Matrix alteration and not residual sodium dodecyl sulfate cytotoxicity affects the cellular repopulation of a decellularized matrix

Reconstruction of the human nipple-areolar complex: a tissue engineering approach

Introduction: Nipple-areolar complex (NAC) reconstruction after breast cancer surgery is challenging and does not always provide optimal long-term esthetic results. Therefore, generating a NAC using tissue engineering techniques, such as a decellularization-recellularization process, is an alternative option to recreate a specific 3D NAC morphological unit, which is then covered with an in vitro regenerated epidermis and, thereafter, skin-grafted on the reconstructed breast. Materials and methods: Human NACs were harvested from cadaveric donors and decellularized using sequential detergent baths. Cellular clearance and extracellular matrix (ECM) preservation were analyzed by histology, as well as by DNA, ECM proteins, growth factors, and residual sodium dodecyl sulfate (SDS) quantification. In vivo biocompatibility was evaluated 30 days after the subcutaneous implantation of native and decellularized human NACs in rats. In vitro scaffold cytocompatibility was assessed by static seeding of human fibroblasts on their hypodermal side for 7 days, while human keratinocytes were seeded on the scaffold epidermal side for 10 days by using the reconstructed human epidermis (RHE) technique to investigate the regeneration of a new epidermis. Results: The decellularized NAC showed a preserved 3D morphology and appeared white. After decellularization, a DNA reduction of 98.3% and the absence of nuclear and HLA staining in histological sections confirmed complete cellular clearance. The ECM architecture and main ECM proteins were preserved, associated with the detection and decrease in growth factors, while a very low amount of residual SDS was detected after decellularization. The decellularized scaffolds were in vivo biocompatible, fully revascularized, and did not induce the production of rat anti-human antibodies after 30 days of subcutaneous implantation. Scaffold in vitro cytocompatibility was confirmed by the increasing proliferation of seeded human fibroblasts during 7 days of culture, associated with a high number of living cells and a similar viability compared to the control cells after 7 days of static culture. Moreover, the RHE technique allowed us to recreate a keratinized pluristratified epithelium after 10 days of culture. Conclusion: Tissue engineering allowed us to create an acellular and biocompatible NAC with a preserved morphology, microarchitecture, and matrix proteins while maintaining their cell growth potential and ability to regenerate the skin epidermis. Thus, tissue engineering could provide a novel alternative to personalized and natural NAC reconstruction.

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.

A bioengineered in situ ovary (ISO) supports follicle engraftment and live-births post-chemotherapy

Female cancer patients who have undergone chemotherapy have an elevated risk of developing ovarian dysfunction and failure. Experimental approaches to treat iatrogenic infertility are evolving rapidly; however, challenges and risks remain that hinder clinical translation. Biomaterials have improved in vitro follicle maturation and in vivo transplantation in mice, but there has only been marginal success for early-stage human follicles. Here, we developed methods to obtain an ovarian-specific extracellular matrix hydrogel to facilitate follicle delivery and establish an in situ ovary (ISO), which offers a permissive environment to enhance follicle survival. We demonstrate sustainable follicle engraftment, natural pregnancy, and the birth of healthy pups after intraovarian microinjection of isolated exogenous follicles into chemotherapy-treated (CTx) mice. Our results confirm that hydrogel-based follicle microinjection could offer a minimally invasive delivery platform to enhance follicle integration for patients post-chemotherapy.

Personalized Scaffolds for Diabetic Foot Ulcer Healing Using Extracellular Matrix from Induced Pluripotent Stem-Reprogrammed Patient Cells

Diabetic foot ulcers (DFU) are chronic wounds sustained by pathological fibroblasts and aberrant extracellular matrix (ECM). Porous collagen-based scaffolds (CS) have shown clinical promise for treating DFUs but may benefit from functional enhancements. Our previous work showed fibroblasts differentiated from induced pluripotent stem cells are an effective source of new ECM mimicking fetal matrix, which notably promotes scar-free healing. Likewise, functionalizing CS with this rejuvenated ECM showed potential for DFU healing. Here, we demonstrate for the first time an approach to DFU healing using biopsied cells from DFU patients, reprogramming those cells, and functionalizing CS with patient-specific ECM as a personalized acellular tissue engineered scaffold. We took a two-pronged approach: 1) direct ECM blending into scaffold fabrication; and 2) seeding scaffolds with reprogrammed fibroblasts for ECM deposition followed by decellularization. The decellularization approach reduced cell number requirements and maintained naturally deposited ECM proteins. Both approaches showed enhanced ECM deposition from DFU fibroblasts. Decellularized scaffolds additionally enhanced glycosaminoglycan deposition and subsequent vascularization. Finally, reprogrammed ECM scaffolds from patient-matched DFU fibroblasts outperformed those from healthy fibroblasts in several metrics, suggesting ECM is in fact able to redirect resident pathological fibroblasts in DFUs towards healing, and a patient-specific ECM signature may be beneficial.

Detergent-Free Decellularization of Notochordal Cell-Derived Matrix Yields a Regenerative, Injectable, and Swellable Biomaterial

Porcine notochordal cell-derived matrix (NCM) has anti-inflammatory and regenerative effects on degenerated intervertebral discs. For its clinical use, safety must be assured. The porcine DNA is concerning because of (1) the transmission of endogenous retroviruses and (2) the inflammatory potential of cell-free DNA. Here, we present a simple, detergent-free protocol: tissue lyophilization lyses cells, and matrix integrity is preserved by limiting swelling during decellularization. DNA is digested quickly by a high nuclease concentration, followed by a short washout. Ninety-four percent of DNA was removed, and there was no loss of glycosaminoglycans or collagen. Forty-three percent of the total proteins remained in the decellularized NCM (dNCM). dNCM stimulated as much GAG production as NCM in nucleus pulposus cells but lost some anti-inflammatory effects. Reconstituted pulverized dNCM yielded a soft, shear-thinning biomaterial with a swelling ratio of 350% that also acted as an injectable cell carrier (cell viability >70%). dNCM can therefore be used as the basis for future biomaterials aimed at disc regeneration on a biological level and may restore joint mechanics by creating swelling pressure within the intervertebral disc.

Basement Membrane of Tissue Engineered Extracellular Matrix Scaffolds Modulates Rapid Human Endothelial Cell Recellularization and Promote Quiescent Behavior After Monolayer Formation

Off-the-shelf small diameter vascular grafts are an attractive alternative to eliminate the shortcomings of autologous tissues for vascular grafting. Bovine saphenous vein (SV) extracellular matrix (ECM) scaffolds are potentially ideal small diameter vascular grafts, due to their inherent architecture and signaling molecules capable of driving repopulating cell behavior and regeneration. However, harnessing this potential is predicated on the ability of the scaffold generation technique to maintain the delicate structure, composition, and associated functions of native vascular ECM. Previous de-cellularization methods have been uniformly demonstrated to disrupt the delicate basement membrane components of native vascular ECM. The antigen removal (AR) tissue processing method utilizes the protein chemistry principle of differential solubility to achieve a step-wise removal of antigens with similar physiochemical properties. Briefly, the cellular components of SV are permeabilized and the actomyosin crossbridges are relaxed, followed by lipophilic antigen removal, sarcomeric disassembly, hydrophilic antigen removal, nuclease digestion, and washout. Here, we demonstrate that bovine SV ECM scaffolds generated using the novel AR approach results in the retention of native basement membrane protein structure, composition (e.g., Collagen IV and laminin), and associated cell modulatory function. Presence of basement membrane proteins in AR vascular ECM scaffolds increases the rate of endothelial cell monolayer formation by enhancing cell migration and proliferation. Following monolayer formation, basement membrane proteins promote appropriate formation of adherence junction and apicobasal polarization, increasing the secretion of nitric oxide, and driving repopulating endothelial cells toward a quiescent phenotype. We conclude that the presence of an intact native vascular basement membrane in the AR SV ECM scaffolds modulates human endothelial cell quiescent monolayer formation which is essential for vessel homeostasis.

Aponeurosis discission, a low-detergent method for tissue-engineered acellular ligament scaffolds

Detergent treatment is the most commonly used method for the decellularization of ligaments and tendon grafts. However, it is well recognized that detergent treatment can also adversely affect the extracellular matrix. This study found that discission into the aponeurosis layer of the patellar tendon (PT) before decellularization is conducive to extracting cells from the PT using a low quantity of detergent in a short time period. The acellular aponeurosis discission ligament (AADL) retains its native collagen fibril structure and mechanical properties. Moreover, the PT retained cell and tissue compatibility in vitro and in vivo. After implantation into a defective allogeneic PT, we found that the AADL healed well in the host, and its collagen structure exhibited gradual improvement 12 months after implantation with satisfactory reconstruction. IMPACT: The aponeurosis of tendons/ligaments is the main barrier to achieving complete decellularization, and it thus prevents complete recellularization for applications in tissue engineering. Aponeurosis can obstruct the removal of cell components. We found that excising the aponeurosis before decellularization allows for the removal of cellular components with a reduced amount of detergent, thus improving the biological properties of the acellular ligament. To the best of our knowledge, no similar studies have been performed. Graphical abstract.

Small-diameter artery decellularization: Effects of anionic detergent concentration and treatment duration on porcine internal thoracic arteries

Engineered replacement materials have tremendous potential for vascular applications where over 400,000 damaged and diseased blood vessels are replaced annually in the United States alone. Unlike large diameter blood vessels, which are effectively replaced by synthetic materials, prosthetic small-diameter vessels are prone to early failure, restenosis, and reintervention surgery. We investigated the differential response of varying 0%-6% sodium dodecyl sulfate and sodium deoxycholate anionic detergent concentrations after 24 and 72 h in the presence of DNase using biochemical, histological, and biaxial mechanical analyses to optimize the decellularization process for xenogeneic vascular tissue sources, specifically the porcine internal thoracic artery (ITA). Detergent concentrations greater than 1% were successful at removing cytoplasmic and cell surface proteins but not DNA content after 24 h. A progressive increase in porosity and decrease in glycosaminoglycan (GAG) content was observed with detergent concentration. Augmented porosity was likely due to the removal of both cells and GAGs and could influence recellularization strategies. The treatment duration on the other hand, significantly improved decellularization by reducing DNA content to trace amounts after 72 h. Prolonged treatment times reduced laminin content and influenced the vessel's mechanical behavior in terms of altered circumferential stress and stretch while further increasing porosity. Collectively, DNase with 1% detergent for 72 h provided an effective and efficient decellularization strategy to be employed in the preparation of porcine ITAs as bypass graft scaffolding materials with minor biomechanical and histological penalties.

Fluorescently visualizing the penetration of anionic surfactants across cytoplasmic membrane and the subsequent damage on human cells

The extensive application of chemically synthesized anionic surfactants would cause serious pollution of water and increase health risk to humans. However, the adverse impact of anionic surfactant on human cells has never been systematically demonstrated. In this paper, a series of fluorescent anionic surfactants containing a varying length of alkyl chain from C8 to C18 and a fixed hydrophilic head of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) were synthesized and utilized for visualizing the interaction between surfactants and cells. The obtained molecules exhibited blue fluorescence presenting a decreasing fluorescent intensity with the increasing length of alkyl chain from C8 to C18 while showed the same sequence of HPTS-C16>HPTS-C18>HPTS-C12>HPTS-C8 on either surface activity, cellular adsorption, or cytotoxicity. In opposite, HPTS which contained no hydrophobic chain and thus exhibited no surface activity showed no cellular adsorption and cytotoxicity. It seems that the ligand of the appropriate chain length (C16) onto the hydrophilic HPTS molecules could cause the largest surface activity, the most distinguished cellular adsorption as well as the most adverse cytotoxicity. As reflected by the dynamic fluorescent visualization, the surfactant molecules of HPTS-C16 initially bound with cell membrane and entered into the intracellular lumen before finally localized at the endoplasmic reticulum (ER) and damaged it into a swollen structure. It is most likely that the structure of hydrophobic chain could determine the surface activities of surfactants and hence affect their cellular uptake and cytotoxicity. This study could help us to understand the adverse impact of anionic surfactant on human cells and its correlation with the surface activities or, in another word, the hydrophobic chain length.

Effect of ethanol washing on porcine pulmonary artery wall decellularization using sodium dodecyl sulfate

BACKGROUND

To determine the effectiveness of ethanol (EtOH) washing on porcine pulmonary artery (PA) wall decellularization using sodium dodecyl sulfate (SDS), we compared three different washing methods (phosphate-buffered saline [PBS], pH 9 alkali, and EtOH washing).

METHODS

Fresh porcine PA walls were decellularized using 0.5% SDS and 0.5% sodium deoxycholate (SDC). The decellularized tissues were rinsed using three different washing techniques. Histological, biochemical, and mechanical analyses were conducted. Implantation into the subcutaneous tissue of rats and patch implantation into the carotid artery of dogs were performed as preliminary in vivo studies.

RESULTS

The decellularization protocol based on SDS and SDC effectively removed the cells. The major extracellular matrix (ECM) structures (collagen, elastic fiber, and glycosaminoglycan) were properly preserved with the 75% EtOH-washing method. Significantly reduced residual SDS content was identified in EtOH-washed tissues compared to that in the other methods. No significant difference in the mechanical strength test was observed between the washing methods, and the EtOH-washing method showed better results in the metabolic activity test compared to the PBS-washing method. In the rat study model, no acute rejection or massive calcification was observed. The in vivo preliminary canine study showed better cell repopulation in the EtOH-washed group.

CONCLUSION

EtOH washing of SDS-based decellularized porcine PA wall can reduce the residual SDS content and preserve ECM structures, especially the elastin content, and could also enhance cell repopulation after re-implantation.

The spatial form periosteal-bone complex promotes bone regeneration by coordinating macrophage polarization and osteogenic-angiogenic events

Bone defects associated with soft tissue injuries are an important cause of deformity that threatens people’s health and quality of life. Although bone substitutes have been extensively explored, effective biomaterials that can coordinate early inflammation regulation and subsequent repair events are still lacking. We prepared a spatial form periosteal bone extracellular matrix (ECM) scaffold, which has advantages in terms of low immunogenicity, good retention of bioactive ingredients, and a natural spatial structure. The periosteal bone ECM scaffold with the relatively low-stiffness periosteum (41.6 ± 3.7 kPa) could inhibit iNOS and IL-1β expression, which might be related to actin-mediated YAP translocation. It also helped to promote CD206 expression with the potential influence of proteins related to immune regulation. Moreover, the scaffold combined the excellent properties of decalcified bone and periosteum, promoted the formation of blood vessels, and good osteogenic differentiation (RUNX2, Col 1α1, ALP, OPN, and OCN), and achieved good repair of a cranial defect in rats. This scaffold, with its natural structural and biological advantages, provides a new idea for bone healing treatment that is aligned with bone physiology.

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We provided a spatial form periosteal-bone complex.

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The scaffold preserved major biological components and spatial structure.

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The periosteum part of the scaffold acted as a physical barrier.

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The scaffold participated in the transformation of the macrophage phenotype.

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The scaffold promoted osteogenesis and angiogenesis.

Preparation and biological characteristics of a bovine acellular tendon fiber material

Acellular tendon matrix is an ideal substitute for constructing tissue engineering ligaments, but using detergents causes damage to collagen and fibrin during the process of decellularization. In this study, fresh tendons were lyophilized and separated into fresh tendon fiber (FTF) bundles, and then the cellular components in FTF were removed to prepare acellular tendon fiber (ATF) without adding chemical detergent. H&E staining and DAPI fluorescence microscopy showed no nucleus and DNA residue. Compared with FTFs, the DNA content of ATFs was significantly lower without the collagen content change before and after decellularization. The microstructure of collagen fibrils in ATFs was intact under scanning electron microscopy (SEM), and the maximum tensile load and elastic modulus between FTFs and ATFs were not statistically different. The ATF bundles were cultured with SD rat tenocytes for 72 hr and cells attachment to fiber surfaces were observed under SEM. ATF bundles were then implanted into paraspinal muscles, and histological analysis showed fibroblast-like cells within the ATFs and was similar to the control group (fresh tendon autograft) in morphology. H&E staining showed that the number of lymphocytes and plasma cells in ATF was less than that in fresh tendon autograft. ATF bundles were twisted into linear fiber materials by hand, of which the maximum breaking strength was similar to silk with same diameter. These findings demonstrated that ATFs retain their original fibril structure and mechanical properties after decellularization by trypsin and pancreatic deoxyribonuclease without detergent. Lyophilized ATFs linear fiber material provides the possibility of preparing personalized ligament and other tissue engineering scaffolds.

Sonication-Assisted Method for Decellularization of Human Umbilical Artery for Small-Caliber Vascular Tissue Engineering

Decellularized vascular grafts are useful for the construction of biological small-diameter tissue-engineered vascular grafts (≤6 mm). Traditional chemical decellularization requires a long treatment time, which may damage the structure and alter the mechanical properties. Decellularization using sonication is expected to solve this problem. The aim of this study was to develop an effective decellularization method using ultrasound followed by washing. Different power values of sonication at 40 kHz were tested for 2, 4, and 8 h followed by a washing procedure. The efficacy of sonication of decellularized human umbilical artery (sDHUA) was evaluated via DNA content, histological staining, mechanical properties, and biocompatibility. The sDHUAs were further implanted into rats for up to 90 days and magnetic resonance angiography (MRA) was performed for the implanted grafts. The results demonstrated that treatment of human umbilical artery (HUA) by sonication at ultrasonic power of 204 W for 4 h followed by washing for 24 h in 2% SDS buffer could eliminate more than 90% of cells and retain similar mechanical properties of the HUA. Recellularization was assessed by scanning electron microscopy (SEM), which indicated that sDHUA provided niches for human umbilical vein endothelial cells (HUVECs) to reside, indicating in vitro cytocompatibility. Further implantation tests also indicated the fitness of the sonication-treated HUA as a scaffold for small-caliber tissue engineering vascular grafts.

An efficient protocol for decellularization of the human endometrial fragments for clinical usage

The present study was aimed to compare different decellularization protocols for human endometrial fragments. The freeze-thaw cycles in combination with treatment by Triton X-100 and four concentrations of sodium dodecyl sulfate (SDS; 0.1, 0.5, 1, and 1.5%) with two exposure times (24 and 72 h) were applied for tissues decellularization. After analysis the morphology and DNA content of tissues the group with better morphology and lower DNA content was selected for further assessments. The nucleus by Acridine orange and extracellular matrix (ECM) using Masson's trichrome, Alcian blue, and periodic acid-Schiff staining were studied. The amount of tissues collagen types I and IV, fibronectin, glycosaminoglycans (GAGs), and elastin was analyzed by Raman spectroscopy. The ultrastructure and porosity of decellularized scaffold were studied by scanning electron microscopy (SEM). The MTT assay was applied for assessments of cytotoxicity of scaffold. The treated group with 1% SDS for 72 h showed the morphology similar to native control in having the minimum level of DNA and well preserved ECM. Raman spectroscopy results demonstrated, the amount of collagen types I and IV, GAG, and fibronectin was not significantly different in decellularized scaffold compared with native group but the elastin protein level was significantly decreased (P < 0.001). SEM micrographs also showed a porous and fiber rich ECM in decellularized sample similar to the native control. This combined protocol for decellularization of human endometrial tissue is effective and it could be suitable for recellularization and clinical applications in the future.

Detection of the residual concentration of sodium dodecyl sulfate in the decellularized whole rabbit kidney extracellular matrix

To optimize rabbit kidney decellularization protocol, using sodium dodecyl sulfate (SDS) as a commonly used detergent, a methylene blue based assay was employed for detecting the minimum nontoxic SDS level for future cell seeding. The rabbit kidney tissues were decellularized with the perfusion-based method and underwent several investigations to determine the efficacy of decellularization in preserving the extracellular matrix (ECM) and cell removal. SDS detection was performed by incubating with methylene blue and subsequent extraction with chloroform. MTT (3-(4, 5-dimethylthiazol-2-yr)-2,5-diphenyltetrazolium bromide) assay and SDS release were also evaluated during the entire process. After the first washing cycle, SDS concentration was 0.036, in 500 mL of the washing liquid, which slowly decreased and reached to 0.009 % after at the end of seventh washing cycle. In the 9th cycle, SDS was gradually decreased and reached to 0.003 %. SDS was significantly released after one week of incubation which ceased after ten washing cycles. The results of MTT assay demonstrated that different cells exhibited various sensitivity levels when exposed to serial concentrations of SDS. Human embryonic kidney cells (HEK293) with 0.003 % threshold for cellular toxicity and 87.4 % cell viability were more resistant compared with mesenchymal stem cells with 0.001 % threshold and 85.4 % cell viability. Colorimetric assay with methylene blue is a straightforward and non-invasive method to detect residual SDS present in tissue and can also prevent ECM destruction after several washings for detergent removal from decellularized tissues.

In vitro recellularization of decellularized bovine carotid arteries using human endothelial colony forming cells

BACKGROUND

Many patients suffering from peripheral arterial disease (PAD) are dependent on bypass surgery. However, in some patients no suitable replacements (i.e. autologous or prosthetic bypass grafts) are available. Advances have been made to develop autologous tissue engineered vascular grafts (TEVG) using endothelial colony forming cells (ECFC) obtained by peripheral blood draw in large animal trials. Clinical translation of this technique, however, still requires additional data for usability of isolated ECFC from high cardiovascular risk patients. Bovine carotid arteries (BCA) were decellularized using a combined SDS (sodium dodecyl sulfate) -free mechanical-osmotic-enzymatic-detergent approach to show the feasibility of xenogenous vessel decellularization. Decellularized BCA chips were seeded with human ECFC, isolated from a high cardiovascular risk patient group, suffering from diabetes, hypertension and/or chronic renal failure. ECFC were cultured alone or in coculture with rat or human mesenchymal stromal cells (rMSC/hMSC). Decellularized BCA chips were evaluated for biochemical, histological and mechanical properties. Successful isolation of ECFC and recellularization capabilities were analyzed by histology.

RESULTS

Decellularized BCA showed retained extracellular matrix (ECM) composition and mechanical properties upon cell removal. Isolation of ECFC from the intended target group was successfully performed (80% isolation efficiency). Isolated cells showed a typical ECFC-phenotype. Upon recellularization, co-seeding of patient-isolated ECFC with rMSC/hMSC and further incubation was successful for 14 (n = 9) and 23 (n = 5) days. Reendothelialization (rMSC) and partial reendothelialization (hMSC) was achieved. Seeded cells were CD31 and vWF positive, however, human cells were detectable for up to 14 days in xenogenic cell-culture only. Seeding of ECFC without rMSC was not successful.

CONCLUSION

Using our refined decellularization process we generated easily obtainable TEVG with retained ECM- and mechanical quality, serving as a platform to develop small-diameter (< 6 mm) TEVG. ECFC isolation from the cardiovascular risk target group is possible and sufficient. Survival of diabetic ECFC appears to be highly dependent on perivascular support by rMSC/hMSC under static conditions. ECFC survival was limited to 14 days post seeding.

Optimization of extracellular matrix extraction from human perirenal adipose tissue

Human adipose tissue includes useful substrates for regenerative medicine such as the extracellular matrix (ECM), but most perirenal fat tissue is wasted after kidney surgery. Since a lot of adipose tissue can be procured after a kidney, we extracted ECM from human perirenal adipose tissue and optimized the extraction process. To verify the efficacy for ECM extraction, we compared the products in several steps. Perirenal adipose tissue was either finely homogenized or underwent crude manual dissection. The amount of extracted ECM was quantified with ELISA for verification of the initial tissue downsizing effect. To validate the drying effect for fast and complete delipidation, tissues were prepared in a dry or wet phase, and residual lipids were visualized with Oil-Red-O staining. The extracted lipid was assayed at each time point to quantify the appropriate delipidation time. To select the optimal decellularization method, tissues were treated with physical, chemical, or enzymatic method, and the residual cell debris were identified with histological staining. The biochemical properties of the ECM extracted by the above methods were analyzed. The ECM extracted by fine homogenization showed a significantly enhanced amount of collagen, laminin and fibronectin compared to the crude dissection method. The dried tissue showed fast and complete lipid elimination compared to the wet tissue. Complete delipidation was achieved at 45 min after acetone treatment. Additionally, 1% triton X-100 chemical treatment showed complete decellularization with well-preserved collagen fibers. Biochemical analysis revealed preserved ECM proteins, a high cell proliferation rate and normal cell morphology without cell debris or lipids. The established process of homogenization, drying, delipidation with acetone, and decellularization with Triton X-100 treatment can be an optimal method for ECM extraction from human perirenal adipose tissue. Using this technique, human perirenal adipose tissue may be a valuable source for tissue engineering and regenerative medicine.

A novel 3D histotypic cartilage construct engineered by supercritical carbon dioxide decellularized porcine nasal cartilage graft and chondrocytes exhibited chondrogenic capability in vitro

Augmentative and reconstructive rhinoplasty surgical procedures use autologous tissue grafts or synthetic grafts to repair the nasal defect and aesthetic reconstruction. Donor site trauma and morbidity are common in autologous grafts. The desperate need for the production of grafted 3D cartilage tissues as rhinoplasty grafts without the adverse effect is the need of the hour. In the present study, we developed a bioactive 3D histotypic construct engineered with the various ratio of adipose-derived stem cells (ADSC) and chondrocytes together with decellularized porcine nasal cartilage graft (dPNCG). We decellularized porcine nasal cartilage using supercritical carbon dioxide (SCCO2) extraction technology. dPNCG was characterized by H&E, DAPI, alcian blue staining, scanning electron microscopy and residual DNA content, which demonstrated complete decellularization. 3D histotypic constructs were engineered using dPNCG, rat ADSC and chondrocytes with different percentage of cells and cultured for 21 days. dPNCG together with 100% chondrocytes produced a solid mass of 3D histotypic cartilage with significant production of glycosaminoglycans. H&E and alcian blue staining showed an intact mass, with cartilage granules bound to one another by extracellular matrix and proteoglycan, to form a 3D structure. Besides, the expression of chondrogenic markers, type II collagen, aggrecan and SOX-9 were elevated indicating chondrocytes cultured on dPNCG substrate facilitates the synthesis of type II collagen along with extracellular matrix to produce 3D histotypic cartilage. To conclude, dPNCG is an excellent substrate scaffold that might offer a suitable environment for chondrocytes to produce 3D histotypic cartilage. This engineered 3D construct might serve as a promising future candidate for cartilage tissue engineering in rhinoplasty.

Characterization of Porcine Urinary Bladder Matrix Hydrogels from Sodium Dodecyl Sulfate Decellularization Method

Urinary bladder matrix (UBM) is one of the most studied extracellular matrixes (ECM) in the tissue engineering field. Although almost all of the UBM hydrogels were prepared by using peracetic acid (PAA), recent studies indicated that PAA was not a trustworthy way to decellularize UBM. A stronger detergent, such as sodium dodecyl sulfate (SDS), may help tackle this issue; however, its effects on the hydrogels’ characteristics remain unknown. Therefore, the objective of this study was to develop a more reliable protocol to decellularize UBM, using SDS, and to compare the characteristics of hydrogels obtained from this method to the widely employed technique, using PAA. The results indicated that SDS was superior to PAA in decellularization efficacy. Different decellularization methods led to dissimilar gelation kinetics; however, the methods did not affect other hydrogel characteristics in terms of biochemical composition, surface morphology and rheological properties. The SDS-treated hydrogels possessed excellent cytocompatibility in vitro. These results showed that the SDS decellularization method could offer a more stable and safer way to obtain acellular UBM, due to reducing immunogenicity. The hydrogels prepared from this technique had comparable characteristics as those from PAA and could be a potential candidate as a scaffold for tissue remodeling.

Fabrication of Decellularized Engineered Extracellular Matrix through Bioreactor-Based Environment for Bone Tissue Engineering

Extracellular matrix (ECM)-contained grafts can be achieved by decellularization of native bones or synthetic scaffolds. Limitations associated with harvesting the native bone has raised interest in preparing in vitro ECM bioscaffold for bone tissue engineering. Here, we intend to develop an ECM-contained construct via decellularizing an engineered gelatin-coated β-tricalcium phosphate (gTCP) scaffold. In order to find an optimal protocol for decellularization of cell-loaded gTCP scaffolds, they were seeded with buccal fat pad-derived stem cells. Then, four decellularization protocols including sodium dodecyl sulfate, trypsin, Triton X-100, and combined solution methods were compared for the amounts of residual cells and remnant collagen and alteration of scaffold structure. Then, the efficacy of the selected protocol in removing cells from gTCP scaffolds incubated in a rotating and perfusion bioreactor for 24 days was evaluated and compared with static condition using histological analysis. Finally, decellularized scaffolds, reloaded with cells, and their cytotoxicity and osteoinductive capability were evaluated. Complete removal of cells from gTCP scaffolds was achieved from all protocols. However, treatment with Triton X-100 showed significantly higher amount of remnant ECM. Bioreactor-incubated scaffolds possessed greater magnitude of ECM proteins including collagen and glycosaminoglycans. Reseeding the decellularized scaffolds also represented higher osteoinductivity of bioreactor-based scaffolds. Application of Triton X-100 as decellularization protocol and usage of bioreactors are suggested as a suitable technique for designing ECM-contained grafts for bone tissue engineering.

Re-endothelialization of non-detergent decellularized porcine vessels

Tissue engineering utilizes an interdisciplinary approach to generate constructs for the treatment and repair of diseased organs. Generation of small vessels as vascular grafts or as envisioned central vessel for vascularized constructs is still a challenge. Here, the decellularization of porcine vessels by a non-detergent based protocol was developed and investigated. Perfusion-decellularization with sodium hydroxide solution resulted in removal of cellular material throughout the whole length of the vessel while preserving structural and mechanical integrity. A re-endothelialization of the retrieved matrix with human umbilical vein endothelial cells and cardiac endothelial cells was achieved through rotation-based seeding employing a custom-made bioreactor. A confluent monolayer was detected on the entire luminal surface. Thus, a non-detergent-based decellularization method allowing the re-endothelialization of the luminal surface was developed in this study, thereby paving the way for future implementation of the resulting construct as vascular graft or as central vessel for tissue engineered constructs in need of a perfusion system with readily available anastomosis sites.

Improved the biocompatibility of cancellous bone with compound physicochemical decellularization process

Due to the unique microstructures and components of extracellular matrix (ECM), decellularized scaffolds had been used widely in clinical. The reaction of the host toward decellularized scaffolds depends on their biocompatibility, which should be satisfied before applied in clinical. The aim of this study is to develop a decellularized xenograft material with good biocompatibility for further bone repair, in an effective and gentle method. The existing chemical and physical decellularization techniques including ethylene diamine tetraacetic acid (EDTA), sodium dodecyl sulfate (SDS) and supercritical carbon dioxide (SC-CO2) were combined and modified to decellularize bovine cancellous bone (CB). After decellularization, almost 100% of ɑ-Gal epitopes were removed, the combination of collagen, calcium and phosphate was reserved. The direct and indirect contact with macrophages was used to evaluate the cytotoxicity and immunological response of the materials. Mesenchymal stem cells (MSCs) were used in the in vitro cells’ proliferation assay. The decellularized CB was proved has no cytotoxicity (grade 1) and no immunological response (NO, IL-2, IL-6 and TNF-α secretion inhibited), and could support MSCs proliferated continuedly. These results were similar to that of commercial decellularized human bone. This study suggests the potential of using this kind of combine decellularization process to fabricate heterogeneous ECM scaffolds for clinical application.

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

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

Limitations of recellularized biological scaffolds for human transplantation

A shortage of donor organs for transplantation and the dependence of the recipients on immunosuppressive therapy have motivated researchers to consider alternative regenerative approaches. The answer may reside in acellular scaffolds generated from cadaveric human and animal tissues. Acellular scaffolds are expected to preserve the architectural and mechanical properties of the original organ, permitting cell attachment, growth, and differentiation. Although theoretically, the use of acellular scaffolds for transplantation should pose no threat to the recipient's immune system, experimental data have revealed significant immune responses to allogeneic and xenogeneic transplanted scaffolds. Herein, we review the various factors of the scaffold that could trigger an inflammatory and/or immune response, thereby compromising its use for human transplant therapy. In addition, we provide an overview of the major cell types that have been considered for recellularization of the scaffold and their potential contribution to triggering an immune response.

The impact of decellularization methods on extracellular matrix derived hydrogels

Tissue-derived decellularized biomaterials are ideal for tissue engineering applications as they mimic the biochemical composition of the native tissue. These materials can be used as hydrogels for cell encapsulation and delivery. The decellularization process can alter the composition of the extracellular matrix (ECM) and thus influence the hydrogels characteristics. The aim of this study was to examine the impact of decellularization protocols in ECM-derived hydrogels obtained from porcine corneas. Porcine corneas were isolated and decellularized with SDS, Triton X-100 or by freeze-thaw cycles. All decellularization methods decreased DNA significantly when measured by PicoGreen and visually assessed by the absence of cell nuclei. Collagen and other ECM components were highly retained, as quantified by hydroxyproline content and sGAG, by histological analysis and by SDS-PAGE. Hydrogels obtained by freeze-thaw decellularization were the most transparent. The method of decellularization impacted gelation kinetics assessed by turbidimetric analysis. All hydrogels showed a fibrillary and porous structure determined by cryoSEM. Human corneal stromal cells were embedded in the hydrogels to assess cytotoxicity. SDS decellularization rendered cytotoxic hydrogels, while the other decellularization methods produced highly cytocompatible hydrogels. Freeze-thaw decellularization produced hydrogels with the overall best properties.

Regenerative Materials for Surgical Reconstruction: Current Spectrum of Materials and a Proposed Method for Classification

Chronic wound management is an enormous economic strain and quality-of-life issue for patients. Current treatments are ineffective or expensive and invasive. Materials (native and artificial) can act as the basis to enhance wound repair but often fall short of complete healing. The therapeutic index of materials have often been enhanced by combining them with drug or biologic elution technologies. Combination of materials with living drugs (cells) presents a new paradigm for enhancing therapy. Cell material interaction and therapeutic output will depend on variables ascribed to the living drug as well as variables ascribed to the underlying matrix. In this article, we review medical matrices currently approved by the US Food and Drug Administration (FDA) that would likely be the first generation of materials to be used in this manner. Currently there are hundreds of different materials on the market. Identification of the right combinations would benefit from a classification scheme to group materials with similar composition or derivation. We provide a classification scheme and FDA documentation references that should provide researchers and clinicians a starting point for testing these materials in the laboratory and rapidly transitioning cell therapies to the bedside.

Evaluation of vacuum washing in the removal of SDS from decellularized bovine pericardium: method and device description

Aims

The aim of this study was to present a new method for removing Sodium dodecyl sulfate (SDS) detergent from decellularized bovine pericardium using vacuum.

Materials and Methods

The cows' pericardia were collected and decellularized. The samples were incubated with SDS1% for 48 h at 40 °C. To perform vacuum washing (VW: negative pressure was used to wash and remove detergents), every decellularized tissue was cut in 75mm diameter and fixed via a stainless-steel ring with 60mm diameter in the center of filtration Buchner Funnel which was connected to glass filtration flask The system was connected to a vacuum pump by a hose, and a negative pressure of -100 mmHg was applied for 15 min. Then, the samples were shaken and washed at 40-rpm in 100 ml of distilled water for 45 min. This process was repeated for samples of each group (6 times for sample VW6h, 12 times for sample VW12h, and 24 times for sample VW24h). At the end of every cycle, the effluent was collected to take a sample for SDS measurement. The normal washing (NW) group containing distilled water (NWd) and PBS (Phosphate buffered saline) (NWp) were used to wash and remove detergents. SDS measurements, MTT Assay, histological and tensile test, to compare two methods were used.

Results

The highest SDS in the effluent was in groups VW12h and VW24h (P ≤ 0.001) and the lowest residual SDS in scaffold was in two groups of VW12h and VW24h (P ≤ 0.001). MTT assay showed that cell survival in the VW12h and VW24h groups was higher than other groups and there' was no significant difference between cell survival in the VW12h and VW24h groups. Histological study showed destruction of tissue in the VW24h group. The results of the tensile test were shown that the native group had the highest module and the lowest amount was the VW24h sample which was reported with P ≤ 0.001 significance for all groups.

Conclusion

VW12h can be used as an effective method for SDS removal from decellularized pericardium which morphologically demonstrated a good structure in ECM.

An overview of decellularisation techniques of native tissues and tissue engineered products for bone, ligament and tendon regeneration

Decellularised tissues and organs have been successfully used in a variety of tissue engineering/regenerative medicine applications. Because of the complexity of each tissue (size, porosity, extracellular matrix (ECM) composition etc.), there is no standardised protocol and the decellularisation methods vary widely, thus leading to heterogeneous outcomes. Physical, chemical, and enzymatic methods have been developed and optimised for each specific application and this review describes the most common strategies utilised to achieve decellularisation of soft and hard tissues. While removal of the DNA is the primary goal of decellularisation, it is generally achieved at the expense of ECM preservation due to the harsh chemical or enzymatic processing conditions. As denaturation of the native ECM has been associated with undesired host responses, decellularisation conditions aimed at effectively achieving simultaneous DNA removal and minimal ECM damage will be highlighted. Additionally, the utilisation of decellularised matrices in regenerative medicine is explored, as are the most recent strategies implemented to circumvent challenges in this field. In summary, this review focusses on the latest advancements and future perspectives in the utilisation of natural ECM for the decoration of synthetic porous scaffolds.

Graft-specific immune tolerance is determined by residual antigenicity of xenogeneic extracellular matrix scaffolds

Antigenicity remains the primary barrier towards expanding the use of unfixed xenogeneic biomaterials in clinical applications. An unfixed xenogeneic biomaterial devoid of antigenicity, with maintained structural and mechanical integrity, has potential to overcome the limitations of current clinically utilized glutaraldehyde-fixed xenogeneic biomaterials, such as heart valve bioprostheses. Unfortunately, the threshold level of residual antigenicity necessary to overcome graft-specific immune responses in unfixed xenogeneic tissue has yet to be determined. Furthermore, little information is known regarding the extent to which in vitro disruption of native ECM properties, resulting from decellularization or antigen removal procedures, are tolerated following in vivo implantation. This manuscript demonstrates that humoral adaptive immune responses are more sensitive to residual xenogeneic biomaterial antigen content than are cell-mediated adaptive responses. Critically, the threshold for tolerable residual antigenicity is identified, with removal of ≥92% of lipophilic antigens required to reduce adaptive immune responses to levels equivalent to glutaraldehyde fixed tissue. Finally, the results demonstrated that the innate immune system tolerates minor changes in protein organization provided that molecular structure is maintained. Antigen removed xenogeneic biomaterials achieving these in vitro success criteria induce in vivo adaptive and innate tolerance, while modulating pro-regenerative constructive remodeling.

STATEMENT OF SIGNIFICANCE

Removal of antigenic components from candidate xenogeneic biomaterials is the primary success criteria for development of extracellular matrix (ECM) scaffolds in tissue engineering applications. Currently, the threshold level of residual biomaterial antigenicity required to overcome recipient graft-specific adaptive immune responses is unknown. Additionally, the extent to which the innate immune response tolerates changes to the native ECM, resulting from the ECM scaffold production process, has yet to be determined. This manuscript not only establishes the threshold for tolerable residual antigenicity, but also demonstrates that deviations in protein organization are tolerated by the innate immune system, provided macromolecular structure remains intact. In doing so, we provide the foundation of an immunologically-acceptable unfixed xenogeneic biomaterial for use in clinical applications.

Growth Factor-Mediated Tenogenic Induction of Multipotent Mesenchymal Stromal Cells Is Altered by the Microenvironment of Tendon Matrix

Age-related degenerative changes in tendon tissue represent a common cause for acute tendon pathologies. Although the regenerative potential of multipotent mesenchymal stromal cells (MSC) was reported to restore functionality in injured tendon tissue, cellular mechanisms of action remain partly unclear. Potential tenogenic differentiation of applied MSC is affected by various intrinsic and extrinsic factors. The current study presents an in vitro model to evaluate the combined extrinsic effects of decellularized equine tendon matrix, transforming growth factor beta 3 (TGFβ3) and bone morphogenetic protein 12 (BMP12) on the tenogenic fate of equine adipose tissue-derived MSC. Monolayer MSC cultures supplemented with TGFβ3 and BMP12 as well as MSC cultured on tendon matrix scaffolds preloaded with the growth factors were incubated for 3 and 5 days. Histological evaluation and real time reverse transcription polymerase chain reaction (RT-PCR) revealed that growth factor-mediated tenogenic induction of MSC was modified by the conditions of the surrounding microenvironment. While the gene expression pattern in monolayer cultures supplemented with TGFβ3 or TGFβ3 and BMP12 revealed an upregulation for collagen 1A2, collagen 3A1, tenascin c, scleraxis and mohawk (p < 0.05), the presence of tendon matrix led to an upregulation of decorin and osteopontin as well as to a downregulation of smad8 (p < 0.05). Preloading of scaffolds with either TGFβ3, or with TGFβ3 and BMP12 promoted a tenocyte-like phenotype and improved cell alignment. Furthermore, gene expression in scaffold culture was modulated by TGFβ3 and/or BMP12, with downregulation of collagen 1A2, collagen 3A1, decorin, scleraxis, smad8 and osteopontin, whereas gene expression of tenascin c was increased. This study shows that growth factor-induced tenogenic differentiation of equine MSC is markedly altered by topographical constraints of decellularized tendon tissue in vitro. While TGFβ3 represents an effective mediator for tenogenic induction, the role of BMP12 in tenogenesis may be of modulatory character and needs further evaluation.

Complex bile duct network formation within liver decellularized extracellular matrix hydrogels

The biliary tree is an essential component of transplantable human liver tissue. Despite recent advances in liver tissue engineering, attempts at re-creating the intrahepatic biliary tree have not progressed significantly. The finer branches of the biliary tree are structurally and functionally complex and heterogeneous and require harnessing innate developmental processes for their regrowth. Here we demonstrate the ability of decellularized liver extracellular matrix (dECM) hydrogels to induce the in vitro formation of complex biliary networks using encapsulated immortalized mouse small biliary epithelial cells (cholangiocytes). This phenomenon is not observed using immortalized mouse large cholangiocytes, or with purified collagen 1 gels or Matrigel. We also show phenotypic stability via immunostaining for specific cholangiocyte markers. Moreover, tight junction formation and maturation was observed to occur between cholangiocytes, exhibiting polarization and transporter activity. To better define the mechanism of duct formation, we utilized three fluorescently labeled, but otherwise identical populations of cholangiocytes. The cells, in a proximity dependent manner, either branch out clonally, radiating from a single nucleation point, or assemble into multi-colored structures arising from separate populations. These findings present liver dECM as a promising biomaterial for intrahepatic bile duct tissue engineering and as a tool to study duct remodeling in vitro.

Evaluation of recellularization on decellularized aorta scaffolds engineered by ultrasonication treatment

Aortic scaffolds prepared using sonication decellularization treatment has provided a successful medium for repopulation with vascular smooth muscle cells (VSMCs). The objective of this study is to explore the potential of tissue decellularization using ultrasonication treatment and its recellularization before implantation of the cell-seeded scaffolds into host. Aorta tissue samples are decellularized in 2% SDS with sonication for 10 hours and compared with the native tissues. The 4',6-diamidino-2-phenylindole (DAPI) staining was used to evaluate the decellularization and Hematoxylin-Eosin (H-E) staining was used to compare the VSMCs infiltrations onto the decellularized tissues at day-0 and day-6 after cell-seeding. The results histologically showed complete DNA removal from scaffolds after decellularization and subsequent recellularization resulted in successful VSMCs infiltration. Accordingly, the decellularized tissues treated with 2% SDS in sonication demonstrated successful VSMCs repopulation afterward and is speculated to have less toxicity and able to be effectively implanted into host.

Recellularization of Decellularized Venous Grafts Using Peripheral Blood: A Critical Evaluation

Vascular disease is a major cause of death worldwide, and the growing need for replacement vessels is not fully met by autologous grafts or completely synthetic alternatives. Tissue engineering has emerged as a compelling strategy for the creation of blood vessels for reconstructive surgeries. One promising method to obtain a suitable vessel scaffold is decellularization of donor vascular tissue followed by recellularization with autologous cells. To prevent thrombosis of vascular grafts, a confluent and functional autologous endothelium is required, and researchers are still looking for the optimal cell source and recellularization procedure. Recellularization of a decellularized scaffold with only a small volume of whole blood was recently put forward as a feasible option. Here we show that, in contrast to the published results, this method fails to re-endothelialize decellularized veins. Only occasional nucleated cells were seen on the luminal surface of the scaffolds. Instead, we saw fibrin threads, platelets and scattered erythrocytes. Molecular remnants of the endothelial cells were still attached to the scaffold, which explains in part why earlier results were misinterpreted. Decellularized vascular tissues may still be the best scaffolds available for vascular tissue engineering. However, for the establishment of an adequate autologous endothelial lining, methods other than exposure to autologous whole blood need to be developed.

Whole Cardiac Tissue Bioscaffolds

Bioscaffolds serve as structures for cells in building complex tissues and full organs including heart. Decellularizing cardiac tissue results in cell-free extracellular matrix (ECM) that can be used as a cardiac tissue bioscaffold. The field of whole-heart tissue engineering has been revolutionized since the 2008 publication of the first perfusion-decellularized whole heart, and since then, studies have shown how decellularized cardiac tissue retains its native architecture and biochemistry following recellularization. Chemical, enzymatic, and physical decellularization methods preserve the ECM to varying degrees with the widely accepted standard of less than 50 ng/mg of double-stranded DNA present in decellularized ECM. Following decellularization, replacement of cells occurs via recellularization: seeding cells into the decellularized ECM structure either via perfusion of cells into the vascular conduits, injection into parenchyma, or a combination of perfusion and injection. Endothelial cells are often perfused through existing vessel conduits to provide an endothelial lining of the vasculature, with cardiomyocytes and other parenchymal cells injected into the myocardium of decellularized ECM bioscaffolds. Uniform cell density and cell retention throughout the bioscaffold still needs to be addressed in larger animal models of the whole heart. Generating the necessary cell numbers and types remains a challenge. Still, recellularized cardiac tissue bioscaffolds offer therapeutic solutions to heart failure, heart valve replacement, and acute myocardial infarction. New technologies allow for decellularized ECM to be bioprinted into cardiac bioscaffolds or formed into a cardiac hydrogel patch. This chapter reviews the advances made in decellularization and recellularization of cardiac ECM bioscaffolds with a discussion of the potential clinical applications of ECM bioscaffolds.

Preparation and Evaluation of Tibia- and Calvarium-Derived Decellularized Periosteum Scaffolds

The periosteum plays a key role in bone regeneration and an artificial bionic material is urgently required. The periostea on the tibia and skull differ with respect to the types of cells, microstructure, and components, leading to different biological functions and biomechanical properties. We aimed to prepare decellularized periosteum scaffolds derived from different origins and evaluate their angiogenic and osteogenic activities. Histological assessment of α-smooth muscle actin, bone morphogenetic protein-2, and alkaline phosphatase in tibial and calvarial periosteum tissues provided preliminary information on their differing angiogenic and osteogenic properties. We developed decellularization protocols to completely remove the periosteum cellular components and for good maintenance of the hierarchical multilayer structures and components of the extracellular matrix (ECM) with no cytotoxicity. Moreover, using a chicken egg chorioallantoic membrane assay and a nude mouse implantation model, we found that tibia-derived periosteum ECM had superior osteogenic activity and calvarium-derived ECM had good angiogenic activity. The preliminary mechanisms of differing activities were then evaluated by osteogenesis- and angiogenesis-related gene expression in human umbilical vein endothelial cell- and MC-3T3 cell-seeded ECM scaffolds. Thus, this study provides periosteum biomaterials that are derived from specific tissues and have different functional properties and structures, for use in bone regeneration.

Residual sodium dodecyl sulfate in decellularized muscle matrices leads to fibroblast activation in vitro and foreign body response in vivo

Detergents such as sodium dodecyl sulfate (SDS) are commonly used to extract cells from tissues in a process called "decellularization". Residual SDS is difficult to completely remove and may lead to an undesirable host response towards an implanted biomaterial. In this study, we developed a modification for SDS cell extraction from muscle equally efficient to previous methods but leading to significantly less residual SDS remnants in the matrices. Muscle-derived matrices were prepared via 2 SDS-based decellularization methods, which led to removal of either 81.4% or 98.4% of the SDS. In vitro, matrices were seeded with thp1 macrophages and primary human foreskin fibroblasts. By Day 2, both matrices demonstrated similar macrophage polarization; however, fibroblasts cultured on matrices with greater residual SDS expressed higher levels of mRNA associated with fibroblast activation: α-smooth muscle actin and connective tissue growth factor. In vivo, Collagen I gels spiked with increasing concentrations of SDS displayed a corresponding decrease in cell infiltration when implanted subcutaneously in rats after 4 days. Finally, as a model for muscle regeneration, matrices produced by each method were implanted in rat latissimus dorsi defects. At POD 30 greater levels of IL-1β mRNA were present in defects treated with matrices containing higher levels of SDS, indicating a more severe inflammatory response. Although matrices containing higher levels of residual SDS became encapsulated by POD 30 and showed evidence of a foreign body response, matrices with the lower levels of SDS integrated into the defect area with lower levels of inflammatory and fibrosis-related gene expression.

Development of a Micronized Meniscus Extracellular Matrix Scaffold for Potential Augmentation of Meniscal Repair and Regeneration

Decellularized scaffolds composed of extracellular matrix (ECM) hold promise for repair and regeneration of the meniscus, given the potential for ECM-based biomaterials to aid in stem cell recruitment, infiltration, and differentiation. The objectives of this study were to decellularize canine menisci to fabricate a micronized, ECM-derived scaffold and to determine the cytocompatibility and repair potential of the scaffold ex vivo. Menisci were decellularized with a combination of physical agitation and chemical treatments. For scaffold fabrication, decellularized menisci were cryoground into a powder and the size and morphology of the ECM particles were evaluated using scanning electron microscopy. Histologic and biochemical analyses of the scaffold confirmed effective decellularization with loss of proteoglycan from the tissue but no significant reduction in collagen content. When washed effectively, the decellularized scaffold was cytocompatible to meniscal fibrochondrocytes, synoviocytes, and whole meniscal tissue based on the resazurin reduction assay and histologic evaluation. In an ex vivo model for meniscal repair, radial tears were augmented with the scaffold delivered with platelet-rich plasma as a carrier, and compared to nonaugmented (standard-of-care) suture techniques. Histologically, there was no evidence of cellular migration or proliferation noted in any of the untreated or standard-of-care treatment groups after 40 days of culture. Conversely, cellular infiltration and proliferation were noted in scaffold-augmented repairs. These data suggest the potential for the scaffold to promote cellular survival, migration, and proliferation ex vivo. Further investigations are necessary to examine the potential for the scaffold to induce cellular differentiation and functional meniscal fibrochondrogenesis.

Systematic Comparison of Protocols for the Preparation of Human Articular Cartilage for Use as Scaffold Material in Cartilage Tissue Engineering

Natural extracellular matrix-derived biomaterials from decellularized allogenic tissues are of increasing interest for tissue engineering because their structure and composition provide a complexity that is not achievable with current manufacturing techniques. The prerequisite to bring allogenic tissue from bench to bedside as a functional biomaterial is the full removal of cells while preserving most of its native characteristics such as structure and composition. The exceptionally dense structure of articular cartilage, however, poses a special challenge for decellularization, scaffold preparation, and reseeding. Therefore, we tested 24 different protocols aiming to remove cells and glycosaminoglycans (GAG) while preserving the collagen backbone and ultrastructure. The resulting matrices were analyzed for cell removal (DNA quantification, haematoxylin and eosin staining), GAG content (dimethyl methylene blue assay, Alcian blue staining and micro-computed tomography), collagen integrity (immunohistochemistry and ultrastructure), and biomechanics (compression test). Furthermore, seeding tests were conducted to evaluate cell viability and attachment to the scaffolds. Sodium dodecyl sulfate-based protocols yielded satisfactory reduction of DNA content, yet had negative effects on cell viability and attachment. Hydrochloric acid efficiently decellularized the scaffold and pepsin emerged as best option for GAG depletion. Combining these two reagents led to our final protocol, most efficient in DNA and GAG depletion while preserving the collagen architecture. The compressive modulus decreased in the absence of GAG to ∼1/3 of native cartilage, which is significantly higher than that by commercially available scaffolds tested as a reference (ranging from 1/25 to 1/100 of native cartilage). Cytocompatibility tests showed that human adipose-derived stromal cells readily adhered to the scaffold. In this study, we established a protocol combining freeze-thaw cycles, osmotic shock, and treatment with hydrochloric acid followed by a pepsin digestion step, achieving successful decellularization and GAG depletion within 1 week, resulting in a cytocompatible material with intact collagen structure. The protocol provides a basis for the generation of allogeneic scaffolds, potentially substituting manufactured scaffolds currently used in clinical articular cartilage treatment.

"Tissue Papers" from Organ-Specific Decellularized Extracellular Matrices

Using an innovative, tissue-independent approach to decellularized tissue processing and biomaterial fabrication, the development of a series of "tissue papers" derived from native porcine tissues/organs (heart, kidney, liver, muscle), native bovine tissue/organ (ovary and uterus), and purified bovine Achilles tendon collagen as a control from decellularized extracellular matrix particle ink suspensions cast into molds is described. Each tissue paper type has distinct microstructural characteristics as well as physical and mechanical properties, is capable of absorbing up to 300% of its own weight in liquid, and remains mechanically robust (E = 1-18 MPa) when hydrated; permitting it to be cut, rolled, folded, and sutured, as needed. In vitro characterization with human mesenchymal stem cells reveals that all tissue paper types support cell adhesion, viability, and proliferation over four weeks. Ovarian tissue papers support mouse ovarian follicle adhesion, viability, and health in vitro, as well as support, and maintain the viability and hormonal function of nonhuman primate and human follicle-containing, live ovarian cortical tissues ex vivo for eight weeks postmortem. "Tissue papers" can be further augmented with additional synthetic and natural biomaterials, as well as integrated with recently developed, advanced 3D-printable biomaterials, providing a versatile platform for future multi-biomaterial construct manufacturing.

Decellularization of Whole Human Liver Grafts Using Controlled Perfusion for Transplantable Organ Bioscaffolds

Liver transplantation is the only effective treatment for end-stage liver disease, but absolute donor shortage remains a limiting factor. Recent advances in tissue engineering focus on generation of native extracellular matrix (ECM) by decellularized complete livers in animal models. Although proof of concept has been reported for human livers, this study aims to perform whole liver decellularization in a clinically relevant series using controlled machine perfusion. In this study, we describe a mild nondestructive decellularization protocol, effective in 11 discarded human whole liver grafts to generate constructs that reliably maintain hepatic architecture and ECM components using machine perfusion, while completely removing cellular DNA and RNA. The decellularization process preserved the ultrastructural ECM components confirmed by histology, electron microscopy, and proteomic analysis. Anatomical characteristics of the native microvascular network and biliary drainage of the liver were confirmed by contrast computed tomography scanning. Decellularized vascular matrix remained suitable for normal suturing and no major histocompatibility complex molecules were detected, suggesting absence of allo-reactivity when used for transplantation. After extensive washing, decellularized scaffolds were nontoxic for cells after reseeding human mesenchymal stromal or umbilical vein endothelial endothelium cells. Indeed, evidence of effective recellularization of the vascular lining was obtained. In conclusion, we established an effective method to generate clinically applicable liver scaffolds from human discarded whole liver grafts and show proof of concept that reseeding of normal human cells in the scaffold is feasible. This supports new opportunities for bioengineering of transplantable grafts in the future.

Natural Scaffolds for Regenerative Medicine: Direct Determination of Detergents Entrapped in Decellularized Heart Valves

The increasing urgency for replacement of pathological heart valves is a major stimulus for research on alternatives to glutaraldehyde-treated grafts. New xenogeneic acellular heart valve substitutes that can be repopulated by host cells are currently under investigation. Anionic surfactants, including bile acids, have been widely used to eliminate the resident cell components chiefly responsible for the immunogenicity of the tissue, even if detergent toxicity might present limitations to the survival and/or functional expression of the repopulating cells. To date, the determination of residual detergent has been carried out almost exclusively on the washings following cell removal procedures. Here, a novel HPLC-based procedure is proposed for the direct quantification of detergent (cholate, deoxycholate, and taurodeoxycholate) residues entrapped in the scaffold of decellularized porcine aortic and pulmonary valves. The method was demonstrated to be sensitive, reproducible, and extendable to different types of detergent. This assessment also revealed that cell-depleted heart valve scaffolds prepared according to procedures currently considered for clinical use might contain significant amount of surfactant.

Decellularized scaffold of cryopreserved rat kidney retains its recellularization potential

The multi-cellular nature of renal tissue makes it the most challenging organ for regeneration. Therefore, till date whole organ transplantations remain the definitive treatment for the end stage renal disease (ESRD). The shortage of available organs for the transplantation has, thus, remained a major concern as well as an unsolved problem. In this regard generation of whole organ scaffold through decellularization followed by regeneration of the whole organ by recellularization is being viewed as a potential alternative for generating functional tissues. Despite its growing interest, the optimal processing to achieve functional organ still remains unsolved. The biggest challenge remains is the time line for obtaining kidney. Keeping these facts in mind, we have assessed the effects of cryostorage (3 months) on renal tissue architecture and its potential for decellularization and recellularization in comparison to the freshly isolated kidneys. The light microscopy exploiting different microscopic stains as well as immuno-histochemistry and Scanning electron microscopy (SEM) demonstrated that ECM framework is well retained following kidney cryopreservation. The strength of these structures was reinforced by calculating mechanical stress which confirmed the similarity between the freshly isolated and cryopreserved tissue. The recellularization of these bio-scaffolds, with mesenchymal stem cells quickly repopulated the decellularized structures irrespective of the kidneys status, i.e. freshly isolated or the cryopreserved. The growth pattern employing mesenchymal stem cells demonstrated their equivalent recellularization potential. Based on these observations, it may be concluded that cryopreserved kidneys can be exploited as scaffolds for future development of functional organ.

The host response to naturally-derived extracellular matrix biomaterials

Biomaterials based on natural materials including decellularized tissues and tissue-derived hydrogels are becoming more widely used for clinical applications. Because of their native composition and structure, these biomaterials induce a distinct form of the foreign body response that differs from that of non-native biomaterials. Differences include direct interactions with cells via preserved moieties as well as the ability to undergo remodeling. Moreover, these biomaterials could elicit adaptive immune responses due to the presence of modified native molecules. Therefore, these biomaterials present unique challenges in terms of understanding the progression of the foreign body response. This review covers this response to natural materials including natural polymers, decellularized tissues, cell-derived matrix, tissue derived hydrogels, and biohybrid materials. With the expansion of the fields of regenerative medicine and tissue engineering, the current repertoire of biomaterials has also expanded and requires continuous investigation of the responses they elicit.

The impact of detergents on the tissue decellularization process: A ToF-SIMS study

Biologic scaffolds are derived from mammalian tissues, which must be decellularized to remove cellular antigens that would otherwise incite an adverse immune response. Although widely used clinically, the optimum balance between cell removal and the disruption of matrix architecture and surface ligand landscape remains a considerable challenge. Here we describe the use of time of flight secondary ion mass spectroscopy (ToF-SIMS) to provide sensitive, molecular specific, localized analysis of detergent decellularized biologic scaffolds. We detected residual detergent fragments, specifically from Triton X-100, sodium deoxycholate and sodium dodecyl sulphate (SDS) in decellularized scaffolds; increased SDS concentrations from 0.1% to 1.0% increased both the intensity of SDS fragments and adverse cell outcomes. We also identified cellular remnants, by detecting phosphate and phosphocholine ions in PAA and CHAPS decellularized scaffolds. The present study demonstrates ToF-SIMS is not only a powerful tool for characterization of biologic scaffold surface molecular functionality, but also enables sensitive assessment of decellularization efficacy.

STATEMENT OF SIGNIFICANCE

We report here on the use of a highly sensitive analytical technique, time of flight secondary ion mass spectroscopy (ToF-SIMS) to characterize detergent decellularized scaffolds. ToF-SIMS detected cellular remnants and residual detergent fragments; increased intensity of the detergent fragments correlated with adverse cell matrix interactions. This study demonstrates the importance of maintaining a balance between cell removal and detergent disruption of matrix architecture and matrix surface ligand landscape. This study also demonstrates the power of ToF-SIMS for the characterization of decellularized scaffolds and capability for assessment of decellularization efficacy. Future use of biologic scaffolds in clinical tissue reconstruction will benefit from the fundamental results described in this work.