Biomedical subjects

Dufei Fang

Publications and source records attributed to Dufei Fang.

11 recordsLinked to original sources

PubMed2006

Designing polymer matrix for microchip-based double-stranded DNA capillary electrophoresis.

Polyacrylamide (PAM) was used as a model polymer to build up an empirical model that relates polymer molecular weight, polymer concentration and solution viscosity. The desired random copolymers of acrylamide (AM) and N,N-dimethylacrylamide (DMA) used as DNA separation media for different specifications were synthesized under the guidance of the empirical model. The separation performances of rationally designed copolymers were tested in a 1.2 cm long separation channel, simulating microchip-based capillary electrophoresis. pBR322/HaeIII digest was successfully separated with good separation resolution and fast speed. Validation of the sieving ability of our polymers was performed in the Agilent 2,100 Bioanalyzer. The results of the 10 bp (base pair) DNA ladder separation demonstrate the potential of our approach for the sieving matrix in microchip-based electrophoresis.

Acrylamides↗

PubMed2005

High flux filtration medium based on nanofibrous substrate with hydrophilic nanocomposite coating.

A novel high flux filtration medium, consisting of a three-tier composite structure, i.e., a nonporous hydrophilic nanocomposite coating top layer, an electrospun nanofibrous substrate midlayer, and a conventional nonwoven microfibrous support, was demonstrated for oil/water emulsion separations for the first time. The nanofibrous substrate was prepared by electrospinning of poly(vinyl alcohol) (PVA) followed by chemical cross-linking with glutaraldehyde (GA) in acetone. The resulting cross-linked PVA substrates showed excellent water resistance and good mechanical properties. The top coating was based on a nanocomposite layer containing hydrophilic polyether-b-polyamide copolymer or a cross-linked PVA hydrogel incorporated with surface-oxidized multiwalled carbon nanotubes (MWNTs). Scanning electron microscopy (SEM) examinations indicated that the nanocomposite layer was nonporous within the instrumental resolution and MWNTs were well dispersed in the polymer matrix. Oil/ water emulsion tests showed that this unique type of filtration media exhibited a high flux rate (up to 330 L/m2-h at the feed pressure of 100 psi) and an excellent total organic solute rejection rate (99.8%) without appreciable fouling. The increase in the concentration of surface-oxidized MWNT in the coating layer generally improves the flux rate, which can be attributed to the generation of more effective hydrophilic nanochannels for water passage in the composite membranes.

Emulsions↗

PubMed2005

Electrospun fine-textured scaffolds for heart tissue constructs.

The structural and functional effects of fine-textured matrices with sub-micron features on the growth of cardiac myocytes were examined. Electrospinning was used to fabricate biodegradable non-woven poly(lactide)- and poly(glycolide)-based (PLGA) scaffolds for cardiac tissue engineering applications. Post-processing was applied to achieve macro-scale fiber orientation (anisotropy). In vitro studies confirmed a dose-response effect of the poly(glycolide) concentration on the degradation rate and the pH value changes. Different formulations were examined to assess scaffold effects on cell attachment, structure and function. Primary cardiomyocytes (CMs) were cultured on the electrospun scaffolds to form tissue-like constructs. Scanning electron microscopy (SEM) revealed that the fine fiber architecture of the non-woven matrix allowed the cardiomyocytes to make extensive use of provided external cues for isotropic or anisotropic growth, and to some extent to crawl inside and pull on fibers. Structural analysis by confocal microscopy indicated that cardiomyocytes had a preference for relatively hydrophobic surfaces. CMs on electrospun poly(L-lactide) (PLLA) scaffolds developed mature contractile machinery (sarcomeres). Functionality (excitability) of the engineered constructs was confirmed by optical imaging of electrical activity using voltage-sensitive dyes. We conclude that engineered cardiac tissue structure and function can be modulated by the chemistry and geometry of the provided nano- and micro-textured surfaces. Electrospinning is a versatile manufacturing technique for design of biomaterials with potentially reorganizable architecture for cell and tissue growth.

Absorbable Implants↗

PubMed2004

Incorporation and controlled release of a hydrophilic antibiotic using poly(lactide-co-glycolide)-based electrospun nanofibrous scaffolds.

The successful incorporation and sustained release of a hydrophilic antibiotic drug (Mefoxin, cefoxitin sodium) from electrospun poly(lactide-co-glycolide) (PLGA)-based nanofibrous scaffolds without the loss of structure and bioactivity was demonstrated. The morphology and density of the electrospun scaffold was found to be dependent on the drug concentration, which could be attributed to the effect of ionic salt on the electrospinning process. The drug release behavior from the electrospun scaffolds and its antimicrobial effects on Staphylococcus aureus cultures were also investigated. In all tested scaffolds, the maximum dosage of drug was released after 1 h of incubation in water at 37 degrees C. The usage of the amphiphilic block copolymer (PEG-b-PLA) reduced the cumulative amount of the released drug at earlier time points and prolonged the drug release rate at longer times (up to a 1-week period). The antibiotic drug released from these electrospun scaffolds was effective in their ability to inhibit Staphylococcus aureus growth (>90%). The combination of mechanical barriers based on non-woven nanofibrous biodegradable scaffolds and their capability for local delivery of antibiotics increases their desired utility in biomedical applications, particularly in the prevention of post-surgical adhesions and infections.

Anti-Bacterial Agents↗

PubMed2004

Prevention of postsurgery-induced abdominal adhesions by electrospun bioabsorbable nanofibrous poly(lactide-co-glycolide)-based membranes.

OBJECTIVES: The objective of this study was to evaluate the efficacy of nonwoven bioabsorbable nanofibrous membranes of poly(lactideco-glycolide) for prevention of postsurgery-induced abdominal adhesions. SUMMARY BACKGROUND DATA: Recent reports indicated that current materials used for adhesion prevention have only limited success. Studies on other bioabsorbable materials using a new fabrication technique demonstrated the promising potential of generating an improved and inexpensive product that is suitable for a variety of surgical applications. METHODS: All rats underwent a midline celiotomy. The cecum was identified and scored using an abrasive pad until serosal bleeding was noted on the anterior surface. A 1 x 1 cm of abdominal wall muscle was excised directly over the cecal wound. The celiotomy was then closed in 2 layers immediately (control) after a barrier was laid in between the cecum and the abdominal wall. All rats underwent a second celiotomy after 28 days to evaluate the extent of abdominal adhesions qualitatively and quantitatively. RESULTS: Cecal adhesions were reduced from 78% in the control group to 50% in the group using biodegradable poly(lactide-co-glycolide) (PLGA) nonwoven nanofibrous membranes (n = 10, P = 0.2) and to 22% in the group using membranes containing PLGA and poly(ethylene glycol)/poly(D,L-lactide) (PEG-PLA) blends (n = 9, P = 0.03). Electrospinning method also enabled us to load an antibiotic drug Cefoxitin sodium (Mefoxin; Merck Inc., West Point, PA) with high efficacy. The electrospun PLGA/PEG-PLA membranes impregnated with 5 wt% cefoxitin sodium, which amounts to approximately 10% of the systemic daily dose typically taken after surgery in humans, completely prevented cecal adhesions (0%) in rats. CONCLUSIONS: Electrospun nonwoven bioabsorbable nanofibrous membranes of poly(lactide-co-glycolide) were effective to reduce adhesions at the site of injury using an objective rat model. The membrane acted as a physical barrier but with drug-delivery capability. The combined advantages of composition adjustment, drug-loading capability, and easy placement handling (relatively hydrophobic) make these membranes potentially successful candidates for further clinical evaluations.

Abdomen↗

PubMed2004

Preparation and characterization of ibuprofen-loaded poly(lactide-co-glycolide)/poly(ethylene glycol)-g-chitosan electrospun membranes.

Ibuprofen-loaded composite membranes composed of poly(lactide-co-glycolide) (PLGA) and poly(ethylene glycol)-g-chitosan (PEG-g-CHN) were prepared by electrospinning. The electrospun membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), mechanical evaluation and contact angle measurements. Shrinkage behavior of the membrane in buffer at 37 degrees C was also evaluated. It was found that PLGA glass transition temperature (Tg) decreased with increasing PEG-g-CHN content in the composite membranes, which results in a decrease in tensile stress at break but an increase in tensile strain of the membranes. The degree of shrinkage of these composite membranes decreased from 76 to only 3% when the PEG-g-CHN content in the membranes increased from 10 to 30%. The presence of PEG-g-CHN significantly moderated the burst release rate of ibuprofen from the electrospun PLGA membranes. Moreover, ibuprofen could be conjugated to the side chains of PEG-g-CHN to prolong its release for more than two weeks. The sustained release capacity of the PLGA/PEG-g-CHN composite membranes, together with their compliant and stable mechanical properties, renders them ideal matrices for atrial fibrillation.

Biochemistry↗

PubMed2003

Control of degradation rate and hydrophilicity in electrospun non-woven poly(D,L-lactide) nanofiber scaffolds for biomedical applications.

Typical properties of poly(D,L-lactide) (PLA)-based scaffolds (films and foams), such as long degradation time, mechanical stiffness and hydrophobicity, are sometimes not suitable for biomedical applications. These properties can be substantially altered by electrospinning of PLA blends with miscible poly(lactide-co-glycolide) (PLGA) random copolymers, poly(lactide-b-ethylene glycol-b-lactide) (PLA-b-PEG-b-PLA) triblock copolymers, and a lactide (used as a hydrolytic catalyst). Electrospun scaffolds based on the multi-component PLA blends, comprised of randomly interconnected webs of sub-micron sized fibers, have a bulk density of 0.3-0.4 g/cm3. In this study, the concentration effects of PLA-b-PEG-b-PLA triblock copolymer and lactide on the cell proliferation and the hydrophilicity of electrospun scaffolds were investigated. Based on in vitro degradation study, we found that the electrospun scaffold having PLA (40 wt%), PLGA (LA/GA=50/50, 25 wt%), PLA-b-PEG-b-PLA (20 wt%), and lactide (15 wt%) underwent a rapid weight loss of approximately 65% in 7 weeks. The hydrophobicity of this membrane, as determined by contact angle measurements in a cell buffer solution, decreased by approximately 50% from 105 degrees (of an electrospun PLA scaffold) to 50 degrees. The selection of suitable chemical compositions in conjunction with the non-invasive electrospinning process is useful in the production of a new kind of biodegradable scaffolds suitable for different biomedical applications such as cell storage and delivery as well as prevention of post-surgical adhesion because of their porosity, mechanical flexibility and tunable biodegradability.

3T3 Cells↗

PubMed2002

Separation of double-stranded DNA fragments by capillary electrophoresis using polyvinylpyrrolidone and poly(N,N-dimethylacrylamide) transient interpenetrating network.

A noncross-linked interpenetrating polymer network (IPN), consisting of poly(N,N-dimethylacrylamide) (PDMA) and polyvinylpyrrolidone (PVP, weight-average molecular weight M(w) = 1 x 10(6) g/mol) was synthesized by polymerizing N,N-dimethylacrylamide (DMA) monomers directly in PVP buffer solution and tested as a separation medium for double-stranded (ds)DNA analysis without further purification. Due to the incompatibility of PVP and PDMA, a simple solution mixture could incur a microphase separation and showed poor performance on dsDNA separation. However, a dramatic improvement was achieved by the formation of an IPN. We attributed the high sieving ability of IPN as due to an increase in the number of entanglements by the more extended polymer chains. Apparent viscosity studies showed that the IPN had a much higher viscosity than the simple mixture containing the same amount of PDMA and PVP. In 1 x Tris-borate-EDTA (TBE) buffer, the concentration ratio of PDMA and PVP had a great effect on the DNA separation. At optimal conditions, the 22 fragments in pBR322/HaeIII DNA were successfully separated within 15 min, with a resolution of better than 1.0 for 123/124 bp.

Acrylamides↗

PubMedDate not supplied

Structure and morphology changes during in vitro degradation of electrospun poly(glycolide-co-lactide) nanofiber membrane.

Electrospun poly(glycolide-co-lactide) (PLA10GA90, LA/GA ratio 10/90) biodegradable nanofiber membranes possessed very high surface area to volume ratios and were completely noncrystalline with a relatively lowered glass transition temperature. These characteristics led to very different structure, morphology, and property changes during in vitro degradation, which were examined systematically. A shrinkage study showed that the electrospun crystallizable but amorphous PLA10GA90 membranes exhibited a very small shrinkage percentage when compared with the electrospun membranes of noncrystallizable poly(lactide-co-glycolide) (PLA75GA25, LA/GA 75/25) and poly(d,l-lactide). Although the weight loss of electrospun PLA10GA90 membranes exhibited a similar degradation behavior as cast thin films, detailed studies showed that the structure and morphology changes in electrospun membranes followed different pathways during the hydrolytic degradation. After 1 day of degradation in buffer solution at 37 degrees C, electrospun PLA10GA90 membranes exhibited a sudden increase in crystallinity and glass transition temperature, due to the fast thermally induced crystallization process. The continuous increase in crystallinity and apparent crystal size, as well as the decrease in long period and lamellae thickness, indicated that the thermally induced crystallization was followed by a chain cleavage induced crystallization process. The mass loss rate was accelerated after 6 days of degradation. The increase in glass transition temperature during this period further confirmed that the degradation of PLA10GA90 nanofibers was initiated from the amorphous region within the lamellar superstructures. A mechanism of structure and morphology changes during in vitro degradation of electrospun PLA10GA90 nanofibers is proposed.

Calorimetry, Differential Scanning↗

PubMedDate not supplied

Optimization and characterization of dextran membranes prepared by electrospinning.

Dextran is soluble in both water and organic solvents, so it could be a versatile biomacromolecule for preparing nanofibrous electrospun membranes by blending with either water-soluble bioactive agents or hydrophobic biodegradable polymers for biomedical applications. We have formulated electrospun dextran membranes, and the effects of various processing parameters on the membrane properties were investigated. It was found that uniform nanofibrous dextran membranes could be formed by using water, DMSO/water, and DMSO/DMF mixtures as solvents through adjusting the processing conditions (solution concentration, voltage, and the distance between the electrode and the collecting plate). When water was used as a solvent, up to 10% (w/w) of bovine serum albumin (BSA) or lysozyme could be directly incorporated into the dextran electrospun membrane without compromising its morphology. No significant effect of the electrospinning process on lysozyme activity was observed. The composite electrospun membranes consisting of poly(D,L-lactide-co-glycolide) (PLGA) and dextran were obtained using DMSO/DMF (50/50, volume ratio) mixture as solvents. For cross-linking the electrospun membrane, dextran was modified by substitution of methacrylate groups at the hydroxyl sites. It was found that the electrospun membranes prepared from methacrylated dextran can be cured by UV irradiation in the presence of 1% of 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoinitiator.

Animals↗

PubMedDate not supplied

Electro-spinning and electro-blowing of hyaluronic acid.

In this study, hyaluronic acid (HA) was electro-spun and electro-blown to prepare nonwoven nanofibrous membranes. Critical parameters for processing and corresponding effects on the membrane morphology were investigated using the methods of rheology and scanning electron microscopy (SEM). During electro-spinning, the optimal HA concentration window for nanofibrous formation was determined within a narrow range of 1.3-1.5 w/v %, corresponding to a solution viscosity range of 3-30 Pa s at a shear rate of 1 s(-1). SEM results indicated that, with increases in (1) the total concentration by blending of low molecular weight HA, (2) the evaporation rate by the addition of ethanol, and/or (3) the feeding rate of solution, the electro-spinning performance for creating nanofibers was improved. However, the improvement was not sufficient to achieve a consistent production of high quality nonwoven nanofiber membranes. This problem was overcome by a new electro-blowing process using the combination of air flow and electro-spinning. Although air blowing at room temperature around the spinneret orifice did not exhibit a remarkable enhancement of nanofiber formation of HA, the performance was significantly improved with an increase in the air blowing rate. SEM results showed that the temperature of air-blowing was the most effective parameter in ensuring HA nanofiber formation. As the temperature of the blown air increased from 25 to 57 degrees C, the nanofiber formation became consistent and uniform. A high quality HA nonwoven membrane of nanofibers was successfully produced by blowing air at 57 degrees C with a 70 ft(3)/hr flow rate.

Electricity↗