Evaluation of dehydrated human umbilical cord biological properties for wound care and soft tissue healing.

Chronic wounds are a significant health care problem with serious implications for quality of life because they do not properly heal and often require therapeutic intervention. Amniotic membrane allografts have been successfully used as a biologic therapy to promote soft tissue healing; however, the umbilical cord, another placental-derived tissue, has also recently garnered interest because of its unique composition but similar placental tissue origin. The aim of this study was to characterize PURION® PLUS Processed dehydrated human umbilical cord (dHUC) and evaluate the biological properties of this tissue that contribute to healing. This was performed through the characterization of the tissue composition, evaluation of in vitro cellular response to dHUC treatment, and in vivo bioresorption and tissue response in a rat model. It was observed that dHUC contains collagen I, hyaluronic acid, laminin, and fibronectin. Additionally, 461 proteins that consist of growth factors and cytokines, inflammatory modulators, chemokines, proteases and inhibitors, adhesion molecules, signaling receptors, membrane-bound proteins, and other soluble regulators were detected. Cell-based assays demonstrated an increase in adipose-derived stem cell and mesenchymal stem cell proliferation, fibroblast migration and endothelial progenitor cell vessel formation in a dose-dependent manner after dHUC treatment. Lastly, rat subcutaneous implantation demonstrated biocompatibility since dHUC allografts were resorbed without fibrous encapsulation. These findings establish that dHUC possesses biological properties that stimulate cellular responses important for soft tissue healing. © 2018 The Authors. Journal Of Biomedical Materials Research Part B: Applied Biomaterials Published By Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1035-1046, 2019.

Feasibility study of particulate extracellular matrix (P-ECM) and left ventricular assist device (HVAD) therapy in chronic ischemic heart failure bovine model.

Myocardial recovery with left ventricular assist device (LVAD) support is uncommon and unpredictable. We tested the hypothesis that injectable particulate extracellular matrix (P-ECM) with LVAD support promotes cell proliferation and improves cardiac function. LVAD, P-ECM, and P-ECM + LVAD therapies were investigated in chronic ischemic heart failure (IHF) calves induced using coronary embolization. Particulate extracellular matrix emulsion (CorMatrix, Roswell, GA) was injected intramyocardially using a 7 needle pneumatic delivery tool. Left ventricular assist devices (HVAD, HeartWare) were implanted in a left ventricle (LV) apex to proximal descending aorta configuration. Cell proliferation was identified using BrdU (5 mg/kg) injections over the last 45 treatment days. Echocardiography was performed weekly. End-organ regional blood flow (RBF) was quantified at study endpoints using fluorescently labeled microspheres. Before treatment, IHF calves had an ejection fraction (EF) of 33 ± 2% and left ventricular end-diastolic volume of 214 ± 18 ml with cardiac cachexia (0.69 ± 0.06 kg/day). Healthy weight gain was restored in all groups (0.89 ± 0.03 kg/day). EF increased with P-ECM + HVAD from 36 ± 5% to 75 ± 2%, HVAD 38 ± 4% to 58 ± 5%, and P-ECM 27 ± 1% to 66 ± 6%. P-ECM + HVAD demonstrated the largest increase in cell proliferation and end-organ RBF. This study demonstrates the feasibility of combined LVAD support with P-ECM injection to stimulate new cell proliferation and improve cardiac function, which warrants further investigation.

In vivo remodeling potential of a novel bioprosthetic tricuspid valve in an ovine model.

OBJECTIVES: A novel bioprosthetic tricuspid valve was constructed from an acellular extracellular matrix (ECM) bioscaffold. The valve's mechanical functionality and potential for histologic regeneration was evaluated in an ovine model. METHODS: The native tricuspid valves of 4 domestic sheep were excised and replaced with bioprosthetic valves constructed from the ECM bioscaffold material shaped into the form of a tube. In vivo function was assessed over time by transthoracic echocardiography. Animals were euthanized at 3, 5, 8, and 12 months after valve implantation, and explanted valves were examined for gross morphology and by qualitative histopathologic analysis. RESULTS: All 4 sheep survived until the specified date. Forward flow by echocardiography was normal with trivial to mild regurgitation. Annular morphology and mobility of the leaflets appeared normal with excellent leaflet coaptation. Explanted valves were grossly normal at all time points and showed evidence of progressive tissue remodeling and integration at the host-tissue interface. Histopathologic analysis demonstrated massive host-cell infiltration, structural reorganization of the ECM bioscaffold, elastin generation at the annulus by 3 months, and increased collagen organization and glycosaminoglycan presence in the leaflets by 5 months, with no evidence of foreign body response. CONCLUSIONS: When implanted in the form of a tubular valve, the acellular ECM bioscaffold demonstrates feasibility as a biomechanically sound bioprosthetic tricuspid valve replacement with evidence of progressive endothelialization and constructive tissue remodeling.

Remodeling of extracellular matrix patch used for carotid artery repair.

BACKGROUND: We evaluated the in vitro strength and in vivo arterial-wall response to an extracellular-matrix-based patch material in a sheep model of carotid artery repair. MATERIALS AND METHODS: A six-ply sheet of acellular, porcine extracellular matrix (ECM) was subjected to in vitro material strength testing and implanted in 15 sheep for 30, 90, and 180 d. Bovine pericardium was used as a control in some animals. In vivo graft patency was assessed by angiography. Explanted grafts were evaluated by histopathology and burst-strength testing. RESULTS: Mean (SD) in vitro suture retention force of the ECM sheet was 14.5 (3.06) N; tensile strength was 29.7 (6.11) N; and probe burst strength was 185 (22.6) N. In vivo, mild stenosis was observed at 30 d for all patches; stenosis was absent at 90 d in the ECM-repaired arteries but not bovine pericardium controls. Pseudoaneurysm was not observed in any animal. Histopathology showed progressive graft degradation, collagen deposition, formation of neocapillaries and fibrocellular neointima, and endothelialization, but no calcification. Mean (SD) burst pressure for unrepaired arteries was 2608 (858) mmHg and 1473 (694) mmHg for ECM-repaired vessels. Mean change in diameter from unloaded state to burst pressure was 29% (9.7) for unrepaired vessels and 24% (13.4) for ECM-repaired vessels. CONCLUSIONS: The six-ply ECM sheet can withstand the forces encountered after carotid artery repair. In sheep, it shows evidence of progressive, constructive remodeling as early as 30 d post-implantation with rapid deposition of endothelium. ECM shows promise as a patch material for CEA repair.

Numerical investigation of the effects of channel geometry on platelet activation and blood damage.

Thromboembolic complications in Bileaflet mechanical heart valves (BMHVs) are believed to be due to the combination of high shear stresses and large recirculation regions. Relating blood damage to design geometry is therefore essential to ultimately optimize the design of BMHVs. The aim of this research is to quantitatively study the effect of 3D channel geometry on shear-induced platelet activation and aggregation, and to choose an appropriate blood damage index (BDI) model for future numerical simulations. The simulations in this study use a recently developed lattice-Boltzmann with external boundary force (LBM-EBF) method [Wu, J., and C. K. Aidun. Int. J. Numer. Method Fluids 62(7):765-783, 2010; Wu, J., and C. K. Aidun. Int. J. Multiphase flow 36:202-209, 2010]. The channel geometries and flow conditions are re-constructed from recent experiments by Fallon [The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets in School of Chemical and Biomolecular Engineering. Atlanta: Georgia Institute of Technology] and Fallon et al. [Ann. Biomed. Eng. 36(1):1]. The fluid flow is computed on a fixed regular 'lattice' using the LBM, and each platelet is mapped onto a Lagrangian frame moving continuously throughout the fluid domain. The two-way fluid-solid interactions are determined by the EBF method by enforcing a no-slip condition on the platelet surface. The motion and orientation of the platelet are obtained from Newtonian dynamics equations. The numerical results show that sharp corners or sudden shape transitions will increase blood damage. Fallon's experimental results were used as a basis for choosing the appropriate BDI model for use in future computational simulations of flow through BMHVs.

Procoagulant properties of flow fields in stenotic and expansive orifices.

In the United States, over 125,000 mechanical heart valves (MHVs) are implanted each year. Flow through the MHV hinge can cause thromboemboli formation. The purpose of this study was to examine various orifice geometries representing the MHV hinge region and how these geometries may contribute to platelet activation and thrombin generation. We also characterized these flow fields with digital particle image velocimetry (DPIV). Citrated human blood at room temperature was forced through the orifices (400 and 800 microm ID) with a centrifugal bypass pump, continuously infusing calcium chloride to partially reverse the citrate anticoagulant. Blood samples were tested for the presence of thrombin-antithrombin complex (TAT) and platelet factor 4 (PF4). Velocity and shear stress were measured with DPIV using a blood analog fluid seeded with fluorescent microbeads. The results indicate that small changes in geometry, although they do not affect the bulk flow, change the coagulation propensity as blood flows through the orifices. A more abrupt geometry allows more stagnation to occur resulting in more thrombin generation. PF4 measurements indicated similar levels of platelet activation for all orifices. DPIV showed differences in the jets with respect to entrainment of stagnant fluid. These results help to pinpoint the important parameters that lead to flow stasis and subsequent thrombus formation.

Thrombin formation in vitro in response to shear-induced activation of platelets.

INTRODUCTION: Thromboembolic events caused by implanted vascular devices present serious medical challenges. In particular bileaflet mechanical heart valves (MHVs) are prone to thrombus formation in the hinge region due to a combination of high shear stress and stagnation regions. Most studies of shear-induced platelet activation and aggregation have been performed using viscometers, parallel plate flow, and other non-physiologic in vitro configurations. The present study investigated these events in a physiogically relevant environment in which thrombin formation in response to shear stress activation of platelets plays a more predominant role. MATERIALS AND METHODS: Anticoagulated (citrated) human blood was placed in a steady flow loop containing a 400 microm round orifice or various MHVs in the leakage position. Simultaneous blood recalcification enhanced the thrombus forming potential of the blood. Aggrastat and AN51 were used to block binding to the platelet GPIIb/IIIa and GPIb receptors, respectively, and aspirin was used to block thromboxane production. Thrombin generation was measured indirectly by the thrombin-antithrombin III assay. RESULTS AND CONCLUSIONS: Aggrastat, AN51, and aspirin all suppressed thrombin formation. Furthermore, histological results suggested important roles for vWF and fibrinogen in a two-step model of thrombus formation. Thus, thrombin is reproducibly formed in this in vitro system, a process that can be suppressed by blocking platelet activation. This system has the potential to investigate mechanisms and interventions for medical devices that contact with blood under varying shear stress conditions.

Flow and thrombosis at orifices simulating mechanical heart valve leakage regions.

BACKGROUND: While it is established that mechanical heart valves (MHVs) damage blood elements during leakage and forward flow, the role in thrombus formation of platelet activation by high shear flow geometries remains unclear. In this study, continuously recalcified blood was used to measure the effects of blood flow through orifices, which model MHVs, on the generation of procoagulant thrombin and the resulting formation of thrombus. The contribution of platelets to this process was also assessed. METHOD OF APPROACH: 200, 400, 800, and 1200 microm orifices simulated the hinge region of bileaflet MHVs, and 200, 400, and 800 microm wide slits modeled the centerline where the two leaflets meet when the MHV is closed. To assess activation of coagulation during blood recirculation, samples were withdrawn over 0-47 min and the plasmas assayed for thrombin-antithrombin-llI (TAT) levels. Model geometries were also inspected visually. RESULTS: The 200 and 400 microm round orifices induced significant TAT generation and thrombosis over the study interval. In contrast, thrombin generation by the slit orifices, and by the 800 and 1200 microm round orifices, was negligible. In additional experiments with nonrecalcified or platelet-depleted blood, TAT levels were markedly reduced versus the studies with fully anticoagulated whole blood (p < 0.05). CONCLUSIONS: Using the present method, a significant increase in TAT concentration was found for 200 and 400 microm orifices, but not 800 and 1200 microm orifices, indicating that these flow geometries exhibit a critical threshold for activation of coagulation and resulting formation of thrombus. Markedly lower TAT levels were produced in studies with platelet-depleted blood, documenting a key role for platelets in the thrombotic process.