Nonglutaraldehyde Fixation for off the Shelf Decellularized Bovine Pericardium in Anticalcification Cardiac Valve Applications

Recent Advances in the Modification and Improvement of Bioprosthetic Heart Valves

Valvular heart disease (VHD) has become a burden and a growing public health problem in humans, causing significant morbidity and mortality worldwide. An increasing number of patients with severe VHD need to undergo heart valve replacement surgery, and artificial heart valves are in high demand. However, allogeneic valves from donors are lacking and cannot meet clinical practice needs. A mechanical heart valve can activate the coagulation pathway after contact with blood after implantation in the cardiovascular system, leading to thrombosis. Therefore, bioprosthetic heart valves (BHVs) are still a promising way to solve this problem. However, there are still challenges in the use of BHVs. For example, their longevity is still unsatisfactory due to the defects, such as thrombosis, structural valve degeneration, calcification, insufficient re-endothelialization, and the inflammatory response. Therefore, strategies and methods are needed to effectively improve the biocompatibility and longevity of BHVs. This review describes the recent research advances in BHVs and strategies to improve their biocompatibility and longevity.

Double crosslinking decellularized bovine pericardium of dialdehyde chondroitin sulfate and zwitterionic copolymer for bioprosthetic heart valves with enhanced antithrombogenic, anti-inflammatory and anti-calcification properties

Due to the increasing aging population and the advancements in transcatheter aortic valve replacement (TAVR), the use of bioprosthetic heart valves (BHVs) in patients diagnosed with valvular disease has increased substantially. Commercially available glutaraldehyde (GA) cross-linked biological valves suffer from reduced durability due to a combination of factors, including the high cell toxicity of GA, subacute thrombus, inflammation and calcification. In this study, oxidized chondroitin sulfate (OCS), a natural polysaccharide derivative, was used to replace GA to cross-link decellularized bovine pericardium (DBP), carrying out the first crosslinking of DBP to obtain OCS-BP. Subsequently, the zwitterion radical copolymerization system was introduced in situ to perform double cross-linking to obtain double crosslinked BHVs with biomimetic modification (P(APM/MPC)-OCS-BP). P(APM/MPC)-OCS-BP presented enhanced mechanical properties, collagen stability and enzymatic degradation resistance due to double crosslinking. The ex vivo AV-shunt assay and coagulation factors test suggested that P(APM/MPC)-OCS-BP exhibited excellent anticoagulant and antithrombotic properties due to the introduction of P(APM/MPC). P(APM/MPC)-OCS-BP also showed good HUVEC-cytocompatibility due to the substantial reduction of its residual aldehyde group. The subcutaneous implantation also demonstrated that P(APM/MPC)-OCS-BP showed a weak inflammatory response due to the anti-inflammatory effect of OCS. Finally, in vivo and in vitro results revealed that P(APM/MPC)-OCS-BP exhibited an excellent anti-calcification property. In a word, this simple cooperative crosslinking strategy provides a novel solution to obtain BHVs with good mechanical properties, and HUVEC-cytocompatibility, anti-coagulation, anti-inflammatory and anti-calcification properties. It might be a promising alternative to GA-fixed BP and exhibited good prospects in clinical applications.

Recent progress in functional modification and crosslinking of bioprosthetic heart valves

Valvular heart disease (VHD), clinically manifested as stenosis and regurgitation of native heart valve, is one of the most prevalent cardiovascular diseases with high mortality. Heart valve replacement surgery has been recognized as golden standard for the treatment of VHD. Owing to the clinical application of transcatheter heart valve replacement technic and the excellent hemodynamic performance of bioprosthetic heart valves (BHVs), implantation of BHVs has been increasing over recent years and gradually became the preferred choice for the treatment of VHD. However, BHVs might fail within 10-15 years due to structural valvular degeneration (SVD), which was greatly associated with drawbacks of glutaraldehyde crosslinked BHVs, including cytotoxicity, calcification, component degradation, mechanical failure, thrombosis and immune response. To prolong the service life of BHVs, much effort has been devoted to overcoming the drawbacks of BHVs and reducing the risk of SVD. In this review, we summarized and analyzed the research and progress on: (i) modification strategies based on glutaraldehyde crosslinked BHVs and (ii) nonglutaraldehyde crosslinking strategies for BHVs.

A Glutaraldehyde-Free Crosslinking Method for the Treatment of Collagen-Based Biomaterials for Clinical Application

Biological bioprostheses such as grafts, patches, and heart valves are often derived from biological tissue like the pericardium. These bioprostheses can be of xenogenic, allogeneic, or autologous origin. Irrespective of their origin, all types are pre-treated via crosslinking to render the tissue non-antigenic and mechanically strong or to minimize degradation. The most widely used crosslinking agent is glutaraldehyde. However, glutaraldehyde-treated tissue is prone to calcification, inflammatory degradation, and mechanical injury, and it is incapable of matrix regeneration, leading to structural degeneration over time. In this work, we are investigating an alternative crosslinking method for an intraoperative application. The treated tissue's crosslinking degree was evaluated by differential scanning calorimetry. To confirm the findings, a collagenase assay was conducted. Uniaxial tensile testing was used to assess the tissue's mechanical properties. To support the findings, the treated tissue was visualized using two-photon microscopy. Additionally, fourier transform infrared spectroscopy was performed to study the overall protein secondary structure. Finally, a crosslinking procedure was identified for intraoperative processing. The samples showed a significant increase in thermal and enzymatic stability after treatment compared to the control, with a difference of up to 22.2 °C and 100%, respectively. Also, the tissue showed similar biomechanics to glutaraldehyde-treated tissue, showing greater extensibility, a higher failure strain, and a lower ultimate tensile strength than the control. The significant difference in the structure band ratio after treatment is proof of the introduction of additional crosslinks compared to the untreated control with regard to differences in the amide-I region. The microscopic images support these findings, showing an alteration of the fiber orientation after treatment. For collagen-based biomaterials, such as pericardial tissue, the novel phenolic crosslinking agent proved to be an equivalent alternative to glutaraldehyde regarding tissue characteristics. Although long-term studies must be performed to investigate superiority in terms of longevity and calcification, our novel crosslinking agent can be applied in concentrations of 1.5% or 2.0% for the treatment of biomaterials.

Differential Immune Response to Bioprosthetic Heart Valve Tissues in the α1,3Galactosyltransferase-Knockout Mouse Model

Structural valve deterioration (SVD) of bioprosthetic heart valves (BHVs) has great clinical and economic consequences. Notably, immunity against BHVs plays a major role in SVD, especially when implanted in young and middle-aged patients. However, the complex pathogenesis of SVD remains to be fully characterized, and analyses of commercial BHVs in standardized-preclinical settings are needed for further advancement. Here, we studied the immune response to commercial BHV tissue of bovine, porcine, and equine origin after subcutaneous implantation into adult α1,3-galactosyltransferase-knockout (Gal KO) mice. The levels of serum anti-galactose α1,3-galactose (Gal) and -non-Gal IgM and IgG antibodies were determined up to 2 months post-implantation. Based on histological analyses, all BHV tissues studied triggered distinct infiltrating cellular immune responses that related to tissue degeneration. Increased anti-Gal antibody levels were found in serum after ATS 3f and Freedom/Solo implantation but not for Crown or Hancock II grafts. Overall, there were no correlations between cellular-immunity scores and post-implantation antibodies, suggesting these are independent factors differentially affecting the outcome of distinct commercial BHVs. These findings provide further insights into the understanding of SVD immunopathogenesis and highlight the need to evaluate immune responses as a confounding factor.

Free-aldehyde neutralized and oligohyaluronan loaded bovine pericardium with improved anti-calcification and endothelialization for bioprosthetic heart valves

The number of patients with valvular heart disease is increasing yearly, and valve replacement is the most effective treatment, during which bioprosthetic heart valves (BHVs) are the most widely used. Commercial BHVs are mainly prepared with glutaraldehyde (Glut) cross-linked bovine pericardial or porcine aortic valves, but the residual free aldehyde groups in these tissues can cause calcification and cytotoxicity. Moreover, insufficient glycosaminoglycans (GAGs) in tissues can further reduce biocompatibility and durability. However, the anti-calcification performance and biocompatibility might be improved by blocking the free aldehyde groups and increasing the GAGs content in Glut-crosslinked tissues. In our study, adipic dihydrazide (ADH) was used to neutralize the residual free aldehyde groups in tissues and provide sites to blind with oligohyaluronan (OHA) to increase the content of GAGs in tissues. The modified bovine pericardium was evaluated for its content of residual aldehyde groups, the amount of OHA loaded, physical/chemical characteristics, biomechanical properties, biocompatibility, and in vivo anticalcification assay and endothelialization effects in juvenile Sprague-Dawley rats. The results showed that ADH could completely neutralize the free aldehyde groups in the Glut-crosslinked bovine pericardium, the amount of OHA loaded increased and the cytotoxicity was reduced. Moreover, the in vivo results also showed that the level of calcification and inflammatory response in the modified pericardial tissue was significantly reduced in a rat subcutaneous implantation model, and the results from the rat abdominal aorta vascular patch repair model further demonstrated the improved capability of the modified pericardial tissues for endothelialization. Furthermore, more α-SMA+ smooth muscle cells and fewer CD68+ macrophages infiltrated in the neointima of the modified pericardial patch. In summary, blocking free-aldehydes and loading OHA improved the anti-calcification, anti-inflammation and endothelialization properties of Glut-crosslinked BHVs and in particularly, this modified strategy may be a promising candidate for the next-generation of BHVs.

A chlorogenic acid functional strategy of anti-inflammation, anti-coagulation and promoted endothelial proliferation for bioprosthetic artificial heart valves

Heart valve replacement has become an optimal choice for the treatment of severe heart valve disease. At present, most commercial bioprosthetic heart valves (BHVs) are made from porcine pericardium or bovine pericardium treated with glutaraldehyde. Nevertheless, due to the toxicity of residual aldehyde groups left after glutaraldehyde cross-linking, these commercial BHVs exhibit poor biocompatibility, calcification, risk of coagulation and endothelialization difficulty, which greatly affects the durability of the BHVs and shortens their service life. In this work, based on a chlorogenic acid functional anti-inflammation, anti-coagulation and endothelialization strategy and dual-functional non-glutaraldehyde cross-linking reagent OX-CO, a kind of functional BHV material OX-CA-PP has been developed from OX-CO cross-linked porcine pericardium (OX-CO-PP) followed by the convenient modification of chlorogenic acid through a reactive oxygen species (ROS) sensitive borate ester bond. The functionalization of chlorogenic acid can reduce the risk of valve leaf thrombosis and promote endothelial cell proliferation, which is beneficial to the formation of a long-term interface with good blood compatibility. Meanwhile, such a ROS responsive behavior can trigger intelligent release of chlorogenic acid on-demand to achieve the inhibition of acute inflammation at the early stage of implantation. The in vivo and in vitro experimental results show that the functional BHV material OX-CA-PP exhibits superior anti-inflammation, improved anti-coagulation, minimal calcification and promoted proliferation of endothelial cells, showing that this non-glutaraldehyde functional strategy has great potential for the application of BHVs and providing a promising reference for other implanted biomaterials.

Development of Innovative Biomaterials and Devices for the Treatment of Cardiovascular Diseases

Cardiovascular diseases have become the leading cause of death worldwide. The increasing burden of cardiovascular diseases has become a major public health problem and how to carry out efficient and reliable treatment of cardiovascular diseases has become an urgent global problem to be solved. Recently, implantable biomaterials and devices, especially minimally invasive interventional ones, such as vascular stents, artificial heart valves, bioprosthetic cardiac occluders, artificial graft cardiac patches, atrial shunts, and injectable hydrogels against heart failure, have become the most effective means in the treatment of cardiovascular diseases. Herein, an overview of the challenges and research frontier of innovative biomaterials and devices for the treatment of cardiovascular diseases is provided, and their future development directions are discussed.

Hybrid heart valves with VEGF-loaded zwitterionic hydrogel coating for improved anti-calcification and re-endothelialization

With the aging of the population in worldwide, valvular heart disease has become one of the most prominent life-threatening diseases in human health, and heart valve replacement surgery is one of the therapeutic methods for valvular heart disease. Currently, commercial bioprosthetic heart valves (BHVs) for clinical application are prepared with xenograft heart valves or pericardium crosslinked by glutaraldehyde. Due to the residual cell toxicity from glutaraldehyde, heterologous antigens, and immune response, there are still some drawbacks related to the limited lifespan of bioprosthetic heart valves, such as thrombosis, calcification, degeneration, and defectiveness of re-endothelialization. Therefore, the problems of calcification, defectiveness of re-endothelialization, and poor biocompatibility from the use of bioprosthetic heart valve need to be solved. In this study, hydrogel hybrid heart valves with improved anti-calcification and re-endothelialization were prepared by taking decellularized porcine heart valves as scaffolds following grafting with double bonds. Then, the anti-biofouling zwitterionic monomers 2-methacryloyloxyethyl phosphorylcholine (MPC) and vascular endothelial growth factor (VEGF) were utilized to obtain a hydrogel-coated hybrid heart valve (PEGDA-MPC-DHVs@VEGF). The results showed that fewer platelets and thrombi were observed on the surface of the PEGDA-MPC-DHVs@VEGF. Additionally, the PEGDA-MPC-DHVs@VEGF exhibited excellent collagen stability, biocompatibility and re-endothelialization potential. Moreover, less calcification deposition and a lower immune response were observed in the PEGDA-MPC-DHVs@VEGF compared to the glutaraldehyde-crosslinked DHVs (Glu-DHVs) after subcutaneous implantation in rats for 30 days. These studies demonstrated that the strategy of zwitterionic hydrogels loaded with VEGF may be an effective approach to improving the biocompatibility, anti-calcification and re-endothelialization of bioprosthetic heart valves.

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A new and promising strategy of overcoming defects of bioprosthetic heart valves.

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The zwitterionic hydrogel with VEGF is utilized to improve anti-calcification and re-endothelialization properties of heart valves.

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The hybrid heart valves with a VEGF-loaded zwitterionic hydrogel coating exhibits excellent biocompatibility.

The hybrid crosslinking method improved the stability and anti-calcification properties of the bioprosthetic heart valves

The bioprosthetic heart valves (BHVs) are the best option for the treatment of valvular heart disease. Glutaraldehyde (Glut) is commonly used as the golden standard reagent for the crosslinking of BHVs. However, the obvious defects of Glut, including residual aldehyde toxicity, degradation and calcification, increase the probability of valve failure in vivo and motivated the exploration of alternatives. Thus, the aim of this study is to develop a non-glutaraldehyde hybrid cross-linking method composed of Neomycin Trisulfate, Polyethylene glycol diglycidyl ether and Tannic acid as a substitute for Glut, which was proven to reduce calcification, degradation, inflammation of the biomaterial. Evaluations of the crosslinked bovine pericardial included histological and ultrastructural characterization, biomechanical performance, biocompatibility and structural stability test, and in vivo anti-inflammation and anti-calcification assay by subcutaneous implantation in juvenile Sprague Dawley rats. The results revealed that the hybrid crosslinked bovine pericardial were superior to Glut crosslinked biomaterial in terms of better hydrophilicity, thermodynamics stability, hemocompatibility and cytocompatibility, higher Young’s Modulus, better stability and resistance to enzymatic hydrolysis, and lower inflammation, degradation and calcification levels in subcutaneous implants. Considering all above performances, it indicates that the hybrid cross-linking method is appropriate to replace Glut as the method for BHV preparation, and particularly this hybrid crosslinked biomaterials may be a promising candidate for next-generation BHVs.

Glutaraldehyde fixation of venous valve tissue: A benchmark for alternative fixation methods

Objective

Bioprosthetic venous valves have yet to achieve long-term patency due to issues with calcification following implantation that is influenced by current xenograft fixation methods, most notably glutaraldehyde. The goal of this study was to investigate the effects of glutaraldehyde fixation on the functional properties of venous tissue to establish a benchmark for the evaluation of alternative fixation methods.

Methods

The degree of crosslinking was evaluated by determining shrink temperature and the stability of tissue with pronase and collagenase digestion.

Results

Glutaraldehyde fixation of venous tissue was confirmed by a significant difference in the shrink temperature between fresh and glutaraldehyde treated samples. Significant differences in the amount of tissue remaining following digestion were observed for venous versus cardiac tissue.

Conclusions

This study demonstrates the importance of tissue-specific evaluation in the development of alternative xenograft fixation methods to improve outcomes with bioprosthetic venous valves.

Decellularization Following Fixation of Explanted Aortic Valves as a Strategy for Preserving Native Mechanical Properties and Function

Mechanical or biological aortic valves are incorporated in physical cardiac simulators for surgical training, educational purposes, and device testing. They suffer from limitations including either a lack of anatomical and biomechanical accuracy or a short lifespan, hence limiting the authentic hands-on learning experience. Medical schools utilize hearts from human cadavers for teaching and research, but these formaldehyde-fixed aortic valves contort and stiffen relative to native valves. Here, we compare a panel of different chemical treatment methods on explanted porcine aortic valves and evaluate the microscopic and macroscopic features of each treatment with a primary focus on mechanical function. A surfactant-based decellularization method after formaldehyde fixation is shown to have mechanical properties close to those of the native aortic valve. Valves treated in this method were integrated into a custom-built left heart cardiac simulator to test their hemodynamic performance. This decellularization, post-fixation technique produced aortic valves which have ultimate stress and elastic modulus in the range of the native leaflets. Decellularization of fixed valves reduced the valvular regurgitation by 60% compared to formaldehyde-fixed valves. This fixation method has implications for scenarios where the dynamic function of preserved valves is required, such as in surgical trainers or device test rigs.

Immobilized Bisphosphonates as Potential Inhibitors of Bioprosthetic Calcification: Effects on Various Xenogeneic Cardiovascular Tissues

Calcification is the major factor limiting the clinical use of bioprostheses. It may be prevented by the immobilization of bisphosphonic compounds (BPs) on the biomaterial. In this study, we assessed the accumulation and structure of calcium phosphate deposits in collagen-rich bovine pericardium (Pe) and elastin-rich porcine aortic wall (Ao) and bovine jugular vein wall (Ve) cross-linked with glutaraldehyde (GA) or diepoxy compound (DE). These tissues were then modified with pamidronic (PAM) acid or 2-(2′-carboxyethylamino)ethylidene-1,1-bisphosphonic (CEABA) acid. Tissue transformations were studied using Fourier-transform infrared spectroscopy. After subcutaneous implantation of the biomaterials in 220 rats, calcification dynamics were examined using atomic absorption spectrophotometry, light microscopy after von Kossa staining, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy The calcium content in all GA-cross-linked tissues and DE-cross-linked Ao increased to 100–160 mg/g on day 60 after implantation. BPs prevented the accumulation of phosphates on the surface of all materials and most effectively inhibited calcification in GA-cross-linked Ao and DE-cross-linked Pe. PAM containing -OH in the R1 group was more effective than CEABA containing -H in R1. The calcification-inhibitory effect of BPs may be realized through their ability to block nucleation and prevent the growth of hydroxyapatite crystals.

Dialdehyde pectin-crosslinked and hirudin-loaded decellularized porcine pericardium with improved matrix stability, enhanced anti-calcification and anticoagulant for bioprosthetic heart valves

To conveniently and effectively cure heart valve diseases or defects, combined with transcatheter valve technology, bioprosthetic heart valves (BHVs) originated from the decellularized porcine pericardium (D-PP) have been broadly used in clinics. Unfortunately, most clinically available BHVs crosslinked with glutaraldehyde (GA) were challenged in their long-term tolerance, degenerative structural changes, and even failure, owing to the synergistic impact of multitudinous elements (cytotoxicity, calcification, immune responses, etc.). In this work, dialdehyde pectin (AP) was prepared by oxidizing the o-dihydroxy of pectin with sodium periodate. Hereafter, the AP-fixed PP model was obtained by crosslinking D-PP with AP with high aldehyde content (6.85 mmol g^-1), for acquiring excellent mechanical properties and outstanding biocompatibility. To further improve the hemocompatibility of the AP-fixed PP, a natural and specific inhibitor of thrombin (hirudin) was introduced to achieve surface modification of the AP-fixed PP. The feasibility of crosslinking and functionalizing AP-fixed PP, which was a potential leaflet material of BHVs, was exhaustively and systematically evaluated. In vitro studies found that hirudin-loaded and AP-fixed PP (AP + Hirudin-PP) had synchronously achieved effective fixation of collagen, highly effective anticoagulation, and good HUVECs-cytocompatibility. In vivo results revealed that the AP + Hirudin-PP specimens recruited the minimum immune cells in the implantation experiment, and also presented an excellent anti-calcification effect. Overall, AP + Hirudin-PP was endowed with competitive collagen stability (compared with GA-fixed PP), excellent hemocompatibility, good HUVECs-cytocompatibility, low immunogenicity and outstanding anti-calcification, suggesting that AP + Hirudin-PP might be a promising alternative to GA-fixed PP and exhibited a bright prospect in the clinical applications of BHVs.

Zwitterionic hydrogel-coated heart valves with improved endothelialization and anti-calcification properties

Valve replacement surgery is the golden standard for end-stage valvular disease due to the lack of self-repair ability. Currently, bioprosthetic heart valves (BHVs) crosslinked by glutaraldehyde (GA) have been the most popular choice in clinic, especially after the emerge of transcatheter aortic valve replacement (TAVR). Nevertheless, the lifespan of BHVs is limited due to severe calcification and deterioration. In this study, to improve the anti-calcification property of BHVs, decellularized heart valves were modified by methacrylic anhydride to introduce double bonds (MADHVs), and a hybrid hydrogel made of sulfobetaine methacrylate (SBMA) and methacrylated hyaluronic acid (MAHA) was then coated onto the surface of MADHVs. Followed by grafting of Arg-Glu-Asp-Val (REDV), an endothelial cell-affinity peptide, the BHVs with improved affinity to endothelial cell (SMHVs-REDV) was obtained. SMHVs-REDV exhibited excellent collagen stability, reliable mechanical property and superior hemocompatibility. Moreover, enhanced biocompatibility and endothelialization potential compared with GA-crosslinked BHVs were achieved. After subcutaneous implantation for 30 days, SMHVs-REDV showed significantly reduced immune response and calcification compared with GA-crosslinked BHVs. Overall, simultaneous endothelialization and anti-calcification can be realized by this strategy, which was supposed to be benefit for improving the main drawbacks for available commercial BHVs products.

Feasibility study of oxidized hyaluronic acid cross-linking acellular bovine pericardium with potential application for abdominal wall repair

Bovine pericardium(BP)is one of the biological membranes with extensive application in tissue engineering. To fully investigate the potential clinical applications of this natural biological material, a suitable cross-linking reagent is hopefully adopted for modification. Glutaraldehyde (GA) is a clinically most common synthetic cross-linking reagent. In the study, oxidized hyaluronic acid (AHA) was developed to substitute GA to fix acellular bovine pericardium (ABP) for lower cytotoxicity, aiming to evaluate the feasibility of AHA as a cross-linking reagent and develop AHA-fixed ABP as a biological patch for abdominal wall repair. The AHA with the feeding ratio (1.8:1.0) has an appropriate molecular weight and oxidation degree, almost no cytotoxicity and good cross-linking effect. The critical cross-linking characteristics and cytocompatibility of AHA-fixed ABP were also investigated. The results demonstrated that 2.0% AHA-fixed ABP had the most suitable mechanical properties, thermal stability, resistance to enzymatic degradation and hydrophilicity. Moreover, 2.0% AHA-fixed samples exhibited an excellent cytocompatibility with human peritoneal mesothelial cells (HPMC) and low antigenicity. It also showed a prominent anti-calcification ability required for abdominal wall repair. Our data provided experimental basis for future research on AHA as a new cross-linking reagent and AHA-fixed ABP for abdominal wall repair.

A novel detergent-based decellularization combined with carbodiimide crosslinking for improving anti-calcification of bioprosthetic heart valve

Currently, valve replacement surgery is the only therapy for the end-stage valvular diseases because of the inability of regeneration for diseased heart valves. Bioprosthetic heart valves (BHVs), which are mainly derived from glutaraldehyde (GA) crosslinked porcine aortic heart valves or bovine pericardium, have been widely used in the last decades. However, it is inevitable that calcification and deterioration may occur within 10-15 years, which are still the main challenges for the BHVs in clinic. In this study, N-Lauroylsarcosine sodium salt (SLS) combined with N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were utilized to decellularize and crosslink the heart valves instead of GA treatment. The obtained BHVs exhibited excellent extracellular matrix stability and mechanical properties, which were similar with GA treatment. Moreover, the obtained BHVs exhibited betterin vitrobiocompatibilities than GA treatment. After subcutaneous implantation for 30 d, the obtained BHVs showed mitigated immune response and reduced calcification compare with GA treatment. Therefore, all the above results indicated that the treatment of SLS-based decellularization combined with EDC/NHS crosslink should be a promising method to fabricate BHVs which can be used in clinic in future.

Crosslinking porcine aortic valve by radical polymerization for the preparation of BHVs with improved cytocompatibility, mild immune response, and reduced calcification

Over one million artificial heart valve transplantations are performed each year due to valvular stenosis or regurgitation. Among them, bioprosthetic heart valves (BHVs) are increasingly being used because of the absence of the need for lifelong anticoagulation. Almost all of the commercial BHVs are treated with Glutaraldehyde (GLUT). As GLUT-treated BHVs are prone to calcification and structural degradation, their durability is greatly reduced with a service life of only 12-15 years. The physiological structure and mechanical properties of the porcine aortic valve (PAV) are closer to that of a human heart valve, so in this study, PAV is used as the model to explore the comprehensive properties of the prepared BHVs by radical polymerization crosslinking method. We found that PAV treated by radical polymerization crosslinking method showed similar ECM stability and biaxial mechanical properties with GLUT-treated PAV. However, radical polymerization crosslinked PAV exhibited better cytocompatibility and endothelialization potential in vitro cell experiment as better anticalcification potential and reduced immune response than GLUT-treated PAV through subcutaneous animal experiments in rats. To conclude, a novel crosslinking method of non-glutaraldehyde fixation of xenogeneic tissues for the preparation of BHVs is expected.

Biofabrication of poly(l-lactide-co-ε-caprolactone)/silk fibroin scaffold for the application as superb anti-calcification tissue engineered prosthetic valve

In this study, electrospun scaffolds were fabricated by blending poly(l-lactide-co-ε-caprolactone) (PLCL) and silk fibroin (SF) with different ratios, and further the feasibility of electrospun PLCL/SF scaffolds were evaluated for application of tissue engineered heart valve (TEHV). Scanning electron microscopy (SEM) results showed that the surface of PLCL/SF electrospun scaffolds was smooth and uniform while the mechanical properties were appropriate as valve prosthesis. In vitro cytocompatibility evaluation results demonstrated that all of the PLCL/SF electrospun scaffolds were cytocompatible and valvular interstitial cells (VICs) cultured on PLCL/SF scaffolds of 80/20 & 70/30 ratios exhibited the best cytocompatibility. The in vitro osteogenic differentiation of VICs including alkaline phosphatase (ALP) activity and quantitative polymerase chain reaction (qPCR) assays indicated that PLCL/SF scaffolds of 80/20 & 90/10 ratios behaved better anti-calcification ability. In the in vivo calcification evaluation model of rat subdermal implantation, PLCL/SF scaffolds of 80/20 & 90/10 ratios presented better anti-calcification ability, which was consistent with the in vitro results. Moreover, PLCL/SF scaffolds of 80/20 & 70/30 ratios showed significantly enhanced cell infiltration and M2 macrophage with higher CD206+/CD68+ ratio. Collectively, our data demonstrated that electrospun scaffolds with the PLCL/SF ratio of 80/20 hold great potential as TEHV materials.

Cross-linking method using pentaepoxide for improving bovine and porcine bioprosthetic pericardia: A multiparametric assessment study

Bioprosthetic heart valves made from bovine pericardium (BP) and porcine pericardium (PP) preserved with glutaraldehyde (GA) are commonly used in valve surgeries but prone to calcification in many patients. In this study, we compared BP and PP preserved with GA, ethylene glycol diglycidyl ether (DE), and 1,2,3,4,6-penta-O-{1-[2-(glycidyloxy)ethoxy]ethyl}-d-glucopyranose (PE). We studied the stabilities of DE and PE in preservation media along with the amino acid (AA) compositions, Fourier-transform infrared spectra, mechanical properties, surface morphologies, thermal stability, calcification, and the cytocompatibility of BP and PP treated with 0.625% GA, 5% DE, 2% PE, and alternating 5% DE and 2% PE for 3 + 11 d and 10 + 10 d, respectively. Both epoxides were stable in the water-buffer solutions (pH 7.4). DE provided high linkage densities in BP and PP owing to reactions with Hyl, Lys, His, Arg, Ser, and Tyr. PE reacted weakly with these AAs but strongly with Met. High cross-linking density obtained using the 10 d + 10 d method provided satisfactory thermal stability of biomaterials. The epoxy preservations improved cytocompatibility and resistance to calcification. PE enhanced the stress/strain properties of the xenogeneic pericardia, perhaps by forming nanostructures that were clearly visualised in BP using scanning electron microscopy. The DE + PE combination, in an alternating cross-linking manner, thus constitutes a promising option for developing bioprosthetic pericardia.

Heart Valves Cross-Linked with Erythrocyte Membrane Drug-Loaded Nanoparticles as a Biomimetic Strategy for Anti-coagulation, Anti-inflammation, Anti-calcification, and Endothelialization

In recent years, valvular heart disease has become a serious disease threatening human life and is a major cause of death worldwide. However, the glutaraldehyde (GLU)-treated biological heart valves (BHVs) fail to meet all requirements of clinical application due to disadvantages such as valve thrombus, cytotoxicity, endothelialization difficulty, immune response, and calcification. Encouragingly, there are a large number of carboxyls as well as a few amino groups on the surface of GLU-treated BHVs that can be modified to enhance biocompatibility. Inspired by natural biological systems, we report a novel approach in which the heart valve was cross-linked with erythrocyte membrane biomimetic drug-loaded nanoparticles. Such modified heart valves not only preserved the structural integrity, stability, and mechanical properties of the GLU-treated BHVs but also greatly improved anti-coagulation, anti-inflammation, anti-calcification, and endothelialization. The in vitro results demonstrated that the modified heart valves had long-term anti-coagulation properties and enhanced endothelialization processes. The modified heart valves also showed good biocompatibility, including blood and cell biocompatibility. Most importantly, the modified heart valves reduced the TNF-α levels and increased IL-10 compared to GLU-treated BHVs. In vivo animal experiments also confirmed that the modified heart valves had an ultrastrong resistance to calcification after implantation in rats for 120 days. The mechanism of anti-calcification in vivo was mainly due to the controlled release of anti-inflammatory drugs that reduced the inflammatory response after valve implantation. In summary, this therapeutic approach based on BHVs cross-linking with erythrocyte membrane biomimetic nanoparticles sparks a novel design for valvular heart disease therapy.

Curcumin-crosslinked acellular bovine pericardium for the application of calcification inhibition heart valves

Glutaraldehyde (GA) crosslinked bovine or porcine pericardium tissues exhibit high cell toxicity and calcification in the construction of bioprosthetic valves, which accelerate the failure of valve leaflets and motivate the exploration for alternatives. Polyphenols, including curcumin, procyanidin and quercetin, etc, have showed great calcification inhibition potential in crosslinking collagen and elastin scaffolds. Herein, we developed an innovative phenolic fixing technique by using curcumin as the crosslinking reagent for valvular materials. X-ray photoelectron spectroscopy and Fourier transform infrared spectrometry assessments confirmed the hydrogen bond between curcumin and acellular bovine pericardium. Importantly, the calcification inhibition capability of the curcumin-crosslinked bovine pericardium was proved by the dramatically reduced Ca²⁺ content in the curcumin-fixed group in in vitro assay, a juvenile rat subcutaneous implants model, as well as an osteogenic differentiation model. In addition, the results showed that the curcumin-fixed bovine pericardium exhibited better performance in the areas of mechanical performance, hemocompatibility and cytocompatibility, in comparison with the GA group and the commercialized product. In summary, we demonstrated that curcumin was a feasible crosslinking reagent to fix acellular bovine pericardium, which showed great potential for biomedical applications, particularly in cardiovascular biomaterials with calcification inhibition capacity.

Epoxy Chitosan-Crosslinked Acellular Bovine Pericardium with Improved Anti-calcification and Biological Properties

Glutaraldehyde (GA) was conventionally used to crosslink bovine pericardium to prepare bioprosthetic heart valves (BHVs), which usually fail within 10 years because of valve deterioration and calcification. To overcome the high cytotoxicity and severe calcification of GA-crosslinked BHVs, a quaternary ammonium salt of epoxy chitosan (epoxy group-modified 3-chlorine-2-hydroxypropyl trimethyl chitosan, abbreviated as "eHTCC") was developed to modify the acellular bovine pericardium to substitute GA and improve its anti-calcification and biocompatible properties. Mechanical test, enzymatic stability test, blood compatibility assay, and cytocompatibility assay were used to investigate its mechanical property and biocompatibility. The anti-calcification effect of the eHTCC-modified bovine pericardium (eHTCC-BP) was assessed by in vitro assay and rat subcutaneous implantation assay. The results showed that eHTCC-BP could improve the mechanical properties and anti-enzymolysis ability of BP, as well as retain the original three-dimensional structure, compared with the uncrosslinked-BP group. Moreover, the in vivo calcification level of the eHTCC-BP group was much lower than that of the GA-BP group, which was 5.1% (2 weeks), 2.3% (4 weeks), and 0.8% (8 weeks) of the GA-BP group. In summary, this study demonstrated that eHTCC could be a potential crosslinking agent for the extracellular matrix for its favorable crosslinking effects, anti-enzymolysis, anti-calcification, and biocompatibility.

Swim Bladder as a Novel Biomaterial for Cardiovascular Materials with Anti-Calcification Properties

Calcification is a major cause of cardiovascular materials failure and deterioration, which leads to the restriction of their wide application. To develop new materials with anti-calcification capability is an urgent clinical requirement. Herein, a natural material derived from swim bladders as one promising candidate is introduced, which is prepared by decellularization and glutaraldehyde (GA) crosslinking. Data show that the swim bladder is mainly composed of collagen I, glycosaminoglycan (GAG), and elastin, especially rich in elastin, in accordance with higher elastic modulus in comparison to bovine pericardium. Moreover, the calcification of this material is proved dramatically lower than that of bovine pericardium by in vitro calcification assessments and in vivo assay using a rat subcutaneous implantation model. Meanwhile, good cytocompatibility, hemocompatibility, and enzymatic stability are demonstrated by in vitro assays. Further, a small diameter vascular graft using this material is successfully developed by rolling method and in situ implantation assay using a rat abdominal artery replacement model shows great performances in the aspect of higher patency and lower calcification. Taken together, these superior properties of swim bladder-derived material in anti-calcification, proper mechanical strength and stability, and excellent hemocompatibility and cytocompatibility endow it a great candidate as cardiovascular biomaterials.

Applications of decellularized materials in tissue engineering: advantages, drawbacks and current improvements, and future perspectives

Decellularized materials (DMs) are attracting more and more attention in tissue engineering because of their many unique advantages, and they could be further improved in some aspects through various means.

Human decellularized and crosslinked pericardium coated with bioactive molecular assemblies

Decellularized human pericardium is under study as an allogenic material for cardiovascular applications. The effects of crosslinking on the mechanical properties of decellularized pericardium were determined with a uniaxial tensile test, and the effects of crosslinking on the collagen structure of decellularized pericardium were determined by multiphoton microscopy. The viability of human umbilical vein endothelial cells seeded on decellularized human pericardium and on pericardium strongly and weakly crosslinked with glutaraldehyde and with genipin was evaluated by means of an MTS assay. The viability of the cells, measured by their metabolic activity, decreased considerably when the pericardium was crosslinked with glutaraldehyde. Conversely, the cell viability increased when the pericardium was crosslinked with genipin. Coating both non-modified pericardium and crosslinked pericardium with a fibrin mesh or with a mesh containing attached heparin and/or fibronectin led to a significant increase in cell viability. The highest degree of viability was attained for samples that were weakly crosslinked with genipin and modified by means of a fibrin and fibronectin coating. The results indicate a method by which in vivo endothelialization of human cardiac allografts or xenografts could potentially be encouraged.