Biocomposite hydrogels with carboxymethylated, nanofibrillated cellulose powder for replacement of the nucleus pulposus.

Biocomposite hydrogels with carboxymethylated, nanofibrillated cellulose (c-NFC) powder were prepared by UV polymerization of N-vinyl-2-pyrrolidone with Tween 20 trimethacrylate as a cross-linking agent for replacement of the native, human nucleus pulposus (NP) in intervertebral disks. The swelling ratios and the moduli of elasticity in compression of neat and biocomposite hydrogels were evaluated in dependence of c-NFC concentration (ranging from 0 to 1.6% v/v) and degree of substitution (DS, ranging from 0 to 0.23). The viscoelastic properties in shear and the material relaxation behavior in compression were measured for neat and biocomposite hydrogels containing 0.4% v/v of fibrils (DS ranging from 0 to 0.23), and their morphologies were characterized by cryo-scanning electron microscopy (cryo-SEM). The obtained results show that the biocomposite hydrogels can successfully mimic the mechanical and swelling behavior of the NP. In addition, the presence of the c-NFC shows lower strain values after cyclic compression tests and consequently creates improved material relaxation properties compared with neat hydrogels. Among the tested samples, the biocomposite hydrogel containing 0.4% v/v of c-NFC with a DS of 0.17 shows the closest behavior to native NP. Further investigation should focus on evaluation and improvement of the long-term relaxation behavior.

Carbon outclasses wood in racket paddles: Ratings of expert and intermediate tennis players.

Wooden racket paddles were modified with rubber and carbon fibre laminates and their differences tested in terms of flexural, damping, and coefficient of restitution properties. Four rackets types were designed: a wood reference, wood with rubber, carbon fibre 0°, and carbon fibre 90°. Seven expert and eight intermediate tennis players tested the rackets. To determine which of the four rackets suited the players best, we asked the players to compare the rackets two by two. After each pair tested, participants had to fill out a 4-item questionnaire in which different aspects of the rackets' performance were judged. The most preferred racket was the 0° carbon fibre racket, followed by the 90° carbon fibre racket, the wood racket and, finally, the 1-mm rubber racket. Thus, rackets with the highest stiffness, least damping, and highest coefficient of restitution were the most preferred. Interestingly, although experts and intermediate players overall judged the rackets in very similar ways according to force, vibration, and control, they were sensitive to quite different physical characteristics of the rackets.

Plasma immunoreactive gamma melanotropin in patients with idiopathic hyperaldosteronism, aldosterone-producing adenomas, and essential hypertension.

A non-ACTH aldosterone-stimulating factor(s) has been implicated in the pathogenesis of idiopathic hyperaldosteronism (IHA). Although this factor has not been fully characterized, some evidence suggests that it may be related to a pro-gamma-melanotropin (pro-gamma-MSH), derived from the NH2-terminal region of pro-opiomelanocortin. In the present study, plasma immunoreactive (IR-) gamma-MSH levels at 0800 h in patients with IHA were evaluated (90 +/- 17 fmol/ml; range: 13-173 fmol/ml) and found to be significantly higher (P less than 0.05) than those in subjects with aldosterone-producing adenomas (33 +/- 8 fmol/ml), essential hypertension (33 +/- 6 fmol/ml), and normotensive controls (19 +/- 2 fmol/ml). Seven of nine IHA subjects had circulating IR-gamma-MSH levels above the normal range (greater than 35 fmol/ml). In plasmas sampled at 1200 h, IR-gamma-MSH was significantly higher in patients with IHA (95 +/- 26 fmol/ml) and adenomas (63 +/- 23 fmol/ml), as compared with essential hypertensives (31 +/- 6 fmol/ml) and normotensives (19 +/- 3 fmol/ml). Mean plasma IR-ACTH, plasma cortisol, and urinary cortisol levels did not differ significantly between any of these groups. In order to evaluate the effect of a pro-gamma-MSH in vitro, adrenal adenoma tissue was obtained from two patients, one with elevated IR-gamma-MSH (61 fmol/ml) and a second with low IR-gamma-MSH (12 fmol/ml). Aldosterone secretion by dispersed adenoma cells from the former, but not the latter, underwent a fourfold dose-dependent (10(-14)-10(-9) M) increase in response to human Lys-gamma 3-MSH. These data suggest that a pro-gamma-MSH may be implicated as a pathogenic factor in a subset of patients with primary aldosteronism, particularly among those differentially diagnosed as having IHA.

Polylactic acid-phosphate glass composite foams as scaffolds for bone tissue engineering.

Phosphate glass (PG) of the composition 0.46(CaO)-0.04(Na(2)O)-0.5(P(2)O(5)) was used as filler in poly-L-lactic acid (PLA) foams developed as degradable scaffolds for bone tissue engineering. The effect of PG on PLA was assessed both in bulk and porous composite foams. Composites with various PG content (0, 5, 10, and 20 wt %) were melt-extruded, and either compression-molded or foamed through supercritical CO(2). Dynamic mechanical analysis on the bulk composites showed that incorporating 20 wt % PG resulted in a significant increase in storage modulus. Aging studies in deionized water in terms of weight loss, pH change, and ion release inferred that the degradation was due to PG dissolution, and dependent on the amount of glass in the composites. Foaming was only possible for composites containing 5 and 10 wt % PG, as an increase in PG increased the foam densities; however, the level of porosity was maintained above 75%. PLA-T(g) in the foams was higher than those obtained for the bulk. Compressive moduli showed no significant reinforcement with glass incorporation in either expansion direction, indicating no anisotropy. Biocompatibility showed that proliferation of human fetal bone cells was more rapid for PLA compared to PLA-PG foams. However, the proliferation rate of PLA-PG foams were similar to those obtained for foams of PLA with either hydroxyapatite or beta-tricalcium phosphate.

Bioresorbable composites prepared by supercritical fluid foaming.

Bone is a natural composite construct, with a gradient structure going from a loose interconnected cellular core to an outer dense wall, thus minimizing bone weight while keeping a high mechanical resistance. Due to this unique and complex structure, bone defects are difficult to replace or repair. Tissue engineering aims at providing artificial bone grafts. Several techniques have been proposed to produce porous structures or scaffolds, but, as yet, with no optimal solutions. This article focuses on bioresorbable ceramic-polymer composite foams obtained by supercritical fluid foaming. This flexible technique enables an adequate morphology and suitable properties for bone tissue engineering to be obtained. Composite scaffolds are biocompatible, allowing cell proliferation and differentiation.

How plate positioning impacts the biomechanics of the open wedge tibial osteotomy; a finite element analysis.

A numerical model of the medial open wedge tibial osteotomy based on the finite element method was developed. Two plate positions were tested numerically. In a configuration, (a), the plate was fixed in a medial position and (b) in an anteromedial position. The simulation took into account soft tissues preload, muscular tonus and maximal gait load.The maximal stresses observed in the four structural elements (bone, plate, wedge, screws) of an osteotomy with plate in medial position were substantially higher (1.13-2.8 times more) than those observed in osteotomy with an anteromedial plate configuration. An important increase (1.71 times more) of the relative micromotions between the wedge and the bone was also observed. In order to avoid formation of fibrous tissue at the bone wedge interface, the osteotomy should be loaded under 18.8% (approximately 50 kg) of the normal gait load until the osteotomy interfaces union is achieved.

Plasma beta-endorphin levels in primary aldosteronism.

Excessive production of an as yet unidentified aldosterone-stimulating factor may cause idiopathic hyperaldosteronism (IHA). This putative factor may be related to proopiomelanocortin-derived peptides, some of which have aldosterone-stimulating properties. The present study evaluated plasma beta-endorphin, ACTH, cortisol, and aldosterone levels in patients with IHA (n = 10), aldosterone-producing adenomas (n = 4), essential hypertension (n = 11), and normal subjects (n = 10). Plasma and urinary hormone measurements were obtained at timed intervals during an isocaloric, fixed electrolyte intake (Na+, 128 meq/day; K+, 80 meq/day) in a metabolic unit. Plasma for beta-endorphin assay was preincubated with sepharose-bound anti-beta-lipotropin to remove beta-lipotropin that cross-reacted with the beta-endorphin RIA. Mean +/- SE plasma beta-endorphin levels at 0800 h were elevated in IHA patients (47 +/- 13 fmol/ml) compared to those in aldosterone-producing adenoma (25 +/- 9), essential hypertension (16 +/- 1), and normal control (20 +/- 2; P less than 0.05) subjects. Plasma ACTH, plasma cortisol, and urinary cortisol levels were not different in these four groups. These data support the hypothesis that excess production of either beta-endorphin or related proopiomelanocortin-derived peptides may function as aldosterone secretogogue(s) in IHA.

Fatigue crack propagation behavior of ultrahigh molecular weight polyethylene.

The relative fatigue crack propagation resistance of plain and carbon fiber-reinforced ultrahigh molecular weight polyethylene (UHMWPE) was determined from cyclic loading tests performed on compact tension specimens machined from the tibial components of total knee prostheses. Both materials were characterized by dynamic mechanical spectroscopy, X-ray diffraction, and differential scanning calorimetry. The cyclic tests used loading in laboratory air at 5 Hz using a sinusoidal wave form. Dynamic mechanical spectroscopy showed that the reinforced UHMWPE had a higher elastic storage modulus than the plain UHMWPE, whereas X-ray diffraction and differential scanning calorimetry showed that the percent crystallinity and degree of order in the crystalline regions were similar for the two materials. Fatigue crack propagation in both materials proved to be very sensitive to small changes in the applied cyclic stress intensity range. A 10% increase in stress intensity resulted in approximately an order of magnitude increase in fatigue crack growth rate. The fatigue crack propagation resistance of the reinforced UHMWPE was found to be significantly worse than that of the plain UHMWPE. This result was attributed to poor bonding between the carbon fibers and the UHMWPE matrix and the ductile nature of the matrix itself.

The effect of a high level of dietary leucine on the niacin status of chicks and rats.

Baby chicks were fed purified diets containing 90 g/kg casein and 100 g/kg gelatin. With low levels of niacin and tryptophan, niacin deficiency resulted: this was not exacerbated by the addition of supplementary leucine (17.4 g/kg). With levels of niacin and tryptophan that supported rapid growth the further addition of supplementary leucine depressed food consumption and weight gain; in most instances this was statistically significant. No evidence was obtained to indicate that a high level of dietary leucine could result in niacin deficiency in chicks. Comparable experiments were carried out with weanling rats given a basal diet containing 60 g/kg casein and 60 g/kg gelatin. Adding 15 g/kg L-leucine gave results similar to those obtained with chicks and the same conclusions were drawn.

The effect of a high level of dietary leucine on the niacin status of dogs.

Two feeding trials were designed to precipitate niacin deficiency in puppies receiving low levels of niacin by adding 15 g/kg supplementary l-leucine to a diet containing 180 g/kg casein. We failed to produce such an effect and, as niacin levels were gradually reduced, the times at which control dogs became deficient (and then responded to injections of the vitamin) were not significantly different from those for dogs receiving the leucine supplement. Differences between the conditions of our experiments and of the experiment in which this effect was found are discussed. Two pairs of littermates in trial 2 died suddenly while apparently in fairly good condition, but revealing fatty livers and/or changes in heart muscle on autopsy. Similar observations have been reported by others using purified diets with dogs over long periods; there is no certain explanation.