Enzyme-oxidative-polymerization method for improving glycosaminoglycans stability and reducing calcification in bioprosthetic heart valves

Mechanisms and Drug Therapies of Bioprosthetic Heart Valve Calcification

Valve replacement is the main therapy for valvular heart disease, in which a diseased valve is replaced by mechanical heart valve (MHV) or bioprosthetic heart valve (BHV). Since the 2000s, BHV surpassed MHV as the leading option of prosthetic valve substitute because of its excellent hemocompatible and hemodynamic properties. However, BHV is apt to structural valve degeneration (SVD), resulting in limited durability. Calcification is the most frequent presentation and the core pathophysiological process of SVD. Understanding the basic mechanisms of BHV calcification is an essential prerequisite to address the limited-durability issues. In this narrative review, we provide a comprehensive summary about the mechanisms of BHV calcification on 1) composition and site of calcifications; 2) material-associated mechanisms; 3) host-associated mechanisms, including immune response and foreign body reaction, oxidative stress, metabolic disorder, and thrombosis. Strategies that target these mechanisms may be explored for novel drug therapy to prevent or delay BHV calcification.

Preclinical study of a self-expanding pulmonary valve for the treatment of pulmonary valve disease

In the past decade, balloon-expandable percutaneous pulmonary valves have been developed and applied in clinical practice. However, all the existing products of pulmonary artery interventional valves in the market have a straight structure design, and they require a preset support frame and balloon expansion. This shape design of the valve limits the application range. In addition, the age of the population with pulmonary artery disease is generally low, and the existing products cannot meet the needs of anti-calcification properties and valve material durability. In this study, through optimization of the support frame and leaflet design, a self-expanding pulmonary valve product with a double bell-shaped frame was designed to improve the match of the valve and the implantation site. A loading and deployment study showed that the biomaterial of the valve was not damaged after being compressed. Pulsatile flow and fatigue in vitro tests showed that the fabricated pulmonary valve met the hydrodynamic requirements after 2 × 10⁸ accelerated fatigue cycles. The safety and efficacy of the pulmonary valve product were demonstrated in studies of pulmonary valve implantation in 11 pigs. Angiography and echocardiography showed that the pulmonary valves were implanted in a good position, and they had normal closure and acceptable valvular regurgitation. The 180 days' implantation results showed that the calcium content was 0.31-1.39 mg/g in the anti-calcification treatment group, which was significantly lower than that in the control valve without anti-calcification treatment (16.69 mg/g). Our new interventional pulmonary valve product was ready for clinical trials and product registration.

Poly(ethylene glycol)-Based Coatings for Bioprosthetic Valve Tissues: Toward Restoration of Physiological Behavior

Bioprosthetic valves (BPVs) have a limited lifespan in the body necessitating repeated surgeries to replace the failed implant. Early failure of these implants has been linked to various surface properties of the valve. Surface properties of BPVs are significantly different from physiological valves because of the fixation process used when processing the xenograft tissue. To improve the longevity of BPVs, efforts need to be taken to improve the surface properties and shield the implant from the bodily interactions that degrade it. Toward this goal, we evaluated the use of hydrogel coatings to attach to the BPV tissue and impart surface properties that are close to physiological. Hydrogels are well characterized for their biocompatibility and highly tunable surface characteristics. Using a previously published coating method, we deposited hydrogel coatings of poly(ethylene glycol)diacrylate (PEGDA) and poly(ethylene glycol)diacrylamide (PEGDAA) atop BPV samples. Coated samples were evaluated against the physiological tissue and uncoated glutaraldehyde-fixed tissue for deposition of hydrogel, surface adherence, mechanical properties, and fixation properties. Results showed both PEGDA- and PEGDAA-deposited coatings were nearly continuous across the valve leaflet surface. Further, the PEGDA- and PEGDAA-coated samples showed restoration of physiological levels of protein adhesion and mechanical stiffness. Interestingly, the coating process rather than the coating itself altered the material behavior yet did not alter the cross-linking from fixation. These results show that the PEG-based coatings for BPVs can successfully alter surface properties of BPVs and help promote physiological characteristics without interfering with the necessary fixation.

The biology of vascular calcification

Vascular calcification (VC), characterized by different mineral deposits (i.e., carbonate apatite, whitlockite and hydroxyapatite) accumulating in blood vessels and valves, represents a relevant pathological process for the aging population and a life-threatening complication in acquired and in genetic diseases. Similarly to bone remodeling, VC is an actively regulated process in which many cells and molecules play a pivotal role. This review aims at: (i) describing the role of resident and circulating cells, of the extracellular environment and of positive and negative factors in driving the mineralization process; (ii) detailing the types of VC (i.e., intimal, medial and cardiac valve calcification); (iii) analyzing rare genetic diseases underlining the importance of altered pyrophosphate-dependent regulatory mechanisms; (iv) providing therapeutic options and perspectives.