Biomedical subjects

Fenghua Meng

Publications and source records attributed to Fenghua Meng.

4 recordsLinked to original sources

PubMed2007

Morphology of a highly asymmetric double crystallizable poly(epsilon-caprolactone-b-ethylene oxide) block copolymer.

The morphology of a highly asymmetric double crystallizable poly(epsilon-caprolactone-b-ethylene oxide) (PCL-b-PEO) block copolymer has been studied with in situ simultaneously small and wide-angle x-ray scattering as well as atomic force microscopy. The molecular masses Mn of the PCL and PEO blocks are 24,000 and 5800, respectively. X-ray scattering and rheological measurements indicate that no microphase separation occurs in the melt. Decreasing the temperature simultaneously triggers off a crystallization of PCL and microphase separation between the PCL and PEO blocks. Coupling and competition between microphase separation and crystallization results in a morphology of PEO spheres surrounded by PCL partially crystallized in lamella. Further decreasing temperature induces the crystallization of PEO spheres, which have a preferred orientation due to the confinements from hard PCL crystalline lamella and from soft amorphous PCL segments in different sides. The final morphology of this highly asymmetric block copolymer is similar to the granular morphology reported for syndiotactic polypropylene and other (co-) polymers. This implies a similar underlying mechanism of coupling and competition of various phase transitions, which is worth further exploration.

Biocompatible Materials↗

PubMed2005

Biodegradable polymersomes as a basis for artificial cells: encapsulation, release and targeting.

The encapsulation of biofunctional compounds, release properties and targetability of polymersomes of amphiphilic block-copolymers based on poly(ethylene glycol) (PEG) and biodegradable polyesters or polycarbonate are described. Carboxyfluorescein (CF), as a model for hydrophilic biofunctional compounds, could be readily incorporated in the polymersomes by adding the compound to the aqueous phase during polymersome preparation. The release of encapsulated material from the polymersomes can be adjusted by changing the copolymer composition, especially the molecular weight and type of hydrophobic block of the copolymer. The presence of plasma proteins other than albumin suppressed the release of CF. CF release in PBS both at room temperature and at 60 degrees C followed first order kinetics, confirming that the CF containing polymersome system is a membrane controlled reservoir system. These biodegradable polymersomes have the potential to be targeted to specific sites in the body as shown by the specific interaction of anti-human serum albumin immobilized polymersomes with a human serum albumin coated sensor surface.

Biodegradation, Environmental↗

PubMed2004

Polyethylene glycol-grafted polystyrene particles.

Densely pegylated particles that can serve as a model system for artificial cells were prepared by covalently grafting amino polyethylene glycol (PEG, molecular weight 3400 or 5000) onto carboxyl polystyrene particles (PS-COOH) using carbodiimide chemistry. PEG-modified particles (PS-PEG) were characterized by determination of the PEG surface concentration, zeta-potential, size, and morphology. Under optimized grafting conditions, a dense "brush-like" PEG layer was formed. A PEG surface concentration of approximately 60 pmol/cm2, corresponding with an average distance between grafted PEG chains of approximately 17 A can be realized. It was shown that grafting of PEG onto PS-COOH reduced the adsorption of proteins from human plasma (85 vol %) in phosphate-buffered saline up to 90%.

Adsorption↗

PubMed2004

Pegylated polystyrene particles as a model system for artificial cells.

Pegylated polystyrene particles (PS-PEG) were prepared as a model system for artificial cells, by modification of carboxyl polystyrene particles (PS-COOH) with homo- and hetero-bifunctional polyethylene glycols (PEG, MW 1500, 3400, and 5000) containing an amino end group for immobilization and an amino, hydroxyl, or methoxy end group that is exposed at the surface after immobilization. Protein adsorption from human plasma dilutions (85 v %) onto PS-PEG with a PEG surface concentration higher than 40 pmol/cm2 was reduced up to 90-95% compared with protein adsorption onto PS-COOH with a final protein surface concentration of approximately 30 ng/cm2. Two-dimensional gel electrophoresis analyses showed that 30% of the total amount of adsorbed proteins onto PS-PEG are dysopsonins (i.e., nonadhesive proteins like albumin and apolipoproteins). For PS-COOH, <15% of the amount of adsorbed proteins are dysopsonins. In addition, the generation of terminal complement compound (TCC) by PS-PEG particles with a PEG surface concentration lower than approximately 55 pmol/cm2 is not significant. The low protein adsorption, the relatively high percentage of adsorbed dysopsonins, and the low level of complement activation may prevent the uptake of PS-PEG by the mononuclear phagocytic system (MPS) in vivo. Moreover, PS-PEG (PEG surface concentration > approximately 35 pmol/cm2) shows minimal interaction with cultured human umbilical vein endothelial cells (HUVEC), which mimics the endothelial lining of the blood vessel wall.

Adsorption↗