Novel synthesis and characterization of a collagen-based biopolymer initiated by hydroxyapatite nanoparticles.

In this study, we developed a novel synthesis method to create a complex collagen-based biopolymer that promises to possess the necessary material properties for a bone graft substitute. The synthesis was carried out in several steps. In the first step, a ring-opening polymerization reaction initiated by hydroxyapatite nanoparticles was used to polymerize d,l-lactide and glycolide monomers to form poly(lactide-co-glycolide) co-polymer. In the second step, the polymerization product was coupled with succinic anhydride, and subsequently was reacted with N-hydroxysuccinimide in the presence of dicyclohexylcarbodiimide as the cross-linking agent, in order to activate the co-polymer for collagen attachment. In the third and final step, the activated co-polymer was attached to calf skin collagen type I, in hydrochloric acid/phosphate buffer solution and the precipitated co-polymer with attached collagen was isolated. The synthesis was monitored by proton nuclear magnetic resonance, infrared and Raman spectroscopies, and the products after each step were characterized by thermal and mechanical analysis. Calculations of the relative amounts of the various components, coupled with initial dynamic mechanical analysis testing of the resulting biopolymer, afforded a preliminary assessment of the structure of the complex biomaterial formed by this novel polymerization process.

Electrical implications of corrosion for osseointegration of titanium implants.

The success rate of titanium implants for dental and orthopedic applications depends on the ability of surrounding bone tissue to integrate with the surface of the device, and it remains far from ideal in patients with bone compromised by physiological factors. The electrical properties and electrical stimulation of bone have been shown to control its growth and healing and can enhance osseointegration. Bone cells are also sensitive to the chemical products generated during corrosion events, but less is known about how the electrical signals associated with corrosion might affect osseointegration. The metallic nature of the materials used for implant applications and the corrosive environments found in the human body, in combination with the continuous and cyclic loads to which these implants are exposed, may lead to corrosion and its corresponding electrochemical products. The abnormal electrical currents produced during corrosion can convert any metallic implant into an electrode, and the negative impact on the surrounding tissue due to these extreme signals could be an additional cause of poor performance and rejection of implants. Here, we review basic aspects of the electrical properties and electrical stimulation of bone, as well as fundamental concepts of aqueous corrosion and its electrical and clinical implications.

Infrared study of the kinetics and mechanism of adsorption of acrylic polymers on alumina surfaces.

In this paper, we studied the kinetics of the adsorption of poly(methyl methacrylate), PMMA, onto native aluminum oxide surfaces by X-ray photoelectron spectroscopy and reflection-absorption infrared spectroscopy, with the intent of tracking the various changes observed in the infrared spectrum of the adsorbed polymer layer as a function of adsorption time. Specifically, we utilized the relative changes in the absorption bands of the carbonyl, carboxylic acid, and carboxylate groups to determine the sequence of events that culminate in the formation of bonds between carboxylate groups on hydrolyzed PMMA and specific sites on the aluminum oxide surface. We have shown that the adsorption process involves the hydrolysis of a fraction of the methoxy groups of the PMMA to generate COOH groups. Unlike previous assumptions, the formation of COOH groups on the PMMA chains does not constitute a sufficient condition for the actual chemisorption of the polymer chains onto the metal oxide surface. To promote bonding, the acid groups must undergo dissociation to form the carboxylate groups, followed subsequently by actual bond formation, that is, active anchoring, on the surface. This process is mediated by the aluminum oxide sites on the surface in the presence of water. Hence, the adsorption process occurs via a two-step mechanism, in which the first step, that is, the hydrolysis step, is a necessary but insufficient condition and the second step, that is, the anchoring step, is largely dependent on the type of interfacial chemistry possible for a particular polymer-metal oxide surface, the polymer conformation, the molecular weight, and the flexibility of the adsorbing molecules.

Methyldopa does not alter the disposition of digoxin.

To investigate whether methyldopa alters digoxin disposition, eight healthy subjects received methyldopa titrated to 250 mg t.i.d. or placebo in a double-blind, cross-over manner for 16 consecutive days, with 0.25 mg intravenous digoxin coadministered on day 5 and 0.25 mg oral digoxin on days 9 to 16. Digoxin concentrations in plasma and urine were measured by RIA. Although assay sensitivity did not allow an adequate assessment of serum AUC(0-infinity) after intravenous administration, mean digoxin AUC(0-24) was 10.2 +/- 3.5 and 10.0 +/- 1.8 ng/ml X hr with placebo and methyldopa, respectively (P greater than 0.05). Mean urinary excretion after digoxin with or without methyldopa treatment was 0.204 +/- 0.34 and 0.197 +/- 0.38 mg, respectively. The mean steady-state serum concentrations of oral digoxin (AUC(0-24)/zeta) with and without methyldopa were 0.65 +/- 0.2 and 0.62 +/- 0.3 ng/ml, respectively. These data revealed no significant differences (P greater than 0.05) for various parameters with power of greater than 0.8 to detect meaningful differences of approximately 30 per cent. Thus, methyldopa did not alter digoxin disposition in healthy subjects, and a pharmacokinetic interaction in patients is unlikely.

Preceptors' views of community pharmacy clerkships: a national survey.

A survey was administered to a random sample of community pharmacy practitioners who participate as preceptors in clerkship programs for colleges of pharmacy throughout the country. The purpose of this survey was to determine (1) in what ways, if any, students have affected the preceptors' practices; (20 whether the students served as a sources of continuing education to the preceptors; (3) whether the preceptors identified areas of students' strengths/deficiencies; and (4) roles of colleges of pharmacy and pharmacy associations in providing continuing education programs for pharmacists. Results of this survey are discussed. Data are cross-tabulated for types of pharmacy services provided, years in practice, length of clerkship rotations, and other essential demographic information needed for evaluation. Based on responses, recommendations are made that will provide guidance to colleges of pharmacy, pharmaceutical associations, and practitioners currently involved or those who are considering involvement in clerkship programs.

Considerations in predicting phenotypic modifications in amino acid profiles of total cell protein of microorganisms.

A mathematical model is presented that describes the concentration of an amino acid in total cell protein as a function of its concentration in individual cell proteins or in sets of cell proteins. The resulting equation makes it possible to calculate how the makeup of cell proteins must change to obtain a specified alteration in the content of an amino acid in the total cell protein. It is recognized that protein species or sets of proteins that are distinguished by being richer or poorer in a key amino acid than the overall protein must undergo considerable variations in content. The necessary extent of these shifts suggests that the amino acid composition of total cell protein is not likely to be affected significantly by variations in the cultivation conditions.

Phenotypic modifications in amino acid profiles of cell residues of Candida utilis and Enterobacter aerogenes.

Glucose-limited chemostat cultures of Candida utilis were cultivated at various pH levels (3.0-7.5), temperatures (15-37.5 degrees C), dilution rates (0.006-0.42 hr-1), and with one of two nitrogen sources (NH+4 or NO-3). Enterobacter aerogenes was also cultivated in the chemostat under nitrogen and phosphorus limitations. The amino acid profile of total cell protein is expressed as the content of each amino acid relative to the sum of all amino acids recovered ater acid hydrolysis. Cell residues obtained after hot trichloracetic acid extraction display small variations in amino acid profile. Some of these variations correlate with the growth rate at satisfactory levels of statistical significance. In C. utilis, the correlations cover increased levels of lysine, arginine, and leucine and decreased levels of serine and glutamic acid with increased "reduced dilution rate" (D/Dc). In E. aerogenes, increased levels of lysine and arginine and a decreased level of glutamic acid correlate with increased dilution rate. The directions of most of these correlations and the extents of those pertaining to lysine and arginine are consistent with the change predicted to occur simultaneously in the relative level of the ribosomal protein group.

Latency of vocalization onset: stutterers versus nonstutterers.

Eleven stutterers and matched controls were asked to produce as quickly as possible each of 26 different syllables following a visual stimulus. Three trials were given for each syllable. Responses were filtered to remove supraglottally produced sounds, and the time between the visual stimulus and the onset of vocalization was measured by a voice-operated relay and a computer's internal clock. The results suggested that stutterers are slower in initiating vocalization across a wide variety of syllables, and the difference averages about 65 msec. Furthermore, when phonologic conditions delayed voice onset by a comparable amount, the stutterers gained enough time so that no significant differences were observed between the two groups. The results are interpreted as suggesting that auditory dysfunction cannot be a cause for slower vocalization reaction time in stutterers but that either vocal dysfunction or a lack of cerebral dominance may be responsible for these differences.