Comparative proteomic analyses of human adipose extracellular matrices decellularized using alternative procedures

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.

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 .

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.

Comparative proteomic analysis of regenerative acellular matrices: The effects of tissue source and processing method

Acellular tissue matrices are used in regenerative medicine from weak tissue re-enforcement to cosmetic augmentation. However, proteomic signatures leading to different clinical outcomes among matrices are not well understood. In an attempt to investigate the effects of tissue source and processing method, we examined by liquid chromatography tandem mass spectrometry (LC-MS/MS) the proteomic profiles of 12 regulatory agency-approved acellular matrices (AlloMax, AlloDerm, CollaMend, Heal-All, JayyaLife, ReGen, Renov, Strattice, SurgiMend, Surgisis, UniTrump and Vidasis). The compositions of acellular matrices varied greatly with the number of identified proteins ranging from 7 to 106. The content of individual proteins was between 0.0001% and 95.8% according to their abundances measured by the M/Z signal intensities. Most acellular matrices still contained numerous cellular proteins. AlloMax, AlloDerm, ReGen, Strattice, SurgiMend and Surgisis retained necessary structural and functional proteins to form the extracellular protein-protein interaction networks for cell adhesion, proliferation and tissue regeneration, whereas CollaMend, Heal-All, JayyaLife, Renov, UniTrump and Vidasis had only retained certain structural collagens. Principal component analysis showed that proteomic variations among acellular matrices were largely attributed to tissue source and processing method. Differences in proteomic profiles among acellular matrices offers insights into molecular interpretation for different clinical outcomes, and can serve as useful references for rational design of regenerative bio-scaffolds.

Evaluating the quality of studies reporting on clinical applications of stromal vascular fraction: A systematic review and proposed reporting guidelines (CLINIC-STRA-SVF)

Background

The stromal vascular fraction (SVF) has been widely explored in a number of therapeutic applications in several specialties. Its therapeutic potential is being increasingly demonstrated, although its mechanism of action is still unclear.

Objective

To evaluate the quality of studies reporting on clinical applications of SVF.

Method

This is a systematic literature review that followed the PRISMA guidelines with the search of the studies from December 1, 2012, to December 1, 2022, in the following databases: MEDLINE, LILACS and EMBASE. The level of evidence of the studies was assessed using the GRADE system, and the rigor used in the publication of the results was assessed in relation to adherence to the guidelines indicated by the EQUATOR Network Group. The CLINIC - STRA-SVF reporting guideline was developed after the completion of this systematic review.

Results

A total of 538 articles were found, and 77 articles were selected after reading the titles and abstracts and removing duplicates. Then, 15 studies were removed for not meeting the inclusion criteria, leaving 62 studies. The CLINIC - STRA-SVF was developed and consists of 33 items and two tables.

Conclusion

There is scientific evidence, although mostly with a low level of evidence, that the use of SVF in clinical applications is safe and effective. The information published in these studies should be standardized, and the CLINIC - STRA-SVF reporting guideline proposed in this study may assist in the design, conduct, recording and reporting of clinical trials and others clinical studies involving the SVF.

Biomechanical and Biological Characterization of XGel, a Human-Derived Hydrogel for Stem Cell Expansion and Tissue Engineering

Hydrogels are 3D scaffolds used as alternatives to in vivo models for disease modeling and delivery of cells and drugs. Existing hydrogel classifications include synthetic, recombinant, chemically defined, plant- or animal-based, and tissue-derived matrices. There is a need for materials that can support both human tissue modeling and clinically relevant applications requiring stiffness tunability. Human-derived hydrogels are not only clinically relevant, but they also minimize the use of animal models for pre-clinical studies. This study aims to characterize XGel, a new human-derived hydrogel as an alternative to current murine-derived and synthetic recombinant hydrogels that features unique physiochemical, biochemical, and biological properties that support adipocyte and bone differentiation. Rheology studies determine the viscosity, stiffness, and gelation features of XGel. Quantitative studies for quality control support consistency in the protein content between lots. Proteomics studies reveal that XGel is predominantly composed of extracellular matrix proteins, including fibrillin, collagens I-VI, and fibronectin. Electron microscopy of the hydrogel provides phenotypic characteristics in terms of porosity and fiber size. The hydrogel demonstrates biocompatibility as a coating material and as a 3D scaffold for the growth of multiple cell types. The results provide insight into the biological compatibility of this human-derived hydrogel for tissue engineering.

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.

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.

Dendritic cell differentiation from human induced pluripotent stem cells: challenges and progress

Dendritic cells (DCs) are the major antigen-presenting cells of the immune system responsible for initiating and coordinating immune responses. These abilities provide potential for several clinical applications, such as the development of immunogenic vaccines. However, difficulty in obtaining DCs from conventional sources, such as bone marrow (BM), peripheral blood (PBMC), and cord blood (CB), is a significantly hinders routine application. The use of human induced pluripotent stem cells (hiPSCs) is a valuable alternative for generating sufficient numbers of DCs to be used in basic and pre-clinical studies. Despite the many challenges that must be overcome to achieve an efficient protocol for obtaining the major DC types from hiPSCs, recent progress has been made. Here we review the current state of developing DCs from hiPSCs, as well as the key elements required to enable the routine use of hiPSC-derived DCs in pre-clinical and clinical assays.

Adipose Stem Cells in Regenerative Medicine: Looking Forward

Over the last decade, stem cell-based regenerative medicine has progressed to clinical testing and therapeutic applications. The applications range from infusions of autologous and allogeneic stem cells to stem cell-derived products. Adult stem cells from adipose tissue (ASCs) show significant promise in treating autoimmune and neurodegenerative diseases, vascular and metabolic diseases, bone and cartilage regeneration and wound defects. The regenerative capabilities of ASCs in vivo are primarily orchestrated by their secretome of paracrine factors and cell-matrix interactions. More recent developments are focused on creating more complex structures such as 3D organoids, tissue elements and eventually fully functional tissues and organs to replace or repair diseased or damaged tissues. The current and future applications for ASCs in regenerative medicine are discussed here.

Matrisome provides a supportive microenvironment for oral squamous cell carcinoma progression

Oral squamous cell carcinoma (OSCC) is a common pernicious tumor in the head and neck regions. However, the function of tumor extracellular matrix (ECM) has not been elucidated. A tissue engineering method was applied for remodeling ECM through decellularization. The cellular components were removed, and the biological composition was mostly preserved. Proteomics was performed to analyze the characterization between normal and tumor ECM. According to LC-MS/MS results, 26 proteins just showed in tumor ECM, and 14 proteins only showed in late-stage tumor ECM. KEGG pathway analysis showed that most variant proteins were linked to metabolic regulation and tumor immunity (such as SCC-Ag1, LOX). To affirm the influence of tumor ECM on the progression of OSCC, tumor cells and macrophages were co-cultured with ECM scaffold. Marked differences in proliferation, apoptosis, and migration of OSCC cells were observed between tumor and normal ECM. Tumor ECM polarized macrophages towards an anti-inflammatory phenotype (higher IL-10 and CD68, and relatively lower CD86 and IL1-β). Collectively, these findings suggest that tumor ECM served as a permissive role in OSCC progression. SIGNIFICANCE: The variation between OSCC ECM and normal ECM confirm tumor ECM plays a significant role in OSCC deterioration, which is conducive to exploring the occurrence and progression mechanisms of OSCC, and further improving the curative effect of this disease.

Methoxy polyethylene glycol modification promotes adipogenesis by inducing the production of regulatory T cells in xenogeneic acellular adipose matrix

Acellular adipose matrix (AAM) has emerged as an important biomaterial for adipose tissue regeneration. Current decellularization methods damage the bioactive components of the extracellular matrix (ECM), and the residual immunogenic antigens may induce adverse immune responses. Here, we adopted a modified decellularization method which can protect more bioactive components with less immune reaction by methoxy polyethylene glycol (mPEG). Then, we determined the adipogenic mechanisms of mPEG-modified AAM after xenogeneic transplantation. AAM transplantation caused significantly lesser adipogenesis in the wild-type group than in the immune-deficient group. The mPEG-modified AAM showed significantly lower immunogenicity and higher adipogenesis than the AAM alone after xenogeneic transplantation. Furthermore, mPEG modification increased regulatory T (Treg) cell numbers in the AAM grafts, which in turn enhanced the M2/M1 macrophage ratio by secreting IL-10, IL-13, and TGF-β1. These findings suggest that mPEG modification effectively reduces the immunogenicity of xenogeneic AAM and promotes adipogenesis in the AAM grafts. Hence, mPEG-modified AAM can serve as an ideal biomaterial for xenogeneic adipose tissue engineering.

Developing a pro-angiogenic placenta derived amniochorionic scaffold with two exposed basement membranes as substrates for cultivating endothelial cells

Decellularized and de-epithelialized placenta membranes have widely been used as scaffolds and grafts in tissue engineering and regenerative medicine. Exceptional pro-angiogenic and biomechanical properties and low immunogenicity have made the amniochorionic membrane a unique substrate which provides an enriched niche for cellular growth. Herein, an optimized combination of enzymatic solutions (based on streptokinase) with mechanical scrapping is used to remove the amniotic epithelium and chorion trophoblastic layer, which resulted in exposing the basement membranes of both sides without their separation and subsequent damages to the in-between spongy layer. Biomechanical and biodegradability properties, endothelial proliferation capacity, and in vivo pro-angiogenic capabilities of the substrate were also evaluated. Histological staining, immunohistochemistry (IHC) staining for collagen IV, and scanning electron microscope demonstrated that the underlying amniotic and chorionic basement membranes remained intact while the epithelial and trophoblastic layers were entirely removed without considerable damage to basement membranes. The biomechanical evaluation showed that the scaffold is suturable. Proliferation assay, real-time polymerase chain reaction for endothelial adhesion molecules, and IHC demonstrated that both side basement membranes could support the growth of endothelial cells without altering endothelial characteristics. The dorsal skinfold chamber animal model indicated that both side basement membranes could promote angiogenesis. This bi-sided substrate with two exposed surfaces for cultivating various cells would have potential applications in the skin, cardiac, vascularized composite allografts, and microvascular tissue engineering.

Human decellularized adipose tissue hydrogels as a culture platform for human adipose-derived stem cell delivery

Adipose-derived stem cells (ADSCs) have been widely researched and used as a drug therapy in many fields like disease treatment and tissue engineering. However, ADSCs are susceptible to the surrounding environment. The emergence of acellular extracellular matrix provides a solution, which can serve as biomaterial scaffold as well as original ecological niche for the stem cells. Therefore, we propose the hypothesis that human decellularized adipose tissues (hDAT) are processed into injectable hydrogels and then mixed evenly with ADSCs. So that the ADSCs embedded-hydrogels could directly carry the stem cells to the appropriate sites. The hDAT hydrogel could provide microenvironmental protection for ADSCs. In this study, we successfully made human decellularized adipose tissue hydrogel (hDAT-gel), which was temperature-sensitive, liquid at 4°C and semi-solid at 37°C. When the ADSCs were embedded in hDAT-gel, they survived well and continued to grow well in layers. When the pre-gel containing ADSCs was injected subcutaneously into nude mice, the sample results after 15 min showed gelation occurred in situ. These results suggested that hDAT-gel could provide a culture platform for ADSCs delivery.

Breast Cancer Reconstruction: Design Criteria for a Humanized Microphysiological System

International regulatory agencies such as the Food and Drug Administration have mandated that the scientific community develop humanized microphysiological systems (MPS) as an in vitro alternative to animal models in the near future. While the breast cancer research community has long appreciated the importance of three-dimensional growth dynamics in their experimental models, there are remaining obstacles preventing a full conversion to humanized MPS for drug discovery and pathophysiological studies. This perspective evaluates the current status of human tissue-derived cells and scaffolds as building blocks for an "idealized" breast cancer MPS based on bioengineering design principles. It considers the utility of adipose tissue as a potential source of endothelial, lymphohematopoietic, and stromal cells for the support of breast cancer epithelial cells. The relative merits of potential MPS scaffolds derived from adipose tissue, blood components, and synthetic biomaterials is evaluated relative to the current "gold standard" material, Matrigel, a murine chondrosarcoma-derived basement membrane-enriched hydrogel. The advantages and limitations of a humanized breast cancer MPS are discussed in the context of in-process and destructive read-out assays. Impact statement Regulatory authorities have highlighted microphysiological systems as an emerging tool in breast cancer research. This has been led by calls for more predictive human models and reduced animal experimentation. This perspective describes how human-derived cells, extracellular matrices, and hydrogels will provide the building blocks to create breast cancer models that accurately reflect diversity at multiple levels, that is, patient ethnicity, pathophysiology, and metabolic status.

In situ Adipogenesis in Biomaterials Without Cell Seeds: Current Status and Perspectives

For cosmetic and reconstructive purposes in the setting of small-volume adipose tissue damage due to aging, traumatic defects, oncological resections, and degenerative diseases, the current strategies for soft tissue replacement involve autologous fat grafts and tissue fillers with synthetic, bioactive, or tissue-engineered materials. However, they all have drawbacks such as volume shrinkage and foreign-body responses. Aiming to regenerate bioactive vascularized adipose tissue on biomaterial scaffolds, adipose tissue engineering (ATE) has emerged as a suitable substitute for soft tissue repair. The essential components of ATE include scaffolds as support, cells as raw materials for fat formation, and a tolerant local environment to allow regeneration to occur. The commonly loaded seeding cells are adipose-derived stem cells (ASCs), which are expected to induce stable and predictable adipose tissue formation. However, defects in stem cell enrichment, such as donor-site sacrifice, limit their wide application. As a promising alternative approach, cell-free bioactive scaffolds recruit endogenous cells for adipogenesis. In biomaterials without cell seeds, the key to sufficient adipogenesis relies on the recruitment of endogenous host cells and continuous induction of cell homing to scaffolds. Regeneration, rather than repair, is the fundamental dominance of an optimal mature product. To induce in situ adipogenesis, many researchers have focused on the mechanical and biochemical properties of scaffolds. In addition, efforts to regulate an angiogenic and adipogenic microenvironment in cell-free settings involve integrating growth factors or extracellular matrix (ECM) proteins onto bioactive scaffolds. Despite the theoretical feasibility and encouraging results in animal models, few of the reported cell-free biomaterials have been tested in humans, and failures of decellularized adipose tissues in adipogenesis have also been reported. In these cases, the most likely reason was the lack of supporting vasculature. This review summarizes the current status of biomaterials without cell seeds. Related mechanisms and influencing factors of in situ adipogenesis in cell-free biomaterials, dilemma in the development of biomaterials, and future perspectives are also addressed.

Decellularized adipose tissue: A key factor in promoting fat regeneration by recruiting and inducing mesenchymal stem cells

BACKGROUND

Decellularized adipose tissue (DAT) has attracted much attention due to its wide range of sources and adipose regeneration capacity. However, the lipogenic efficiency of DAT is still controversial due to its unclear mechanism. To this point, it is crucial to clarify the mechanism of DAT in promoting adipose regeneration Objective: This study aims to explore the mechanism of DAT promoting adipose regeneration and survival mechanism of DAT transplantation in vivo.

METHODS

DAT preparation by repeated freeze-thaw, enzymatic digestion, and isopropanol degreasing. Histology, DAPI, immunohistochemistry, immunofluorescence and scanning electron microscopy confirmed the efficacy and reproducibility of these approaches. BM-MSCs, ADSCs and UCMSCs were cocultured with DAT for 14 days and then stained with oil red O. Adipogenic genes of three MSCs were detected by RT-PCR. DAT and adipose tissue were transplanted subcutaneously into the back of nude mice to observe medium and long-term morphological changes, vascularization, and lipid-forming efficiency. Mass spectrometry (MS)-based proteomic to analyze the adipogenic protein contents of DAT and adipose tissue.

RESULTS

The DAT without any cellular components but with an abundance of collagen; neither DNA nor lipids were detected. Seeding experiments with MSCs indicated that the DAT provided an inductive microenvironment for adipogenesis, supporting the expression of the master regulators PPARγ. Within four months after transplantation, HE morphology of DAT was identical to adipose cells. Immunofluorescence markers CD31 and perilipin were increased in DAT, while the retention rate gradually decreased over time, eventually accounting for 33.7% of the original volume. MS-based proteomic analyses identified 1013 types of proteins in adipose tissue and 29 proteins in the DAT. Analyses of GO and KEGG databases suggested that DAT contained a variety of proteins involved in fat metabolism.

CONCLUSIONS

DAT can interact with different types of MSCs and ultimately achieve adipose regeneration. The presence of multiple adipogenic proteins in DAT make it play a vital role in adipose regeneration. DAT is expected to be an ideal bio-derived scaffold for adipose tissue engineering.

The Application of Decellularized Adipose Tissue Promotes Wound Healing

BACKGROUND

Due to adipose-derived stem cells (ASCs) being easy to obtain, their rapid proliferation rate, and their multidirectional differentiation capabilities, they have been widely used in the field of regenerative medicine. With the progress of decellularized adipose tissue (DAT) and adipose tissue engineering research, the role of DAT in promoting angiogenesis has gradually been emphasized.

METHODS

We examined the biological characteristics and biosafety of DAT and evaluated the stem cell maintenance ability and promotion of growth factor secretion through conducting in vitro and in vivo studies.

RESULTS

The tested ASCs showed high rat:es of proliferation and adhered well to DAT. The expression levels of essential genes for cell stem maintenance, including OCT4, SOX2, and Nanog were low at 2-24 h and much higher at 48 and 96 h. The Adipogenic expression level of markers for ASCs proliferation including PPARγ, C/EPBα, and LPL increased from 2 to 96 h. Co-culture of ASCs and DAT increased the secretion of local growth factors, such as VEGF, PDGF-bb, bFGF, HGF, EGF, and FDGF-bb, and secretion gradually increased from 0 to 48 h. A model of full-thickness skin defects on the back of nude mice was established, and the co-culture of ASCs and DAT showed the best in vivo treatment effect.

CONCLUSION

The application of DAT promotes wound healing, and DAT combined with ASCs may be a promising material in adipose tissue engineering and regenerative medicine.

Clinical Translational Potential in Skin Wound Regeneration for Adipose-Derived, Blood-Derived, and Cellulose Materials: Cells, Exosomes, and Hydrogels

Acute and chronic skin wounds due to burns, pressure injuries, and trauma represent a substantial challenge to healthcare delivery with particular impacts on geriatric, paraplegic, and quadriplegic demographics worldwide. Nevertheless, the current standard of care relies extensively on preventive measures to mitigate pressure injury, surgical debridement, skin flap procedures, and negative pressure wound vacuum measures. This article highlights the potential of adipose-, blood-, and cellulose-derived products (cells, decellularized matrices and scaffolds, and exosome and secretome factors) as a means to address this unmet medical need. The current status of this research area is evaluated and discussed in the context of promising avenues for future discovery.

Characterization and Proteomic Analysis of Decellularized Adipose Tissue Hydrogels Derived from Lean and Overweight/Obese Human Donors

While decellularized adipose tissue (DAT) has potential as an "off-the-shelf" biomaterial product for regenerative medicine, it remains to be determined if donor-source body mass index (BMI) impacts the functionality of DAT. This study set out to comparatively characterize lean versus overweight/obese-donor derived DAT hydrogel based on proteome and to analyze their respective effects on adipose stromal/stem cell (ASC) viability, and differentiation in vitro. Decellularized adipose tissue from lean (lDAT) and overweight/obese (oDAT) donors is produced and characterized. Variability in the fibril microstructures is found, with dense fibrotic fiber clusters and large pore area uniquely present in the oDAT samples. Proteomic analysis reveals that lDAT contains a greater proportion of enriched extracellular proteins and a smaller proportion of enriched intracellular proteins relative to oDAT. Biocompatibility studies show that ASCs cultured in lDAT and oDAT hydrogels remain viable. The adipogenic and osteogenic differentiation capability of ASCs seeded in lDAT and oDAT hydrogels is confirmed by an upregulation in marker gene expression and phenotypic analysis. In conclusion, this study establishes that DAT hydrogels derived from lean and overweight/obese adipose donors present similar physicochemical profiles with some distinctive features while comparably supporting the viability and adipogenic differentiation of ASCs in vitro.

Decellularized adipose matrix provides an inductive microenvironment for stem cells in tissue regeneration

Stem cells play a key role in tissue regeneration due to their self-renewal and multidirectional differentiation, which are continuously regulated by signals from the extracellular matrix (ECM) microenvironment. Therefore, the unique biological and physical characteristics of the ECM are important determinants of stem cell behavior. Although the acellular ECM of specific tissues and organs (such as the skin, heart, cartilage, and lung) can mimic the natural microenvironment required for stem cell differentiation, the lack of donor sources restricts their development. With the rapid development of adipose tissue engineering, decellularized adipose matrix (DAM) has attracted much attention due to its wide range of sources and good regeneration capacity. Protocols for DAM preparation involve various physical, chemical, and biological methods. Different combinations of these methods may have different impacts on the structure and composition of DAM, which in turn interfere with the growth and differentiation of stem cells. This is a narrative review about DAM. We summarize the methods for decellularizing and sterilizing adipose tissue, and the impact of these methods on the biological and physical properties of DAM. In addition, we also analyze the application of different forms of DAM with or without stem cells in tissue regeneration (such as adipose tissue), repair (such as wounds, cartilage, bone, and nerves), in vitro bionic systems, clinical trials, and other disease research.

Human Adipose Derived Cells in Two- and Three-Dimensional Cultures: Functional Validation of an In Vitro Fat Construct

Obesity, defined as a body mass index of 30 kg/m² or above, has increased considerably in incidence and frequency within the United States and globally. Associated comorbidities including cardiovascular disease, type 2 diabetes mellitus, metabolic syndrome, and nonalcoholic fatty liver disease have led to a focus on the mechanisms promoting the prevention and treatment of obesity. Commonly utilized in vitro models employ human or mouse preadipocyte cell lines in a 2-dimensional (2D) format. Due to the structural, biochemical, and biological limitations of these models, increased attention has been placed on "organ on a chip" technologies for a 3-dimensional (3D) culture. Herein, we describe a method employing cryopreserved primary human stromal vascular fraction (SVF) cells and a human blood product-derived biological scaffold to create a 3D adipose depot in vitro. The "fat-on-chip" 3D cultures have been validated relative to 2D cultures based on proliferation, flow cytometry, adipogenic differentiation, confocal microscopy/immunofluorescence, and functional assays (adipokine secretion, glucose uptake, and lipolysis). Thus, the in vitro culture system demonstrates the critical characteristics required for a humanized 3D white adipose tissue (WAT) model.

Human Adipose Tissue Derivatives as a Potent Native Biomaterial for Tissue Regenerative Therapies

BACKGROUND

Human adipose tissue is a great source of translatable biomaterials owing to its ease of availability and simple processing. Reusing discardable adipose tissue for tissue regeneration helps in mimicking the exact native microenvironment of tissue. Over the past 10 years, extraction, processing, tuning and fabrication of adipose tissue have grabbed the attention owing to their native therapeutic and regenerative potential. The present work gives the overview of next generation biomaterials derived from human adipose tissue and their development with clinical relevance.

METHODS

Around 300 articles have been reviewed to widen the knowledge on the isolation, characterization techniques and medical applications of human adipose tissue and its derivatives from bench to bedside. The prospective applications of adipose tissue derivatives like autologous fat graft, stromal vascular fraction, stem cells, preadipocyte, adipokines and extracellular matrix, their behavioural mechanism, rational property of providing native bioenvironment, circumventing their translational abilities, recent advances in featuring them clinically have been reviewed extensively to reveal the dormant side of human adipose tissue.

RESULTS

Basic understanding about the molecular and structural aspect of human adipose tissue is necessary to employ it constructively. This review has nailed the productive usage of human adipose tissue, in a stepwise manner from exploring the methods of extracting derivatives, concerns during processing and its formulations to turning them into functional biomaterials. Their performance as functional biomaterials for skin regeneration, wound healing, soft tissue defects, stem cell and other regenerative therapies under in vitro and in vivo conditions emphasizes the translational efficiency of adipose tissue derivatives.

CONCLUSION

In the recent years, research interest has inclination towards constructive tissue engineering and regenerative therapies. Unravelling the maximum utilization of human adipose tissue derivatives paves a way for improving existing tissue regeneration and cellular based therapies and other biomedical applications.

Matrix decoded - A pancreatic extracellular matrix with organ specific cues guiding human iPSC differentiation

The extracellular matrix represents a dynamic microenvironment regulating essential cell functions in vivo. Tissue engineering approaches aim to recreate the native niche in vitro using biological scaffolds generated by organ decellularization. So far, the organ specific origin of such scaffolds was less considered and potential consequences for in vitro cell culture remain largely elusive. Here, we show that organ specific cues of biological scaffolds affect cellular behavior. In detail, we report on the generation of a well-preserved pancreatic bioscaffold and introduce a scoring system allowing standardized inter-study quality assessment. Using multiple analysis tools for in-depth-characterization of the biological scaffold, we reveal unique compositional, physico-structural, and biophysical properties. Finally, we prove the functional relevance of the biological origin by demonstrating a regulatory effect of the matrix on multi-lineage differentiation of human induced pluripotent stem cells emphasizing the significance of matrix specificity for cellular behavior in artificial microenvironments.

Acellular Biologic Nipple-Areolar Complex Graft: In Vivo Murine and Nonhuman Primate Host Response Evaluation

There are more than 3 million breast cancer survivors living in the United States of which a significant number have undergone mastectomy followed by breast and nipple-areolar complex (NAC) reconstruction. Current strategies for NAC reconstruction are dependent on nonliving or nonpermanent techniques, including tattooing, nipple prosthetics, or surgical nipple-like structures. Described herein is a tissue engineering approach demonstrating the feasibility of an allogeneic acellular graft for nipple reconstruction. Nonhuman primate (NHP)-derived NAC tissues were decellularized and their extracellular matrix components analyzed by both proteomic and histological analyses. Decellularized NHP nipple tissue showed the removal of intact cells and greatly diminished profiles for intracellular proteins, as compared with intact NHP nipple tissue. We further evaluated the biocompatibility of decellularized grafts and their potential to support host-mediated neovascularization against commercially available acellular dermal grafts by performing in vivo studies in a murine model. A follow-up NHP pilot study evaluated the host-mediated neovascularization and re-epithelialization of onlay engrafted decellularized NAC grafts. The murine model revealed greater neovascularization in the decellularized NAC than in the commercially available control grafts, with no observed biocompatibility issues. The in vivo NHP model confirmed that the decellularized NAC grafts encourage neovascularization as well as re-epithelialization. These results support the concept that a biologically derived acellular nipple graft is a feasible approach for nipple reconstruction, supporting neovascularization in the absence of adverse systemic responses. Impact statement Currently, women in the United States most often undergo a mastectomy, followed by reconstruction, after being diagnosed with breast cancer. These breast cancer survivors are often left with nipple-areolar complex (NAC) reconstructions that are subsatisfactory, nonliving, and/or nonpermanent. Utilizing an acellular biologically derived whole NAC graft would allow these patients a living and permanent tissue engineering solution to nipple reconstruction.

Clinical Evaluation of an Off-the-Shelf Allogeneic Adipose Matrix for Soft Tissue Reconstruction

Biomaterials derived from human adipose extracellular matrix have shown promise in vitro and in animal studies as an off-the-shelf adipogenic matrix for sustained volume replacement. Herein, we report the results of a randomized prospective study conducted with allograft adipose matrix (AAM) grafted into the pannus of presurgical abdominoplasty patients 3 or 6 months before scheduled surgery. This is the first report of a longitudinal histologic analysis of AAM in clinical use.

METHODS

Ten healthy patients undergoing elective abdominoplasty were recruited to receive AAM before surgery. Enrolled subjects were randomized into either a 3-month follow-up cohort or a 6-month follow-up cohort. Subjects were monitored for adverse events associated with AAM grafting in addition to undergoing serial biopsy. Following surgical excision of the pannus, representative samples from the AAM surgical sites were stained and evaluated with hematoxylin and eosin for tissue morphology, Masson's trichrome for collagen, and perilipin for adipocytes.

RESULTS

All subjects tolerated AAM with no severe adverse events reported. At 3 months following implantation, AAM remained visible within the confines of the subjects' native surrounding adipose tissue with sparse adipocytes apparent within the matrix. By 6 months, AAM had remodeled and was primarily composed of perilipin-positive adipocytes. Histologic analysis confirmed tissue remodeling (hematoxylin and eosin), adipogenesis (perilipin), and angiogenesis (Masson's trichrome) occurred with the presence of AAM.

CONCLUSIONS

AAM is a safe, allogeneic, off-the-shelf regenerative matrix that is adipogenic and noninflammatory and promotes angiogenesis.

Human Adipose-Derived Hydrogel Characterization Based on In Vitro ASC Biocompatibility and Differentiation

Hydrogels serve as three-dimensional scaffolds whose composition can be customized to allow attachment and proliferation of several different cell types. Extracellular matrix-derived hydrogels are considered close replicates of the tissue microenvironment. They can serve as scaffolds for in vitro tissue engineering and are a useful tool to study cell-scaffold interaction. The aim of the present study was to analyze the effect of adipose-derived stromal/stem cells (ASCs) and decellularized adipose tissue-derived (DAT) hydrogel interaction on ASC morphology, proliferation, differentiation, and DAT hydrogel microstructure. First, the ASCs were characterized using flow cytometry, adipogenic/osteogenic differentiation, colony-forming unit fibroblast assay and doubling time. The viability and proliferation assays showed that ASCs seeded in DAT hydrogel at different concentrations and cultured for 21 days remained viable and displayed proliferation. ASCs were seeded on DAT hydrogel and cultured in stromal, adipogenic, or osteogenic media for 14 or 28 days. The analysis of adipogenic differentiation demonstrated the upregulation of adipogenic marker genes and accumulation of oil droplets in the cells. Osteogenic differentiation demonstrated the upregulation of osteogenic marker genes and mineral deposition in the DAT hydrogel. The analysis of DAT hydrogel fiber metrics revealed that ASC seeding, and differentiation altered both the diameter and arrangement of fibers in the matrix. Matrix metalloproteinase-2 (MMP-2) activity was assessed to determine the possible mechanism for DAT hydrogel remodeling. MMP-2 activity was observed in all ASC seeded samples, with the osteogenic samples displaying the highest MMP-2 activity. These findings indicate that DAT hydrogel is a cytocompatible scaffold that supports the adipogenic and osteogenic differentiation of ASCs. Furthermore, the attachment of ASCs and differentiation along adipogenic and osteogenic lineages remodels the microstructure of DAT hydrogel.

Decellularized Adipose Tissue Hydrogel Promotes Bone Regeneration in Critical-Sized Mouse Femoral Defect Model

Critical-sized bone defects fail to heal and often cause non-union. Standard treatments employ autologous bone grafting, which can cause donor tissue loss/pain. Although several scaffold types can enhance bone regeneration, multiple factors limit their level of success. To address this issue, this study evaluated a novel decellularized human adipose tissue (DAT) hydrogel as an alternative. In this study, DAT hydrogel alone, or in combination with adipose-derived stromal/stem cells (ASC), osteo-induced ASCs (OIASC), and hydroxyapatite were tested for their ability to mediate repair of a critical-sized (3 mm) femoral defect created in C57BL/6 mice. Micro-computed tomography results showed that all DAT hydrogel treated groups significantly enhanced bone regeneration, with OIASC + hydroxyapatite treated group displaying the most robust bone regeneration. Histological analyses revealed that all treatments resulted in significantly higher tissue areas with the relative mineralized tissue area significantly increased at 12 weeks; however, cartilaginous content was lowest among treatment groups with OIASC. Immunohistochemical analyses showed that DAT hydrogel enhanced collagen I and osteopontin expression, while the addition of OIASCs to the hydrogel reduced collagen II levels. Thus, DAT hydrogel promotes bone regeneration in a critical-sized femoral defect model that is further enhanced in the presence of OIASCs and hydroxyapatite.

Decellularized Adipose Tissue: Biochemical Composition, in vivo Analysis and Potential Clinical Applications

Decellularized tissues are gaining popularity as scaffolds for tissue engineering; they allow cell attachment, proliferation, differentiation, and are non-immunogenic. Adipose tissue is an abundant resource that can be decellularized and converted in to a bio-scaffold. Several methods have been developed for adipose tissue decellularization, typically starting with freeze thaw cycles, followed by washes with hypotonic/hypertonic sodium chloride solution, isopropanol, detergent (SDS, SDC and Triton X-100) and trypsin digestion. After decellularization, decellularized adipose tissue (DAT) can be converted into a powder, solution, foam, or sheet to allow for convenient subcutaneous implantation or to repair external injuries. Additionally, DAT bio-ink can be used to 3D print structures that closely resemble physiological tissues and organs. Proteomic analysis of DAT reveals that it is composed of collagens (I, III, IV, VI and VII), glycosaminoglycans, laminin, elastin, and fibronectin. It has also been found to retain growth factors like VEGF and bFGF after decellularization. DAT inherently promotes adipogenesis when seeded with adipose stem cells in vitro, and when DAT is implanted subcutaneously it is capable of recruiting host stem cells and forming adipose tissue in rodents. Furthermore, DAT has promoted healing in rat models of full-thickness skin wounds and peripheral nerve injury. These findings suggest that DAT is a promising candidate for repair of soft tissue defects, and is suitable for breast reconstruction post-mastectomy, wound healing, and adipose tissue regeneration. Moreover, since DAT's form and stiffness can be altered by physicochemical manipulation, it may prove suitable for engineering of additional soft and hard tissues.

Tissue-Engineered Grafts from Human Decellularized Extracellular Matrices: A Systematic Review and Future Perspectives

Tissue engineering and regenerative medicine involve many different artificial and biologic materials, frequently integrated in composite scaffolds, which can be repopulated with various cell types. One of the most promising scaffolds is decellularized allogeneic extracellular matrix (ECM) then recellularized by autologous or stem cells, in order to develop fully personalized clinical approaches. Decellularization protocols have to efficiently remove immunogenic cellular materials, maintaining the nonimmunogenic ECM, which is endowed with specific inductive/differentiating actions due to its architecture and bioactive factors. In the present paper, we review the available literature about the development of grafts from decellularized human tissues/organs. Human tissues may be obtained not only from surgery but also from cadavers, suggesting possible development of Human Tissue BioBanks from body donation programs. Many human tissues/organs have been decellularized for tissue engineering purposes, such as cartilage, bone, skeletal muscle, tendons, adipose tissue, heart, vessels, lung, dental pulp, intestine, liver, pancreas, kidney, gonads, uterus, childbirth products, cornea, and peripheral nerves. In vitro recellularizations have been reported with various cell types and procedures (seeding, injection, and perfusion). Conversely, studies about in vivo behaviour are poorly represented. Actually, the future challenge will be the development of human grafts to be implanted fully restored in all their structural/functional aspects.