Ruiwei Guo

Bioadhesive film formed from a novel organic–inorganic hybrid gel for transdermal drug delivery system

A novel organic-inorganic hybrid film-forming agent for TDDS was developed by a modified poly(vinyl alcohol) (PVA) gel using γ-(glycidyloxypropyl)trimethoxysilane (GPTMS) as an inorganic-modifying agent, poly(N-vinyl pyrrolidone) (PVP) as a tackifier and glycerol (GLY) as a plasticizer. The prepared gels can be applied to the skin by a coating method and in situ form very thin and transparent films with good performance, comfortable feel and cosmetic attractiveness. The key properties of the bioadhesive films produced from the hybrid gels were investigated and the results showed that the incorporation of appropriate GPTMS (GPTMS/(PVA+GPTMS) in the range of 20-30%) into the PVA matrix not only can significantly enhance mechanical strength and skin adhesion properties of the resultant film, but also can decrease the crystalline regions of PVA and hence facilitate the diffusion of water vapor and drug. Furthermore, the investigations into in vivo skin irritation suggested the films caused non-irritation to skin after topical application for 120 h. In conclusion, the bioadhesive films formed from organic-inorganic hybrid gels possessed very good qualities for application on the skin and may provide a promising formulation for TDDS, especially when the patient acceptability from an aesthetic perspective of the dosage form is a prime consideration.

Facile Access to Multisensitive and Self-Healing Hydrogels with Reversible and Dynamic Boronic Ester and Disulfide Linkages

Multifunctional and multiresponsive hydrogels have presented a promising platform to design and fabricate smart devices for application in a wide variety of fields. However, their preparations often involve multistep preparation of multiresponsive polymer precursors, tedious reactions to introduce functional groups or sophisticated molecular designs. In this work, a multifunctional boronic acid-based cross-linker bis(phenylboronic acid carbamoyl) cystamine (BPBAC) was readily prepared from inexpensive commercially available 3-carboxylphenylboronic acid (CPBA) and cystamine dihydrochloride, which has the ability to cross-link the cis-diols and catechol-containing hydrophilic polymers to form hydrogels. Due to the presence of the reversible and dynamic boronate ester and disulfide bonds, the obtained hydrogels were demonstrated to not only possess pH, glucose, and redox triresponsive features, but also have autonomic self-healing properties under ambient conditions. Moreover, we can modulate the rheological and mechanical properties by simply adjusting the BPBAC amount. The features, such as commercially available starting materials, easy-to-implement approach, and versatility in controlling cross-linking network and mechanical properties, make the strategy described here a promising platform for fabricating multifunctional and smart hydrogels.

Separation and quantification of dead species in styrene RAFT polymerization by gradient polymer elution chromatography

In living polymerization, the inevitable dead chain impurities, due to bimolecular termination and side reactions, are not only an obstacle for the synthesis of pure block copolymers but also an impairment in the application performance of the resulting polymer materials. In this paper, a simple separation and quantification method based on gradient polymer elution chromatography (GPEC) was developed to experimentally investigate the dead species in RAFT polymerization of styrene. The RAFT-prepared polystyrene (PSt) was extended with methyl acrylate in a specially-designed chain extension reaction, in which the living PSt chains were extended and transformed into block copolymer, but the remaining dead PSt chains (D-PSt) will remain constant and can be separated and quantified by GPEC. The systematic experimental investigation of the effect of various polymerization parameters on the mass fraction of dead species (fD-PSt) in RAFT-prepared polystyrene (PSt) was implemented. The results clearly demonstrated the initiator concentration and RAFT agent concentration can exhibit a linear and inversely proportional dependence on fD-PSt, respectively. In addition, the dead chains were found to be formed throughout the entire RAFT process. These unambiguous experimental data confirmed the previous theoretical calculation and model prediction, which may be beneficial to understand RAFT processes, optimize polymerization conditions and to minimize dead polymer contaminations. Moreover, the method based on GPEC proposed here was able to fractionate and quantify the dead and living species, which can serve as a powerful tool in the mechanistic study of the living radical polymerizations.

Surface modification by self-assembled coating with amphiphilic comb-shaped block copolymers: A solution to the trade-off among solubility, adsorption and coating stability

AbstractSurface coating with amphiphilic block copolymers containing a long hydrophobic anchor block in polar solvent often suffered from the damaging impact of micelles, often leading to a significant decrease in adsorption amount and packing density. In this study, a series of amphiphilic comb-shape block copolymers, poly[poly(ethylene glycol) methyl ether acrylate]-b-poly(styrene-co-N,N-dimethylacrylamide) (P(PEGMEA)-b-P(St-DMA)) were synthesized successfully by reversible addition-fragmentation chain transfer (RAFT) polymerization with fluorescencelabelled RAFT agent. The chain structure and chemical composition of copolymers were characterized by 1H NMR, FTIR and GPC. The surface self-assembled coating through physical adsorption of P(PEGMEA)-b-P(St-DMA) in ethanol on the surface of polyacrylonitrile (PAN) membrane was investigated by XPS, ATR-FTIR, SEM and water contact angle measurements. The antifouling properties of the modified membranes were evaluated using BSA as a model protein. It was found that the introduction of appropriate DMA (DMA/St in the range of about 0.1 to 0.2) into the hydrophobic segment can significantly increase the solubility of copolymers and alter their aggregation behaviors, alleviate the impact of micelles, increase adsorbed amount of copolymers, and thus can enhance the hydrophilicity and anti-fouling properties of membranes. Moreover, the stability analysis indicated that P(PEGMEA)-b-P(St-DMA) with appropriate DMA in the hydrophobic anchor block can form a relatively stable coating on the surface of PAN membrane. Consequently, the adjustment of the structure and composition of anchor segment may be a potential solution to the trade-off among solubility, adsorption amount and coating stability when amphiphilic block copolymers were used to surface modification by self-assembled coatings.

A facile strategy to fabricate covalently linked raspberry-like nanocomposites with pH and thermo tunable structures

The preparations of covalently linked raspberry-like composite particles often suffer from uncontrolled particle shape and surface morphology, tedious reactions to introduce surface reactive groups, inefficient inter-particle reactions, and rigorous requirements for the formation of hierarchical structure. In this study, we developed a facile strategy to fabricate a kind of size-controlled, positively charged, alkoxysilanes-functionalized nanoparticles (Tsi-PDMAEMA-PSt NPs) via a combination of the ability of RAFT polymerization to design macromolecular architectures and the process of polymer self-assembly to produce well-defined NPs. Tsi-PDMAEMA-PSt NPs can effectively deposit on the outer surface of negatively charged silica microspheres and then form stable silica@polymer particles by the reaction between alkoxysilanes and surface silanols. The surface morphology, particle size, ζ-potential, structure stability as well as pH and thermo-responsiveness of the prepared composite particles were investigated. The results indicated that the prepared silica@polymer particles possessed unique raspberry-like surface structures with high stability and controllability. Moreover, the surface morphology and dispersion state of silica@polymer particles in water can respond to the change of pH and temperature. Consequently, considering the high simplicity and controllability, the design herein provided a promising route to prepare the long-stable raspberry-like composite microspheres with unique surface morphologies and stimuli-responsive properties for a wide range of possible applications.

Determination and correlation of regioselectivity and dead dormant species from head addition in acrylate RAFT polymerization

Regioselectivity, a fundamental feature of radical addition reactions, has not received enough attention in reversible deactivation radical polymerization, especially for acrylates. However, in RAFT polymerization, the primary alkyl radicals, derived from “abnormal” head addition, will react with RAFT agents and produce non-active macro-RAFT agents, i.e. dead dormant species (DDS). Herein, a formula was proposed to correlate the content of DDS (α) with the incidence of head addition (ρ1) according to a detailed RAFT process involving head addition. And then, by combining a well-designed chain-extension reaction with gradient polymer elution chromatography (GPEC), the DDS in benzyl N-carbazolecarbodithioate-mediated RAFT polymerization of benzyl acrylate (BzA) were readily separated and quantitatively determined using the characteristic UV absorption of the N-carbazolecarbodithioate terminal. Based on these results, typically, the ρ1 of BzA at 60 °C was estimated to be 0.14%, demonstrating the utility of the method described to determine the incidence of head addition in radical polymerization. This study should be beneficial for a better understanding of RAFT processes, and meanwhile provides a powerful tool to determine regioselectivity of monomers in radical polymerization.

Initiation Mechanisms of Styrene with Methyl Ethyl Ketone Peroxide-Cobalt System

Unsaturated polyester resins (UPR) cured with styrene has been widely used in the various industrial fields. Methyl ethyl ketone peroxides (MEKP)-cobalt(II) system is the most common initiator for the curing of UPR. However, its initiation mechanisms currently remain elusive. In this study, the monomeric MEKP (MEKP-1) was firstly separated out from the commercial MEKP products, and then the radical initiation mechanisms of MEKP-1 catalyzed by cobalt isooctoate in the presence and absence of styrene were comparatively investigated by a combination of nitroxide radical trapping technique and HPLC-ESI/MS (high performance liquid chromatography-electrospray ionization/mass spectrometry). The amount of trapped products originated from methyl radical, ethyl radical and hydroxyl radical was significantly larger than that of trapped products from other radicals. These results indicated that methyl, ethyl and hydroxyl radicals were the dominant intermediate radicals formed in the initiation process of MEKP-cobalt(II) system, which would serve as the primary source to initiate styrene polymerization.