3D cell printing of in vitro stabilized skin model and in vivo pre-vascularized skin patch using tissue-specific extracellular matrix bioink: A step towards advanced skin tissue engineering

Elastic Modulus of ECM Hydrogels Derived from Decellularized Tissue Affects Capillary Network Formation in Endothelial Cells

Recent applications of decellularized tissue have included the use of hydrogels for injectable materials and three-dimensional (3D) bioprinting bioink for tissue regeneration. Microvascular formation is required for the delivery of oxygen and nutrients to support cell growth and regeneration in tissues and organs. The aim of the present study was to evaluate the formation of capillary networks in decellularized extracellular matrix (d-ECM) hydrogels. The d-ECM hydrogels were obtained from the small intestine submucosa (SIS) and the urinary bladder matrix (UBM) after decellularizing with sodium deoxycholate (SDC) and high hydrostatic pressure (HHP). The SDC d-ECM hydrogel gradually gelated, while the HHP d-ECM hydrogel immediately gelated. All d-ECM hydrogels had low matrix stiffness compared to that of the collagen hydrogel, according to a compression test. D-ECM hydrogels with various elastic moduli were obtained, irrespective of the decellularization method or tissue source. Microvascular-derived endothelial cells were seeded on d-ECM hydrogels. Few cells attached to the SDC d-ECM hydrogel with no network formation, while on the HHP d-ECM hydrogel, a capillary network structure formed between elongated cells. Long, branched networks formed on d-ECM hydrogels with lower matrix stiffness. This suggests that the capillary network structure that forms on d-ECM hydrogels is closely related to the matrix stiffness of the hydrogel.

Microphysiological systems for the modeling of wound healing and evaluation of pro-healing therapies

Wound healing is a multivariate process involving the coordinated response of numerous proteins and cell types. Accordingly, biomedical research has seen an increased adoption of the use of in vitro wound healing assays with complexity beyond that offered by traditional well-plate constructs. These microphysiological systems (MPS) seek to recapitulate one or more physiological features of the in vivo microenvironment, while retaining the analytical capacity of more reductionist assays. Design efforts to achieve relevant wound healing physiology include the use of dynamic perfusion over static culture, the incorporation of multiple cell types, the arrangement of cells in three dimensions, the addition of biomechanically and biochemically relevant hydrogels, and combinations thereof. This review provides a brief overview of the wound healing process and in vivo assays, and we critically review the current state of MPS and supporting technologies for modelling and studying wound healing. We distinguish between MPS that seek to inform a particular phase of wound healing, and constructs that have the potential to inform multiple phases of wound healing. This distinction is a product of whether analysis of a particular process is prioritized, or a particular physiology is prioritized, during design. Material selection is emphasized throughout, and relevant fabrication techniques discussed.

Natural 3D-Printed Bioinks for Skin Regeneration and Wound Healing: A Systematic Review

Three-dimensional bioprinting has rapidly paralleled many biomedical applications and assisted in advancing the printing of complex human organs for a better therapeutic practice. The objective of this systematic review is to highlight evidence from the existing studies and evaluate the effectiveness of using natural-based bioinks in skin regeneration and wound healing. A comprehensive search of all relevant original articles was performed based on prespecified eligibility criteria. The search was carried out using PubMed, Web of Science, Scopus, Medline Ovid, and ScienceDirect. Eighteen articles fulfilled the inclusion and exclusion criteria. The animal studies included a total of 151 animals with wound defects. A variety of natural bioinks and skin living cells were implanted in vitro to give insight into the technique through different assessments and findings. Collagen and gelatin hydrogels were most commonly used as bioinks. The follow-up period ranged between one day and six weeks. The majority of animal studies reported that full wound closure was achieved after 2–4 weeks. The results of both in vitro cell culture and in vivo animal studies showed the positive impact of natural bioinks in promoting wound healing. Future research should be focused more on direct the bioprinting of skin wound treatments on animal models to open doors for human clinical trials.

Decellularized Extracellular Matrix-based Bioinks for Engineering Tissue- and Organ-specific Microenvironments

Biomaterials-based biofabrication methods have gained much attention in recent years. Among them, 3D cell printing is a pioneering technology to facilitate the recapitulation of unique features of complex human tissues and organs with high process flexibility and versatility. Bioinks, combinations of printable hydrogel and cells, can be utilized to create 3D cell-printed constructs. The bioactive cues of bioinks directly trigger cells to induce tissue morphogenesis. Among the various printable hydrogels, the tissue- and organ-specific decellularized extracellular matrix (dECM) can exert synergistic effects in supporting various cells at any component by facilitating specific physiological properties. In this review, we aim to discuss a new paradigm of dECM-based bioinks able to recapitulate the inherent microenvironmental niche in 3D cell-printed constructs. This review can serve as a toolbox for biomedical engineers who want to understand the beneficial characteristics of the dECM-based bioinks and a basic set of fundamental criteria for printing functional human tissues and organs.

Distinct phenotypes of cancer cells on tissue matrix gel

BACKGROUND

Breast cancer cells invading the connective tissues outside the mammary lobule or duct immerse in a reservoir of extracellular matrix (ECM) that is structurally and biochemically distinct from that of their site of origin. The ECM is a spatial network of matrix proteins, which not only provide physical support but also serve as bioactive ligands to the cells. It becomes evident that the dimensional, mechanical, structural, and biochemical properties of ECM are all essential mediators of many cellular functions. To better understand breast cancer development and cancer cell biology in native tissue environment, various tissue-mimicking culture models such as hydrogel have been developed. Collagen I (Col I) and Matrigel are the most common hydrogels used in cancer research and have opened opportunities for addressing biological questions beyond the two-dimensional (2D) cell cultures. Yet, it remains unclear whether these broadly used hydrogels can recapitulate the environmental properties of tissue ECM, and whether breast cancer cells grown on CoI I or Matrigel display similar phenotypes as they would on their native ECM.

METHODS

We investigated mammary epithelial cell phenotypes and metabolic profiles on animal breast ECM-derived tissue matrix gel (TMG), Col I, and Matrigel. Atomic force microscopy (AFM), fluorescence microscopy, acini formation assay, differentiation experiments, spatial migration/invasion assays, proliferation assay, and nuclear magnetic resonance (NMR) spectroscopy were used to examine biological phenotypes and metabolic changes. Student's t test was applied for statistical analyses.

RESULTS

Our data showed that under a similar physiological stiffness, the three types of hydrogels exhibited distinct microstructures. Breast cancer cells grown on TMG displayed quite different morphologies, surface receptor expression, differentiation status, migration and invasion, and metabolic profiles compared to those cultured on Col I and Matrigel. Depleting lactate produced by glycolytic metabolism of cancer cells abolished the cell proliferation promoted by the non-tissue-specific hydrogel.

CONCLUSION

The full ECM protein-based hydrogel system may serve as a biologically relevant model system to study tissue- and disease-specific pathological questions. This work provides insights into tissue matrix regulation of cancer cell biomarker expression and identification of novel therapeutic targets for the treatment of human cancers based on tissue-specific disease modeling.

3D Printing Approach in Dentistry: The Future for Personalized Oral Soft Tissue Regeneration

Three-dimensional (3D) printing technology allows the production of an individualized 3D object based on a material of choice, a specific computer-aided design and precise manufacturing. Developments in digital technology, smart biomaterials and advanced cell culturing, combined with 3D printing, provide promising grounds for patient-tailored treatments. In dentistry, the "digital workflow" comprising intraoral scanning for data acquisition, object design and 3D printing, is already in use for manufacturing of surgical guides, dental models and reconstructions. 3D printing, however, remains un-investigated for oral mucosa/gingiva. This scoping literature review provides an overview of the 3D printing technology and its applications in regenerative medicine to then describe 3D printing in dentistry for the production of surgical guides, educational models and the biological reconstructions of periodontal tissues from laboratory to a clinical case. The biomaterials suitable for oral soft tissues printing are outlined. The current treatments and their limitations for oral soft tissue regeneration are presented, including "off the shelf" products and the blood concentrate (PRF). Finally, tissue engineered gingival equivalents are described as the basis for future 3D-printed oral soft tissue constructs. The existing knowledge exploring different approaches could be applied to produce patient-tailored 3D-printed oral soft tissue graft with an appropriate inner architecture and outer shape, leading to a functional as well as aesthetically satisfying outcome.

Potential use of 3D-printed graphene oxide scaffold for construction of the cartilage layer

Background

Three-dimensional (3D) printing involves the layering of seed cells, biologically compatible scaffolds, and biological activity factors to precisely recapitulate a biological tissue. Graphene oxide (GO), a type of micro material, has been utilized as a small molecule-transport vehicle. With the proliferation of GO, the biocompatibility of chondrocytes in a microenvironment constructed by 3D printed scaffolds and GO is innovative. Accordingly, we speculate that, as a type of micro material, GO can be used with 3D scaffolds for a uniform distribution in the cartilage layer.

Results

A qualitative analysis of the chondrocyte-proliferation potential revealed that the culture of 3D printing with a 10% GO scaffold was higher than that of the other groups. Meanwhile, the progress of cell apoptosis was activated. Through scanning electron microscopy, immunofluorescence, and in vivo research, we observed that the newborn cartilage matrix extended along the border of the cartilage and scaffold and matured. After an analysis with immunohistochemical staining with aggrecan and collagen I, the cartilage following the 3D-printed scaffold was thinner than that of the 3D-printed GO scaffold. Furthermore, the collagen I of the cartilage expression in treatment with the GO scaffold was significant from week 2 to 6.

Conclusions

The findings indicate that a 3D-printed GO scaffold can potentially be utilized for the construction of a cartilage matrix. However, the optimum concentration of GO requires further research and discussion.

Advanced Strategies for the Regeneration of Lumbar Disc Annulus Fibrosus

Damage to the annulus fibrosus (AF), the outer region of the intervertebral disc (IVD), results in an undesirable condition that may accelerate IVD degeneration causing low back pain. Despite intense research interest, attempts to regenerate the IVD have failed so far and no effective strategy has translated into a successful clinical outcome. Of particular significance, the failure of strategies to repair the AF has been a major drawback in the regeneration of IVD and nucleus replacement. It is unlikely to secure regenerative mediators (cells, genes, and biomolecules) and artificial nucleus materials after injection with an unsealed AF, as IVD is exposed to significant load and large deformation during daily activities. The AF defects strongly change the mechanical properties of the IVD and activate catabolic routes that are responsible for accelerating IVD degeneration. Therefore, there is a strong need to develop effective therapeutic strategies to prevent or reconstruct AF damage to support operational IVD regenerative strategies and nucleus replacement. By the way of this review, repair and regenerative strategies for AF reconstruction, their current status, challenges ahead, and future outlooks were discussed.

Bioprinting stem cells: building physiological tissues one cell at a time

Bioprinting aims to direct the spatial arrangement in three dimensions of cells, biomaterials, and growth factors. The biofabrication of clinically relevant constructs for the repair or modeling of either diseased or damaged tissues is rapidly advancing, resulting in the ability to three-dimensional (3D) print biomimetic platforms which imitate a large number of tissues in the human body. Primary tissue-specific cells are typically isolated from patients and used for the fabrication of 3D models for drug screening or tissue repair purposes. However, the lack of resilience of these platforms, due to the difficulties in harnessing, processing, and implanting patient-specific cells can limit regeneration ability. The printing of stem cells obviates these hurdles, producing functional in vitro models or implantable constructs. Advancements in biomaterial science are helping the development of inks suitable for the encapsulation and the printing of stem cells, promoting their functional growth and differentiation. This review specifically aims to investigate the most recent studies exploring innovative and functional approaches for the printing of 3D constructs to model disease or repair damaged tissues. Key concepts in tissue physiology are highlighted, reporting stem cell applications in biofabrication. Bioprinting technologies and biomaterial inks are listed and analyzed, including recent advancements in biomaterial design for bioprinting applications, commenting on the influence of biomaterial inks on the encapsulated stem cells. Ultimately, most recent successful efforts and clinical potentials for the manufacturing of functional physiological tissue substitutes are reported here, with a major focus on specific tissues, such as vasculature, heart, lung and airways, liver, bone and muscle.

Composite Hydrogels in Three-Dimensional in vitro Models

3-dimensional (3D) in vitro models were developed in order to mimic the complexity of real organ/tissue in a dish. They offer new possibilities to model biological processes in more physiologically relevant ways which can be applied to a myriad of applications including drug development, toxicity screening and regenerative medicine. Hydrogels are the most relevant tissue-like matrices to support the development of 3D in vitro models since they are in many ways akin to the native extracellular matrix (ECM). For the purpose of further improving matrix relevance or to impart specific functionalities, composite hydrogels have attracted increasing attention. These could incorporate drugs to control cell fates, additional ECM elements to improve mechanical properties, biomolecules to improve biological activities or any combinations of the above. In this Review, recent developments in using composite hydrogels laden with cells as biomimetic tissue- or organ-like constructs, and as matrices for multi-cell type organoid cultures are highlighted. The latest composite hydrogel systems that contain nanomaterials, biological factors, and combinations of biopolymers (e.g., proteins and polysaccharide), such as Interpenetrating Networks (IPNs) and Soft Network Composites (SNCs) are also presented. While promising, challenges remain. These will be discussed in light of future perspectives toward encompassing diverse composite hydrogel platforms for an improved organ environment in vitro.

Advances in the Research of Bioinks Based on Natural Collagen, Polysaccharide and Their Derivatives for Skin 3D Bioprinting

The skin plays an important role in protecting the human body, and wound healing must be set in motion immediately following injury or trauma to restore the normal structure and function of skin. The extracellular matrix component of the skin mainly consists of collagen, glycosaminoglycan (GAG), elastin and hyaluronic acid (HA). Recently, natural collagen, polysaccharide and their derivatives such as collagen, gelatin, alginate, chitosan and pectin have been selected as the matrix materials of bioink to construct a functional artificial skin due to their biocompatible and biodegradable properties by 3D bioprinting, which is a revolutionary technology with the potential to transform both research and medical therapeutics. In this review, we outline the current skin bioprinting technologies and the bioink components for skin bioprinting. We also summarize the bioink products practiced in research recently and current challenges to guide future research to develop in a promising direction. While there are challenges regarding currently available skin bioprinting, addressing these issues will facilitate the rapid advancement of 3D skin bioprinting and its ability to mimic the native anatomy and physiology of skin and surrounding tissues in the future.

Microskin-Inspired Injectable MSC-Laden Hydrogels for Scarless Wound Healing with Hair Follicles

Scarless skin regeneration with functional tissue remains a challenge for full-thickness wounds. Here, mesenchymal stem cell (MSC)-laden hydrogels are developed for scarless wound healing with hair follicles. Microgels composed of aligned silk nanofibers are used to load MSCs to modulate the paracrine. MSC-laden microgels are dispersed into injectable silk nanofiber hydrogels, forming composites biomaterials containing the cells. The injectable hydrogels protect and stabilize the MSCs in the wounds. The synergistic action of silk-based composite hydrogels and MSCs stimulated angiogenesis and M1-M2 phenotype switching of macrophages, provides a suitable niche for functional recovery of wounds. Compared to skin defects treated with MSC-free hydrogels, the defects treated with the MSC-laden composite hydrogels heal faster and form scarless tissues with hair follicles. Wound healing can be further improved by adjusting the ratio of silk nanofibers and particles and the loaded MSCs, suggesting tunability of the system. To the best of current knowledge, this is the first time scarless skin regeneration with hair follicles based on silk material systems is reported. The improved wound healing capacity of the systems suggests future in vivo studies to compare to other biomaterial systems related to clinical goals in skin regeneration in the absence of scarring.

Template-based fabrication of spatially organized 3D bioactive constructs using magnetic low-concentration gelation methacrylate (GelMA) microfibers

Low concentrations of gelatin methacrylate (GelMA) microfibers are more favorable for cellular activity compared with high concentrations. However, applying low-concentration GelMA microfibers as building blocks for higher-order cellular assembly remains challenging owing to their poor mechanical properties. Herein, we report a new template-based method to solve this problem. GelMA microfibers (5%, w/v) containing magnetic nanoparticles were synthesized by a microfluidic spinning method. A 9 × 9 micropillar array surrounded by a magnetic substrate was constructed to form 8 × 8 microgaps arranged in a crisscross pattern as a magnetic template. In DMEM solution, magnetic attraction facilitated efficient arrangement of the microfibers according to the template with micron assembly accuracy, with a microgrid-like construct (microGC) generated after removing all micropillars. MicroGCs were shown to effectively support the activities of surface seeded or encapsulated cells and be flexibly constructed with various organized spatial patterns. Owing to the low mechanical property requirements of assembled microfibers and the easy-to-implement operation, the proposed method provides a versatile pathway for the assembly of various microfluidic spun microfibers. Furthermore, the resulting 3D microgrid-like cellular constructs with organized spatiotemporal composition offer a convenient platform for the study of tissue engineering.

Polysaccharide-Based Bioink Formulation for 3D Bioprinting of an In Vitro Model of the Human Dermis

Limitations in wound management have prompted scientists to introduce bioprinting techniques for creating constructs that can address clinical problems. The bioprinting approach is renowned for its ability to spatially control the three-dimensional (3D) placement of cells, molecules, and biomaterials. These features provide new possibilities to enhance homology to native skin and improve functional outcomes. However, for the clinical value, the development of hydrogel bioink with refined printability and bioactive properties is needed. In this study, we combined the outstanding viscoelastic behavior of nanofibrillated cellulose (NFC) with the fast cross-linking ability of alginate (ALG), carboxymethyl cellulose (CMC), and encapsulated human-derived skin fibroblasts (hSF) to create a bioink for the 3D bioprinting of a dermis layer. The shear thinning behavior of hSF-laden bioink enables construction of 3D scaffolds with high cell density and homogeneous cell distribution. The obtained results demonstrated that hSF-laden bioink supports cellular activity of hSF (up to 29 days) while offering proper printability in a biologically relevant 3D environment, making it a promising tool for skin tissue engineering and drug testing applications.

Tissue Engineering and Regenerative Medicine: Achievements, Future, and Sustainability in Asia

Exploring innovative solutions to improve the healthcare of the aging and diseased population continues to be a global challenge. Among a number of strategies toward this goal, tissue engineering and regenerative medicine (TERM) has gradually evolved into a promising approach to meet future needs of patients. TERM has recently received increasing attention in Asia, as evidenced by the markedly increased number of researchers, publications, clinical trials, and translational products. This review aims to give a brief overview of TERM development in Asia over the last decade by highlighting some of the important advances in this field and featuring major achievements of representative research groups. The development of novel biomaterials and enabling technologies, identification of new cell sources, and applications of TERM in various tissues are briefly introduced. Finally, the achievement of TERM in Asia, including important publications, representative discoveries, clinical trials, and examples of commercial products will be introduced. Discussion on current limitations and future directions in this hot topic will also be provided.

Progressive 3D Printing Technology and Its Application in Medical Materials

Three-dimensional (3D) printing enables patient-specific anatomical level productions with high adjustability and resolution in microstructures. With cost-effective manufacturing for high productivity, 3D printing has become a leading healthcare and pharmaceutical manufacturing technology, which is suitable for variety of applications including tissue engineering models, anatomical models, pharmacological design and validation model, medical apparatus and instruments. Today, 3D printing is offering clinical available medical products and platforms suitable for emerging research fields, including tissue and organ printing. In this review, our goal is to discuss progressive 3D printing technology and its application in medical materials. The additive overview also provides manufacturing techniques and printable materials.

The topography of fibrous scaffolds modulates the paracrine function of Ad-MSCs in the regeneration of skin tissues

Injuries to the skin are common in daily life, and a certain type or size of defect is not easily restored using conventional dressings or naturally. The repair of these defects requires restoration of function in regenerated tissues. In this study, a tissue engineered skin was designed and fabricated using a bio-3D printing system. Polycaprolactone and bacterial cellulose comprised the scaffold, due to their excellent biocompatibility and multifunctionality. Adipose-derived mesenchymal stem cells (Ad-MSCs) were seeded onto the scaffold to functionalize it as an artificial skin. The finished artificial skin had mechanical properties similar to that of natural skin, and its fibrous structure providing a unique micro-environment that could regulate the paracrine function of the Ad-MSCs. This effect could be greatly increased by changes in the characteristics of the biomaterials. The artificial skin exhibited high biological activity, strong induction of cell recruitment, migration, growth and up-regulation of gene expression of relevant factors, resulting in excellent wound healing characteristics. This study clarified novel design aspects of cell-material interactions in which the topographical characteristics of materials can be further developed to establish cell signaling or communication networks that take advantage of the paracrine actions of Ad-MSCs to promote specific tissue regeneration or repair characteristics.

Adipose-derived stromal cells in regulation of hematopoiesis

Over the past decade, mesenchymal stromal cells (MSCs) found in the bone marrow microenvironment have been considered to be important candidates in cellular therapy. However, the application of MSCs in clinical settings is limited by the difficulty and low efficiency associated with the separation of MSCs from the bone marrow. Therefore, distinct sources of MSCs have been extensively explored. Adipose-derived stromal cells (ASCs), a cell line similar to MSCs, have been identified as a promising source. ASCs have become increasingly popular in many fields, as they can be conveniently extracted from fat tissue. This review focuses on the properties of ASCs in hematopoietic regulation and the underlying mechanisms, as well as the current applications and future perspectives in ASC-based therapy.

From Shape to Function: The Next Step in Bioprinting

In 2013, the "biofabrication window" was introduced to reflect the processing challenge for the fields of biofabrication and bioprinting. At that time, the lack of printable materials that could serve as cell-laden bioinks, as well as the limitations of printing and assembly methods, presented a major constraint. However, recent developments have now resulted in the availability of a plethora of bioinks, new printing approaches, and the technological advancement of established techniques. Nevertheless, it remains largely unknown which materials and technical parameters are essential for the fabrication of intrinsically hierarchical cell-material constructs that truly mimic biologically functional tissue. In order to achieve this, it is urged that the field now shift its focus from materials and technologies toward the biological development of the resulting constructs. Therefore, herein, the recent material and technological advances since the introduction of the biofabrication window are briefly summarized, i.e., approaches how to generate shape, to then focus the discussion on how to acquire the biological function within this context. In particular, a vision of how biological function can evolve from the possibility to determine shape is outlined.

Free and hydrogel encapsulated exosome-based therapies in regenerative medicine

Over the last few decades, mesenchymal stem cells-derived exosomes (MSCs-Ex) have attracted a lot of attention as a therapeutic tool in regenerative medicine. Exosomes are extracellular vehicles (EVs) that play important roles in cell-cell communication through various processes such as stress response, senescence, angiogenesis, and cell differentiation. Success in the field of regenerative medicine sparked exploration of the potential use of exosomes as key therapeutic effectors of MSCs to promote tissue regeneration. Various approaches including direct injection, intravenous injection, intraperitoneal injection, oral administration, and hydrogel-based encapsulation have been exploited to deliver exosomes to target tissues in different disease models. Despite significant advances in exosome therapy, it is unclear which approach is more effective for administering exosomes. Herein, we critically review the emerging progress in the applications of exosomes in the form of free or association with hydrogels as therapeutic agents for applications in regenerative medicine.

Pilot Study of the Biological Properties and Vascularization of 3D Printed Bilayer Skin Grafts

The skin is the largest human organ, and defects in the skin with a diameter greater than 4 cm do not heal without treatment. Allogeneic skin transplantation has been used to allow wound healing, but many grafts do not survive after implantation, due to multiple complications in the procedure. In the present study, the vascularization of three-dimensional (3D) printed full-thickness skin grafts was investigated. Dermal-epithelial grafts were transplanted into a nude mouse model to evaluate integration with the host tissue and the extent of wound healing. To create microvessels in the skin grafts, a bilayer structure consisting of human dermal fibroblasts, keratinocytes, and microvascular endothelial cells was designed and fabricated using an extruded 3D printer. Human dermal fibroblasts and human microvascular endothelial cells were mixed with gelatin-sodium alginate composite hydrogel as the dermis, and human keratinocytes were mixed with gel as the epithelium. Confocal imaging allowed visualization of the location of the cells in the double-layer skin grafts. A full-thickness wound was created on the backs of nude mice and then covered with a double-layer skin graft. Various groups of mice were tested. Animals were euthanized and tissue samples collected after specified time points. Compared with the control group, wound contraction improved by approximately 10%. Histological analysis demonstrated that the new skin had an appearance similar to that of normal skin and with a significant degree of angiogenesis. The results of the immunohistochemical analysis demonstrated that the transplanted cells survived and participated in the healing process.

Three Dimensional Bioprinting of a Vascularized and Perfusable Skin Graft Using Human Keratinocytes, Fibroblasts, Pericytes, and Endothelial Cells

Multilayered skin substitutes comprising allogeneic cells have been tested for the treatment of nonhealing cutaneous ulcers. However, such nonnative skin grafts fail to permanently engraft because they lack dermal vascular networks important for integration with the host tissue. In this study, we describe the fabrication of an implantable multilayered vascularized bioengineered skin graft using 3D bioprinting. The graft is formed using one bioink containing human foreskin dermal fibroblasts (FBs), human endothelial cells (ECs) derived from cord blood human endothelial colony-forming cells (HECFCs), and human placental pericytes (PCs) suspended in rat tail type I collagen to form a dermis followed by printing with a second bioink containing human foreskin keratinocytes (KCs) to form an epidermis. In vitro, KCs replicate and mature to form a multilayered barrier, while the ECs and PCs self-assemble into interconnected microvascular networks. The PCs in the dermal bioink associate with EC-lined vascular structures and appear to improve KC maturation. When these 3D printed grafts are implanted on the dorsum of immunodeficient mice, the human EC-lined structures inosculate with mouse microvessels arising from the wound bed and become perfused within 4 weeks after implantation. The presence of PCs in the printed dermis enhances the invasion of the graft by host microvessels and the formation of an epidermal rete. Impact Statement Three Dimensional printing can be used to generate multilayered vascularized human skin grafts that can potentially overcome the limitations of graft survival observed in current avascular skin substitutes. Inclusion of human pericytes in the dermal bioink appears to improve both dermal and epidermal maturation.

Advances in Hydrogels in Organoids and Organs-on-a-Chip

Significant advances in materials, microscale technology, and stem cell biology have enabled the construction of 3D tissues and organs, which will ultimately lead to more effective diagnostics and therapy. Organoids and organs-on-a-chip (OOC), evolved from developmental biology and bioengineering principles, have emerged as major technological breakthrough and distinct model systems to revolutionize biomedical research and drug discovery by recapitulating the key structural and functional complexity of human organs in vitro. There is growing interest in the development of functional biomaterials, especially hydrogels, for utilization in these promising systems to build more physiologically relevant 3D tissues with defined properties. The remarkable properties of defined hydrogels as proper extracellular matrix that can instruct cellular behaviors are presented. The recent trend where functional hydrogels are integrated into organoids and OOC systems for the construction of 3D tissue models is highlighted. Future opportunities and perspectives in the development of advanced hydrogels toward accelerating organoids and OOC research in biomedical applications are also discussed.

Microtopography-Guided Radial Gradient Circle Array Film with Nanoscale Resolution

Distribution of multimaterials at arbitrary positions with nanoscale resolution and over a large area substrate is essential to future advances in functional graded materials. Such stringent requirements are highly beyond the reach of current techniques, although newly developed 3D printing technologies are addressed. Here, a radial gradient circle array film with the distribution accuracy up to ≈18 nm is fabricated by using microtopographic substrate. A mathematical model is developed to guide the distribution of position, size, shape, and type of materials on an arbitrary section for the given morphology of substrate. The periodic electrical and mechanical properties of the radial gradient circle film are identified, which can be beneficial for further functionalization and applications, such as gradient refractive index lenses, microcoils, and microantennas.

Endothelialized microrods for minimally invasive in situ neovascularization

Despite the significant advancements in fabricating various scaffolding systems over the past decades, generation of functional tissues towards vascularization remains challenging for the currently available biofabrication approaches. On the other hand, the applicability of traditional surgical transplantation of vascularized tissue constructs is sometimes limited due to the sophisticated surgical procedures, which are invasive, leading to increased risks of scar formation and infection. Considering these facts, we present an innovative platform, the angiogenic microrods composed of sodium alginate/gelatin harboring proliferating endothelial cells using a specially designed double T-junction microfluidic device with an expansion chamber, for achieving minimally invasive neovascularization in situ. Such vessel-like microarchitectures could be derived through controlled penetration of the crosslinker genepin for the gelatin phase, ensuing differential degrees in crosslinking of peripheral and central portions of the microstructures, thus resulting in the formation of vascular lumen-like hollow cavities via endothelial cell migration and proliferation during culture in vitro. Furthermore, in vivo performance of the microrods was explored. We believe that the development of these modular microrods for minimally invasive delivery is of great interest and offers a convenient approach for vascularization in situ.

A potential dermal substitute using decellularized dermis extracellular matrix derived bio-ink

Upon bioprinting, cells are mixed with a biomaterial to fabricate a living tissue, thus emphasizing the importance of biomaterials. The biomaterial used in this study was a bio-ink prepared using skin decellularized extracellular matrix (dECM). Skin dECM was extracted by treating the dermis with chemicals and enzymes; the basic structural and functional proteins of the ECM, including collagen, glycosaminoglycans (GAGs), bioreactive materials and growth factors, were preserved, whereas the resident cells that might cause immune rejection or inflammatory responses were removed. The bio-ink based on dECM powder, together with human dermal fibroblasts (HDFs), was loaded into the nozzle of the 3D bioprinter to create the 3D construct. This construct underwent gelation with changing temperature while its shape was maintained for 7 days. The cells showed over 90% viability and proliferation. By analysing the gene expression pattern in the cells of the construct, the skin regenerative mechanism of the bio-ink was verified. Microarray results confirmed that the gene expression related to skin morphology and development had been enhanced because the bioreactive molecules and growth factors, in addition to residual ECM in dECM, provided an optimal condition for the HDFs.

Three-dimensional bioprinting for organ bioengineering: promise and pitfalls

PURPOSE OF REVIEW

Loss of organ function is a critical issue that threatens a patient's life. Currently, the only available treatment is organ transplantation; however, shortage of donor organs, histocompatibility, and life-long immunosuppression present major challenges. Three-dimensional bioprinting technology holds a promising solution for treating organ failure by fabricating autologous tissues and organs for transplantation. To biofabricate a functional tissue, target-cell types are combined with an appropriate biomaterial for structural support and a bioink that supports cell function and maturation. Bioprinted structures can mimic the native tissue shape and functionality.

RECENT FINDINGS

The main goal of three-dimensional bioprinting is to produce functional tissues/organs; however, whole organ printing has not been achieved. There have been recent advances in the successful three-dimensional bioprinting of numerous tissues. This review will discuss the types of bioprinters, biomaterials, bioinks, and the fabrication of various constructs for repair of vascular, cartilage, skin, cardiac, and liver tissues. These bioprinted tissue constructs have the potential to be used to treat tissues and organs that have been damaged by injury or disease.

SUMMARY

Three-dimensional bioprinting technology offers the ability to fabricate three-dimensional tissue structures with high precision, fidelity, and stability at human clinical scale. The creation of complex tissue architectures with heterogeneous compositions has the potential to revolutionize transplantation of tissues and organs.

Recent Trends in Decellularized Extracellular Matrix Bioinks for 3D Printing: An Updated Review

The promise of regenerative medicine and tissue engineering is founded on the ability to regenerate diseased or damaged tissues and organs into functional tissues and organs or the creation of new tissues and organs altogether. In theory, damaged and diseased tissues and organs can be regenerated or created using different configurations and combinations of extracellular matrix (ECM), cells, and inductive biomolecules. Regenerative medicine and tissue engineering can allow the improvement of patients' quality of life through availing novel treatment options. The coupling of regenerative medicine and tissue engineering with 3D printing, big data, and computational algorithms is revolutionizing the treatment of patients in a huge way. 3D bioprinting allows the proper placement of cells and ECMs, allowing the recapitulation of native microenvironments of tissues and organs. 3D bioprinting utilizes different bioinks made up of different formulations of ECM/biomaterials, biomolecules, and even cells. The choice of the bioink used during 3D bioprinting is very important as properties such as printability, compatibility, and physical strength influence the final construct printed. The extracellular matrix (ECM) provides both physical and mechanical microenvironment needed by cells to survive and proliferate. Decellularized ECM bioink contains biochemical cues from the original native ECM and also the right proportions of ECM proteins. Different techniques and characterization methods are used to derive bioinks from several tissues and organs and to evaluate their quality. This review discusses the uses of decellularized ECM bioinks and argues that they represent the most biomimetic bioinks available. In addition, we briefly discuss some polymer-based bioinks utilized in 3D bioprinting.

Directed differential behaviors of multipotent adult stem cells from decellularized tissue/organ extracellular matrix bioinks

The decellularized tissue/organ extracellular matrix (dECM) is a naturally derived biomaterial that inherits various functional components from the native tissue or organ. Recently, various kinds of tissue/organ dECM bioinks capable of encapsulating cells, combined with 3D cell printing, have enabled remarkable progress in tissue engineering and regenerative medicine. However, the way in which the dECM component compositions of each tissue of different origins interact with cells and dictate tissue-specific cell behavior in the 3D microenvironment remains mostly unknown. To address this issue, in-depth differential proteomic analyses of four porcine dECMs were performed. Specifically, the differential variations of matrisome protein composition in each decellularized tissue type were also uncovered, which can play a significant role by affecting the resident cells in specific tissues. Furthermore, microarray analyses of human bone marrow mesenchymal stem cells (hBMMSCs) printed with various dECM bioinks were conducted to reveal the effect of compositional variations in a tissue-specific manner at the cellular level depending on the multipotency of MSCs. Through whole transcriptome analysis, differential expression patterns of genes were observed in a tissue-specific manner, and this research provides strong evidence of the tissue-specific functionalities of dECM bioinks.

Healing of Chronic Wounds: An Update of Recent Developments and Future Possibilities

Chronic wounds are the result of disruptions in the body's usual process of healing. They are not only a source of significant pain and discomfort but also, more importantly, an unguarded port of entry for pathogens into the body. While our current understanding of this phenomenon is far from complete, findings in physiological patterns and advancements in wound healing technologies have helped develop wound management and healing solutions to this long-standing medical challenge. This review presents an overview of known wound healing mechanics, abnormalities that lead to chronic wounds, and a summary of established and new wound healing technologies. Various approaches to heal wounds are discussed, from dermal replacements to advanced biomaterial-based treatments, from cell-, synthetic-, and composite-based approaches to preclinical approaches, which make developing such products possible. While tested breakthrough products are described, the authors focused more on recently developed innovations, which are at varying stages of maturity. The review concludes with a note on future perspectives and opinions on where the field and industry are headed and where they should be. Impact Statement Wound healing is an important area of research and clinical practice, and has captured the attention of tissue engineers since the nascent beginnings of the discipline. Tissue-engineered skin was the first FDA-approved product, achieved in 1996. Despite this success, and the passage of time, healing wounds, particularly chronic wounds, remains a vexing challenge. This comprehensive review article will provide readers with a synopsis of current issues, research approaches, animal models, technologies, and products that span the continuum from early development to clinical studies, in the hope of fueling new interests and ideas to overcome this long-standing medical challenge.

Biofabrication of thick vascularized neo-pedicle flaps for reconstructive surgery

Wound chronicity due to intrinsic and extrinsic factors perturbs adequate lesion closure and reestablishment of the protective skin barrier. Immediate and proper care of chronic wounds is necessary for a swift recovery and a reduction of patient vulnerability to infection. Advanced therapies supplemented with standard wound care procedures have been clinically implemented to restore aberrant tissue; however, these treatments are ineffective if local vasculature is too compromised to support minimally-invasive strategies. Autologous "flaps", which are tissues equipped with their own hierarchical vascular supply, can be harvested from one region of the patient and transplanted to the wound where it is reperfused upon microsurgical anastomosis to appropriate recipient vessels. Despite the success of autologous flap transfer, these procedures are extremely invasive, incur obligatory donor-site morbidity, and require sufficient donor-tissue availability, microsurgical expertise, and specialized equipment. 3D-bioprinting modalities, such as extrusion-based bioprinting, can be used to address the clinical constraints of autologous flap transfer, primarily addressing donor-site morbidity and tissue availability. This advancement in regenerative medicine allows the biofabrication of heterogeneous tissue structures with high shape fidelity and spatial resolution to generate biomimetic constructs with the anatomically-precise geometries of native tissue to ensure tissue-specific function. Yet, meaningful progress toward this clinical application has been limited by the lack of vascularization required to meet the nutrient and oxygen demands of clinically relevant tissue volumes. Thus, various criteria for the fabrication of functional tissues with hierarchical, patent vasculature must be considered when implementing 3D-bioprinting technologies for deep, chronic wounds.

Recent advances in 3D printing: vascular network for tissue and organ regeneration

Over the past years, the fabrication of adequate vascular networks has remained the main challenge in engineering tissues due to technical difficulties, while the ultimate objective of tissue engineering is to create fully functional and sustainable organs and tissues to transplant in the human body. There have been a number of studies performed to overcome this limitation, and as a result, 3D printing has become an emerging technique to serve in a variety of applications in constructing vascular networks within tissues and organs. 3D printing incorporated technical approaches allow researchers to fabricate complex and systematic architecture of vascular networks and offer various selections for fabrication materials and printing techniques. In this review, we will discuss materials and strategies for 3D printed vascular networks as well as specific applications for certain vascularized tissue and organ regeneration. We will also address the current limitations of vascular tissue engineering and make suggestions for future directions research may take.

3D and 4D Printing of Polymers for Tissue Engineering Applications

Three-dimensional (3D) and Four-dimensional (4D) printing emerged as the next generation of fabrication techniques, spanning across various research areas, such as engineering, chemistry, biology, computer science, and materials science. Three-dimensional printing enables the fabrication of complex forms with high precision, through a layer-by-layer addition of different materials. Use of intelligent materials which change shape or color, produce an electrical current, become bioactive, or perform an intended function in response to an external stimulus, paves the way for the production of dynamic 3D structures, which is now called 4D printing. 3D and 4D printing techniques have great potential in the production of scaffolds to be applied in tissue engineering, especially in constructing patient specific scaffolds. Furthermore, physical and chemical guidance cues can be printed with these methods to improve the extent and rate of targeted tissue regeneration. This review presents a comprehensive survey of 3D and 4D printing methods, and the advantage of their use in tissue regeneration over other scaffold production approaches.

Akermanite bioceramic enhances wound healing with accelerated reepithelialization by promoting proliferation, migration, and stemness of epidermal cells

Reepithelialization is an important step of wound healing, which is mainly completed by proliferation and migration of epidermal cells. Akermanite is a Ca-, Mg-, and Si-containing bioceramic. This study evaluated the effects of Akermanite on wound healing and investigated the mechanisms. Using scald burn mice models, we demonstrated that local Akermanite treatment significantly accelerated wound healing by increasing reepithelialization and the stemness of epidermal cells. Epidermal cells were cultured in medium containing Akermanite extracts to explore the cellular mechanism of reepithelialization. Akermanite promoted the cell proliferation and migration, maintaining more cells in the S and G₂ /M phases of the cell cycle. An additional study showed that Akermanite enhanced the expressions of integrinβ1, Lgr4, Lgr5, and Lgr6, which are specific molecular markers of epidermal stem cells, accompanied by the activation of the Wnt/β-catenin pathway. These results suggested that Akermanite accelerated reepithelialization by increasing the proliferation, migration, and stemness of epidermal cells in a manner related to the Wnt/β-catenin pathway, which might contribute, at least partially, to accelerated wound healing by Akermanite therapy.

Fabrication of Bioengineered Skin by Injection Molding: A Feasibility Study on Automation

The use of bioengineered skin has facilitated fundamental and applied research because it enables the investigation of complex interactions between various cell types as well as the extracellular matrix. The predominantly manual fabrication of these living tissues means, however, that their quality, standardization, and production volume are extremely dependent on the technician's experience. Simple laboratory automation could facilitate the use of living tissues by a greater number of research groups. We developed and present here an injection molding technique for the fabrication of bilayered skin equivalents. The tissue was formed automatically by two separate injections into a customized mold to produce the dermal and epidermal skin layers. We demonstrated the biocompatibility of this fabrication process and confirmed the resulting bilayered morphology of the bioengineered skin using histology and immunohistochemistry. Our findings highlight the possibility of fabricating multilayered living tissue by injection molding, suggesting that further investigation into this automation method could result in the rapid and low-cost fabrication of standardized bioengineered skin.

A novel strategy to engineer pre-vascularized 3-dimensional skin substitutes to achieve efficient, functional engraftment

Autologous split-thickness skin grafts are the preferred treatment for excised burn wounds, but donor sites for autografting are often limited in patients with extensive burns. A number of alternative treatments are already in use to treat large burns and ulcers. Despite intense efforts to develop tissue-engineered skin, delayed or absent vascularization is one of the major reasons for tissue-engineered skin engraftment failure. To overcome these problems, we developed a scaffold-free 3-dimensional (3D) skin substitute containing vascular networks that combine dermal fibroblasts, endothelial cells, and epidermal keratinocytes based on our layer-by-layer cell coating technique. We transplanted the pre-vascularized 3D skin substitutes onto full-thickness skin defects on severe combined immunodeficiency mice to assess their integration with the host tissue and effects on wound healing. We used non-vascularized 3D skin substitutes as a control. Vessels containing red blood cells were evident in the non-vascularized control by day 14. However, blood perfusion of the human-derived vasculature could be detected within 7 days of grafting. Moreover, the pre-vascularized 3D skin substitutes had high graft survival and their epidermal layers were progressively replaced by mouse epidermis. We propose that a novel dermo-epidermal 3D skin substitute containing blood vessels can promote efficient reconstruction of full-thickness skin defects.

Coacervate-mediated exogenous growth factor delivery for scarless skin regeneration

Although there are numerous medical applications to recover damaged skin tissue, scarless wound healing is being extensively investigated to provide a better therapeutic outcome. The exogenous delivery of therapeutic growth factors (GFs) is one of the engineering strategies for skin regeneration. This study presents an exogenous GF delivery platform developed using coacervates (Coa), a tertiary complex of poly(ethylene argininyl aspartate diglyceride) (PEAD) polycation, heparin, and cargo GFs (i.e., transforming growth factor beta 3 (TGF-β3) and interleukin 10 (IL-10)). Coa encompasses the advantage of high biocompatibility, facile preparation, protection of cargo GFs, and sustained GF release. We therefore speculated that coacervate-mediated dual delivery of TGF-β3/IL-10 would exhibit synergistic effects for the reduction of scar formation during physiological wound healing. Our results indicate that the exogenous administration of dual GF via Coa enhances the proliferation and migration of skin-related cells. Gene expression profiles using RT-PCR revealed up-regulation of ECM formation at early stage of wound healing and down-regulation of scar-related genes at later stages. Furthermore, direct injection of the dual GF Coa into the edges of damaged skin in a rat skin wound defect model demonstrated accelerated wound closure and skin regeneration after 3 weeks. Histological evaluation and immunohistochemical staining also revealed enhanced formation of the epidermal layer along with facilitated angiogenesis following dual GF Coa delivery. Based on these results, we conclude that polycation-mediated Coa fabrication and exogenous dual GF delivery via the Coa platform effectively augments both the quantity and quality of regenerated skin tissues without scar formation. STATEMENT OF SIGNIFICANCE: This study was conducted to develop a simple administration platform for scarless skin regeneration using polycation-based coacervates with dual GFs. Both in vitro and in vivo studies were performed to confirm the therapeutic efficacy of this platform toward scarless wound healing. Our results demonstrate that the platform developed by us enhances the proliferation and migration of skin-related cells. Sequential modulation in various gene expression profiles suggests a balanced collagen-remodeling process by dual GFs. Furthermore, in vivo histological evaluation demonstrates that our technique enhances clear epidermis formation with less scab and thicker woven structure of collagen bundle, similar to that of a normal tissue. We propose that simple administration of dual GFs with Coa has the potential to be applied as a clinical approach for fundamental scarless skin regeneration.

Decellularized ECM-derived bioinks: Prospects for the future

Decellularization aims to remove cells from tissue ultrastructure while preserving the mechanical and biological properties, which makes the decellularized extracellular matrix (dECM) an appropriate scaffold for tissue engineering applications. Three-dimensional (3D) bioprinting technology as a reproducible and accurate method can print the combination of ECM and autologous cells layer by layer to fabricate patient based cell-laden structures representing the intrinsic cues of natural ECM. This review defines ECM, classifies decellularization agents and techniques, and explains different sources of ECM. Then, bioprinting techniques, bioink concept, applications of dECM bioinks, and finally the future perspectives of 3d bioprinting technology are discussed.

3D Cell Printing of Perfusable Vascularized Human Skin Equivalent Composed of Epidermis, Dermis, and Hypodermis for Better Structural Recapitulation of Native Skin

Although skin cell-printing has exhibited promises for fabrication of functional skin equivalents, existing skin models through 3D cell printing are still composed of dermal and epidermal layers. However, a key hope for printing skin is to improve structural complexity of human skin over conventional construction, enabling the precise localization of multiple cell types and biomaterials. Here, the complexity of skin anatomy is increased using 3D cell printing. A novel printing platform is suggested for engineering a matured perfusable vascularized 3D human skin equivalent composed of epidermis, dermis, and hypodermis. The skin model is evaluated using functional markers representing each region of epidermis, dermis, and hypodermis to confirm tissue maturation. It is hypothesized that the vascularized dermal and hypodermal compartments that provide a more realistic microenvironment can promote cross-talks with the epidermal compartment, producing better recapitulation of epidermal morphogenesis. Skin stemness in epithelial tissue is investigated. These findings reveal that the full-thickness skin has more similarities to the native human skin compared with the dermal and epidermal skin model, indicating that it better reflects the actual complexity of native human skin. It is envisioned that it offers better predictive and reliable in vitro platform for investigation of mechanisms of pathological research and skin disease modeling.

One-pot reactive electrospinning of chitosan/PVA hydrogel nanofibers reinforced by halloysite nanotubes with enhanced fibroblast cell attachment for skin tissue regeneration

In this study, in situ glyoxal crosslinked chitosan/poly (vinyl alcohol) (PVA) hydrogel nanofibers reinforced with halloysite nanotubes (HNT) were prepared by the electrospinning method without needing post-treatment for stabilization of the nanofibers in aqueous media. FTIR spectroscopy approved the formation of acetal bonds between glyoxal and hydroxyl groups of PVA and chitosan. Morphological studies by SEM/EDX and TEM in accordance with XRD patterns proved that HNT was successfully incorporated into the crosslinked chitosan/PVA nanofibers. The crosslinked nanofibers were insoluble in water. Due to the hydrophilic nature of HNT, the swelling of the nanofibers was increased from 272% for crosslinked chitosan/PVA nanofibers to around 400% for the HNT reinforced nanocomposite nanofibers. Comparing to chitosan/PVA nanofibers, the tensile strength of the crosslinked nanocomposite nanofibers was increased to 2.4 and 3.5 fold by incorporation of 3 and 5% HNT, respectively. Presence of HNT in chitosan/PVA nanofibers reduced the contact angle with water and increased the hydrophilicity of HNT-reinforced nanofibers favoring the attachment of fibroblast cells. Cytotoxicity studies by AlamarBlue assay showed that presence of HNT increased the biocompatibility of the nanofibers. It was also concluded that glyoxal can be used safely for crosslinking of chitosan/PVA nanofibers without any cytotoxic effect for fibroblast cells. From the results of this work, HNT reinforced chitosan/PVA nanofibers crosslinked by glyoxal are introduced as promising nanomaterials for skin tissue regeneration.

Decellularized Extracellular Matrix Materials for Cardiac Repair and Regeneration

Decellularized extracellular matrix (dECM) is a promising biomaterial for repairing cardiovascular tissue, as dECM most effectively captures the complex array of proteins, glycosaminoglycans, proteoglycans, and many other matrix components that are found in native tissue, providing ideal cues for regeneration and repair of damaged myocardium. dECM can be used in a variety of forms, such as solid scaffolds that maintain native matrix structure, or as soluble materials that can form injectable hydrogels for tissue repair. dECM has found recent success in many regeneration and repair therapies, such as for musculoskeletal, neural, and liver tissues. This review focuses on dECM in the context of cardiovascular applications, with variations in tissue and species sourcing, and specifically discusses advances in solid and soluble dECM development, in vitro studies, in vivo implementation, and clinical translation.

Current and Future Perspectives on Skin Tissue Engineering: Key Features of Biomedical Research, Translational Assessment, and Clinical Application

The skin is responsible for several important physiological functions and has enormous clinical significance in wound healing. Tissue engineered substitutes may be used in patients suffering from skin injuries to support regeneration of the epidermis, dermis, or both. Skin substitutes are also gaining traction in the cosmetics and pharmaceutical industries as alternatives to animal models for product testing. Recent biomedical advances, ranging from cellular-level therapies such as mesenchymal stem cell or growth factor delivery, to large-scale biofabrication techniques including 3D printing, have enabled the implementation of unique strategies and novel biomaterials to recapitulate the biological, architectural, and functional complexity of native skin. This progress report highlights some of the latest approaches to skin regeneration and biofabrication using tissue engineering techniques. Current challenges in fabricating multilayered skin are addressed, and perspectives on efforts and strategies to meet those limitations are provided. Commercially available skin substitute technologies are also examined, and strategies to recapitulate native physiology, the role of regulatory agencies in supporting translation, as well as current clinical needs, are reviewed. By considering each of these perspectives while moving from bench to bedside, tissue engineering may be leveraged to create improved skin substitutes for both in vitro testing and clinical applications.

Magnetic Nanoparticle-Embedded Hydrogel Sheet with a Groove Pattern for Wound Healing Application

Endothelial progenitor cells (EPCs) can induce a pro-angiogenic response during tissue repair. Recently, EPC transplantations have been widely investigated in wound healing applications. To maximize the healing efficacy by EPCs, a unique scaffold design that allows cell retention and function would be desirable for in situ delivery. Herein, we fabricated an alginate/poly-l-ornithine/gelatin (alginate-PLO-gelatin) hydrogel sheet with a groove pattern for use as a cell delivery platform. In addition, we demonstrate the topographical modification of the hydrogel sheet surface with a groove pattern to modulate cell proliferation, alignment, and elongation. We report that the patterned substrate prompted morphological changes of endothelial cells, increased cell-cell interaction, and resulted in the active secretion of growth factors such as PDGF-BB. Additionally, we incorporated magnetic nanoparticles (MNPs) into the patterned hydrogel sheet for the magnetic field-induced transfer of cell-seeded hydrogel sheets. As a result, enhanced wound healing was observed via efficient transplantation of the EPCs with an MNP-embedded patterned hydrogel sheet (MPS). Finally, enhanced vascularization and dermal wound repair were observed with EPC seeded MPS.