In vitro calcification studies on bioprosthetic and decellularized heart valves under quasi-physiological flow conditions

Abstract

The lifespan of biological heart valve prostheses available in the market is limited due to structural alterations caused by calcium phosphate deposits formed from blood plasma in contact with the tissues. The objective of this work is to present a comparative methodology for the investigation of the formation of calcium phosphate deposits on bioprosthetic and tissue-engineered scaffolds in vitro and the influence of mechanical forces on tissue mineralization. Based on earlier investigations on biological mineralization at constant supersaturation, a circulatory loop simulating dynamic blood flow and physiological pressure conditions was developed. The system was appropriately adapted to evaluate the calcification potential of decellularized (DCV) and glutaraldehyde-fixed (GAV) porcine aortic valves. Results indicated that DCV calcified at higher, statistically non-significant, rates in comparison with GAV. This difference was attributed to the tissue surface modifications and cell debris leftovers from the decellularization process. Morphological analysis of the solids deposited after 20 h by Scanning Electron Microscopy (SEM) in combination with chemical microanalysis electron dispersive spectroscopy (EDS) identified the solid formed as octacalcium phosphate (Ca8(PO4)6H2•5H2O, OCP). OCP crystallites were preferentially deposited in high mechanical stress areas of the test tissues. Moreover, GAV tissues developed a significant transvalvular pressure gradient increase past 36 h with a calcium deposition distribution similar to the one found in explanted prostheses. In conclusion, the presented in vitro circulatory model serves as a valuable pre-screening methodology for the investigation of the calcification process of bioprosthetic and tissue-engineered valves under physiological mechanical load.

Prosthetic heart valves for transcatheter aortic valve replacement

“…D'Alessandro et al reported a model to assess the calcification potential of biological valves and found that the aldehyde groups have an effect on the activity of phospholipids, which could provide nucleation sites for Ca 3 (PO 4 ) 2 . [61,62] The toxicity of the aldehyde group leads to apoptosis, and the dead cells release phospholipids in response to enzymatic lysis, resulting in calcification. Gendler et al reported that the GA-fixed pericardium stored in a mixed solution of propylhydroxy-benzoate or methyl-hydroxy-benzoate and further washed three times with normal saline reduces the residual toxicity when implanted in mice.…”

“…D’Alessandro et al. reported a model to assess the calcification potential of biological valves and found that the aldehyde groups have an effect on the activity of phospholipids, which could provide nucleation sites for Ca 3 (PO 4 ) 2 [61,62] . The toxicity of the aldehyde group leads to apoptosis, and the dead cells release phospholipids in response to enzymatic lysis, resulting in calcification.…”

Cells, growth factors and biomaterials used in tissue engineering for hair follicles regeneration

“…However, the safety in clinical application of Matrigel for HF regeneration is still unclear due to the tumor cell-derived source. Decellularized ECM (dECM) has been widely used due to its similar structural, biochemical, and biophysical properties as native tissues, allowing adequate mechanical and chemical support for tissue engineering [ 128 , 129 ]. Human placenta dECM (HPECM) hydrogel cultured with DPCs restored the protein expression that observed in vivo and the co-transplantation in nude mice regenerated de novo HF [ 25 ].…”

Bisphosphonates as Potential Inhibitors of Calcification in Bioprosthetic Heart Valves (Review)

“…These bonds contain several active oxygen atoms capable of forming strong complexes with calcium cations. Calcification can be provoked by the bond of polymerized GA molecules, which is similar to pyridine bases found in bone tissue collagen [ 84 - 86 ], a degree of mineralization being directly dependent on the density of cross-links in the collagen matrix. In addition, the level of glycosaminoglycans and proteoglycans cross-linked with collagen and preventing spontaneous precipitation of calcium salts in soft tissues decreases in the biomaterial during conservation [ 87 - 89 ].…”