The mineralized extracellular matrix (ECM) of bone is essential in vertebrates to provide structure, locomotion, and protect vital organs, while also acting as a calcium and phosphate reservoir to maintain homeostasis. Bone's structure comprises mainly structural collagen fibrils, hydroxyapatite nanocrystals and water, and it is the organization of the densely-packed collagen matrix that directs the organization of the mineral crystallites. Biogenic mineralization occurs when osteoblasts release "mineral bearing globules" which fuse into the preformed collagen matrix, and upon crystallization of this amorphous precursor, the fibrils become embedded with [001] oriented nanocrystals of hydroxyapatite. Our prior work has shown that this nanostructured organization of bone can be reproduced in vitro using the polymer-induced liquid-precursor (PILP) process. In this report, our focus is on using biomimetic processing to recreate both the nano- and micro-structure of lamellar bone. We first applied molecular crowding techniques to acidic, type-I collagen solutions to form dense, liquid crystalline collagen (LCC) scaffolds with cholesteric order. We subsequently mineralized these LCCs via the PILP process to achieve a high degree of intrafibrillar mineral, with compositions and organization similar to that of native bone and with a "lamellar" microstructure generated by the twisting LCC template. In depth characterization of the nano- and micro-structure was performed, including optical and electron microscopy, X-ray and electron diffraction, and thermogravimetric analyses. The results of this work lead us closer to our goal of developing hierarchically structured, collagen-hydroxyapatite composites which can serve as fully synthetic, bioresorbable, load-bearing bone substitutes that are remodeled by the native BRU.
Polymers of substituted norbornenes were produced using palladium catalysts in the presence of formic acid (FA) as a chain transfer agent (CTA) which act to control molecular weight as well as to increase conversion. Spectroscopic analysis of these polymers by 1 H NMR and MALDI-TOF MS confirmed that hydrogen-terminated polynorbornenes are generated leading to extremely low optical densities at 193 nm. Deuterium labeling studies were conducted in order to discern possible chain transfer mechanisms.
Two new 5-substituted 1,3,4-thiadiazole-2-carboxylate esters have been synthesized via ring closure of appropriate tricarbonyl precursors using Lawesson's reagent. The chemistry described is the first report of such methodology in the organic literature. The new materials display broad smectic C phases and show considerable potential for use in electrooptic display devices.
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