A novel small animal model for biocompatibility assessment of polymeric materials for use in prosthetic heart valves

Hypotony in the early postoperative period after MicroShunt implantation versus trabeculectomy: A registry study

PURPOSE

A comparison of the safety and efficacy of the MicroShunt versus trabeculectomy in the early postoperative period, with a particular focus on hypotony.

METHODS

In this registry study, we evaluated 200 eyes of 200 glaucoma patients who underwent filtration surgery at Oslo University Hospital between 2017 and 2021. Of these patients, 100 had a Preserflo MicroShunt (Santen) implantation and 100 had a trabeculectomy procedure. The patients were examined per standard hospital protocol after filtration surgery. Data were extracted from the 4- and 8-week visits. We defined hypotony as intraocular pressure (IOP) < 6 mmHg.

RESULTS

The mean preoperative IOP was 20.6 ± 7.1 mmHg in the MicroShunt group and 21.6 ± 7.1 mmHg in the trabeculectomy group, and the patients used a mean of 3.0 ± 0.9 and 3.1 ± 0.9 glaucoma medications, respectively. After 8 weeks, IOP was reduced to 10.4 ± 5.4 mmHg and 11.3 ± 4.6 mmHg, respectively (p = 0.23). During the early postoperative period, hypotony was registered in 63% of the MicroShunt patients and in 21% of the patients in the trabeculectomy group (p < 0.001); and 11% and 1%, respectively, of the patients developed choroidal detachments (p < 0.003). One patient in the MicroShunt group required reoperation due to hypotony.

CONCLUSIONS

In this registry study, we found that the Preserflo MicroShunt and trabeculectomy had equally satisfactory IOP-lowering effects during the early postoperative period. In this same period, a high number of patients in the MicroShunt group developed hypotony.

Physical Characterization and Platelet Interactions under Shear Flows of a Novel Thermoset Polyisobutylene-based Co-polymer

Over the years, several polymers have been developed for use in prosthetic heart valves as alternatives to xenografts. However, most of these materials are beset with a variety of issues, including low material strength, biodegradation, high dynamic creep, calcification, and poor hemocompatibility. We studied the mechanical, surface, and flow-mediated thrombogenic response of poly(styrene-coblock-4-vinylbenzocyclobutene)-polyisobutylene-poly(styrene-coblock-4-vinylbenzocylcobutene) (xSIBS), a thermoset version of the thermoplastic elastomeric polyolefin poly(styrene-block-isobutylene-block-styrene) (SIBS), which has been shown to be resistant to in vivo hydrolysis, oxidation, and enzymolysis. Uniaxial tensile testing yielded an ultimate tensile strength of 35 MPa, 24.5 times greater than that of SIBS. Surface analysis yielded a mean contact angle of 82.05° and surface roughness of 144 nm, which was greater than for poly(ε-caprolactone) (PCL) and poly(methyl methacrylate) (PMMA). However, the change in platelet activation state, a predictor of thrombogenicity, was not significantly different from PCL and PMMA after fluid exposure to 1 dyn/cm(2) and 20 dyn/cm(2). In addition, the number of adherent platelets after 10 dyn/cm(2) flow exposure was on the same order of magnitude as PCL and PMMA. The mechanical strength and low thrombogenicity of xSIBS therefore suggest it as a viable polymeric substrate for fabrication of prosthetic heart valves and other cardiovascular devices.

Three-dimensional printing of nanomaterial scaffolds for complex tissue regeneration

Three-dimensional (3D) printing has recently expanded in popularity, and become the cutting edge of tissue engineering research. A growing emphasis from clinicians on patient-specific care, coupled with an increasing knowledge of cellular and biomaterial interaction, has led researchers to explore new methods that enable the greatest possible control over the arrangement of cells and bioactive nanomaterials in defined scaffold geometries. In this light, the cutting edge technology of 3D printing also enables researchers to more effectively compose multi-material and cell-laden scaffolds with less effort. In this review, we explore the current state of 3D printing with a focus on printing of nanomaterials and their effect on various complex tissue regeneration applications.

Formation of Nanocones on Highly Oriented Pyrolytic Graphite by Oxygen Plasma

Improvement in hemocompatibility of highly oriented pyrolytic graphite (HOPG) by formation of nanostructured surface by oxygen plasma treatment is reported. We have showed that by appropriate fine tuning of plasma and discharge parameters we are able to create nanostructured surface which is densely covered with nanocones. The size of the nanocones strongly depended on treatment time. The optimal results in terms of material hemocompatibility were obtained after treatment with oxygen plasma for 15 s, when both the nanotopography and wettability were the most favorable, since marked reduction in adhesion and activation of platelets was observed on this surface. At prolonged treatment times, the rich surface topography was lost and thus also its antithrombogenic properties. Chemical composition of the surface was always more or less the same, regardless of its morphology and height of the nanocones. Namely, on all plasma treated samples, only a few atomic percent of oxygen was found, meaning that plasma caused mostly etching, leading to changes in the surface morphology. This indicates that the main preventing mechanism against platelets adhesion was the right surface morphology.

Polymeric trileaflet prosthetic heart valves: evolution and path to clinical reality

Present prosthetic heart valves, while hemodynamically effective, remain limited by progressive structural deterioration of tissue valves or the burden of chronic anticoagulation for mechanical valves. An idealized valve prosthesis would eliminate these limitations. Polymeric heart valves (PHVs), fabricated from advanced polymeric materials, offer the potential of durability and hemocompatibility. Unfortunately, the clinical realization of PHVs to date has been hampered by findings of in vivo calcification, degradation and thrombosis. Here, the authors review the evolution of PHVs, evaluate the state of the art of this technology and propose a pathway towards clinical reality. In particular, the authors discuss the development of a novel aortic PHV that may be deployed via transcatheter implantation, as well as its optimization via device thrombogenicity emulation.

In vitro evaluation of a novel hemodynamically optimized trileaflet polymeric prosthetic heart valve

Calcific aortic valve disease is the most common and life threatening form of valvular heart disease, characterized by stenosis and regurgitation, which is currently treated at the symptomatic end-stages via open-heart surgical replacement of the diseased valve with, typically, either a xenograft tissue valve or a pyrolytic carbon mechanical heart valve. These options offer the clinician a choice between structural valve deterioration and chronic anticoagulant therapy, respectively, effectively replacing one disease with another. Polymeric prosthetic heart valves (PHV) offer the promise of reducing or eliminating these complications, and they may be better suited for the new transcatheter aortic valve replacement (TAVR) procedure, which currently utilizes tissue valves. New evidence indicates that the latter may incur damage during implantation. Polymer PHVs may also be incorporated into pulsatile circulatory support devices such as total artificial heart and ventricular assist devices that currently employ mechanical PHVs. Development of polymer PHVs, however, has been slow due to the lack of sufficiently durable and biocompatible polymers. We have designed a new trileaflet polymer PHV for surgical implantation employing a novel polymer-xSIBS-that offers superior bio-stability and durability. The design of this polymer PHV was optimized for reduced stresses, improved hemodynamic performance, and reduced thrombogenicity using our device thrombogenicity emulation (DTE) methodology, the results of which have been published separately. Here we present our new design, prototype fabrication methods, hydrodynamics performance testing, and platelet activation measurements performed in the optimized valve prototype and compare it to the performance of a gold standard tissue valve. The hydrodynamic performance of the two valves was comparable in all measures, with a certain advantage to our valve during regurgitation. There was no significant difference between the platelet activation rates of our polymer valve and the tissue valve, indicating that similar to the latter, its recipients may not require anticoagulation. This work proves the feasibility of our optimized polymer PHV design and brings polymeric valves closer to clinical viability.

Biomaterial applications in cardiovascular tissue repair and regeneration

Cardiovascular disease physically damages the heart, resulting in loss of cardiac function. Medications can help alleviate symptoms, but it is more beneficial to treat the root cause by repairing injured tissues, which gives patients better outcomes. Besides heart transplants, cardiac surgeons use a variety of methods for repairing different areas of the heart such as the ventricular septal wall and valves. A multitude of biomaterials are used in the repair and replacement of impaired heart tissues. These biomaterials fall into two main categories: synthetic and natural. Synthetic materials used in cardiovascular applications include polymers and metals. Natural materials are derived from biological sources such as human donor or harvested animal tissues. A new class of composite materials has emerged to take advantage of the benefits of the strengths and minimize the weaknesses of both synthetic and natural materials. This article reviews the current and prospective applications of biomaterials in cardiovascular therapies.