Bin Cao

Biodegradable interpolyelectrolyte complexes based on methoxy poly(ethylene glycol)-b-poly(alpha,L-glutamic acid) and chitosan.

We synthesized methoxy poly(ethylene glycol)-b-poly(alpha,L-glutamic acid) (mPEGGA) diblock copolymer by ring-opening polymerization of N-carboxy anhydride of gamma-benzyl-L-glutamate (NCA) using amino-terminated methoxy polyethylene glycol (mPEG) as macroinitiator. Polyelectrolyte complexation between mPEGGA as neutral-block-polyanion and chitosan (CS) as polycation has been scrutinized in aqueous solution as well as in the solid state. Water-soluble polyelectrolyte complexes (PEC) can be formed only under nonstoichiometric condition while phase separation is observed when approaching 1:1 molar mixing ratio in spite of the existence of hydrophilic mPEG block. This is likely due to mismatch in chain length between polyanion block of the copolymer and the polycation or hydrogen bonding between the components. Hydrodynamic size of primary or soluble PEC is determined to be about 200 nm, which is larger than those reported in some literatures. The increase in polyion chain length of the copolymer leads to the increase in the hydrodynamic size of the water-soluble PEC. Formation of spherical micelles by the mPEGGA/CS complex at nonstoichiometirc condition has been confirmed by the scanning electron microscopy observation and transmission electron microscopy observations. The homopolymer CS experiences attractive interaction with both mPEGA and PGA blocks within the copolymer. Competition of hydrogen bonding and electrostatic force in the system or hydrophilic mPEG segments weakens the electrostatic interaction between the oppositely charged polyions. The existence of hydrogen bonding restrains the mobility of mPEG chains of the copolymer and completely prohibits crystallization of mPEG segments. In vitro culture of human fibroblasts indicates that mPEGGA/CS-based materials have potential in biomedical application, especially in tissue engineering.

Fabrication of poly(L-glutamic acid)/chitosan polyelectrolyte complex porous scaffolds for tissue engineering

Porous scaffolds composed of polypeptides and polysaccharides have remarkable biocompatibility and potential to mimic an extracellular matrix for tissue engineering. This study presented a novel design of polyelectrolyte complex porous scaffolds of a synthetic polypeptide poly(l-glutamic acid) (PLGA) and a natural polysaccharide chitosan (CS) using a freeze drying method. The microstructure of the porous scaffolds could be adjusted by changing the freezing temperature and solid content of the reacting polymer. PLGA/CS scaffolds fabricated from 2% solid content and at a freezing temperature of -20 °C exhibited an interconnected porous structure with average pore size between 150 and 200 μm. The contact angle of less than 75° and high swelling ratio of more than 700% showed the excellent hydrophilic performance of these scaffolds. Degradation of the PLGA/CS composite scaffolds could be modified and more CS content contributed a higher resistance to biodegradation. The mechanical properties of the scaffolds could be controlled by varying the PLGA/CS molar ratio and solid content. The scaffolds exhibited good elastic behavior in wet state. In vitro culture of rabbit adipose-derived stem cells (ASCs) indicated that the selected PLGA/CS porous scaffolds supported cell attachment and growth. In summary, the PLGA/CS porous scaffolds show excellent properties, such as an interconnected porous structure, mechanical strength, hydrophilicity, biodegradability and biocompatibility. The successful repair of articular cartilage defects showed the potentiality of using PLGA/CS scaffolds in cartilage tissue engineering.

Porous scaffolds based on cross-linking of poly(L-glutamic acid).

Porous scaffolds based on water-soluble PLGA and CS were prepared. The pores were verified to be alveolate, uniform and continuous. The effects of freezing temperature, freeze-drying time, solid content and molecular weight of reactants on the pore structure of the scaffolds were studied. The scaffold morphology could be adjusted by changing the freezing temperature and solid content of reacting polymer. Their degradation rate can be adjusted by changing the proportion of PLGA and CS. The porosity of scaffolds was higher than 90% and the high swelling ratio showed that these scaffolds had excellent hydrophilic performance. The in vitro culture of chondrocytes indicates that the obtained PLGA/CS porous scaffolds are very promising biomaterials for tissue engineering applications.

A Poly(acrylic acid)-block-Poly(L-glutamic acid) Diblock Copolymer with Improved Cell Adhesion for Surface Modification

A novel PAA-b-PLGA diblock copolymer is synthesized and characterized that has excellent cell adhesion and biocompatibility. Fluorescent DiO labeling is used to monitor the attachment and growth of hASCs on the film surface, and cell proliferation over time is studied. Results show that PLLA modified by a CS/PAA-b-PLGA multilayer film can promote the attachment of human hASCs and provide an advantageous environment for their proliferation. The multilayer film presents excellent biocompatibility and cell adhesive properties, which will provide a new choice for improving the cell attachment in surface modification for tissue engineering. Hydroxyl, carboxyl and amine groups in the CS/PAA-b-PLGA multilayer film may be combined with drugs and growth factors for therapy and differentiation.

Adipose tissue engineering with human adipose tissue-derived adult stem cells and a novel porous scaffold

We investigated the effect of a novel porous scaffold composed with water-soluble poly(L-glutamic acid) (PLGA) and chitosan (CS) on the attachment, proliferation, and adipogenic differentiation of human adipose tissue-derived adult stem cells (ADSCs) in vitro and in vivo. Scanning electron microscope and fluorescent Dil labeling were used to reveal the attachment and growth of ADSCs on scaffolds; cell proliferation was detected by DNA assay. The adipogenic differentiation potential of ADSCs on the scaffolds was assayed by Oil-red O staining and further confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) for adipogenic gene markers (peroxisome proliferator-activated receptor γ2, lipoprotein lipase, fatty acid-binding protein, adiponectin). Cell-seeded constructs exposed to adipogenic medium for 2 weeks in vitro were implanted in severe combined immunodeficient (SCID) mice for 6 weeks. It was shown that ADSCs attached and spread well on scaffolds with good proliferation behaviors and abundance of extracellular matrix deposition. Oil-red O staining and RT-PCR showed adipogenic differentiation potential of ADSCs on scaffolds. Newly formed adipose-like tissue was confirmed in vivo in SCID mice by Oil-red O staining. PLGA/CS porous scaffolds exhibit good compatibility to ADSCs and can be promising biomaterials for adipose tissue engineering.

Layer-by-Layer Assembled Multilayer Films of Methoxypoly(ethylene glycol)-block-poly(α,L-glutamic acid) and Chitosan with Reduced Cell Adhesion

A methoxypoly(ethylene glycol)-block-poly(α,L-glutamic acid) (mPEGGA) diblock copolymer is synthesized. Using QCM measurements, it is shown that (CS/mPEGGA)(n) film construction takes place over two build-up stages (exponential-to-linear). UV-vis spectra reveal the regular increase of the multilayer film growth at different molecular weights of mPEGGA. Contact angle and surface morphology investigation prove that the hydrophilicity of CS/mPEGGA multilayer film-modified substrate becomes better and the surface becomes rough. Significantly reduced cell adhesion is observed on the CS/mPEGGA multilayer film coated surface.