Genipin crosslinking reduced the immunogenicity of xenogeneic decellularized porcine whole-liver matrices through regulation of immune cell proliferation and polarization

Modulating smooth muscle cell response by the release of TGFβ2 from tubular scaffolds for vascular tissue engineering

Tissue engineering has gained considerable attention in the development of small diameter tissue engineered vascular grafts (TEVGs) for treating coronary heart disease. A properly designed acellular and biodegradable TEVG must encourage the infiltration and growth of vascular smooth muscle cells (SMCs). Our group has previously shown that increasing levels of TGFβ2 can differentially modulate SMC migration and proliferation. In this study, tubular electrospun scaffolds loaded with TGFβ2 were fabricated using various ratios of gelatin/polycaprolactone (PCL), resulting in scaffolds with porous nano-woven architecture suitable for tissue ingrowth. Scaffold morphology, degradation rate, TGβ2 release kinetics, and bioactivity were assessed. TGFβ2 was successfully integrated into the electrospun biomaterial that resulted in a differential release profile depending on the gelatin/PCL ratio over the course of 42 days. Higher TGFβ2 elution was obtained in scaffolds with higher gelatin content, which may be related to the biodegradation of gelatin in culture media. The biological activity of the released TGFβ2 was evaluated by its ability to affect SMC proliferation as a function of its concentration. SMCs seeded on TGFβ2-loaded scaffolds also showed higher densities and infiltration after 5 days in culture as compared to scaffolds without TGFβ2. Our results demonstrate that the ratio of synthetic and natural polymers in electrospun blends can be used to tune the release of TGFβ2. This method can be used to intelligently modulate the SMC response in gelatin/PCL scaffolds making the TGFβ2-loaded conduits attractive for cardiovascular tissue engineering applications.

Electrospun polycaprolactone/collagen nanofibers cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide and genipin facilitate endothelial cell regeneration and may be a promising candidate for vascular scaffolds

Purpose

A promising vascular scaffold must possess satisfying mechanical properties, great hemocompatibility, and favorable tissue regeneration. Combining natural with synthetic materials is a popular method of creating/enhancing such scaffolds. However, the effect of additional modification on the materials requires further exploration.

Materials and methods

We selected polycaprolactone (PCL), which has excellent mechanical properties and biocompatibility and can be combined with collagen. Electrospun fibers created using a PCL/collagen solution were used to fashion mixed nanofibers, while separate syringes of PCL and collagen were used to create separated nanofibers, resulting in different pore sizes. Mixed and separated nanofibers were cross-linked with glutaraldehyde (GA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), and genipin; hence, we named them as mixed GA, mixed EDC (ME), mixed genipin (MG), separated GA, separated EDC (SE), and separated genipin (SG).

Results

Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction showed that cross-linking did not affect the main functional groups of fibers in all groups. ME, MG, SE, and SG met the requisite mechanical properties, and they also resisted collagenase degradation. In hemocompatibility assays, only ME and MG demonstrated ideal safety. Furthermore, ME and MG presented the greatest cytocompatibility. For vascular scaffolds, rapid endothelialization helps to prevent thrombosis. According to human umbilical vein endothelial cell migration on different nanofibers, ME and MG are also successful in promoting cell migration.

Conclusion

ME and MG may be promising candidates for vascular tissue engineering. The study suggests that collagen cross-linked by EDC/N-hydroxysuccinimide or genipin facilitates endothelial cell regeneration, which could be of great benefit in tissue engineering of vascular scaffolds.

Hemocompatibility improvement of decellularized spleen matrix for constructing transplantable bioartificial liver

Thrombogenicity is the predominant obstacle to successful implantation of decellularized spleen matrix (DSM). The aim of this study was to construct a transplantable functional bioartificial liver (BAL) with the use of DSM. This was achieved by layer-by-layer electrostatic immobilization technique by using poly dimethyl diallyl ammonium chloride and heparin. After heparin immobilization, DSM gradually turned from translucent into completely opaque milky white. Toluidine blue staining showed strong positive staining of the entire coated DSM. In vitro diluted blood perfusion test showed that the splenic arterial pressure of the heparin-coated DSM was much lower than that of the non-coated DSM (p < 0.01). Then, we heterotopically transplanted the modified DSM into rat hepatic injury model for 6 h to evaluate the hemocompatibility in vivo. Overall, HE staining and vWF immunohistochemistry all confirmed that heparin-coated DSM has a satisfactory anticoagulant effect. Based on the heparin-coated DSM, BALs were built with the use of rat primary hepatocytes. Our results demonstrate that these heparin-coated BALs satisfied anticoagulant effects even after 6 h. Immunofluorescence of ALB and G6PC also showed that hepatocytes in heparin-coated BAL have significantly higher cell viability and function than the non-coated group. However, serum analysis did not indicate a significant difference between the two groups but a slight trend of improvement with respect to serum albumin (p = 0.156) and aspartate transaminase (p = 0.140). In conclusion, we demonstrated that the BAL constructed by heparin-coated DSM can exert satisfactory short-term anticoagulant effects and can compensate for a certain degree of liver function.

Novel Biomedical Applications of Crosslinked Collagen

Collagen is one of the most useful biopolymers because of its low immunogenicity and biocompatibility. The biomedical potential of natural collagen is limited by its poor mechanical strength, thermal stability, and enzyme resistance, but exogenous chemical, physical, or biological crosslinks have been used to modify the molecular structure of collagen to minimize degradation and enhance mechanical stability. Although crosslinked collagen-based materials have been widely used in biomedicine, there is no standard crosslinking protocol that can achieve a perfect balance between stability and functional remodeling of collagen. Understanding the role of crosslinking agents in the modification of collagen performance and their potential biomedical applications are crucial for developing novel collagen-based biopolymers for therapeutic gain.

Decellularization and genipin crosslinking of amniotic membrane suitable for tissue engineering applications

Amniotic membrane has the potential to be used as scaffold in various tissue engineering applications. However, increasing its biostability at the same time maintaining its biocompatibility is important to enhance its usage as a scaffold. This studied characteristics genipin-crosslinked amniotic membrane as a bioscaffold. Redundant human amniotic membranes (HAM) divided into native (nAM), decellularized (dAM) and genipin-crosslinked (clAM) groups. The dAM and clAM group were decellularized using thermolysin (TL) and sodium hydroxide (NaOH) solution. Next, clAM group was crosslinked with 0.5% and 1.0% (w/v) genipin. The HAM was then studied for in vitro degradation, percentage of swelling, optical clarity, ultrastructure and mechanical strength. Meanwhile, fibroblasts isolated from nasal turbinates were then seeded onto nAM, dAM and clAM for biocompatibility studies. clAM had the slowest degradation rate and were still morphologically intact after 30 days of incubation in 0.01% collagenase type 1 solution. The dAM had a significantly highest percentage of swelling than other groups (p < 0.05). Besides, the dAM retained the collagen content at similar level of nAM. Although the dAM had highest mechanical strength compared to the rest of the groups, the differences were statistically insignificant. Cell attachment on dAM and 0.5% clAM was higher compared to that on nAM and 1.0% clAM. In conclusion, clAM have better biostability and biocompatibility compared to the nAM and dAM. Together with other suitable characteristics of the clAM such as percentage of swelling, structural integrity and ECM content, clAM is suitable as scaffold for various tissue engineering applications.

Trans-differentiation of human adipose-derived mesenchymal stem cells into cardiomyocyte-like cells on decellularized bovine myocardial extracellular matrix-based films

In this study, we aimed at fabricating decellularized bovine myocardial extracellular matrix-based films (dMEbF) for cardiac tissue engineering (CTE). The decellularization process was carried out utilizing four consecutive stages including hypotonic treatment, detergent treatment, enzymatic digestion and decontamination, respectively. In order to fabricate the dMEbF, dBM were digested with pepsin and gelation process was conducted. dMEbF were then crosslinked with N-hydroxysuccinimide/1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (NHS/EDC) to increase their durability. Nuclear contents of native BM and decellularized BM (dBM) tissues were determined with DNA content analysis and agarose-gel electrophoresis. Cell viability on dMEbF for 3rd, 7th, and 14th days was assessed by MTT assay. Cell attachment on dMEbF was also studied by scanning electron microscopy. Trans-differentiation capacity of human adipose-derived mesenchymal stem cells (hAMSCs) into cardiomyocyte-like cells on dMEbF were also evaluated by histochemical and immunohistochemical analyses. DNA contents for native and dBM were, respectively, found as 886.11 ± 164.85 and 47.66 ± 0.09 ng/mg dry weight, indicating a successful decellularization process. The results of glycosaminoglycan and hydroxyproline assay, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), performed in order to characterize the extracellular matrix (ECM) composition of native and dBM tissue, showed that the BM matrix was not damaged during the proposed method. Lastly, regarding the histological study, dMEbF not only mimics native ECM, but also induces the stem cells into cardiomyocyte-like cells phenotype which brings it the potential of use in CTE.

Investigating the Synthesis and Characterization of a Novel "Green" H₂O₂-Assisted, Water-Soluble Chitosan/Polyvinyl Alcohol Nanofiber for Environmental End Uses

The present work highlights the formation of a novel green nanofiber based on H₂O₂-assisted water-soluble chitosan/polyvinyl alcohol (W_SCHT/PVA) by using water as an ecofriendly solvent and genipin used as a nontoxic cross-linker. The 20/80 blend ratio was found to have the most optimum uniform fiber morphology. W_SCHT retained the same structure as W_ISCHT. The prepared nanofibers were characterized by Scanning electron microscopy (SEM), Fourier transform spectroscopy (FTIR), Thermo gravimetric analysis (TGA), Differential scanning calorimeter (DSC), X-ray diffraction (XRD), Water Contact Angle (WCA) and Ultraviolet-visible spectroscopy (UV-vis). During electrospinning, the crystalline microstructure of the W_SCHT/PVA underwent better solidification and after cross-linking there was an increase in the melting temperature of the fiber. Swelling ratio studies revealed noticeable increase in hydrophilicity with increase of W_SCHT, which was further demonstrated by the decrease of contact angle from 64.74° to 14.68°. W_SCHT/PVA nanofiber mats exhibit excellent UV blocking protection with less than 5% transmittance value and also showed improved in vitro drug release properties with stable release for longer duration (cross-linked fibers) and burst release for shorter duration (uncross linked) fibers. Finally our experimental data demonstrates excellent adsorption ability of Colour Index (C.I.) reactive black 5 (RB5) due to protonated amino groups.

Incorporation of nanoparticles into transplantable decellularized matrices: Applications and challenges

Decellularization of tissues can significantly improve regenerative medicine and tissue engineering by producing natural, less immunogenic, three-dimensional, acellular matrices with high biological activity for transplantation. Decellularized matrices retain specific critical components of native tissues such as stem cell niche, various growth factors, and the ability to regenerate in vivo. However, recellularization and functionalization of these matrices remain limited, highlighting the need to improve the characteristics of decellularized matrices. Incorporating nanoparticles into decellularized tissues can overcome these limitations because nanoparticles possess unique properties such as multifunctionality and can modify the surface of decellularized matrices with additional growth factors, which can be loaded onto the nanoparticles. Therefore, in this minireview, we highlight the various approaches used to improve decellularized matrices with incorporation of nanoparticles and the challenges present in these applications.

Silver nanoparticles improve structural stability and biocompatibility of decellularized porcine liver

No ideal cross-linking agent has been identified for decellularized livers (DLs) yet. In this study, we evaluated structural improvements and biocompatibility of porcine DLs after cross-linking with silver nanoparticles (AgNPs). Porcine liver slices were decellularized and then loaded with AgNPs (100 nm) after optimization of the highest non-toxic concentration (5 µg/mL) using Human hepatocellular carcinoma (HepG2) and EAhy926 human endothelial cell lines. The cross-linking effect of AgNPs was evaluated and compared to that of glutaraldehyde and ethyl carbodiimide hydrochloride and N-hydroxysuccinimide. The results indicated that AgNPs improved the ultra-structure of DLs' collagen fibres with good porosity and increased DLs' resistance against in vitro degradation with good cytocompatibility. AgNPs decreased the host inflammatory reaction against implanted porcine DL slices in vivo and increased the polarization of M2 macrophages. Thus, structural and functional improvements of Porcine DLs could be achieved using AgNPs.

Chronic graft-specific cell-mediated immune response toward candidate xenogeneic biomaterial

Despite rabbits becoming an increasingly popular animal model, a flow cytometry panel that combines T cell markers (CD3, CD4, CD8, CD25, FOXP3) with a method for monitoring proliferation is lacking in this species. It has been shown that the rabbit model can be used to identify xenoantigens within bovine pericardium (BP), a common biological heart valve replacement material; however, these methods rely on monitoring the humoral immune response. The development of a rabbit T cell proliferation assay has utility in monitoring graft-specific cell-mediated immune responses toward bovine pericardium. Isolation and culture conditions were optimized to avoid cell death, red blood cell contamination, and non-specific proliferation. Effect of cell culture and stimulation on distribution and intensity of T cell markers was analyzed and compared between cells isolated from naïve and BP-immunized rabbits. Submaximal levels (0.25 μg/mL) of concavalin A were used to stimulate proliferation toward BP extract, with resultant proliferation compared between naïve and BP-immunized rabbits. Density stratification followed by ammonium potassium chloride (ACK) lysis yielded the greatest number of viable peripheral blood mononuclear cells with the least amount of erythrocyte contamination. Flat-bottomed plates were necessary to reduce non-specific proliferation in culture. T cells responded appropriately to maximal mitogenic stimulation (5 μg/mL concavalin A). Interestingly, immunization increased the intensity of FOXP3 in T regulatory cells compared to cells from naïve animals. With addition of submaximal levels of concavalin A, T cells from immunized rabbits proliferated in response to BP protein extract, while cells from naïve rabbits did not. In immunized rabbits, not only did more CD4⁺ T cells proliferate in response to BP re-stimulation, but the intensity of CD25 was increased indicating cell activation. This research provides a functional cell-mediated screening assay for assessment of BP-based biomaterials in rabbits, overcoming the limitations of previous humoral immune system-based assessments of biomaterial antigenicity in this important experimental animal species.

Recent Advances in Decellularization and Recellularization for Tissue-Engineered Liver Grafts

Liver transplantation from deceased or living human donors remains the only proven option for patients with end-stage liver disease. However, the shortage of donor organs is a significant clinical concern that has led to the pursuit of tissue-engineered liver grafts generated from decellularized liver extracellular matrix and functional cells. Investigative efforts on optimizing both liver decellularization and recellularization protocols have been made in recent decades. In the current review, we briefly summarize these advances, including the generation of high-quality liver extracellular matrix scaffolds, evaluation criteria for quality control, modification of matrix for enhanced properties, and reseeding strategies. These efforts to optimize the methods of decellularization and recellularization lay the groundwork towards generating a transplantable, human-sized liver graft for the treatment of patients with severe liver disease.

Cross-linking of a biopolymer-peptide co-assembling system

The ability to guide molecular self-assembly at the nanoscale into complex macroscopic structures could enable the development of functional synthetic materials that exhibit properties of natural tissues such as hierarchy, adaptability, and self-healing. However, the stability and structural integrity of these kinds of materials remains a challenge for many practical applications. We have recently developed a dynamic biopolymer-peptide co-assembly system with the capacity to grow and undergo morphogenesis into complex shapes. Here we explored the potential of different synthetic (succinimidyl carboxymethyl ester, poly (ethylene glycol) ether tetrasuccinimidyl glutarate and glutaraldehyde) and natural (genipin) cross-linking agents to stabilize membranes made from these biopolymer-peptide co-assemblies. We investigated the cross-linking efficiency, resistance to enzymatic degradation, and mechanical properties of the different cross-linked membranes. We also compared their biocompatibility by assessing the metabolic activity and morphology of adipose-derived stem cells (ADSC) cultured on the different membranes. While all cross-linkers successfully stabilized the system under physiological conditions, membranes cross-linked with genipin exhibited better resistance in physiological environments, improved stability under enzymatic degradation, and a higher degree of in vitro cytocompatibility compared to the other cross-linking agents. The results demonstrated that genipin is an attractive candidate to provide functional structural stability to complex self-assembling structures for potential tissue engineering or in vitro model applications.

STATEMENT OF SIGNIFICANCE

Molecular self-assembly is widely used for the fabrication of complex functional biomaterials to replace and/or repair any tissue or organ in the body. However, maintaining the stability and corresponding functionality of these kinds of materials in physiological conditions remains a challenge. Chemical cross-linking strategies (natural or synthetic) have been used in an effort to improve their structural integrity. Here we investigate key performance parameters of different cross-linking strategies for stabilising self-assembled materials with potential biomedical applications using a novel protein-peptide co-assembling membrane as proof-of-concept. From the different cross-linkers tested, the natural cross-linker genipin exhibited the best performance. This cross-linker successfully enhanced the mechanical properties of the system enabling the maintenance of the structure in physiological conditions without compromising its bioactivity and biocompatibility. Altogether, we provide a systematic characterization of cross-linking alternatives for self-assembling materials focused on biocompatibility and stability and demonstrate that genipin is a promising alternative for the cross-linking of such materials with a wide variety of potential applications such as in tissue engineering and drug delivery.

Detergent-free decellularization of bovine costal cartilage for chondrogenic differentiation of human adipose mesenchymal stem cells in vitro

In this study, we report a novel, detergent-free decellularization protocol for the preparation of intact cartilage ECM-based scaffolds (CEbS) during an effective decalcification process.