Crosslinking of decellularized porcine heart valve matrix by procyanidins

Novel non-glutaraldehyde bioprosthetic heart valve construction strategy based on ATRP with enhanced anticoagulant and anti-calcification properties

Minimally invasive transcatheter heart valve replacement (THVR) has provided a more convenient and effective means for curing heart valve diseases and defects. Bioprosthetic heart valves (BHVs), with superior hemodynamic performance and no need for long-term anticoagulation, have become the first choice for THVR in recent years. However, almost all the clinically used BHVs are crosslinked by glutaraldehyde, and due to calcification, inflammation, difficulty in endothelialization and other factors, the service cycle of these glutaraldehyde crosslinked BHVs is affected, thus limiting their further application. To avoid defects of these glutaraldehyde crosslinked BHVs, a novel non-glutaraldehyde synergistic crosslinking and modification strategy based on ATRP (atom transfer radical polymerization) has been developed in this study. Firstly, the decellularized porcine pericardium (D-PP) is grafted with an alkyl bromine group (Br-PP) to initiate the ATRP reaction, and then the four-arm double-bond substance is used to achieve crosslinked PP (PT-PP) through the in situ ATRP reaction to endow PT-PP with good mechanical properties. Finally, utilizing the advantage of controllable and active polymerization of ATRP, the surface of PT-PP can be further functionalized with sulfonic acid groups by the secondary polymerization to obtain the functionalized PP (PT-BS-PP). The feasibility of non-glutaraldehyde crosslinked and functionalized PPs has been further systematically evaluated as a potential leaflet material of BHVs. Good biocompatibility, superior anticoagulation properties, minimal immune rejection, enhanced endothelialization potential and excellent anti-calcification effects of the functionalized PT-BS-PP have been proven by in vitro and in vivo investigations, suggesting that PT-BS-PP is a great potential candidate for the further clinical applications of BHVs.

Bioprosthetic heart valves with zwitterionic copolymer grafting to improve the properties of endothelialization and anti-calcification

Heart valve replacement surgery has been the most effective treatment for severe valvular heart disease. Bioprosthetic heart valves (BHVs) crosslinked by glutaraldehyde (GA) have non-negligible advantages in clinical applications. However, structural valve degeneration, calcification, insufficient re-endothelialization and other factors lead to a shortened service life of BHVs. In this study, GA-crosslinked decellularized heart valves (GADHVs) were grafted with zwitterionic copolymer (PSBG) of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide and glycidyl methacrylate, and further treated with Arg-Glu-Asp-Val (REDV) peptide to obtain REDV-PSBG-GADHVs with anti-fouling ability and endothelial cell affinity. REDV-PSBG-GADHVs exhibited good collagen stability, reliable mechanical property and excellent hemocompatibility. Moreover,in vitroandin vivoexperiments demonstrated that REDV-PSBG-GADHVs exhibited better endothelialization property, lower immune responses and reduced calcification than GADHVs. This modified strategy for heart valve fabrication, which can improve the effect of anti-calcification and endothelialization while maintaining the original advantages of BHVs, shows great potential for application in heart valve replacement.

Multiscale Mechanical Study of Proanthocyanidins for Recovering Residual Stress in Decellularized Blood Vessels

Decellularized artificial blood vessels prepared using physical and chemical methods often exhibit limitations, including poor mechanical performance, susceptibility to inflammation and calcification, and reduced patency. Cross-linking techniques can enhance the stiffness, as well as anti-inflammatory and anti-calcification properties of decellularized vessels. However, conventional cross-linking methods fail to effectively alleviate residual stress post-decellularization, which significantly impacts the patency and vascular remodeling following the implantation of artificial vessels. This study enhances vascular residual stress through varied conditions of proanthocyanidin (PC) cross-linking on decellularized vessels. Microstructural analysis and mechanical investigations across various scales of fresh, decellularized, and residual stress-recovered vessels are performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), and uniaxial tensile testing. Results demonstrate substantial alterations in the morphology of elastic and collagen fibers post-decellularization, which remarkably resemble fresh vessels following residual stress recovery. Furthermore, both the micro- and macro-mechanical characteristics of vessels post-residual stress recovery, including Young's modulus, viscoelasticity, and adhesion, closely resemble those of fresh vessels. Finite element modeling (FEM) confirms the distribution of residual stress and its role in enhancing vascular mechanical integrity. This experimental investigation provides a theoretical foundation at both micro and macroscopic levels for the development of biomimetic blood vessels.

A New Type of Bioprosthetic Heart Valve: Synergistic Modification with Anticoagulant Polysaccharides and Anti-inflammatory Drugs

Valvular heart disease (VHD) poses a significant threat to human health, and the transcatheter heart valve replacement (THVR) is the best treatment for severe VHD. Currently, the glutaraldehyde cross-linked commercial bioprosthetic heart valves (BHVs) remain the first choice for THVR. However, the cross-linking by glutaraldehyde exhibits several drawbacks, including calcification, inflammatory reactions, and difficult endothelialization, which limits the longevity and applicability of BHVs. In this study, λ-carrageenan with anticoagulant function was modified by carboxymethylation into carboxymethyl λ-carrageenan (CM-λC); subsequently, CM-λC was used as a cross-linking agent to stabilize decellularized bovine pericardial tissue through amide bonds formed by a 1-(3-(Dimethylamino)propyl)-3-ethylcarbodiimide/N-Hydroxysuccinimide (EDC/NHS)-catalyzed reaction between the amino functional groups within pericardium and the carboxyl group located on CM-λC. Lastly, the inclusion complex (CD/Rutin) (formed by encapsulating the rutin molecule through the hydrophobic cavity of the mono-(6-ethylenediamine-6-deoxy)-β-cyclodextrin) was immobilized onto above BHVs materials (λCar-BP) through the amidation reaction. The treated sample exhibited mechanical properties and collagen stability similar to those of GA-BP, except for improved flexibility. Because of the presence of sulfonic acid groups and absence of aldehyde group as well as the Rutin release from CD/Rutin immobilized onto BHVs, the hemocompatibility, anti-inflammatory, HUVEC-cytocompatibility, and anticalcification properties, of the CM-λC-fixed BP modified with CD/Rutin was significantly better than that of GA-BP. In summary, this nonaldehyde-based natural polysaccharide cross-linking strategy utilizing the combination of CM-λC and CD/Rutin provides a novel solution to obtain BHVs with durable and stable anticoagulant, anticalcification, and anti-inflammatory properties, and has a wide range of potential applications in improving the various properties of BHVs.

Thermosensitive Porcine Myocardial Extracellular Matrix Hydrogel Coupled with Proanthocyanidins for Cardiac Tissue Engineering

Currently, there are no therapies that prevent the negative myocardial remodeling process that occurs after a heart attack. Injectable hydrogels are a treatment option because they may replace the damaged extracellular matrix and, in addition, can be administered minimally invasively. Reactive oxygen species generated by ischemia-reperfusion damage can limit the therapeutic efficacy of injectable hydrogels. In order to overcome this limitation, grape seed proanthocyanidins were incorporated as antioxidant compounds into a thermosensitive myocardial extracellular matrix hydrogel in this study. For the fabrication of the hydrogel, the extracellular matrix obtained by decellularization of porcine myocardium was solubilized through enzymatic digestion, and the proanthocyanidins were incorporated. After exposing this extracellular matrix solution to 37 °C, it self-assembled into a hydrogel with a porous structure. According to the physicochemical and biological evaluation, the coupling of proanthocyanidins in the hydrogel has a positive effect on the antioxidant capacity, gelation kinetics, in vitro degradation, and cardiomyocyte viability, indicating that the hydrogel coupled with this type of antioxidants represents a promising alternative for potential application in post-infarction myocardial regeneration. Furthermore, this study proposes the best concentrations of proanthocyanidins that resulted in the hydrogels for future studies in cardiac tissue engineering.

Crosslinking strategies of decellularized extracellular matrix in tissue regeneration

By removing the immunogenic cellular components through various decellularization methods, decellularized extracellular matrix (dECM) is considered a promising material in the field of tissue engineering and regenerative medicine with highly preserved physicochemical properties and superior biocompatibility. However, decellularization treatment can lead to some loss of structural integrity, mechanical strength, degradation stability, and biological performance of dECM biomaterials. Therefore, physical and chemical crosslinking methods are preferred to restore or even improve the biomechanical properties, stability, and bioactivity, and to achieve a delicate balance between degradation of the implanted biomaterial and regeneration of the host tissue. This review provides an overview of dECM biomaterials, and describes and compares the mechanisms and characteristics of commonly used crosslinking methods for dECM, with a focus on the potential applications of versatile dECM-based biomaterials derived from skin, cardiac tissues (pericardium, heart valves, myocardial tissue), blood vessels, liver, and kidney, modified with different chemical crosslinking reagents, in tissue and organ regeneration.

Swim bladder-derived biomaterials: structures, compositions, properties, modifications, and biomedical applications

Animal-derived biomaterials have been extensively employed in clinical practice owing to their compositional and structural similarities with those of human tissues and organs, exhibiting good mechanical properties and biocompatibility, and extensive sources. However, there is an associated risk of infection with pathogenic microorganisms after the implantation of tissues from pigs, cattle, and other mammals in humans. Therefore, researchers have begun to explore the development of non-mammalian regenerative biomaterials. Among these is the swim bladder, a fish-derived biomaterial that is rapidly used in various fields of biomedicine because of its high collagen, elastin, and polysaccharide content. However, relevant reviews on the biomedical applications of swim bladders as effective biomaterials are lacking. Therefore, based on our previous research and in-depth understanding of this field, this review describes the structures and compositions, properties, and modifications of the swim bladder, with their direct (including soft tissue repair, dural repair, cardiovascular repair, and edible and pharmaceutical fish maw) and indirect applications (including extracted collagen peptides with smaller molecular weights, and collagen or gelatin with higher molecular weights used for hydrogels, and biological adhesives or glues) in the field of biomedicine in recent years. This review provides insights into the use of swim bladders as source of biomaterial; hence, it can aid biomedicine scholars by providing directions for advancements in this field.

Influences of Polyphenols on the Properties of Crosslinked Acellular Fish Swim Bladders: Experiments and Molecular Dynamic Simulations

Acellular fish swim bladders (AFSBs) are a promising biomaterial in tissue engineering, however, they may suffer from rapid degradation due to enzyme invasion. In this work, natural polyphenols, including epigallocatechin gallate (EGCG), proanthocyanidin (PC), tannic acid (TA) and protocatechuic acid (PCA), were utilized to improve the properties of AFSBs through crosslinking modifications. Fourier transform infrared (FTIR) results indicate that the triple helix of the collagen in AFSBs is well preserved after crosslinking. The differential scanning calorimetry (DSC), water contact angle (WCA) and in vitro degradation tests indicate that the polyphenol-crosslinked AFSBs exhibit improved thermal stability, enzymatic stability, hydrophilicity and mechanical properties. Among them, EGCG with multiple phenolic hydroxyl groups and low potential resistance is more favorable for the improvement of the mechanical properties and enzymatic stability of AFSBs, as well as their biocompatibility and integrity with the collagen triple helix. Moreover, the crosslinking mechanism was demonstrated to be due to the hydrogen bonds between polyphenols and AFSBs, and was affected by the molecular size, molecular weight and the hydroxyl groups activity of polyphenol molecules, as clarified by molecular dynamic (MD) simulations. The approach presented in this work paves a path for improving the properties of collagen materials.

Hydrogel-polyurethane fiber composites with enhanced microarchitectural control for heart valve replacement

Polymeric heart valves offer the potential to overcome the limited durability of tissue based bioprosthetic valves and the need for anticoagulant therapy of mechanical valve replacement options. However, developing a single-phase material with requisite biological properties and target mechanical properties remains a challenge. In this study, a composite heart valve material was developed where an electrospun mesh provides tunable mechanical properties and a hydrogel coating confers an antifouling surface for thromboresistance. Key biological responses were evaluated in comparison to glutaraldehyde-fixed pericardium. Platelet and bacterial attachment were reduced by 38% and 98%, respectively, as compared to pericardium that demonstrated the antifouling nature of the hydrogel coating. There was also a notable reduction (59%) in the calcification of the composite material as compared to pericardium. A custom 3D-printed hydrogel coating setup was developed to make valve composites for device-level hemodynamic testing. Regurgitation fraction (9.6 ± 1.8%) and effective orifice area (1.52 ± 0.34 cm2 ) met ISO 5840-2:2021 requirements. Additionally, the mean pressure gradient was comparable to current clinical bioprosthetic heart valves demonstrating preliminary efficacy. Although the hemodynamic properties are promising, it is anticipated that the random microarchitecture will result in suboptimal strain fields and peak stresses that may accelerate leaflet fatigue and degeneration. Previous computational work has demonstrated that bioinspired fiber microarchitectures can improve strain homogeneity of valve materials toward improving durability. To this end, we developed advanced electrospinning methodologies to achieve polyurethane fiber microarchitectures that mimic or exceed the physiological ranges of alignment, tortuosity, and curvilinearity present in the native valve. Control of fiber alignment from a random fiber orientation at a normalized orientation index (NOI) 14.2 ± 6.9% to highly aligned fibers at a NOI of 85.1 ± 1.4%. was achieved through increasing mandrel rotational velocity. Fiber tortuosity and curvilinearity in the range of native valve features were introduced through a post-spinning annealing process and fiber collection on a conical mandrel geometry, respectively. Overall, these studies demonstrate the potential of hydrogel-polyurethane fiber composite as a heart valve material. Future studies will utilize the developed advanced electrospinning methodologies in combination with model-directed fabrication toward optimizing durability as a function of fiber microarchitecture.

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 synergistic strategy of dual-crosslinking and loading intelligent nanogels for enhancing anti-coagulation, pro-endothelialization and anti-calcification properties in bioprosthetic heart valves

Currently, glutaraldehyde (GA)-crosslinked bioprosthetic heart valves (BHVs) still do not guarantee good biocompatibility and long-term effective durability for clinical application due to their subacute thrombus, inflammation, calcification, tearing and limited durability. In this study, double-modified xanthan gum (oxidized/vinylated xanthan gum (O2CXG)) was acquired from xanthan gum for subsequent double crosslinking and modification platform construction. Sulfonic acid groups with anticoagulant properties were also introduced through the free radical polymerization of vinyl sulfonate (VS) and vinyl on O2CXG. Taking advantage of the drug-loading function of xanthan gum, the treated pericardium was further loaded with inflammation-triggered dual drug-loaded nanogel (heparin (Hep) and atorvastatin (Ator)). Mechanical properties of O2CXG-crosslinked porcine pericardium (O2CXG-PP) were significantly improved via the first network formed by Schiff base bonds and the second C-C bonds network. Due to the presence of sulfonic acid groups as well as the dual drug release from nanogels under the stimulation of H2O2, the hemocompatibility, anti-inflammatory, pro-endothelialization and anti-calcification properties of the crosslinked pericardium modified with nanogels loaded with Hep and Ator (O2CXG+VS+(Hep+Ator) nanogel-PP) was significantly better than that of GA-crosslinked PP (GA-PP). The collaborative strategy of double crosslinking and sequential release of anticoagulant/endothelium-promoting drugs triggered by inflammation could effectively meet the requirement of enhanced multiple performance and long-term durability of bioprosthetic heart valves and provide a valuable pattern for multi-functionalization of blood contacting materials. STATEMENT OF SIGNIFICANCE: Currently, glutaraldehyde-crosslinked bioprosthetic heart valves (BHVs) are subject to subacute thrombus, inflammation, calcification and tearing, which would not guarantee good biocompatibility and long-term effective durability. We developed a cooperative strategy of double crosslinking and surface modification in which double-modified xanthan gum plays a cornerstone. The mechanical properties of this BHV were significantly improved via the first network formed by Schiff base bonds and the second C-C bonds network. Inflammation-triggered combination delivery of heparin and atorvastatin has been demonstrated to enhance anticoagulation, anti-inflammatory and pro-endothelialization of BHVs by utilizing local inflammatory response. The collaborative strategy could effectively meet the requirement of enhanced multiple performance and long-term durability of BHVs and provide a valuable pattern for the multi-functionalization of blood-contacting materials.

Research progress of biomaterials and innovative technologies in urinary tissue engineering

Substantial interests have been attracted to multiple bioactive and biomimetic biomaterials in recent decades because of their ability in presenting a structural and functional reconstruction of urinary tissues. Some innovative technologies have also been surging in urinary tissue engineering and urological regeneration by providing insights into the physiological behavior of the urinary system. As such, the hierarchical structure and tissue function of the bladder, urethra, and ureter can be reproduced similarly to the native urinary tissues. This review aims to summarize recent advances in functional biomaterials and biomimetic technologies toward urological reconstruction. Various nanofirous biomaterials derived from decellularized natural tissues, synthetic biopolymers, and hybrid scaffolds were developed with desired microstructure, surface chemistry, and mechanical properties. Some growth factors, drugs, as well as inorganic nanomaterials were also utilized to enhance the biological activity and functionality of scaffolds. Notably, it is emphasized that advanced approaches, such as 3D (bio) printing and organoids, have also been developed to facilitate structural and functional regeneration of the urological system. So in this review, we discussed the fabrication strategies, physiochemical properties, and biofunctional modification of regenerative biomaterials and their potential clinical application of fast-evolving technologies. In addition, future prospective and commercial products are further proposed and discussed.

Characterization of a Decellularized Sheep Pulmonary Heart Valves and Analysis of Their Capability as a Xenograft Initial Matrix Material in Heart Valve Tissue Engineering

In order to overcome the disadvantages of existing treatments in heart valve tissue engineering, decellularization studies are carried out. The main purpose of decellularization is to eliminate the immunogenicity of biologically derived grafts and to obtain a scaffold that allows recellularization while preserving the natural tissue architecture. SD and SDS are detergent derivatives frequently used in decellularization studies. The aim of our study is to decellularize the pulmonary heart valves of young Merino sheep by using low-density SDS and SD detergents together, and then to perform their detailed characterization to determine whether they are suitable for clinical studies. Pulmonary heart valves of 4-6-month-old sheep were decellularized in detergent solution for 24 h. The amount of residual DNA was measured to determine the efficiency of decellularization. Then, the effect of decellularization on the ECM by histological staining was examined. In addition, the samples were visualized by SEM to determine the surface morphologies of the scaffolds. A uniaxial tensile test was performed to examine the effect of decellularization on biomechanical properties. In vitro stability of scaffolds decellularized by collagenase treatment was determined. In addition, the cytotoxic effect of scaffolds on 3T3 cells was examined by MTT assay. The results showed DNA removal of 94% and 98% from the decellularized leaflet and pulmonary wall portions after decellularization relative to the control group. No cell nuclei were found in histological staining and it was observed that the three-layer leaflet structure was preserved. As a result of the tensile test, it was determined that there was no statistically significant difference between the control and decellularized groups in the UTS and elasticity modulus, and the biomechanical properties did not change. It was also observed that decellularized sheep pulmonary heart valves had no cytotoxic effect. In conclusion, we suggest that the pulmonary valves of decellularized young Merino sheep can be used as an initial matrix in heart valve tissue engineering studies.

Dialdehyde xanthan gum and curcumin synergistically crosslinked bioprosthetic valve leaflets with anti-thrombotic, anti-inflammatory and anti-calcification properties

Currently commercial glutaraldehyde (GA)-crosslinked bioprosthetic valve leaflets (BVLs) suffer from thromboembolic complications, calcification, and limited durability, which are the major stumbling block to wider clinical application of BVLs. Thus, developing new-style BVLs will be an urgent need to enhance the durability of BVLs and alleviate thromboembolic complications. In this study, a quick and effective collaborative strategy of the double crosslinking agents (oxidized polysaccharide and natural active crosslinking agent) was reported to realize enhanced mechanical, and structural stability, excellent hemocompatibility and anti-calcification properties of BVLs. Dialdehyde xanthan gum (AXG) exhibiting excellent stability to heat, acid-base, salt, and enzymatic hydrolysis was first introduced to crosslink decellularized porcine pericardium (D-PP) and then curcumin with good properties of anti-inflammatory, anti-coagulation, anti-liver fibrosis, and anti-atherosclerosis was used to synergistically crosslink and multi-functionalize D-PP to obtain AXG + Cur-PP. A comprehensive evaluation of structural characterization, hemocompatibility, endothelialization potential, mechanical properties and component stability showed that AXG + Cur-PP exhibited better anti-thrombotic properties and endothelialization potential, milder immune responses, excellent anti-calcification properties and enhanced mechanical properties compared with GA-crosslinked PP. Overall, this cooperative crosslinking strategy provides a novel solution to achieve BVLs with enhanced mechanical properties and excellent anti-coagulation, anti-inflammatory, anti-calcification, and the ability to promote endothelial cell proliferation.

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 universal strategy for the construction of polymer brush hybrid non-glutaraldehyde heart valves with robust anti-biological contamination performance and improved endothelialization potential

With the intensification of the aging population and the development of transcatheter heart valve replacement technology (THVR), clinical demand for bioprosthetic valves is increasing rapidly. However, commercial bioprosthetic heart valves (BHVs), mainly manufactured from glutaraldehyde cross-linked porcine or bovine pericardium, generally undergo degeneration within 10-15 years due to calcification, thrombosis and poor biocompatibility, which are closely related to glutaraldehyde cross-linking. In addition, endocarditis caused by post-implantation bacterial infection also accelerates the failure of BHVs. Herein, a functional cross-linking agent bromo bicyclic-oxazolidine (OX-Br) has been designed and synthesized to crosslink BHVs and construct a bio-functionalization scaffold for subsequent in-situ atom transfer radical polymerization (ATRP). The porcine pericardium cross-linked by OX-Br (OX-PP) exhibits better biocompatibility and anti-calcification property than the glutaraldehyde-treated porcine pericardium (Glut-PP) as well as comparable physical and structural stability to Glut-PP. Furthermore, the resistance to biological contamination especially bacterial infection of OX-PP along with anti-thrombus and endothelialization need to be enhanced to reduce the risk of implantation failure due to infection. Therefore, amphiphilic polymer brush is grafted to OX-PP through in-situ ATRP polymerization to prepare polymer brush hybrid BHV material SA@OX-PP. SA@OX-PP has been demonstrated to significantly resist biological contamination including plasma proteins, bacteria, platelets, thrombus and calcium, and facilitate the proliferation of endothelial cells, resulting in reduced risk of thrombosis, calcification and endocarditis. Altogether, the proposed crosslinking and functionalization strategy synergistically achieves the improvement of stability, endothelialization potential, anti-calcification and anti-biofouling performances for BHVs, which would resist the degeneration and prolong the lifespan of BHVs. The facile and practical strategy has great potential for clinical application in fabricating functional polymer hybrid BHVs or other tissue-based cardiac biomaterials. STATEMENT OF SIGNIFICANCE: Bioprosthetic heart valves (BHVs) are widely used in valve replacements for severe heart valve disease, and clinical demand is increasing year over year. Unfortunately, the commercial BHVs, mainly cross-linked by glutaraldehyde, can serve for only 10-15 years because of calcification, thrombus, biological contamination, and difficulties in endothelialization. Many studies have been conducted to explore non-glutaraldehyde crosslinkers, but few can meet high requirements in all aspects. A new crosslinker, OX-Br, has been developed for BHVs. It can not only crosslink BHVs but also serve as a reactive site for in-situ ATRP polymerization and construct a bio-functionalization platform for subsequent modification. The proposed crosslinking and functionalization strategy synergistically achieves the high requirements for stability, biocompability, endothelialization, anti-calcification, and anti-biofouling propeties of BHVs.

A versatile modification strategy for functional non-glutaraldehyde cross-linked bioprosthetic heart valves with enhanced anticoagulant, anticalcification and endothelialization properties

Valvular heart disease is a major threat to human health and transcatheter heart valve replacement (THVR) has emerged as the primary treatment option for severe heart valve disease. Bioprosthetic heart valves (BHVs) with superior hemodynamic performance and compressibility have become the first choice for THVR, and more BHVs have been requested for clinical use in recent years. However, several drawbacks remain for the commercial BHVs cross-linked by glutaraldehyde, including calcification, thrombin, poor biocompatibility and difficulty in endothelialization, which would further reduce the BHVs' lifetime. This study developed a dual-functional non-glutaraldehyde crosslinking reagent OX-VI, which can provide BHV materials with reactive double bonds (CC) for further bio-function modification in addition to the crosslinking function. BHV material PBAF@OX-PP was developed from OX-VI treated porcine pericardium (PP) after the polymerization with 4-vinylbenzene boronic acid and the subsequent modification of poly (vinyl alcohol) and fucoidan. Based on the functional anti-coagulation and endothelialization strategy and dual-functional crosslinking reagent, PBAF@OX-PP has better anti-coagulation and anti-calcification properties, higher biocompatibility, and improved endothelial cells proliferation when compared to Glut-treated PP, as well as the satisfactory mechanical properties and enhanced resistance effect to enzymatic degradation, making it a promising candidate in the clinical application of BHVs. STATEMENT OF SIGNIFICANCE: Transcatheter heart valve replacement (THVR) has become the main solution for severe valvular heart disease. However, bioprosthetic heart valves (BHVs) used in THVR exhibit fatal drawbacks such as calcification, thrombin and difficulty for endothelialization, which are due to the glutaraldehyde crosslinking, resulting in a limited lifetime to 10-15 years. A new non-glutaraldehyde cross-linker OX-VI has been designed, which can not only show great crosslinking ability but also offer the BHVs with reactive double bonds (CC) for further bio-function modification. Based on the dual-functional crosslinking reagent OX-VI, a versatile modification strategy was developed and the BHV material (PBAF@OX-PP) has been developed and shows significantly enhanced anticoagulant, anti-calcification and endothelialization properties, making it a promising candidate in the clinical application of BHVs.

A versatile drug-controlled release polymer brush hybrid non-glutaraldehyde bioprosthetic heart valves with enhanced anti-inflammatory, anticoagulant and anti-calcification properties, and superior mechanical performance

Transcatheter heart valve replacement (THVR) is a novel treatment modality for severe heart valves diseases and has become the main method for the treatment of heart valve diseases in recent years. However, the lifespan of the commercial glutaraldehyde cross-linked bioprosthetic heart valves (BHVs) used in THVR can only serve for 10-15 years, and the essential reason for the failure of the valve leaflet material is due to these problems such as calcification, coagulation, and inflammation caused by glutaraldehyde cross-linking. Herein, a kind of novel non-glutaraldehyde cross-linking agent bromo-bicyclic-oxazolidine (OX-Br) has been designed and synthesized with both crosslinking ability and in-situ atom transfer radical polymerization (ATRP) function. Then OX-Br treated porcine pericardium (OX-Br-PP) are stepwise modified with co-polymer brushes of reactive oxygen species (ROS) response anti-inflammatory drug conjugated block and anti-adhesion polyzwitterion polymer block through the in-situ ATRP reaction to obtain the functional BHV material MPQ@OX-PP. Along with the great mechanical properties and anti-enzymatic degradation ability similar to glutaraldehyde-crosslinked porcine pericardium (Glut-PP), good biocompatibility, improved anti-inflammatory effect, robust anti-coagulant ability and superior anti-calcification property have been verified for MPQ@OX-PP by a series of in vitro and in vivo investigations, indicating the excellent application potential as a multifunctional heart valve cross-linking agent for OX-Br. Meanwhile, the strategy of synergistic effect with in situ generations of reactive oxygen species-responsive anti-inflammatory drug blocks and anti-adhesion polymer brushes can effectively meet the requirement of multifaceted performance of bioprosthetic heart valves and provide a valuable reference for other blood contacting materials and functional implantable materials with great comprehensive performance.

Cross-linking porcine peritoneum by oxidized konjac glucomannan: a novel method to improve the properties of cardiovascular substitute material

The use of natural polysaccharide crosslinkers for decellularized matrices is an effective approach to prepare cardiovascular substitute materials. In this research, NaIO4 was applied to oxidize konjac glucomannan to prepare the polysaccharide crosslinker oxidized konjac glucomannan (OKGM). The as-prepared crosslinker was then used to stabilize collagen-rich decellularized porcine peritoneum (DPP) to construct a cardiovascular substitute material (OKGM-fixed DPP). The results demonstrated that compared with GA-fixed DPP and GNP-fixed DPP, 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP demonstrated suitable mechanical properties, as well as good hemocompatibility, excellent anti-calcification capability, and anti-enzymolysis in vitro. Furthermore, 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP was suitable for vascular endothelial cell adhesion and rapid proliferation, and a single layer of endothelial cells was formed on the fifth day of culture. The in vivo experimental results also showed excellent histocompatibility. The current results demonstrted that OKGM was a novel polysaccharide cross-linking reagent for crosslinking natural tissues featured with rich collagen content, and 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP was a potential cardiovascular substitute material.

Graphical Abstract

Dual-crosslinked bioprosthetic heart valves prepared by glutaraldehyde crosslinked pericardium and poly-2-hydroxyethyl methacrylate exhibited improved antithrombogenicity and anticalcification properties

Bioprosthetic heart valves (BHVs) have been widely used due to the revolutionary transcatheter aortic valve replacement (TAVR) techniques but suffer from a limited lifespan. Previous modification methods of BHVs mainly rely on glutaraldehyde precrosslinking and subsequent modification. In this study, we have engineered a Poly-2-Hydroxyethyl methacrylate (pHEMA) coated BHV based on co-crosslinking and co-polymerization strategies. Our BHV overcomes previous limitations of glutaraldehyde prefixation by introducing free molecules before crosslinking to achieve the crosslinking and allyl moiety immobilization simultaneously. Decellularized porcine pericardium and 2-Amino-4-pentenoic acid (APA) are firstly co-crosslinked by glutaraldehyde to obtain alkenylated porcine pericardium (APA-PP), then APA-PP is copolymerized with hydrophilic monomer 2-Hydroxyethyl methacrylate (HEMA) to prepare pHEMA grafted porcine pericardium (HEMA-PP). Compared with traditional glutaraldehyde crosslinked pericardium (GA), HEMA-PP exhibits decreased cytotoxicity and significantly increased endothelialial cells proliferation (7-folds higher than GA after 3-day incubation). In vitro and ex vivo hemocompatibility studies demonstrate the superiority of HEMA-PP in anti-thrombogenicity, where the platelet adhesion decreased by levels of approximately 89% compared to GA. Moreover, HEMA-PP maintains structurally stable with a low level of calcification in the subcutaneous model. The hydrodynamic performance and durability are proven to meet the requirements of ISO 5840-3. Altogether, HEMA-PP may have the potential for future clinical application. STATEMENT OF SIGNIFICANCE: Currently, bioprosthetic heart valves (BHVs) have drawbacks including cytotoxicity, calcification and thrombosis, which would accelerate structural valvular degeneration and limit the service life of BHVs. We developed a new modification strategy that could simultaneously improve the biocompatibility, anti-calcification and anti-thrombotic properties of BHVs. Moreover, the appropriate durability and hydrodynamic property demonstrated the potential of our strategy for clinical application. This work will potentially prolong the service life of BHVs and provide new insight for the modification of BHVs.

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.

Arginine-grafted porcine pericardium by copolymerization to improve cytocompatibility, hemocompatibility and anti-calcification properties of bioprosthetic heart valve materials

Bioprosthetic heart valves (BHVs) have been used widely due to the development of transcatheter heart valve replacement technology. However, glutaraldehyde crosslinked pericardium (GA), which is widely used as a leaflet...

Novel Digital Light Processing Printing Strategy Using a Collagen-Based Bioink with Prospective Cross-Linker Procyanidins

Three-dimensional (3D) bioink plays a vital role in the construction of tissues and organs by 3D bioprinting. Collagen has outstanding biocompatibility and is widely used in the field of tissue engineering. However, due to poor mechanical properties and slow self-assembly, it is challenging to manufacture high-precision 3D bioprinted collagen scaffolds. Herein, a novel digital light processing (DLP) bioink which can satisfy the printing of complex structures has been developed. This photocurable bioink is based on collagen and supplemented with a small amount of procyanidins (PA) as a cross-linking agent. The low concentration of collagen gives the bioink good fluidity and excellent biocompatibility, and a small amount of PA increases the cross-linking density of the system to obtain better mechanical properties. Using commercial digital light processing (DLP) printers, this collagen-based ink can effectively print structures with micrometer resolution, and the fidelity of the 3D structures can reach above 90%. Cells were able to be loaded in the bioink and distributed uniformly in the collagen scaffold in an unscathed way. This photocurable collagen bioink has broad application potential in DLP 3D bioprinting.

A promising potential candidate for vascular replacement materials with anti-inflammatory action, good hemocompatibility and endotheliocyte-cytocompatibility: phytic acid-fixed amniotic membrane

Due to its excellent biocompatibility and anti-inflammatory activity, amniotic membrane (AM) has attracted much attention from scholars. However, its clinical application in vascular reconstruction was limited for poor processability, rapid biodegradation, and insufficient hemocompatibility. A naturally extracted substance with good cytocompatibility, phytic acid (PA), which can quickly form strong and stable hydrogen bonds on the tissue surface, was used to crosslink decellularized AM (DAM) to prepare a novel vascular replacement material. The results showed that PA-fixed AM had excellent mechanical strength and resistance to enzymatic degradation as well as appropriate surface hydrophilicity. Among all samples, 2% PA-fixed specimen showed excellent human umbilical vein endothelial cells (HUVECs)-cytocompatibility and hemocompatibility. It could also stimulate the secretion of vascular endothelial growth factor and endothelin-1 from seeded HUVECs, indicating that PA might promote neovascularization after implantation of PA-fixed specimens. Also, 2% PA-fixed specimen could inhibit the secretion of tumor necrosis factor-αfrom co-cultured macrophages, thus might reduce the inflammatory response after sample implantation. Finally, the results ofex vivoblood test andin vivoexperiments confirmed our deduction that PA might promote neovascularization after implantation. All the results indicated that prepared PA-fixed DAM could be considered as a promising small-diameter vascular replacement material.

A bioprosthetic heart valve cross-linked by a non-glutaraldehyde reagent with improved biocompatibility, endothelialization, anti-coagulation and anti-calcification properties

Valvular heart disease is an important disease that endangers human health and heart valve replacement has become one of the main treatments for patients with severe valvular heart disease. However, the traditional surgical valve replacement (SVR) suffers several drawbacks such as high risk, great trauma and long recovery time, and more than 30% of patients are intolerant to SVR, especially elderly patients. In recent years, with the development of minimally invasive technology, transcatheter heart valve replacement (THVR) as a method of implantation without thoracotomy has become an optimal treatment for severe valvular heart disease due to its advantages of minimal trauma, low risk and fast recovery. Meanwhile, the usage of bioprosthetic heart valves (BHVs) has been enlarged greatly with the rapid development of THVR and the aging population. Most BHVs in clinics are crosslinked by glutaraldehyde (Glut), which shows great mechanical properties and chemical stability. However, some problems such as poor biocompatibility, calcification, coagulation and endothelialization difficulty also need to be solved urgently for Glut-treated BHVs. In this work, a non-Glut treated BHV from 7a-ethyltetrahydro-oxazolo[3,4-c]oxazole (OX-Et) crosslinked porcine pericardium (PP) has been developed. Compared with glutaraldehyde-crosslinked porcine pericardium (Glut-PP), good physical and chemical properties similar to Glut-PP are shown for OX-Et treated porcine pericardium (OX-Et-PP). It is noteworthy that better biocompatibility, endothelialization performance, and anti-coagulant effect as well as the improved anti-calcification property can also be observed for OX-Et-PP in the in vitro and in vivo study, potentially making OX-Et-PP a good candidate in the application of BHVs.

Transcatheter Heart Valves: A Biomaterials Perspective

Heart valve disease is prevalent throughout the world, and the number of heart valve replacements is expected to increase rapidly in the coming years. Transcatheter heart valve replacement (THVR) provides a safe and minimally invasive means for heart valve replacement in high-risk patients. The latest clinical data demonstrates that THVR is a practical solution for low-risk patients. Despite these promising results, there is no long-term (>20 years) durability data on transcatheter heart valves (THVs), raising concerns about material degeneration and long-term performance. This review presents a detailed account of the materials development for THVRs. It provides a brief overview of THVR, the native valve properties, the criteria for an ideal THV, and how these devices are tested. A comprehensive review of materials and their applications in THVR, including how these materials are fabricated, prepared, and assembled into THVs is presented, followed by a discussion of current and future THVR biomaterial trends. The field of THVR is proliferating, and this review serves as a guide for understanding the development of THVs from a materials science and engineering perspective.

Procyanidins-crosslinked small intestine submucosa: A bladder patch promotes smooth muscle regeneration and bladder function restoration in a rabbit model

Currently the standard surgical treatment for bladder defects is augmentation cystoplasty with autologous tissues, which has many side effects. Biomaterials such as small intestine submucosa (SIS) can provide an alternative scaffold for the repair as bladder patches. Previous studies have shown that SIS could enhance the capacity and compliance of the bladder, but its application is hindered by issues like limited smooth muscle regeneration and stone formation since the fast degradation and poor mechanical properties of the SIS. Procyanidins (PC), a natural bio-crosslinking agent, has shown anti-calcification, anti-inflammatory and anti-oxidation properties. More importantly, PC and SIS can crosslink through hydrogen bonds, which may endow the material with enhanced mechanical property and stabilized functionalities. In this study, various concentrations of PC-crosslinked SIS (PC-SIS) were prepared to repair the full-thickness bladder defects, with an aim to reduce complications and enhance bladder functions. In vitro assays showed that the crosslinking has conferred the biomaterial with superior mechanical property and anti-calcification property, ability to promote smooth muscle cell adhesion and upregulate functional genes expression. Using a rabbit model with bladder defects, we demonstrated that the PC-SIS scaffold can rapidly promote in situ tissue regrowth and regeneration, in particular smooth muscle remodeling and improvement of urinary functions. The PC-SIS scaffold has therefore provided a promising material for the reconstruction of a functional bladder.

The study of dry biological valve crosslinked with a combination of carbodiimide and polyphenol

The glutaraldehyde crosslinked pericardium has been used in bioprosthetic valves for about 50 years. However, problems such as glutaraldehyde residue and calcification still exist in current commercial products. Non-glutaraldehyde crosslinked dry valve is an important strategy to solve those problems. In this study, a non-glutaraldehyde crosslinked dry biological valve material was obtained by the combined crosslinking of carbodiimide (EDC) and polyphenol. The results showed that the comprehensive properties of EDC and curcumin crosslinked pericardium were superior to glutaraldehyde crosslinked pericardium, including unfolding property, anti-calcification, cytotoxicity, anticoagulant properties, mechanical properties, enzyme degradation resistance and thermal shrinkage temperature. EDC and curcumin crosslinked dry pericardium could flatten after being folded at 40°C for 3 days while glutaraldehyde crosslinked pericardium could not. The calcification of pericardium treated with EDC and curcumin was 1.21 ± 0.36 mg/g in rats after 60 days’ subdermal implantation, much lower than that of glutaraldehyde treated control group (22.06 ± 3.17 mg/g).

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

Decellularized materials (DMs) are attracting more and more attention because of their native structures, comparatively high bioactivity, low immunogenicity and good biodegradability, which are difficult to be imitated by synthetic materials. Recently, DMs have been demonstrated to possess great potential to overcome the disadvantages of autografts and have become a kind of promising material for tissue engineering. In this systematic review, we aimed to not only provide a quick access for understanding DMs, but also bring new ideas to utilize them more appropriately in tissue engineering. Firstly, the preparation of DMs was introduced. Then, the updated applications of DMs derived from different tissues and organs in tissue engineering were comprehensively summarized. In particular, their advantages, drawbacks and current improvements were emphasized. Moreover, we analyzed and proposed future perspectives.

Natural cross-linker-stabilized acellular porcine corneal stroma for lamellar keratoplasty

Acellular porcine corneal stroma (APCS) is a promising alternative to human donor cornea for lamellar keratoplasty (LKP). However, the detergents, enzymes and physical forces used during decellularization unavoidably alter the cornea's extracellular matrix composition and disrupt its ultrastructure, making it less mechanically stable and liable to degradation both in vitro and in vivo. Herein, we systematically analyzed the low biomechanics and easy degradability of APCS in terms of structure and protein composition. Then, we introduced natural cross-linkers, namely proanthocyanidin (PA), epigallocatechin-3-gallate and genipin, to stabilize the APCS that exhibited color variations during crosslinking. Then, we developed a protective crosslinking system by combining cross-linkers with bovine serum albumin (BSA) to reduce color change, maintain transparency and improve the mechanical property of APCS. PA/BSA-crosslinked APCS (PA/BSA-APCS) shows favorable corneal transparency and swelling property; the improved overall and surface corneal biomechanics were comparable to those of human cornea, revealing strong resistance to enzymatic degradation and good biocompatibility. Results from LKP in the rabbit model showed complete re-epithelialization without graft melting, the stitches were scarcely loosened after the operation and more host keratocytes had migrated in PA/BSA-APCS at six months post-operation. Therefore, PA/BSA-APCS could be useful as a corneal substitute for tissue regeneration and the protective crosslinking system could be applicable in other bioengineering fields.

Decellularized Extracellular Matrix-based Bioinks for Engineering Tissue- and Organ-specific Microenvironments

Biomaterials-based biofabrication methods have gained much attention in recent years. Among them, 3D cell printing is a pioneering technology to facilitate the recapitulation of unique features of complex human tissues and organs with high process flexibility and versatility. Bioinks, combinations of printable hydrogel and cells, can be utilized to create 3D cell-printed constructs. The bioactive cues of bioinks directly trigger cells to induce tissue morphogenesis. Among the various printable hydrogels, the tissue- and organ-specific decellularized extracellular matrix (dECM) can exert synergistic effects in supporting various cells at any component by facilitating specific physiological properties. In this review, we aim to discuss a new paradigm of dECM-based bioinks able to recapitulate the inherent microenvironmental niche in 3D cell-printed constructs. This review can serve as a toolbox for biomedical engineers who want to understand the beneficial characteristics of the dECM-based bioinks and a basic set of fundamental criteria for printing functional human tissues and organs.

Radical polymerization-crosslinking method for improving extracellular matrix stability in bioprosthetic heart valves with reduced potential for calcification and inflammatory response

In recent years, the number of heart valve replacements has multiplied with valve diseases because of aging populations and the surge in rheumatic heart disease in young people. Among them, bioprosthetic heart valves (BHVs) have become increasingly popular. Transcatheter aortic valve implantation (TAVI) valve as an emerging BHV has been increasingly applied to patients. However, the current commercially used BHVs treated with glutaraldehyde (Glut) still face the problem of durability. BHVs derived from Glut-treated xenogenetic tissues would undergo structural degeneration and calcification sometimes even as short as less than 10 years. This issue has already become a big challenge considering more and more young patients at the age of 50-60 s are receiving the BHV replacement. In our study, an approach that is totally different from the previous techniques named by us as the radical polymerization-crosslinking (RPC) method was developed to improve extracellular matrix stability, prevent calcification, and reduce inflammatory response in BHVs. The porcine pericardium (PP) tissue was decellularized, functionalized with methacryloyl groups, and subsequently crosslinked by radical polymerization. We found that high-density RPC treatment remarkably improved the stability of collagen and elastin of PP, enhanced its endothelialization potential, and provided reliable biomechanical performance as compared to Glut treatment. The in vivo rat model also confirmed the increased componential stability and the reduced inflammatory response of RPC-treated PP. Moreover, the RPC-treated PP showed better in vivo anticalcification potential than Glut-treated PP. STATEMENT OF SIGNIFICANCE: Bioprosthetic heart valves (BHVs) manufactured from glutaraldehyde (Glut)-treated xenogeneic tissues have been used to treat valve-related diseases for several decades. However, the durability of BHVs remains unresolved and becomes more pronounced particularly in younger patients. Although a number of new alternative methods for Glut crosslinking have been proposed, their overall performance is still far from ready to use in humans. In this study, radical polymerization was investigated for crosslinking the porcine pericardium (PP). This treatment was found to have advantages compared to Glut-treated PP in terms of stability, biocompatibility, and anticalcification potential with the hope of addressing the needs of more robust biomaterials for the fabrication of BHVs.

Polyphenol uses in biomaterials engineering

Polyphenols are micronutrients obtained from diet that have been suggested to play an important role in health. The health benefits of polyphenols and their protective effects in food systems as antioxidant compounds are well known and have been extensively investigated. However, their functional roles as a "processing cofactor" in tissue engineering applications are less widely known. This review focuses on the functionality of polyphenols and their application in biomaterials. Polyphenols have been used to stabilize collagen and to improve its resistance to degradation in biological systems. Therefore, they have been proposed to improve the performance of biomedical devices used in cardiovascular systems by improving the mechanical properties of grafted heart valves, enhancing microcirculation through the relaxation of the arterial walls and improving the capillary blood flow and pressure resistance. Polyphenols have been found to stimulate bone formation, mineralization, as well as the proliferation, differentiation, and the survival of osteoblasts. These effects are brought about by the stimulatory effect of polyphenols on osteoblast cells and their protective effect against oxidative stress and inflammatory cytokines. In addition, polyphenols inhibit the differentiation of the osteoclast cells. Collectively, these actions lead to promote bone formation and to reduce bone resorption, respectively. Moreover, polyphenols can increase the cross-linking of dentine and hence its mechanical stability. Overall, polyphenols provide interesting properties that will stimulate further research in the bioengineering field.

Recellularization of decellularized heart valves: Progress toward the tissue-engineered heart valve

The tissue-engineered heart valve portends a new era in the field of valve replacement. Decellularized heart valves are of great interest as a scaffold for the tissue-engineered heart valve due to their naturally bioactive composition, clinical relevance as a stand-alone implant, and partial recellularization in vivo. However, a significant challenge remains in realizing the tissue-engineered heart valve: assuring consistent recellularization of the entire valve leaflets by phenotypically appropriate cells. Many creative strategies have pursued complete biological valve recellularization; however, identifying the optimal recellularization method, including in situ or in vitro recellularization and chemical and/or mechanical conditioning, has proven difficult. Furthermore, while many studies have focused on individual parameters for increasing valve interstitial recellularization, a general understanding of the interacting dynamics is likely necessary to achieve success. Therefore, the purpose of this review is to explore and compare the various processing strategies used for the decellularization and subsequent recellularization of tissue-engineered heart valves.

Comparison of glutaraldehyde and procyanidin cross-linked scaffolds for soft tissue engineering

Soft tissue injuries are among the most difficult orthopaedic conditions to treat, and regenerative medicine holds the promise of better treatments of these injuries. There is therefore a requirement for substrates and porous scaffolds which provide an appropriate chemical and mechanical environment for cell attachment, growth, proliferation and differentiation. In this study, cross-linked porous gelatin-chitosan (Gel/Chi) scaffolds with high porosity (>90%) were fabricated and their internal morphology, pore sizes and porosities were characterized using scanning electron microscopy (SEM), micro computed tomography (micro-CT) and mercury intrusion porosimetry. The cross-linking agents chosen for this study were Procyanidin (PA), chosen for its biocompatibility, and glutaraldehyde (GA), chosen for comparison as a highly effective cross-linker. Concentrations of these cross-linkers varied from 0.1% to 1% (w/v) and controls had the same gelatin-chitosan blend but were untreated. It was found that the water absorption of cross-linked scaffolds decreased as the cross-linker concentration increased and in vitro collagenase degradation test showed both cross-linkers increased the biostability of the scaffolds. Scaffolds were also tested under compressive load to investigate their resistance to deformation. The results indicated that both cross-linkers increase the stiffness of the scaffolds both initially and at higher strains, but GA cross-linked scaffolds had a higher compressive stiffness than scaffolds cross-linked with PA for a given concentration. Results from cyclic compression and stress relaxation tests showed that PA cross-linked scaffolds recover more rapidly after deformation. 3T3 fibroblasts were cultured on the scaffolds to assess cytotoxicity and biocompatibility. The results indicated that PA was non-cytotoxic and promoted the attachment and proliferation of the seeded cells, while fewer cells were seen on GA cross-linked scaffolds, indicating that the GA had conferred some cytotoxicity. PA cross-linked Gel/Chi porous scaffolds show promise as three dimentional porous scaffolds in tissue engineering, as porous substrates for biomimetic culture environments, and for regenerative medicine applications, due to their excellent biocompatibility and easily adaptable mechanical properties, as well as their lower cost compared to collagen and fibrin based substrates.

New insights and perspectives into biological materials for flexible electronics

Materials based on biological materials are becoming increasingly competitive and are likely to be critical components in flexible electronic devices.

Glutaraldehyde Cross-linking Modification of Decellularized Rat Kidney Scaffolds

The decellularized (DC) scaffolds retain three-dimensional structures for the stimulation of cell growth, with components of the extracellular matrix (ECM) relatively conserved between species. The strategy based on decellularized scaffolds provides a new way for organ regeneration, with a number of prominent advances having been reported in the past few years. While their lack of biomechanical strength and excessive degradation limit the clinical applications, therefore it is urgent to modify the DC scaffolds to improve the performance.In this article we describe a simple and robust modification protocol for DC rat kidney scaffolds. To modify, we perfuse DC rat kidneys with glutaraldehyde through the perfusion circulation of the decellularization. After cross-linking, kidney scaffolds are harvested for evaluation of histology, structural stability, and biocompatibility, involving water absorption testing, biomechanical testing, scanning electron microscopy, and several different histological and immunofluorescent analyses.

Preparation of decellularized vascular matrix by co-crosslinking of procyanidins and glutaraldehyde

BACKGROUND

Vascular extracellular matrices (vECMs) have shown potential for small-diameter blood vessel tissue engineering applications. However, problems such as chemical instability and easy calcification are still remained. Chemical crosslinking using crosslinkers such as glutaraldehyde (GA) can improve mechanical properties and proteolysis resistance of vECMs, but leads to calcification and cytotoxicity. Procyanidins (PC) can crosslink ECMs with anti-calcification property and cytocompatibility, but the mechanical properties and chemical stability are unsatisfactory.

OBJECTIVE

A novel co-crosslinking technique using PC and GA was developed, which combines the advantages of both PC and GA for enhancing mechanical properties and stability of vECMs with reduced calcification and cytotoxicity.

METHODS

Fresh carotid were decellularized and then crosslinked by PC and subsequent GA for 6 h respectively. The mechanical properties, dynamic release of PC, enzymatic degradation, calcification and cytotoxicity of crosslinked samples were evaluated.

RESULTS

The co-crosslinked vECMs showed enhanced tensile strength, chemical and biological stability, comparable anti-calcification property as compared to pure PC-crosslinked samples. Cytotoxicity assay showed that the co-crosslinked vECMs were cytocompatible for supporting the adhesion and proliferation of HUVECs.

CONCLUSIONS

Co-crosslinking with PC and GA might be a useful method for preparation of vECM scaffolds with potential applications in small-diameter blood vessel tissue engineering.

Comparison of natural crosslinking agents for the stabilization of xenogenic articular cartilage

Osteochondral xenografts are potentially inexpensive, widely available alternatives to fresh allografts. However, antigen removal from xenogenic cartilage may damage the extracellular matrix and reduce compressive stiffness. Non-crosslinked xenogenic cartilage may also undergo rapid enzymatic degradation in vivo. We hypothesized that natural crosslinking agents could be used in place of glutaraldehyde to improve the mechanical properties and enzymatic resistance of decellularized cartilage. This study compared the effects of genipin (GNP), proanthocyanidin (PA), and epigallocatechin gallate (EGCG), on the physical and mechanical properties of decellularized porcine cartilage. Glutaraldehyde (GA) served as a positive control. Porcine articular cartilage discs were decellularized in 2% sodium dodecyl sulfate and DNase I followed by fixation in 0.25% GNP, 0.25% PA, 0.25% EGCG, or 2.5% GA. Decellularization decreased DNA by 15% and GAG by 35%. For natural crosslinkers, the average degree of crosslinking ranged from approximately 50% (EGCG) to 78% (GNP), as compared to 83% for the GA control. Among the natural crosslinkers, only GNP significantly affected the disc diameter, and shrinkage was under 2%. GA fixation had no significant effect on disc diameter. Decellularization decreased aggregate modulus; GA and GNP, but not EGCG and PA, were able to restore it to its original level. GNP, PA, and GA conferred a similar, almost complete resistance to collagenase degradation. EGCG also conferred substantial resistance but to a lesser degree. Overall, the data support our hypothesis and suggest that natural crosslinkers may be suitable alternatives to glutaraldehyde for stabilization of decellularized cartilage. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1037-1046, 2016.

Design considerations and challenges for mechanical stretch bioreactors in tissue engineering

With the increase in average life expectancy and growing aging population, lack of functional grafts for replacement surgeries has become a severe problem. Engineered tissues are a promising alternative to this problem because they can mimic the physiological function of the native tissues and be cultured on demand. Cyclic stretch is important for developing many engineered tissues such as hearts, heart valves, muscles, and bones. Thus a variety of stretch bioreactors and corresponding scaffolds have been designed and tested to study the underlying mechanism of tissue formation and to optimize the mechanical conditions applied to the engineered tissues. In this review, we look at various designs of stretch bioreactors and common scaffolds and offer insights for future improvements in tissue engineering applications. First, we summarize the requirements and common configuration of stretch bioreactors. Next, we present the features of different actuating and motion transforming systems and their applications. Since most bioreactors must measure detailed distributions of loads and deformations on engineered tissues, techniques with high accuracy, precision, and frequency have been developed. We also cover the key points in designing culture chambers, nutrition exchanging systems, and regimens used for specific tissues. Since scaffolds are essential for providing biophysical microenvironments for residing cells, we discuss materials and technologies used in fabricating scaffolds to mimic anisotropic native tissues, including decellularized tissues, hydrogels, biocompatible polymers, electrospinning, and 3D bioprinting techniques. Finally, we present the potential future directions for improving stretch bioreactors and scaffolds. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:543-553, 2016.

The effects of decellularization and cross-linking techniques on the fatigue life and calcification of mitral valve chordae tendineae

In cases of severely diseased mitral valves (MV), the required treatment is often valve replacement. Bioprosthetic and stentless replacement valves are usually either fully or partially composed of animal derived tissue treated with a decellularization process, a cross-linking process, or both. In this study, we analysed the effects of these treatments on the fatigue properties of porcine MV chordae tendineae (CT), as well as on the calcification of the CT using an in vitro technique. CT were tested in 4 groups; (1) native, (2) decellularized (DC), (3) decellularized and cross-linked with glutaraldehyde (DC-GTH), and (4) decellularized and cross-linked with 1-ehtyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)(DC-EDC). CT were tested in both uniaxial tension, and in fatigue at 10MPa peak stress (1Hz). The cycles to failure (mean±SD) for the four groups are as follows; Native- 53,397±55,798, DC- 28,013±30,634, DC-GTH- 97,665±133,556, DC-EDC- 318,601±322,358. DC-EDC CT were found to have a slightly longer fatigue life than the native and DC groups. The DC-EDC group also had a marginally lower dynamic creep rate, meaning those CT elongate more slowly. After in vitro calcification, X-ray microtomography was used to determine relative levels of calcification. The DC-EDC and DC-GTH groups had the lowest volume of calcific deposits. Under uniaxial testing, the ultimate tensile strength (UTS) of the DC-GTH CT was statistically significantly reduced after calcification, while the UTS was relatively unchanged for the DC-EDC group. Overall, these results indicate that a treatment of decellularization plus cross-linking with EDC may improve the fatigue life of porcine CT, reduce the rate of elongation, and help the CT resist the negative effects of calcification. This may be a preferable treatment in the preparation of porcine MVs for the replacement of diseased MVs.

Preparation of calcium silicate/decellularized porcine myocardial matrix crosslinked by procyanidins for cardiac tissue engineering

CS-incorporated myocardial ECM scaffolds release functional ions gradually, which stimulate expression of the proangiogenic factors in endothelia cells.

Effects of pH on the alginate dialdehyde (ADA)-crosslinking of natural biological tissues and in vitro study of the endothelial cell compatibility of ADA-crosslinked biological tissues

Investigating the optimal pH-environment for ADA fixation and the HUVECs compatibility of the ADA-fixed biological vascular scaffolds.