Guangzhi Yang

Nanosized sustained-release drug depots fabricated using modified tri-axial electrospinning

Nanoscale drug depots, comprising a drug reservoir surrounded by a carrier membrane, are much sought after in contemporary pharmaceutical research. Using cellulose acetate (CA) as a filament-forming polymeric matrix and ferulic acid (FA) as a model drug, nanoscale drug depots in the form of core-shell fibers were designed and fabricated using a modified tri-axial electrospinning process. This employed a solvent mixture as the outer working fluid, as a result of which a robust and continuous preparation process could be achieved. The fiber-based depots had a linear morphology, smooth surfaces, and an average diameter of 0.62±0.07μm. Electron microscopy data showed them to have clear core-shell structures, with the FA encapsulated inside a CA shell. X-ray diffraction and IR spectroscopy results verified that FA was present in the crystalline physical form. In vitro dissolution tests revealed that the fibers were able to provide close to zero-order release over 36h, with no initial burst release and minimal tailing-off. The release properties of the depot systems were much improved over monolithic CA/FA fibers, which exhibited a significant burst release and also considerable tailing-off at the end of the release experiment. Here we thus demonstrate the concept of using modified tri-axial electrospinning to design and develop new types of heterogeneous nanoscale biomaterials. STATEMENT OF SIGNIFICANCE Nanoscale drug depots with a drug reservoir surrounded by a carrier are highly attractive in biomedicine. A cellulose acetate based drug depot was investigated in detail, starting with the design of the nanostructure, and moving through its fabrication using a modified tri-axial electrospinning process and a series of characterizations. The core-shell fiber-based drug depots can provide a more sustained release profile with no initial burst effect and less tailing-off than equivalent monolithic drug-loaded fibers. The drug release mechanisms are also distinct in the two systems. This proof-of-concept work can be further expanded to conceive a series of new structural biomaterials with improved or new functional performance.

Preparation of nanoporous carbons with hierarchical pore structure for CO2 capture

Abstract Nanoporous carbons with a hierarchical pore structure were prepared by a combination of hard-templating of a thermosetting phenolic resin containing silica nanoparticles, pyrolysis and KOH activation. The influence of the amount of KOH on the pore structure of the templated and activated carbons was investigated by N2 adsorption and the effect of pore structure on the CO2 adsorption capacity was investigated by thermogravimetric analysis. Results indicated that KOH activation promoted the formation of micropores and small mesopores for the templated carbon. The utilization ratio of mesopores for the capture of CO2 is high compared with that of micropores. The porous carbon prepared under a mass ratio of KOH to templated carbon of 2:1 has both developed mesopores and micropores, and has a largest adsorption capacity for CO2 among all samples investigated.

Facile self-templating preparation of polyacrylonitrile-derived hierarchical porous carbon nanospheres for high-performance supercapacitors

A green, facile and efficient strategy was proposed to successfully synthesize polyacrylonitrile-derived hierarchical porous carbon nanospheres (HPCNs) for high-performance supercapacitors by surfactant-free emulsion polymerization followed with one-step KOH activation. The as-obtained HPCNs show favorable features for electrochemical energy storage such as a high specific surface area of up to 3130 m2 g−1, high volume of hierarchical pores up to 1.87 cm3 g−1, hierarchical porosity consisting of micro, meso, and macropores, turbostratic carbon structure, controlled and tunable pore size and stable thermal and chemical properties. The symmetric supercapacitor exhibits a reversible specific capacitance of 240 F g−1 at a current density of 1 A g−1 and displays a high energy density of 77 W h kg−1 at a power density of 875 W kg−1. A high specific capacitance retention of 96% could be maintained even after 3000 cycles. Moreover, we used different electrolytes to study the capacitive behavior with controlled pore size. The facile, efficient and template-free synthesis strategy for novel HPCNs from polymer sources could find use in supercapacitors, lithium ion batteries and fuel cells.

The comparison of macroporous ceramics fabricated through the protein direct foaming and sponge replica methods

The macroporous ceramic samples fabricated using the sponge replica and protein direct foaming methods were compared in terms of porosity, density, compressive strength and microstructure. The egg white protein was applied in both fabrication methods as the binder or foaming agent. The samples fabricated using the protein direct foaming method were stronger and more uniform pore structures in the similar porosity. This result was supported through the Weibull modulus analysis and the scanning electron microscope microstructure observation.

Influence of Working Temperature on The Formation of Electrospun Polymer Nanofibers

Temperature is an important parameter during electrospinning, and virtually, all solution electrospinning processes are conducted at ambient temperature. Nanofiber diameters presumably decrease with the elevation of working fluid temperature. The present study investigated the influence of temperature variations on the formation of polymeric nanofibers during single-fluid electrospinning. The surface tension and viscosity of the fluid decreased with increasing working temperature, which led to the formation of high-quality nanofibers. However, the increase in temperature accelerated the evaporation of the solvent and thus terminated the drawing processes prematurely. A balance can be found between the positive and negative influences of temperature elevation. With polyacrylonitrile (PAN, with N,N-dimethylacetamide as the solvent) and polyvinylpyrrolidone (PVP, with ethanol as the solvent) as the polymeric models, relationships between the working temperature (T, K) and nanofiber diameter (D, nm) were established, with D = 12598.6 − 72.9T + 0.11T2 (R = 0.9988) for PAN fibers and D = 107003.4 − 682.4T + 1.1T2 (R = 0.9997) for PVP nanofibers. Given the fact that numerous polymers are sensitive to temperature and numerous functional ingredients exhibit temperature-dependent solubility, the present work serves as a valuable reference for creating novel functional nanoproducts by using the elevated temperature electrospinning process.

Preparation of ordered mesoporous carbons with an intergrown p6mm and cubic Fd3m pore structure using a copolymer as a template

Ordered mesoporous carbons (OMCs) with an intergrown two-dimensional p6mm and three-dimensional Fd3m pore structure have been prepared by the carbonization of reverse copolymer-phenolic resin composites, which were themselves formed by a soft-template method by simply adjusting the ratios of ethanol and hexane. The microstructure of the OMCs was analyzed by small-angle X-ray scattering, nitrogen adsorption isotherms, and transmission electron microscopy. The results showed the structure of the OMCs obtained have the mesophase transition from p6mm to the intergrowth of p6mm/Fd3m and finally to Fd3m as the ratio of ethanol to hexane is changed.

Direct fabrication of ordered mesoporous carbons with super-micropore/small mesopore using mixed triblock copolymers.

Ordered mesoporous carbons (OMCs) have been prepared by the strategy of evaporation-induced organic-organic self-assembly method by employing a mixture of amphiphilic triblock copolymers poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) and reverse PPO-PEO-PPO as templates, with soluble in ethanol, low-molecular-weight phenolic resin as precursor, followed by carbonization. It has been found that the as prepared OMCs with porosity that combines super-micropore and small mesopore size distributed from 0.8 to 4 nm, which bridges the pore size from 2 to 3 nm and also for the diversification of the soft-templating synthesis of OMCs. Furthermore, the results showed that the OMCs obtained have mesophase transition from cylindrical p6 mm to centered rectangular c2 mm structure by simply tuning the ratio of PPO-PEO-PPO/PEO-PPO-PEO.