Tissue Level Mechanical Properties and Extracellular Matrix Investigation of the Bovine Jugular Venous Valve Tissue

Biohybrid elastin-like venous valve with potential for in situ tissue engineering

Chronic venous insufficiency (CVI) is a leading vascular disease whose clinical manifestations include varicose veins, edemas, venous ulcers, and venous hypertension, among others. Therapies targeting this medical issue are scarce, and so far, no single venous valve prosthesis is clinically available. Herein, we have designed a bi-leaflet transcatheter venous valve that consists of (i) elastin-like recombinamers, (ii) a textile mesh reinforcement, and (iii) a bioabsorbable magnesium stent structure. Mechanical characterization of the resulting biohybrid elastin-like venous valves (EVV) showed an anisotropic behavior equivalent to the native bovine saphenous vein valves and mechanical strength suitable for vascular implantation. The EVV also featured minimal hemolysis and platelet adhesion, besides actively supporting endothelialization in vitro, thus setting the basis for its application as an in situ tissue engineering implant. In addition, the hydrodynamic testing in a pulsatile bioreactor demonstrated excellent hemodynamic valve performance, with minimal regurgitation (<10%) and pressure drop (<5 mmHg). No stagnation points were detected and an in vitro simulated transcatheter delivery showed the ability of the venous valve to withstand the implantation procedure. These results present a promising concept of a biohybrid transcatheter venous valve as an off-the-shelf implant, with great potential to provide clinical solutions for CVI treatment.

Current development of bovine jugular vein conduit for right ventricular outflow tract reconstruction

Right ventricular outflow tract (RVOT) reconstruction is a common surgical method to treat congenital cardiac lesions, and bovine jugular vein conduit (BJVC) has become a prevalent candidate of prosthetic material for this procedure since 1999. Although many clinical studies have shown encouraging results on BJVCs, complications such as stenosis, aneurysmal dilatation, valve insufficiency, and infective endocarditis revealed in other clinical outcomes still remain problematic. This review describes the underlying mechanisms causing respective complications, and summarizes the current technological development that may address those causative factors. Novel crosslinking agents, decellularization techniques, conduit coatings, and physical reinforcement materials have improved the performances of BJVCs. The authors expect that the breakthroughs in the clinical application of BJVC may come from new genetic research findings and advanced characterization apparatuses and bioreactors, and are optimistic that the BJVC will in the future provide sophisticated therapies for next-generation RVOT reconstruction.

Bovine jugular vein conduit: What affects its elastomechanical properties and thermostability?

The aim of this study was to compare the mechanical properties and thermal stability of the venous wall depending on the treatment method used, and, accordingly, on those structural changes in the tissue that this treatment causes. Bovine jugular vein walls (BJVWs) cross-linked with glutaraldehyde (GA), ethylene glycol diglycidyl ether (DE), and Contegra commercial conduit were evaluated using uniaxial stretching [with and without pre-conditioning (PreC)], differential scanning calorimetry, amino acid analysis, and attenuated total reflection infrared spectroscopy. Fresh BJVW was used as a control. It was shown that failure stress in non-PreC GA-treated and DE-treated materials was lower than that in fresh and Contegra counterparts. Contegra samples were the stiffest among the tested materials. Cyclic preloading leads to distortion of the mechanical behavior of this material, which is heterogeneous in composition and structure. The denaturation temperatures (T_d ) of all cross-linked BJVWs were higher than the T_d of the fresh vein. The microstructures of the tested BJVWs did not exhibit any differences, but the cross-linking density and hydration of the DE-vein were the highest. GA-cross-linking or DE-cross-linking and isopropanol exposure (Contegra) changed the protein secondary structures of the tested materials in different ways. We hypothesized that the protein secondary structure and hydration degree are the main causes of differences in the mechanical properties and thermal stability of BJVW.

Microengineered 3D Collagen Gels with Independently Tunable Fiber Anisotropy and Directionality

Cellular processes, including differentiation, proliferation, and migration, have been linked to the alignment (anisotropy) and orientation (directionality) of collagen fibers in the native extracellular matrix (ECM). Given the critical role that biophysical cell-matrix interactions play in regulating biological functions, several microfluidic-based methods have been used to establish 3D collagen gels with defined fiber properties; these gels have helped to establish quantitative relationships between structural ECM cues and observed cell responses. Although existing microfluidic fabrication methods provide excellent definition over collagen fiber anisotropy, they have not demonstrated the independent control over fiber anisotropy and directionality necessary to replicate in vivo collagen architecture. Therefore, to advance collagen microengineering capabilities, we present a user-friendly technology platform that uses controlled fluid flows within a non-uniform microfluidic channel network to create collagen landscapes that can be tuned as a function of extensional strain rate. Herein, we demonstrate capabilities to i) control the degree of fiber anisotropy, ii) create spatial gradients in fiber anisotropy, iii) independently define fiber directionality, and iv) generate multi-material interfaces within a 3D environment. We then address the practical issue of integrating cells into microfluidic systems by using a peel-off template technique to provide direct access to microengineered collagen gels, and demonstrate that cells respond to the defined properties of the landscape. Finally, the platform's modular capability is highlighted by integrating a sub-micrometer thick porous parylene membrane onto the microengineered collagen as a method to define cell-substrate interactions.

Advances in Engineering Venous Valves: The Pursuit of a Definite Solution for Chronic Venous Disease

Native venous valves enable proper return of blood to the heart. Under pathological conditions (e.g., chronic venous insufficiency), venous valves malfunction and fail to prevent backward flow. Clinically, this can result in painful swelling, varicose veins, edema, and skin ulcerations leading to a chronic wound situation. Surgical correction of venous valves has proven to drastically reduce these symptoms. However, the absence of intact leaflets in many patients limits the applicability of this strategy. In this context, the development of venous valve replacements represents an appealing approach. Despite acceptable results in animal models, no venous valve has succeeded in clinical trials, and so far no single prosthetic venous valve is commercially available. This calls for advanced materials and fabrication approaches to develop clinically relevant venous valves able to restore natural flow conditions in the venous circulation. In this study, we critically discuss the approaches attempted in the last years, and we highlight the potential of tissue engineering to offer new avenues for valve fabrication. Impact statement Venous valves prosthesis offer the potential to restore normal venous flow, and to improve the prospect of patients that suffer from chronic venous disease. Current venous valve replacements are associated with poor outcomes. A deeper understanding of the approaches attempted so far is essential to establish the next steps toward valve development, and importantly, tissue engineering constitutes a unique toolbox to advance in this quest.

Prosthetic venous valves: Short history and advancements from 2012 to 2020

Chronic Venous Disease is estimated at 83.6% of the global population. Patients experience pain, discomfort and severe complications with few effective therapies being available. Current strategies for the treatment of malfunctioning venous valves are invasive with a high recurrence rate. A prosthetic venous valve replacement is imminent, possibly providing better outcomes and improved general quality of life. In this review, prosthetic venous valves history is presented and assesses the advantages and disadvantages of developed venous valves. Articles that discussed potential designs of prosthetic venous valves were examined. A systematic search produced thirty-five papers fitting the inclusion criteria. Our understanding of the ideal abilities required in prosthetic valves has evolved. Developed valves are reported for regurgitation, migration and leakage. Issues have been resolved, but we are still away from the ideal valve. Improvements within the last eight years provided information on the importance of sinuses and prosthetic to venous wall-size mismatch.