ABSTRACT
Mineralized collagen fibrils are important basic building blocks of calcified tissues, such as bone and dentin. Polydopamine (PDA) can introduce functional groups, i.e., hydroxyl and amine groups, on the surfaces of type I collagen (Col-I) as possible nucleation sites of calcium phosphate (CaP) crystallization. Molecular bindings in between PDA and Col-I fibrils (Col-PDA) have been found to significantly reduce the interfacial energy. The wetting effect, mainly hydrophilicity due to the functional groups, escalates the degree of mineralization. The assembly of Col-I molecules into fibrils was initiated at the designated number of collagenous molecules and PDA. In contrast to the infiltration of amorphous calcium phosphate (ACP) precursors into the Col-I matrix by polyaspartic acid (pAsp), this collagen assembly process allows nucleation and ACP to exist in advance by PDA in the intrafibrillar matrix. PDA bound to specific sites, i.e., gap and overlap zones, by the regular arrangement of Col-I fibrils enhanced ACP nucleation and thus mineralization. As a result, the c-axis-oriented platelets of crystalline hydroxyapatite in the Col-I fibril matrix were observed in the enhanced mineralization through PDA functionalization.
ABSTRACT
Hydroxyapatite (HAp) is a major inorganic component in bone minerals and is often used for bone tissue engineering. Herein, we synthesized HAp using sebacic acid as an additive at different pH values by a hydrothermal method. Sebacic acid, which has two carboxyl group ends of the carbonate chain, binds with Ca ions during the hydrothermal process to become a crystal nucleation site in (001) and at the same time could act as an inhibitor in a specific direction [i.e., (110)] for the HAp crystal growth. Sebacic acid and the hydroxyl ion (OH-) are competitively attracted to the a(b)-plane of HAp. Depending on the pH condition, the crystal growth resulted in different morphologies depending on the ratio of sebacic acid and hydroxide ions. It was confirmed through Fourier-transform infrared spectroscopy and Raman spectroscopy that dicalcium phosphate anhydrous with HPO4 was produced under acidic conditions and HAp was produced under neutral and basic conditions. The plate- and nanorod-HAp crystals' preferential growth along the c-axis, which were obtained under neutral and basic conditions, was analyzed by transmission electron microscopy. Growth control in the c-axis direction of HAp is necessary for the understanding of crystallization of bone minerals because the mineral inside the collagen fibrils in bone tissue also shows a c-axis orientation.
ABSTRACT
Numerous studies have reported the use of halide perovskites as highly functional light-harvesting materials. The development of optimized compositions and deposition approaches has led to impressive improvements; however, no noticeable breakthrough in performance has been observed for these materials recently. Here, a breakthrough that enables the fabrication of vertically grown halide perovskite (VGHP) nanopillar photodetectors via a nanoimprinting crystallization technique is demonstrated. We used engraved nanopatterned polymer stamps to form VGHP nanopillars during the pressurized crystallization of the softly baked gel state of a methylammonium lead iodide (CH3NH3PbI3, denoted MAPI) film. The VGHP films exhibit much lower defect density and higher conductivity, as supported by current-voltage characteristic measurements and conductive atomic force microscopy measurements. Ultimately, two-terminal lateral photodetectors based on the VGHP nanopillar films show a greatly enhanced photoresponse compared with flat film-based photodetectors. We expect that the deposition method presented here will help surpass the technical limits and contribute to further improvements in various halide-perovskite-based devices.
