infections: A Review

Bacterial biofilms are a significant concern in various medical contexts due to their resilience to our immune system as well as antibiotic therapy. Biofilms often require surgical removal and frequently lead to recurrent or chronic infections. Therefore, there is an urgent need for improved strategies to treat biofilm infections. Ultrasound-mediated drug delivery is a technique that combines ultrasound application, often with the administration of acoustically-active agents, to enhance drug delivery to specific target tissues or cells within the body. This method involves using ultrasound waves to assist in the transportation or activation of medications, improving their penetration, distribution, and efficacy at the desired site. The advantages of ultrasound-mediated drug delivery include targeted and localized delivery, reduced systemic side effects, and improved efficacy of the drug at lower doses. This review scrutinizes recent advances in the application of ultrasound-mediated drug delivery for treating biofilm infections, focusing on in vivo studies. We examine the strengths and limitations of this technology in the context of wound infections, device-associated infections, lung infections and abscesses, and discuss current gaps in knowledge and clinical translation considerations.

Vascular Perspectives of the Midfacial Superficial Musculoaponeurotic System

Objectives: Presently, data on the vascularization of the superficial musculoaponeurotic system of the face (SMAS) are lacking. Thus, the present study aimed to provide new conclusive data about the topography, density, and relationship of the SMAS blood vessels with other components, namely, the fibrous connective tissue and muscles. Methods: The study included a control lot of 42 cases from the archive of the radiology department. In this group, nuclear magnetic resonance angiography (MRA) was performed in order to identify the main sources of vascular supply. In the second group, tissue samples were collected from the midfacial region of 45 patients from the Oro-Maxillo-Facial and Plastic and Reconstructive Surgery clinics of 'St. Spiridon' County Clinical Emergency Hospital, Iasi. These patients received surgery for excision of tumoral formations that did not involve SMAS components. These samples underwent micro-CT analysis, hematoxylin and eosin (HE) staining, as well as immunohistochemical (IHC) staining for collagen type III, muscle tissue, and the vascular endothelium. Results: We discovered the particular way in which the SMAS components interrelate with vascularization and the regional differences between them. We have discovered a new vascular network specific to the SMAS, highlighted by both the micro-CT technique and microscopy on slides with special IHC staining. Significant differences were observed in the topographic arrangement, density, and relationships of the microscopic vasculature across midfacial regions. IHC staining provided morphological and functional information about the structure and vascularization of SMAS. Conclusions: The MRA technique could not detect the structural blood vessels of the SMAS and other methods for their in vivo visualization must be sought. The blood vessels of the SMAS mainly follow the topography of the muscle fibers. From the SMAS layer where they are found, the distribution branches reach the stroma of the region and the hypoderm. Our data can contribute to the development of surgical techniques tailored to each individual patient, as well as the enhancement of methods for stimulating cutaneous angiogenesis, improving scarring in this region, and advancing biotissue engineering techniques.

Advances in, and prospects of, 3D preclinical models for skin drug discovery

The skin has an important role in regulating homeostasis and protecting the body from endogenous and exogenous microenvironments. Although 3D models for drug discovery have been extensively studied, there is a growing demand for more advanced 3D skin models to enhance skin research. The use of these advanced skin models holds promise across domains such as cosmetics, skin disease treatments, and toxicity testing of new therapeutics. Recent advances include the development of skin-on-a-chip, spheroids, reconstructed skin, organoids, and computational approaches, including quantitative structure-activity relationship (QSAR) and quantitative structure-property relationship (QSPR) research. These innovations are bridging the gap between traditional 2D and advanced 3D models, moving progress from research to clinical applications. In this review, we highlight in vitro and computational skin models with advanced drug discovery for skin-related applications.

Fabricating Multiphasic Angiogenic Scaffolds Using Amyloid/Roxadustat-Assisted High-Temperature Protein Printing

Repairing multiphasic defects is cumbersome. This study presents new soft and hard scaffold designs aimed at facilitating the regeneration of multiphasic defects by enhancing angiogenesis and improving cell attachment. Here, the nonimmunogenic, nontoxic, and cost-effective human serum albumin (HSA) fibril (HSA-F) was used to fabricate thermostable (up to 90 °C) and hard printable polymers. Additionally, using a 10.0 mg/mL HSA-F, an innovative hydrogel was synthesized in a mixture with 2.0% chitosan-conjugated arginine, which can gel in a cell-friendly and pH physiological environment (pH 7.4). The presence of HSA-F in both hard and soft scaffolds led to an increase in significant attachment of the scaffolds to the human periodontal ligament fibroblast (PDLF), human umbilical vein endothelial cell (HUVEC), and human osteoblast. Further studies showed that migration (up to 157%), proliferation (up to 400%), and metabolism (up to 210%) of these cells have also improved in the direction of tissue repair. By examining different in vitro and ex ovo experiments, we observed that the final multiphasic scaffold can increase blood vessel density in the process of per-vascularization as well as angiogenesis. By providing a coculture environment including PDLF and HUVEC, important cross-talk between these two cells prevails in the presence of roxadustat drug, a proangiogenic in this study. In vitro and ex ovo results demonstrated significant enhancements in the angiogenic response and cell attachment, indicating the effectiveness of the proposed design. This approach holds promise for the regeneration of complex tissue defects by providing a conducive environment for vascularization and cellular integration, thus promoting tissue healing.

Navigating the challenges and exploring the perspectives associated with emerging novel biomaterials

The field of biomaterials is a continuously evolving interdisciplinary field encompassing biological sciences, materials sciences, chemical sciences, and physical sciences with a multitude of applications realized every year. However, different biomaterials developed for different applications have unique challenges in the form of biological barriers, and addressing these challenges simultaneously is also a challenge. Nevertheless, immense progress has been made through the development of novel materials with minimal adverse effects such as DNA nanostructures, specific synthesis strategies based on supramolecular chemistry, and modulating the shortcomings of existing biomaterials through effective functionalization techniques. This review discusses all these aspects of biomaterials, including the challenges at each level of their development and application, proposed countermeasures for these challenges, and some future directions that may have potential benefits.

Enhancing Osteoblast Differentiation from Adipose-Derived Stem Cells Using Hydrogels and Photobiomodulation: Overcoming In Vitro Limitations for Osteoporosis Treatment

Osteoporosis represents a widespread and debilitating chronic bone condition that is increasingly prevalent globally. Its hallmark features include reduced bone density and heightened fragility, which significantly elevate the risk of fractures due to the decreased presence of mature osteoblasts. The limitations of current pharmaceutical therapies, often accompanied by severe side effects, have spurred researchers to seek alternative strategies. Adipose-derived stem cells (ADSCs) hold considerable promise for tissue repair, albeit they encounter obstacles such as replicative senescence in laboratory conditions. In comparison, employing ADSCs within three-dimensional (3D) environments provides an innovative solution, replicating the natural extracellular matrix environment while offering a controlled and cost-effective in vitro platform. Moreover, the utilization of photobiomodulation (PBM) has emerged as a method to enhance ADSC differentiation and proliferation potential by instigating cellular stimulation and facilitating beneficial performance modifications. This literature review critically examines the shortcomings of current osteoporosis treatments and investigates the potential synergies between 3D cell culture and PBM in augmenting ADSC differentiation towards osteogenic lineages. The primary objective of this study is to assess the efficacy of combined 3D environments and PBM in enhancing ADSC performance for osteoporosis management. This research is notably distinguished by its thorough scrutiny of the existing literature, synthesis of recent advancements, identification of future research trajectories, and utilization of databases such as PubMed, Scopus, Web of Science, and Google Scholar for this literature review. Furthermore, the exploration of biomechanical and biophysical stimuli holds promise for refining treatment strategies. The future outlook suggests that integrating PBM with ADSCs housed within 3D environments holds considerable potential for advancing bone regeneration efforts. Importantly, this review aspires to catalyse further advancements in combined therapeutic strategies for osteoporosis regeneration.

Enhancing angiogenesis in peri-implant soft tissue with bioactive silk fibroin microgroove coatings on zirconia surfaces

Zirconia abutments and restorations have improved the aesthetic appeal of implant restoration, yet peri-implantitis poses a significant threat to long-term success. The soft tissue surrounding implants is a crucial biological barrier against inflammation and subsequent bone loss. Peri-implantitis, akin to periodontitis, progresses rapidly and causes extensive tissue damage. Variations in tissue structure significantly influence disease progression, particularly the lower vascular density in peri-implant connective tissue, compromising its ability to combat infection and provide essential nutrients. Blood vessels within this tissue are vital for healing, with angiogenesis playing a key role in immune defense and tissue repair. Enhancing peri-implant soft tissue angiogenesis holds promise for tissue integration and inflammation control. Microgroove surfaces have shown potential in guiding vessel growth, but using subtractive technologies to carve microgrooves on zirconia surfaces may compromise mechanical integrity. In this study, we utilized inkjet printing to prepare bioactive silk fibroin microgrooves (SFMG) coating with different sizes on zirconia surfaces. SFMG coating, particularly with 90 µm width and 10 µm depth, effectively directed human umbilical vein endothelial cells (HUVECs) along microgrooves, promoting their proliferation, migration, and tube formation. The expression of vascular endothelial growth factor A and fibroblast growth factor in HUVECs growing on SFMG coating was upregulated. Additionally, the SFMG coating activated the PI3K-AKT pathway and increased glycolytic enzyme gene expression in HUVECs. In conclusion, SFMG coating enhances HUVEC growth and angiogenesis potential by activating the PI3K-AKT pathway and glycolysis, showing promise for improving tissue integration and mitigating inflammation in zirconia abutments and restorations.

Breathing new life into tissue engineering: exploring cutting-edge vascularization strategies for skin substitutes

Tissue-engineered skin substitutes (TESS) emerged as a new therapeutic option to improve skin transplantation. However, establishing an adequate and rapid vascularization in TESS is a critical factor for their clinical application and successful engraftment in patients. Therefore, several methods have been applied to improve the vascularization of skin substitutes including (i) modifying the structural and physicochemical properties of dermal scaffolds; (ii) activating biological scaffolds with growth factor-releasing systems or gene vectors; and (iii) developing prevascularized skin substitutes by loading scaffolds with capillary-forming cells. This review provides a detailed overview of the most recent and important developments in the vascularization strategies for skin substitutes. On the one hand, we present cell-based approaches using stem cells, microvascular fragments, adipose tissue derived stromal vascular fraction, endothelial cells derived from blood and skin as well as other pro-angiogenic stimulation methods. On the other hand, we discuss how distinct 3D bioprinting techniques and microfluidics, miRNA manipulation, cell sheet engineering and photosynthetic scaffolds like GelMA, can enhance skin vascularization for clinical applications. Finally, we summarize and discuss the challenges and prospects of the currently available vascularization techniques that may serve as a steppingstone to a mainstream application of skin tissue engineering.

Enhancing the Repair of Substantial Volumetric Muscle Loss by Creating Different Levels of Blood Vessel Networks Using Pre-Vascularized Nerve Hydrogel Implants

Volumetric muscle loss (VML), a severe muscle tissue loss from trauma or surgery, results in scarring, limited regeneration, and significant fibrosis, leading to lasting reductions in muscle mass and function. A promising approach for VML recovery involves restoring vascular and neural networks at the injury site, a process not extensively studied yet. Collagen hydrogels have been investigated as scaffolds for blood vessel formation due to their biocompatibility, but reconstructing blood vessels and guiding innervation at the injury site is still difficult. In this study, collagen hydrogels with varied densities of vessel-forming cells are implanted subcutaneously in mice, generating pre-vascularized hydrogels with diverse vessel densities (0-145 numbers/mm2) within a week. These hydrogels, after being transplanted into muscle injury sites, are assessed for muscle repair capabilities. Results showed that hydrogels with high microvessel densities, filling the wound area, effectively reconnected with host vasculature and neural networks, promoting neovascularization and muscle integration, and addressing about 63% of the VML.

Improving the mechanical and biological functions of cell sheet constructs: The interplay of human-derived periodontal ligament stem cells, endothelial cells and plasma rich in growth factors

OBJECTIVE

The aim of this study was to produce and characterize triple-layered cell sheet constructs with varying cell compositions combined or not with the fibrin membrane scaffold obtained by the technology of Plasma Rich in Growth Factors (mPRGF).

MATERIALS AND METHODS

Human primary cultures of periodontal ligament stem cells (hPDLSCs) were isolated, and their stemness nature was evaluated. Three types of triple-layered composite constructs were generated, composed solely of hPDLSCs or combined with human umbilical vein endothelial cells (HUVECs), either as a sandwiched endothelial layer or as coculture sheets of both cell phenotypes. These three triple-layered constructs were also manufactured using mPRGF as cell sheets' support. Necrosis, glucose consumption, secretion of extracellular matrix proteins and synthesis of proangiogenic factors were determined. Histological evaluations and proteomic analyses were also performed.

RESULTS

The inclusion of HUVECs did not clearly improve the properties of the multilayered constructs and yet hindered their optimal conformation. The presence of mPRGF prevented the shrinkage of cell sheets, stimulated the metabolic activity and increased the matrix synthesis. At the proteome level, mPRGF conferred a dramatic advantage to the hPDLSC constructs in their ability to provide a suitable environment for tissue regeneration by inducing the expression of proteins necessary for bone morphogenesis and cellular proliferation.

CONCLUSIONS

hPDLSCs' triple-layer construct onto mPRGF emerges as the optimal structure for its use in regenerative therapeutics.

CLINICAL RELEVANCE

These results suggest the suitability of mPRGF as a promising tool to support cell sheet formation by improving their handling and biological functions.

Multifunctional MXene-Based Platforms for Soft and Bone Tissue Regeneration and Engineering

MXenes and their composites hold great promise in the field of soft and bone tissue regeneration and engineering (TRE). However, there are challenges that need to be overcome, such as ensuring biocompatibility and controlling the morphologies of MXene-based scaffolds. The future prospects of MXenes in TRE include enhancing biocompatibility through surface modifications, developing multifunctional constructs, and conducting in vivo studies for clinical translation. The purpose of this perspective about MXenes and their composites in soft and bone TRE is to critically evaluate their potential applications and contributions in this field. This perspective aims to provide a comprehensive analysis of the challenges, advantages, limitations, and future prospects associated with the use of MXenes and their composites for soft and bone TRE. By examining the existing literature and research, the review seeks to consolidate the current knowledge and highlight the key findings and advancements in MXene-based TRE. It aims to contribute to the understanding of MXenes' role in promoting soft and bone TRE, addressing the challenges faced in terms of biocompatibility, morphology control, and tissue interactions.

Influencing Endothelial Cells' Roles in Inflammation and Wound Healing Through Nucleic Acid Delivery

Tissue engineering and wound-healing interventions are often designed for use in diseased and inflamed environments. In this space, endothelial cells (ECs) are crucial regulators of inflammation and healing, as they are the primary contact for recruitment of immune cells, as well as production of proinflammatory cytokines, which can stimulate or reduce inflammation. Alternatively, proliferation and spreading of ECs result in the formation of new vascular tissue or repair of damaged tissue, both critical for wound healing. Targeting ECs with specific nucleic acids could reduce unwanted inflammation or promote tissue regeneration as needed, which are two large issues involved in many regenerative medicine goals. Polymeric delivery systems are tools that can control the delivery of nucleic acids and prolong their effects. This review describes the use of polymeric vehicles for the delivery of nucleic acids to ECs for tissue engineering. Impact statement Tissue engineering is a rapidly growing field that has the potential to resolve many disease states and improve the quality of life of patients. In some applications, tissue-engineered strategies or constructs are developed to rebuild spaces damaged by disease or degeneration. To rebuild the native tissue, these constructs may need to interact with unwanted immune activity and cells. Various immune cells are often the focus of therapies as they are critical players in the inflammatory response; however, endothelial cells are also an extremely important and promising target in these cases. In addition, controlled delivery of specific-acting molecules, such as nucleic acids, is of growing interest for the regeneration and health of a variety of different tissues. It is important to understand what has been done and the potential of these targets and therapeutics for future investigation and advancements in tissue engineering.

Generating human skeletal myoblast spheroids for vascular myogenic tissue engineering

Engineered myogenic microtissues derived from human skeletal myoblasts offer unique opportunities for varying skeletal muscle tissue engineering applications, such asin vitrodrug-testing and disease modelling. However, more complex models require the incorporation of vascular structures, which remains to be challenging. In this study, myogenic spheroids were generated using a high-throughput, non-adhesive micropatterned surface. Since monoculture spheroids containing human skeletal myoblasts were unable to remain their integrity, co-culture spheroids combining human skeletal myoblasts and human adipose-derived stem cells were created. When using the optimal ratio, uniform and viable spheroids with enhanced myogenic properties were achieved. Applying a pre-vascularization strategy, through addition of endothelial cells, resulted in the formation of spheroids containing capillary-like networks, lumina and collagen in the extracellular matrix, whilst retaining myogenicity. Moreover, sprouting of endothelial cells from the spheroids when encapsulated in fibrin was allowed. The possibility of spheroids, from different maturation stages, to assemble into a more large construct was proven by doublet fusion experiments. The relevance of using three-dimensional microtissues with tissue-specific microarchitecture and increased complexity, together with the high-throughput generation approach, makes the generated spheroids a suitable tool forin vitrodrug-testing and human disease modeling.

Evaluating the Efficacy of Dedifferentiated Fat Cells (DFATs) vs Adipose-Derived Stem Cells (ASCs) in Enhancing the Viability of Fat Grafts

BACKGROUND

Enhancing graft fat survival remains a paramount challenge in autologous fat transplantation surgeries. Dedifferentiated fat cells (DFATs) and adipose-derived stem cells (ASCs) represent 2 pivotal cells with potential to improve fat graft survival rates.

OBJECTIVES

In this study we aimed to compare the effectiveness of DFATs and ASCs in promoting fat graft survival, emphasizing their adipogenic and angiogenic capabilities.

METHODS

Both in vitro and in vivo experiments were conducted. In vitro assessments compared adipogenesis, angiogenesis, osteogenesis, chondrogenesis, cell migration abilities, and surface markers. For in vivo evaluation, a cell-assisted lipotransfer animal model was employed to gauge graft volume retention and histological morphology. Analysis techniques included hematoxylin and eosin staining, Western blotting, and real-time polymerase chain reaction.

RESULTS

In vitro findings suggested a slight superiority of DFATs in adipogenesis and angiogenesis compared to ASCs. In vivo tests demonstrated both cell types surpassed the control in terms of graft volume retention, with the DFATs group marginally outperforming in retention rates and the ASC group presenting a slightly enhanced graft tissue structure.

CONCLUSIONS

Our study underscores the distinct advantages of DFATs and ASCs in bolstering fat graft survival, offering potentially novel insights for plastic surgeons aiming to elevate fat graft survival rates.

Bioassembly of hemoglobin-loaded photopolymerizable spheroids alleviates hypoxia-induced cell death

The delivery of oxygen within tissue engineered constructs is essential for cell survivability; however, achieving this within larger biofabricated constructs poses a significant challenge. Efforts to overcome this limitation often involve the delivery of synthetic oxygen generating compounds. The application of some of these compounds is problematic for the biofabrication of living tissues due to inherent issues such as cytotoxicity, hyperoxia and limited structural stability due to oxygen inhibition of radical-based crosslinking processes. This study aims to develop an oxygen delivering system relying on natural-derived components which are cytocompatible, allow for photopolymerization and advanced biofabrication processes, and improve cell survivability under hypoxia (1% O2). We explore the binding of human hemoglobin (Hb) as a natural oxygen deposit within photopolymerizable allylated gelatin (GelAGE) hydrogels through the spontaneous complex formation of Hb with negatively charged biomolecules (heparin, hyaluronic acid, and bovine serum albumin). We systematically study the effect of biomolecule inclusion on cytotoxicity, hydrogel network properties, Hb incorporation efficiency, oxygen carrying capacity, cell viability, and compatibility with 3D-bioassembly processes within melt electrowritten (MEW) scaffolds. All biomolecules were successfully incorporated within GelAGE hydrogels, displaying controllable mechanical properties and cytocompatibility. Results demonstrated efficient and tailorable Hb incorporation within GelAGE-Heparin hydrogels. The developed system was compatible with microfluidics and photopolymerization processes, allowing for the production of GelAGE-Heparin-Hb spheres. Hb-loaded spheres were assembled into MEW polycaprolactone scaffolds, significantly increasing the local oxygen levels. Ultimately, cells within Hb-loaded constructs demonstrated good cell survivability under hypoxia. Taken together, we successfully developed a hydrogel system that retains Hb as a natural oxygen deposit post-photopolymerization, protecting Hb from free-radical oxidation while remaining compatible with biofabrication of large constructs. The developed GelAGE-Heparin-Hb system allows for physoxic oxygen delivery and thus possesses a vast potential for use across broad tissue engineering and biofabrication strategies to help eliminate cell death due to hypoxia.

Adipose-Derived Stem Cells: Angiogenetic Potential and Utility in Tissue Engineering

Adipose tissue (AT) is a large and important energy storage organ as well as an endocrine organ with a critical role in many processes. Additionally, AT is an enormous and easily accessible source of multipotent cell types used in our day for all types of tissue regeneration. The ability of adipose-derived stem cells (ADSCs) to differentiate into other types of cells, such as endothelial cells (ECs), vascular smooth muscle cells, or cardiomyocytes, is used in tissue engineering in order to promote/stimulate the process of angiogenesis. Being a key for future successful clinical applications, functional vascular networks in engineered tissue are targeted by numerous in vivo and ex vivo studies. The article reviews the angiogenic potential of ADSCs and explores their capacity in the field of tissue engineering (TE).

4-Axis 3D-Printed Tubular Biomaterials Imitating the Anisotropic Nanofiber Orientation of Porcine Aortae

Many of the peculiar properties of the vasculature are related to the arrangement of anisotropic proteinaceous fibers in vessel walls. Understanding and imitating these arrangements can potentially lead to new therapies for cardiovascular diseases. These can be pre-surgical planning, for which patient-specific ex vivo anatomical models for endograft testing are of interest. Alternatively, therapies can be based on tissue engineering, for which degradable in vitro cell growth substrates are used to culture replacement parts. In both cases, materials are desirable that imitate the biophysical properties of vessels, including their tubular shapes and compliance. This work contributes to these demands by offering methods for the manufacturing of anisotropic 3D-printed nanofibrous tubular structures that have similar biophysical properties as porcine aortae, that are biocompatible, and that allow for controlled nutrient diffusion. Tubes of various sizes with axial, radial, or alternating nanofiber orientation along the blood flow direction are manufactured by a customized method. Blood pressure-resistant, compliant, stable, and cell culture-compatible structures are obtained, that can be degraded in vitro on demand. It is suggested that these healthcare materials can contribute to the next generation of cardiovascular therapies of ex vivo pre-surgical planning or in vitro cell culture.

Mechanism and application of β-adrenoceptor blockers in soft tissue wound healing

Soft tissue damage stimulates sympathetic nerves to release large amounts of catecholamine hormones which bind to β-adrenergic receptors (β-ARs) on the cell membrane surface. It activates the downstream effector molecules and impairs soft tissue wound healing. β-blockers specifically inhibit β-ARs activation in acute/chronic skin lesions and ulcerative hemangiomas. They also accelerate soft tissue wound healing by shortening the duration of inflammation, speeding keratinocyte migration and reepithelialization, promoting wound contraction and angiogenesis, and inhibiting bacterial virulence effects. In addition, β-blockers shorten wound healing periods in patients with severe thermal damage by reducing the hypermetabolic response. While β-blockers promote/inhibit corneal epithelial cell regeneration and restores limbal stem/progenitor cells function, it could well accelerate/delay corneal wound healing. Given these meaningful effects, a growing number of studies are focused on examining the efficacy and safety of β-blockers in soft tissue wound repair, including acute and chronic wounds, severe thermal damage, ulcerated infantile hemangioma, corneal wounds, and other soft tissue disorders. However, an intensive investigation on their acting mechanisms is imperatively needed. The purpose of this article is to summerize the roles of β-blockers in soft tissue wound healing and explore their clinical applications.

Unlocking the regenerative key: Targeting stem cell factors for bone renewal

Stem cell factors (SCFs) are pivotal factors existing in both soluble and membrane-bound forms, expressed by endothelial cells (ECs) and fibroblasts throughout the body. These factors enhance cell growth, viability, and migration in multipotent cell lineages. The preferential expression of SCF by arteriolar ECs indicates that arterioles create a unique microenvironment tailored to hematopoietic stem cells (HSCs). Insufficiency of SCF within bone marrow (BM)-derived adipose tissue results in decreased their overall cellularity, affecting HSCs and their immediate progenitors critical for generating diverse blood cells and maintaining the hematopoietic microenvironment. SCF deficiency disrupts BM function, impacting the production and differentiation of HSCs. Additionally, deleting SCF from adipocytes reduces lipogenesis, highlighting the crucial role of SCF/c-kit signaling in controlling lipid accumulation. This review elucidates the sources, roles, mechanisms, and molecular strategies of SCF in bone renewal, offering a comprehensive overview of recent advancements, challenges, and future directions for leveraging SCF as a key agent in regenerative medicine.

Vitamin D3-incorporated chitosan/collagen/fibrinogen scaffolds promote angiogenesis and endothelial transition via HIF-1/IGF-1/VEGF pathways in dental pulp stem cells

Effective vascularization during wound healing remains a critical challenge in the regeneration of skin tissue. On the other hand, mesenchymal stem cell (MSC) to endothelial phenotype transition (MEnDoT) is a potential phenomenon grossly underexplored in vascularized skin tissue engineering. Vitamin D3 has a proven role in promoting MEnDoT. Hence, a D3-incorporated scaffold made with biocompatible materials such as chitosan, collagen and fibrinogen should be able to promote endothelial lineage transition in vitro for tissue engineering purposes. In this study, we developed vitamin D3 incorporated chitosan-collagen-fibrinogen (CCF-D3) scaffolds physically crosslinked under UV and conducted thorough physicochemical and biological assays on it compared to a control scaffold without vitamin D3. Our study for the first time reports the potential vascularization property of the CCF-D3 scaffold by inducing the transitions of dental pulp MSC to endothelial lineage via the HIF-1/IGF-1/VEGF pathways. MSC seeded on UV-exposed CCF-D3 scaffolds had higher cell viability and transitioned towards endothelial lineage was observed by elevated proliferative and endothelial-specific gene expressions and flow cytometric analysis of SCA-1+ antibody. The difference in VEGF-A and α-SMA expressions was also observed in the D3-CCF scaffold compared to the scaffolds without D3.

Engineering large and geometrically controlled vascularized nerve tissue in collagen hydrogels to restore large-sized volumetric muscle loss

Developing scalable vascularized and innervated tissue is a critical challenge for the successful clinical application of tissue-engineered constructs. Collagen hydrogels are extensively utilized in cell-mediated vascular network formation because of their naturally excellent biological properties. However, the substantial increase in hydrogel contraction induced by populated cells limits their long-term use. Previous studies attempted to mitigate this issue by concentrating collagen pre-polymer solutions or synthesizing covalently crosslinked collagen hydrogels. However, these methods only partially reduce hydrogel contraction while hindering blood vessel formation within the hydrogels. To address this challenge, we introduced additional support in the form of a supportive spacer to counteract the contraction forces of populated cells and prevent hydrogel contraction. This approach was found to promote cell spreading, resist hydrogel contraction, control hydrogel/tissue geometry, and even facilitate the engineering of functional blood vessels and host nerve growth in just one week. Subsequently, implanting these engineered tissues into muscle defect sites resulted in timely anastomosis with the host vasculature, leading to enhanced myogenesis, increased muscle innervation, and the restoration of injured muscle functionality. Overall, this innovative strategy expands the applicability of collagen hydrogels in fabricating large vascularized nerve tissue constructs for repairing volumetric muscle loss (∼63 %) and restoring muscle function.

Cartilage's Contribution in Otology: A Comprehensive Review of Its Role in Ear Surgery

This comprehensive review thoroughly examines the pivotal role of cartilage in otologic surgery, elucidating its multifaceted contributions to both cosmetic and functional outcomes. From reconstructing the external ear to reinforcing the tympanic membrane and restoring the ossicular chain, cartilage emerges as a versatile and resilient biological material with unique properties that make it an invaluable resource for otologic surgeons. The review explores the nuances of cartilage's applications in various surgical contexts, emphasizing its significance in promoting tissue regeneration and healing. The text delves into advancements in tissue engineering, biodegradable scaffolds, and 3D printing technology, pointing toward a future where more precise and personalized interventions may redefine the landscape of otologic surgery. The convergence of these innovations holds the promise of elevating the standard of care, minimizing complications, and improving the quality of life for patients undergoing cartilage-based otologic procedures. This synthesis of current knowledge and future possibilities provides a valuable resource for otologists, surgeons, and researchers in the dynamic field of otology.

New Insights and Advanced Strategies for In Vitro Construction of Vascularized Tissue Engineering

Inadequate vascularization is a significant barrier to clinical application of large-volume tissue engineered grafts. In contrast to in vivo vascularization, in vitro prevascularization shortens the time required for host vessels to grow into the graft core and minimizes necrosis in the core region of the graft. However, the challenge of prevascularization is to construct hierarchical perfusable vascular networks, increase graft volume, and form a vascular tip that can anastomose with host vessels. Understanding advances in in vitro prevascularization techniques and new insights into angiogenesis could overcome these obstacles. In the present review, we discuss new perspectives on angiogenesis, the differences between in vivo and in vitro tissue vascularization, the four elements of prevascularized constructs, recent advances in perfusion-based in vitro prevascularized tissue fabrication, and prospects for large-volume prevascularized tissue engineering.

A review of the evidence to support electrical stimulation-induced vascularization in engineered tissue

Tissue engineering presents a promising solution for regenerative medicine and the success depends on the supply of oxygen/nutrients to the cells by rapid vascularization. More and more technologies are being developed to facilitate vascularization of engineered tissues. In this review, we indicated that a regulatory system which influences all angiogenesis associated cells to achieve their desired functional state is ideal for the construction of vascularized engineered tissues in vitro. We presented the evidence that electrical stimulation (ES) enhances the synergistic promotion of co-cultured angiogenesis associated cells and its potential regulatory mechanisms, highlighted the potential advantages of a combination of mesenchymal stem cells (MSCs), endothelial cells (ECs) and ES to achieve tissue vascularization, with particular emphasis on the different biological pathways of ES-regulated ECs. Finally, we proposed the future direction of using ES to reconstruct engineered tissue blood vessels, pointed out the potential advantages and disadvantages of ES application on tissue vascularization.

Histological assessment of nanostructured fibrin-agarose skin substitutes grafted in burnt patients. A time-course study

A previously developed fibrin-agarose skin model-UGRSKIN-showed promising clinical results in severely burnt patients. To determine the histological parameters associated to the biocompatibility and therapeutic effects of this model, we carried out a comprehensive structural and ultrastructural study of UGRSKIN grafted in severely burnt patients after 3 months of follow-up. The grafted epidermis was analogue to native human skin from day 30th onward, revealing well-structured strata with well-differentiated keratinocytes expressing CK5, CK8, CK10, claudin, plakoglobin, filaggrin, and involucrin in a similar way to controls, suggesting that the epidermis was able to mature and differentiate very early. Melanocytes and Langerhans cells were found from day 30th onward, together with a basement membrane, abundant hemidesmosomes and lack of rete ridges. At the dermal layer, we found an interface between the grafted skin and the host tissue at day 30th, which tended to disappear with time. The grafted superficial dermis showed a progressive increase in properly-oriented collagen fibers, elastic fibers and proteoglycans, including decorin, similarly to control dermis at day 60-90th of in vivo follow-up. Blood vessels determined by CD31 and SMA expression were more abundant in grafted skin than controls, whereas lymphatic vessels were more abundant at day 90th. These results contribute to shed light on the histological parameters associated to biocompatibility and therapeutic effect of the UGRSKIN model grafted in patients and demonstrate that the bioengineered skin grafted in patients is able to mature and differentiate very early at the epithelial level and after 60-90 days at the dermal level.

Engineered short forms of perlecan enhance angiogenesis by potentiating growth factor signalling

Growth factors are key molecules involved in angiogenesis, a process critical for tissue repair and regeneration. Despite the potential of growth factor delivery to stimulate angiogenesis, limited clinical success has been achieved with this approach. Growth factors interact with the extracellular matrix (ECM), and particularly heparan sulphate (HS), to bind and potentiate their signalling. Here we show that engineered short forms of perlecan, the major HS proteoglycan of the vascular ECM, bind and signal angiogenic growth factors, including fibroblast growth factor 2 and vascular endothelial growth factor-A. We also show that engineered short forms of perlecan delivered in porous chitosan biomaterial scaffolds promote angiogenesis in a rat full thickness dermal wound model, with the fusion of perlecan domains I and V leading to superior vascularisation compared to native endothelial perlecan or chitosan scaffolds alone. Together, this study demonstrates the potential of engineered short forms of perlecan delivered in chitosan scaffolds as next generation angiogenic therapies which exert biological activity via the potentiation of growth factors.

Small intestinal submucosa promotes angiogenesis via the Hippo pathway to improve vaginal repair

Vaginal reconstruction has incorporated the use of gastrointestinal segments for decades, but the technique is inevitably associated with complications. Tissue-engineering techniques, however, have brought great hope for vaginal reconstruction. This study aimed to evaluate the utility of small intestinal submucosa (SIS) in reconstructing clinically significant large vaginal defects in a porcine model and to investigate the role of the Hippo pathway in the vascular remodeling process. The composition and mechanical properties of SIS were characterized. Full-thickness vaginal defects were established in 10 minipig donors, with 4 cm lengths removed and replaced by an equal sized SIS scaffolds. The neovaginas were subjected to macroscopic, histological, immunohistochemical and molecular evaluations at 4 and 12 weeks after the surgery. Four weeks after the operation, extracellular matrix reorganization and complete coverage of the surface of the luminal matrix by vaginal epithelium were observed, accompanied by the formation of a microvascular network and the regeneration of smooth muscles, albeit disorderly arranged. Twelve weeks after implantation, enhancements were seen in the formation of the multi-layered squamous epithelium, angiogenesis, and large muscle bundle formation in the vagina. Additionally, the expression levels of angiogenesis-related proteins, proliferation-related proteins and Hippo pathway-related proteins in the neovagina were significantly increased. These results indicate that SIS could be used to reconstruct large vaginal defects and that the vascular remodeling process is potentially regulated by the Hippo pathway.

Human Dental Pulp Mesenchymal Stem Cell-Derived Soluble Factors Combined with a Nanostructured Scaffold Support the Generation of a Vascular Network In Vivo

Among all strategies directed at developing new tools to support re-vascularization of damaged tissues, the use of pro-angiogenic soluble factors, derived from mesenchymal stem cells (MSCs), appears a promising approach for regenerative medicine. Here, we compared the feasibility of two devices, generated by coupling soluble factors of human dental pulp mesenchymal stem cells (DPSCs), with a nanostructured scaffold, to support angiogenesis once transplanted in mice. DPSCs were obtained from impacted wisdom tooth removal, usually considered surgical waste material. After 28 days, we verified the presence of active blood vessels inside the scaffold through optical and scansion electron microscopy. The mRNA expression of surface antigens related to macrophage polarization (CD68, CD80, CD86, CD163, CD206), as well as pro-angiogenic markers (CD31, CD34, CD105, Angpt1, Angpt2, CDH5) was evaluated by real-time PCR. Our results demonstrate the capability of DPSC-scaffold and DPSC soluble factors-scaffold to support angiogenesis, similarly to adipose stem cells, whereas the absence of blood vessels was found in the scaffold grafted alone. Our results provide evidence that DPSC-conditioned medium can be proposed as a cell-free preparation able to support angiogenesis, thus, providing a relevant tool to overcome the issues and restrictions associated with the use of cells.

Perfusion in vivo bioreactor promotes regeneration of vascularized tissue-engineered bone

Aim: This study improved the in vivo bioreactor (IVB) for bone regeneration by enhancing stem cell survival and promoting vascularized tissue-engineered bone. Methods: 12 New Zealand rabbits received β-TCP scaffolds with rabbit bone mesenchymal stem cells (BMSCs) implanted. Perfusion IVB with a perfusion electronic pump was compared with the control group using micro-CT, Microfil perfusion, histological staining and RT-PCR for gene expression. Results: Perfusion IVB demonstrated good biocompatibility, increased neoplastic bone tissue, neovascularization and upregulated osteogenic and angiogenesis-related genes in rabbits (p < 0.05). Conclusion: Perfusion IVB holds promise for bone regeneration and tissue engineering in orthopedics and maxillofacial surgery.

Dissolving microneedles for alopecia treatment

Alopecia is a treatable benign disease, however, approximately 15-30% of women and 50% of men suffer from alopecia, which greatly affects patient's self-esteem and quality of life. Currently, commercial products for alopecia treatment include topical minoxidil solution, oral finasteride tablets and oral baricitinib tablets. However, the barrier of stratum corneum, systemic adverse effects and poor cure rate limit the application of commercial products. Therefore, researchers investigated the mechanism of alopecia, and developed new drugs that could target lactate dehydrogenase-related pathways, remove excessive reactive oxygen in hair follicles, and reduce the escape of hair follicle stem cells, thus injecting new strength into the treatment of alopecia. Moreover, starting from improving drug stratum corneum penetration and reducing side effects, researchers have developed hair loss treatment strategies based on dissolved microneedles (MNs), such as drug powders/microparticles, nanoparticles, biomimetic cell membranes, phototherapy and magnetically responsive soluble microneedles, which show exciting alopecia treatment effects. However, there are still some challenges in the practical application of the current alopecia treatment strategy with soluble microneedles, and further studies are needed to accelerate its clinical translation.

Scaffolds with high oxygen content support osteogenic cell survival under hypoxia

Regeneration of large bone defects is a significant clinical challenge with variable success, but tissue engineering strategies are promising for rapid and effective bone regeneration. Maintaining an adequate oxygen level within implanted scaffolds is a major obstacle in bone tissue engineering. We developed a new oxygen-generating scaffold by electrospinning polycaprolactone with calcium peroxide (CaO2) nanocuboids (CPNCs) and characterized the physical, chemical, and biological properties of the resulting composites. Our scaffolds are highly porous and composed of submicron fibers that include CPNC as confirmed with XRD and FTIR analyses. Scaffolds containing CPNC provided controlled oxygen release for 14-days and supported cell proliferation while protecting preosteoblasts from hypoxia-induced cell death. Oxygen-generating scaffolds also facilitated bone mimetic defect contraction in vitro. The results suggest that our approach can be used to develop tissue-engineered products which target bone defects.

Resorbable Biomaterials Used for 3D Scaffolds in Tissue Engineering: A Review

This article provides a thorough overview of the available resorbable biomaterials appropriate for producing replacements for damaged tissues. In addition, their various properties and application possibilities are discussed as well. Biomaterials are fundamental components in tissue engineering (TE) of scaffolds and play a critical role. They need to exhibit biocompatibility, bioactivity, biodegradability, and non-toxicity, to ensure their ability to function effectively with an appropriate host response. With ongoing research and advancements in biomaterials for medical implants, the objective of this review is to explore recently developed implantable scaffold materials for various tissues. The categorization of biomaterials in this paper includes fossil-based materials (e.g., PCL, PVA, PU, PEG, and PPF), natural or bio-based materials (e.g., HA, PLA, PHB, PHBV, chitosan, fibrin, collagen, starch, and hydrogels), and hybrid biomaterials (e.g., PCL/PLA, PCL/PEG, PLA/PEG, PLA/PHB PCL/collagen, PCL/chitosan, PCL/starch, and PLA/bioceramics). The application of these biomaterials in both hard and soft TE is considered, with a particular focus on their physicochemical, mechanical, and biological properties. Furthermore, the interactions between scaffolds and the host immune system in the context of scaffold-driven tissue regeneration are discussed. Additionally, the article briefly mentions the concept of in situ TE, which leverages the self-renewal capacities of affected tissues and highlights the crucial role played by biopolymer-based scaffolds in this strategy.

Neutrophil-like Biomimic AIE Nanoparticles with High-Efficiency Inflammatory Cytokine Targeting Enable Precise Photothermal Therapy and Alleviation of Inflammation

Although photothermal therapy (PTT) has thrived as a promising treatment for drug-resistant bacterial infections by avoiding the abuse of antibiotics, the remaining challenges that limit the treatment efficiency are the poor targeting properties of infected lesions and low penetration to the cell membrane of Gram-negative bacteria. Herein, we developed a biomimetic neutrophil-like aggregation-induced emission (AIE) nanorobot (CM@AIE NPs) for precise inflammatory site homing and efficient PTT effects. Due to their surface-loaded neutrophil membranes, CM@AIE NPs can mimic the source cell and thus interact with immunomodulatory molecules that would otherwise target endogenous neutrophils. Coupled with the secondary near-infrared region absorption and excellent photothermal properties of AIE luminogens (AIEgens), precise localization, and treatment in inflammatory sites can be achieved, thereby minimizing damage to surrounding normal tissues. Moreover, CM@AIE NP-mediated PTT was stimulated in vivo by a 980 nm laser irradiation, which contributed to the extent of the therapeutic depth and limited the damage to skin tissues. The good biocompatibility and excellent in vitro and in vivo antibacterial effects prove that CM@AIE NPs can provide a strategy for broad-spectrum antibacterial applications.

Strategies for Improving Vascularization in Kidney Organoids: A Review of Current Trends

Kidney organoids possess the potential to revolutionize the treatment of renal diseases. However, their growth and maturation are impeded by insufficient growth of blood vessels. Through a PubMed search, we have identified 34 studies that attempted to address this challenge. Researchers are exploring various approaches including animal transplantation, organ-on-chips, and extracellular matrices (ECMs). The most prevalent method to promote the maturation and vascularization of organoids involves transplanting them into animals for in vivo culture, creating an optimal environment for organoid growth and the development of a chimeric vessel network between the host and organoids. Organ-on-chip technology permits the in vitro culture of organoids, enabling researchers to manipulate the microenvironment and investigate the key factors that influence organoid development. Lastly, ECMs have been discovered to aid the formation of blood vessels during organoid differentiation. ECMs from animal tissue have been particularly successful, although the underlying mechanisms require further research. Future research building upon these recent studies may enable the generation of functional kidney tissues for replacement therapies.

Single-stage transplantation combined with epidermal stem cells promotes the survival of tissue-engineered skin by inducing early angiogenesis

BACKGROUND

The composite transplantation of a split-thickness skin graft (STSG) combined with an acellular dermal matrix (ADM) is a promising repair method for full-thickness skin defects. Due to delayed vascularization of the ADM, no currently available engineered skin tissue is able to permanently cover full-thickness skin defects via a single-stage procedure. Epidermal stem cells (EpSCs) have been found to promote angiogenesis in the wound bed. Whether EpSCs can induce early angiogenesis of dermal substitutes and promote the survival of single-stage tissue-engineered skin transplantation needs to be further studied.

METHODS

In vitro, rat vascular endothelial cells (RVECs) were treated with the supernatant of EpSCs cultured in ADM and stimulated for 48 h. RVECs were analysed by RNA sequencing and tube formation assays. For the in vivo experiment, 75 rats were randomly divided into five groups: ADM, ADM + EpSCs (AE), STSG, ADM + STSG (AS), and ADM + STSG + EpSCs (ASE) groups. The quality of wound healing was estimated by general observation and H&E and Masson staining. The blood perfusion volume was evaluated using the LDPI system, and the expression of vascular markers was determined by immunohistochemistry (IHC).

RESULTS

The active substances secreted by EpSCs cultured in ADM promoted angiogenesis, as shown by tube formation experiments and RNA-seq. EpSCs promoted epithelialization of the ADM and vascularization of the ADM implant. The ASE group showed significantly increased skin graft survival, reduced skin contraction, and an improved cosmetic appearance compared with the AS group and the STSG control group.

CONCLUSIONS

In summary, our findings suggest that EpSCs promote the formation of new blood vessels in dermal substitutes and support one-step transplantation of tissue-engineered skin, and thereby provide new ideas for clinical application.

Development of fibroblast/endothelial cell-seeded collagen scaffolds for in vitro prevascularization

The development of vascularized scaffolds remains one of the major challenges in tissue engineering, and co-culturing with endothelial cells is known as one of the possible approaches for this purpose. In this approach, optimization of cell culture conditions, scaffolds, and fabrication techniques is needed to develop tissue equivalents that will enable in vitro formation of a capillary network. Prevascularized equivalents will be more physiologically comparable to the native tissues and potentially prevent insufficient vascularization after implantation. This study aimed to culture human umbilical vein endothelial cells (HUVECs), alone or in co-culture with fibroblasts, on collagen scaffolds prepared by simple fabrication approaches for in vitro prevascularization. Different concentrations and ratios of HUVECs and fibroblasts seeded on collagen gel and sponge scaffolds under several culture conditions were examined. Cell viability, scaffolds morphology, and structure were analyzed. Collagen gel scaffolds showed good cell proliferation and viability, with higher proliferation rates for cells cultured in a 2:1 (fibroblasts: HUVECs) ratio and kept in endothelial cell growth medium. However, these matrices were unable to support endothelial cell sprouting. Collagen sponges were highly porous and showed good cell viability. However, they became fragile over time in culture, and they still lack signs of vascularization. Collagen scaffolds were a good platform for cell growth and viability. However, under the experimental conditions of this study, the HUVEC/fibroblast-seeded scaffolds were not suitable platforms to generate in vitro prevascularized equivalents. Our findings will be a valuable starting point to optimize culture microenvironments and scaffolds during fabrication of prevascularized scaffolds.

Silk Fibroin Bioink for 3D Printing in Tissue Regeneration: Controlled Release of MSC extracellular Vesicles

Sodium alginate (SA)-based hydrogels are often employed as bioink for three-dimensional (3D) scaffold bioprinting. They offer a suitable environment for cell proliferation and differentiation during tissue regeneration and also control the release of growth factors and mesenchymal stem cell secretome, which is useful for scaffold biointegration. However, such hydrogels show poor mechanical properties, fast-release kinetics, and low biological performance, hampering their successful clinical application. In this work, silk fibroin (SF), a protein with excellent biomechanical properties frequently used for controlled drug release, was blended with SA to obtain improved bioink and scaffold properties. Firstly, we produced a printable SA solution containing SF capable of the conformational change from Silk I (random coil) to Silk II (β-sheet): this transition is a fundamental condition to improve the scaffold's mechanical properties. Then, the SA-SF blends' printability and shape fidelity were demonstrated, and mechanical characterization of the printed hydrogels was performed: SF significantly increased compressive elastic modulus, while no influence on tensile response was detected. Finally, the release profile of Lyosecretome-a freeze-dried formulation of MSC-secretome containing extracellular vesicles (EV)-from scaffolds was determined: SF not only dramatically slowed the EV release rate, but also modified the kinetics and mechanism release with respect to the baseline of SA hydrogel. Overall, these results lay the foundation for the development of SA-SF bioinks with modulable mechanical and EV-release properties, and their application in 3D scaffold printing.

Gelatin and Bioactive Glass Composites for Tissue Engineering: A Review

Nano-/micron-sized bioactive glass (BG) particles are attractive candidates for both soft and hard tissue engineering. They can chemically bond to the host tissues, enhance new tissue formation, activate cell proliferation, stimulate the genetic expression of proteins, and trigger unique anti-bacterial, anti-inflammatory, and anti-cancer functionalities. Recently, composites based on biopolymers and BG particles have been developed with various state-of-the-art techniques for tissue engineering. Gelatin, a semi-synthetic biopolymer, has attracted the attention of researchers because it is derived from the most abundant protein in the body, viz., collagen. It is a polymer that can be dissolved in water and processed to acquire different configurations, such as hydrogels, fibers, films, and scaffolds. Searching "bioactive glass gelatin" in the tile on Scopus renders 80 highly relevant articles published in the last ~10 years, which signifies the importance of such composites. First, this review addresses the basic concepts of soft and hard tissue engineering, including the healing mechanisms and limitations ahead. Then, current knowledge on gelatin/BG composites including composition, processing and properties is summarized and discussed both for soft and hard tissue applications. This review explores physical, chemical and mechanical features and ion-release effects of such composites concerning osteogenic and angiogenic responses in vivo and in vitro. Additionally, recent developments of BG/gelatin composites using 3D/4D printing for tissue engineering are presented. Finally, the perspectives and current challenges in developing desirable composites for the regeneration of different tissues are outlined.

Multi-functional nanofilms capable of angiogenesis, near-infrared-triggered anti-bacterial activity and inflammatory regulation for infected wound healing

Chronic infected wound healing is a critical challenge in clinical practice owing to the involvement of multiple physiological processes, including bacteria-related, inflammatory regulation and angiogenesis. Therefore, a multi-functional strategy with synergistic anti-bacterial, anti-inflammatory and pro-angiogenic effects should be developed. Owing to their biomimetic structural features and controlled delivery of active agents, electrospun nanofilms are promising biomaterials for the treatment of skin defects. In this study, we fabricated multi-functional nanofilms with pro-angiogenic, anti-bacterial and anti-inflammatory capacities. First, strontium (Sr) ions were incorporated into poly(L-lactic-co-caprolactone) (PLCL) nanofilms. Subsequently, polydopamine (PDA) and zinc oxide (ZnO) were decorated onto the surface of Sr-loaded PLCL nanofilms to prepare ZnO/PDA@PLCL@Sr nanofilms. In vitro results showed that ZnO/PDA@PLCL@Sr nanofilms were biocompatible, exhibited angiogenic activity and significantly inhibited the growth of Staphylococcus aureus and Escherichia coli upon near-infrared -light irradiation. Furthermore, ZnO/PDA@PLCL@Sr nanofilms were found to drive the transformation of macrophages into the M2 phenotype. In vivo results further validated that ZnO/PDA@PLCL@Sr nanofilms exhibited pro-angiogenic and anti-bacterial activities and regulated inflammation to accelerate wound -healing in a rat model of bacteria-infected skin defects. In conclusion, we successfully developed a multi-functional biomaterial with pro-angiogenic, anti-bacterial and anti-inflammatory capacities to treat chronic infected wounds.

Development and characterisation of 3D collagen-gelatin based scaffolds for breast cancer research

While 2D culture presents a useful tool for cancer research, it fails to replicate the tumor microenvironment as it lacks proper three-dimensional cell-cell/cell-matrix interactions, often resulting in exaggerated responses to therapeutic agents. 3D models that aim to overcome the issues associated with 2D culture research offer a new frontier for cancer research with cell growth, morphology and genetic properties that more closely match in vivo cancers. Herein, we aim to develop a collagen-based scaffold that supports the attachment and proliferation of breast cancer (BC) cells as a 3D culture model. Scaffolds were produced on a repeatable basis using a freeze-drying procedure. The constructs were highly porous (>99%) with homogenous pore sizes (150-300 μm) and an interconnected structure. The application of 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) crosslinking resulted in scaffolds with elastic moduli in the range of 1-2 kPa, mimicking cancerous breast tissue stiffness. Furthermore, the incorporation of gelatin into the scaffolds enabled the porosity, pore size and mechanical properties to be tailored, resulting in scaffolds with stiffness values that accurately replicate the stiffness of human BC extracellular matrix (ECM) (1.3-1.7 kPa). Scaffolds displayed high in vitro stability with 90% of mass remaining after 14 days of culture. The scaffolds were shown to be highly biocompatible, and capable of supporting the attachment, infiltration and proliferation of MCF7 breast cancer (BC) cells over +14 days. These results confirm the suitability of these scaffolds as culture models for BC cells. These collagen-based scaffolds offer significant potential for the exploration of aspects of BC, such as gene expression profiles and patterns, and for the assessment of the efficacy of therapeutic agents in treating BC.

Engineering Spatiotemporal Control in Vascularized Tissues

A major challenge in engineering scalable three-dimensional tissues is the generation of a functional and developed microvascular network for adequate perfusion of oxygen and growth factors. Current biological approaches to creating vascularized tissues include the use of vascular cells, soluble factors, and instructive biomaterials. Angiogenesis and the subsequent generation of a functional vascular bed within engineered tissues has gained attention and is actively being studied through combinations of physical and chemical signals, specifically through the presentation of topographical growth factor signals. The spatiotemporal control of angiogenic signals can generate vascular networks in large and dense engineered tissues. This review highlights the developments and studies in the spatiotemporal control of these biological approaches through the coordinated orchestration of angiogenic factors, differentiation of vascular cells, and microfabrication of complex vascular networks. Fabrication strategies to achieve spatiotemporal control of vascularization involves the incorporation or encapsulation of growth factors, topographical engineering approaches, and 3D bioprinting techniques. In this article, we highlight the vascularization of engineered tissues, with a focus on vascularized cardiac patches that are clinically scalable for myocardial repair. Finally, we discuss the present challenges for successful clinical translation of engineered tissues and biomaterials.

In Vivo Bone Tissue Engineering Strategies: Advances and Prospects

Reconstruction of critical-sized bone defects remains a tremendous challenge for surgeons worldwide. Despite the variety of surgical techniques, current clinical strategies for bone defect repair demonstrate significant limitations and drawbacks, including donor-site morbidity, poor anatomical match, insufficient bone volume, bone graft resorption, and rejection. Bone tissue engineering (BTE) has emerged as a novel approach to guided bone tissue regeneration. BTE focuses on in vitro manipulations with seed cells, growth factors and bioactive scaffolds using bioreactors. The successful clinical translation of BTE requires overcoming a number of significant challenges. Currently, insufficient vascularization is the critical limitation for viability of the bone tissue-engineered construct. Furthermore, efficacy and safety of the scaffolds cell-seeding and exogenous growth factors administration are still controversial. The in vivo bioreactor principle (IVB) is an exceptionally promising concept for the in vivo bone tissue regeneration in a predictable patient-specific manner. This concept is based on the self-regenerative capacity of the human body, and combines flap prefabrication and axial vascularization strategies. Multiple experimental studies on in vivo BTE strategies presented in this review demonstrate the efficacy of this approach. Routine clinical application of the in vivo bioreactor principle is the future direction of BTE; however, it requires further investigation for overcoming some significant limitations.

Natural polymer-based scaffolds for soft tissue repair

Soft tissues such as skin, muscle, and tendon are easily damaged due to injury from physical activity and pathological lesions. For soft tissue repair and regeneration, biomaterials are often used to build scaffolds with appropriate structures and tailored functionalities that can support cell growth and new tissue formation. Among all types of scaffolds, natural polymer-based scaffolds attract much attention due to their excellent biocompatibility and tunable mechanical properties. In this comprehensive mini-review, we summarize recent progress on natural polymer-based scaffolds for soft tissue repair, focusing on clinical translations and materials design. Furthermore, the limitations and challenges, such as unsatisfied mechanical properties and unfavorable biological responses, are discussed to advance the development of novel scaffolds for soft tissue repair and regeneration toward clinical translation.

Tissue engineering application combining epoxidized natural rubber blend and mesenchymal stem cells in in vivo response

This study aimed to investigate biocompatibility, integration, and tissue host response of the Poly (Lactic-co-Glycolic acid) (PLGA)/Poly (isoprene) (PI) epoxidized (PLGA/PIepox) innovative scaffold combined with adipose derived mesenchymal stem cells (ADSC). We implanted the scaffold subcutaneously on the back of 18 female rats and monitored them for up to 14 days. When compared to controls, PLGA/PIepox + ADSC demonstrated an earlier vascularization, a tendency of inflammation reduction, an adequate tissue integration, higher cell proliferation, and a tendency of expression of collagen decreasing. However, 14 days post-implantation we found similar levels of CD31, Ki67 and AE1/AE3 in PLGA/PIepox when compared to control groups. The interesting results, lead us to the assumption that PLGA/PIepox is able to provide an effective delivery system for ADSC on tissue host. This animal study assesses PLGA/PIepox + ADSC in in vivo tissue functionality and validation of use, serving as a proof of concept for future clinical translation as it presents an innovative and promising tissue engineering opportunity for the use in tissue reconstruction.

Characterization of an Innovative Biomaterial Derived From Human Wharton’s Jelly as a New Promising Coating for Tissue Engineering Applications

The extracellular matrix (ECM) offers the opportunity to create a biomaterial consisting of a microenvironment with interesting biological and biophysical properties for improving and regulating cell functions. Animal-derived ECM are the most widely used as an alternative to human tissues that are of very limited availability. However, incomplete decellularization of these tissues presents a high risk of immune rejection and disease transmission. In this study, we present an innovative method to extract human ECM derived from the Wharton’s jelly (WJ-ECMaa) of umbilical cords as a novel biomaterial to be used in tissue engineering. WJ-ECMaa was very efficiently decellularized, suggesting its possible use in allogeneic conditions. Characterization of its content allowed the identification of type I collagen as its main component. Various other matrix proteins, playing an important role in cell adhesion and proliferation, were also detected. WJ-ECMaa applied as a surface coating was analyzed by fluorescent labeling and atomic force microscopy. The results revealed a particular arrangement of collagen fibers not previously described in the literature. This biomaterial also presented better cytocompatibility compared to the conventional collagen coating. Moreover, it showed adequate hemocompatibility, allowing its use as a surface with direct contact with blood. Application of WJ-ECMaa as a coating of the luminal surface of umbilical arteries for a use in vascular tissue engineering, has improved significantly the cellularization of this surface by allowing a full and homogeneous cell coverage. Taking these results together, our novel extraction method of human ECM offers a very promising biomaterial with many potential applications in tissue engineering such as the one presented direct in vascular tissue engineering. Further characterization of the composition and functionality will help explore the ways it can be used in tissue engineering applications, especially as a scaffold or a surface coating.

The Therapeutic Potential of Exosomes in Soft Tissue Repair and Regeneration

Soft tissue defects are common following trauma and tumor extirpation. These injuries can result in poor functional recovery and lead to a diminished quality of life. The healing of skin and muscle is a complex process that, at present, leads to incomplete recovery and scarring. Regenerative medicine may offer the opportunity to improve the healing process and functional outcomes. Barriers to regenerative strategies have included cost, regulatory hurdles, and the need for cell-based therapies. In recent years, exosomes, or extracellular vesicles, have gained tremendous attention in the field of soft tissue repair and regeneration. These nanosized extracellular particles (30-140 nm) can break the cellular boundaries, as well as facilitate intracellular signal delivery in various regenerative physiologic and pathologic processes. Existing studies have established the potential of exosomes in regenerating tendons, skeletal muscles, and peripheral nerves through different mechanisms, including promoting myogenesis, increasing tenocyte differentiation and enhancing neurite outgrowth, and the proliferation of Schwann cells. These exosomes can be stored for immediate use in the operating room, and can be produced cost efficiently. In this article, we critically review the current advances of exosomes in soft tissue (tendons, skeletal muscles, and peripheral nerves) healing. Additionally, new directions for clinical applications in the future will be discussed.