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To improve the oral absorption of poorly water-soluble drugs by overcoming the intestinal epithelium barrier, calcium carbonate nanoparticles targeting to intestine peptide transporter 1 (PepT1) were fabricated by modification of the surface of calcium carbonate nanoparticles with Gly-Sar. Gly-Sar-conjugated TPGS was successfully synthesized and characterized, and coumarin 6-loaded Gly-Sar modified calcium carbonate nanoparticles were then prepared and characterized to have a nano-scaled size of about 193 nm in diameter, cracked surface morphology under a scanning electron microscope, and high drug loading efficiency (60.5±5.9)%. Moreover, the Gly-Sar-modified calcium carbonate nanoparticles exhibited better drug loading stability during the process of their transcellular transport, and evidently enhanced intestinal absorption of poorly water-soluble agents. Therefore, the designed intestine PepT1-targeted calcium carbonate nanoparticles might have a promising potential for oral delivery of poorly water-soluble drugs. [ABSTRACT FROM AUTHOR]

The intestinal epithelium is the main barrier to the oral delivery of poorly water-soluble drugs. Based on the specific transporters expressed on the apical membrane of the intestinal epithelium, novel polymer micelles targeting to the organic cation transporter 2 (OCTN2) were constructed by combining carnitine conjugated poly(2 -ethyl-2-oxazoline)-poly(D,L-lactide) (Car-PEOz-PLA) with monomethoxy poly(ethylene glycol)-poly(D,L-lactide) (mPEG-PLA). The structure of the synthesized Car-PEOz-PLA was confirmed by ¹H NMR, TLC and ammonium reineckate precipitation reaction, and the number-average molecular weight determined by GPC was 7260 g/mol with a low PDI of 1.44. Coumarin 6-loaded carnitine modified polymeric micelles prepared by film hydration method were characterized to have a nano-scaled size of about 31 nm in diameter, uniform spherical morphology, high drug loading content of 0.098%±0.03% and encapsulation efficiency of 92.67%±2.80%. Moreover, the carnitine-modified micelles exhibited the similar in vitro release behavior in SGF and SIF, and evidently enhanced intestinal absorption of poorly water-soluble agent. Therefore, the designed OCTN2-targeted micelles might have a promising potential for oral delivery of poorly water-soluble drugs. [ABSTRACT FROM AUTHOR]

• The influence of load factors on the damage of sleeper is analyzed by discrete element method. • The parallel bond degradation model is introduced to realize damage. • The influence of the range of sleeper suspension and the stiffness of the bottom support on the damage is analyzed. To analyze the damage development of concrete sleepers during railway operation, the discrete element method and the parallel bond degradation model are introduced into the damage analysis of concrete sleepers for the first time. The cracking resistance and dynamic characteristics of the sleeper model are verified by comparing the existing literature. The influence of load and the stiffness of the bottom support on the damage development of the sleeper is considered and the following conclusions are drawn: with the increase in the load amplitude, the damage of the sleeper will increase nonlinearly; under the conditions of the same time and the same load amplitude, the number of cracks of the sleeper will increase with the increase of load frequency, and increase exponentially with the number of loads. Different support stiffness at the bottom of the sleeper will change the dynamic characteristics of the sleeper under load, thus changing the damage development of the sleeper. For the sleeper with full support at the bottom, when the support stiffness at the bottom is low, the center of the sleeper is more likely to be damaged. When the support stiffness at the bottom of the sleeper is large, hanging the center of the sleeper about 1/3 of the length of the sleeper can reduce the damage to the center of the sleeper. The research results show that this method can be applied to the study of sleeper damage and provide a new idea for the structural damage of sleepers. [ABSTRACT FROM AUTHOR]

In the present study, we designed and fabricated pH-sensitive polymeric micelles based on the conjugate of poly(2-ethyl- 2-oxazoline)-poly(D,L-lactide) (PEOz-PLA) with doxorubicin (PEOz-PLA-imi-DOX) to efficiently inhibit tumor cell growth. Hence, PEOz-PLA-imi-DOX was successfully synthesized by connecting DOX to the hydrophobic end of pH-sensitive PEOz-PLA via acid cleavable benzoic imine linker and characterized by 1H NMR spectrum and thin layer chromatography. The critical micelle concentration of PEOz-PLA-imi-DOX was determined to be (14.84±3.85) mg/L. The conjugate micelles (denoted as PP-DOX-PM) formed by PEOz-PLA-imi-DOX using film-hydration method were characterized to have a nano-scaled size of about 21 nm in diameter, and the drug loading content was 1.67%. PP-DOX-PM showed pH-dependent drug release behavior with gradually accelerated release of DOX with decrease of pH value, illustrating the micelles' distinguishing feature of endo/lysosomal pH from physiological pH by accelerating drug release. As anticipated, PP-DOX-PM maintained the cytotoxicity of DOX against MDA-MB-231 cells. Collectively, PP-DOX-PM might have great potential for effective suppression of tumor growth. [ABSTRACT FROM AUTHOR]