Mechanical characterization of collagen fibers and scaffolds for tissue engineering

Engineered tissues must utilize scaffolding biomaterials that support desired cellular functions and possess or can develop appropriate mechanical characteristics. This study assessed properties of collagen as a scaffolding biomaterial for ligament replacements. Mechanical properties of extruded bovine achilles tendon collagen fibers were significantly affected by fiber diameter, with smaller fibers displaying higher tangent moduli and peak stresses. Mechanical properties of 125 micrometer-diameter extruded fibers (tangent modulus of 359.6+/-28.4MPa; peak stress of 36.0+/-5.4MPa) were similar to properties reported for human ligaments. Scaffolds of extruded fibers did not exhibit viscoelastic creep properties similar to natural ligaments. Collagen fibers from rat tail tendon (a well-studied comparison material) displayed characteristic strain-softening behavior, and scaffolds of rat tail fibers demonstrated a non-intuitive relationship between tangent modulus and specimen length. Composite scaffolds (extruded collagen fibers cast within a gel of Type I rat tail tendon collagen) were maintained with and without fibroblasts under standard culture conditions for 25 days; cell-incorporated scaffolds displayed significantly higher tangent moduli and peak stresses than those without cells. Because tissue-engineered products must possess appropriate mechanical as well as biological/chemical properties, data from this study should help enable the development of improved tissue analogues.     

Autogeny in Ochlerotatus vigilax (Diptera: Culicidae) from southeast Queensland, Australia

Field and laboratory investigations were undertaken to determine the level of expression of autogeny in the mosquito Ochlerotatus vigilax (Skuse) from southeast Queensland, Australia, and whether there was evidence of seasonal variation. At two field sites in southeast Queensland, Wellington Point and Donnybrook, autogeny rates were determined on six occasions between January 2001 and January 2002. The autogeny rate varied between 71 and 100% at Wellington Point and between 63 and 100% at Donnybrook. Autogenous fecundity ranged from 17 to 63 eggs per female at Wellington Point and from 13 to 88 eggs per female at Donnybrook. Positive relationships were found between adult body size (indicated by wing length), autogeny rate, and fecundity. A laboratory study was conducted to investigate the influence of larval nutrition and adult diet (water versus sucrose) on the expression of autogeny. The autogeny rate at a low-diet treatment was between 73 and 90% when sucrose was withheld from females and 100% when sucrose was provided. All high-diet females were autogenous. Autogenous egg development required 80 +/- 6 h from emergence at 27 degrees C. We conclude that autogeny rates are consistently high in Oc. vigilax from the southeast Queensland region.     

Widespread IgE-mediated hypersensitivity in the Sudan to the 'green nimitti' midge, Cladotanytarsus lewisi (Diptera: Chironomidae) II. Identification of a major allergen.

A major allergen has been identified in an aqueous extract of the 'green nimitti' midge, Cladotanytarsus lewisi (Diptera: Chironomidae). Following chromatography on Sephadex G-100 allergenic activity, as assessed by skin ('prick') testing, eluted as two closely related peaks (pools I and II) at about 50% bed volume. When these pools were applied separately to columns of CM-cellulose, activity in each eluted with 0 . 05 M NaCl. Isoelectric focusing of the unfractionated allergen gave a single peak of activity at pI 4 . 3. By SDS--PAGE, biological activity in the whole 'green nimitti' extract and the material eluting from both pools I and II of the Sephadex G-100 column migrated to the same positions and were associated with a molecular size of 15,000--20,000 daltons. Skin test reactivity of the unfractionated material and the Sephadex G-100 pool I and II eluates were all destroyed following incubation with trypsin, chymotrypsin, thermolysin and neuraminidase. These experiments indicate that a major allergen derived from the 'green nimitti' midge, a cause of widespread and severe immediate-type allergy in the Sudan, is an acidic glycoprotein of 15,000--20,000 molecular weight.     

ZZ domain is essentially required for the physiological binding of dystrophin and utrophin to beta-dystroglycan

An intracellular protein, dystrophin, plays an important role in keeping muscle fibers intact by binding at its N-terminal end to the subsarcolemmal cytoskeletal actin network and via its C-terminal end to the transmembraneous protein beta-dystroglycan. Duchenne muscular dystrophy is caused by the loss of dystrophin, which can result from the loss of this binding. The N-terminal part of the latter binding site of dystrophin has been well documented using overlay assay and X-ray diffraction assays. However, the binding site at the C-terminal region of dystrophin has not been examined in detail. In the present work, we report a detailed analysis of the C-terminal binding domain as follows. (1). The full binding activity corresponding to the effective binding in vivo is expressed by the dystrophin fragment spanning amino acids 3026-3345 containing the ZZ domain at the C-terminus. Determination of this binding range is important not only for understanding of the mechanism of dystrophy, but also useful for the design of truncated dystrophin constructs for gene therapy. (2). The ZZ domain binds to EF1 domain in the dystrophin fragment to reinforce the binding activity. (3). The cysteine 3340 in the ZZ domain is essential for the binding of dystrophin to beta-dystroglycan. A reported case of DMD due to missense mutation C3340Y may be caused by inability to fix dystrophin beneath the cell membrane. (4). The binding mode of utrophin is different from that of dystrophin. The difference is conspicuous concerning the cysteine residues present in the ZZ domain.     

Adherence-Facilitating Behaviors of a Multidisciplinary Pediatric Rheumatology Staff

Investigated the behaviors of pediatric rheumatology healthcare providers that were expected to be related to patient orparent adherence. Medical charts of 108 patients ages 1 to 20years diagnosed with Juvenile Rheumatoid Arthritis were examined.The 473 outpatient visits over 15 months yielded a total of2,578 treatment recommendations, but only 1,390 adherence-facilitatingbehaviors by medical staff were documented. Providing informationabout how often to perform the recommendation was the most commonstaff behavior. In contrast, care providers rarely indicatedthat they addressed their patients' concerns and barriers toimplementing the recommendations, or employed behavior modificationstrategies to increase adherence. Implications of these findingsfor development of programs designed to increase treatment adherencein children with chronic diseases requiring time-consuming,intrusive medical regimens are discussed.     

Histamine increases histidine uptake by basophils.

Histamine, at high concentrations, enhanced the uptake of isotopic histidine by guinea-pig basophils. The effect was partially reversed by H1-, but not H2-, histamine receptor antagonists. These data suggest that histamine has a bioregulatory role in its own synthesis.     

Accuracy of reporting endocervical component adequacy--a continuous quality improvement project

Inaccurate reporting of the absence of an endocervical (EC) component on Pap smears often results in slide rescreens, amended reports, clinician dissatisfaction, and sometimes unnecessary repeat smears. Therefore, the accuracy of reporting EC component adequacy was selected as a quality indicator for the laboratory continuous quality improvement program (CQI). The process consisted of problem identification, analysis of the situation, collection of data, implementation of solutions, and evaluation of results. The objective of the study was to determine if the accuracy of reporting EC component adequacy on Pap smears improved after application of such a program. During the first phase, 150 Pap smears originally reported with the absence of an adequate EC component and 150 smears reported with the presence of an adequate EC component were rescreened to measure the baseline accuracy of EC component adequacy reporting. The improvement process was then implemented. A cause-and-effect diagram was developed and root cause was determined. A presentation was then made to the cytology staff. Criteria for EC component adequacy were reviewed, examples were shown, and standardized marking of EC component was implemented. Following improvement actions, a second audit of 150 Pap smears reported with the absence of an adequate EC component as well as 150 smears reported with the presence of an adequate EC component was undertaken to measure change in performance in assessing EC component adequacy. For the baseline rescreening, before initiation of the CQI program, 98% accuracy was achieved with smears that were reported as adequate for EC component present. However, the accuracy with smears reported as absence of an adequate EC component was only 71%, i.e., an adequate EC component was identified in almost 1/3 of these cases on rescreen. After the implementation of improvement actions, the accuracy with smears reported with the presence of EC component remained high (98%) and the accuracy of reporting the absence of EC component was 90%. The difference of the latter before and after the implementation was statistically significant (P = 0.015, z-test). The accuracy of reporting EC component adequacy increased following the CQI process. Using reporting EC component adequacy as an example, we demonstrate that by treating clinical problems as quality control issues and applying basic quality improvement tools, a positive outcome can be effected.