Neutron Total Scattering Investigation of the Dissolution Mechanism of Trehalose in Alkali/Urea Aqueous Solution.

The atomic picture of cellulose dissolution in alkali/urea aqueous solution is still not clear. To reveal it, we use trehalose as the model molecule and total scattering as the main tool. Three kinds of alkali solution, i.e., LiOH, NaOH and KOH are compared. The most probable all-atom structures of the solution are thus obtained. The hydration shell of trehalose has a layered structure. The smaller alkali ions can penetrate into the glucose rings around oxygen atoms to form the first hydration layer. The larger urea molecules interact with hydroxide groups to form complexations. Then, the electronegative complexation can form the second hydration layer around alkali ions via electrostatic interaction. Therefore, the solubility of alkali aqueous solution for cellulose decreases with the alkali cation radius, i.e., LiOH > NaOH > KOH. Our findings are helpful for designing better green solvents for cellulose.

A Biodegradable Trilayered Barrier Membrane Composed of Sponge and Electrospun Layers: Hemostasis and Antiadhesion.

Placing a physical barrier between the injured site and the adjacent tissues is a very common and highly effective approach to prevent abdominal adhesions in these days. A biodegradable trilayered barrier was fabricated to prevent formation of abdominal adhesions, in which a poly(lactide-co-glycolide)/poly(lactide)-b-poly(ethylene glycol) (PLGA/PLA-b-PEG) electrospun layer was sandwiched between layers of carboxymethyl chitosan (CMCS) sponge. The hydrophilic CMCS sponge layers with glycerin (GL) could adhere to the surface of wound easily, and present great hemostatic capability. The mechanism of the formation of adhesion related to blood clots acting with fibroblast cells was evaluated in detail. The blood clot acted as a "medium" inducing the fibroblast cells growth and proliferation, but had no special attraction on epithelial cells. CMCS sponge layer took away the blood clots during the swelling and dissolution stages. The electrospun layer promoted the growth of epithelial cells, but exhibited inhibition on the adhesion and spread of fibroblast cells, which ensured excellent effect of adhesion prevention. Evaluated by a rat model of sidewall defect-bowel abrasion, significant reductions of postoperative adhesion in its level and occurrence were observed in animals treated by the trilayered barrier.

Crystallization-driven surface segregation and surface structures in poly(L-lactide)-block-poly(ethylene glycol) copolymer thick films.

In this work, we used poly(L-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) copolymer thick films to investigate the effect of crystallization on surface segregation, surface crystal orientation, and morphology by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), reflection optical microscopy (ROM), and two-dimensional grazing incident wide-angle X-ray scattering (2D GIWAXS) methods. ATR-FTIR results indicated that the surface fraction of PLLA block increased from 0.48 to 0.79 when T(c,PLLA) increased from 70 to 110 °C. Polarized ATR-FTIR and 2D GIWAXS results indicated that PLLA crystal lamellae preferentially oriented parallel to the film surface with increasing T(c,PLLA). The surface crystallinity of PLLA was almost independent of T(c,PLLA), while the surface crystallinity of PEG decreased with increasing T(c,PLLA). On the basis of surface crystal orientation and crystallization kinetics, we suggested that the excess of PLLA component at the surface was mainly dominated by a coupling effect of crystallization behavior and surface segregation.

Perspectives on the Novel Multifunctional Nerve Guidance Conduits: From Specific Regenerative Procedures to Motor Function Rebuilding.

Peripheral nerve injury potentially destroys the quality of life by inducing functional movement disorders and sensory capacity loss, which results in severe disability and substantial psychological, social, and financial burdens. Autologous nerve grafting has been commonly used as treatment in the clinic; however, its rare donor availability limits its application. A series of artificial nerve guidance conduits (NGCs) with advanced architectures are also proposed to promote injured peripheral nerve regeneration, which is a complicated process from axon sprouting to targeted muscle reinnervation. Therefore, exploring the interactions between sophisticated NGC complexes and versatile cells during each process including axon sprouting, Schwann cell dedifferentiation, nerve myelination, and muscle reinnervation is necessary. This review highlights the contribution of functional NGCs and the influence of microscale biomaterial architecture on biological processes of nerve repair. Progressive NGCs with chemical molecule induction, heterogenous topographical morphology, electroactive, anisotropic assembly microstructure, and self-powered electroactive and magnetic-sensitive NGCs are also collected, and they are expected to be pioneering features in future multifunctional and effective NGCs.

Multiple targeted drugs carrying biodegradable membrane barrier: anti-adhesion, hemostasis, and anti-infection.

A multiple targeted drug carrying bilayer membrane for preventing an abdominal adhesion is prepared by electrospinning. Two bioactive drugs were successfully incorporated into this bilayer membrane and can be independently released from nanofibrous scaffolds without losing structural integrity and functionality of the anti-adhesion membrane. Besides, the drug release profile could be easily adjusted by optimizing the swelling behavior of the fibrous scaffold. The inner layer of the bilayered fibrous membranes loaded with carbazochrome sodium sulfonate (CA) showed an excellent vascular hemostatic efficacy and formed little clot during in vivo experiment. The outer layer loaded with tinidazole (TI) had outstanding antibacterial effect against the anaerobe. We believe this approach could serve as a model technique to guide the design of implants with drug delivery functions.

Concentric ring pattern formation in a competing crystallization and phase separation process.

Spherulitic patterns usually form in the single process of crystallization in polymer blends. But when phase separation intervenes under deep quench, the radial growth of the initial spherulitic patterns tends to invert into concentric alternating crystalline-/amorphous-rich ring structures. Within crystalline-rich regions, lateral lamellae orient in the tangential direction rather than in the usual radial direction. We demonstrate the determining factor for this first observed phenomenon is the concentration deviation enhanced phase separation dynamics at the growth interface of crystals.

Controlled drug release: On the evolution of physically entrapped drug inside the electrospun poly(lactic-co-glycolic acid) matrix.

The drug loading and releasing properties of poly(lactic-co-glycolic acid) (PLGA) were approached with the application of neutron techniques. The neutron reflection (NR) study on the response of PLGA material to vapor and to bulk water revealed that the hydration of PLGA origins from the molecular compatibility between water and PLGA. Hydration is reversible with regard to the change in humidity and temperature. Capecitabine as drug was embedded in the electrospun PLGA fibers. Small angle neutron scattering (SANS) was able to disclose the domain of entrapped drug inside the fibers and trace its evolution over time when the electrospun membrane was incubated in D2O buffer solution. The evolution of drug domains is discussed in terms of the concentration dependence, the temperature dependence, and the relevance between the drug diffusion inside the polymer matrix and the drug release out to the medium. It was observed that, at 20 °C the drug-related domains are relatively small (~ 100 Å) and relax extremely slow while at 37 °C the drug-related domains are relatively larger (~ 200 Å) and relax faster. These behaviors can be related to the glassy property of structural material. The transportation of drug through the polymer matrix relies on the global relaxation of PLGA chains. The variation of fiber diameter vs. incubation time was followed by ultra-small angle neutron scattering (USANS). The bi-phasic or tri-phasic release kinetics from a series of fibers with different drug loading (2%, 5%, 10%, 20%, 30%, 40%, 50%) were discussed based on the SANS and USANS discovery.

Origin of cononsolvency, based on the structure of tetrahydrofuran-water mixture.

The origin of poly(N-isopropylacrylamide) (PNIPAM) cononsolvency in tetrahydrofuran-water (THF-water) mixture was studied from the point of view of mixed solvent structure. The dynamic equilibrium of THF-water composition fluctuation in the mixed solvent system was found to be the main variable for this cononsolvency effect. Temperature and THF content dependences of composition fluctuation were studied by a combination of small angle neutron scattering (SANS), dynamic laser light scattering, and viscometry. A lower critical solution temperature (LCST) type phase diagram for THF-water mixture was established by SANS. The composition fluctuation in THF-water system reaches the maximum at about 20 mol % THF content at constant temperature and increases with temperature as getting closer to the phase boundary. This kind of composition fluctuation induces PNIPAM cononsolvency. When the THF content is lower than 4.5 mol %, the composition fluctuation influence of the THF-water structure is quite weak and most of water structure is not disturbed. Then, at low THF content, poly(N-isopropylacrylamide-co-ethylene glycol) (PNIPAM-co-PEG) microgel can still form hydrogen bonds with water and exist in the swollen state. The basic phase transition behavior of the microgel in THF-water is relatively similar to that in pure water, except for the shift of LCST to lower temperature. With THF content increasing to 20 mol %, the influence of composition fluctuation in the THF-water mixture becomes dominant. Solvent-solvent interaction is stronger than mixed solvent-polymer interaction. So PNIPAM does not dissolve in the mixed solvent, and the microgel is in the collapsed state. Further increase in THF content abates the contribution of composition fluctuation, and the structures of mixed solvents tend to be that in pure THF. PNIPAM becomes soluble again via Van der Waals interaction between THF and polymer.

Mechanism of a long-term controlled drug release system based on simple blended electrospun fibers.

BACKGROUND: Drug delivery systems based on electrospun fibers have been under development for many years. However, studies of controllable long-term drug release from electrospun membrane systems and the underlying release mechanisms have seldom been reported. METHODS: In this study, electrospun membrane drug delivery systems consisting of the antibiotic ciprofloxacin hydrochloride and FDA-approved polymers are fabricated. Different second-component polymers are introduced to change the properties of a poly(d,l-lactide-co-glycolide) (PLGA) matrix, thereby altering the drug release behavior. On the basis of observations of morphology, cumulative release profiles, and determinations of release duration, the drug release kinetics and critical characteristics influencing drug release behavior are discussed. RESULTS: It is found that the drug release profiles can be divided into three stages according to the rate of drug release. Stage I is controlled by fiber swelling and diffusion according to Fick's second law. Stage II is controlled by diffusion through a fused membrane structure, which results in very slow drug release. Stage III is controlled by polymer degradation and involves release of the remaining drug. CONCLUSIONS: The results of this study of release mechanisms should provide a basis for adjustments of drug release dosage and duration, thereby contributing to the development of drug delivery systems satisfying clinical requirements.

Controlled Antibiotics Release System through Simple Blended Electrospun Fibers for Sustained Antibacterial Effects.

Implantation of sustained antibacterial system after abdominal surgery could effectively prevent complicated intra-abdominal infection. In this study, a simple blended electrospun membrane made of poly(D,L-lactic-co-glycolide) (PLGA)/poly(dioxanone) (PDO)/Ciprofloxacin hydrochloride (CiH) could easily result in approximately linear drug release profile and sustained antibacterial activity against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The addition of PDO changed the stack structure of PLGA, which in turn influenced the fiber swelling and created drug diffusion channels. It could be a good candidate for reducing postoperative infection or be associated with other implant to resist biofilm formation.

Improving the ordering and photovoltaic properties by extending π-conjugated area of electron-donating units in polymers with D-A structure.

A systematic molecular design process from PBDTTT-S to PBDTDTTT-S-T, a high-performance semiconducting polymer for organic photovoltaics, has been achieved by enhancing structural order, self-assembly and carrier mobility. Solar cells made from PBDTDTTT-S-T blended with PC(70) BM show a power conversion efficiency (PCE) of 7.81%, which is 25% higher than that of the parent PBDTTT-S.

Water repellency on a fluorine-containing polyurethane surface: toward understanding the surface self-cleaning effect.

Surface geometrical microstructure and low surface free energy are the two most important factors for a self-cleaning surface. In this study, multiform geometrical microstructured surfaces were fabricated by casting and electrospinning polyurethanes with and without low surface energy segments. The effect of low surface energy on water repellency was evaluated. Low surface energy seems to make a more significant contribution to the static wetting behavior than do dynamic properties such as the improvement of sliding behavior. Sucking disk behavior was brought forward to explain the pinning state of a water droplet on hydrophobic surfaces with high water contact angles (>150 degrees ). A better understanding of the relationship between the static contact angle and the dynamic sliding property was provided.

Light-scattering study of the aggregation of syndiotactic poly(methyl methacrylate) in solution.

Syndiotactic poly(methyl methacrylate (s-PMMA) may undergo aggregation in n-butyl chloride (n-BuCl) at temperatures below the theta temperature. The aggregation behavior of the s-PMMA with weight-average molecular weight M(w) =6.06 x 10(5) g mol(-1) was studied by a combination of static and dynamic laser-light-scattering experiments. A solution of concentration 1.12 x 10(-4) g mL(-1) was quenched from 50 degrees C (above the theta temperature in n-BuCl, 35 degrees C to 12 degrees C, and the aggregation process was measured over 60 h. The time dependence of M(w) the root-mean-square z-average radius of gyration < R(g) >, and the average hydrodynamic radius were used to monitor the growth of the aggregates, with the result M(w) approximately < R(g) > d(f) (where d(f) = 1.98 +/- 0.02), which implies the formation of a fractal aggregate. The observed fractal dimension, d(f), is close to that expected for a reaction-limited cluster aggregation for which d(f) = 2.1. In addition, atomic force microscopy was used to image the aggregates.