The role of urea on the dissolution of starch in NaOH-urea aqueous solutions

General fabrication of bioactive dissolving microneedles from whole grain seeds derived starch for transdermal application

Dissolving microneedles (DMNs) have gained increasing attraction for transdermal drug delivery. However, their manufacture is limited due to the lack of suitable fabricating materials. It is highly demanded to explore new materials for DMN preparation. Herein, we were the first to discover that natural grain powders were promising material candidates for DMN manufacture. MD was first used to determine the solvent to prepare microneedles. Then, mold method was used to fabricate five grain seed powders into microneedles. Afterwards, FTIR, XRD, MTT, live/dead assay and antioxidative assays (DPPH and Fenton) were applied to assess the chemical and biological properties of the microneedles. Finally, both in vitro and in vivo experiments were used to assess the transdermal effects of the microneedles. The results demonstrated that the microneedles had excellent biosafety with >90 % of living cells and <5 % of hemolysis rate. Also, the microneedles displayed up to 100 % eradication of free radicals, implying their good antioxidative capabilities. The transdermal study demonstrated that the microneedles could pierce mouse skins and undergo completely and fast dissolving in the skin as quickly as 30 s. This work will motivate more attempts to develop novel transdermal microneedles from natural products for biological applications.

Comparative analysis of multi-angle structural alterations and cold-water solubility of kudzu starch modifications using different methods

Kudzu, a plant known for its medicinal value and health benefits, is typically consumed in the form of starch. However, the use of native kudzu starch is limited by its high pasting temperature and low solubility, leading to a poor consumer experience. In this study, kudzu starch was treated using six modification techniques: ball milling, extrusion puffing, alcoholic-alkaline, urea-alkaline, pullulanase, and extrusion puffing-pullulanase. The results of the Fourier transform infrared spectrum showed that the intensity ratio of 1047/1022 cm-1 for the modified starches (1.02-1.21) was lower than that of the native kudzu starch (1.22). The relative crystallinity of modified kudzu starch significantly decreased, especially after ball milling, extrusion puffing, and alcoholic-alkaline treatment. Furthermore, scanning electron microscopy and confocal laser scanning microscopy revealed significant changes in the granular structures of the modified starches. After modification, the pasting temperature of kudzu starch decreased (except for the urea-alkaline treatment), and the apparent viscosity of kudzu starch decreased from 517.95 Pa·s to 0.47 Pa·s. The cold-water solubility of extrusion-puffing and extrusion puffing-pullulanase modified kudzu starch was >70 %, which was significantly higher than that of the native starch (0.11 %). These findings establish a theoretical basis for the potential development of instant kudzu powder.

A novel efficient wet process for preparing cross-linked starch: Impact of urea on cross-linking performance

Although wet processes are promising for preparing cross-linked starch, they are currently challenged by lower cross-linking efficiency and the requirement of large amounts of salts. Herein, an efficient and greener wet process was proposed, in which the cross-linking performance between sodium hexametaphosphate (SHMP) and starch was enhanced with the aid of urea. The maximum degree of substitution (DS) of the urea-phosphorylated cross-linked starch (UPCS) was 0.040 at 35 °C, while that of the conventional phosphorylated cross-linked starch (CPCS) was 0.031 at 45 °C. Compared with CPCS, the maximum DS of UPCS was elevated by 29.03 %, but its optimum cross-linking temperature was reduced by 10 °C, indicating that the cross-linking efficiency of this novel wet process was greatly improved by urea. The structural difference between UPCS and CPCS was confirmed by using a series of techniques including 31P NMR and 13C NMR. Zeta potential results suggested that urea may promote starch cross-linking by preventing the closure of active sites through hydrophobic interactions. Due to the structural reinforcement of starch by urea, UPCS showed better thermal stability, water resistance, acid and alkali resistance, and steady shear tolerance properties. This study provides a facile wet process for the fabrication and application of cross-linked starch materials.