Biomaterials, medical devices, and artificial organs最新文献

Biomedical applications of various Cellulosics have been reviewed and their interaction with blood is discussed. A new haemostatic agent 2,3,6 - tricarboxy cellulose "Supercel" has been produced by NO2 oxidation of 2,3 - dialdehyde cellulose and a possible mechanism for blood clotting initiated by Supercel is presented.

An attempt has been made to understand and correlate surface - and interface energy parameters with the blood compatibility of an implant surface. Although, it is realized that such concepts alone may not be enough to explain the complex multiparameter processes of such interactions at the interface.

The effect of in vivo aging and surface texturing on the mechanical properties of dense aluminum oxide were studied. The modulus of rupture and Weibull modulus were determined in air and Ringer's solution using a 3-point bend test. The results showed that the in vivo environment sealed off microcracks either chemically or by tissue ingrowth which strengthened the alumina. The surface modification, however, tended to create more microcracks and stress concentrations at the surface indentations which tended to weaken the alumina.

There are good reasons to believe that adhesion of particulate matter in all wet, salty, biochemically active circumstances follows a common pattern, and that such adhesion can be effectively controlled by adjusting the surface properties - especially surface energy--of the substrate involved. One of the most compelling proofs of, at least, the bioengineering utility of surface energy modification to maximize or minimize biological adhesion is the successful, now long-term, implantation of total artificial hearts. These pumps, and the related intra-aortic balloons and left ventricular assist devices, do not accumulate blood clots or thrombotic masses during their contact with natural blood. Since surfaces contacting blood have received most careful scrutiny for more than a decade, the instruction gained from examining the usual and unusual sequelae of blood cell adhesion to nonphysiologic surfaces has been most valuable in revealing the general features of biological adhesion in other, less well-studied, circumstances. The initial events of blood contact with foreign solid surfaces are briefly reviewed, and the impressive similarities of these events to sequences in oceanic fouling of heat exchangers, cell culture experiments and dental plaque formation are highlighted. A unifying concept, based on control of the surface free energy through an empirical correlate called the "critical surface tension," is presented as an explanation for the common features of biological adhesion in all of Nature's domains.

The stress vs. cycles (S-N) behavior for four amalgams is reported. At 10 cycles/min and for 37 degrees C air and artificial saliva environments, linear regression lines fit the data with high correlations between 10(2) and 10(4) cycles. Significance at 50% exists between the environments and with saliva decreasing failure resistance. The open circuit potential (OCP), the OCP-time transients at constant anodic currents, and the cyclic voltammetry all exhibit changes with loading. With static loading the OCP decreases, while with dynamic loading the OCP exhibits a sinusoidal pattern and a pattern with two maxima and two minima after the loading has progressed and which continues up until failure. The maximum anodic current in voltammetry increases with continual potential cycling (or load cycling), while decreases when performed without loading. The application of anodic currents to the amalgams has, however, not significantly reduced the number of cycles to failure, nor has the application of cathodic currents increased the number of cycles. Rearrangement and coalesence of voids takes place with loading and with microcracking forming preferentially between them. Crack propagation occurs predominantly within the gamma-1 matrix.

The surface free energy is a definite factor in the adhesion of micro-organisms to host surfaces, such as tooth surfaces. The surface free energy gamma s can experimentally be determined by means of a series of contact angle measurements with various liquids. Employing the concept of polar and dispersion components, it was found, that gamma s of ground and polished human enamel is 88 +/- 9 erg.cm-2. This value is of the same order of magnitude as obtained for hydroxyapatite (the main mineral component of enamel) and fluorapatite. Fluoride applications on human enamel, frequently employed in dentistry, greatly influence the surface free energy. Application of various fluorides gave different results: Aminfluorides reduced gamma s to 62 +/- 5 erg.cm-2; APF raised gamma s to 107 +/- 11 erg.cm-2; NaF hardly influenced gamma s X gamma s remained 87 +/- 9 erg.cm-2. Adsorption of salivary proteins (pellicle formation) influences these differences. In vivo pellicle formation on FEP (gamma s = 17 erg.cm-2) increased gamma s to 41 erg.cm-2, Diacryl (gamma s = 76 erg.cm-2) increased gamma s to 117 erg.cm-2, while on sintered hydroxyapatite (gamma s = 80 erg.cm-2) gamma s increased to 118 erg.cm-2.

Proteins are biological molecules par excellence. They have evolved as elements of structure, catalysis and control. The conflict between the requirement of structural stability and the requirement of functional specificity and efficiency, under varying environmental conditions in which they are often called upon to function, has been evolutionarily solved by a process of thermodynamic compensation. In the simplest form of thermodynamic compensation the Gibb's free energy change (delta G) of a process occurring under different environmental conditions is kept constant (linear compensation) or allowed to vary slightly (non linear compensation) by compensating a large change in enthalpy (delta H) by an equally (or nearly 80) large change in entropy, delta S. In processes like protein adsorption to surfaces the number of various types of interactions involved is so large that compensatory or augmenting changes in the same type of thermodynamic parameter may occur and complicate the picture. Published data do, however, suggested the occurrence of thermodynamic compensation in protein adsorption. It is pointed out that the simultaneous measurement of two thermodynamic parameters, namely, enthalpy change (delta H), and heat capacity change (delta Cp), under appropriate conditions could often lead to an understanding of the dominant types of forces involved in adsorption.

Natural rubber with C = C bonds had been modified by reaction with chlorosulfonyl isocyanate (CSI) and 70% of the products were obtained, which yielded polyelectrolyte on treatment with NaOH, having sulfamate and carboxylate groups. The polyelectrolyte showed anticoagulant activity. This might be due to the presence of both sulfamate and carboxylate groups arranged in a steric manner in the molecule as that of Heparin. Surface energy parameters, platelet adhesion and plasma recalcification time were investigated. Possible comparison with heparin had been demonstrated.