Tissue engineered scaffolds for an effective healing and regeneration: reviewing orthotopic studies

Preclinical and clinical orthotopic transplantation of decellularized/engineered tracheal scaffolds: A systematic literature review

Severe tracheal injuries that cannot be managed by mobilization and end-to-end anastomosis represent an unmet clinical need and an urgent challenge to face in surgical practice; within this scenario, decellularized scaffolds (eventually bioengineered) are currently a tempting option among tissue engineered substitutes. The success of a decellularized trachea is expression of a balanced approach in cells removal while preserving the extracellular matrix (ECM) architecture/mechanical properties. Revising the literature, many Authors report about different methods for acellular tracheal ECMs development; however, only few of them verified the devices effectiveness by an orthotopic implant in animal models of disease. To support translational medicine in this field, here we provide a systematic review on studies recurring to decellularized/bioengineered tracheas implantation. After describing the specific methodological aspects, orthotopic implant results are verified. Furtherly, the only three clinical cases of compassionate use of tissue engineered tracheas are reported with a focus on outcomes.

Implants with Sensing Capabilities

Because of the aging human population and increased numbers of surgical procedures being performed, there is a growing number of biomedical devices being implanted each year. Although the benefits of implants are significant, there are risks to having foreign materials in the body that may lead to complications that may remain undetectable until a time at which the damage done becomes irreversible. To address this challenge, advances in implantable sensors may enable early detection of even minor changes in the implants or the surrounding tissues and provide early cues for intervention. Therefore, integrating sensors with implants will enable real-time monitoring and lead to improvements in implant function. Sensor integration has been mostly applied to cardiovascular, neural, and orthopedic implants, and advances in combined implant-sensor devices have been significant, yet there are needs still to be addressed. Sensor-integrating implants are still in their infancy; however, some have already made it to the clinic. With an interdisciplinary approach, these sensor-integrating devices will become more efficient, providing clear paths to clinical translation in the future.

Creative and Innovative Methods and Techniques for the Challenges in the Management of Adult Craniopharyngioma

Craniopharyngioma remains a major challenge in daily clinical practice. The pathobiology of the tumor is still elusive, and there are no consensus or treatment guidelines on the optimal management strategy for this relatively rare tumor. However, recent technical and scientific advances, including genomic and radiomic profiling, innovation in surgical approaches, more precise radiotherapy protocols, targeted therapy, and restoration of lost functions all have the potential to significantly improve the outcome of patients with craniopharyngioma in the near future. Although many of these innovative tools in the new armamentarium of the clinician are still in their infancy, they could reduce craniopharyngioma-related morbidity and mortality and improve the patients' quality of life. In this article, we discuss these creative and innovative approaches that may offer solutions to the obstacles faced in treating craniopharyngioma and future possibilities in improving the care of these patients.

Incorporation of a Poly-ε-Caprolactone Scaffold in a ;Circular Stapled End-To-End Small Intestine Anastomosis Does Not Have Any Adverse Effects Within 30 days: A Study in Piglets

Background. Incorporation of a poly-ε-caprolactone (PCL) scaffold in circular stapled anastomoses has been shown to increase the anastomotic tensile strength on postoperative day (POD) 5 in a pig model. The aim of this study was to investigate the effects of incorporation of a PCL scaffold in a circular stapled end-to-end small intestine anastomosis, with stricture formation and anastomotic histology as primary outcomes in a 30-day observation period. Methods. A total of 15 piglets were included. In each piglet, three circular stapled end-to-end anastomoses were made in the small intestines. Two were interventional and one was a control. On POD 10, 20, or 30, the anastomoses were subjected to in vivo intraluminal contrast study, and the index for anastomotic lumen was calculated. The anastomotic segment was resected and subjected to a tensile strength test and histological examination. Results. At POD 10, the mean ± SD value for anastomotic index was .749 ± .065 in control anastomoses and .637 ± .051 in interventional anastomosis (P = .0046), at POD 20, .541 ± .150 and .724 ± .07 (P = .051), and at POD 30, .645 ± .103 and .686 ± .057 (P = .341), respectively. No significant difference was observed in maximum tensile strength and histology at POD 30. Conclusions. The incorporation of a PCL scaffold in a circular stapled end-to-end small intestine anastomosis does not increase the risk of stricture or impair wound healing after 30 days.

A Graded, Porous Composite of Natural Biopolymers and Octacalcium Phosphate Guides Osteochondral Differentiation of Stem Cells

Lesions involving the osteochondral unit are difficult to treat. Biomimetic scaffolds are previously shown as promising alternative. Such devices often lack multiple functional layers that mimic bone, cartilage, and the interface. In this study, multilayered scaffolds are developed based on the use of natural extracellular matrix (ECM)-like biopolymers. Particular attention is paid to obtain a complex matrix that mimics the native osteochondral transition. Porous, sponge-like chitosan-collagen-octacalcium phosphate (OCP) scaffolds are obtained. Collagen content increases while the amount of OCP particles decreases toward the cartilage layer. The scaffolds are bioactive as a mineral layer is deposited containing hydroxyapatite at the bony side. The scaffolds stimulate proliferation of human adipose-derived mesenchymal stem cells, but the degree of proliferation depends on the cell seeding density. The scaffolds give rise to a zone-specific gene expression. RUNX2, COL1A1, BGLAP, and SPP1 are upregulated in the bony layer of the scaffold. SOX9 is upregulated concomitant with COL2A1 expression in the cartilage zone. Mineralization in presence of the cells is prominent in the bone area with Ca and P steadily increasing over time. These results are encouraging for the fabrication of biomimetic scaffolds using ECM-like materials and featuring gradients that mimic native tissues and their interface.

3D Printing Decellularized Extracellular Matrix to Design Biomimetic Scaffolds for Skeletal Muscle Tissue Engineering

Functional engineered muscles are still a critical clinical issue to be addressed, although different strategies have been considered so far for the treatment of severe muscular injuries. Indeed, the regenerative capacity of skeletal muscle (SM) results inadequate for large-scale defects, and currently, SM reconstruction remains a complex and unsolved task. For this aim, tissue engineered muscles should provide a proper biomimetic extracellular matrix (ECM) alternative, characterized by an aligned/microtopographical structure and a myogenic microenvironment, in order to promote muscle regeneration. As a consequence, both materials and fabrication techniques play a key role to plan an effective therapeutic approach. Tissue-specific decellularized ECM (dECM) seems to be one of the most promising material to support muscle regeneration and repair. 3D printing technologies, on the other side, enable the fabrication of scaffolds with a fine and detailed microarchitecture and patient-specific implants with high structural complexity. To identify innovative biomimetic solutions to develop engineered muscular constructs for the treatment of SM loss, the more recent (last 5 years) reports focused on SM dECM-based scaffolds and 3D printing technologies for SM regeneration are herein reviewed. Possible design inputs for 3D printed SM dECM-based scaffolds for muscular regeneration are also suggested.

Soy Protein Nanofiber Scaffolds for Uniform Maturation of Human Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium

Retinal pigment epithelium (RPE) differentiated from human induced pluripotent stem cells, called induced retinal pigment epithelium (iRPE), is being explored as a cell-based therapy for the treatment of retinal degenerative diseases, especially age-related macular degeneration. The success of RPE implantation is linked to the use of biomimetic scaffolds that simulate Bruch's membrane and promote RPE maturation and integration as a functional tissue. Due to difficulties associated with animal protein-derived scaffolds, including sterility and pro-inflammatory responses, current practices favor the use of synthetic polymers, such as polycaprolactone (PCL), for generating nanofibrous scaffolds. In this study, we tested the hypothesis that plant protein-derived fibrous scaffolds can provide favorable conditions permissive for the maturation of RPE tissue sheets in vitro. Our natural, soy protein-derived nanofibrous scaffolds exhibited a J-shaped stress-strain curve that more closely resembled the mechanical properties of native tissues than PCL with significantly higher hydrophilicity of the natural scaffolds, favoring in vivo implantation. We then demonstrate that iRPE sheets growing on these soy protein scaffolds are equivalent to iRPE monolayers cultured on synthetic PCL nanofibrous scaffolds. Immunohistochemistry demonstrated RPE-like morphology and functionality with appropriate localization of RPE markers RPE65, PMEL17, Ezrin, and ZO1 and with anticipated histotypic polarization of vascular endothelial growth factor and pigment epithelium-derived growth factor as indicated by enzyme-linked immunosorbent assay. Scanning electron microscopy revealed dense microvilli on the cell surface and homogeneous tight junctional contacts between the cells. Finally, comparative transcriptome analysis in conjunction with principal component analysis demonstrated that iRPE on nanofibrous scaffolds, either natural or synthetic, matured more consistently than on nonfibrous substrates. Taken together, our studies suggest that the maturation of cultured iRPE sheets for subsequent clinical applications might benefit from the use of nanofibrous scaffolds generated from natural proteins. Impact statement Induced retinal pigment epithelium (iRPE) from patient-derived induced pluripotent stem cells (iPSCs) may yield powerful treatments of retinal diseases, including age-related macular degeneration. Recent studies, including early human clinical trials, demonstrate the importance of selecting appropriate biomaterial scaffolds to support tissue-engineered iRPE sheets during implantation. Electrospun scaffolds show particular promise due to their similarity to the structure of the native Bruch's membrane. In this study, we describe the use of electroprocessed nanofibrous soy protein scaffolds to generate polarized sheets of human iPSC-derived iRPE sheets. Our evaluation, including RNA-seq transcriptomics, indicates that these scaffolds are viable alternatives to scaffolds electrospun from synthetic polymers.

Mesenchymal Stem Cells Seeded Decellularized Tendon Scaffold for Tissue Engineering

Tendon is a collagenous tissue to connect bone and muscle. Healing of damaged/injured tendon is the primary clinical challenge in musculoskeletal regeneration because they often react poorly to treatment. Tissue engineering (a triad strategy of scaffolds, cells and growth factors) may have the potential to improve the quality of tendon tissue healing under such impaired situations. Tendon tissue engineering aims to synthesize graft alternatives to repair the injured tendon. Biological scaffolds derived from decellularized tissue may be a better option as their biomechanical properties are similar to the native tissue. This review is designed to provide background information on the current challenges in curing torn/worn out the tendon and the clinical relevance of decellularized scaffolds for such applications.

Multi-layered Free-form 3D Cell-printed Tubular Construct with Decellularized Inner and Outer Esophageal Tissue-derived Bioinks

The incidences of various esophageal diseases (e.g., congenital esophageal stenosis, tracheoesophageal fistula, esophageal atresia, esophageal cancer) are increasing, but esophageal tissue is difficult to be recovered because of its weak regenerative capability. There are no commercialized off-the-shelf alternatives to current esophageal reconstruction and regeneration methods. Surgeons usually use ectopic conduit tissues including stomach and intestine, presumably inducing donor site morbidity and severe complications. To date, polymer-based esophageal substitutes have been studied as an alternative. However, the fabrication techniques are nearly limited to creating only cylindrical outer shapes with the help of additional apparatus (e.g., mandrels for electrospinning) and are unable to recapitulate multi-layered characteristic or complex-shaped inner architectures. 3D bioprinting is known as a suitable method to fabricate complex free-form tubular structures with desired pore characteristic. In this study, we developed a extrusion-based 3D printing technique to control the size and the shape of the pore in a single extrusion process, so that the fabricated structure has a higher flexibility than that fabricated in the conventional process. Based on this suggested technique, we developed a bioprinted 3D esophageal structure with multi-layered features and converged with biochemical microenvironmental cues of esophageal tissue by using decellularizedbioinks from mucosal and muscular layers of native esophageal tissues. The two types of esophageal tissue derived-decellularized extracellular matrix bioinks can mimic the inherent components and composition of original tissues with layer specificity. This structure can be applied to full-thickness circumferential esophageal defects and esophageal regeneration.

Aspects of Nanomaterials in Wound Healing

Wound infections impose a remarkable clinical challenge that has a considerable influence on morbidity and mortality of patients, influencing the cost of treatment. The unprecedented advancements in molecular biology have come up with new molecular and cellular targets that can be successfully applied to develop smarter therapeutics against diversified categories of wounds such as acute and chronic wounds. However, nanotechnology-based diagnostics and treatments have achieved a new horizon in the arena of wound care due to its ability to deliver a plethora of therapeutics into the target site, and to target the complexity of the normal wound-healing process, cell type specificity, and plethora of regulating molecules as well as pathophysiology of chronic wounds. The emerging concepts of nanobiomaterials such as nanoparticles, nanoemulsion, nanofibrous scaffolds, graphene-based nanocomposites, etc., and nano-sized biomaterials like peptides/proteins, DNA/RNA, oligosaccharides have a vast application in the arena of wound care. Multi-functional, unique nano-wound care formulations have acquired major attention by facilitating the wound healing process. In this review, emphasis has been given to different types of nanomaterials used in external wound healing (chronic cutaneous wound healing); the concepts of basic mechanisms of wound healing process and the promising strategies that can help in the field of wound management.

Puncturing of lyophilized tissue engineered vascular matrices enhances the efficiency of their recellularization

Data on in vitro engineered "off the shelf" matrices support the concept of endogenous cellular repopulation driving the graft's remodeling via immune-mediated response. This seems important to further accelerate the cell reconstitution and may play a crucial role when mononuclear cells are used. Nevertheless, studies on decellularized xenogeneic grafts showed only limited host cell repopulation post-implantation. This study aims at a systematic comparison of reseeding methods (dripping, injection, bathing in a cell suspension and combined puncturing-dripping method) to define the most efficient technique enhancing recellularization of tissue engineered vascular matrices (patches, vessels, small diameter and standard size valves) prior implantation. The constructs were analyzed histologically, biochemically and biomechanically. Various preconditioning treatments (wet, lyophilized and air-dried) combined with reseeding methods demonstrated the highest cell loading efficiency, despite applied crimping and flow stress, of lyophilization followed by puncturing-dripping technique. This novel seeding method allows for an efficient, time-saving graft reseeding that can be used within a one-step cardiovascular clinical intervention.

STATEMENT OF SIGNIFICANCE

The concept of living tissue engineered, self-repairing, autologous cardiovascular replacements, was proposed alternatively to existing synthetic/xenogeneic prostheses. Recent studies in animal models demonstrate faster in vivo recellularization after grafts pre-seeding with cells prior implantation. Pre-seeded cells hold either, the ability to differentiate directionally or attract host cells, crucial for graft integration and remodeling. It is unclear, however, how efficient the pre-loading is and how well cells withstand the flow. The study presents a systematic overview of cell loading techniques of different cardiovascular constructs, tested under static and dynamic conditions. Comparison illustrates a significantly higher efficiency of cells loading in lyophilized tissues punctured before their standard seeding. This technique may beneficially accelerate remodeling of cardiovascular grafts in further in vivo studies.

Mesenchymal Stem/Stromal Cells in Regenerative Medicine: Past, Present, and Future

The concept of Regenerative Medicine combined with Cell based Therapy and Tissue Engineering represents the fourth pillar of healthcare and provides a promising approach for the treatment of serious diseases. Recently, cell based therapies are focused on the use of mesenchymal stem/stromal cells (MSCs). Human MSCs, that represent a mesoderm derived population of progenitors, are easily expanded in culture. They are capable to differentiate into osteoblasts, chondrocytes, and adipocytes and exhibit the potential to repair or regenerate damaged tissues. The best characterized source of human MSCs to date is the bone marrow; recently, fetal sources, such as amniotic fluid, umbilical cord, amniotic membranes, or placenta, have also attracted increased attention. Thus, MSCs may represent a valuable tool for tissue repair and cell therapeutic applications. To this end, the main focus of this review is to summarize and evaluate the key characteristics, the sources, and the potential use of MSCs in therapeutic approaches and modalities.

A novel scale-down cell culture and imaging design for the mechanistic insight of cell colonisation within porous substrate

At the core of translational challenges in tissue engineering is the mechanistic understanding of the underpinning biological processes and the complex relationships among components at different levels, which is a challenging task due to the limitations of current tissue culture and assessment methodologies. Therefore, we proposed a novel scale-down strategy to deconstruct complex biomatrices into elementary building blocks, which were resembled by thin modular substrate and then evaluated separately in miniaturised bioreactors using various conventional microscopes. In order to investigate cell colonisation within porous substrate in this proof-of-concept study, TEM specimen supporters (10-30 μm thick) with fine controlled open pores (100∼600 μm) were selected as the modular porous substrate and suspended in 3D printed bioreactor systems. Noninvasive imaging of human dermal fibroblasts cultured on these free-standing substrate using optical microscopes illustrated the complicated dynamic processes used by both individual and coordinated cells to bridge and segment porous structures. Further in situ analysis via SEM and TEM provided high-quality micrographs of cell-cell and cell-scaffold interactions at microscale, depicted cytoskeletal structures in stretched and relaxed areas at nanoscale. Thus this novel scaled-down design was able to improve our mechanistic understanding of tissue formation not only at single- and multiple-cell levels, but also at micro- and nanoscales, which could be difficult to obtain using other methods.

Autologous Cells for Kidney Bioengineering

Worldwide, increasing numbers of patients are developing end-stage renal disease, and at present, the only treatment options are dialysis or kidney transplantation. Dialysis is associated with increased morbidity and mortality, poor life quality and high economic costs. Transplantation is by far the better option, but there are insufficient numbers of donor kidneys available. Therefore, there is an urgent need to explore alternative approaches. In this review, we discuss how this problem could potentially be addressed by using autologous cells and appropriate scaffolds to develop 'bioengineered' kidneys for transplantation. In particular, we will highlight recent breakthroughs in pluripotent stem cell biology that have led to the development of autologous renal progenitor cells capable of differentiating to all renal cell types and will discuss how these cells could be combined with appropriate scaffolds to develop a bioengineered kidney.

Biomimetic collagenous scaffold to tune inflammation by targeting macrophages

The inflammatory response following implantation of a biomaterial is one of the major regulatory aspects of the overall regenerative process. The progress of inflammation determines whether functional tissue is restored or if nonfunctional fibrotic tissue is formed. This delicate balance is directed by the activity of different cells. Among these, macrophages and their different phenotypes, the inflammatory M1 to anti-inflammatory M2, are considered key players in the process. Recent approaches exploit macrophage’s regenerative potential in tissue engineering. Here, we propose a collagen scaffold functionalized with chondroitin sulfate (CSCL), a glycosaminoglycan known to be able to tune inflammation. We studied CSCL effects on bone-marrow-derived macrophages in physiological, and lipopolysaccharides-inflamed, conditions in vitro. Our data demonstrate that CSCL is able to modulate macrophage phenotype by inhibiting the LPS/CD44/NF-kB cascade. As a consequence, an upregulation of anti-inflammatory markers (TGF-β, Arg, MRC1, and IL-10) was found concomitantly with a decrease in the expression of pro-inflammatory markers (iNOS, TNF-α, IL-1β, IL-12β). We then implanted CSCL subcutaneously in a rat model to test whether the same molecular mechanism could be maintained in an in vivo environment. In vivo data confirmed the in vitro studies. A significant reduction in the number of infiltrating cells around and within the implants was observed at 72 h, with a significant downregulation of pro-inflammatory genes expression. The present work provides indications regarding the immunomodulatory potential of molecules used for the development of biomimetic materials and suggests their use to direct macrophage immune modulation for tissue repair.

Wnt1a maintains characteristics of dermal papilla cells that induce mouse hair regeneration in a 3D preculture system

Hair follicle morphogenesis and regeneration depend on intensive but well-orchestrated interactions between epithelial and mesenchymal components. Therefore, an alternative strategy to reproduce the process of epithelial-mesenchymal interaction in vitro could use a 3D system containing appropriate cell populations. The 3D air-liquid culture system for reproducibly generating hair follicles from dissociated epithelial and dermal papilla (DP) cells combined with a collagen-chitosan scaffold is described in this study. Wnt-CM was prepared from the supernatant of Wnt1a-expressing bone marrow mesenchymal stem cells (BM-MSCs) that maintain the hair-inducing gene expression of DP cells. The collagen-chitosan scaffold cells (CCS cells) were constructed using a two-step method by inoculating the Wnt-CM-treated DP cells and epidermal (EP) cells into the CCS. The cells in the air-liquid culture formed dermal condensates and a proliferative cell layer in vitro. The CCS cells were able to induce hair regeneration in nude mice. The results demonstrate that Wnt-CM can maintain the hair induction ability of DP cells in expansion cultures, and this approach can be used for large-scale preparation of CCS cells in vitro to treat hair loss. Copyright © 2015 John Wiley & Sons, Ltd.