Biodegradable polyurethanes: Comparative study of electrospun scaffolds and films

The development of elastomeric, bioresorbable, and biocompatible segmented polyurethanes (SPUs) for use in tissue‐engineering applications has attracted considerable interest in recent years. In this work, nonporous films and microfiber/nanofiber scaffolds, which were prepared from two different poly(?‐caprolactone)‐based SPUs previously synthesized from 1,6‐hexamethylene diisocyanate and novel chain extenders containing urea groups or an aromatic amino acid derivative, were studied. Their thermal properties were influenced by both the different chemical structures of the hard segments and the processing conditions. The mechanical properties of the scaffolds (the elastic modulus, ultimate strain, and tensile stress) were adequate for engineered soft‐tissue constructs (e.g., myocardial tissue). The film samples displayed a low swelling degree (<2 wt %) in a phosphate‐buffered solution at 37°C. The introduction of the amino acid derivative chain extender with hydrolyzable ester bonds contributed to greater degradation. The fibrous scaffolds exhibited higher hydrolytic stability than the films after short assay times because of their more crystalline structures and higher degrees of association by hydrogen bonding, but they also experienced higher mass losses under accelerated conditions (70°C). This suggested that the degradation rate was not constant but depended on the degradation time and the processing technique. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Prevention of arachnoiditis and postoperative tethering of the spinal cord with Gore-Tex surgical membrane: an experimental study with rats

OBJECTIVE: Arachnoidal adhesions and inflammation were evaluated in 72 rats after spinal dural repair with one of three materials, i.e., Gore-Tex surgical membrane, collagen-coated Vicryl mesh, or lyophilized spinal dural allograft. METHODS: Laminectomy at L1 was performed, and then a 3- x 4-mm segment of spinal dura mater and arachnoid membrane was excised. After implantation of the dural substitute, the animals were divided into normal and injured groups. In the injured group, a spinal cord injury was produced at the midpoint of the duraplasty site by the clip compression technique, with 25-g force for 1 minute. Neurological performance was assessed by the inclined plane technique, and groups of rats were killed at 8 to 24 weeks after surgery. The spinal column was removed en bloc and processed for histological examination. RESULTS: There were no differences in neurological function among the three dural substitutes in either injured or noninjured rats. However, there were major differences among the groups in the incidence and severity of arachnoid adhesions and tethering. The neural tissue was bound to a thick neomembrane surrounding the lyophilized dural allograft and the collagen-coated Vicryl mesh. In contrast, the Gore-Tex surgical membrane induced only a thin membranous adhesion, which was loose and flexible. The inflammatory and foreign body response was most pronounced in rats treated with collagen-coated Vicryl mesh, at 8 and 24 weeks. CONCLUSION: In the present study, Gore-Tex surgical membrane was a very good material for the surgical repair of spinal dural defects. Additional experimental studies are required to compare Gore-Tex membrane with autologous tissues.     

Use of the tongue flap for intraoral reconstruction: a report of 16 cases

PURPOSE: This article reports the authors' experience with the use of the tongue flap for intraoral soft tissue reconstruction. PATIENTS AND METHODS: From May 1992 to December 1996, 16 patients were treated with a tongue flap for reconstruction of a variety of intraoral soft tissue defects. Ages ranged from 16 to 65 years with a mean of 39.6 years. RESULTS: The procedure was successful in 15 patients. There were six complications: one total necrosis, four partial necroses, and one infection. Partial necrosis and infection were well controlled by conservative treatment. CONCLUSION: Use of the tongue flap is a versatile method for reconstruction of a variety of intraoral soft tissue defects.     

Photocatalytic degradation of nitrotoluene in aqueous TiO2 suspension.

TiO2-mediated photocatalytic degradation process was employed to treat aqueous 2-, 3- and 4-NT (nitrotoluene) pollutants. The NT disappearance and TOC removal rates for three isomers showed no significant differences. Three hydroxylated aromatic intermediates resulting from the photocatalytic degradation of 4-NT were identified; this suggested two (initial) degradation pathways. Formation of acetic acid, formic acid, and formaldehyde was also noted. The mineralization products included NH4+, NO3- and CO2. N2 bubbling or the presence of a positive hole acceptor during 4-NT degradation resulted in a high 4-aminotoluene formation. This indicated an effective reduction of 4-NT's nitro group to amino moiety. Generally, Pt-loaded TiO2 (Pt-TiO2) had no influence on the disappearance rate of 4-NT. However, the use of Pt-TiO2 along with a higher light intensity source resulted in an accelerated TOC removal.     

Surface Segmental Mobility and Adhesion—Effects of Filler and Molecular Mass

The adhesion of thin films of poly(methyl acrylate) (PMA) on glass slides in contact with tape has been measured as a function of thickness, molecular mass, and amount of silica-based filler. In all cases studied the polymer thin-film, tape-peel tests resulted in linear force-velocity plots. The best-fit lines were extrapolated to find the fracture energies at zero velocity. For thin layers of rubbery PMA on glass slides the PMA-tape fracture energies were found to decrease (from 55-20 J/m²) with increasing PMA thickness (50-1000 nm). Thin films made from glassy poly(methyl methacrylate) (PMMA) were found to have no thickness dependence and much higher fracture energies (∼ 140 J/m²). The effect of PMA molecular mass was found to be smaller than the effect of film thickness. Including silica in the films at low levels dramatically increased the fracture energies, with a maximum (182 J/m²) found with 5.2% silica. With larger amounts of silica, the fracture energy declined significantly.     

Recombinant human growth hormone decreases lung and liver tissue lipid peroxidation and increases antioxidant activity after thermal injury in rats

The effects of pulsed direct current (dc) electric fields on the frequency of spontaneous bursting in a model epileptic focus were studied. The high potassium hippocampal slice model was used to generate spontaneous burst firing activity similar to interictal spikes in the pyramidal cell layer of CA3. Electric fields were generated from platinum subdural electrodes placed in the perfusion bath. Three hundred and seventy-eight experimental trials were performed on 10 hippocampal slices from 10 rats and the effects of field polarity, field strength and duration of stimuli on firing frequency was examined. Hippocampal slices were oriented horizontally with the CA3 layer towards the positive electrode, the average interburst interval did not correlate significantly with polarity of the delivering pulses (one-way ANOVA, p = 0.96). Average interburst interval showed a significant correlation with pulse duration of 200 and 400 msec (p = 0.030 and p = 0.004, respectively). As a function of field strength, there were significant average interval changes for fields of 33, 46, and 73 mV/mm (p = 0.024, p = 0.001 and p = 0.001, respectively). In conclusion, CA3 burst firing activity in high potassium concentration can therefore be altered by electric fields.     

Involvement of heat shock elements and basal transcription elements in the differential induction of the 70-kDa heat shock protein and its cognate by cadmium chloride in 9L rat brain tumor cells

The EphA3 receptor tyrosine kinase has been implicated in guiding the axons of retinal ganglion cells as they extend in the optic tectum. A repulsive mechanism involving opposing gradients of the EphA3 receptor on retinal axons and its ligands, ephrin-A2 and ephrin-A5, in the tectum influences topographic mapping of the retinotectal projection. To investigate the overall role of the Eph family in patterning of the visual system, we have used in situ hybridization to localize nine Eph receptors in the chicken retina and optic tectum at Embryonic Day 8. Three of the receptors examined correspond to the novel chicken homologs of EphA2, EphA6, and EphA7. Unexpectedly, we found that many Eph receptors are expressed not only in retinal ganglion cells, but also in tectal cells, In particular, EphA3 mRNA is prominently expressed in the anterior tectum, with a pattern reciprocal to that of ephrin-A2 and ephrin-A5. Similarly, ephrin-A5 is expressed not only in tectal cells but also in the nasal retina, with a pattern reciprocal to that of its receptor EphA3 and partially overlapping with that of its other receptor EphA4. Consistent with the even distribution of EphA4 and the polarized distribution of EphA4 ligands in the retina, probing EphA4 immunoprecipitates from different sectors of the retina with anti-phosphotyrosine antibodies revealed spatial differences in receptor phosphorylation. These complex patterns of expression and tyrosine phosphorylation suggest that Eph receptors and ephrins contribute to establishing topography of retinal axons through multiple mechanisms, in addition to playing a role in intraretinal and intratectal organization.     

Essential role of E2-25K/Hip-2 in mediating amyloid-beta neurotoxicity

The ubiquitin/proteasome system has been proposed to play an important role in Alzheimer's disease (AD) pathogenesis. However, the critical factor(s) modulating both amyloid-beta peptide (Abeta) neurotoxicity and ubiquitin/proteasome system in AD are not known. We report the isolation of an unusual ubiquitin-conjugating enzyme, E2-25K/Hip-2, as a mediator of Abeta toxicity. The expression of E2-25K/Hip-2 was upregulated in the neurons exposed to Abeta(1-42) in vivo and in culture. Enzymatic activity of E2-25K/Hip-2 was required for both Abeta(1-42) neurotoxicity and inhibition of proteasome activity. E2-25K/Hip-2 functioned upstream of apoptosis signal-regulating kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK) in Abeta(1-42) toxicity. Further, the ubiquitin mutant, UBB+1, a potent inhibitor of the proteasome which is found in Alzheimer's brains, was colocalized and functionally interacted with E2-25K/Hip-2 in mediating neurotoxicity. These results suggest that E2-25K/Hip-2 is a crucial factor in regulating Abeta neurotoxicity and could play a role in the pathogenesis of Alzheimer's disease.     

Flow-dependent pulmonary vasodilation during acute unilateral pulmonary artery occlusion in Jungle Fowl

Giant Jungle Fowl previously were shown to be highly resistant to the onset of pulmonary hypertension syndrome (PHS, ascites) under conditions that induce a substantial incidence of PHS in broiler chickens. In the present study, lightly anesthetized, clinically healthy 12- to 13-wk-old male Giant Jungle Fowl maintained a lower respiratory rate, a similar hematocrit, and superior arterial blood gas values when compared with 6-wk-old male broilers. Giant Jungle Fowl weighed less than broilers (1,860 +/- 19 vs 2,788 +/- 63 g, respectively) and had equivalent absolute values for pulmonary arterial pressure, cardiac output, and pulmonary vascular resistance. Acute unilateral pulmonary artery occlusion in Giant Jungle Fowl doubled the pulmonary vascular resistance and forced the right ventricle to propel a sustained 60% increase in blood flow through the vasculature of the unoccluded lung. A transient increase in pulmonary arterial pressure initially was required to overcome the vascular resistance of the unoccluded lung; however, flow-dependent vasodilation gradually reduced the pulmonary vascular resistance and permitted pulmonary arterial pressure to return toward control levels. Unilateral pulmonary artery occlusion also triggered an immediate reduction in the partial pressure of oxygen in arterial blood, and the gradual return of pulmonary arterial pressure toward control levels did not eliminate this ventilation-perfusion mismatch, which has been attributed to blood flowing too rapidly through the unoccluded lung to permit diffusive gas equilibration. The inherent capacity for flow-dependent pulmonary vasodilation may reduce the susceptibility of Giant Jungle Fowl to PHS by reducing the increment in pulmonary arterial pressure required to propel an elevated blood flow through the lungs.