Platelet adhesion is a key event in thrombus development on blood-contacting medical devices. It has been demonstrated that changes to the chemistry of a material surface can reduce platelet adhesion. In this work, it is hypothesized that sub-micron surface textures may also reduce adhesion via a decrease in the surface area of material with which platelets can make contact, and hence a decreased probability of interaction with adhesive ligands. A polyether(urethane urea) was textured with two different sizes of sub-micron pillars using a replication molding technique that did not alter the material surface chemistry. Adhesion of platelets was assessed in a physiologically relevant shear stress range of 0-67 dyn/cm2 using a rotating disk system. Platelets were immunofluorescently labeled and adhesion was compared on smooth and textured samples. Platelet adhesion was greatest at low shear stress ranging from 0 to 5 dyn/cm2, and sub-micron textures were observed to reduce platelet adhesion in this range. Additionally, non-adherent platelets did not demonstrate large-scale activation after exposure to textured samples. We conclude that surface textures with sub-platelet dimensions may reduce platelet adhesion from plasma to polyether(urethane urea) at low shear stress.

In this article we describe our continuing research on a novel nanocomposite approach for reducing gas permeability through biomedical polyurethane membranes. Nanocomposites were prepared using commercially available poly(urethane urea)s (PUU) and two organically modified layered silicates (OLS). Wide-angle X-ray diffraction experiments showed that the silicate layer spacing in the nanocomposites increased significantly compared with the neat OLS, signifying the formation of intercalated PUU/OLS structures. The nanocomposite materials exhibit increased modulus with increasing OLS content, while maintaining polymer strength and ductility. Water vapor permeability was reduced by about fivefold at the highest OLS contents, as a result of PUU/inorganic composite formation.

The electromechanical behavior of dielectric elastomers is to be exploited for medical application in artificial blood pumps. It is required that the pump diaphragm achieves a swept volume increase of 70 cc into a systolic pressure of 120 mmHg with the main design objective being volumetric efficiency. As such, a model that accommodates large deformation behavior is used. In order to design prosthetic blood pumps that closely mimic the natural pumping chambers of the heart, a dielectric elastomer diaphragm design is proposed. The elastomer's change in shape in response to the applied electric field will permit it to be the active element of the pump just as the ventricular walls are in the natural heart. A comprehensive analytical model that accounts for the combined elastic and dielectric behavior of the membrane is used to compute the stresses and deformations of the inflated membrane. Dielectric elastomers are often pre-strained in order to obtain optimal electromechanical performance. The resulting model incorporates pre-strain and shows how system parameters such as pre-strain, pressure, electric field, and edge constraints affect membrane deformation. The model predicts more than adequate volume displacement for moderate pre-strain of the elastomer.

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This study demonstrated that laparoscopic instruments are often used to perform a variety of maneuvers in addition to their primary function. Furthermore, there are common patterns in instrument exchange that provide a potential source of design parameters for improved surgical efficiency.

Facial recession defects were created on maxillary canine teeth of six Macaca irus monkeys and left untreated and exposed to oral fluids for 6 to 12 weeks. Notches were placed in the exposed root surfaces at the level of the free gingival margins. Following root planing with the addition of topical citric acid application on experimental surfaces, pedicle flaps were coronally positioned over the previously exposed roots. After euthanasia, block sections representing postsurgical time periods of 0, 3, 7, 14, 21, 28 and 42 days were secured and tissues were processed for histologic evaluation. All citric acid-treated surfaces exhibited new connective tissue attachment of pedicle flaps to previously exposed areas by 14 days with transmission electron micrographs confirming beginning cementum deposition. In contrast, controls demonstrated epithelial migration to, or apical to, reference notches. Although the total number of samples available for statistical comparison was small, a two-tailed t test for correlated samples showed citric acid application did not result in enhanced clinical root coverage, but did result in significantly greater amounts of new connective tissue attachment (P less than 0.05, df = 3). Pedicle flap healing against teeth with devital pulps was identical to that seen in teeth with vital pulps, while citric acid application to root-planed surfaces of vital teeth had no observable effect upon pulpal tissues.

Unreliable quantification of flow pulsatility has hampered many efforts to assess the importance of pulsatile perfusion. Generation of pulsatile flow depends upon an energy gradient. It is necessary to quantify pressure flow waveforms in terms of hemodynamic energy levels to make a valid comparison between perfusion modes during chronic support. The objective of this study was to quantify pressure flow waveforms in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) levels in an adult mock loop using a pulsatile ventricle assist system (VAD). A 70 cc Pierce-Donachy pneumatic pulsatile VAD was used with a Penn State adult mock loop. The pump flow rate was kept constant at 5 L/min with pump rates of 70 and 80 bpm and mean aortic pressures (MAP) of 80, 90, and 100 mm Hg, respectively. Pump flows were adjusted by varying the systolic pressure, systolic duration, and the diastolic vacuum of the pneumatic drive unit. The aortic pressure was adjusted by varying the systemic resistance of the mock loop EEP (mm Hg) = (integral of fpdf)/(integral of fdt) SHE (ergs/cm3) = 1,332 [((integral of fpdt)/(integral of fdt))--MAP] were calculated at each experimental stage. The difference between the EEP and the MAP is the extra energy generated by this device. This difference is approximately 10% in a normal human heart. The EEP levels were 88.3 +/- 0.9 mm Hg, 98.1 +/- 1.3 mm Hg, and 107.4 +/- 1.0 mm Hg with a pump rate of 70 bpm and an aortic pressure of 80 mm Hg, 90 mm Hg, and 100 mm Hg, respectively. Surplus hemodynamic energy in terms of ergs/cm3 was 11,039 +/- 1,236 ergs/cm3, 10,839 +/- 1,659 ergs/cm3, and 9,857 +/- 1,289 ergs/cm3, respectively. The percentage change from the mean aortic pressure to EEP was 10.4 +/- 1.2%, 9.0 +/- 1.4%, and 7.4 +/- 1.0% at the same experimental stages. Similar results were obtained when the pump rate was changed from 70 bpm to 80 bpm. The EEP and SHE formulas are adequate to quantify different levels of pulsatility for direct and meaningful comparisons. This particular pulsatile VAD system produces near physiologic hemodynamic energy levels at each experimental stage.

To determine the relationship between blood pressure (BP) variability and the open-loop frequency domain transfer function (TF) of the baroreflexes, we measured the pre- and postsinoaortic denervation (SAD) spectra and the effects of periodic and step inputs to the aortic depressor nerve and isolated carotid sinus of central nervous system-intact, neuromuscular-blocked (NMB) rats. Similar to previous results in freely moving rats, SAD greatly increased very low frequency (VLF) (0.01-0.2 Hz) systolic blood pressure (SBP) noise power. Step response-frequency measurements for SBP; interbeat interval (IBI); venous pressure; mesenteric, femoral, and skin blood flow; and direct modulation analyses of SBP showed that only VLF variability could be substantially attenuated by an intact baroreflex. The -3-dB frequency for SBP is 0.035-0.056 Hz; femoral vascular conductance is similar to SBP, but mesenteric vascular conductance has a reliably lower and IBI has a reliably higher -3-dB point. The overall open-loop transportation lag, of which