Methacryloxyethyl phosphate‐grafted expanded polytetrafluoroethylene membranes for biomedical applications

Expanded polytetrafluoroethylene (ePTFE) membranes were modified by graft copolymerization with methacryloxyethyl phosphate (MOEP) in methanol and 2‐butanone (methyl ethyl ketone (MEK)) at ambient temperature using gamma irradiation. The effect of dose rate (0.46 and 4.6 kGy h^?1), monomer concentration (1–40 %) and solvent were studied and the modified membranes were characterized by weight increase, X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XPS was used to determine the % degree of surface coverage using the C? F (ePTFE membrane) and the C? C (MOEP graft copolymer) peaks. Grafting yield, as well as surface coverage, were found to increase with increasing monomer concentration and were significantly higher for samples grafted in MEK than in methanol solution. SEM images showed distinctly different surface morphologies for the membranes grafted in methanol (smooth) and MEK (globular), hence indicating phase separation of the homopolymer in MEK. We propose that in our system, the non‐solvent properties of MEK for the homopolymer play a more important role than solvent chain transfer reactions in determining grafting outcomes. Copyright © 2005 Society of Chemical Industry     

Associative retuning in the thalamic source of input to the amygdala and auditory cortex: Receptive field plasticity in the medial division of the medial geniculate body.

The medial division of the medial geniculate body (MGm) projects to the lateral amygdala and the upper layer of the auditory cortex and develops physiological plasticity rapidly during classical conditioning. The effects of learning on frequency receptive fields (RFs) in the MGm of the guinea pig have been determined. Classical conditioning (tone–footshock), as indexed by rapid development of conditioned bradycardia, produced conditioned stimulus (CS)–frequency specific RF plasticity: increased response at the CS frequency with decreased responses at other frequencies, both immediately and after a 1-hr retention period. Sensitization training produced only general changes in RFs. These findings are considered with reference to both the elicitation of amygdala-mediated, fear-conditioned responses and the mechanism of retrieval of information stored in the auditory cortex during acquisition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A miniature photorefractive circuit for principal component extraction

The optical feature extractor is a photorefractive ring oscillator that can identify the strongest spatiotemporal component of its input space. The theoretical sections discuss the design and performance limitations of the signal extractor. A simple model of the filter's nonlinear functioning enables the reader to go directly to the experimental section that describes the making of the filter and experimental results. The device, also called the auto-tuning filter, is 5 cm2 in size, has a 3 GHz processing bandwidth, and requires less than 5 mW of continuous optical power to operate.     

Calcium phosphate nucleation on surface-modified PTFE membranes

Highly porous PTFE membranes are currently being used in facial reconstructive surgery. The present study aims at improving this biomaterial through creating a more bioactive surface by introducing ionic groups onto the surface. The unmodified PTFE membrane does not induce inorganic growth after immersion in simulated body fluid (SBF) for up to 4 weeks. Copolymeric grafting with acrylic acid (AAc) by means of gamma irradiation and subsequent in vitro testing in SBF reveals that this copolymer initially acts as an ion-exchange material and subsequently induces growth of a calcium phosphate phase (Ca/P=2.7) when large amounts (15%) of pAAc are introduced onto the membrane surface. This copolymer is not expected to function well from a biomaterials perspective since SEM showed the pores on the surface to be partly blocked. In contrast, the surface of monoacryloxyethyl phosphate (MAEP)-modified samples is altered at a molecular level only. Yet the modified materials are able to induce calcium phosphate nucleation when the external surface coverage is 44% or above. The initial inorganic growth on these membranes in SBF has a (Ca+Mg)/P ratio of 1.1 (presumably Brushite or Monetite). The secondary growth, possibly calcium-deficient apatite or tricalcium phosphate, has a (Ca+Mg)/P ratio of 1.5. This result is a promising indicator of a bioactive biomaterial.     

Self-purification of rivers a two-phase model for bacterial biodegradation

A simple two-phase model has been developed, which accounts for up to 95% of the total oxygen consumption during the bacterial phase of river self-purification. The two phases are characterized by a logistic model. The first corresponds roughly to a destruction of of the substrate, and is accompanied by the formation of cellular reserves. The second is the consumption of these stored substances, and begins when the external substrate ceases to be more attractive than the endogenous reserves. The cell yield as well as the stored material proportion appear to be constant, while the kinetic parameter ( ) is strongly S₀ dependent. All this can be studied through oxygen balances.     

Graft copolymerization of methoxyacrylethyl phosphate onto expanded poly(tetrafluoroethylene) facial membranes

Expanded poly(tetrafluoroethylene) (ePTFE) membranes were modified by graft copolymerization with methoxyacrylethyl phosphate (MOEP) in methyl ethyl ketone (MEK) solutions at ambient temperature using gamma irradiation. The effect of monomer concentration (3–30%) was studied and the modified membranes were characterized by weight increase, x‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), contact angle measurements, and differential scanning calorimetry (DSC). Results show that the ePTFE membrane had a degree of crystallinity of 59% and that this did not significantly change after grafting indicating that grafting occurs in the amorphous regions. SEM images showed a globular surface morphology for the grafted membranes. XPS was used to evaluate the chemical structure of the graft copolymer and to determine the XPS grafting extent using the C‐F (ePTFE membrane) and the C‐C (MOEP graft copolymer) peaks. The graft yield as well as grafting extent was found to increase with increasing monomer concentration. Concomitantly, the contact angle was found to decrease with increasing monomer concentration. No direct correlation was found between XPS grafting extent and the advancing water contact angle illustrating that the former does not adequately give an indication of the copolymer surface coverage of the first molecular layer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rapid development of learning-induced receptive field plasticity in the auditory cortex.

Classical conditioning induces frequency-specific receptive field (RF) plasticity in the auditory cortex after relatively brief training (30 trials), characterized by increased response to the frequency of the CS and decreased responses to other frequencies, including the pretraining best frequency (BF). This experiment determined the development of this CS-specific RF plasticity. Guinea pigs underwent classical conditioning to a tonal frequency, and receptive fields of neurons in the auditory cortex were determined before and after 5, 15, and 30 CS–UCS (unconditioned stimulus) pairings, as well as 1 hr posttraining. Highly selective RF changes were observed as early as the first 5 training trials. They culminated after 15 trials, then stabilized after 30 trials and 1 hr posttraining. The rapid development of RF plasticity satisfies a criterion for its involvement in the neural bases of a specific associative memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulation at a site of auditory-somatosensory convergence in the medial geniculate nucleus is an effective unconditioned stimulus for fear conditioning.

The medial division of the medial geniculate nucleus (MGm) and the posterior intralaminar nucleus (PIN) are necessary for conditioning to an auditory conditioned stimulus/stimuli (CS), receive both auditory and somatosensory input, and project to the amygdala, which is involved in production of fear conditioned responses (CRs). If CS–unconditioned stimulus (UCS) convergence in the MGm-PIN is critical for fear conditioning, then microstimulation of this area should serve as an effective UCS during classical conditioning, in place of standard footshock. Guinea pigs underwent conditioning (40–60 trials) using a tone as the CS and medial geniculate complex microstimulation as the UCS. Conditioning bradycardia developed when the UCS electrodes were in the PIN. However, microstimulation was not an effective UCS for conditioning in other parts of the medial geniculate or for sensitization training in the PIN or elsewhere. Learning curves were similar to those found previously for footshock UCS. Thus, the PIN can be a locus of functional CS–UCS convergence for fear conditioning to acoustic stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factor analysis as a means of determining response to chemotherapy in patients with osteogenic sarcoma

The prognosis of localized osteogenic sarcoma (OS) has improved considerably since the introduction of neoadjuvant chemotherapy. However, there is a subset of patients who do not show full benefit from neoadjuvant chemotherapy because of chemoresistance. The early identification of poor responders to chemotherapy during neoadjuvant therapy remains difficult. In order to evaluate the role of bone scintigraphy we report our experience of dynamic technetium-99m hydroxymethylene diphosphonate bone scintigraphy in 19 cases of paediatric osteogenic sarcomas. Before the beginning of chemotherapy, a dynamic scan was recorded during 30 min followed by static images at 3 h. The procedure was repeated halfway through the course of chemotherapy (6th week). Histological grading of the response to chemotherapy was carried out in the 12th week, showing nine good responses and ten poor responses. Factor analysis of dynamic structures (FADS) applied to dynamic scans allowed us to identify three factors termed vascular, "soft tissue" and osseous factors. The effect of chemotherapy on each factor was evaluated. Using FADS we were able to detect all the poor histological responders with the combination of vascular and osseous factors. Six out of nine good histological responders were also classified as scintigraphic responders. FADS applied to dynamic bone scans allowed us to identify at an early stage all the poor histological responders to neoadjuvant chemotherapy. This method may have clinical relevance for the therapeutic strategy in patients with OS.     

FT-IR spectroscopy of fluoro-substituted hydroxyapatite: strengths and limitations

Fluoro substituted hydroxyapatite (FHAp) samples were prepared by a cyclic pH method. Both calcined and uncalcined samples were subjected to elemental analysis (F, Ca, P) and X-ray diffraction (XRD) analysis to verify composition and phase purity. Good correlation between a-axis parameters and fluoride ion content was found for calcined samples, however, for uncalcined samples the fluoride ion content was higher than estimated from the a-axis values. Fourier transform infra red (FT-IR) spectroscopy analysis of the calcined samples showed OH band shifts and splitting in accordance with F-HO interactions affecting the OH vibration. We conclude that the OH libration (620–780 cm^-1 range) is more suited for estimation of fluoride ion content than the OH stretching. In contrast, uncalcined samples all displayed FT-IR spectra similar to that of hydroxyapatite (HAp) despite the presence of fluoride ions (18–73%). FT-IR emission spectroscopy was used to probe the changes occurring in the FT-IR spectra of HAp and FHAp samples upon heating. Interpretation of the spectral changes occurring during heating to 1,000 °C and subsequent cooling is given. Room temperature spectra of samples heated to various temperatures was used to determine the temperature necessary to produce FT-IR spectra displaying the expected OH bands. A model accounting for the combined observations is proposed.