Papers by Author: Min Wang

Abstract: Electrospinning is investigated by many groups around the world for constructing fibrous tissue engineering scaffolds. Incorporating biomolecules such as growth factors in fibers is becoming common for enhancing the biological performance of electrospun scaffolds. However, biomolecules may lose bioactivity if they are exposed to organic solvent during electrospinning. In emulsion electrospinning, an aqueous biomolecule solution is emulsified and water-in-oil emulsions are then electrospun into core-shell structured fibers, with biomolecules being contained in the core of fibers, which helps to avoid biomolecule-solvent contact and also reduce the initial burst release. In this investigation, for a comparative study, poly (L-lactic acid) was made into solid and core-shell structured fibers via conventional electrospinning and emulsion electrospinning, respectively. The two electrospinning techniques and resultant fibers were compared in terms of processing parameters (polymer concentration, applied voltage, working distance, etc.) and fiber characteristics (morphology, diameter, structure, etc.). Solvent properties such as conductivity and volatility affected fiber morphology and diameter. The polymer concentration range usable for emulsion electrospinning was narrower than that for conventional electrospinning owing to changes in viscosity.

Abstract: Electrospinning is a popular technique for producing micro-or nanofibers for diverse applications including filtration, catalysis, sensors, cosmetics, wound dressing and tissue engineering. In some applications such as controlled drug/biomolecule delivery, core-shell structured nanofibers are desired. There are two major electrospinning processes for making core-shell structured fibers: emulsion electrospinning and coaxial electrospinning. In this study, the formation of core-shell structured fibers of poly (L-lactic acid) (PLLA) through emulsion electrospinning was investigated. To study the electrospinability of emulsions based on PLLA solutions, two solvents, pure chloroform and mixed solvent of chloroform and N,N-dimethylformamide, were used separately for making PLLA solutions. In the study of the formation of controlled release systems for biomolecules, bovine serum albumin, a model protein, was dissolved in de-ionized water to make the water phase in emulsions. In emulsion electrospinning, parameters such as applied voltage, working distance and feeding rate, were systematically investigated. The morphology, diameter and core-shell structure of emulsion electrospun fibers was studied using electron microscopies.

Abstract: Over the past decade, intensive research has been conducted on electrospinning of fibrous tissue engineering scaffolds and their applications in body tissue regeneration. For providing multifunctions and/or enhancing the biological performance, drugs or biomolecules can be incorporated in electrospun fibers using normally one of these techniques: (1) direct dissolution, (3) emulsion electrospinning, and (3) coaxial electrospinning. In this investigation, for constructing nanofibrous delivery vehicles, conventional electrospinning using polymer solutions with directly dissolved drugs or biomolecules and emulsion electrospinning were studied and compared. Bovine serum albumin (BSA) was used as a model protein and the drug was rifamycin, a hydrophobic antibiotic. A poly (lactic-co-glycolic acid) containing the protein or drug was electrospun into fibers. In these two routes of fabricating drug-or biomolecule-loaded nanofibers, different polymer concentrations and emulsion formulations were investigated. Various aspects of the fibrous delivery vehicles were investigated using several techniques and the in vitro release behaviour was studied.

Abstract: Electrospinning is a popular technique for constructing nanofibrous tissue engineering scaffolds. Electrospinning is also amenable to the incorporation of drugs or biomolecules in fibers, which can provide local and sustained delivery of biological signals, such as growth factors, for the seeded cells. Drugs can normally be dissolved in polymer solutions for electrospinning, forming nanofibrous drug delivery systems. However, simply blending biomolecules in polymer solutions can result in denaturation of biomolecules and large initial burst release. Therefore, emulsion electrospinning, which can provide protection for biomolecules during electrospinning, is of great interest. In this investigation, biomolecule-containing scaffolds were emulsion electrospun using bovine serum albumin (BSA) as the model protein. Two polymers, poly (lactic-co-glycolic acid) and poly (D,L-lactic acid), were used due to their different degradation characteristics. Nanofibers with core-shell structures were electrospun from water-in-oil emulsions formulated by polymer solution, BSA-containing deionized water and a surfactant. By changing the polymer concentration and water phase volume, the fiber diameter and core-shell structure were varied. With different polymers and different fiber structures, the in vitro BSA release behaviours from fibrous scaffolds were different.

Abstract: A new type of in-situ composite nano-multilayer plate with ultra-high strength (b 2112 MPa), Q235 steel plate with nano-layered structure of lath martensite produced by severe cold-rolling, was developed. After cold-rolling, subsequent annealing has great effect on the deformed lath morphology and grain refinement. Microstructure recrystallizing course have taken place after long time annealing at 350 °C. The recrystallization activation energy is 151 kJmol-1. Microstructure characteristics along rolling direction arrangement was decreased after annealing at 400 °C. In addition to the ultrafine ferrite grains, nano-carbides precipitated uniformly in the specimen annealed at 500 °C. Annealing at and above 600 °C resulted in coarse ferrite grains with spheroidized coarse carbides, causing grain growth. The average crystal size is about 4.7 m after annealing for 60 min at 600 °C.

Abstract: To improve the biocompatibility and bioactivity of NiTi shape memory alloy (SMA), apatite/collagen composite coatings were fabricated on the surface of NiTi SMA at room temperature using the electrochemical deposition technique. Spherical apatite particles and fibrous collagen that formed the composite coating were visible under scanning electron microscope (SEM). The Ca/P ratio of the apatite component in the coating, as determined by energy dispersive X-ray spectroscopy (EDX), was about 1.38 which is slightly higher than that of octocalcium phosphate (OCP). X-ray diffraction result showed that the apatite was amorphous, which was due to the low temperature (i.e., room temperature) deposition process. The structure of the composite coatings was further characterized using Fourier transform infrared reflection spectroscopy (FTIR). It was also found that, compared to bare NiTi SMA samples, the wettability of as-deposited samples was increased because of the formation of the composite coating.

Abstract: Metallic biomaterials such as stainless steel and Co-based alloys are corrosion resistant and possess excellent mechanical properties and hence can be used in load-bearing implants for human tissue repair. However, these materials are bioinert and some of them can cause concerns over their long-term implantation as they release cytotoxic metal ions to surrounding body tissues. Forming a bioactive coating on implantable metals combats these problems and makes these materials very attractive for medical applications. This paper gives an overview of our research work over the past decade on using a number of surface modification techniques (plasma spraying, spraying-and-sintering, ion beam assisted deposition, biomimetic deposition, etc.) to improve the osteoconductivity of metallic biomaterials (Ti, Ti-6Al-4V and NiTi SMA).

Abstract: The aim of this study was to investigate the feasibility of utilizing selective laser sintering (SLS) to build 3D porous tissue engineering scaffolds from small quantities of poly(L-lactide) (PLLA). PLLA microspheres with suitable particle sizes for the SLS process were produced by the oil-in-water emulsion solvent evaporation technique. A miniature build platform was designed, fabricated and incorporated in an existing Sinterstation® 2000 system to enable small quantities of polymer powder to be used for the production of 3D porous scaffolds. Trial runs were first performed using the DuraForm™ polyamide powder and interfacing problems between the miniature build platform and the existing machine were solved. Then 3D porous scaffolds were successfully built from the PLLA microspheres using the modified SLS machine. This study paved the way for further comprehensive studies on selective laser sintering of tissue engineering scaffolds using expensive biopolymers and their composites.

Abstract: Electrospinning of poly(L-lactic acid) (PLLA) and gelatin separately to form nonwoven PLLA or gelatin nanofibrous membranes was investigated. Factors that could affect the fiber morphology and fiber diameter were studies for PLLA and gelatin, respectively. The polymer solution concentration was found to play a dominant role in the formation of defected or nondefected ultrafine fibers. Using a specially designed experimental setup with separate syringe pumps for polymer solutions and separate power supplies for high voltages for electrospinning, PLLA-gelatin bicomponent fibrous membranes were formed with PLLA fibers interweaving with gelatin fibers. Multicomponent fibrous scaffolds can be very useful for tissue engineering and/or controlled release applications.

Abstract: To improve the biocompatibility and bioactivity of titanium and titanium alloys, a titanium oxide layer was synthesized on Ti, Ti-6Al-4V and NiTi shape memory alloy (SMA) using a H2O2-oxidation and hot water aging technique. The surface of these metals before and after the oxidation treatment was characterized using scanning electron microscopy and energy dispersive X-ray spectroscopy. Because of the synthetic titanium oxide surface layer, the Al and V contents on the surface of as-oxidized Ti-6Al-4V decreased significantly. Similarly, the Ni content on the surface of as-oxidized NiTi SMA was also significantly reduced. Potentiodynamic polarization curves indicated that the synthetic titania layer was more chemically stable than the spontaneous titania film on the metals. Among the three metals, the oxide layer on Ti was the most stable chemically. The in vitro bioactivity of as-oxidized metals was assessed through incubation in simulated body fluid (SBF). Compared to as-oxidized Ti-6Al-4V and NiTi SMA, as-oxidized Ti was the most bioactive.