Regenerative medicine and developmental biology: the role of the extracellular matrix

Human Chorionic Membrane-derived Tunable Hydrogels for Vascular Tissue Engineering Strategies

One of the foremost targets in the advancement of biomaterials to engineer vascularized tissues is not only to replicate the composition of the intended tissue but also to create thicker structures incorporating a vascular network for adequate nutrients and oxygen supply. For the first time, to the best of current knowledge, a clinically relevant biomaterial is developed, demonstrating that hydrogels made from the human decellularized extracellular matrix can exhibit robust mechanical properties (in the kPa range) and angiogenic capabilities simultaneously. These properties enable the culture and organization of human umbilical vein endothelial cells into tubular structures, maintaining their integrity for 14 days in vitro without the need for additional polymers or angiogenesis-related factors. This is achieved by repurposing the placenta chorionic membrane (CM), a medical waste with an exceptional biochemical composition, into a valuable resource for bioengineering purposes. After decellularization, the CM underwent chemical modification with methacryloyl groups, giving rise to methacrylated CM (CMMA). CMMA preserved key proteins, as well as glycosaminoglycans. The resulting hydrogels rapidly photopolymerize and have enhanced strength and customizable mechanical properties. Furthermore, they demonstrate angio-vasculogenic competence in vitro and in vivo, holding significant promise as a humanized platform for the engineering of vascularized tissues.

Modular Microgel-Based Bioassembly Scaffold Induced Chondrogenic and Osteogenic Differentiation of BMSCs

Bioactive scaffolds capable of simultaneously repairing osteochondral defects remain a big challenge due to the heterogeneity of bone and cartilage. Currently modular microgel-based bioassembly scaffolds are emerged as potential solution to this challenge. Here, microgels based on methacrylic anhydride (MA) and dopamine modified gelatin (GelMA-DA) are loaded with chondroitin sulfate (CS) (the obtained microgel named GC Ms) or bioactive glass (BG) (the obtained microgel named GB Ms), respectively. GC Ms and GB Ms show good biocompatibility with BMSCs, which suggested by the adhesion and proliferation of BMSCs on their surfaces. Specially, GC Ms promote chondrogenic differentiation of BMSCs, while GB Ms promote osteogenic differentiation. Furthermore, the injectable GC Ms and GB Ms are assembled integrally by bottom-up in situ cross-linking to obtain modular microgel-based bioassembly scaffold (GC-GB/HM), which show a distinct bilayer structure and good porous properties and swelling properties. Particularly, the results of in vivo and in vitro experiments show that GC-GB/HM can simultaneously regulate the expression levels of chondrogenic- and osteogenesis-related genes and proteins. Therefore, modular microgel-based assembly scaffold in this work with the ability to promote bidirectional differentiation of BMSCs and has great potential for application in the minimally invasive treatment of osteochondral tissue defects.

Advances, challenges, and future directions in the clinical translation of ECM biomaterials for regenerative medicine applications

Extracellular Matrix (ECM) scaffolds and biomaterials have been widely used for decades across a variety of diverse clinical applications and have been implanted in millions of patients worldwide. ECM-based biomaterials have been especially successful in soft tissue repair applications but their utility in other clinical applications such as for regeneration of bone or neural tissue is less well understood. The beneficial healing outcome with the use of ECM biomaterials is the result of their biocompatibility, their biophysical properties and their ability to modify cell behavior after injury. As a consequence of successful clinical outcomes, there has been motivation for the development of next-generation formulations of ECM materials ranging from hydrogels, bioinks, powders, to whole organ or tissue scaffolds. The continued development of novel ECM formulations as well as active research interest in these materials ensures a wealth of possibilities for future clinical translation and innovation in regenerative medicine. The clinical translation of next generation formulations ECM scaffolds faces predictable challenges such as manufacturing, manageable regulatory pathways, surgical implantation, and the cost required to address these challenges. The current status of ECM-based biomaterials, including clinical translation, novel formulations and therapies currently under development, and the challenges that limit clinical translation of ECM biomaterials are reviewed herein.

Evaluation of Interdental Papilla Regeneration Using Injectable Hyaluronic Acid: A Clinical Study

AIM

This study aimed to assess the efficacy of hyaluronic acid (HA) gel injections in deficient papillae and record the effects for four weeks.

MATERIALS AND METHODS

Fifteen deficient class 1 papilla sites according to Nordland and Tarnow classification were included. After scaling and root planing, 0.5 ml HA gel was injected into the papillae. Measurements of black triangle height (BTH) and black triangle area (BTA) from the contact point to the most coronal level of the visible papilla tip were done on the clinical photographs using ImageJ software at baseline, one week, and four weeks postoperatively, and a comparison was made. Descriptive data were examined using the mean and standard deviation (SD). Paired t-test was used for intragroup comparisons, with p-values <0.05 considered significant. All the data analysis was done using SPSS software version 25.0.

RESULTS

There was a mean decrease in the BTA from baseline (0.54 mm2), one week (0.13 mm2), to four weeks (0.26 mm2) with a slight loss of papilla volume from the first week to the fourthweek, and this decrease in area was statistically significant. A mean decrease in the BTH throughout the follow-ups from baseline (1.36 mm) to the first week (0.30 mm) to the fourth week (0.73) was recorded with a slight loss of papilla volume from the first week to the fourthweek, and this decrease in height was also statistically significant (p < 0.05). However, the decrease in the BTA and BTH recorded was more from baseline to the first week as compared to baseline to the fourth week postoperatively.

CONCLUSION

HA gel is an effective treatment for minimally invasive papilla augmentation, particularly in class I Nordland and Tarnow papilla deficits.

Dynamical properties of solid and hydrated collagen: Insight from nuclear magnetic resonance relaxometry

1H spin-lattice Nuclear Magnetic Resonance relaxometry experiments have been performed for collagen and collagen-based artificial tissues in the frequency range of 10 kHz-20 MHz. The studies were performed for non-hydrated and hydrated materials. The relaxation data have been interpreted as including relaxation contributions originating from 1H-1H and 1H-14N dipole-dipole interactions, the latter leading to Quadrupole Relaxation Enhancement effects. The 1H-1H relaxation contributions have been decomposed into terms associated with dynamical processes on different time scales. A comparison of the parameters for the non-hydrated and hydrated systems has shown that hydration leads to a decrease in the dipolar relaxation constants without significantly affecting the dynamical processes. In the next step, the relaxation data for the hydrated systems were interpreted in terms of a model assuming two-dimensional translational diffusion of water molecules in the vicinity of the macromolecular surfaces and a sub-diffusive motion leading to a power law of the frequency dependencies of the relaxation rates. It was found that the water diffusion process is slowed down by at least two orders of magnitude compared to bulk water diffusion. The frequency dependencies of the relaxation rates in hydrated tissues and hydrated collagen are characterized by different power laws (ωH-β, where ωH denotes the 1H resonance frequency): the first of about 0.4 and the second close to unity.

Recent Trends in Macromolecule-Based Approaches for Hair Loss Treatment

Macromolecules are large, complex molecules composed of smaller subunits known as monomers. The four primary categories of macromolecules found in living organisms are carbohydrates, lipids, proteins, and nucleic acids; they also encompass a broad range of natural and synthetic polymers. Recent studies have shown that biologically active macromolecules can help regenerate hair, providing a potential solution for current hair regeneration therapies. This review examines the latest developments in the use of macromolecules for the treatment of hair loss. The fundamental principles of hair follicle (HF) morphogenesis, hair shaft (HS) development, hair cycle regulation, and alopecia have been introduced. Microneedle (MN) and nanoparticle (NP) delivery systems are innovative treatments for hair loss. Additionally, the application of macromolecule-based tissue-engineered scaffolds for the in vitro and in vivo neogenesis of HFs is discussed. Furthermore, a new research direction is explored wherein artificial skin platforms are adopted as a promising screening method for hair loss treatment drugs. Through these multifaceted approaches, promising aspects of macromolecules for future hair loss treatments are identified.

Structural and biomechanical characterizations of acellular porcine mitral valve scaffolds: anterior leaflets, posterior leaflets, and chordae tendineae

Mitral valve (MV) tissue engineering is still in its early stage, and one major challenge in MV tissue engineering is to identify appropriate scaffold materials. With the potential of acellular MV scaffolds being demonstrated recently, it is important to have a full understanding of the biomechanics of the native MV components and their acellular scaffolds. In this study, we have successfully characterized the structural and mechanical properties of porcine MV components, including anterior leaflet (AL), posterior leaflet (PL), strut chordae, and basal chordae, before and after decellularization. Quantitative DNA assay showed more than 90% reduction in DNA content, and Griffonia simplicifolia (GS) lectin immunohistochemistry confirmed the complete lack of porcine α-Gal antigen in the acellular MV components. In the acellular AL and PL, the atrialis, spongiosa, and fibrosa trilayered structure, along with its ECM constitutes, i.e., collagen fibers, elastin fibers, and portion of GAGs, were preserved. Nevertheless, the ECM of both AL and PL experienced a certain degree of disruption, exhibiting a less dense, porous ECM morphology. The overall anatomical morphology of the strut and basal chordae were also maintained after decellularization, with longitudinal morphology experiencing minimum disruption, but the cross-sectional morphology exhibiting evenly-distributed porous structure. In the acellular AL and PL, the nonlinear anisotropic biaxial mechanical behavior was overall preserved; however, uniaxial tensile tests showed that the removal of cellular content and the disruption of structural ECM did result in small decreases in maximum tensile modulus, tissue extensibility, failure stress, and failure strain for both MV leaflets and chordae.

Changes in extracellular matrix in failing human non-ischemic and ischemic hearts with mechanical unloading

Ischemic and non-ischemic cardiomyopathies have distinct etiologies and underlying disease mechanisms, which require in-depth investigation for improved therapeutic interventions. The goal of this study was to use clinically obtained myocardium from healthy and heart failure patients, and characterize the changes in extracellular matrix (ECM) in ischemic and non-ischemic failing hearts, with and without mechanical unloading. Using tissue engineering methodologies, we also investigated how diseased human ECM, in the absence of systemic factors, can influence cardiomyocyte function. Heart tissues from heart failure patients with ischemic and non-ischemic cardiomyopathy were compared to explore differential disease phenotypes and reverse remodeling potential of left ventricular assisted device (LVAD) support at transcriptomic, proteomic and structural levels. The collected data demonstrated that the differential ECM compositions recapitulated the disease microenvironment and induced cardiomyocytes to undergo disease-like functional alterations. In addition, our study also revealed molecular profiles of non-ischemic and ischemic heart failure patients and explored the underlying mechanisms of etiology-specific impact on clinical outcome of LVAD support and tendency towards reverse remodeling.

Regenerative Engineering: Current Applications and Future Perspectives

Many pathologies, congenital defects, and traumatic injuries are untreatable by conventional pharmacologic or surgical interventions. Regenerative engineering represents an ever-growing interdisciplinary field aimed at creating biological replacements for injured tissues and dysfunctional organs. The need for bioengineered replacement parts is ubiquitous among all surgical disciplines. However, to date, clinical translation has been limited to thin, small, and/or acellular structures. Development of thicker tissues continues to be limited by vascularization and other impediments. Nevertheless, currently available materials, methods, and technologies serve as robust platforms for more complex tissue fabrication in the future. This review article highlights the current methodologies, clinical achievements, tenacious barriers, and future perspectives of regenerative engineering.

Circumferential esophageal replacement by a decellularized esophageal matrix in a porcine model

BACKGROUND

Tissue engineering is an attractive alternative to conventional esophageal replacement techniques using intra-abdominal organs which are associated with a substantial morbidity. The objective was to evaluate the feasibility of esophageal replacement by an allogenic decellularized esophagus in a porcine model. Secondary objectives were to evaluate the benefit of decellularized esophagus recellularization with autologous bone marrow mesenchymal stromal cells and omental maturation of the decellularized esophagus.

METHODS

Eighteen pigs divided into 4 experimental groups according to mesenchymal stromal cells recellularization and omental maturation underwent a 5-cm long circumferential replacement of the thoracic esophagus. Turbo green florescent protein labelling was used for in vivo mesenchymal stromal cells tracking. The graft area was covered by a stent for 3 months. Clinical and histologic outcomes were analyzed over a 6-month period.

RESULTS

The median follow-up was 112 days [5; 205]. Two animals died during the first postoperative month, 2 experienced an anastomotic leakage, 13 experienced a graft area stenosis following stent migration of which 3 were sacrificed as initially planned after successful endoscopic treatment. The stent could be removed in 2 animals: the graft area showed a continuous mucosa without stenosis. After 3 months, the graft area showed a tissue specific regeneration with a mature epithelium and muscular cells. Clinical and histologic results were similar across experimental groups.

CONCLUSION

Circumferential esophageal replacement by a decellularized esophagus was feasible and allowed tissue remodeling toward an esophageal phenotype. We could not demonstrate any benefit provided by the omental maturation of the decellularized esophagus nor its recellularization with mesenchymal stromal cells.

Type II Collagen Sponges Facilitate Tendon Stem/Progenitor Cells to Adopt More Chondrogenic Phenotypes and Promote the Regeneration of Fibrocartilage-Like Tissues in a Rabbit Partial Patellectomy Model

Objective

Fibrocartilage transition zone (FC) is difficult to regenerate after surgical re-attachment of tendon to bone. Here, we investigated whether type II collagen-sponges (CII-sponges) facilitated tendon stem/progenitor cells (TSPCs) to adopt chondrogenic phenotypes and further observed if this material could increase the FC areas in bone-tendon junction (BTJ) injury model.

Methods

CII-sponges were made as we previously described. The appearance and pore structure of CII-sponges were photographed by camera and microscopies. The viability, proliferation, and differentiation of TSPCs were examined by LIVE/DEAD assay, alamarBlue, and PKH67 in vitro tracking. Subsequently, TSPCs were seeded in CII-sponges, Matrigel or monolayer, and induced under chondrogenic medium for 7 or 14 days before being harvested for qPCR or being transplanted into nude mice to examine the chondrogenesis of TSPCs. Lastly, partial patellectomy (PP) was applied to establish the BTJ injury model. CII-sponges were interposed between the patellar fragment and tendon, and histological examination was used to assess the FC regeneration at BTJ after surgery at 8 weeks.

Results

CII-sponges were like sponges with interconnected pores. TSPCs could adhere, proliferate, and differentiate in this CII-sponge up to 14 days at least. Both qPCR and immunostaining data showed that compared with TSPCs cultured in monolayer or Matrigel, cells in CII-sponges group adopted more chondrogenic phenotypes with an overall increase of chondrocyte-related genes and proteins. Furthermore, in PP injured model, much more new formed cartilage-like tissues could be observed in CII-sponges group, evidenced by a large amount of positive proteoglycan expression and typical oval or round chondrocytes in this area.

Conclusion

Our study showed that CII-sponges facilitated the TSPCs to differentiate toward chondrocytes and increased the area of FCs, which suggests that CII-sponges are meaningful for the reconstruction of FC at bone tendon junction. However, the link between the two phenomena requires further research and validation.

Novel Use of a Porcine Bladder Extracellular Matrix Scaffold to Treat Postoperative Seroma in a Total Knee Arthroplasty Patient

Seroma formation in a knee arthroplasty surgery is a rare complication. When seromas occur, they act as a nidus for bacterial growth and create an optimal environment for surgical site infections. In this case report, a 52-year-old woman presented with a seroma after multiple revision operations on the left knee. Owing to multiple failures of standard irrigation and drainage procedures to resolve the seroma, an orthoplastic colleague was consulted. Over five-and-a-half months, the patient underwent multiple procedures that failed to treat the seroma. However, in a final exploratory procedure, 3000 mg of urinary bladder matrix and negative pressure wound vacuum were placed. Seven months after the intervention, the patient had complete resolution.

Graphene Hybrid Materials for Controlling Cellular Microenvironments

Cellular microenvironments are known as key factors controlling various cell functions, including adhesion, growth, migration, differentiation, and apoptosis. Many materials, including proteins, polymers, and metal hybrid composites, are reportedly effective in regulating cellular microenvironments, mostly via reshaping and manipulating cell morphologies, which ultimately affect cytoskeletal dynamics and related genetic behaviors. Recently, graphene and its derivatives have emerged as promising materials in biomedical research owing to their biocompatible properties as well as unique physicochemical characteristics. In this review, we will highlight and discuss recent studies reporting the regulation of the cellular microenvironment, with particular focus on the use of graphene derivatives or graphene hybrid materials to effectively control stem cell differentiation and cancer cell functions and behaviors. We hope that this review will accelerate research on the use of graphene derivatives to regulate various cellular microenvironments, which will ultimately be useful for both cancer therapy and stem cell-based regenerative medicine.

Antigen removal process preserves function of small diameter venous valved conduits, whereas SDS-decellularization results in significant valvular insufficiency

Chronic venous disease (CVD) is the most common reported chronic condition in the United States, affecting more than 25 million Americans. Regardless of its high occurrence, current therapeutic options are far from ideal due to their palliative nature. For best treatment outcomes, challenging cases of chronic venous insufficiency (CVI) are treated by repair or replacement of venous valves. Regrettably, the success of venous valve transplant is dependent on the availability of autologous venous valves and hindered by the possibility of donor site complications and increased patient morbidity. Therefore, the use of alternative tissue sources to provide off-the-shelf venous valve replacements has potential to be extremely beneficial to the field of CVI. This manuscript demonstrates the capability of producing off-the-shelf fully functional venous valved extracellular matrix (ECM) scaffold conduits from bovine saphenous vein (SV), using an antigen removal (AR) method. AR ECM scaffolds maintained native SV structure-function relationships and associated venous valves function. Conversely, SDS decellularization caused significant changes to the collagen and elastin macromolecular structures, resulting in collagen fibril merging, elimination of fibril crimp, amalgaming collagen fibers and fragmentation of the inner elastic lamina. ECM changes induced by SDS decellularization resulted in significant venous valve dysfunction. Venous valved conduits generated using the AR approach have potential to serve as off-the-shelf venous valve replacements for CVI. STATEMENT OF SIGNIFICANCE: Retention of the structure and composition of extracellular matrix (ECM) proteins within xenogeneic scaffolds for tissue engineering is of crucial importance, due to the undeniable effect ECM proteins can impose on repopulating cells and function of the resultant biomaterial. This manuscript demonstrates that alteration or elimination of ECM proteins via commonly utilized decellularization approach results in complete disruption of venous valve function. Conversely, retention of the delicate ECM structure and composition of native venous tissue, using an antigen removal tissue processing method, results in preservation of native venous valve function.

Phage-Based Artificial Niche: The Recent Progress and Future Opportunities in Stem Cell Therapy

Self-renewal and differentiation of stem cells can be the best option for treating intractable diseases in regenerative medicine, and they occur when these cells reside in a special microenvironment, called the "stem cell niche." Thus, the niche is crucial for the effective performance of the stem cells in both in vivo and in vitro since the niche provides its functional cues by interacting with stem cells chemically, physically, or topologically. This review provides a perspective on the different types of artificial niches including engineered phage and how they could be used to recapitulate or manipulate stem cell niches. Phage-based artificial niche engineering as a promising therapeutic strategy for repair and regeneration of tissues is also discussed.

ROCK isoforms differentially modulate cancer cell motility by mechanosensing the substrate stiffness

Tumors are characterized by extracellular matrix (ECM) remodeling and stiffening. The importance of ECM stiffness in cancer is well known. However, the biomechanical behavior of tumor cells and the underlying mechanotransduction pathways remain unclear. Here, we used polyacrylamide (PAA) substrates to simulate tissue stiffness at different progress stages of breast cancer in vitro, and we observed that moderate substrate stiffness promoted breast cancer cell motility. The substrate stiffness directly activated integrin β1 and focal adhesion kinase (FAK), which accelerate focal adhesion (FA) maturation and induce the downstream cascades of intracellular signals of the RhoA/ROCK pathway. Interestingly, the differential regulatory mechanism between two ROCK isoforms (ROCK1 and ROCK2) in cell motility and mechanotransduction was clearly identified. ROCK1 phosphorylated the myosin regulatory light chain (MRLC) and facilitated the generation of traction force, while ROCK2 phosphorylated cofilin and regulated the cytoskeletal remodeling by suppressing F-actin depolymerization. The ROCK isoforms differentially regulated the pathways of RhoA/ROCK1/p-MLC and RhoA/ROCK2/p-cofilin in a coordinate fashion to modulate breast cancer cell motility in a substrate stiffness-dependent manner through integrin β1-activated FAK signaling. Our findings provide new insights into the mechanisms of matrix mechanical property-induced cancer cell migration and malignant behaviors. STATEMENT OF SIGNIFICANCE: Here, we examined the relationship between substrate stiffness and tumor cellular motility by using polyacrylamide (PAA) substrates to simulate the stages in vivo of breast cancer. The results elucidated the different regulatory roles between the two ROCK isoforms in cell motility and demonstrated that stiff substrate (38 kPa) mediated RhoA/ROCK1/p-MLC and RhoA/ROCK2/p-cofilin pathways through integrin β1-FAK activation and eventually promoted directional migration. Our discoveries would have significant implications in the understanding of the interaction between cancer cells and tumor microenvironments, and hence, it might provide new insights into the metastasis inhibition, which could be an adjuvant way of cancer therapy.

A Photo-Crosslinkable Kidney ECM-Derived Bioink Accelerates Renal Tissue Formation

3D bioprinting strategies in tissue engineering aim to fabricate clinically applicable tissue constructs that can replace the damaged or diseased tissues and organs. One of the main prerequisites in 3D bioprinting is finding an appropriate bioink that provides a tissue-specific microenvironment supporting the cellular growth and maturation. In this respect, decellularized extracellular matrix (dECM)-derived hydrogels have been considered as bioinks for the cell-based bioprinting due to their capability to inherit the intrinsic cues from native ECM. Herein, a photo-crosslinkable kidney ECM-derived bioink (KdECMMA) is developed that could provide a kidney-specific microenvironment for renal tissue bioprinting. Porcine whole kidneys are decellularized through a perfusion method, dissolved in an acid solution, and chemically modified by methacrylation. A KdECMMA-based bioink is formulated and evaluated for rheological properties and printability for the printing process. The results show that the bioprinted human kidney cells in the KdECMMA bioink are highly viable and mature with time. Moreover, the bioprinted renal constructs exhibit the structural and functional characteristics of the native renal tissue. The potential of the tissue-specific ECM-derived bioink is demonstrated for cell-based bioprinting that could enhance the cellular maturation and eventually tissue formation.

Generation of novel hyaluronic acid biomaterials for study of pain in third molar intervention: a review

Hyaluronic acid (HA) has long been studied in diverse applications. It is a naturally occurring linear polysaccharide in a family of unbranched glycosaminoglycans, which consists of repeating di-saccharide units of N-acetyl-D-glucosamine and D-glucuronic acid. It is almost ubiquitous in humans and other vertebrates, where it participates in many key processes, including cell signaling, tissue regeneration, wound healing, morphogenesis, matrix organization, and pathobiology. HA is biocompatible, biodegradable, muco-adhesive, hygroscopic, and viscoelastic. These unique physico-chemical properties have been exploited for several medicinal purposes, including recent uses in the adjuvant treatment for chronic inflammatory disease and to reduce pain and accelerate healing after third molar intervention. This review focuses on the post-operative effect of HA after third molar intervention along with its various physio-chemical, biochemical, and pharmaco-therapeutic uses.

Collagen/Cellulose Nanofiber Blend Scaffolds Prepared at Various pH Conditions

Living tissues modules consist of highly organized cells and extracellular matrices (ECMs) in a hierarchical manner. Among these ECMs, type I collagen (COL), which is the most abundant protein, is widely accepted in the tissue engineering field due to its biocompatibility. However, improvement of mechanical properties of COL scaffolds still remains a challenge. We prepared the scaffold sheets with blends of COL and 2,2,6,6-tetramethylpiperidine-1-oxil(TEMPO)-oxidized cellulose nanofiber (TOCN). TOCNs with high mechanical properties reinforced COL scaffolds. Moreover, we prepared their blends under various pH conditions and investigated their mechanical properties and biocompatibilities. Sheets prepared at a higher pH possess a better mechanical performance. From Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy measurements, it is proved that the higher mechanical properties were attributed to COL triple inter helix structure, hydrogen interaction, and electrostatic interaction with TOCN. The biocompatibilities of COL/TOCN prepared at a higher pH were increased. We successfully demonstrated COL/TOCN blend materials with a high mechanical strength and high biocompatibility for scaffold materials.

Ultrastructural analysis of collagen fibril diameter distribution in cleft lip

OBJECTIVE

A preliminary study to determine collagen fibril diameter (CF-ED) distribution on medial and lateral sides of cleft lip (CL).

MATERIAL AND METHODS

Tissue samples from medial and lateral sides of CL were fixed in 2.5% glutaraldehyde and 1% osmium tetroxide and embedded in Araldite CY212 resin for transmission electron microscopy. The analysis of CF-ED was performed using the ImageJ program. To characterize the packaging of collagen fibrils (CFs) in the two tissues, we estimated the collagen number density (CF-ND) and fibril-area-fraction (FAF). Differences in measurements across the two sides were calculated using Wilcoxon signed-rank test.

RESULTS

The CF-ED was statistically significantly (p < 0.001) smaller on the medial side (45.69 ± 7.89 nm) than on the lateral side (54.18 ± 7.62 nm). The medial side had a higher CF-ND and a higher percentage of FAF than the lateral side.

CONCLUSION

Our finding of a smaller CF-ED and higher CF-ND and FAF for the medial side suggests possible differences in size and distribution of CFs between medial and lateral sides of CL. This finding provides knowledge toward underlying tissue biomechanics that may help reconstruction of perioral tissue scaffolds, ultimately resulting in better treatment of patients with oral clefts.

Efficient decellularization of rabbit trachea to generate a tissue engineering scaffold biomatrix

OBJECTIVES

Most tracheal decellularization protocols are lengthy and can lead to reduced biomechanical stability. The objectives of this study were: 1) to generate a tracheal extracellular matrix scaffold using an efficient decellularization process and 2) to characterize the decellularized scaffold to assess its suitability for tissue engineering applications.

METHODS

Twelve rabbit tracheae underwent a decellularization process that involved enzymatic-detergent treatments. For characterization, fresh (control) and decellularized tissues underwent histological, immunohistochemical, and biochemical analyses. Tensile testing, scanning electron microscopy, and biocompatibility assay were also conducted.

RESULTS

Post-decellularization, the tracheal tissue had significantly less genetic material while the structural integrity was maintained. Specifically, the deoxyribonucleic acid content was significantly reduced and the glycosaminoglycan content was unchanged. Cell and cellular components were largely removed; at the same time the tensile properties and surface ultrastructural characteristics were unaltered. Biocompatibility was confirmed by contact cytotoxicity assay.

CONCLUSIONS

Overall, an efficient decellularization process was used to treat rabbit tracheal tissue. The effectiveness of the decellularization process was demonstrated and at the same time there was preservation of the underlying extracellular matrix structure. This decellularized material may serve as a potential scaffold for tracheal tissue engineering.

Extracellular Matrix Membrane Induces Cementoblastic/Osteogenic Properties of Human Periodontal Ligament Stem Cells

Objective: Periodontitis affects nearly 90% of adults over the age of 70, resulting to periodontal tissue infection, destruction, and ultimately tooth loss. Guided tissue regeneration (GTR) is a method widely used to treat severe periodontal disease, and involves placement of an occlusive barrier to facilitate regeneration of the damaged area by periodontal ligament stem cells (PDLSCs). In this study, we evaluate natural extracellular matrix (ECM) as a scaffold material to provide a suitable microenvironment to support the proliferation, differentiation, and tissue-regenerating properties of PDLSCs. Design: The viability, proliferation, apoptosis, and migration of PDLSCs cultured on ECM membrane, that was isolated from porcine urinary bladders, were compared with those cultured on type I collagen membrane, a commonly used scaffold in GTR. To evaluate the effects of ECM vs. type I collagen on the tissue-regenerating properties of PDLSCs, the bio-attachment and cementoblastic/osteogenic differentiation of PDLSCs were evaluated. Results: Incubation of PDLSCs with ECM resulted in increased viability, proliferation, and reduced apoptosis, compared with type I collagen treated PDLSCs. Co-culture with ECM membrane also increased the migration and bio-attachment of PDLSCs. Incubation of PDLSCs with ECM membrane increased expression of the cementoblastic/osteogenic differentiation markers BSP, RUNX2, ALP, OPN, OCN, and periostin. Conclusion: ECM membrane enhances the proliferation and regenerative properties of PDLSCs, indicating that ECM membrane can serve as a suitable scaffold in the application of GTR to treat periodontal disease.

Inducing hair follicle neogenesis with secreted proteins enriched in embryonic skin

Organ development is a sophisticated process of self-organization. However, despite growing understanding of the developmental mechanisms, little is known about how to reactivate them postnatally for regeneration. We found that treatment of adult non-hair fibroblasts with cell-free extract from embryonic skin conferred upon them the competency to regenerate hair follicles. Proteomics analysis identified three secreted proteins enriched in the embryonic skin, apolipoprotein-A1, galectin-1 and lumican that together were essential and sufficient to induce new hair follicles. These 3 proteins show a stage-specific co-enrichment in the perifolliculogenetic embryonic dermis. Mechanistically, exposure to embryonic skin extract or to the combination of the 3 proteins altered the gene expression to an inductive hair follicle dermal papilla fibroblast-like profile and activated Igf and Wnt signaling, which are crucial for the regeneration process. Therefore, a cocktail of organ-specific extracellular proteins from the embryonic environment can render adult cells competent to re-engage in developmental interactions for organ neogenesis. Identification of factors that recreate the extracellular context of respective developing tissues can become an important strategy to promote regeneration in adult organs.

Understanding the Impact of Preservation Methods on the Integrity and Functionality of Placental Allografts

INTRODUCTION

Human placental membranes (hPMs) have a long history in treating burns and wounds. The composition of hPMs includes structural matrix, growth factors, and neonatal cells, all of which contribute to their regenerative potential. However, most hPM products are devitalized after dehydration and irradiation. We compared the functionality of single-layer viable cryopreserved human amniotic membrane (vCHAM) with multilayer devitalized dehydrated human amnion/chorion membrane (dHACM) in wound-relevant models to determine the effect of different processing methods on hPMs.

METHODS

Viable cryopreserved human amniotic membrane and dHACM were compared with fresh hPM for structural integrity and viability. Viable cell persistence in vCHAM over time was evaluated in vitro and in vivo in a diabetic chronic wound mouse model. Proliferation of cells within fresh hPM and vCHAM was evaluated with bromodeoxyuridine and Ki-67 staining, and proliferation of isolated cells in culture was evaluated. Growth factor release over time and in vitro response to chronic wound stimuli (tumor necrosis factor α, lipopolysaccharide, and hypoxia) were used to compare the functionality of vCHAM and dHACM.

RESULTS

The structure and thickness of fresh hPM were retained in vCHAM but were compromised in dHACM. Similar to fresh hPM, vCHAM contained viable cells, whereas dHACM did not. Cells in vCHAM remained viable after 4 and 7 days in culture and in an in vitro chronic wound environment and after 4 and 8 days in vivo after application to a mouse chronic wound. Staining for bromodeoxyuridine and Ki-67 did not reveal proliferative cells within fresh hPM and vCHAM. However, isolated cells proliferated in culture. Viable cryopreserved human amniotic membrane increased platelet-derived growth factor BB, hepatocyte growth factor, and epidermal growth factor levels over time and responded to chronic wound stimuli in vitro by significantly increasing levels of vascular endothelial growth factor and prostaglandin E2. Dehydrated human amnion/chorion membrane showed no significant accumulation of growth factors and did not respond to chronic wound stimuli.

CONCLUSIONS

These results indicate that vCHAM retains intact, native matrix, and viable, active cells and responds to chronic wound stimuli in vitro. The inclusion of multiple layers of hPM does not compensate for structural degradation and loss of viability caused by dehydration as evidenced by a lack of functional response by dHACM. The clinical significance of these results remains to be answered.

Abdominal wall reconstruction following resection of large abdominal aggressive neoplasms using tensor fascia lata flap with or without mesh reinforcement

PURPOSE

Abdominal wall defects caused by neoplasms with large extended resection defects remain a challenging problem. Autologous flaps, meshes, and component separation techniques are effective in reconstructing these defects. We retrospectively reviewed and assessed the success of reconstruction using tensor fascia lata flap with or without meshes.

METHODS

18 patients with abdominal wall neoplasms were identified during the period from 2007 to 2016. A retrospective review of office charts and hospital records was performed.

RESULTS

A total of 18 patients received corresponding treatment according to the degree of defects, with a mean age of 53.89 ± 14.56 years old, a mean body mass index (BMI) of 22.89 ± 4.09 kg/m², and a mean American Society of Anesthesiologist (ASA) score of 2.18 ± 0.75. Operative details included the mean defect size (303.44 ± 175.67 cm²), the mean mesh size (265.92 ± 227.99 cm²), and the mean operative time (382.33 ± 180.38 min). Postoperative wound complications were identified in 7 (39%) patients, including incisional infection, edema and thrombus. Neoplasm recurrence was observed in 2 (13%) primary neoplasms patients. No hernias were present in any patient.

CONCLUSIONS

Abdominal wall defects caused by neoplasms should be repaired by autologous flaps combined with or without mesh reinforcement. Most type I defects should be primary sutured; type II or III defects should be repaired well by flaps, with or without mesh; if the incision is infected or contaminated, biological mesh or flaps are the best choice.

Vision for Functionally Decorated and Molecularly Imprinted Polymers in Regenerative Engineering

The emerging field of regenerative engineering offers a great challenge and an even greater opportunity for materials scientists and engineers. How can we develop materials that are highly porous to permit cellular infiltration, yet possess sufficient mechanical integrity to mimic native tissues? How can we retain and deliver bioactive molecules to drive cell organization, proliferation, and differentiation in a predictable manner? In the following perspective, we highlight recent studies that have demonstrated the vital importance of each of these questions, as well as many others pertaining to scaffold development. We posit hybrid materials synthesized by molecular decoration and molecular imprinting as intelligent biomaterials for regenerative engineering applications. These materials have potential to present cell adhesion molecules and soluble growth factors with fine-tuned spatial and temporal control, in response to both cell-driven and external triggers. Future studies in this area will address a pertinent clinical need, expand the existing repertoire of medical materials, and improve the field's understanding of how cells and materials respond to one another.

Monomeric, porous type II collagen scaffolds promote chondrogenic differentiation of human bone marrow mesenchymal stem cells in vitro

Osteoarthritis (OA) is a common cause of pain and disability and is often associated with the degeneration of articular cartilage. Lesions to the articular surface, which are thought to progress to OA, have the potential to be repaired using tissue engineering strategies; however, it remains challenging to instruct cell differentiation within a scaffold to produce tissue with appropriate structural, chemical and mechanical properties. We aimed to address this by driving progenitor cells to adopt a chondrogenic phenotype through the tailoring of scaffold composition and physical properties. Monomeric type-I and type-II collagen scaffolds, which avoid potential immunogenicity associated with fibrillar collagens, were fabricated with and without chondroitin sulfate (CS) and their ability to stimulate the chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells was assessed. Immunohistochemical analyses showed that cells produced abundant collagen type-II on type-II scaffolds and collagen type-I on type-I scaffolds. Gene expression analyses indicated that the addition of CS - which was released from scaffolds quickly - significantly upregulated expression of type II collagen, compared to type-I and pure type-II scaffolds. We conclude that collagen type-II and CS can be used to promote a more chondrogenic phenotype in the absence of growth factors, potentially providing an eventual therapy to prevent OA.

Matrix regenerative therapy

The extracellular matrix (ECM) is responsible for many of the cell behavior processes, including cell proliferation and growth, survival, change in cell shape, migration, and differentiation. The most important component of the ECM is heparan sulfate (HS), because it insures the storage of many cell communication proteins, necessary for the continuous and identical renewal of cells and thus for tissue regeneration. Regenerating agents (RGTA®) are bioengineered structural analogues of heparan sulfate glycosaminoglycans that replace the degraded endogenous HS of the ECM. In the ophthalmological field, RGTA® represents an innovative approach for the improvement of the ocular surface wound healing and matrix remodeling and plays a role in controlling and regulating the wound healing process in various ocular diseases.

Intra-articular Injection of Urinary Bladder Matrix Reduces Osteoarthritis Development

Micronized porcine urinary bladder matrix (UBM) is an extracellular matrix biomaterial that has immunomodulatory and pro-regenerative properties. The objective of this study was to assess the ability of UBM to alter disease progression in a mouse model of post-traumatic osteoarthritis (OA). Ten-week-old wild-type C57BL/6 male mice underwent anterior cruciate ligament transection (ACLT) to induce OA. Two weeks after ACLT, UBM (50 mg/mL) or saline was injected into the mouse joint. At 4 and 8 weeks post-ACLT, cartilage integrity was assessed using OARSI scoring of histology, pain was evaluated, and joints were harvested for quantitative RT-PCR analysis of cartilage-specific and inflammatory gene expression. UBM-treated animals showed improved cartilage integrity at 4 and 8 weeks and reduced pain at 4 weeks compared to saline-injected mice. Animals injected with UBM expressed higher levels of genes encoding structural cartilage proteins, such as collagen2α1 and aggrecan, as well as anti-inflammatory cytokines, including interleukins 10 and 4. UBM decreased cartilage degeneration in the murine ACLT model of OA, which may be due to reduced inflammation in the joint and maintenance of high expression levels of proteoglycans.

Use of Scaffolding Tissue Biografts To Bolster Vesicourethral Anastomosis During Salvage Robot-assisted Prostatectomy Reduces Leak Rates and Catheter Times

BACKGROUND

One of the key factors contributing to morbidity associated with salvage radical prostatectomy is a significant vesicourethral anastomosis (VUA) disruption or postoperative tissue dehiscence in the region of the distal bladder neck that causes a large prolonged urinary leak, perineal pain, and delayed catheter removal.

OBJECTIVE

To describe our surgical technique using a urinary bladder extracellular matrix (UB-ECM) scaffold incorporated into the base of the VUA and the distal bladder neck during salvage robot-assisted radical prostatectomy (sRARP) and to assess outcomes and safety.

DESIGN, SETTING, AND PARTICIPANTS

From March to July 2015, 15 patients underwent sRARP performed after primary therapy failure by a single surgeon. Two other groups were identified via analysis of propensity score matching. Group 2 (n=45) underwent sRARP with standard suturing without use of the graft. Group 3 (control group; n=45) underwent primary RARP with no graft placement. These two groups were compared group 1 (n=15), in which patients underwent sRARP and received the scaffold in a 1:3:3 match.

SURGICAL PROCEDURE

sRARP with use of a UB-ECM scaffold in the posterior aspect of the VUA and distal bladder neck.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Clinical data were prospectively collected in a customized database and retrospectively analyzed. Analysis of variance and Student's t-test were used to test the equality of means for continuous variables, while the χ² test was used to test categorical variables.

RESULTS AND LIMITATIONS

There were no anastomotic leaks in the control group, with an average catheter time of 6.3 d (5-7 d). However, a clinically significant VUA/bladder neck disruption was observed in 16 patients (35.5%) in group 2, with a median catheterization time of 17.4 d (9-47 d), while in group 1 only one patient (6.66%) had a significant anastomotic leak on cystography (p=0.045), with median catheterization time of 11.2 d (10-52 d) for this group (p<0.05).

CONCLUSIONS

Incorporation of a UB-ECM scaffold into the base of the VUA and distal bladder neck should be considered as an option to decrease morbidity associated with sRARP since it decreased the rate of VUA disruption, enhanced healing, and reduced catheterization time. This technique could be a valuable tool for all surgeons performing sRARP.

PATIENT SUMMARY

We investigated the use of a scaffolding tissue graft when connecting the urethra to the bladder during salvage robot-assisted laparoscopic prostatectomy. This technique was found to be effective and safe.

Diversification and enrichment of clinical biomaterials inspired by Darwinian evolution

Regenerative medicine and biomaterials design are driven by biomimicry. There is the essential requirement to emulate human cell, tissue, organ and physiological complexity to ensure long-lasting clinical success. Biomimicry projects for biomaterials innovation can be re-invigorated with evolutionary insights and perspectives, since Darwinian evolution is the original dynamic process for biological organisation and complexity. Many existing human inspired regenerative biomaterials (defined as a nature generated, nature derived and nature mimicking structure, produced within a biological system, which can deputise for, or replace human tissues for which it closely matches) are without important elements of biological complexity such as, hierarchy and autonomous actions. It is possible to engineer these essential elements into clinical biomaterials via bioinspired implementation of concepts, processes and mechanisms played out during Darwinian evolution; mechanisms such as, directed, computational, accelerated evolutions and artificial selection contrived in the laboratory. These dynamos for innovation can be used during biomaterials fabrication, but also to choose optimal designs in the regeneration process. Further evolutionary information can help at the design stage; gleaned from the historical evolution of material adaptations compared across phylogenies to changes in their environment and habitats. Taken together, harnessing evolutionary mechanisms and evolutionary pathways, leading to ideal adaptations, will eventually provide a new class of Darwinian and evolutionary biomaterials. This will provide bioengineers with a more diversified and more efficient innovation tool for biomaterial design, synthesis and function than currently achieved with synthetic materials chemistry programmes and rational based materials design approach, which require reasoned logic. It will also inject further creativity, diversity and richness into the biomedical technologies that we make. All of which are based on biological principles. Such evolution-inspired biomaterials have the potential to generate innovative solutions, which match with existing bioengineering problems, in vital areas of clinical materials translation that include tissue engineering, gene delivery, drug delivery, immunity modulation, and scar-less wound healing.

STATEMENT OF SIGNIFICANCE

Evolution by natural selection is a powerful generator of innovations in molecular, materials and structures. Man has influenced evolution for thousands of years, to create new breeds of farm animals and crop plants, but now molecular and materials can be molded in the same way. Biological molecules and simple structures can be evolved, literally in the laboratory. Furthermore, they are re-designed via lessons learnt from evolutionary history. Through a 3-step process to (1) create variants in material building blocks, (2) screen the variants with beneficial traits/properties and (3) select and support their self-assembly into usable materials, improvements in design and performance can emerge. By introducing biological molecules and small organisms into this process, it is possible to make increasingly diversified, sophisticated and clinically relevant materials for multiple roles in biomedicine.

N-terminal specific conjugation of extracellular matrix proteins to 2-pyridinecarboxaldehyde functionalized polyacrylamide hydrogels

Polyacrylamide hydrogels have been used extensively to study cell responses to the mechanical and biochemical properties of extracellular matrix substrates. A key step in fabricating these substrates is the conjugation of cell adhesion proteins to the polyacrylamide surfaces, which typically involves nonspecifically anchoring these proteins via side-chain functional groups. This can result in a loss of presentation control and altered bioactivity. Here, we describe a new functionalization strategy in which we anchor full-length extracellular matrix proteins to polyacrylamide substrates using 2-pyridinecarboxaldehyde, which can be co-polymerized into polyacrylamide gels and used to immobilize proteins by their N-termini. This one-step reaction proceeds under mild aqueous conditions and does not require additional reagents. We demonstrate that these substrates can readily conjugate to various extracellular matrix proteins, as well as promote cell adhesion and spreading. Notably, this chemistry supports the assembly and cellular remodeling of large collagen fibers, which is not observed using conventional side-chain amine-conjugation chemistry.

In-vivo oesophageal regeneration in a human being by use of a non-biological scaffold and extracellular matrix

BACKGROUND

Tissue-engineered extracellular matrix populated with autologous pluripotent cells can result in de-novo organogenesis, but the technique is complex, not widely available, and has not yet been used to repair large oesophageal defects in human beings. We aimed to use readily available stents and extracellular matrix to regenerate the oesophagus in vivo in a human being to re-establish swallowing function.

METHODS

In a patient aged 24 years, we endoscopically placed a readily available, fully covered, self-expanding, metal stent (diameter 18 mm, length 120 mm) to bridge a 5 cm full-thickness oesophageal segment destroyed by a mediastinal abscess and leading to direct communication between the hypopharynx and the mediastinum. A commercially available extracellular matrix was used to cover the stent and was sprayed with autologous platelet-rich plasma adhesive gel. The sternocleidomastoid muscle was placed over the matrix. After 4 weeks, stent removal was needed due to stent migration, and was replaced with three stents telescopically aligned to improve anchoring. The stents were removed after 3·5 years and the oesophagus was assessed by endoscopy, biopsy, endoscopic ultrasonography, and high-resolution impedance manometry.

FINDINGS

After stent removal we saw full-thickness regeneration of the oesophagus with stratified squamous epithelium, a normal five-layer wall, and peristaltic motility with bolus transit. 4 years after stent removal, the patient was eating a normal diet and maintaining a steady weight.

INTERPRETATION

Maintenance of the structural morphology of the oesophagus with off-the-shelf non-biological scaffold and stimulation of regeneration with commercially available extracellular matrix led to de-novo structural and functional regeneration of the oesophagus.

FUNDING

None.

Pluripotent stem cell-derived kidney organoids: An in vivo-like in vitro technology

Organoids are self-organizing, multicellular structures that contain multiple cell types, represent organ structure and function, and can be used to model organ development, maintenance and repair ex vivo. Organoids, derived from embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) or adult stem cells, are cultured in extracellular matrix (ECM). Organoid cultures have been developed for multiple organs and for the kidney, pluripotent stem cell (PSCs) derived organoid technology has rapidly developed in the last three years. Here, we review available PSC differentiation protocols, focusing on the pluripotent stem cells to initiate the organoid culture, as well as on growth factors and ECM used to regulate differentiation and expansion. In addition, we will discuss the read out strategies to evaluate organoid phenotype and function. Finally, we will indicate how the choice of both culture parameters and read out strategy should be tailored to specific applications of the organoid culture.

Development and characterization of decellularized human nasoseptal cartilage matrix for use in tissue engineering

OBJECTIVES/HYPOTHESIS

Reconstruction of cartilage defects in the head and neck can require harvesting of autologous cartilage grafts, which can be associated with donor site morbidity. To overcome this limitation, tissue-engineering approaches may be used to generate cartilage grafts. The objective of this study was to decellularize and characterize human nasoseptal cartilage with the aim of generating a biological scaffold for cartilage tissue engineering.

STUDY DESIGN

Laboratory study using nasoseptal cartilage.

METHODS

Remnant human nasoseptal cartilage specimens were collected and subjected to a novel decellularization treatment. The decellularization process involved several cycles of enzymatic detergent treatments. For characterization, decellularized and fresh (control) specimens underwent histological, biochemical, and mechanical analyses. Scanning electron microscopy and biocompatibility assay were also performed.

RESULTS

The decellularization process had minimal effect on glycosaminoglycan content of the cartilage extracellular matrix. Deoxyribonucleic acid (DNA) analysis revealed the near-complete removal of genomic DNA from decellularized tissues. The effectiveness of the decellularization process was also confirmed on histological and scanning electron microscopic analyses. Mechanical testing results showed that the structural integrity of the decellularized tissue was maintained, and biocompatibility was confirmed.

CONCLUSION

Overall, the current decellularization treatment resulted in significant reduction of genetic/cellular material with preservation of the underlying extracellular matrix structure. This decellularized material may serve as a potential scaffold for cartilage tissue engineering.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 126:2226-2231, 2016.

Biocompatibility evaluation of tissue-engineered decellularized scaffolds for biomedical application

Biomaterials based on seeding of cells on decellularized scaffolds have gained increasing interest in the last few years and suggested to serve as an alternative approach to bioengineer artificial organs and tissues for transplantation. The reaction of the host toward the decellularized scaffold and transplanted cells depends on the biocompatibility of the construct. Before proceeding to the clinical application step of decellularized scaffolds, it is greatly important to apply a number of biocompatibility tests in vitro and in vivo. This review describes the different methodology involved in cytotoxicity, pathogenicity, immunogenicity and biodegradability testing for evaluating the biocompatibility of various decellularized matrices obtained from human or animals.

Matrix dimensionality and stiffness cooperatively regulate osteogenesis of mesenchymal stromal cells

Osteogenic potential of mesenchymal stromal cells (MSCs) is mechanosensitive. It's affected by the mechanical properties of the cellular microenvironment, particularly its mechanical modulus. To explore the effect of mechanical modulus on osteogenesis in the third dimension (3D), this study used a novel polyacrylamide (PA) scaffold whose pores are monodisperse and spherical, the mechanical moduli of which can be tuned across a wide range. It was found that MSCs have similar proliferation rates in PA scaffolds independent of the matrix stiffness. The contractile force exerted by MSCs inside PA scaffolds was strong enough to deform the pores of scaffolds made of more compliant PAs (whose shear modulus, G'scaffold<4 kPa). Only scaffolds of the highest stiffness (G'scaffold=12 kPa) can withhold the contraction from MSCs. After osteogenic induction for 21 days, the expression profiles of marker genes showed that PA scaffolds of G'scaffold=12 kPa promoted osteogenesis of MSCs. Confocal image analysis demonstrated that there are more F-actin cytoskeletons and bundled stress fibers at higher matrix moduli in 2D and 3D. Moreover, the 3D porous structure promotes osteogenesis of MSCs more than 2D flat substrates. Together, the differences of cellular behaviors when cultured in 2D and 3D systems are evident. The PA scaffolds developed in the present study can be used for further investigation into the mechanism of MSC mechanosensing in the 3D context.

STATEMENT OF SIGNIFICANCE

Mechanical properties of the microenvironment affect cellular behaviors, such as matrix stiffness. Traditionally, cell biological investigations have mostly employed cells growing on 2D substrates. The 3D porous PA scaffolds with the same topological conformation and pore sizes but different stiffness generated in this study showed that the differences of cellular behaviors in 2D and 3D systems are evident. Our 3D scaffolds provide insights into tissue engineering when stem cells incorporated with 3D scaffolds and support the future studies of cellular mechanobiology as well as the elucidation the role mechanical factor plays on the physiology and fate determination of MSCs in the 3D context.

Simple surface engineering of polydimethylsiloxane with polydopamine for stabilized mesenchymal stem cell adhesion and multipotency

Polydimethylsiloxane (PDMS) has been extensively exploited to study stem cell physiology in the field of mechanobiology and microfluidic chips due to their transparency, low cost and ease of fabrication. However, its intrinsic high hydrophobicity renders a surface incompatible for prolonged cell adhesion and proliferation. Plasma-treated or protein-coated PDMS shows some improvement but these strategies are often short-lived with either cell aggregates formation or cell sheet dissociation. Recently, chemical functionalization of PDMS surfaces has proved to be able to stabilize long-term culture but the chemicals and procedures involved are not user- and eco-friendly. Herein, we aim to tailor greener and biocompatible PDMS surfaces by developing a one-step bio-inspired polydopamine coating strategy to stabilize long-term bone marrow stromal cell culture on PDMS substrates. Characterization of the polydopamine-coated PDMS surfaces has revealed changes in surface wettability and presence of hydroxyl and secondary amines as compared to uncoated surfaces. These changes in PDMS surface profile contribute to the stability in BMSCs adhesion, proliferation and multipotency. This simple methodology can significantly enhance the biocompatibility of PDMS-based microfluidic devices for long-term cell analysis or mechanobiological studies.

Successful tissue engineering of competent allogeneic venous valves

OBJECTIVE

The purpose of this study was to evaluate whether tissue-engineered human allogeneic vein valves have a normal closure time (competency) and tolerate reflux pressure in vitro.

METHODS

Fifteen human allogeneic femoral vein segments containing valves were harvested from cadavers. Valve closure time and resistance to reflux pressure (100 mm Hg) were assessed in an in vitro model to verify competency of the vein valves. The segments were tissue engineered using the technology of decellularization (DC) and recellularization (RC). The decellularized and recellularized vein segments were characterized biochemically, immunohistochemically, and biomechanically.

RESULTS

Four of 15 veins with valves were found to be incompetent immediately after harvest. In total, 2 of 4 segments with incompetent valves and 10 of 11 segments with competent valves were further decellularized using detergents and DNAse. DC resulted in significant decrease in host DNA compared with controls. DC scaffolds, however, retained major extracellular matrix proteins and mechanical integrity. RC resulted in successful repopulation of the lumen and valves of the scaffold with endothelial and smooth muscle cells. Valve mechanical parameters were similar to the native tissue even after DC. Eight of 10 veins with competent valves remained competent even after DC and RC, whereas the two incompetent valves remained incompetent even after DC and RC. The valve closure time to reflux pressure of the tissue-engineered veins was <0.5 second.

CONCLUSIONS

Tissue-engineered veins with valves provide a valid template for future preclinical studies and eventual clinical applications. This technique may enable replacement of diseased incompetent or damaged deep veins to treat axial reflux and thus reduce ambulatory venous hypertension.

Engineering vascularized adipose tissue using the stromal-vascular fraction and fibrin hydrogels

The development of vascularized and functional adipose tissue substitutes is required to improve soft tissue augmentation. In this study, vascularized adipose tissue constructs were generated using uncultured cells from the stromal-vascular fraction (SVF) of adipose tissue as an alternative cell source to adipose-derived stem cells. SVF cell behavior and tissue formation were compared in a stable fibrin formulation developed by our group and a commercial fibrin sealant (TissuCol; Baxter) upon direct subcutaneous implantation in a nude mouse model. Further, the effect of in vitro adipogenic induction on SVF cell development was investigated by implanting stable fibrin constructs after 1 week of precultivation (adipogenic vs. noninduced control). Constructs were thoroughly analyzed before implantation regarding adipogenic differentiation status, cell viability, and distribution as well as the presence of endothelial cells. Before implantation, in vitro precultivation strongly promoted adipogenesis (under adipogenic conditions) and the formation of CD31(+) prevascular structures by SVF cells (under nonadipogenic conditions). Tissue development in vivo was determined after 4 weeks by histology (hematoxylin and eosin, human vimentin) and quantified histomorphometrically. In stable fibrin gels, adipogenic precultivation was superior to noninduced conditions, resulting in mature adipocytes and the formation of distinct vascular structures of human origin in vivo. Strong neovascularization by the implanted cells predominated in noninduced constructs. Without pretreatment, the SVF in stable fibrin gels displayed only a weak differentiation capability. In contrast, TissuCol gels strongly supported the formation of coherent and well-vascularized adipose tissue of human origin, displaying large unilocular adipocytes. The developed native-like tissue architecture was highlighted by a whole mount staining technique. Taken together, SVF cells from human adipose tissue were shown to successfully lead to adipose tissue formation in fibrin hydrogels in vivo. The results render the SVF a promising cell source for subsequent studies both in vitro and in vivo with the aim of engineering clinically applicable soft tissue substitutes.

Emerging concepts in liver graft preservation

The urgent need to expand the donor pool in order to attend to the growing demand for liver transplantation has obliged physicians to consider the use of suboptimal liver grafts and also to redefine the preservation strategies. This review examines the different methods of liver graft preservation, focusing on the latest advances in both static cold storage and machine perfusion (MP). The new strategies for static cold storage are mainly designed to increase the fatty liver graft preservation via the supplementation of commercial organ preservation solutions with additives. In this paper we stress the importance of carrying out effective graft washout after static cold preservation, and present a detailed discussion of the future perspectives for dynamic graft preservation using MP at different temperatures (hypothermia at 4 °C, normothermia at 37 °C and subnormothermia at 20 °C-25 °C). Finally, we highlight some emerging applications of regenerative medicine in liver graft preservation. In conclusion, this review discusses the "state of the art" and future perspectives in static and dynamic liver graft preservation in order to improve graft viability.

Rethinking regenerative medicine: a macrophage-centered approach

Regenerative medicine, a multi-disciplinary approach that seeks to restore form and function to damaged or diseased tissues and organs, has evolved significantly during the past decade. By adapting and integrating fundamental knowledge from cell biology, polymer science, and engineering, coupled with an increasing understanding of the mechanisms which underlie the pathogenesis of specific diseases, regenerative medicine has the potential for innovative and transformative therapies for heretofore unmet medical needs. However, the translation of novel technologies from the benchtop to animal models and clinical settings is non-trivial and requires an understanding of the mechanisms by which the host will respond to these novel therapeutic approaches. The role of the innate immune system, especially the role of macrophages, in the host response to regenerative medicine based strategies has recently received considerable attention. Macrophage phenotype and function have been suggested as critical and determinant factors in downstream outcomes. The constructive and regulatory, and in fact essential, role of macrophages in positive outcomes represents a significant departure from the classical paradigms of host-biomaterial interactions, which typically consider activation of the host immune system as a detrimental event. It appears desirable that emerging regenerative medicine approaches should not only accommodate but also promote the involvement of the immune system to facilitate positive outcomes. Herein, we describe the current understanding of macrophage phenotype as it pertains to regenerative medicine and suggest that improvement of our understanding of context-dependent macrophage polarization will lead to concurrent improvement in outcomes.

Comparison of cryopreserved amniotic membrane and umbilical cord tissue with dehydrated amniotic membrane/chorion tissue

OBJECTIVE

To evaluate how the different processing methods cryopreservation and dehydration affect the structural integrity and biological composition of key signalling molecules within amniotic membrane and umbilical cord tissues.

METHOD

We directly compared cryopreserved amniotic membrane (AM) and umbilical cord (UC) tissues with dehydrated amniotic membrane/chorion (dHACM) tissue using biochemical and functional assays including histological and histochemical staining, BCA, agarose gel electrophoresis, western blot, ELISA, and proliferation and cell death assays.

RESULTS

Cryopreservation retains the native architecture of the AM/UC extracellular matrix and maintains the quantity and activity of key biological signals present in fresh AM/UC, including high molecular weight hyaluronic acid, heavy chain-HA complex, and pentraxin 3. In contrast, dehydrated tissues were structurally compromised and almost completely lacked these crucial components.

CONCLUSION

The results presented here indicate that cryopreservation better preserves the structural and biological signaling molecules of foetal tissues.