Determining the optimal protocol for preparing an acellular scaffold of tissue engineered small-diameter blood vessels

Supercritical carbon dioxide-decellularized arteries exhibit physiologic-like vessel regeneration following xenotransplantation in rats

Currently, many techniques are used for decellularization of grafts, including physical, enzymatic, and chemical treatments. Indeed, decellularized xenogenic grafts provide superior outcomes than alternative synthetic conduits. However, vascular grafts produced by these methods are not perfect; their defects include defective vessel wall structures, detergent residues, and the development of aneurysms after grafting. Therefore, it is essential to develop a more appropriate process to produce decellularized vascular grafts. Supercritical carbon dioxide (ScCO₂) has been used in decellularization technologies in recent years. It is beneficial for the long-term preservation of tissues and regeneration of new vessels. We have previously reported that ScCO₂-produced acellular porcine corneas show excellent biocompatibility following lamellar corneal transplantation in rabbits. In this study, we wanted to use this method to fabricate vascular grafts (ScCO₂-decellularized rabbit femoral artery (DFA)) and analyze their efficacy, parameters regarding rejection by the recipient's (ACI/NKyo rats) immune system and biocompatibility, structural regeneration, and functionality in vivo. The results indicated that the ScCO₂-DFA showed higher biocompatibility, enhanced chemotactic migration of endothelial progenitor cells, lower risk of vasculopathy, lower inflammatory and splenic immune responses, and better physiological-like tension responses after xenotransplantation (XTP) in ACI/NKyo rats compared with the results obtained after XTP using detergent decellularized vascular grafts (SDS-DFA). In conclusion, ScCO₂ is an excellent decellularization technique in the fabrication of biocompatible vascular grafts and has tremendous application in vascular regenerative medicine.

Vascular endothelial growth factor attenuates neointimal hyperplasia of decellularized small-diameter vascular grafts by modulating the local inflammatory response

Small-diameter vascular grafts (diameter <6 mm) are in high demand in clinical practice. Neointimal hyperplasia, a common complication after implantation of small-diameter vascular grafts, is one of the common causes of graft failure. Modulation of local inflammatory responses is a promising strategy to attenuates neointimal hyperplasia. Vascular endothelial growth factor (VEGF) is an angiogenesis stimulator that also induces macrophage polarization and modulates inflammatory responses. In the present study, we evaluated the effect of VEGF on the neointima hyperplasia and local inflammatory responses of decellularized vascular grafts. In the presence of rhVEGF-165 in RAW264.6 macrophage culture, rhVEGF-165 induces RAW264.6 macrophage polarization to M2 phenotype. Decellularized bovine internal mammary arteries were implanted into the subcutaneous and infrarenal abdominal aorta of New Zealand rabbits, with rhVEGF-165 applied locally to the adventitial of the grafts. The vascular grafts were removed en-bloc and submitted to histological and immunofluorescence analyses on days 7 and 28 following implantation. The thickness of the fibrous capsule and neointima was thinner in the VEGF group than that in the control group. In the immunofluorescence analysis, the number of M2 macrophages and the ratio of M2/M1 macrophages in vascular grafts in the VEGF group were higher than those in the control group, and the proinflammatory factor IL-1 was expressed less than in the control group, but the anti-inflammatory factor IL-10 was expressed more. In conclusion, local VEGF administration attenuates neointimal hyperplasia in decellularized small-diameter vascular grafts by inducing macrophage M2 polarization and modulating the inflammatory response.

An efficient strategy to recellularization of a rat aorta scaffold: an optimized decellularization, detergent removal, and Apelin-13 immobilization

Background

Tissue engineering of native vessels is an alternative approach for patients with vascular disease who lack sufficient saphenous vein or other suitable conduits for autologous vascular graft. Moreover, the harvest of vessels prolongs the surgical procedure and it may lead to the morbidity of donor site in elder patients: therefore, it seems that the use of tissue-engineered vessels would be an attractive and less invasive substitute for autologous vascular grafts. Apelin-13 plays a pivotal role in cell proliferation, survival, and attachment; therefore, covalent attachment of apelin-13 to the acellular scaffolds might be a favorable approach for improving recellularization efficacy.

Methods

In the present study, the decellularization process was performed using various detergents. Afterward, the efficacy of decellularization procedure was evaluated using multiple approaches including assessment of DNA, hydroxyproline, and GAG content as well as Masson’s trichrome and orcein staining used for collagen and elastin determination. Subsequently, the scaffold was bioconjugated with apelin-13 using the EDC-NHS linker and acellular scaffolds were recellularized using fibroblasts, endothelial cells, and smooth muscle cells. SEM images and characterization methods were also used to evaluate the effect of apelin-13 attachment to the acellular scaffold on tissue recellularization. We also developed a novel strategy to eliminate the remnant detergents from the scaffold and increase cell viability by incubating acellular scaffolds with Bio-Beads SM-2 resin. Testometric tensile testing machine was also used for the assessment of mechanical properties and uniaxial tensile strength of decellularized and recellularized vessels compared to that of native tissues.

Results

Our results proposed 16-h perfusion of 0.25% sodium dodecyl sulfate (SDS) + 0.5% Triton X-100 combination to the vessel as an optimal decellularization protocol in terms of cell elimination as well as extracellular matrix preservation. Furthermore, the results demonstrated considerable elevation of cell adhesion and proliferation in scaffolds bioconjugated with apelin-13. The immunohistochemical (IHC) staining of CD31, α-SMA, and vimentin markers suggested placement of seeded cells in the suitable sites and considerable elevation of cell attachment within the scaffolds bioconjugated with apelin-13 compared to the non-bioconjugated, and decellularized groups. Moreover, the quantitative analysis of IHC staining of CD31, α-SMA, and vimentin markers suggested considerable elevation in the number of endothelial, smooth muscle, and fibroblast cells in the recellularized scaffolds bioconjugated with apelin-13 group (1.4% ± 0.02, 6.66% ± 0.23, and 9.87% ± 0.13%, respectively) compared to the non-bioconjugated scaffolds (0.03% ± 0.01, 0.28% ± 0.01, and 1.2% ± 0.09%, respectively) and decellularized groups (0.03% ± 0.007, 0.05% ± 0.01, and 0.13% ±0.005%, respectively). Although the maximum strain to the rupture was reduced in tissues decellularized using 0.5% SDS and CHAPS compared to that of native ones (116% ± 6.79, 139.1% ± 3.24, and 164% ± 8.54%, respectively), ultimate stress was decreased in all decellularized and recellularized groups. Besides, our results indicated that cell viability on the 1st, 3rd, and 7th day was 100.79% ± 0.7, 100.34% ± 0.08, and 111.24% ± 1.7% for the decellularized rat aorta conjugated with apelin-13, which was incubated for 48-h with Bio-Beads SM-2, and 73.37% ± 7.99, 47.6% ± 11.69, and 27.3% ± 7.89% for decellularized rat aorta scaffolds conjugated with apelin-13 and washed 48-h by PBS, respectively. These findings reveal that the incubation of the scaffold with Bio-Beads SM-2 is a novel and promising approach for increasing cell viability and growth within the scaffold.

Conclusions

In conclusion, our results provide a platform in which xenograft vessels are decellularized properly in a short time, and the recellularization process is significantly improved after the bioconjugation of the acellular scaffold with apelin-13 in terms of cell adhesion and viability within the scaffold.

Graphical Abstract

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.

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.

Generation and Evaluation of Novel Biomaterials Based on Decellularized Sturgeon Cartilage for Use in Tissue Engineering

Because cartilage has limited regenerative capability, a fully efficient advanced therapy medicinal product is needed to treat severe cartilage damage. We evaluated a novel biomaterial obtained by decellularizing sturgeon chondral endoskeleton tissue for use in cartilage tissue engineering. In silico analysis suggested high homology between human and sturgeon collagen proteins, and ultra-performance liquid chromatography confirmed that both types of cartilage consisted mainly of the same amino acids. Decellularized sturgeon cartilage was recellularized with human chondrocytes and four types of human mesenchymal stem cells (MSC) and their suitability for generating a cartilage substitute was assessed ex vivo and in vivo. The results supported the biocompatibility of the novel scaffold, as well as its ability to sustain cell adhesion, proliferation and differentiation. In vivo assays showed that the MSC cells in grafted cartilage disks were biosynthetically active and able to remodel the extracellular matrix of cartilage substitutes, with the production of type II collagen and other relevant components, especially when adipose tissue MSC were used. In addition, these cartilage substitutes triggered a pro-regenerative reaction mediated by CD206-positive M2 macrophages. These preliminary results warrant further research to characterize in greater detail the potential clinical translation of these novel cartilage substitutes.

A novel decellularization method to produce brain scaffolds

Scaffolds composed of extracellular matrix (ECM) can assist tissue remodeling and repair following injury. The ECM is a complex biomaterial composed of proteins, glycoproteins, proteoglycans, and glycosaminoglycans, secreted by cells. The ECM contains fundamental biological cues that modulate cell behavior and serves as a structural scaffold for cell adhesion and growth. For clinical applications, where immune rejection is a constraint, ECM can be processed using decellularization methods intended to remove cells and donor antigens from tissue or organs, while preserving native biological cues essential for cell growth and differentiation. Recent studies show bioengineered organs composed by a combination of a diversity of materials and stem cells as a possibility of new therapeutic strategies to treat diseases that affect different tissues and organs, including the central nervous system (CNS). Nevertheless, the methodologies currently described for brain decellularization involve the use of several chemical reagents with many steps that ultimately limit the process of organ or tissue recellularization. Here, we describe for the first time a fast and straightforward method for complete decellularization of mice brain by the combination of rapid freezing and thawing following the use of only one detergent (Sodium dodecyl sulfate (SDS)). Our data show that using the protocol we describe here, the brain was entirely decellularized, while still maintaining ECM components that are essential for cell survival on the scaffold. Our results also show the cell-loading of the decellularized brain matrix with Neuro2a cells, which were identified by immunohistochemistry in their undifferentiated form. We conclude that this novel and simple method for brain decellularization can be used as a scaffold for cell-loading.

Characterization of a heparinized decellularized scaffold and its effects on mechanical and structural properties

Decellularization is a promising approach in tissue engineering to generate small-diameter blood vessels. However, some challenges still exist. We performed two decellularization phases to develop an optimal decellularized scaffold and analyze the relationship between the extracellular matrix (ECM) composition and mechanical properties. In decellularization phase I, we tested sodium dodecylsulfate (SDS), Triton X-100 (TX100) and trypsin at different concentrations and exposure times. In decellularization phase II, we systematically compared five combined decellularization protocols based on the results of phase I to identify the optimal method. These protocols tested cell removal, ECM preservation, mechanical properties, and residual cytotoxicity. We further immobilized heparin to optimal decellularized scaffolds and determined its anticoagulant activity and mechanical properties. The combined decellularization protocol comprising treatment with 0.5% SDS followed by 1% TX100 could completely remove the cellular contents and preserve the mechanical properties and ECM architecture better. In addition, the heparinized decellularized scaffolds not only had sustained anticoagulant activity, but also similar mechanical properties to native vessels. In conclusion, heparinized decellularized scaffolds represent a promising direction for small-diameter vascular grafts, although further in vivo studies are needed.

Optimizing the decellularization process of an upper limb skeletal muscle; implications for muscle tissue engineering

Upper limb muscle reconstruction is required following cancer resection, trauma, and congenital deformities. Current surgical reconstruction of the muscle involves local, regional and free flaps. However, muscle reconstruction is not always possible due to the size of the defect and functional donor site morbidity. These challenges could be addressed with the production of scaffolds composed of an extracellular matrix (ECM) derived from decellularized human skeletal muscle. This study aimed to find an optimal technique to decellularize a flexor digitorum superficialis muscle. The first two protocols were based on a detergent only (DOT) and a detergent-enzymatic protocol (DET). The third protocol avoided the use of detergents and proteolytic enzymes (NDNET). The decellularized scaffolds were characterized using qualitative techniques including histological and immunofluorescent staining and quantitative techniques assessing deoxyribonucleic acid (DNA), glycosaminoglycan (GAG), and collagen content. The DOT protocol consisting of 2% SDS for 4 hours was successful at decellularizing human FDS, as shown by DNA content assay and nuclei immunofluorescence staining. The DOT protocol maintained the microstructure of the scaffolds as shown by Masson's trichrome staining and collagen and GAG content. DET and NDNET protocols maintained the ECM, but were unsuccessful in removing all DNA content after two cycles of decellularization. Decellularization of skeletal muscle is a viable option for muscle reconstruction using a detergent only technique for upper limb defects. Further testing in vivo will assess the effectiveness of decellularized scaffolds for upper limb muscle skeletal tissue engineering.

Porcine pulmonary valve decellularization with NaOH-based vs detergent process: preliminary in vitro and in vivo assessments

Background

Glutaraldehyde fixed xenogeneic heart valve prosthesis are hindered by calcification and lack of growth potential. The aim of tissue decellularization is to remove tissue antigenicity, avoiding the use of glutaraldehyde and improve valve integration with low inflammation and host cell recolonization. In this preliminary study, we investigated the efficacy of a NaOH-based process for decellularization and biocompatibility improvement of porcine pulmonary heart valves in comparison to a detergent-based process (SDS-SDC0, 5%).

Methods

Native cryopreserved porcine pulmonary heart valves were treated with detergent and NaOH-based processes.

Decellularization was assessed by Hematoxylin and eosin/DAPI/alpha-gal/SLA-I staining and DNA quantification of native and processed leaflets, walls and muscles.

Elongation stress test investigated mechanical integrity of leaflets and walls (n = 3 tests/valve component) of valves in the native and treated groups (n = 4/group).

Biochemical integrity (collagen/elastin/glycosaminoglycans content) of leaflet-wall and muscle of the valves (n = 4/group) was assessed and compared between groups with trichrome staining (Sirius Red/Miller/Alcian blue).

Secondly, a preliminary in vivo study assessed biocompatibility (CD3 and CD68 immunostaining) and remodeling (Hematoxylin and eosin/CD31 and ASMA immunofluorescent staining) of NaOH processed valves implanted in orthotopic position in young Landrace pigs, at 1 (n = 1) and 3 months (n = 2).

Results

Decellularization was better achieved with the NaOH-based process (92% vs 69% DNA reduction in the wall). Both treatments did not significantly alter mechanical properties. The detergent-based process induced a significant loss of glycosaminoglycans (p < 0,05).

In vivo, explanted valves exhibited normal morphology without any sign of graft dilatation, degeneration or rejection. Low inflammation was noticed at one and three months follow-up (1,8 +/− 3,03 and 0,9836 +/− 1,3605 CD3 cells/0,12 mm² in the leaflets). In one animal, at three months we documented minimal calcification in the area of sinus leaflet and in one, microthrombi formation on the leaflet surface at 1 month. The endoluminal side of the valves showed partial reendothelialization.

Conclusions

NaOH-based process offers better porcine pulmonary valve decellularization than the detergent process. In vivo, the NaOH processed valves showed low inflammatory response at 3 months and partial recellularization. Regarding additional property of securing, this treatment should be considered for the new generation of heart valves prosthesis.

Graphical abstract

Graphical abstract of the study

Optimization of Human Myocardium Decellularization Method for the Construction of Implantable Patches

Cardiac tissue engineering by means of synthetic or natural scaffolds combined with stem/progenitor cells is emerging as the response to the unsatisfactory outcome of approaches based solely on the injection of cells. Parenchymal and supporting cells are surrounded, in vivo, by a specialized and tissue-specific microenvironment, consisting mainly of extracellular matrix (ECM) and soluble factors incorporated in the ECM. Since the naturally occurring ECM is the ideal platform for ensuring cell engraftment, survival, proliferation, and differentiation, the acellular native ECM appears by far the most promising and appealing substrate among all biomaterials tested so far. To obtain intact scaffold of human native cardiac ECM while preserving its composition, we compared the decellularized ECM (d-ECM) produced through five different protocols of decellularization (named Pr1, Pr2, Pr3, Pr4, and Pr5) in terms of efficiency of decellularization, composition, and three-dimensional architecture of d-ECM scaffolds and of their suitability for cell repopulation. The decellularization procedures proved substantially different. Specifically, only three, of the five protocols tested, proved effective in producing thoroughly acellular d-ECM. In addition, the d-ECM delivered differed in architecture and composition and, more importantly, in its ability to support engraftment, survival, and differentiation of cardiac primitive cells in vitro.