scholarly journals Residual Bioprosthetic Valve Immunogenicity: Forgotten, Not Lost

2022 ◽  
Vol 8 ◽  
Author(s):  
Paul Human ◽  
Deon Bezuidenhout ◽  
Elena Aikawa ◽  
Peter Zilla
Keyword(s):  
Extracellular Matrix ◽  
Host Response ◽  
Heart Valves ◽  
Bioprosthetic Valve ◽  
Dystrophic Calcification ◽  
Mechanical Stiffness ◽  
Link Density ◽  
Inflammatory Processes ◽  
Cross Link Density ◽  
Valve Pathology

Despite early realization of the need to control inherent immunogenicity of bioprosthetic replacement heart valves and thereby mitigate the ensuing host response and its associated pathology, including dystrophic calcification, the problem remains unresolved to this day. Concerns over mechanical stiffness associated with prerequisite high cross-link density to effect abrogation of this response, together with the insinuated role of leaching glutaraldehyde monomer in subsequent dystrophic mineralization, have understandably introduced compromises. These have become so entrenched as a benchmark standard that residual immunogenicity of the extracellular matrix has seemingly been relegated to a very subordinate role. Instead, focus has shifted toward the removal of cellular compartment antigens renowned for their implication in the failure of vascularized organ xenotransplants. While decellularization certainly offers advantages, this review aims to refocus attention on the unresolved matter of the host response to the extracellular matrix. Furthermore, by implicating remnant immune and inflammatory processes to bioprosthetic valve pathology, including pannus overgrowth and mineralization, the validity of a preeminent focus on decellularization, in the context of inefficient antigen and possible residual microbial remnant removal, is questioned.

Boron nitride for modification of rubber based on isoprene elastomer

2020 ◽  
pp. 105-112
Author(s):  
K. S. Zhansakova ◽  
E. N. Eremin ◽  
G. S. Russkikh ◽  
O. V. Kropotin
Keyword(s):  
Mechanical Properties ◽  
Boron Nitride ◽  
Gradual Increase ◽  
Physical And Mechanical Properties ◽  
Curing Time ◽  
Cross Link ◽  
Start Time ◽  
Link Density ◽  
Cross Link Density ◽  
Isoprene Rubber

The work studies vulcanization characteristics of elastomers based on isoprene rubber filled with carbon black N330 and boron nitride (BN). The influence of the boron nitride (BN) concentration on technological, dynamic, physical and mechanical properties of elastomers has been researched. The application of boron nitride for producing rubber with good properties has been considered. With a gradual increase of the inert filler BN concentration up to 35%, a decrease in the curing rate by 33% and polymer cross-link density by 26% is observed. Moreover, the start time of vulcanization increases by almost 300%, the optimal curing time by 200%.

scholarly journals In Situ “Humanization” of Porcine Bioprostheses: Demonstration of Tendon Bioprostheses Conversion into Human ACL and Possible Implications for Heart Valve Bioprostheses

2021 ◽  
Vol 8 (1) ◽  
pp. 10
Author(s):  
Uri Galili ◽  
Kevin R. Stone
Keyword(s):  
Extracellular Matrix ◽  
Heart Valves ◽  
Cruciate Ligament ◽  
Anticoagulation Therapy ◽  
Young Patients ◽  
Collagen Fibers ◽  
Reconstruction Process ◽  
Bioprosthetic Heart Valves ◽  
Porcine Tissue ◽  
Anterior Cruciate

This review describes the first studies on successful conversion of porcine soft-tissue bioprostheses into viable permanently functional tissue in humans. This process includes gradual degradation of the porcine tissue, with concomitant neo-vascularization and reconstruction of the implanted bioprosthesis with human cells and extracellular matrix. Such a reconstruction process is referred to in this review as “humanization”. Humanization was achieved with porcine bone-patellar-tendon-bone (BTB), replacing torn anterior-cruciate-ligament (ACL) in patients. In addition to its possible use in orthopedic surgery, it is suggested that this humanization method should be studied as a possible mechanism for converting implanted porcine bioprosthetic heart-valves (BHV) into viable tissue valves in young patients. Presently, these patients are only implanted with mechanical heart-valves, which require constant anticoagulation therapy. The processing of porcine bioprostheses, which enables humanization, includes elimination of α-gal epitopes and partial (incomplete) crosslinking with glutaraldehyde. Studies on implantation of porcine BTB bioprostheses indicated that enzymatic elimination of α-gal epitopes prevents subsequent accelerated destruction of implanted tissues by the natural anti-Gal antibody, whereas the partial crosslinking by glutaraldehyde molecules results in their function as “speed bumps” that slow the infiltration of macrophages. Anti-non gal antibodies produced against porcine antigens in implanted bioprostheses recruit macrophages, which infiltrate at a pace that enables slow degradation of the porcine tissue, neo-vascularization, and infiltration of fibroblasts. These fibroblasts align with the porcine collagen-fibers scaffold, secrete their collagen-fibers and other extracellular-matrix (ECM) components, and gradually replace porcine tissues degraded by macrophages with autologous functional viable tissue. Porcine BTB implanted in patients completes humanization into autologous ACL within ~2 years. The similarities in cells and ECM comprising heart-valves and tendons, raises the possibility that porcine BHV undergoing a similar processing, may also undergo humanization, resulting in formation of an autologous, viable, permanently functional, non-calcifying heart-valves.

Mechanical and structural consequences of associative dynamic cross-linking in acrylic diblock copolymers

2021 ◽  
Author(s):  
Jacob Ishibashi ◽  
Ian Pierce ◽  
Alice Chang ◽  
Aristotelis Zografos ◽  
Bassil El-Zaatari ◽  
...  
Keyword(s):  
Viscoelastic Properties ◽  
Diblock Copolymers ◽  
Microphase Separation ◽  
Network Connectivity ◽  
Ethyl Acrylate ◽  
Cross Linking ◽  
Cross Link ◽  
Block Polymers ◽  
Link Density ◽  
Cross Link Density

<p>The composition of low-T<sub>g</sub> <i>n</i>-butylacrylate-<i>block</i>-(acetoxyaceto)ethyl acrylate block polymers is investigated as a strategy to tune the properties of dynamically cross-linked vinylogous urethane vitrimers. As the proportion of the cross-linkable block is increased, the thermorheological properties, structure, and stress relaxation evolve in ways that cannot be explained by increasing cross-link density alone. Evidence is presented that network connectivity defects such as loops and dangling ends are increased by microphase separation. The thermomechanical and viscoelastic properties of block copolymer-derived vitrimers arise from the subtle interplay of microphase separation and network defects.</p><div><br></div><p></p>

Mechanical behavior of poly(methyl methacrylate)-based ionogels

Soft Matter ◽  
2014 ◽  
Vol 10 (40) ◽  
pp. 7993-8000 ◽  
Author(s):  
Mingyu Li ◽  
Jianyu Li ◽  
Hui Na ◽  
Joost J. Vlassak
Keyword(s):  
Methyl Methacrylate ◽  
Mechanical Behavior ◽  
Fracture Energy ◽  
Cross Link ◽  
Poly Methyl Methacrylate ◽  
Link Density ◽  
Cross Link Density ◽  
The Cross ◽  
The Ideal

We demonstrate that the fracture energy of ionogels correlates inversely with the cross-link density. The behavior of ionogels is well captured by the ideal elastomeric gel model.

scholarly journals Magnetic composites based on NR and strontium ferrite

2019 ◽  
Vol 12 (1) ◽  
pp. 63-69
Author(s):  
Ján Kruželák ◽  
Andrea Kvasničáková ◽  
Rastislav Dosoudil ◽  
Ivan Hudec
Keyword(s):  
Carbon Black ◽  
Strontium Ferrite ◽  
Rubber Matrix ◽  
Cross Link ◽  
Magnetic Composites ◽  
Link Density ◽  
Cross Links ◽  
Cross Link Density ◽  
The Cross ◽  
Thermo Physical Properties

Abstract Two types of composites based on natural rubber (NR) and strontium ferrite were tested in this study. Composites of the first type were prepared by incorporation of strontium ferrite in the concentration range ranging from 0 to 100 phr (parts per hundred rubber) into pure NR based rubber matrix, while with those of the second type, strontium ferrite was dosed in the same concentration level into NR based rubber batch with constant amount of carbon black — 25 phr. For rubber matrices cross-linking, a standard sulfur based curing system was used. This work is focused on the effect of magnetic filler content on physico-mechanical, magnetic and thermo-physical properties of composite materials. Subsequently, the cross-link density and the structure of the formed sulfidic cross-links were examined. The results showed that the cross-link density of both types of composites increased with the increasing content of magnetic filler, while the structure of the sulfidic cross-links was almost not influenced by the amount of strontium ferrite. Tensile strength of rubber composites with pure rubber matrix was slightly improved by the incorporation of ferrite, while in case of composites based on a carbon black batch, the incorporation of magnetic filler resulted in the decrease of this characteristic. The presence of magnetic filler in both types of composites leads to a significant increase of the remanent magnetic induction.

Barium and strontium ferrite-filled composites based on NBR and SBR

2018 ◽  
Vol 51 (5) ◽  
pp. 421-439 ◽  
Author(s):  
Ján Kruželák ◽  
Martina Matvejová ◽  
Rastislav Dosoudil ◽  
Ivan Hudec
Keyword(s):  
Barium Ferrite ◽  
Strontium Ferrite ◽  
Styrene Butadiene Rubber ◽  
Magnetic Characteristics ◽  
Butadiene Rubber ◽  
Magnetic Composites ◽  
Link Density ◽  
Cross Link Density ◽  
The Cross ◽  
Styrene Butadiene

In the first part of the research, rubber magnetic composites were prepared by incorporation of strontium and barium ferrite in concentration scale ranging from 0 to 200 phr into rubber matrices based on acrylonitrile–butadiene rubber and styrene–butadiene rubber. The main objective was to investigate the influence of the type and content of magnetic filler on the cross-link density, physical–mechanical and magnetic characteristics of the prepared composites. In the second part of the study, the content of magnetic fillers was kept on constant level—200 phr and the main aim was to investigate the change in mutual combination of both fillers on the cross-linking and properties of the rubber magnets. The results revealed that both fillers show reinforcement effect in the rubber matrices. The higher tensile strength of composites was achieved by application of barium ferrite. Magnetic properties of composite materials were significantly influenced by magnetic characteristics of magnetic fillers. Higher remanent magnetic induction of barium ferrite was reflected in higher remanent magnetization of the equivalent composites. On the other hand, higher coercivity of strontium ferrite resulted in higher coercivity of strontium ferrite-filled composites.

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