Engineering organs

Scaffold-based tissue engineering strategies for urethral repair and reconstruction

Urethral strictures are common in urology; however, the reconstruction of long urethral strictures remains challenging. There are still unavoidable limitations in the clinical application of grafts for urethral injuries, which has facilitated the advancement of urethral tissue engineering. Tissue-engineered urethral scaffolds that combine cells or bioactive factors with a biomaterial to mimic the native microenvironment of the urethra, offer a promising approach to urethral reconstruction. Despite the recent rapid development of tissue engineering materials and techniques, a consensus on the optimal strategy for urethral repair and reconstruction is still lacking. This review aims to collect the achievements of urethral tissue engineering in recent years and to categorize and summarize them to shed new light on their design. Finally, we visualize several important future directions for urethral repair and reconstruction.

Constructing appropriate bioprinting regulations: the ethical importance of recognising a liminal technology

This article provides an analysis of bioprinting personalised medical device technology and its ethical challenges to regulation and research ethics. I argue the inclusion of bioprinting applications within existing regulatory frameworks does not adequately address the technologies disruption to the traditionally siloed activities of research and treatment. Using the conceptual framework of liminality, I offer a meaningful way to engage with this technology and address some identified concerns with how it will be categorised and the appropriate recognition of its evidentiary thresholds. I demonstrate these concerns through the exploration of limited conventional research methodologies tasked with the production of generalisable knowledge, specifically population-based evidence that is derived from Randomised Clinical Trials. I use Australian regulatory amendments introduced in 2021 as an example of current regulatory trajectories and highlight why I believe this approach to be insufficient. The significance of this argument will be to demonstrate the disruption of bioprinting applications to current approaches in medical policy, and how various jurisdictions are enacting regulation that is not fit for purpose.

Enhancing the mechanical strength of 3D printed GelMA for soft tissue engineering applications

Gelatin methacrylate (GelMA) hydrogels have gained significant traction in diverse tissue engineering applications through the utilization of 3D printing technology. As an artificial hydrogel possessing remarkable processability, GelMA has emerged as a pioneering material in the advancement of tissue engineering due to its exceptional biocompatibility and degradability. The integration of 3D printing technology facilitates the precise arrangement of cells and hydrogel materials, thereby enabling the creation of in vitro models that simulate artificial tissues suitable for transplantation. Consequently, the potential applications of GelMA in tissue engineering are further expanded. In tissue engineering applications, the mechanical properties of GelMA are often modified to overcome the hydrogel material's inherent mechanical strength limitations. This review provides a comprehensive overview of recent advancements in enhancing the mechanical properties of GelMA at the monomer, micron, and nano scales. Additionally, the diverse applications of GelMA in soft tissue engineering via 3D printing are emphasized. Furthermore, the potential opportunities and obstacles that GelMA may encounter in the field of tissue engineering are discussed. It is our contention that through ongoing technological progress, GelMA hydrogels with enhanced mechanical strength can be successfully fabricated, leading to the production of superior biological scaffolds with increased efficacy for tissue engineering purposes.

A bioartificial and vasculomorphic bone matrix-based organoid mimicking microanatomy of flat and short bones

We engineered an in vitro model of bioartificial 3D bone organoid consistent with an anatomical and vascular microenvironment common to mammalian flat and short bones. To achieve this, we chose the decellularized-decalcified matrix of the adult male rat scapula, implemented with the reconstruction of its intrinsic vessels, obtained through an original intravascular perfusion with polylevolactic (PLLA), followed by coating of the PLLA-fabricated vascularization with rat tail collagen. As a result, the 3D bone and vascular geometry of the native bone cortical and cancellous compartments was reproduced, and the rat tail collagen-PLLA biomaterial could in vitro act as a surrogate of the perivascular extracellular matrix (ECM) around the wall of the biomaterial-reconstituted cancellous vessels. As a proof-of-concept of cell compatibility and site-dependent osteoinductive properties of this bioartificial 3D construct, we show that it in vitro leads to a time-dependent microtopographic positioning of rat mesenchymal stromal cells (MSCs), initiating an osteogenic fate in relation to the bone compartment. In addition, coating of PLLA-reconstructed vessels with rat tail collagen favored perivascular attachment and survival of MSC-like cells (mouse embryonic fibroblasts), confirming its potentiality as a perivascular stroma for triggering competence of seeded MSCs. Finally, in vivo radiographic topography of bone lesions in the human jaw and foot tarsus of subjects with primary osteoporosis revealed selective bone cortical versus cancellous involvement, suggesting usefulness of a human 3D bone organoid engineered with the same principles of our rat organoid, to in vitro investigate compartment-dependent activities of human MSC in flat and short bones under experimental osteoporotic challenge. We conclude that our 3D bioartificial construct offers a reliable replica of flat and short bones microanatomy, and promises to help in building a compartment-dependent mechanistic perspective of bone remodeling, including the microtopographic dysregulation of osteoporosis.

Cell-Based Therapy for Urethral Regeneration: A Narrative Review and Future Perspectives

Urethral stricture is a common urological disease that seriously affects quality of life. Urethroplasty with grafts is the primary treatment, but the autografts used in clinical practice have unavoidable disadvantages, which have contributed to the development of urethral tissue engineering. Using various types of seed cells in combination with biomaterials to construct a tissue-engineered urethra provides a new treatment method to repair long-segment urethral strictures. To date, various cell types have been explored and applied in the field of urethral regeneration. However, no optimal strategy for the source, selection, and application conditions of the cells is available. This review systematically summarizes the use of various cell types in urethral regeneration and their characteristics in recent years and discusses possible future directions of cell-based therapies.

Silk Fibroin Hybrids for Biological Scaffolds with Adhesive Surface and Adaptability to the Target Tissue Change

Background Regenerative Medicine (RM) is a branch of medicine that aims to regenerate tissues and organs to overcome the problems transplants entail (poor availability, risk of rejection and intense immunosuppression). To do this, RM makes use of tissue engineering (TE). This fundamental branch deals with creating biological scaffolds capable of performing the role that physiologically belongs to the extracellular matrix (ECM). In this review, we report how specific characteristics of the scaffolds (bio-compatibility, biodegradability and mechanical and conformal properties) can be obtained using 3D printing, which facilitates the emulation of physiological tissues and organs.

Purpose and scope This review reports recent advances in the fabrication method of bioactive scaffolds that can be used clinically, providing support for cell seeding and proliferation. To this end, silk fibroin, tannin and graphene were used to improve the scaffold’s electro-bio-mechanical properties. These materials in different compositions are studied to demonstrate their potential use as bio-ink in bioadhesives and cellularized and implantable 3D-printed scaffolds.

Summary of new synthesis and conclusions reached in the review Silk fibroin is a natural biopolymer; tannin, on the other hand, is a biological polyphenol, highly reactive with other molecules by nature and with promising antioxidant capabilities. Finally, graphene is nothing more than a monolayer of graphite that has been shown to implement the mechanics and electrical conductivity of the compounds in which it is inserted; it also has excellent biocompatibility and surface area, qualities that promote cell adhesion and growth.

Conclusion Polyphenols and graphene have been shown to work in synergy in improving the electro-mechanical properties of silk fibroin scaffolds. We reported optimal and potentially market-competitive bioadhesives, but above all, the proliferation of neuronal precursor cells in vitro was successfully demonstrated.

Establishment of decellularized extracellular matrix scaffold derived from caprine pancreas as a novel alternative template over porcine pancreatic scaffold for prospective biomedical application

In this study, the caprine pancreas has been presented as an alternative to the porcine organ for pancreatic xenotransplantation with lesser risk factors. The obtained caprine pancreas underwent a systematic cycle of detergent perfusion for decellularization. It was perfused using anionic (0.5% w/v sodium dodecyl sulfate) as well as non-ionic (0.1% v/v triton X-100, t-octyl phenoxy polyethoxy ethanol) detergents and washed intermittently with 1XPBS supplemented with 0.1% v/v antibiotic and nucleases in a gravitation-driven set-up. After 48 h, a white decellularized pancreas was obtained, and its extracellular matrix (ECM) content was examined for scaffold-like properties. The ECM content was assessed for removal of cellular content, and nuclear material was evaluated with temporal H&E staining. Quantified DNA was found to be present in a negligible amount in the resultant decellularized pancreas tissue (DPT), thus prohibiting it from triggering any immunogenicity. Collagen and fibronectin were confirmed to be preserved upon trichrome and immunohistochemical staining, respectively. SEM and AFM images reveal interconnected collagen fibril networks in the DPT, confirming that collagen was unaffected. sGAG was visualized using Prussian blue staining and quantified with DMMB assay, where DPT has effectively retained this ECM component. Uniaxial tensile analysis revealed that DPT possesses better elasticity than NPT (native pancreatic tissue). Physical parameters like tensile strength, stiffness, biodegradation, and swelling index were retained in the DPT with negligible loss. The cytocompatibility analysis of DPT has shown no cytotoxic effect for up to 72 h on normal insulin-producing cells (MIN-6) and cancerous glioblastoma (LN229) cells in vitro. The scaffold was recellularized using isolated mouse islets, which have established in vitro cell proliferation for up to 9 days. The scaffold received at the end of the decellularization cycle was found to be non-toxic to the cells, retained biological and physical properties of the native ECM, suitable for recellularization, and can be used as a safer and better alternative as a transplantable organ from a xenogeneic source.

Decellularization Detergents As Methodological Variables in Mass Spectrometry of Stromal Matrices

Collagens, elastin, fibrillin, decorin, and laminin are key constituents of the extracellular matrix and basement membrane of mammalian organs. Thus, changes in their quantities may influence the mechanochemical regulation of resident cells. Since maintenance of a native stromal composition is a requirement for three-dimensional (3D) matrix-based recellularization techniques in tissue engineering, we studied the influence of the decellularization detergents on these proteins in porcine kidney, liver, pancreas, and skin. Using a quick thawing/quick microwave-assisted decellularization protocol and two different detergents, sodium dodecyl sulfate (SDS) vs Triton X-100 (TX100), at identical concentration, variations in matrix conservation of stromal proteins were detected by liquid chromatography-mass spectrometry coupled to light and scanning electron microscopies, in dependence on each detergent. In all organs tested except pancreas, collagens were retained to a statistically significant level using the TX100-based protocol. In contrast fibrillin, elastin (except in kidney), and decorin (only in liver) were better preserved with the SDS-dependent protocol. Irrespective of the detergent used, laminin always remained at an irrelevant level. Our results prompt attention to the type of detergent in organ decellularization, suggesting that its choice may influence morphoregulatory inputs peculiar to the type of 3D bioartificial mammalian organ to be reconstructed. Impact statement Simple change of the protocol's main detergent leads to a very substantial difference in the panel of the stromal proteins detected by qualitative and semiquantitative mass spectrometry in acellular porcine matrices. This remarkable methodological variable promises to yield proteomic reference panels in a number of different species-specific acellular matrices allowing for selective retainment of peculiar mechanochemical inputs, to differently address the development of the seeded cells in relation to the type of organ to be bioartificially reconstructed.

Evaluation of the Reproducibility and Robustness of Extrusion-Based Bioprinting Processes Applying a Flow Sensor

Bioprinting is increasingly regarded as a suitable additive manufacturing method in biopharmaceutical process development and formulation. In order to manage the leap from research to industrial application, higher levels of reproducibility and a standardized bioprinting process are prerequisites. This said, the concept of process analytical technologies, standard in the biopharmaceutical industry, is still at its very early steps. To date most extrusion-based printing processes are controlled over penumatic pressure and thus not adaptive to environmental or system related changes over several experimental runs. A constant set pressure applied over a number of runs, might lead to variations in flow rate and thus to unreliable printed constructs. With this in mind, the simple question arises whether a printing process based on a set flow rate could improve reproduciblity and transfer to different printing systems. The control and monitoring of flow rate aim to introduce the concept of PAT in the field of bioprinting. This study investigates the effect of different processing modes (set pressure vs. set flow rate) on printing reproducibility occurring during an extrusion-based printing process consisting of 6 experimental runs consisting of 3 printed samples each. Additionally, the influence of different filling levels of the ink containing cartridge during a printing process was determined. Different solutions based on a varying amount of alginate polymer and Kolliphor hydrogels in varying concentrations showed the need for individual setting of printing parameter. To investigate parameter transferability among different devices two different printers were used and the flow was monitored using a flow sensor attached to the printing unit. It could be demonstrated that a set flow rate controlled printing process improved accuracy and the filling level also affects the accuracy of printing, the magnitude of this effects varies as the cartridge level declined. The transferability between printed devices was eased by setting the printing parameters according to a set flow rate of each bioink disregarding the value of the set pressure. Finally, by a bioprinting porcess control based on a set flow rate, the coefficient of variance for printed objects could be reduced from 0.2 to 0.02 for 10% (w/v) alginate polymer solutions.

Elastin-like Polypeptide-Based Bioink: A Promising Alternative for 3D Bioprinting

Three-dimensional (3D) bioprinting offers a great alternative to traditional techniques in tissue reconstruction, based on seeding cells manually into a scaffold, to better reproduce organs' complexity. When a suitable bioink is engineered with appropriate physicochemical properties, such a process can advantageously provide a spatial control of the patterning that improves tissue reconstruction. The design of an adequate bioink must fulfill a long list of criteria including biocompatibility, printability, and stability. In this context, we have developed a bioink containing a precisely controlled recombinant biopolymer, namely, elastin-like polypeptide (ELP). This material was further chemoselectively modified with cross-linkable moieties to provide a 3D network through photopolymerization. ELP chains were additionally either functionalized with a peptide sequence Gly-Arg-Gly-Asp-Ser (GRGDS) or combined with collagen I to enable cell adhesion. Our ELP-based bioinks were found to be printable, while providing excellent mechanical properties such as stiffness and elasticity in their cross-linked form. Besides, they were demonstrated to be biocompatible, showing viability and adhesion of dermal normal human fibroblasts (NHF). Expressions of specific extracellular matrix (ECM) protein markers as pro-collagen I, elastin, fibrillin, and fibronectin were revealed within the 3D network containing cells after only 18 days of culture, showing the great potential of ELP-based bioinks for tissue engineering.

Chitosan/hydroxyapatite nanocomposite scaffolds to modulate osteogenic and inflammatory response

Considerable attention has been given to the use of chitosan (CS)‐based materials reinforced with inorganic bioactive signals such as hydroxyapatite (HA) to treat bone defects and tissue loss. It is well known that CS/HA based materials possess minimal foreign body reactions, good biocompatibility, controlled biodegradability and antibacterial property. Herein, the bioactivity of these composite systems was analyzed on in vitro bone cell models for their applications in the field of bone tissue engineering (BTE). The combination of sol–gel approach and freeze‐drying technology was used to obtain CS/HA scaffolds with three‐dimensional (3D) porous structure suitable for cell in‐growth. Specifically, our aim was to investigate the influence of bioactive composite scaffolds on cellular behavior in terms of osteoinductivity and anti‐inflammatory effects for treating bone defects. The results obtained have demonstrated that by increasing inorganic component concentration, CS/HA (60 and 70% v/v) scaffolds induced a good biological response in terms of osteogenic differentiation of human mesenchymal stem cells (hMSC) towards osteoblast phenotype. Furthermore, the scaffolds with higher concentration of inorganic fillers are able to modulate the production of pro‐inflammatory (TGF‐β) and anti‐inflammatory (IL‐4, IL‐10) cytokines. Our results highlight the possibility of achieving smart CS/HA based composites able to promote a great osteogenic differentiation of hMSC by increasing the amount of HA nanoparticles used as bioactive inorganic signal. Contemporarily, these materials allow avoiding the induction of a pro‐inflammatory response in bone implant site.

Implant Fibrosis and the Underappreciated Role of Myofibroblasts in the Foreign Body Reaction

Body implants and implantable medical devices have dramatically improved and prolonged the life of countless patients. However, our body repair mechanisms have evolved to isolate, reject, or destroy any object that is recognized as foreign to the organism and inevitably mounts a foreign body reaction (FBR). Depending on its severity and chronicity, the FBR can impair implant performance or create severe clinical complications that will require surgical removal and/or replacement of the faulty device. The number of review articles discussing the FBR seems to be proportional to the number of different implant materials and clinical applications and one wonders, what else is there to tell? We will here take the position of a fibrosis researcher (which, coincidentally, we are) to elaborate similarities and differences between the FBR, normal wound healing, and chronic healing conditions that result in the development of peri-implant fibrosis. After giving credit to macrophages in the inflammatory phase of the FBR, we will mainly focus on the activation of fibroblastic cells into matrix-producing and highly contractile myofibroblasts. While fibrosis has been discussed to be a consequence of the disturbed and chronic inflammatory milieu in the FBR, direct activation of myofibroblasts at the implant surface is less commonly considered. Thus, we will provide a perspective how physical properties of the implant surface control myofibroblast actions and accumulation of stiff scar tissue. Because formation of scar tissue at the surface and around implant materials is a major reason for device failure and extraction surgeries, providing implant surfaces with myofibroblast-suppressing features is a first step to enhance implant acceptance and functional lifetime. Alternative therapeutic targets are elements of the myofibroblast mechanotransduction and contractile machinery and we will end with a brief overview on such targets that are considered for the treatment of other organ fibroses.

Potential strategies to prevent encrustations on urinary stents and catheters - thinking outside the box: a European network of multidisciplinary research to improve urinary stents (ENIUS) initiative

Introduction: Urinary stents have been around for the last 4 decades, urinary catheters even longer. They are associated with infections, encrustation, migration, and patient discomfort. Research efforts to improve them have shifted onto molecular and cellular levels. ENIUS brought together translational scientists to improve urinary implants and reduce morbidity.Methods & materials: A working group within the ENIUS network was tasked with assessing future research lines for the improvement of urinary implants.Topics were researched systematically using Embase and PubMed databases. Clinicaltrials.gov was consulted for ongoing trials.Areas covered: Relevant topics were coatings with antibodies, enzymes, biomimetics, bioactive nano-coats, antisense molecules, and engineered tissue. Further, pH sensors, biodegradable metals, bactericidal bacteriophages, nonpathogenic uropathogens, enhanced ureteric peristalsis, electrical charges, and ultrasound to prevent stent encrustations were addressed.Expert opinion: All research lines addressed in this paper seem viable and promising. Some of them have been around for decades but are yet to proceed to clinical application (i.e. tissue engineering). Others are very recent and, at least in urology, still only conceptual (i.e. antisense molecules). Perhaps the most important learning point resulting from this pan-European multidisciplinary effort is that collaboration between all stakeholders is not only fruitful but also truly essential.

Biomedical application of photo-crosslinked gelatin hydrogels

Abstract

During the past decades, photo-crosslinked gelatin hydrogel (methacrylated gelatin, GelMA) has gained a lot of attention due to its remarkable application in the biomedical field. It has been widely used in cell transplantation, cell culture and drug delivery, based on its crosslinking to form hydrogels with tunable mechanical properties and excellent bio-compatibility when exposed to light irradiation to mimic the micro-environment of native extracellular matrix (ECM). Because of its unique biofunctionality and mechanical tenability, it has also been widely applied in the repair and regeneration of bone, heart, cornea, epidermal tissue, cartilage, vascular, peripheral nerve, oral mucosa, and skeletal muscle et al. The purpose of this review is to summarize the recent application of GelMA in drug delivery and tissue engineering field. Moreover, this review article will briefly introduce both the development of GelMA and the characterization of GelMA. Finally, we discuss the challenges and future development prospects of GelMA as a tissue engineering material and drug or gene delivery carrier, hoping to contribute to accelerating the development of GelMA in the biomedical field.

Graphical abstract

Bioinspired Scaffold Designs for Regenerating Musculoskeletal Tissue Interfaces

The musculoskeletal system works at a very advanced level of synchrony, where all the physiological movements of the body are systematically performed through well-organized actions of bone in conjunction with all the other musculoskeletal soft tissues, such as ligaments, tendons, muscles, and cartilage through tissue-tissue interfaces. Interfaces are structurally and compositionally complex, consisting of gradients of extracellular matrix components, cell phenotypes as well as biochemical compositions and are important in mediating load transfer between the distinct orthopedic tissues during body movement. When an injury occurs at interface, it must be re-established to restore its function and stability. Due to the structural and compositional complexity found in interfaces, it is anticipated that they presuppose a concomitant increase in the complexity of the associated regenerative engineering approaches and scaffold designs to achieve successful interface regeneration and seamless integration of the engineered orthopedic tissues. Herein, we discuss the various bioinspired scaffold designs utilized to regenerate orthopedic tissue interfaces. First, we start with discussing the structure-function relationship at the interface. We then discuss the current understanding of the mechanism underlying interface regeneration, followed by discussing the current treatment available in the clinic to treat interface injuries. Lastly, we comprehensively discuss the state-of-the-art scaffold designs utilized to regenerate orthopedic tissue interfaces.

Full-thickness tissue engineered oral mucosa for genitourinary reconstruction: A comparison of different collagen-based biodegradable membranes

Tissue engineering is a method of growing importance regarding clinical application in the genitourinary region. One of the key factors in successfully development of an artificially tissue engineered mucosa equivalent (TEOM) is the optimal choice of the scaffold. Collagen scaffolds are regarded as gold standard in dermal tissue reconstruction. Four distinct collagen scaffolds were evaluated for the ability to support the development of an organotypical tissue architecture. TEOMs were established by seeding cocultures of primary oral epithelial cells and fibroblasts on four distinct collagen membranes. Cell viability was assessed by MTT-assay. The 3D architecture and functionality of the tissue engineered oral mucosa equivalents were evaluated by confocal laser-scanning microscopy and immunostaining. Cell viability was reduced on the TissuFoil E® membrane. A multi-stratified epithelial layer was established on all four materials, however the TEOMs on the Bio-Gide® scaffold showed the best fibroblast differentiation, secretion of tenascin and fibroblast migration into the membrane. The TEOMs generated on Bio-Gide® scaffold exhibited the optimal cellular organization into a cellular 3D network. Thus, the Bio-Gide® scaffold is a suitable matrix for engineering of mucosa substitutes in vitro.

Innervation: the missing link for biofabricated tissues and organs

Innervation plays a pivotal role as a driver of tissue and organ development as well as a means for their functional control and modulation. Therefore, innervation should be carefully considered throughout the process of biofabrication of engineered tissues and organs. Unfortunately, innervation has generally been overlooked in most non-neural tissue engineering applications, in part due to the intrinsic complexity of building organs containing heterogeneous native cell types and structures. To achieve proper innervation of engineered tissues and organs, specific host axon populations typically need to be precisely driven to appropriate location(s) within the construct, often over long distances. As such, neural tissue engineering and/or axon guidance strategies should be a necessary adjunct to most organogenesis endeavors across multiple tissue and organ systems. To address this challenge, our team is actively building axon-based "living scaffolds" that may physically wire in during organ development in bioreactors and/or serve as a substrate to effectively drive targeted long-distance growth and integration of host axons after implantation. This article reviews the neuroanatomy and the role of innervation in the functional regulation of cardiac, skeletal, and smooth muscle tissue and highlights potential strategies to promote innervation of biofabricated engineered muscles, as well as the use of "living scaffolds" in this endeavor for both in vitro and in vivo applications. We assert that innervation should be included as a necessary component for tissue and organ biofabrication, and that strategies to orchestrate host axonal integration are advantageous to ensure proper function, tolerance, assimilation, and bio-regulation with the recipient post-implant.

Human periodontal ligament stem cells on calcium phosphate scaffold delivering platelet lysate to enhance bone regeneration

Human periodontal ligament stem cells (hPDLSCs) are promising for tissue engineering applications but have received relatively little attention. Human platelet lysate (HPL) contains a cocktail of growth factors. To date, there has been no report on hPDLSC seeding on scaffolds loaded with HPL. The objectives of this study were to develop a calcium phosphate cement (CPC)-chitosan scaffold loaded with HPL and investigate their effects on hPDLSC viability, osteogenic differentiation and bone mineral synthesis for the first time. hPDLSCs were harvested from extracted human teeth. Scaffolds were formed by mixing CPC powder with a chitosan solution containing HPL. Four groups were tested: CPC-chitosan + 0% HPL (control); CPC-chitosan + 2.66% HPL; CPC-chitosan + 5.31% HPL; CPC-chitosan + 10.63% HPL. Scanning electron microscopy, live/dead staining, CCK-8, qRT-PCR, alkaline phosphatase and bone minerals assay were applied for hPDLSCs on scaffolds. hPDLSCs attached well on CPC-chitosan scaffold. Adding 10.63% HPL into CPC increased cell proliferation and viability (p < 0.05). ALP gene expression of CPC-chitosan + 10.63% HPL was 7-fold that of 0% HPL at 14 days. Runx2, OSX and Coll1 of CPC-chitosan + 10.63% HPL was 2-3 folds those at 0% HPL (p < 0.05). ALP activity of CPC-chitosan + 10.63% HPL was 2-fold that at 0% HPL (p < 0.05). Bone minerals synthesized by hPDLSCs for CPC-chitosan + 10.63% HPL was 3-fold that at 0% HPL (p < 0.05). This study showed that CPC-chitosan scaffold was a promising carrier for HPL delivery, and HPL in CPC exerted excellent promoting effects on hPDLSCs for bone tissue engineering for the first time. The novel hPDLSC-CPC-chitosan-HPL construct has great potential for orthopedic, dental and maxillofacial regenerative applications.

Bioengineered Scaffolds as Substitutes for Grafts for Urethra Reconstruction

Urethral defects originating from congenital malformations, trauma, inflammation or carcinoma still pose a great challenge to modern urology. Recent therapies have failed many times and have not provided the expected results. This negatively affects patients' quality of life. By combining cells, bioactive molecules, and biomaterials, tissue engineering can provide promising treatment options. This review focused on scaffold systems for urethra reconstruction. We also discussed different technologies, such as electrospinning and 3D bioprinting which provide great possibility for the preparation of a hollow structure with well-defined architecture.

Nanosensors for therapeutic drug monitoring: implications for transplantation

The number of patients requiring organ transplantations is exponentially increasing. New organs are either provided by healthy or deceased donors, or are grown in laboratories by tissue engineers. Post-surgical follow-up is vital for preventing any complications that can cause organ rejection. Physiological monitoring of a patient who receives newly transplanted organs is crucial. Many efforts are being made to enhance follow-up technologies for monitoring organ recipients, and point-of-care devices are beginning to emerge. Here, we describe the role of biosensors and nanosensors in improving organ transplantation efficiency, managing post-surgical follow-up and reducing overall costs. We provide an overview of the state-of-the-art biosensing technologies and offer some perspectives related to their further development.

Shear-resistant hydrogels to control permeability of porous tubular scaffolds in vascular tissue engineering

Aiming to perfuse porous tubular scaffolds for vascular tissue engineering (VTE) with controlled flow rate, prevention of leakage through the scaffold lumen is required. A gel coating made of 8% w/v alginate and 6% w/v gelatin functionalized with fibronectin was produced using a custom-made bioreactor-based method. Different volumetric proportions of alginate and gelatin were tested (50/50, 70/30, and 90/10). Gel swelling and stability, and rheological, and uniaxial tensile tests reveal superior resistance to the aggressive biochemical microenvironment, and their ability to withstand physiological deformations (~10%) and wall shear stresses (5-20 dyne/cm²). These are prerequisites to maintain the physiologic phenotypes of vascular smooth muscle cells and endothelial cells (ECs), mimicking blood vessels microenvironment. Gels can induce ECs proliferation and colonization, especially in the presence of fibronectin and higher percentages of gelatin. The custom-designed bioreactor enables the development of reproducible and homogeneous tubular gel coating. The permeability tests show the effectiveness of tubular scaffolds coated with 70/30 alginate/gelatin gel to occlude wadding pores, and therefore prevent leakages. The synthesized double-layered tubular scaffolds coated with alginate/gelatin gel and fibronectin represent both promising substrate for ECs and effective leakproof scaffolds, when subjected to pulsatile perfusion, for VTE applications.

Graphene-based 3D scaffolds in tissue engineering: fabrication, applications, and future scope in liver tissue engineering

Tissue engineering embraces the potential of recreating and replacing defective body parts by advancements in the medical field. Being a biocompatible nanomaterial with outstanding physical, chemical, optical, and biological properties, graphene-based materials were successfully employed in creating the perfect scaffold for a range of organs, starting from the skin through to the brain. Investigations on 2D and 3D tissue culture scaffolds incorporated with graphene or its derivatives have revealed the capability of this carbon material in mimicking in vivo environment. The porous morphology, great surface area, selective permeability of gases, excellent mechanical strength, good thermal and electrical conductivity, good optical properties, and biodegradability enable graphene materials to be the best component for scaffold engineering. Along with the apt microenvironment, this material was found to be efficient in differentiating stem cells into specific cell types. Furthermore, the scope of graphene nanomaterials in liver tissue engineering as a promising biomaterial is also discussed. This review critically looks into the unlimited potential of graphene-based nanomaterials in future tissue engineering and regenerative therapy.

Patterned human microvascular grafts enable rapid vascularization and increase perfusion in infarcted rat hearts

Vascularization and efficient perfusion are long-standing challenges in cardiac tissue engineering. Here we report engineered perfusable microvascular constructs, wherein human embryonic stem cell-derived endothelial cells (hESC-ECs) are seeded both into patterned microchannels and the surrounding collagen matrix. In vitro, the hESC-ECs lining the luminal walls readily sprout and anastomose with de novo-formed endothelial tubes in the matrix under flow. When implanted on infarcted rat hearts, the perfusable microvessel grafts integrate with coronary vasculature to a greater degree than non-perfusable self-assembled constructs at 5 days post-implantation. Optical microangiography imaging reveal that perfusable grafts have 6-fold greater vascular density, 2.5-fold higher vascular velocities and >20-fold higher volumetric perfusion rates. Implantation of perfusable grafts containing additional hESC-derived cardiomyocytes show higher cardiomyocyte and vascular density. Thus, pre-patterned vascular networks enhance vascular remodeling and accelerate coronary perfusion, potentially supporting cardiac tissues after implantation. These findings should facilitate the next generation of cardiac tissue engineering design.

Amnion-derived mesenchymal stem cells improve viability of endothelial cells exposed to shear stress in ePTFE grafts

PURPOSE:

Blood vessel reconstruction is an increasing need of patients suffering from cardiovascular diseases. For the development of microvascular prostheses, efficient endothelialization is mandatory to prevent graft occlusion. Here, we assessed the impact of amnion-derived mesenchymal stem/stromal cells (hAMSC), known for their important angiogenic potential, on the integrity and stability of endothelial cells exposed to shear stress in vascular grafts.

METHODS:

Human placental endothelial cells (hPEC) were cultured at the inner surface of an expanded polytetrafluoroethylene (ePTFE) graft positioned within a bioreactor and exposed to a minimal shear stress of 0.015 dyne/cm² or a physiological shear stress of 0.92 dyne/cm². hAMSC attached to the outer graft surface were able to interact with human placental endothelial cells by paracrine factors.

RESULTS:

Microscopical analysis and evaluation of glucose/lactate metabolism evidenced successful cell seeding of the graft: hPEC formed a stable monolayer, hAMSC showed a continuous growth during 72 h incubation. hAMSC improved the viability of hPEC exposed to 0.015 dyne/cm² as shown by a decreased lactate dehydrogenase release of 13% after 72 h compared to hPEC single culture. The viability-enhancing effect of hAMSC on hPEC was further improved by 13% under physiological shear stress. Angiogenesis array analysis revealed that hPEC exposed to physiological shear stress and hAMSC co-culture reduced the secretion of angiogenin, GRO, MCP-1, and TIMP-2.

CONCLUSION:

hAMSC exerted best survival-enhancing effects on hPEC under exposure to physiological shear stress and modulated endothelial function by paracrine factors. Our data support further studies on the development of grafts functionalized with hAMSC-derived secretomes to enable fast clinical application.

What will it take before a bioengineered heart will be implanted in patients?

PURPOSE OF REVIEW

Heart transplantation is the only curative treatment option for end-stage heart failure. However, a shortage of donor organs is a major limitation of this approach. Regenerative medicine targets the goal of increasing the number of available hearts for transplantation. In this review, we highlight the state of the art of building a bioartificial heart. We summarize the components needed, the hurdles, and likely translational steps to make the dream of transplanting a totally functional bioartificial heart a possibility.

RECENT FINDINGS

The therapies being developed in regenerative medicine aim not only to repair, but also to regenerate or replace failing tissues and organs. The engineering of bioartificial hearts utilizing patient-derived cells could theoretically solve the two main complications of heart transplantations: graft rejection and lifelong immunosuppression. Although many hurdles remain, scientists have reached a point in which some of these hurdles have been overcome. Decellularized heart scaffolds have emerged over the past decade as one of the most promising biofabrications. Two possible options for organ scaffolds exist: nontransplantable human hearts and porcine hearts. The use of these scaffolds could lead to the availability of an unlimited number of transplantable organs. The current challenge remains improving processes required for recellularization - including those for cells, bioreactors, and physiologic conditioning. Researchers should focus to solve these hurdles and pave the way toward the dream of in-vivo bioengineered heart maturation.

SUMMARY

Regenerative medicine has emerged as one of the most promising fields of translational research and has the potential to both minimize the need for donor organs and increase their availability. Meeting the challenge of implanting a totally functional bioengineered heart lies in solving multiple issues simultaneously. Dwarfing the technical hurdles, cost is the largest barrier to success. The scientific hurdles mainly involve scaling up and scaling out of laboratory cell processes, building bioreactors, and delivering cells into every needed region of an organ scaffold. Maintaining sterility and quantifying readiness of the nascent organs are also critical for success.

Patient-specific devices and population-level evidence: evaluating therapeutic interventions with inherent variation

Designing and manufacturing medical devices for specific patients is becoming increasingly feasible with developments in 3D printing and 3D imaging software. This raises the question of how patient-specific devices can be evaluated, since our 'gold standard' method for evaluation, the randomised controlled trial (RCT), requires that an intervention is standardised across a number of individuals in an experimental group. I distinguish several senses of patient-specific device, and focus the discussion on understanding the problem of variations between instances of an intervention for RCT evaluation. I argue that, despite initial appearances, it is theoretically possible to use RCTs to evaluate some patient-specific medical devices. However, the argument reveals significant difficulties for ensuring the validity of such trials, with implications for how we should think about methods of evidence gathering and regulatory approaches for these technologies.

Advances in Regenerative Medicine and Tissue Engineering: Innovation and Transformation of Medicine

Humans and animals lose tissues and organs due to congenital defects, trauma, and diseases. The human body has a low regenerative potential as opposed to the urodele amphibians commonly referred to as salamanders. Globally, millions of people would benefit immensely if tissues and organs can be replaced on demand. Traditionally, transplantation of intact tissues and organs has been the bedrock to replace damaged and diseased parts of the body. The sole reliance on transplantation has created a waiting list of people requiring donated tissues and organs, and generally, supply cannot meet the demand. The total cost to society in terms of caring for patients with failing organs and debilitating diseases is enormous. Scientists and clinicians, motivated by the need to develop safe and reliable sources of tissues and organs, have been improving therapies and technologies that can regenerate tissues and in some cases create new tissues altogether. Tissue engineering and/or regenerative medicine are fields of life science employing both engineering and biological principles to create new tissues and organs and to promote the regeneration of damaged or diseased tissues and organs. Major advances and innovations are being made in the fields of tissue engineering and regenerative medicine and have a huge impact on three-dimensional bioprinting (3D bioprinting) of tissues and organs. 3D bioprinting holds great promise for artificial tissue and organ bioprinting, thereby revolutionizing the field of regenerative medicine. This review discusses how recent advances in the field of regenerative medicine and tissue engineering can improve 3D bioprinting and vice versa. Several challenges must be overcome in the application of 3D bioprinting before this disruptive technology is widely used to create organotypic constructs for regenerative medicine.

A review on fabricating tissue scaffolds using vat photopolymerization

Vat Photopolymerization (stereolithography, SLA), an Additive Manufacturing (AM) or 3D printing technology, holds particular promise for the fabrication of tissue scaffolds for use in regenerative medicine. Unlike traditional tissue scaffold fabrication techniques, SLA is capable of fabricating designed scaffolds through the selective photopolymerization of a photopolymer resin on the micron scale. SLA offers unprecedented control over scaffold porosity and permeability, as well as pore size, shape, and interconnectivity. Perhaps even more significantly, SLA can be used to fabricate vascular networks that may encourage angio and vasculogenesis. Fulfilling this potential requires the development of new photopolymers, the incorporation of biochemical factors into printed scaffolds, and an understanding of the effects scaffold geometry have on cell viability, proliferation, and differentiation. This review compares SLA to other scaffold fabrication techniques, highlights significant advances in the field, and offers a perspective on the field's challenges and future directions.

STATEMENT OF SIGNIFICANCE

Engineering de novo tissues continues to be challenging due, in part, to our inability to fabricate complex tissue scaffolds that can support cell proliferation and encourage the formation of developed tissue. The goal of this review is to first introduce the reader to traditional and Additive Manufacturing scaffold fabrication techniques. The bulk of this review will then focus on apprising the reader of current research and provide a perspective on the promising use of vat photopolymerization (stereolithography, SLA) for the fabrication of complex tissue scaffolds.

3D bioprinting and decellularized ECM-based biomaterials for in vitro CV tissue engineering

Advanced extrusion-based 3D printing strategies allow the rapid fabrication of complex anatomically relevant architectures. Moreover, they have the potential to fabricate 3D-bioprinted cardiac constructs by depositing cardiac cells with appropriate biomaterials. Heart-derived decellularized extracellular matrices containing a complex mixture of various extracellular molecules provide a comprehensive microenvironmental niche similar to native cardiac tissue. Nonetheless, a major concern persists pertaining to insufficient vascularization and mimicking of the complex 3D architectural features, which can be tackled using 3D printing approaches. In this review, we discuss the advantage and application of decellularized extracellular matrix-based hydrogels for the 3D printing of engineered cardiac tissues. We also briefly talk about the integration of electroactive materials within cardiac patches to improve the myocardium's electrophysiological properties.

Human Adipose-Derived and Amniotic Fluid-Derived Stem Cells: A Preliminary In Vitro Study Comparing Myogenic Differentiation Capability

Background

Around the world, disabilities due to musculoskeletal disorders have increased and are a major health problem worldwide. In recent years, stem cells have been considered to be powerful tools for musculoskeletal tissue engineering. Human adipose-derived stem cells (hADSCs) and amniotic fluid-derived stem cells (hAFSCs) undergo typical differentiation process into cells of mesodermal origin and can be used to treat muscular system diseases. The aim of the present study was to compare the biological characteristic of stem cells isolated from different human tissues (adipose tissue and amniotic fluid) with respect to myogenic capacity and skeletal and smooth muscle differentiation under the same conditions.

Material/Methods

hAFSCs and hADSCs were isolated during standard medical procedures and widely characterized by specific markers expression and differentiation potential. Both cell types were induced toward smooth and striated muscles differentiation, which was assessed with the use of molecular techniques.

Results

For phenotypic characterization, both stem cell types were assessed for the expression of OCT-4, SOX2, CD34, CD44, CD45, and CD90. Muscle-specific markers appeared in both stem cell types, but the proportion of positive cells showed differences depending on the experimental conditions used and the source from which the stem cells were isolated.

Conclusions

In this study, we demonstrated that hADSCs and hAFSCs have different capability of differentiation toward both muscle types. However, hADSCs seem to be a better source for myogenic protocols and can promote skeletal and smooth muscle regeneration through either direct muscle differentiation or by paracrine mechanism.

An Immunopathological Evaluation of the Porcine Cholecyst Matrix as a Muscle Repair Graft in a Male Rat Abdominal Wall Defect Model

With the increasing use of animal-based biomaterials for regenerative medical applications, the need for their safety assessment is paramount. A porcine cholecyst-derived scaffold (CDS), intended as a muscle repair graft, prepared by a nondetergent/enzymatic method was engrafted in a rat abdominal wall defect model. Host tissue–scaffold interface samples were collected 2, 8, and 16 weeks postimplantation and evaluated by histopathology, immunohistochemistry, and electron microscopy. The nature of the tissue reaction was compared with those induced by a jejunum-derived scaffold (JDS) prepared by the same method and a commercial-grade small intestinal submucosa (CSIS) scaffold. A study of the immunopathological response in major lymphoid tissues and immunophenotyping for M1 and M2 macrophages was performed at the host tissue–scaffold interface. Further, “irritancy scores” for CDS and JDS were determined using CSIS as the reference material. Both CDS and JDS appeared to be potential biomaterials for muscle grafts, but the former stimulated a skeletal muscle tissue remodeling response predominated by M2 macrophages. The data support the notion that biomaterials with similar biocompatibility, based on local tissue response on implantation, may cause differential immunogenicity. Additionally, CDS compared to JDS and CSIS was found to be less immunotoxic.

[New approaches to ocular surface reconstruction beyond the cornea]

BACKGROUND

Reconstruction of the conjunctiva is an essential part of ocular surface reconstruction. Clinically applied and experimentally tested tissue- and stem-cell-based approaches are presented and evaluated.

MATERIALS AND METHODS

Current literature and our own results will be presented.

RESULTS

Autologous conjunctiva, mucous membrane of the mouth or nose, and amniotic membrane are routinely used for conjunctival reconstruction. Limitations are limited availability, involvement in autoimmune diseases, donor heterogeneity, and degradation in an inflamed environment. Experimentally tested matrices as tissues made from extracellular matrix proteins, synthetic polymers, temperature-sensitive culture dishes, and decellularized conjunctiva have been tested in vitro and partly in vivo. To replace conjunctival cells, cells of conjunctiva and mucous membrane of mouth and nose have been evaluated and show progenitor cell properties as well as secretory capacity (goblet cell differentiation).

CONCLUSIONS

Although different matrices are available for conjunctival reconstruction there is-due to specific limitations of existing tissues-a need for the development of new therapies for conjunctival replacement. Matrices produced in the laboratory have already been partly investigated in vivo and may thus be clinically applicable in the near future. Adult mucous membrane cells show many properties of conjunctival epithelium after expansion in vitro and thus are a promising cell source for conjunctival tissue engineering. Other stem cells sources require further evaluation.

Biomimetic matrix fabricated by LMP-1 gene-transduced MC3T3-E1 cells for bone regeneration

Bone healing is regulated by multiple microenvironmental signals provided by the extracellular matrix (ECM). This study aimed to mimic the native osteoinductive microenvironment by developing an ECM using gene-transduced cells. The LIM mineralization protein-1 (LMP-1) gene was transferred to murine pre-osteoblast cells (MC3T3-E1) using lentiviral vectors. Western blotting assay indicated that the MC3T3-E1 cells expressed an increased level of bone morphologic protein-2, -4 and -7 (BMP-2, -4 and -7) after LMP-1 gene transduction. The transduced cells were then seeded into calcined bovine bone scaffolds and cultured for 7, 14, and 21 days to construct ECMs on the scaffolds. The ECM-scaffold composites were then decellularized using the freeze-drying method. Scaffolds without ECM deposition were used as controls. The composites and controls were implanted into critical-sized bone defects created in the distal femurs of New Zealand rabbits. Twelve weeks after the surgery, both microcomputed tomography and histologic results indicated that the 7-day-cell-modified ECM-scaffold composites induced bone regeneration with significantly larger volume, trabecular thickness and connectivity than the controls. However, the 14- and 21-day-cell-modified ECM-scaffold composites triggered sustained inflammation response even at 12 weeks after the surgery and showed less bone ingrowth and integration than their 7-day-cell-modified counterparts. In conclusion, these results highlight the viable gene transfer techniques for manipulating cells in a constructed microenvironment of ECM for bone regeneration. However, the unresolved inflammation relating to the duration of ECM modification needs to be considered.

Transplantation of Amniotic Scaffold-Seeded Mesenchymal Stem Cells and/or Endothelial Progenitor Cells From Bone Marrow to Efficiently Repair 3-cm Circumferential Urethral Defect in Model Dogs

The treatment options for patients with a urethral defect are limited by the availability of autologous tissues. We hypothesized that transplantation of decellularized human amniotic scaffolds (dHAS) seeded with allogeneic bone marrow mesenchymal cells (BMSCs) and/or endothelial progenitor cells (EPCs) may serve as a promising repair strategy for long segment of circumferential urethral defect. To verify the hypothesis, with urinary catheterization, a 3-cm segment of whole urethra in 25 male mongrel dogs was excised and replaced by dHAS seeded with allogeneic BMSCs and/or EPCs. Postoperative observation and ascending urethrogram found that dHAS+BMSCs+EPCs and dHAS+EPCs groups demonstrated unhindered urination and capacious urethral caliber, which were similar to the normal group, while urethrostenosis was revealed in dHAS+BMSCs, dHAS, and sham-operated groups, with the shortest narrow section in dHAS+BMSCs group and the longest in sham-operated group. Urethral anatomy check and histological analyses showed that new urethral mucosa composed of stratified columnar epithelium completely covered on the inner surface of the graft site in dHAS+BMSCs+EPCs and dHAS+EPCs groups, but the middle epithelium was thin in dHAS+EPCs group, while incompletely covered in dHAS+BMSCs, dHAS, and sham-operated groups, and there were monolayer epithelial cells at the urethrostenosis in dHAS+BMSCs and dHAS groups. In addition, abundant new vessel and blood sinus showed at submucosa in dHAS+BMSCs+EPCs and dHAS+EPCs groups, instead of the scar tissue of collagen deposition and structural distortion at the urethrostenosis in dHAS+BMSCs, dHAS, and sham-operated groups. This study demonstrates that dHAS seeded with BMSCs+EPCs or EPCs can successfully repair a 3-cm circumferential urethral defect in model dogs, but the former works best. This technology may provide some references for human clinical trials on long segment of circumferential urethral defect repair.

Organ reconstruction: Dream or reality for the future

The relevance of research on reconstructed organs is justified by the lack of organs available for transplant and the growing needs for the ageing population. The development of a reconstructed organ involves two parallel complementary steps: de-cellularization of the organ with the need to maintain the structural integrity of the extracellular matrix and vascular network and re-cellularization of the scaffold with stem cells or resident cells.Whole organ engineering for liver, heart, lung or kidneys, is particularly difficult because of the structural complexity of organs and heterogeneity of cells. Rodent, porcine and rhesus monkey organs have been de-cellularized to obtain a scaffold with preserved extracellular matrix and vascular network. As concern the cells for re-cellularization, embryonic, foetal, adult, progenitor stem cells and also iPS have been proposed.Heart construction could be an alternative option for the treatment of cardiac insufficiency. It is based on the use of an extra-cellular matrix coming from an animal's heart and seeded with cells likely to reconstruct a normal cardiac function. Though de-cellularization techniques now seem controlled, the issues posed by the selection of cells capable of generating the various components of cardiac tissue are not settled yet. In addition, the recolonisation of the matrix does not only depend on the phenotype of cells that are used, but it is also impacted by the nature of biochemical signals emitted.Recent researches have shown that it is possible to use decellularized whole liver treated by detergents as scaffold, which keeps the entire network of blood vessels and the integrated extracellular matrix (ECM). Beside of decellularized whole organ scaffold seeding cells selected to repopulate a decellularized liver scaffold are critical for the function of the bioengineered liver. At present, potential cell sources are hepatocyte, and mesenchymal stem cells.Pulmonary regeneration using engineering approaches is complex. In fact, several types of local progenitor cells that contribute to cell repair have been described at different levels of the respiratory tract. Moving towards the alveoles, one finds bronchioalveolar stem cells as well as epithelial cells and pneumocytes. A promising option to increase the donor organ pool is to use allogeneic or xenogeneic decellularized lungs as a scaffold to engineer functional lung tissue ex vivo.The kidney is certainly one of the most difficult organs to reconstruct due to its complex nature and the heterogeneous nature of the cells. There is relatively little research on auto-construction, and experiments have been performed on rats, pigs and monkeys.Nevertheless, before these therapeutic approaches can be applied in clinical practice, many researches are necessary to understand and in particular the behaviour of cells on the decellularized organs as well as the mechanisms of their interaction with the microenvironment. Current knowledges allow optimism for the future but definitive answers can only be given after long term animal studies and controlled clinical studies.

Tissue engineering for urinary tract reconstruction and repair: Progress and prospect in China

Several urinary tract pathologic conditions, such as strictures, cancer, and obliterations, require reconstructive plastic surgery. Reconstruction of the urinary tract is an intractable task for urologists due to insufficient autologous tissue. Limitations of autologous tissue application prompted urologists to investigate ideal substitutes. Tissue engineering is a new direction in these cases. Advances in tissue engineering over the last 2 decades may offer alternative approaches for the urinary tract reconstruction. The main components of tissue engineering include biomaterials and cells. Biomaterials can be used with or without cultured cells. This paper focuses on cell sources, biomaterials, and existing methods of tissue engineering for urinary tract reconstruction in China. The paper also details challenges and perspectives involved in urinary tract reconstruction.

Induced Remodeling of Porcine Tendons to Human Anterior Cruciate Ligaments by α-GAL Epitope Removal and Partial Cross-Linking

This review describes a novel method developed for processing porcine tendon and other ligament implants that enables in situ remodeling into autologous ligaments in humans. The method differs from methods using extracellular matrices (ECMs) that provide postoperative orthobiological support (i.e., augmentation grafts) for healing of injured ligaments, in that the porcine bone-patellar-tendon-bone itself serves as the graft replacing ruptured anterior cruciate ligament (ACL). The method allows for gradual remodeling of porcine tendon into autologous human ACL while maintaining the biomechanical integrity. The method was first evaluated in a preclinical model of monkeys and subsequently in patients. The method overcomes detrimental effects of the natural anti-Gal antibody and harnesses anti-non-gal antibodies for the remodeling process in two steps: Step 1. Elimination of α-gal epitopes—this epitope that is abundant in pigs (as in other nonprimate mammals) binds the natural anti-Gal antibody, which is the most abundant natural antibody in humans. This interaction, which can induce fast resorption of the porcine implant, is avoided by enzymatic elimination of α-gal epitopes from the implant with recombinant α-galactosidase. Step 2. Partial cross-linking of porcine tendon with glutaraldehyde—this cross-linking generates covalent bonds in the ECM, which slow infiltration of macrophages into the implant. Anti-non-gal antibodies are produced in recipients against the multiple porcine antigenic proteins and proteoglycans because of sequence differences between human and porcine homologous proteins. Anti-non-gal antibodies bind to the implant ECM, recruit macrophages, and induce the implant destruction by directing proteolytic activity of macrophages. Partial cross-linking of the tendon ECM decreases the extent of macrophage infiltration and degradation of the implant and enables concomitant infiltration of fibroblasts that follow the infiltrating macrophages. These fibroblasts align with the implant collagen fibers and secrete their own collagen and other ECM proteins, which gradually remodel the porcine tendon into human ACL. This ligamentization process lasts ∼2 years and the biomechanical integrity of the graft is maintained throughout the whole period. These studies are the first, and so far the only, to demonstrate remodeling of porcine tendon implants into permanently functional autologous ACL in humans.

In vitro skin models and tissue engineering protocols for skin graft applications

In this review, we present a brief introduction of the skin structure, a concise compilation of skin-related disorders, and a thorough discussion of different in vitro skin models, artificial skin substitutes, skin grafts, and dermal tissue engineering protocols. The advantages of the development of in vitro skin disorder models, such as UV radiation and the prototype model, melanoma model, wound healing model, psoriasis model, and full-thickness model are also discussed. Different types of skin grafts including allografts, autografts, allogeneic, and xenogeneic are described in detail with their associated applications. We also discuss different tissue engineering protocols for the design of various types of skin substitutes and their commercial outcomes. Brief highlights are given of the new generation three-dimensional printed scaffolds for tissue regeneration applications.

Tissue Engineering: Toward a New Era of Medicine

The goal of tissue engineering is to mitigate the critical shortage of donor organs via in vitro fabrication of functional biological structures. Tissue engineering is one of the most prominent examples of interdisciplinary fields, where scientists with different backgrounds work together to boost the quality of life by addressing critical health issues. Many different fields, such as developmental and molecular biology, as well as technologies, such as micro- and nanotechnologies and additive manufacturing, have been integral for advancing the field of tissue engineering. Over the past 20 years, spectacular advancements have been achieved to harness nature's ability to cure diseased tissues and organs. Patients have received laboratory-grown tissues and organs made out of their own cells, thus eliminating the risk of rejection. However, challenges remain when addressing more complex solid organs such as the heart, liver, and kidney. Herein, we review recent accomplishments as well as challenges that must be addressed in the field of tissue engineering and provide a perspective regarding strategies in further development.

3D printing of PLGA scaffolds for tissue engineering

We proposed a novel method of generation of bioresorbable polymeric scaffolds with specified architectonics for tissue engineering using extrusion three-dimensional (3D) printing with solutions of polylactoglycolide in tetraglycol with their subsequent solidifying in aqueous medium. On the basis of 3D computer models, we obtained the matrix structures with interconnected system of pores ranging in size from 0.5 to 500 µm. The results of in vitro studies using cultures of line NIH 3Т3 mouse fibroblasts, floating islet cultures of newborn rabbit pancreas, and mesenchymal stem cells of human adipose tissue demonstrated the absence of cytotoxicity and good adhesive properties of scaffolds in regard to the cell cultures chosen. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 104-109, 2017.

Three-dimensional bioprinting speeds up smart regenerative medicine

Biological materials can actively participate in the formation of bioactive organs and can even control cell fate to form functional tissues that we name as the smart regenerative medicine (SRM). The SRM requires interdisciplinary efforts to finalize the pre-designed organs. Three-dimensional (3D) printing, as an additive manufacturing technology, has been widely used in various fields due to its high resolution and individuation. In SRM, with the assistance of 3D printing, cells and biomaterials could be precisely positioned to construct complicated tissues. This review summarizes the state of the SRM advances and focuses in particular on the 3D printing application in biofabrication. We further discuss the issues of SRM development and finally propose some approaches for future 3D printing, which involves SRM.