Katherine S. Tweden

Platelet interaction with pyrolytic carbon heart-valve leaflets

Although the newest generation of mechanical heart-valve prosthetics constructed either partially or wholly of lowtemperature isotropic pyrolytic carbon (LTIC) have significantly reduced thromboembolic complications compared with early-generation mechanical valves (e.g., Starr-Edwards), thromboembolism remains an important clinical complication. In the present study, high-resolution, lowvoltage scanning electron microscopy (HR-LV-SEM) was used to examine the structure and platelet interaction properties of LTIC valve leaflets manufactured by both Carbo Medics, Inc. and by St. Jude Medical, Inc. Valve leaflets from both manufacturers, prepared and polished exactly as used in clinical heart valves, had similar surface energetics and elemental composition. Examination with LV-SEM revealed a rough and complex three-dimensional surface structure with nanometer- to micron-size features. In vitro adhesion of human platelets on the LTIC materials and Formvar were evaluated in the presence of 1 mg/mL albumin. Platelet-surface activation, as evaluated by shape change, spread area, and deposition, was extremely extensive on the LTIC materials compared with the Formvar positive control material. LTIC-adherent platelets were extremely thin, and closely followed the rough LTIC contours, greatly limiting their visibility with conventional SEM. These observations demonstrate that LTIC surfaces can extensively activate platelets even in the presence of albumin, thereby suggesting that platelet interactions with pyrolytic carbon may have a significant role in mechanical-valve thromboembolism.

Comparative biophysical study of adsorbed calf serum, fetal bovine serum and mussel adhesive protein films

Varying concentrations of different sera and adhesive agents are routinely used to increase cellular attachment to substrata. The surface-chemical effects of some of these surface-altering materials have been examined using ellipsometry, contact angle analysis and multiple-attenuated internal reflection infrared (MAIR-IR) spectroscopy. Specifically, 15% fetal bovine serum (FBS), Hams F-12 (containing 10% FBS + 1% penicillin/streptomycin), 10% calf serum and mussel adhesive protein (MAP) were allowed to adsorb on to similar and different surfaces and then compared. Each of these preparations is capable of altering the surface-chemical properties of substrata with varying resultant surface energies. It is therefore important to characterize serum in the proper concentrations on the substrata under consideration in order to understand the interfacial effects.

Silver Modification of Polyethylene Terephthalate Textiles for Antimicrobial Protection

The safety and in vitro effectiveness of applying silver to polyethylene terephthalate fabric mechanical heart valve (MHV) sewing cuffs for the prevention of prosthetic valve endocarditis (PVE) were evaluated. PVE is an infrequent but grave complication of cardiac surgery associated with mortality rates potentially exceeding 50%. A poor response to antibiotic therapy is partly responsible for the high mortality rates. Silver is a well known antimicrobial agent with broad effectiveness. Preliminary in vitro microbial challenge studies of the coated fabric using the New York State 63 bacteriostatic test and Dow Corning Shake Flask test showed a s>97% reduction for most organisms tested. Sheep mitral valve replacement studies suggest

Human serum albumin and fibrinogen interactions with an adsorbed RGD-containing peptide

The modification of polyethylene terephthalate (PET) and polytetrafluoroethylene (PTFE) with an arginine-glycine-aspartic acid cell adhesion peptide, RGD peptide (PepTite Adhesive Coating; Telios Pharmaceuticals, San Diego, CA) has been previously investigated. Initial animal studies showed this RGD peptide to accelerate healing and assist in the formation of an endothelial cell lining of the lumenal side of PET and PTFE fabrics in a cardiovascular application. It is of interest to determine how this RGD peptide is able to influence cellular events through intervening layers of plasma proteins that spontaneously adsorb upon implantation. This study examined the interaction of predeposited RGD-containing peptide with human serum albumin (HSA) or fibrinogen that was characterized using multiple attenuated internal reflection infrared (MAIR-IR) spectroscopy, ellipsometry, and contact angle analysis. It was determined that fibrinogen-containing films consistently exhibited more mass than films of the RGD peptide, HSA, or HSA adsorbed onto RGD peptide-containing films. MAIR-IR spectra of RGD peptide films before and after HSA adsorption were similar in absorption and intensity; however, ellipsometry indicated HSA introduction had created thicker, less dense films. Fibrinogen, on the other hand, when adsorbed onto RGD peptide films provided increased relative mass in a more compact arrangement. Contact angle analyses of each of the dried films showed their surface energies to remain high, but the polar components of RGD peptide films were reduced after either serum protein adsorption. These phenomena may be related to the minimal thrombus accumulation that was noted during the initial animal studies, that promoted subsequent healing.

Platelets are deposited early post-operatively on the leaflet of a mechanical heart valve in sheep without post-operative anticoagulants or antiplatelet agents: A scanning electron microscopic observation of the pyrolytic carbon surface in a mechanical heart valve

Pyrolytic carbon has been used for mechanical heart valves as a thromboresistant, wear resistant, and fatigue resistant material. Thrombosis and thromboembolism, however, remain major mechanical heart valve associated complications and may frequently occur during the early post-operative period. In depth morphologic studies on blood-pyrolytic carbon surface interactions are limited. The purpose of this study was to evaluate the blood compatibility of the pyrolytic carbon surface of St. Jude Medical mechanical heart valves that were implanted in the mitral position of sheep without the administration of post-operative anticoagulants or antiplatelet agents for 2, 4, and 6 weeks. Almost the entire leaflet and orifice ring surfaces were observed by scanning electron microscopy. Although the surfaces appeared clean macroscopically, when observed by electron microscopy, the surface were mottled, mainly by solitary platelets and aggregations. There were only a few leukocytes or red blood cells observed. No fibrin clots were observed on the leaflets. The density of platelet deposition was higher in the vicinity of the pivots and near the edges of the leaflets. The sizes of the platelet aggregations decreased with longer duration. The outer surfaces of the pivot guards were covered by various amounts of deposition composed of platelet aggregations and thrombi. Thus, the administration of antiplatelet agents is recommended during the early post-operative period after mechanical heart valve implantation.