We present the design of a novel pH-responsive drug release system that is achieved by solventless encapsulation of drugs within a microporous membrane using a thin capping layer of biodegradable poly­(methacrylic anhydride) (PMAH) coating. The coating was synthesized via a mild vapor polymerization process, namely, initiated chemical vapor deposition, which allowed perfect retention of the anhydride groups during deposition. The synthesized polyanhydride underwent degradation upon exposure to aqueous buffers, resulting in soluble poly­(methacrylic acid). The degradation behavior of PMAH is highly pH-dependent, and the degradation rate under pH 10 is 15 times faster than that under pH 1. The release profile of a model drug rifampicin clearly exhibited two stages: the initial stage when the coatings were being degraded but the drugs were well stored and the second stage when drugs were gradually exposed to the medium and released. The drug release also showed strong pH responsiveness where the duration of the initial stage under pH 1 was more than 7 and 3 times longer than that under pH 10 and 7.4, respectively, and the release rates at pH 7.4 and 10 were significantly faster than that at pH 1. The pH-dependent degradation of the encapsulant thus enabled good preservation of drugs under low-pH environment but high drug release efficiency under neutral and alkaline environment, suggesting potential applications in site-specific drug delivery systems.

No abstract

Polymer grafting has been a powerful tool in the surface modification of biomaterials. Traditional solventbased grafting, however, often requires laborious procedures taken under harsh conditions, which seriously hinders its practical applications. Here, we report a facile solvent-free graft-from method that is able to achieve a superior surface functionality as compared to most reported results from traditional solvent-based grafting. The grafting was proceeded by conformally coating a cross-linked polyvinylpyrrolidone (PVP) prime layer in the vacuum, immediately followed by in situ grafting of PVP homopolymer chains from the propagating sites on the coating surface. The resultant coating exhibited enriched surface pyrrolidone content compared to the single-layer cross-linked counterpart and a water contact angle of 22°, lower than most reported PVP-grafted surfaces. Medical catheters grafted with PVP achieved a more than 99.9% bacterial antifouling enhancement compared to the pristine catheter, and significantly improved biocompatibility during a 4 week in vivo test in mice. The achieved surface functionality is attributed to the synergistic effect from the functional groups distributed both on the grafted chains and on the cross-linked primer. The effectiveness and simplicity of the vapor grafting method thus suggest a promising surface modification route for biomaterials and beyond.

No abstract

The effects of spheroidizing annealing process on SWRH72B heavily cold drawn pearlite steel wires were studied and the mechanisms of low-temperature spheroidizing annealing were discussed. The results show that, with increasing drawing strain, the spheroidizing annealing temperature and time decreased and uniformity of the spheroidizing increased; the mechanism of low-temperature spheroidizing annealing was different from the traditional one of heavily cold drawn pearlite steel wires. When the true strains were between 2.85 and 5.1, the spheroidizing process of carbide could be divided into two stages: partial dissolution of lamellar carbide, and the precipitation and accumulation of compulsory dissolved cementite. When the true strains were larger than 5.1, the spheroidizing process of carbide was only characterized by precipitation and accumulation of compulsory dissolved cementite.