Formation Of Chemical Gradients Research Articles

The formation of chemical/structural gradients in strong covalent bonded SiBN fibers under active nitrogen atmosphere

In this work, SiBN fibers with chemical/structural gradients under the radial direction were fabricated by one-step treatment at 1700 °C under active nitrogen atmosphere. The formation of chemical gradient should be contributed to the boron atoms diffusion from the fiber interior to the surface, under the driven force of BN bond-breaking in Si–N–B networks to form stable BN bonds in the BNB networks at the fiber surface. Meanwhile, the structural gradients with graded phase separation of Si–N–B networks and crystallization behavior of Si3N4 phase could form under the effect of graded boron content distribution. The SiBN fibers with chemical/structural gradients showed better high-temperature stability due to the possibly synergistic effect of the decomposition resistant of boron-rich surface and the optimization of graded boron distribution. We expect our finding as a universal method to fabricate chemical/structural gradients on other boron-containing multinary ceramics with various shapes.

Rapid Generation of Biologically Relevant Hydrogels Containing Long‐Range Chemical Gradients

Many biological processes are regulated by gradients of bioactive chemicals. Thus, the generation of materials with embedded chemical gradients may be beneficial for understanding biological phenomena and generating tissue-mimetic constructs. Here we describe a simple and versatile method to rapidly generate materials containing centimeter-long gradients of chemical properties in a microfluidic channel. The formation of chemical gradient was initiated by a passive-pump-induced forward flow and further developed during an evaporation-induced backward flow. The gradient was spatially controlled by the backward flow time and the hydrogel material containing the gradient was synthesized via photopolymerization. Gradients of a cell-adhesion ligand, Arg-Gly-Asp-Ser (RGDS), was incorporated in the poly(ethylene glycol)-diacrylate (PEG-DA) hydrogels to test the response of endothelial cells. The cells attached and spread along the hydrogel material in a manner consistent with the RGDS gradient profile. A hydrogel containing PEG-DA concentration gradient and constant RGDS concentration was also generated. The morphology of cells cultured on such hydrogel changed from round in the lower PEG-DA concentration regions to well-spread in the higher PEG-DA concentration regions. This approach is expected to be a valuable tool to investigate the cell-material interactions in a simple and high-throughput manner and to design graded biomimetic materials for tissue engineering applications.

Tonsillolith: Not just a stone but a living biofilm

Objective To study the morphology and activity of tonsilloliths, demonstrating oxygen respiration, denitrification, and acidification on exposure to sucrose. Study Design Tonsilloliths were extracted in atraumatic conditions during tonsillectomy from 16 adults and sent to two different laboratories for histological, bacteriological, and biofilm studies under sterile conditions. Setting Multicenter laboratory study. Subjects and Methods Multiple tonsilloliths from two patients examined by confocal microscopy and microelectrodes were used to measure aerobic/anaerobic respiration and acid production (dissolved oxygen, nitrous oxide, pH) when exposed to saliva following addition of sucrose and fluoride. Results Morphologically, tonsilloliths were similar to dental biofilms, containing corncob structures, filaments, and cocci. Microelectrodes showed that the microorganisms respired oxygen and nitrate. The oxygen concentration in the center of the tonsillolith was depleted to approximately one-tenth of that of the overlying fluid. The addition of sucrose resulted in acid production within the tonsillolith, dropping the pH from 7.3 to 5.8. The data showed stratification with oxygen respiration at the outer layer of tonsillolith, denitrification toward the middle, and acidification toward the bottom. The depletion of oxygen and acid production following addition of sucrose may allow the proliferation of anaerobic/acidophilic bacteria. Fluoride suppressed acid production in the presence of sucrose. Conclusions Tonsilloliths exhibit biofilm structure and the formation of chemical gradients through physiological activity. Although tonsillectomy is an option for treating cryptic infections, understanding the morphology and biofilm characteristics of tonsilloliths may stimulate scientists to use limited or targeted remedies in the future.

Tonsillolith: Not Just a Stone But a Living Biofilm

ProblemTo study the morphology and activity of tonsilloliths ex vivo, using confocal microscopy and microelectrodes. Understanding the similarities of tonsilloliths to dental biofilm by demonstrating oxygen respiration, de‐nitrification, and acid production.MethodsTonsilloliths were harvested from several patients with cryptic pockets and sent to the laboratory under sterile conditions. The tonsilloliths were examined by confocal microscopy to determine the presence and distribution of bacteria. Microelectrodes (dissolved oxygen, nitrous oxide, and pH) were used to measure the rates of aerobic and anaerobic respiration, and acid production, when exposed to saliva (10%) and after sucrose and fluoride addition.ResultsMorphologically, the tonsilloliths were similar to dental‐plaque biofilms, containing ‘corn‐cob’ structures, filaments and cocci. The microorganisms respired both oxygen and nitrate in physiological concentrations. The oxygen concentration in the center of the tonsillolith (500 microns) was depleted to approximately 1/10th that of the overlying fluid. The addition of 10% sucrose resulted in the production of acid within the tonsillolith by dropping the pH from 7.3 to 5.8 at a depth of 200 microns. On addition of fluoride (1000 pm) the pH increased to 6.1, suggesting that fluoride suppressed the acid fermentation of sucrose. The profiles showed, aerobic respiration near the top, de‐nitrification slightly lower and acidification towards the center. The tonsillolith therefore, had stratified layers, similar to dental (and other) biofilms. The depletion of oxygen and acid production following addition of sucrose may encourage the proliferation of anaerobic/acidophilic bacteria within the tonsillolith.ConclusionTonsilloliths exhibit biofilm structure and the formation of chemical gradients through physiological activity.SignificanceWhile complete or intracapsular tonsillectomy is an option for treating chronic cryptic infections, understanding the morphology and biofilm characteristics of tonsilloliths may stimulate scientists in using limited or non‐surgical remedies in treating chronic cryptic infections in the future.SupportThis study was funded by Valam and Philips Oral Healthcare.