Amoxicillin-loaded bionanocomposite hydrogels: swelling, dehydration, and in vitro drug release kinetics and mechanism.

This study deals with preparing and characterizing polyvinyl alcohol/egg white/montmorillonite bionanocomposite hydrogels as antibacterial drug delivery systems. The cyclic freezing/thawing method was utilized to fabricate the hydrogels. To study the performance of the prepared hydrogels as drug delivery systems, amoxicillin, as a model antibiotic drug, was loaded into the hydrogels by mixing with the precursor polymer solution and gelation. From the diverse microstructural characterization techniques, i.e. XRD, SEM, AFM, DLS, and gel fraction estimation, it was possible to infer that montmorillonite has been successfully incorporated into the hydrogel network and acted as an additional crosslinker to bind the chains of egg white and polyvinyl alcohol. Scrutinizing the physical properties of the produced hydrogels demonstrated that increasing incorporated montmorillonite content adversely affects the prepared hydrogels' swelling ability and prolongs their dehydration period. Additionally, the Swelling characteristics of the hydrogels were evaluated at different pHs. Results showed an increase in the swelling ability of all samples by raising the pH value of the medium. Additionally, it was proved that both swelling and dehydration of the hydrogels follow non-Fickian diffusion. In vitro drug delivery experiments demonstrated that the cumulative fractional release of amoxicillin was adversely dependent on the amount of incorporated montmorillonite into the hydrogels and positively dependent on the pH of the release solution. It was also found that, in all examined samples, the mechanism by which the release of clindamycin happens is non-Fickian or anomalous transport.

Clindamycin releasing bionanocomposite hydrogels as potential wound dressings for the treatment of infected wounds.

The bionanocomposite hydrogels based on polyvinyl alcohol and egg white (as the matrix) and montmorillonite nanoclay (as reinforcement) were fabricated via the freezing-thawing technique. The prepared bionanocomposite hydrogels were loaded with clindamycin, as an effective antibiotic, to attain new potential wound dressings for healing the infected wounds. The microstructural properties of the bionanocomposite hydrogel wound dressings were characterized using the X-ray diffractometry, transmission electron microscopy, atomic force microscopy and gel fraction measurement. It was shown that all of the bionanocomposite hydrogel wound dressings had an exfoliated morphology and the montmorillonite layers acted as additional crosslinking zones to interconnect the polyvinyl alcohol and egg white chains. The characteristics of the prepared wound dressings were investigated using different experiments, including the water content, drying, water vapor transmission rate (WVTR), transparency and in vitro drug release tests. It was found that the equilibrium water content and WVTR were tended to decrease by increasing the loading level of montmorillonite in samples. The results showed that the drying period of bionanocomposite hydrogel wound dressings was prolonged by increasing the content of the incorporated montmorillonite. In vitro drug delivery experiments showed the cumulative fractional release of clindamycin and the clindamycin diffusion coefficient were decreased either by increasing the weight percentage of the incorporated montmorillonite into the wound dressings or by decreasing the pH of the release medium. It was also shown that the mechanism governing the release of clindamycin in all examined samples was the non-Fickian (anomalous) transport.

In vitro and in vivo assays on egg white/polyvinyl alcohol/clay nanocomposite hydrogel wound dressings.

Novel nanocomposite hydrogel wound dressings on the basis of egg white and polyvinyl alcohol, as matrix, and natural Na-montmorillonite clay, as reinforcing agent, were prepared and their performances on wound healing investigated in vitro and in vivo. In vitro cytotoxicity assay revealed non-cytotoxic activity and excellent biocompatibility level of prepared nanocomposite hydrogel wound dressings. The bacterial penetration assay showed the prepared nanocomposite hydrogel wound dressings are excellent barriers against microorganisms and could protect the wound from infection during the wound healing. In vivo animal study showed that the wound healing process was considerably faster in wounds covered with nanocomposite hydrogel wound dressings compared to the conventional wound dressing, i.e. sterile gauze, due to creation of a moist environment on the wound surface and faster migration rate of the epidermal cells. The mechanical properties of healed wounds with nanocomposite hydrogel wound dressings were better than those control wounds covered with sterile gauze due to their better collagen formation ability as a result of created moist healing condition as well as the presence of egg white, as a source of proteins, in their structures.

Egg white/poly (vinyl alcohol)/MMT nanocomposite hydrogels for wound dressing.

Nanocomposite hydrogels on the basis of egg white and poly (vinyl alcohol) (PVA) containing 0, 5, and 10 wt.% of montmorillonite (MMT) nanoclay were prepared by a facile cyclic freezing-thawing technique and their properties investigated for wound dressing application. The morphological, structural, thermal, physical, and in vitro cytotoxic properties of the prepared nanocomposite hydrogel wound dressings (NHWDs) were experimentally studied. The NHWDs had an exfoliated morphology with a porous structure having pores sizes in the nanometric scale. It was shown that MMT acted as cross-linker in the network of NHWDs and improved their thermal stabilities. The prepared wound dressings were transparent and their equilibrium water contents and water vapor transmission rates, as two important factors of wound dressings, were very close to the properties of human skin which means that the prepared wound dressings could interact appropriately with the damaged tissues of wounds and protect them like an artificial skin during the wound healing process. The in vitro cytotoxicity assay also confirmed the non-cytotoxic nature of the prepared NHWDs. It was finally concluded that the prepared egg white/PVA/MMT nanocomposite hydrogels are promising materials to be used as novel wound dressings in wound and burn care.

Functional connectivity in the brain estimated by analysis of gamma events.

It is known that gamma activity is generated by local networks. In this paper we introduced a new approach for estimation of functional connectivity between neuronal networks by measuring temporal relations between peaks of gamma event amplitudes. We have shown in freely moving rats that gamma events recorded between electrodes 1.5 mm apart in the majority of cases, are generated by different neuronal modules interfering with each other. The map of functional connectivity between brain areas during the resting state, created based on gamma event temporal relationships is in agreement with anatomical connections and with maps described by fMRI methods during the resting state. The transition from the resting state to exploratory activity is accompanied by decreased functional connectivity between most brain areas. Our data suggest that functional connectivity between interhemispheric areas depends on GABAergic transmission, while intrahemispheric functional connectivity is kainate receptor dependent. This approach presents opportunities for merging electrographic and fMRI data on brain functional connectivity in normal and pathological conditions.

Functional connectivity between brain areas estimated by analysis of gamma waves.

The goal of this study is to investigate functional connectivity between different brain regions by analyzing the temporal relationship of the maxima of gamma waves recorded in multiple brain areas. Local field potentials were recorded from motor cortex, hippocampus, entorhinal cortex and piriform cortex of rats. Gamma activity was filtered and separated into two bands; high (65-90Hz) and low (30-55Hz) gamma. Maxima for gamma activity waves were detected and functional connectivity between different brain regions was determined using Shannon entropy for perievent histograms for each pair channels. Significant Shannon entropy values were reported as connectivity factors. We defined a connectivity matrix based the connectivity factors between different regions. We found that maxima of low and high frequency gamma occur in strong temporal relationship between some brain areas, indicating the existence of functional connections between these areas. The spatial pattern of functional connections between brain areas was different for slow wave sleep and waking states. However for each behavioral state in the same animal the pattern of functional connections was stable over time within 30min of continuous analysis and over a 5 day period. With the same electrode montage the pattern of functional connectivity varied from one subject to another. Analysis of the temporal relationship of maxima of gamma waves between various brain areas could be a useful tool for investigation of functional connections between these brain areas. This approach could be applied for analysis of functional alterations occurring in these connections during different behavioral tasks and during processes related to learning and memory. The specificity in the connectivity pattern from one subject to another can be explained by the existence of unique functional networks for each subject.

Non-linear classification of heart rate parameters as a biomarker for epileptogenesis.

PURPOSE: To characterize a biomarker for epileptogenesis based on cardiac interbeat interval characteristics. METHODS: Electrocardiograph (ECG) and electroencephalogram (EEG) signals were recorded from freely moving rats (n = 23) before status epilepticus (SE) induced by i.p. pilocarpine (PILO) injection as baseline, and on days 1, 3 and 7 after SE. We assessed several features from cardiac interbeat intervals, including linear, non-linear and frequency parameters of interbeat intervals, and power spectra of interpolated intervals during epileptogenesis. After thresholding, the altered values were applied to a non-linear classifier. The non-linear classifier divided animals into two groups; with and without epilepsy, based on all collected data. RESULTS: We found that none of the single altered parameters in cardiac activity emerged as a sole biomarker for epileptogenesis. However, the non-linear classifier distinguished animals that later developed from those and did not develop epilepsy. The non-linear classification was performed on preliminary findings from 23 animals; six did not develop epilepsy and the rest did. The average positive predictive value (precision rate) was 78%. This was calculated based on the average sensitivity and specificity, which were 80.6% and 35.2% respectively, for the 100 classification passes. We also showed that these numbers would have increased as the number of subjects increased. CONCLUSION: Changes to the brain caused by status epilepticus that lead to epileptogenesis have systemic effects, and alter cardiac activity. A non-linear classifier performed on several extracted features of cardiac interbeat intervals may be useful as a biomarker to identify animals with low and high probability of developing epilepsy after status epilepticus.

Further evidence that pathologic high-frequency oscillations are bursts of population spikes derived from recordings of identified cells in dentate gyrus.

PURPOSE: To analyze activity of identified dentate gyrus granular cells and interneurons during pathologic high-frequency oscillations (pHFOs). METHODS: Pilocarpine-treated epileptic mice were anesthetized with urethane and ketamine. Their heads were fixed in a stereotaxic frame. Extracellular unit activity was recoded with glass micropipettes, whereas multiunit and local field activity was simultaneously recorded with attached tungsten microelectrodes. After electrophysiologic experiments, recorded cells were labeled by neurobiotin and visualized by immunohistochemical methods. KEY FINDINGS AND SIGNIFICANCES: pHFOs containing more than three waves were recorded in our experiments, but pathologic single-population spikes also occurred. Identified granular cells discharged preferentially in synchrony with pHFOs and single population spikes, whereas interneurons decreased their discharge frequency during this time. These experiments provide additional confirmation that pHFOs in the dentate gyrus represent single or recurrent population spikes, which in turn reflect summated hypersynchronous discharges of principal cells.