The use of decellularized adipose tissue to provide an inductive microenvironment for the adipogenic differentiation of human adipose-derived stem cells

Mammary tissue-derived extracellular matrix hydrogels reveal the role of irradiation in driving a pro-tumor and immunosuppressive microenvironment

Radiation therapy (RT) is essential for triple negative breast cancer (TNBC) treatment. However, patients with TNBC continue to experience recurrence after RT. The role of the extracellular matrix (ECM) of irradiated breast tissue in tumor recurrence is still unknown. In this study, we evaluated the structure, molecular composition, and mechanical properties of irradiated murine mammary fat pads (MFPs) and developed ECM hydrogels from decellularized tissues (dECM) to assess the effects of RT-induced ECM changes on breast cancer cell behavior. Irradiated MFPs were characterized by increased ECM deposition and fiber density compared to unirradiated controls, which may provide a platform for cell invasion and proliferation. ECM component changes in collagens I, IV, and VI, and fibronectin were observed following irradiation in both MFPs and dECM hydrogels. Encapsulated TNBC cell proliferation and invasive capacity was enhanced in irradiated dECM hydrogels. In addition, TNBC cells co-cultured with macrophages in irradiated dECM hydrogels induced M2 macrophage polarization and exhibited further increases in proliferation. Our study establishes that the ECM in radiation-damaged sites promotes TNBC invasion and proliferation as well as an immunosuppressive microenvironment. This work represents an important step toward elucidating how changes in the ECM after RT contribute to breast cancer recurrence.

Assessment and process optimization of high throughput biofabrication of immunocompetent breast cancer model for drug screening applications

Recent advancements in 3D cancer modeling have significantly enhanced our ability to delve into the intricacies of carcinogenesis. Despite the pharmaceutical industry's substantial investment of both capital and time in the drug screening and development pipeline, a concerning trend persists: drug candidates screened on conventional cancer models exhibit a dismal success rate in clinical trials. One pivotal factor contributing to this discrepancy is the absence of drug testing on pathophysiologically biomimetic 3D cancer models during pre-clinical stages. Unfortunately, current manual methods of 3D cancer modeling, such as spheroids and organoids, suffer from limitations in reproducibility and scalability. In our study, we have meticulously developed 3D bioprinted breast cancer model utilizing decellularized adipose tissue-based hydrogel obtained via a detergent-free decellularization method. Our innovative printing techniques allows for rapid, high-throughput fabrication of 3D cancer models in a 96-well plate format, demonstrating unmatched scalability and reproducibility. Moreover, we have conducted extensive validation, showcasing the efficacy of our platform through drug screening assays involving two potent anti-cancer drugs, 5-Fluorouracil and PRIMA-1Met. Notably, our platform facilitates effortless imaging and gene expression analysis, streamlining the evaluation process. In a bid to enhance the relevance of our cancer model, we have introduced a heterogeneous cell population into the DAT-based bioink. Through meticulous optimization and characterization, we have successfully developed a biomimetic immunocompetent breast cancer model, complete with microenvironmental cues and diverse cell populations. This breakthrough paves the way for rapid multiplex drug screening and the development of personalized cancer models, marking a paradigm shift in cancer research and pharmaceutical development.

Comparison of Stored and Fresh Injectable Acellular Adipose Matrix in Soft Tissue Reconstruction in a Murine Model

BACKGROUND

We previously showed comparable volume effects of injections of acellular adipose matrix (AAM), an adipose tissue-derived extracellular matrix, and conventional fat grafting in a murine model. Thus, AAM could be a novel allogenic injectable product. However, its retention rate poses a concern, as repeated AAM injections may be required in some cases. This study investigated the biological properties and therapeutic value of stored AAM and compared them with those of fresh AAM, in a murine model.

METHODS

AAM was manufactured from fresh human abdominoplasty fat. Fresh and stored injectable AAM was prepared within 24 h and 3 months after generation, respectively. Either fresh or stored injectable AAM was injected into the scalp of athymic nude mice (0.2 mL/sample, n = 6 per group). After 8 weeks, graft retention was assessed through weight measurement, and histological analysis was performed, including immunofluorescence staining for CD31 and perilipin.

RESULTS

Retention rate was significantly reduced in the stored compared to the fresh injectable AAM group. Nevertheless, histological analysis revealed comparable inflammatory cell presence, with minimal capsule formation, in both groups. Adipogenesis occurred in both groups, with no significant difference in the blood vessel area (%) between groups.

CONCLUSIONS

Although the volume effects of stored AAM for soft tissue reconstruction were limited compared to those of fresh injectable AAM, stored AAM had similar capacity for adipogenesis and angiogenesis. This promising allogeneic injectable holds the potential to serve as an effective "off-the-shelf" alternative for repeated use within a 3-month storage period.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors https://link.springer.com/journal/00266 .

Perfusable adipose decellularized extracellular matrix biological scaffold co-recellularized with adipose-derived stem cells and L6 promotes functional skeletal muscle regeneration following volumetric muscle loss

Muscle tissue engineering is a promising therapeutic strategy for volumetric muscle loss (VML). Among them, decellularized extracellular matrix (dECM) biological scaffolds have shown certain effects in restoring muscle function. However, researchers have inconsistent or even contradictory results on whether dECM biological scaffolds can efficiently regenerate muscle fibers and restore muscle function. This suggests that therapeutic strategies based on dECM biological scaffolds need to be further optimized and developed. In this study, we used a recellularization method of perfusing adipose-derived stem cells (ASCs) and L6 into adipose dECM (adECM) through vascular pedicles. On one hand, this strategy ensures sufficient quantity and uniform distribution of seeded cells inside scaffold. On the other hand, auxiliary L6 cells addresses the issue of low myogenic differentiation efficiency of ASCs. Subsequently, the treatment of VML animal experiments showed that the combined recellularization strategy can improve muscle regeneration and angiogenesis than the single ASCs recellularization strategy, and the TA of former had greater muscle contraction strength. Further single-nucleus RNA sequencing (snRNA-seq) analysis found that L6 cells induced ASCs transform into a new subpopulation of cells highly expressing Mki67, CD34 and CDK1 genes, which had stronger ability of oriented myogenic differentiation. This study demonstrates that co-seeding ASCs and L6 cells through vascular pedicles is a promising recellularization strategy for adECM biological scaffolds, and the engineered muscle tissue constructed based on this has significant therapeutic effects on VML. Overall, this study provides a new paradigm for optimizing and developing dECM-based therapeutic strategies.

Effect of Injectable Acellular Adipose Matrix on Soft Tissue Reconstruction in a Murine Model

BACKGROUND

The extracellular matrix isolated from adipose tissue, known as acellular adipose matrix (AAM), represents a novel biomaterial. AAM functions as a scaffold that not only supports stem cell proliferation and differentiation but also induces adipogenesis and angiogenesis. This study aims to investigate the volumetric effects and microenvironmental changes associated with injectable AAM in comparison to conventional fat grafting.

METHODS

AAM was manufactured from fresh human abdominoplasty fat using a mechanically modified method and then transformed into an injectable form. Lipoaspirate was harvested employing the Coleman technique. A weight and volume study was conducted on athymic nude mice by injecting either injectable AAM or lipoaspirate into the scalp (n=6 per group). After eight weeks, graft retention was assessed through weight measurement and volumetric analysis using micro-computed tomography (micro-CT) scanning. Histological analysis was performed using immunofluorescence staining for perilipin and CD31.

RESULTS

Injectable AAM exhibited similar weight and volume effects in murine models. Histological analysis revealed comparable inflammatory cell presence with minimal capsule formation when compared to conventional fat grafts. Adipogenesis occurred in both AAM-injected and conventional fat graft models, with no significant difference in the blood vessel area (%) between the two.

CONCLUSIONS

In summary, injectable AAM demonstrates effectiveness comparable to conventional fat grafting concerning volume effects and tissue regeneration in soft tissue reconstruction. This promising allogeneic injectable holds the potential to serve as a safe and effective "Off-the-Shelf" alternative in both aesthetic and reconstructive clinical practices.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Challenges in Application: Gelation Strategies of DAT-Based Hydrogel Scaffolds

Decellularized adipose tissue (DAT) has great clinical applicability, owing to its abundant source material, natural extracellular matrix microenvironment, and nonimmunogenic attributes, rendering it a versatile resource in the realm of tissue engineering. However, practical implementations are confronted with multifarious limitations. Among these, the selection of an appropriate gelation strategy serves as the foundation for adapting to diverse clinical contexts. The cross-linking strategies under varying physical or chemical conditions exert profound influences on the ultimate morphology and therapeutic efficacy of DAT. This review sums up the processes of DAT decellularization and subsequent gelation, with a specific emphasis on the diverse gelation strategies employed in recent experimental applications of DAT. The review expounds upon methodologies, underlying principles, and clinical implications of different gelation strategies, aiming to offer insights and inspiration for the application of DAT in tissue engineering and advance research for tissue engineering scaffold development.

High Throughput Bioprinting Using Decellularized Adipose Tissue-Based Hydrogels for 3D Breast Cancer Modeling

3D bioprinting allows rapid automated fabrication and can be applied for high throughput generation of biomimetic constructs for in vitro drug screening. Decellularized extracellular matrix (dECM) hydrogel is a popular biomaterial choice for tissue engineering and studying carcinogenesis as a tumor microenvironmental mimetic. This study proposes a method for high throughput bioprinting with decellularized adipose tissue (DAT) based hydrogels for 3D breast cancer modeling. A comparative analysis of decellularization protocol using detergent-based and detergent-free decellularization methods for caprine-origin adipose tissue is performed, and the efficacy of dECM hydrogel for 3D cancer modeling is assessed. Histological, biochemical, morphological, and biological characterization and analysis showcase the cytocompatibility of DAT hydrogel. The rheological property of DAT hydrogel and printing process optimization is assessed to select a bioprinting window to attain 3D breast cancer models. The bioprinted tissues are characterized for cellular viability and tumor cell-matrix interactions. Additionally, an approach for breast cancer modeling is shown by performing rapid high throughput bioprinting in a 96-well plate format, and in vitro drug screening using 5-fluorouracil is performed on 3D bioprinted microtumors. The results of this study suggest that high throughput bioprinting of cancer models can potentially have downstream clinical applications like multi-drug screening platforms and personalized disease models.

Bioprinting of Perfusable, Biocompatible Vessel-like Channels with dECM-Based Bioinks and Living Cells

There is a growing interest in the production of bioinks that on the one hand, are biocompatible and, on the other hand, have mechanical properties that allow for the production of stable constructs that can survive for a long time after transplantation. While the selection of the right material is crucial for bioprinting, there is another equally important issue that is currently being extensively researched-the incorporation of the vascular system into the fabricated scaffolds. Therefore, in the following manuscript, we present the results of research on bioink with unique physico-chemical and biological properties. In this article, two methods of seeding cells were tested using bioink B and seeding after bioprinting the whole model. After 2, 5, 8, or 24 h of incubation, the flow medium was used in the tested systems. At the end of the experimental trial, for each time variant, the canals were stored in formaldehyde, and immunohistochemical staining was performed to examine the presence of cells on the canal walls and roof. Cells adhered to both ways of fiber arrangement; however, a parallel bioprint with the 5 h incubation and the intermediate plating of cells resulted in better adhesion efficiency. For this test variant, the percentage of cells that adhered was at least 20% higher than in the other analyzed variants. In addition, it was for this variant that the lowest percentage of viable cells was found that were washed out of the tested model. Importantly, hematoxylin and eosin staining showed that after 8 days of culture, the cells were evenly distributed throughout the canal roof. Our study clearly shows that neovascularization-promoting cells effectively adhere to ECM-based pancreatic bioink. Summarizing the presented results, it was demonstrated that the proposed bioink compositions can be used for bioprinting bionic organs with a vascular system formed by endothelial cells and fibroblasts.

Adipose tissue reconstruction facilitated with low immunogenicity decellularized adipose tissue scaffolds

There is currently an urgent need to develop engineered scaffolds to support new adipose tissue formation and facilitate long-term maintenance of function and defect repair to further generate prospective bioactive filler materials capable of fulfilling surgical needs. Herein, adipose regeneration methods were optimized and decellularized adipose tissue (DAT) scaffolds with good biocompatibility were fabricated. Adipose-like tissues were reconstructed using the DAT and 3T3-L1 preadipocytes, which have certain differentiation potential, and the regenerative effects of the engineered adipose tissuesin vitroandin vivowere explored. The method improved the efficiency of adipose removal from tissues, and significantly shortened the time for degreasing. Thus, the DAT not only provided a suitable space for cell growth but also promoted the proliferation, migration, and differentiation of preadipocytes within it. Following implantation of the constructed adipose tissuesin vivo, the DAT showed gradual degradation and integration with surrounding tissues, accompanied by the generation of new adipose tissue analogs. Overall, the combination of adipose-derived extracellular matrix and preadipocytes for adipose tissue reconstruction will be of benefit in the artificial construction of biomimetic implant structures for adipose tissue reconstruction, providing a practical guideline for the initial integration of adipose tissue engineering into clinical medicine.

Application of Decellularized Adipose Matrix as a Bioscaffold in Different Tissue Engineering

With the development of tissue engineering, the application of decellularized adipose matrix as scaffold material in tissue engineering has been intensively explored due to its wide source and excellent potential in tissue regeneration. Decellularized adipose matrix is a promising candidate for adipose tissue regeneration, while modification of decellularized adipose matrix scaffold can also allow it to transcend the limitations of adipose tissue source properties and applied to other tissue engineering fields, including cartilage and bone tissue engineering, neural tissue engineering, and skin tissue engineering. In this review, we summarized the development of the applications of decellularized adipose matrix in different tissue engineering and present future perspectives.Level of Evidence III This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Decellularization and Their Significance for Tissue Regeneration in the Era of 3D Bioprinting

Three-dimensional bioprinting is an emerging technology that has high potential application in tissue engineering and regenerative medicine. Increasing advancement and improvement in the decellularization process have led to an increase in the demand for using a decellularized extracellular matrix (dECM) to fabricate tissue engineered products. Decellularization is the process of retaining the extracellular matrix (ECM) while the cellular components are completely removed to harvest the ECM for the regeneration of various tissues and across different sources. Post decellularization of tissues and organs, they act as natural biomaterials to provide the biochemical and structural support to establish cell communication. Selection of an effective method for decellularization is crucial, and various factors like tissue density, geometric organization, and ECM composition affect the regenerative potential which has an impact on the end product. The dECM is a versatile material which is added as an important ingredient to formulate the bioink component for constructing tissue and organs for various significant studies. Bioink consisting of dECM from various sources is used to generate tissue-specific bioink that is unique and to mimic different biometric microenvironments. At present, there are many different techniques applied for decellularization, and the process is not standardized and regulated due to broad application. This review aims to provide an overview of different decellularization procedures, and we also emphasize the different dECM-derived bioinks present in the current global market and the major clinical outcomes. We have also highlighted an overview of benefits and limitations of different decellularization methods and various characteristic validations of decellularization and dECM-derived bioinks.

Comprehensive Matrisome Profiling of Human Adipose Tissue for Soft Tissue Reconstruction

For effective translation of research from tissue engineering and regenerative medicine domains, the cell-instructive extracellular matrix (ECM) of specific tissues must be accurately realized. As adipose tissue is gaining traction as a biomaterial for soft tissue reconstruction, with highly variable clinical outcomes obtained, a quantitative investigation of the adipose tissue matrisome is overdue. In this study, the human adipose tissue matrisome is profiled using quantitative sequential windowed acquisition of all theoretical fragment ion spectra - mass spectrometry (SWATH-MS) proteomics across a cohort of 13 fat-grafting patients, to provide characterization of ECM proteins within the tissue, and to understand human population variation. There are considerable differences in the expression of matrisome proteins across the patient cohort, with age and lipoaspirate collection technique contributing to the greatest variation across the core matrisome. A high abundance of basement membrane proteins (collagen IV and heparan sulfate proteoglycan) is detected, as well as fibrillar collagens I and II, reflecting the hierarchical structure of the tissue. This study provides a comprehensive proteomic evaluation of the adipose tissue matrisome and contributes to an enhanced understanding of the influence of the matrisome in adipose-related pathologies by providing a healthy reference cohort and details an experimental pipeline that can be further exploited for future biomaterial development.

Combined Use of Autologous Sustained-Release Scaffold of Adipokines and Acellular Adipose Matrix to Construct Vascularized Adipose Tissue

BACKGROUND

Adipose tissue engineering plays a key role in the reconstruction of soft-tissue defects. The acellular adipose matrix (AAM) is a promising biomaterial for the construction of engineered adipose tissue. However, AAM lacks sufficient adipoinduction potency because of the abundant loss of matrix-bound adipokines during decellularization.

METHODS

An adipose-derived extracellular matrix collagen scaffold, "adipose collagen fragment" (ACF), was prepared using a novel mechanical method that provides sustained release of adipokines. Here, the authors used label-free proteomics methods to detect the protein components in AAM and ACF. In vivo, ACF was incorporated into AAM or acellular dermal matrix and implanted into nude mice to evaluate adipogenesis. Neoadipocytes, neovessels, and corresponding gene expression were evaluated. The effects of ACF on adipogenic differentiation of human adipose-derived stem cells and tube formation by human umbilical vein endothelial cells were tested in vitro.

RESULTS

Proteomics analysis showed that ACF contains diverse adipogenic and angiogenic proteins. ACF can release diverse adipokines and induce highly vascularized, mature adipose tissue in AAM, and even in nonadipogenic acellular dermal matrix. Higher expression of adipogenic markers peroxisome proliferator-activated receptor gamma and CCAAT/enhancer-binding protein alpha and greater numbers of tubule structures were observed in ACF-treated groups in vitro.

CONCLUSION

The combination of ACF and AAM could serve as a novel and promising strategy to construct mature, vascularized adipose tissue for soft-tissue reconstruction.

CLINICAL RELEVANCE STATEMENT

The combined use of AAM and ACF has been proven to induce a highly vascularized, mature, engineered adipose tissue in the nude mouse model, which may serve as a promising strategy for soft-tissue reconstruction.

Effectiveness of a New Enzyme-Free Method for the Preparation of a Decellularized Adipose-Derived Matrix

BACKGROUND

Decellularized adipose-derived matrix (DAM) represents a new alternative to tissue fillers. The function of DAM is closely associated with the decellularization technique used for its preparation. However, most techniques are time-consuming and expensive, and this might reduce the popularity of DAM.

OBJECTIVES

The study aimed to investigate an enzyme-free adipose decellularization method and generate a DAM capable of adipose tissue regeneration.

METHODS

DAMs prepared by the enzyme-free and Flynn's methods were compared and co-cultured with human adipose-derived stem cells (hADSCs) to investigate cytocompatibility. Adipose tissue formation was evaluated by injecting the DAMs into the backs of nude mice over 4 weeks. Samples were harvested for gross and perilipin immunohistochemistry analysis at 1 and 4 weeks.

RESULTS

The enzyme-free method is effective for adipose decellularization because it removes adipocytes and preserves the microstructure. In vitro, the DAM made by the enzyme-free method could support the attachment, growth, proliferation, and differentiation of hADSCs, and promote the enhanced secretion of vascular endothelial growth factor by hADSCs; this DAM also induced the formation and maturity of adipocytes in vivo.

CONCLUSIONS

This study describes a highly effective enzyme-free method for adipose tissue decellularization that also promotes adipocyte formation and adipose tissue volume stability in vitro and in vivo, resulting in a new alternative tissue filler.

Preparation and Modification of Collagen/Sodium Alginate-Based Biomedical Materials and Their Characteristics

(1) Background: Collagen and sodium alginate are commonly used in the field of biomedical materials due to their excellent biocompatibility. This study focuses on the preparation, modification, and characterization of collagen/sodium alginate (C/SA)-based biomedical materials. (2) Methods: The characteristics, including surface chemistry, mechanical properties, hygroscopicity, and porosity, were analyzed. The hemostatic activity in vitro was measured using a blood clotting assay and dynamic blood clotting assay. (3) Results: The results from microstructure and porosity measurement revealed that all of the sponges exhibited a porosity of more than 95 percent. The sponge cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) showed better tensile strength and lower elongation at break. The sponges cross-linked with EDC/NHS and oxidized sodium alginate (OSA) exhibited the highest hygroscopicity in comparison with the uncross-linked sponge. (4) Conclusions: Our study demonstrated that the C/SA-based material we prepared exhibited a high level of porosity, enabling efficient absorption of tissue exudate and blood. Additionally, the materials revealed excellent hemocompatibility, making them suitable for use as a hemostatic dressing in the field of biomedical materials.

Rehabilitation exercise-driven symbiotic electrical stimulation system accelerating bone regeneration

Electrical stimulation can effectively accelerate bone healing. However, the substantial size and weight of electrical stimulation devices result in reduced patient benefits and compliance. It remains a challenge to establish a flexible and lightweight implantable microelectronic stimulator for bone regeneration. Here, we use self-powered technology to develop an electric pulse stimulator without circuits and batteries, which removes the problems of weight, volume, and necessary rigid packaging. The fully implantable bone defect electrical stimulation (BD-ES) system combines a hybrid tribo/piezoelectric nanogenerator to provide biphasic electric pulses in response to rehabilitation exercise with a conductive bioactive hydrogel. BD-ES can enhance multiple osteogenesis-related biological processes, including calcium ion import and osteogenic differentiation. In a rat model of critical-sized femoral defects, the bone defect was reversed by electrical stimulation therapy with BD-ES and subsequent bone mineralization, and the femur completely healed within 6 weeks. This work is expected to advance the development of symbiotic electrical stimulation therapy devices without batteries and circuits.

Bioactive decellularized adipose matrix prepared using a rapid, nonchemical/enzymatic method for adipogenesis

Recent developments in the field of regenerative surgeries and medical applications have led to a renewed interest in adipose tissue-enriched mesenchymal stem cell scaffolds. Various advantages declared for the decellularized adipose matrix (DAM) have caused its extensive use in the transfer of stem cells or growth factors for soft tissue regeneration induction. Meanwhile, the long-term application of detergents toward DAM regeneration has been assumed as a risky obstacle in this era. Herein, a rapid, mechanical protocol was developed to prepare DAM (M-DAM) without chemicals/enzymes and was comprehensively compared with the ordinary DAM (traditional chemical method). Accordingly, this method could effectively hinder oils and cells, sustain the structural and biological elements, and contain a superior level of collagen content. In addition, more protein numbers, as well as higher basement membrane elements, glycoproteins, and extracellular matrix-related proteins were detected in the regenerated M-DAM. Also, superior adipogenesis and angiogenesis proteins were distinguished. The noncytotoxicity of the M-DAM was also approved, and a natural ecological niche was observed for the proliferation and differentiation of stem cells, confirming its great potential for vascularization and adipogenesis in vivo. The suggested technique could effectively prepare the modified DAM in variant constructions of tablets, powders, emulsions, hydrogels, and different three-dimensional-printed structures. Hence, this rapid, mechanical process can produce bioactive DAM, which has the potential to be widely used in various research fields of regenerative medicine.

Decellularized extracellular matrix and silk fibroin-based hybrid biomaterials: A comprehensive review on fabrication techniques and tissue-specific applications

Biomaterials play a fundamental role in tissue engineering by providing biochemical and physical cues that influence cellular fate and matrix development. Decellularized extracellular matrix (dECM) as a biomaterial is distinguished by its abundant composition of matrix proteins, such as collagen, elastin, fibronectin, and laminin, as well as glycosaminoglycans and proteoglycans. However, the mechanical properties of only dECM-based constructs may not always meet tissue-specific requirements. Recent advancements address this challenge by utilizing hybrid biomaterials that harness the strengths of silk fibroin (SF), which contributes the necessary mechanical properties, while dECM provides essential cellular cues for in vitro studies and tissue regeneration. This review discusses emerging trends in developing such biopolymer blends, aiming to synergistically combine the advantages of SF and dECM through optimal concentrations and desired cross-linking density. We focus on different fabrication techniques and cross-linking methods that have been utilized to fabricate various tissue-engineered hybrid constructs. Furthermore, we survey recent applications of such biomaterials for the regeneration of various tissues, including bone, cartilage, trachea, bladder, vascular graft, heart, skin, liver, and other soft tissues. Finally, the trajectory and prospects of the constructs derived from this blend in the tissue engineering field have been summarized, highlighting their potential for clinical translation.

Decellularized bladder as scaffold to support proliferation and functionality of insulin-secreting pancreatic cells

Loss in the number or function of insulin-producing β-cells in pancreatic islets has been associated with diabetes mellitus. Although islet transplantation can be an alternative treatment, complications such as apoptosis, ischaemia and loss of viability have been reported. The use of decellularized organs as scaffolds in tissue engineering is of interest owing to the unique ultrastructure and composition of the extracellular matrix (ECM) believed to act on tissue regeneration. In this study, a cell culture system has been designed to study the effect of decellularized porcine bladder pieces on INS-1 cells, a cell line secreting insulin in response to glucose stimulation. Porcine bladders were decellularized using two techniques: a detergent-containing and a detergent-free methods. The resulting ECMs were characterized for the removal of both cells and dsDNA. INS-1 cells were not viable on ECM produced using detergent (i.e., sodium dodecyl sulfate). INS-1 cells were visualized following 7 days of culture on detergent-free decellularized bladders using a cell viability and metabolism assay (MTT) and cell proliferation quantified (CyQUANT™ NF Cell Proliferation Assay). Further, glucose-stimulated insulin secretion and immunostaining confirmed that cells were functional in response to glucose stimulation, as well as they expressed insulin and interacted with the detergent-free produced ECM, respectively.

Application of decellularization-recellularization technique in plastic and reconstructive surgery

ABSTRACT

In the field of plastic and reconstructive surgery, the loss of organs or tissues caused by diseases or injuries has resulted in challenges, such as donor shortage and immunosuppression. In recent years, with the development of regenerative medicine, the decellularization-recellularization strategy seems to be a promising and attractive method to resolve these difficulties. The decellularized extracellular matrix contains no cells and genetic materials, while retaining the complex ultrastructure, and it can be used as a scaffold for cell seeding and subsequent transplantation, thereby promoting the regeneration of diseased or damaged tissues and organs. This review provided an overview of decellularization-recellularization technique, and mainly concentrated on the application of decellularization-recellularization technique in the field of plastic and reconstructive surgery, including the remodeling of skin, nose, ears, face, and limbs. Finally, we proposed the challenges in and the direction of future development of decellularization-recellularization technique in plastic surgery.

A Bibliometric Analysis of Research on Decellularized Matrix for Two Decades

The articles and reviews in the field of decellularized extracellular matrix (dECM) from 2001 to 2021 were retrieved and extracted from the Web of Science Core Collection. The R package Bibliometrix, CiteSpace, VOSviewer, and the online BIBLIOMETRC platform were utilized for bibliometric analysis, including specific characteristics of annual publications, influential countries/regions, core journals, leading institutions, keywords, key references, cocited authors, journals and institutions, cooperation, and historical direct citations. Our study concluded core references that fueled the development of dECM and highlighted current research directions, hotpots, and trends. From 2001 to 2021, 3,046 publications were retrieved in total, including 2,700 articles and 349 reviews. The United States (n = 895) produced the majority of publications, and the University of Pittsburgh (n = 318) published most productions. Biomaterials were identified as the most productive and influential journal in the dECM field considering the number of publications (n = 194), and total citations (n = 15,694). Immunomodulation, bioreactors, aging, three-dimensional (3D) bioprinting, bone tissue engineering, bioink, hydrogel, biomaterials, and regeneration were the latest high-frequency keywords, indicating the emerging frontiers of dECM. In the field, decellularization techniques lay the foundation. Orthotopic transplantation of recellularized dECM and induction of specific cell differentiation promoted the bursts of research. The 3D bioprinting and hydrogel based on dECM were extensively studied in recent years. The present study provided developmental trajectories, current research status, global collaboration patterns, hotpots, and trending topics of dECM. Decellularization techniques, tissue engineering to regenerate organs, and improvements in application are the major themes over the past two decades. Impact Statement The review article is significant because decellularized extracellular matrix (dECM), which derived from biological tissues and removal of immunogenic cells, is characterized by safety, biocompatibility, and low in toxicity. Showing great application prospects, dECM has been applied in multiple scenarios of tissue repairment and reconstruction, among the most popular topics in tissue engineering. Thus, analyzing and concluding the development, current condition and future trends are of great significance. Comparing to conventional review, this review article systemically and comprehensively concluded the historical development, current status, and research trending topics. Thus, it allows scholars to get a rapid overview of the dECM field, and plan research directions.

Combining Allograft Adipose and Fascia Matrix as an Off-the-Shelf Scaffold for Adipose Tissue Engineering Stimulates Angiogenic Responses and Activates a Proregenerative Macrophage Profile in a Rodent Model

OBJECTIVE

Bioscaffolds for treating soft tissue defects have limitations. As a bioscaffold, allograft adipose matrix (AAM) is a promising approach to treat soft tissue defects. Previously, we revealed that combining superficial adipose fascia matrix with AAM, components of the hypodermis layer of adipose tissue, improved volume retention, adipogenesis, and angiogenesis in rats 8 weeks after it was implanted compared with AAM alone. Here, we modified the fascia matrix and AAM preparation, examined the tissue over 18 weeks, and conducted a deeper molecular investigation. We hypothesized that the combined matrices created a better scaffold by triggering angiogenesis and proregenerative signals.

METHODS

Human AAM and fascia matrix were implanted (4 [1 mL] implants/animal) into the dorsum of male Fischer rats (6-8 weeks old; ~140 g) randomly as follows: AAM, fascia, 75/25 (AAM/fascia), 50/50, and 50/50 + hyaluronic acid (HA; to improve extrudability) (n = 4/group/time point). After 72 hours, as well as 1, 3, 6, 9, 12, and 18 weeks, graft retention was assessed by a gas pycnometer. Adipogenesis (HE), angiogenesis (CD31), and macrophage infiltration (CD80 and CD163) were evaluated histologically at all time points. The adipose area and M1/M2 macrophage ratio were determined using ImageJ. RNA sequencing (RNA-seq) and bioinformatics were conducted to evaluate pathway enrichments.

RESULTS

By 18 weeks, the adipose area was 2365% greater for 50/50 HA (281.6 ± 21.6) than AAM (11.4 ± 0.9) (P < 0.001). The M1/M2 macrophage ratio was significantly lower for 50/50 HA (0.8 ± 0.1) than AAM (0.9 ± 0.1) at 6 weeks (16%; P < 0.05). This inversely correlated with adipose area (r = -0.6; P > 0.05). The RNA-seq data revealed that upregulated adipogenesis, angiogenesis, and macrophage-induced tissue regeneration genes were temporally different between the groups.

CONCLUSIONS

Combining the fascia matrix with AAM creates a bioscaffold with an improved retention volume that supports M2 macrophage-mediated angiogenesis and adipogenesis. This bioscaffold is worthy of further investigation.

Extracellular matrix cues regulate the differentiation of pluripotent stem cell-derived endothelial cells

The generation of endothelial cells (ECs) from human pluripotent stem cells (PSCs) has been a promising approach for treating cardiovascular diseases for several years. Human PSCs, particularly induced pluripotent stem cells (iPSCs), are an attractive source of ECs for cell therapy. Although there is a diversity of methods for endothelial cell differentiation using biochemical factors, such as small molecules and cytokines, the efficiency of EC production varies depending on the type and dose of biochemical factors. Moreover, the protocols in which most EC differentiation studies have been performed were in very unphysiological conditions that do not reflect the microenvironment of native tissue. The microenvironment surrounding stem cells exerts variable biochemical and biomechanical stimuli that can affect stem cell differentiation and behavior. The stiffness and components of the extracellular microenvironment are critical inducers of stem cell behavior and fate specification by sensing the extracellular matrix (ECM) cues, adjusting the cytoskeleton tension, and delivering external signals to the nucleus. Differentiation of stem cells into ECs using a cocktail of biochemical factors has been performed for decades. However, the effects of mechanical stimuli on endothelial cell differentiation remain poorly understood. This review provides an overview of the methods used to differentiate ECs from stem cells by chemical and mechanical stimuli. We also propose the possibility of a novel EC differentiation strategy using a synthetic and natural extracellular matrix.

Selection of Mechanical Fragmentation Methods Based on Enzyme-Free Preparation of Decellularized Adipose-Derived Matrix

BACKGROUND

The decellularized adipose-derived matrix (DAM) has emerged as a promising biomaterial for inducing adipose tissue regeneration. Various methods have been employed to produce DAM, among which the enzyme-free method is a relatively recent preparation technique. The mechanical fragmentation step plays a crucial role in determining the efficacy of the enzyme-free preparation.

METHODS

The adipose tissue underwent fragmentation through the application of ultrasonication, homogenization, and freeze ball milling. This study compared the central temperature of the mixture immediately following crushing, the quantity of oil obtained after centrifugation, and the thickness of the middle layer. Fluorescence staining was utilized to compare the residual cell activity of the broken fat in the middle layer, while electron microscopy was employed to assess the integrity and properties of the adipocytes among the three methods. The primary products obtained through the three methods were subsequently subjected to processing using the enzyme-free method DAM. The assessment of degreasing and denucleation of DAM was conducted through HE staining, oil red staining, and determination of DNA residues. Subsequently, the ultrasonication-DAM (U-DAM) and homogenation-DAM (H-DAM) were implanted bilaterally on the back of immunocompromised mice, and a comparative analysis of their adipogenic and angiogenic effects in vivo was performed.

RESULTS

Oil discharge following ultrasonication and homogenization was significantly higher compared to that observed after freeze ball milling (p < 0.001), despite the latter exhibiting the lowest center temperature (p < 0.001). The middle layer was found to be thinnest after ultrasonication (p < 0.001), and most of the remaining cells were observed to be dead following fragmentation. Except for DAM obtained through freeze ball milling, DAM obtained through ultrasonication and homogenization could be completely denucleated and degreased. In the in vivo experiment, the first adipocytes were observed in U-DAM as early as 1 week after implantation, but not in H-DAM. After 8 weeks, a significant number of adipocytes were regenerated in both groups, but the U-DAM group demonstrated a more efficient adipose regeneration than in H-DAM (p = 0.0057).

CONCLUSIONS

Ultrasonication and homogenization are effective mechanical fragmentation methods for breaking down adipocytes at the initial stage, enabling the production of DAM through an enzyme-free method that facilitates successful regeneration of adipose tissues in vivo. Furthermore, the enzyme-free method, which is based on the ultrasonication pre-fragmentation approach, exhibits superior performance in terms of denucleation, degreasing, and the removal of non-adipocyte matrix components, thereby resulting in the highest in vivo adipogenic induction efficiency.

Unraveling White Adipose Tissue Heterogeneity and Obesity by Adipose Stem/Stromal Cell Biology and 3D Culture Models

The immune and endocrine dysfunctions of white adipose tissue are a hallmark of metabolic disorders such as obesity and type 2 diabetes. In humans, white adipose tissue comprises distinct depots broadly distributed under the skin (hypodermis) and as internal depots (visceral). Depot-specific ASCs could account for visceral and subcutaneous adipose tissue properties, by regulating adipogenesis and immunomodulation. More importantly, visceral and subcutaneous depots account for distinct contributions to obesity and its metabolic comorbidities. Recently, distinct ASCs subpopulations were also described in subcutaneous adipose tissue. Interestingly, the superficial layer closer to the dermis shows hyperplastic and angiogenic capacities, whereas the deep layer is considered as having inflammatory properties similar to visceral. The aim of this focus review is to bring the light of recent discoveries into white adipose tissue heterogeneity together with the biology of distinct ASCs subpopulations and to explore adipose tissue 3D models revealing their advantages, disadvantages, and contributions to elucidate the role of ASCs in obesity development. Recent advances in adipose tissue organoids opened an avenue of possibilities to recreate the main cellular and molecular events of obesity leading to a deep understanding of this inflammatory disease besides contributing to drug discovery. Furthermore, 3D organ-on-a-chip will add reproducibility to these adipose tissue models contributing to their translation to the pharmaceutical industry.

Trends in mechanobiology guided tissue engineering and tools to study cell-substrate interactions: a brief review

Sensing the mechanical properties of the substrates or the matrix by the cells and the tissues, the subsequent downstream responses at the cellular, nuclear and epigenetic levels and the outcomes are beginning to get unraveled more recently. There have been various instances where researchers have established the underlying connection between the cellular mechanosignalling pathways and cellular physiology, cellular differentiation, and also tissue pathology. It has been now accepted that mechanosignalling, alone or in combination with classical pathways, could play a significant role in fate determination, development, and organization of cells and tissues. Furthermore, as mechanobiology is gaining traction, so do the various techniques to ponder and gain insights into the still unraveled pathways. This review would briefly discuss some of the interesting works wherein it has been shown that specific alteration of the mechanical properties of the substrates would lead to fate determination of stem cells into various differentiated cells such as osteoblasts, adipocytes, tenocytes, cardiomyocytes, and neurons, and how these properties are being utilized for the development of organoids. This review would also cover various techniques that have been developed and employed to explore the effects of mechanosignalling, including imaging of mechanosensing proteins, atomic force microscopy (AFM), quartz crystal microbalance with dissipation measurements (QCMD), traction force microscopy (TFM), microdevice arrays, Spatio-temporal image analysis, optical tweezer force measurements, mechanoscanning ion conductance microscopy (mSICM), acoustofluidic interferometric device (AID) and so forth. This review would provide insights to the researchers who work on exploiting various mechanical properties of substrates to control the cellular and tissue functions for tissue engineering and regenerative applications, and also will shed light on the advancements of various techniques that could be utilized to unravel the unknown in the field of cellular mechanobiology.

Biofabrication of vascularized adipose tissues and their biomedical applications

Recent advances in adipose tissue engineering and cell biology have led to the development of innovative therapeutic strategies in regenerative medicine for adipose tissue reconstruction. To date, the many in vitro and in vivo models developed for vascularized adipose tissue engineering cover a wide range of research areas, including studies with cells of various origins and types, polymeric scaffolds of natural and synthetic derivation, models presented using decellularized tissues, and scaffold-free approaches. In this review, studies on adipose tissue types with different functions, characteristics and body locations have been summarized with 3D in vitro fabrication approaches. The reason for the particular focus on vascularized adipose tissue models is that current liposuction and fat transplantation methods are unsuitable for adipose tissue reconstruction as the lack of blood vessels results in inadequate nutrient and oxygen delivery, leading to necrosis in situ. In the first part of this paper, current studies and applications of white and brown adipose tissues are presented according to the polymeric materials used, focusing on the studies which could show vasculature in vitro and after in vivo implantation, and then the research on adipose tissue fabrication and applications are explained.

Recent advances in decellularized biomaterials for wound healing

The skin is one of the most essential organs in the human body, interacting with the external environment and shielding the body from diseases and excessive water loss. Thus, the loss of the integrity of large portions of the skin due to injury and illness may lead to significant disabilities and even death. Decellularized biomaterials derived from the extracellular matrix of tissues and organs are natural biomaterials with large quantities of bioactive macromolecules and peptides, which possess excellent physical structures and sophisticated biomolecules, and thus, promote wound healing and skin regeneration. Here, we highlighted the applications of decellularized materials in wound repair. First, the wound-healing process was reviewed. Second, we elucidated the mechanisms of several extracellular matrix constitutes in facilitating wound healing. Third, the major categories of decellularized materials in the treatment of cutaneous wounds in numerous preclinical models and over decades of clinical practice were elaborated. Finally, we discussed the current hurdles in the field and anticipated the future challenges and novel avenues for research on decellularized biomaterials-based wound treatment.

Decellularized Extracellular Matrix for Remodeling Bioengineering Organoid's Microenvironment

Over the past decade, stem cell- and tumor-derived organoids are the most promising models in developmental biology and disease modeling, respectively. The matrix is one of three main elements in the construction of an organoid and the most important module of its extracellular microenvironment. However, the source of the currently available commercial matrix, Matrigel, limits the application of organoids in clinical medicine. It is worth investigating whether the original decellularized extracellular matrix (dECM) can be exploited as the matrix of organoids and improving organoid construction are very important. In this review, tissue decellularization protocols and the characteristics of decellularization methods, the mechanical support and biological cues of extraccellular matrix (ECM), methods for construction of multifunctional dECM and responsive dECM hydrogel, and the potential applications of functional dECM are summarized. In addition, some expectations are provided for dECM as the matrix of organoids in clinical applications.

Microphysiological system recapitulating the pathophysiology of adipose tissue in obesity

A growing body of evidence has indicated that white adipose tissue (AT) remodeling is a major trigger for obesity-associated metabolic complications. However, the scarcity of translational models is an obstacle to the development of medicines that act on adipose restoration. Here, we describe a microphysiological system (MPS) that emulates the unique features of reprogrammed AT as a new in vitro tool for studying AT pathophysiology in obesity. The AT MPS contained mature adipocytes embedded in an extracellular matrix (ECM) hydrogel interfaced with AT microvascular endothelium, which was constantly perfused with fresh media. The unique biochemical signals due to the remodeled ECM in obesity were recapitulated using a decellularized AT ECM (AT dECM) hydrogel, which preserves the features of altered ECM composition in obesity. The mature adipocytes embedded in the AT dECM hydrogel maintained their function and morphology for a week without dedifferentiation. Using the AT MPS, we successfully modeled inflammation-induced AT microvascular dysfunction, the recruitment of immune cells due to the upregulation of cell adhesion molecules, and higher cancer cell adhesion as an indicator of metastasis, which are observed in obese individuals. The AT MPS may therefore represent a promising platform for understanding the dynamic cellular interplay in obesity-induced AT remodeling and validating the efficacy of drugs targeting AT in obesity. STATEMENT OF SIGNIFICANCE: The lack of translational in vitro white adipose tissue (AT) models is one of the main obstacles for understanding the obesity-induced reprogramming and the development of medicines. We report herein the AT microphysiological system (MPS), which recapitulates obesity and normal conditions and yields cell- and AT dECM-derived signals, thereby allowing accurate comparative in vitro analyses. Using the AT MPS, we successfully modeled reprogrammed AT in obesity conditions, including inflammation-induced AT vascular dysfunction, the recruitment of immune cells, and higher cancer cell metastasis, which are observed in obese individuals. Our proposed adipose tissue model providing physiological relevance and complexity may therefore enhance the understanding of obesity-associated disorders and be used to investigate their underlying molecular mechanisms to develop pharmacologic treatment strategies.

Insulin modified Decellularized Adipose Tissue/Tremella Polysaccharide hydrogel loaded with ADSCs for skin wound healing

Full-thickness skin wounds still represent a challenge for clinical treatment. Adipose-derived stem cells (ADSCs) therapy is a promising approach to achieve efficient healing in skin wounds. The excellent cell scaffold can promote proliferation, differentiation and paracrine of ADSCs in wound microenvironment, and is a key factor in ADSCs application. Herein, we first prepared the composite hydrogel with decellularized adipose tissue (DAT) and tremella polysaccharide (TPS), and loaded insulin (INS) into the DAT/TPS composite hydrogel (DAT/TPS-gel) to fabricate an efficient carrier for ADSCs in treating skin wound. Our study showed that INS modified DAT/TPS-gel (INS-DAT/TPS-gel) can promote the proliferation, differentiation and paracrine of ADSCs. INS-DAT/TPS-gel laden with ADSCs (ADSCs/INS-DAT/TPS-gel) effectively facilitated the skin wound healing in SD rats. These findings indicated that INS-DAT/TPS-gel was an effective scaffold for ADSCs transplantation, and ADSCs/INS-DAT/TPS-gel provides a potential strategy for the treatment of skin wounds.

Probing the effects of matrix-derived microcarrier composition on human adipose-derived stromal cells cultured dynamically within spinner flask bioreactors

Recognizing the cell-instructive capacity of the extracellular matrix (ECM), this study investigated the effects of expanding human adipose-derived stromal cells (hASCs) on ECM-derived microcarriers fabricated from decellularized adipose tissue (DAT) or decellularized cartilage tissue (DCT) within spinner flask bioreactors. Protocols were established for decellularizing porcine auricular cartilage and electrospraying methods were used to generate microcarriers comprised exclusively of DAT or DCT, which were compositionally distinct, but had matching Young's moduli. Both microcarrier types supported hASC attachment and growth over 14 days within a low-shear spinner culture system, with a significantly higher cell density observed on the DCT microcarriers at 7 and 14 days. Irrespective of the ECM source, dynamic culture on the microcarriers altered the expression of genes and proteins associated with cell adhesion and ECM remodeling. Label-free mass spectrometry analysis showed upregulation of proteins associated with cartilage development and ECM in the hASCs expanded on the DCT microcarriers. Based on Luminex analysis, the hASCs expanded on the DCT microcarriers secreted significantly higher levels of IL-8 and PDGFAA, supporting that the ECM source can modulate hASC paracrine factor secretion. Finally, the hASCs expanded on the microcarriers were extracted for analysis of adipogenic and chondrogenic differentiation relative to baseline controls. The microcarrier-cultured hASCs showed enhanced intracellular lipid accumulation at 7 days post-induction of adipogenic differentiation. In the chondrogenic studies, a low level of differentiation was observed in all groups. Future studies are warranted using alternative cell sources with greater chondrogenic potential to further assess the chondro-inductive properties of the DCT microcarriers.

Bioengineering liver tissue by repopulation of decellularised scaffolds

Liver transplantation is the only curative therapy for end stage liver disease, but is limited by the organ shortage, and is associated with the adverse consequences of immunosuppression. Repopulation of decellularised whole organ scaffolds with appropriate cells of recipient origin offers a theoretically attractive solution, allowing reliable and timely organ sourcing without the need for immunosuppression. Decellularisation methodologies vary widely but seek to address the conflicting objectives of removing the cellular component of tissues whilst keeping the 3D structure of the extra-cellular matrix intact, as well as retaining the instructive cell fate determining biochemicals contained therein. Liver scaffold recellularisation has progressed from small rodent in vitro studies to large animal in vivo perfusion models, using a wide range of cell types including primary cells, cell lines, foetal stem cells, and induced pluripotent stem cells. Within these models, a limited but measurable degree of physiologically significant hepatocyte function has been reported with demonstrable ammonia metabolism in vivo. Biliary repopulation and function have been restricted by challenges relating to the culture and propagations of cholangiocytes, though advances in organoid culture may help address this. Hepatic vasculature repopulation has enabled sustainable blood perfusion in vivo, but with cell types that would limit clinical applications, and which have not been shown to have the specific functions of liver sinusoidal endothelial cells. Minority cell groups such as Kupffer cells and stellate cells have not been repopulated. Bioengineering by repopulation of decellularised scaffolds has significantly progressed, but there remain significant experimental challenges to be addressed before therapeutic applications may be envisaged.

Preparation of extracellular matrix of fish swim bladders by decellularization with supercritical carbon dioxide

Fish swim bladders used to be considered as byproducts or waste in fishery; however, they are potential materials for biological medicine with abundant collagen. In this work, an efficient noncytotoxic decellularization process using sodium dodecyl sulfate (SDS) ternary system assisted with supercritical carbon dioxide (scCO2) as the green extraction fluid and ethanol (ET) as the cosolvent has been developed to harvest acellular fish swim bladders (AFSBs). The experimental results show that the tissue treated by SDS assisted with scCO2 and ethanol at 37 °C and 25 MPa can be decellularized thoroughly and maintains intact fibers and uniform pore distribution, which resulting in a tensile strength of 5.61 MPa and satisfactory biocompatibility. Meanwhile, the residual SDS content in scCO2/SDS/ET ternary system is 0.0122% which is significantly lower than it in scCO2/SDS system due to the enhanced mass transfer rate of SDS in tissues by scCO2 with ethanol. The synergy between SDS and ethanol can enhance the diffusion coefficient and the solubility of SDS in scCO2, which reduced the contact time between SDS and tissues. Meaningfully, the results obtained in this work can not only provide a novel strategy to produce acellular matrix with superior properties, but also offer a further understanding of the decellularization through scCO2 extraction processing with the synergy of suitable detergent/cosolvent.

Decellularized extracellular matrix (d-ECM): the key role of the inflammatory process in pre-regeneration after implantation

Clinical medicine is encountering the challenge of repairing soft-tissue defects. Currently, natural and synthetic materials have been developed as natural scaffolds. Among them, the decellularized extracellular matrix (d-ECM) can achieve tissue remodeling following injury and, thus, replace defects due to its advantages of the extensiveness of the source and excellent biological and mechanical properties. However, by analyzing the existing decellularization techniques, we found that different preparation methods directly affect the residual components of the d-ECM, and further have different effects on inflammation and regeneration of soft tissues. Therefore, we analyzed the role of different residual components of the d-ECM after decellularization. Then, we explored the inflammatory process and immune cells in an attempt to understand the mechanisms and causes of tissue degeneration and regeneration after transplantation. In this paper, we summarize the current studies related to updated protocols for the preparation of the d-ECM, biogenic and exogenous residual substances, inflammation, and immune cells influencing the fate of the d-ECM.

Development of Brain-Derived Bioscaffolds for Neural Progenitor Cell Culture

Biomaterials derived from brain extracellular matrix (ECM) have the potential to promote neural tissue regeneration by providing instructive cues that can direct cell survival, proliferation, and differentiation. This study focused on the development and characterization of microcarriers derived from decellularized brain tissue (DBT) as a platform for neural progenitor cell culture. First, a novel detergent-free decellularization protocol was established that effectively reduced the cellular content of porcine and rat brains, with a >97% decrease in the dsDNA content, while preserving collagens (COLs) and glycosaminoglycans (GAGs). Next, electrospraying methods were applied to generate ECM-derived microcarriers incorporating the porcine DBT that were stable without chemical cross-linking, along with control microcarriers fabricated from commercially sourced bovine tendon COL. The DBT microcarriers were structurally and biomechanically similar to the COL microcarriers, but compositionally distinct, containing a broader range of COL types and higher sulfated GAG content. Finally, we compared the growth, phenotype, and neurotrophic factor gene expression levels of rat brain-derived progenitor cells (BDPCs) cultured on the DBT or COL microcarriers within spinner flask bioreactors over 2 weeks. Both microcarrier types supported BDPC attachment and expansion, with immunofluorescence staining results suggesting that the culture conditions promoted BDPC differentiation toward the oligodendrocyte lineage, which may be favorable for cell therapies targeting remyelination. Overall, our findings support the further investigation of the ECM-derived microcarriers as a platform for neural cell derivation for applications in regenerative medicine.

Deconstructing Allograft Adipose and Fascia Matrix: Fascia Matrix Improves Angiogenesis, Volume Retention, and Adipogenesis in a Rodent Model

BACKGROUND

Autologous fat grafting is commonly used for soft-tissue repair (approximately 90,000 cases per year in the United States), but outcomes are limited by volume loss (20% to 80%) over time. Human allograft adipose matrix (AAM) stimulates de novo adipogenesis in vivo, but retention requires optimization. The extracellular matrix derived from superficial fascia, interstitial within the adipose layer, is typically removed during AAM processing. Thus, fascia, which contains numerous important proteins, might cooperate with AAM to stimulate de novo adipogenesis, improving long-term retention compared to AAM alone.

METHODS

Human AAM and fascia matrix proteins (back and upper leg regions) were identified by mass spectrometry and annotated by gene ontology. A three-dimensional in vitro angiogenesis assay was performed. Finally, AAM and/or fascia (1 mL) was implanted into 6- to 8-week-old male Fischer rats. After 8 weeks, the authors assessed graft retention by gas pycnometry and angiogenesis (CD31) and adipocyte counts (hematoxylin and eosin) histologically.

RESULTS

Gene ontology annotation revealed an angiogenic enrichment pattern unique to the fascia, including lactadherin, collagen alpha-3(V) chain, and tenascin-C. In vitro, AAM stimulated 1.0 ± 0.17 angiogenic sprouts per bead. The addition of fascia matrix increased sprouting by 88% (2.0 ± 0.12; P < 0.001). A similar angiogenic response (CD31) was observed in vivo. Graft retention volume was 25% (0.25 ± 0.13) for AAM, significantly increasing to 60% (0.60 ± 0.14) for AAM/fascia ( P < 0.05). De novo adipogenesis was 12% (12.4 ± 7.4) for AAM, significantly increasing to 51% (51.2 ± 8.0) for AAM/fascia ( P < 0.001) by means of adipocyte quantification.

CONCLUSIONS

Combining fascia matrix with AAM improves angiogenesis and adipogenesis compared to AAM alone in rats. These preliminary in vitro and pilot animal studies should be further validated before definitive clinical adoption.

CLINICAL RELEVANCE STATEMENT

When producing an off-the-shelf adipose inducing product by adding a connective tissue fascial component (that is normally discarded) to the mix of adipose matrix, vasculogenesis is increased and, thus, adipogenesis and graft survival is improved. This is a significant advance in this line of product.

Scaffolds Based on Silk Fibroin with Decellularized Rat Liver Microparticles: Investigation of the Structure, Biological Properties and Regenerative Potential for Skin Wound Healing

The development of advanced biomaterials and constructs for accelerated recovery of damaged tissues is a key direction in regenerative medicine. Biocompatible scaffolds based on natural biopolymers are widely used for these tasks. Organ decellularization enables obtaining a cell-free extracellular matrix (ECM) with preserved composition and biological activity. The objectives of the present work were combining these two approaches for the development of a composite scaffold based on silk fibroin and ECM microparticles and assessing its structure, biological properties, and regenerative potential. ECM microparticles were obtained by grinding the decellularized matrix of Wistar rat liver in liquid nitrogen. Scaffolds in the form of films were prepared by the casting method. The sinuous and rough topography of the scaffold surface was assessed by the scanning probe nanotomography (SPNT) technique. The inclusion of ECM microparticles in the composition did not affect the elasticity and tensile strength of the scaffolds. The obtained scaffold was non-toxic to cells, maintained high levels of adhesion and proliferation of mouse 3T3 fibroblast and Hep-G2 cells, and showed high regenerative potential, which was studied in the experimental model of full-thickness rat skin wound healing. The wound healing was accelerated by 1.74 times in comparison with the control.

Decellularized Adipose Matrices Can Alleviate Radiation-Induced Skin Fibrosis

Objective: Radiation therapy is commonplace for cancer treatment but often results in fibrosis and atrophy of surrounding soft tissue. Decellularized adipose matrices (DAMs) have been reported to improve these soft tissue defects through the promotion of adipogenesis. These matrices are decellularized by a combination of physical, chemical, and enzymatic methods to minimize their immunologic effects while promoting their regenerative effects. In this study, we aimed at exploring the regenerative ability of a DAM (renuva®; MTF biologics, Edison, NJ) in radiation-induced soft tissue injury. Approach: Fresh human lipoaspirate or DAM was injected into the irradiated scalp of CD-1 nude mice, and volume retention was monitored radiographically over 8 weeks. Explanted grafts were histologically assessed, and overlying skin was examined histologically and biomechanically. Irradiated human skin was also evaluated from patients after fat grafting or DAM injection. However, integrating data between murine and human skin in all cohorts is limited given the genetic variability between the two species. Results: Volume retention was found to be greater with fat grafts, though DAM retention was, nonetheless, appreciated at irradiated sites. Improvement in both mouse and human irradiated skin overlying fat and DAM grafts was observed in terms of biomechanical stiffness, dermal thickness, collagen density, collagen fiber networks, and skin vascularity. Innovation: This is the first demonstration of the use of DAMs for augmenting the regenerative potential of irradiated mouse and human skin. Conclusions: These findings support the use of DAMs to address soft tissue atrophy after radiation therapy. Morphological characteristics of the irradiated skin can also be improved with DAM grafting.

Impact of Three Different Processing Techniques on the Strength and Structure of Juvenile Ovine Pulmonary Homografts

Homografts are routinely stored by cryopreservation; however, donor cells and remnants contribute to immunogenicity. Although decellularization strategies can address immunogenicity, additional fixation might be required to maintain strength. This study investigated the effect of cryopreservation, decellularization, and decellularization with additional glutaraldhyde fixation on the strength and structure of ovine pulmonary homografts harvested 48 h post-mortem. Cells and cellular remnants were present for the cryopreserved group, while the decellularized groups were acellular. The decellularized group had large interfibrillar spaces in the extracellular matrix with uniform collagen distribution, while the additional fixation led to the collagen network becoming dense and compacted. The collagen of the cryopreserved group was collapsed and appeared disrupted and fractured. There were no significant differences in strength and elasticity between the groups. Compared to cryopreservation, decellularization without fixation can be considered an alternative processing technique to maintain a well-organized collagen matrix and tissue strength of homografts.

Enhanced Adipogenic Differentiation of Human Dental Pulp Stem Cells in Enzymatically Decellularized Adipose Tissue Solid Foams

Simple Summary

Obesity shortens human lifespan and represents one of the most important public health problems causing significant economic and societal consequences worldwide. However, the current development of physiological human 3D adipose tissue models for in vitro research on preclinical personalized medicine is limited and expensive. Here, we designed, produced, and characterized 3D solid foams using a mixture of bovine collagen I and decellularized human adipose tissue to serve as a 3D matrix mimicking in vivo adipose microenvironment for cell culture purposes. Furthermore, we sought to validate its compatibility for the culture of human mesenchymal stem cells isolated from the dental pulp. We demonstrated that 3D solid foams are able to integrate the stem cells from the dental pulp and provide the appropriate cues to differentiate them into mature adipocytes. The results represent an advance of in vitro 3D models using a human extracellular matrix derived material for future personalized stem cell therapies.

Abstract

Engineered 3D human adipose tissue models and the development of physiological human 3D in vitro models to test new therapeutic compounds and advance in the study of pathophysiological mechanisms of disease is still technically challenging and expensive. To reduce costs and develop new technologies to study human adipogenesis and stem cell differentiation in a controlled in vitro system, here we report the design, characterization, and validation of extracellular matrix (ECM)-based materials of decellularized human adipose tissue (hDAT) or bovine collagen-I (bCOL-I) for 3D adipogenic stem cell culture. We aimed at recapitulating the dynamics, composition, and structure of the native ECM to optimize the adipogenic differentiation of human mesenchymal stem cells. hDAT was obtained by a two-enzymatic step decellularization protocol and post-processed by freeze-drying to produce 3D solid foams. These solid foams were employed either as pure hDAT, or combined with bCOL-I in a 3:1 proportion, to recreate a microenvironment compatible with stem cell survival and differentiation. We sought to investigate the effect of the adipogenic inductive extracellular 3D-microenvironment on human multipotent dental pulp stem cells (hDPSCs). We found that solid foams supported hDPSC viability and proliferation. Incubation of hDPSCs with adipogenic medium in hDAT-based solid foams increased the expression of mature adipocyte LPL and c/EBP gene markers as determined by RT-qPCR, with respect to bCOL-I solid foams. Moreover, hDPSC capability to differentiate towards adipocytes was assessed by PPAR-γ immunostaining and Oil-red lipid droplet staining. We found out that both hDAT and mixed 3:1 hDAT-COL-I solid foams could support adipogenesis in 3D-hDPSC stem cell cultures significantly more efficiently than solid foams of bCOL-I, opening the possibility to obtain hDAT-based solid foams with customized properties. The combination of human-derived ECM biomaterials with synthetic proteins can, thus, be envisaged to reduce fabrication costs, thus facilitating the widespread use of autologous stem cells and biomaterials for personalized medicine.

Non-homologous use of adipose-derived cell and tissue therapies: Osteoarthritis as a case study

Adipose tissue is widely recognized as an abundant and accessible human tissue that serves as a source of cells and extracellular matrix scaffolds for regenerative surgical applications. Increasingly, orthopedic surgeons are turning to adipose tissue as a resource in their treatment of osteoarthritis and related conditions. In the U.S., the regulatory landscape governing the orthopedic surgical utilization of autologous and allogeneic adipose tissue remains complex. This manuscript reviews the Food and Drug Administration's nomenclature and guidance regarding adipose tissue products. Additionally, it surveys recent pre-clinical and clinical trial literature relating to the application of adipose-derived cells and tissues in the treatment of osteoarthritis.

Additive manufactured macroporous chambers facilitate large volume soft tissue regeneration from adipose-derived extracellular matrix

Breast tissue engineering is a promising alternative intervention for breast reconstruction. Due to their low immunogenicity and well-preserved adipogenic microenvironment, decellularized adipose tissue (DAT) can potentially regenerate adipose tissue in vivo. However, the volume of adipose tissue regenerated from DAT can hardly satisfy the demand for breast reconstruction. Tissue engineering chamber (TEC) is an effective technique for generation of large adipose tissue volumes. However, TEC applications necessitate reoperation to remove non-degradable plastic chambers and harvest autologous tissue flaps, which prolongs the operation time and causes potential damage to donor sites. We improved the TEC strategy by combining bioresorbable polycaprolactone (PCL) chambers and decellularized adipose tissues (DAT). A miniaturized porous PCL chamber was fabricated based on scaling differences between human and rabbit chests, and basic fibroblast growth factor (bFGF)-loaded DAT successfully prepared. In rabbit models, a highly vascularized adipose tissue that nearly filled up the PCL chamber (5 mL) was generated de novo from 0.5 mL bFGF-loaded DAT. The newly formed tissue had significantly high expressions of adipogenic genes, compared to the endogenous adipose tissue. The concept described here can be exploited for breast tissue engineering. STATEMENT OF SIGNIFICANCE: Decellularized adipose tissue (DAT), which provides infiltrated cells adipogenic microenvironment, can potentially regenerate adipose tissue in vivo. Nevertheless, the volume of regenerated adipose tissue is insufficient to repair large sized tissue defect. Tissue engineering chamber (TEC) could provide a protective space for in situ regeneration of large volume tissue. Herein, a new strategy by combining biodegradable polycaprolactone chambers and basic fibroblast growth factor-loaded decellularized adipose tissue is proposed. In rabbit model, newly formed adipose tissue regenerated from DAT successfully filled the dome shaped chamber with ten folds higher volume than DAT, which is proportionally similar to women breast. This work highlighted the importance of adipogenic microenvironment and protective space for adipose tissue regeneration.

Fat Graft with Allograft Adipose Matrix and Magnesium Hydroxide-Incorporated PLGA Microspheres for Effective Soft Tissue Reconstruction

BACKGROUND

Autologous fat grafting is one of the most common procedures used in plastic surgery to correct soft tissue deficiency or depression deformity. However, its clinical outcomes are often suboptimal, and lack of metabolic and architectural support at recipient sites affect fat survival leading to complications such as cyst formation, calcification. Extracellular matrix-based scaffolds, such as allograft adipose matrix (AAM) and poly(lactic-co-glycolic) acid (PLGA), have shown exceptional clinical promise as regenerative scaffolds. Magnesium hydroxide (MH), an alkaline ceramic, has attracted attention as a potential additive to improve biocompatibility. We attempted to combine fat graft with regenerative scaffolds and analyzed the changes and viability of injected fat graft in relation to the effects of injectable natural, and synthetic (PLGA/MH microsphere) biomaterials.

METHODS

In vitro cell cytotoxicity, angiogenesis of the scaffolds, and wound healing were evaluated using human dermal fibroblast cells. Subcutaneous soft-tissue integration of harvested fat tissue was investigated in vivo in nude mouse with random fat transfer protocol Fat integrity and angiogenesis were identified by qRT-PCR and immunohistochemistry.

RESULTS

In vitro cell cytotoxicity was not observed both in AAM and PLGA/MH with human dermal fibroblast. PLGA/MH and AAM showed excellent wound healing effect. In vivo, the AAM and PLGA/MH retained volume compared to that in the only fat group. And the PLGA/MH showed the highest angiogenesis and anti-inflammation.

CONCLUSION

In this study, a comparison of the volume retention effect and angiogenic ability between autologous fat grafting, injectable natural, and synthetic biomaterials will provide a reasonable basis for fat grafting.

Developing a clinical grade human adipose decellularized biomaterial

While tissue engineering investigators have appreciated adipose tissue as a repository of stromal/stem cells, they are only now beginning to see its value as a decellularized tissue resource. Independent academic investigators have successfully extracted lipid, genomic DNA and proteins from human fat to create a decellularized extracellular matrix enriched in collagen, glycoproteins, and proteoglycans. Pre-clinical studies have validated its compatibility with stromal/stem cells and its ability to support adipogenesis in vitro and in vivo in both small (murine) and large (porcine) subcutaneous implant models. Furthermore, Phase I safety clinical trials have injected decellularized human adipose tissue scaffolds in human volunteers without incident for periods of up to 127 days. This commentary takes an opinionated look at the under-appreciated but potential benefits of obesity as an increasingly available biomaterial resource.

Decellularization for the retention of tissue niches

Decellularization of natural tissues to produce extracellular matrix is a promising method for three-dimensional scaffolding and for understanding microenvironment of the tissue of interest. Due to the lack of a universal standard protocol for tissue decellularization, recent investigations seek to develop novel methods for whole or partial organ decellularization capable of supporting cell differentiation and implantation towards appropriate tissue regeneration. This review provides a comprehensive and updated perspective on the most recent advances in decellularization strategies for a variety of organs and tissues, highlighting techniques of chemical, physical, biological, enzymatic, or combinative-based methods to remove cellular contents from tissues. In addition, the review presents modernized approaches for improving standard decellularization protocols for numerous organ types.

Decellularized Human Adipose Tissue as an Alternative Graft Material for Bone Regeneration

BACKGROUND

Tissue engineering approaches to treat damaged bone include various tissue transplants such as autologous, allogeneic, and xenografts. Artificial materials have been widely introduced to meet the demand for graft materials, but insufficiency in supply is still not resolved. In this study, human adipose tissue, easily obtained from the human body, was harvested, and the tissue was decellularized to fabricate a decellularized human adipose tissue matrix (DM) as an alternative graft material.

METHODS

Human adipose tissue was obtained via liposuction. The obtained fresh adipose tissue sample was cut into pieces then put into decellularization solution (1% antibiotic-antimycotic solution and 1% phenylmethanesulphonyl fluoride). Lipids were further removed via treatment in isopropanol. The sample was then subjected to another enzymatic digestion and lipid removal processes. The obtained decellularized adipose tissue matrix was lyophilized to form a graft material in disc shape.

RESULTS

Decellularization was confirmed by nuclear staining methods and detection of RNA and DNA via PCR. Bone morphogenetic protein 2 (BMP2)-loaded DM showed the ability to form new bone tissue when implanted in subcutaneous tissue. In recovery of a mouse calvarial defect model, BMP2-loaded DM exhibited similar levels of bone tissue regeneration efficiency compared with a well-defined commercial product, BMP2-loaded CollaCote®.

CONCLUSION

The DM developed in this study is expected to address the problem of insufficient supply of graft materials and contribute to the treatment of bone defects of critical size as an alternative bone graft material with preserved extracellular matrix components.