Numerical Simulation of a Core-Shell Polymer Strand in Material Extrusion Additive Manufacturing.

Material extrusion additive manufacturing (ME-AM) techniques have been recently introduced for core-shell polymer manufacturing. Using ME-AM for core-shell manufacturing offers improved mechanical properties and dimensional accuracy over conventional 3D-printed polymer. Operating parameters play an important role in forming the overall quality of the 3D-printed manufactured products. Here we use numerical simulations within the framework of computation fluid dynamics (CFD) to identify the best combination of operating parameters for the 3D printing of a core-shell polymer strand. The objectives of these CFD simulations are to find strands with an ultimate volume fraction of core polymer. At the same time, complete encapsulations are obtained for the core polymer inside the shell one. In this model, the deposition flow is controlled by three dimensionless parameters: (i) the diameter ratio of core material to the nozzle, d/D; (ii) the normalised gap between the extruder and the build plate, t/D; (iii) the velocity ratio of the moving build plate to the average velocity inside the nozzle, V/U. Numerical results of the deposited strands' cross-sections demonstrate the effects of controlling parameters on the encapsulation of the core material inside the shell and the shape and size of the strand. Overall we find that the best operating parameters are a diameter ratio of d/D=0.7, a normalised gap of t/D=1, and a velocity ratio of V/U=1.

Polymeric acrylate-based hybrid films containing lead and iron patterned by UV photo-polymerization.

The development and processing of hybrid inorganic-organic thin film materials plays a critical role in advancing interdisciplinary sciences and device manufacturing. Here we present a novel approach to synthesize and deposit acrylate-containing organic/inorganic hybrid films. The material is based on a chemical solution and includes specifically desired metal dopants that are fully integrated into the backbone of the polymer structure. The film can be deposited by simple spin coating, and we confer photosensitive properties to the material making it directly patterned by traditional UV photolithography techniques. Film thickness, chemical characterization, and wet/dry etching capability of the film are also investigated. We believe this innovative material has the potential to be used in a broad range of applications for electronic, photonic, biology, and other interdisciplinary fields.

Expression of beta-defensins in gingival health and in periodontal disease.

BACKGROUND: Human beta-defensins (HBDs) are epithelial-derived antimicrobial peptides. The expression of three HBDs (HBD-1, HBD-2, and HBD-3) has been reported in oral mucosa, gingiva, and salivary glands. However, their role in protection against oral infections is not well understood. This study examined the expression of HBD-1, HBD-2, and HBD-3 mRNAs in gingival health and periodontal disease. METHODS: Gingival tissue discarded from periodontal procedures was obtained from 20 periodontally healthy and 29 periodontally diseased sites. Total RNA was isolated, and expression of beta-defensins was analyzed by both 35-cycle and semiquantitative (25-cycle) reverse transcription-polymerase chain reaction (RT-PCR). The level of expression was assigned ordinal scores of no expression, low expression, or high expression. mRNA expression was compared between healthy and diseased groups using exact tests of homogeneity and Cochran-Mantel-Haenszel tests; associations among the variables were assessed using exact tests and Kendall's tau-b statistic. RESULTS: All 49 samples demonstrated basal mRNA expression of HBD-1, HBD-2, and HBD-3. Significantly higher levels of HBD-3 (P = 0.012) expression were found in the healthy tissues as compared to the diseased ones. There was also a suggestion of higher expression of HBD-2 in the healthy tissues (P = 0.12). Levels of HBD-1, HBD-2, and HBD-3 mRNA expression were correlated with one another (P < 0.001). CONCLUSIONS: High levels of HBD-3 mRNA expression in healthy tissues suggest a potentially important protective role for defensins in the host immune response to infection by periodontal pathogens.