Junjie Li

Formation and characterization of natural polysaccharide hollow nanocapsules via template layer-by-layer self-assembly.

With natural polysaccharides carrageenan (Car) and chitosan (Cs) as the polyanion and polycation, respectively, multilayer hollow nanocapsules have been fabricated via sequential layer-by-layer (LbL) electrostatic self-assembly from the sacrificed templates nanospheres (SiO(2)-NH(2)). The LbL assembly process with the polysaccharides on SiO(2)-NH(2) core was followed by ζ-potential and size analysis. The fabrication of (Car/Cs)(x) nanocapsules and the removing of the SiO(2)-NH(2) core templates were confirmed by TGA and EDS analysis. The morphology of SiO(2)(Car/Cs)(x) nanospheres and (Car/Cs)(x) nanocapsules were observed by TEM analysis. The size analysis of (Car/Cs)(x) nanocapsules indicated that the cyst wall thickness and cavity volume of the nanocapsules are pH and ionic strength dual responsive. Due to the biocompatibility of the natural polysaccharides carrageenan and chitosan and the responsiveness of nanocapsules to pH and ionic strength, the (Car/Cs)(x) multilayer nanocapsules are expected to be used as nanoreactors or nanocontainers to control the synthesis, encapsulation, and releasing behaviors of bioactive molecules.

A thermoresponsive poly(N-vinylcaprolactam-co-sulfobetaine methacrylate) zwitterionic hydrogel exhibiting switchable anti-biofouling and cytocompatibility

Non-specific protein adsorption adversely affects the application of thermoresponsive polymers in the biomedical field. To overcome this disadvantage, thermoresponsive N-vinylcaprolactam (VCL) and anti-biofouling zwitterionic sulfobetaine methacrylate (SBMA) monomers with various VCL/SBMA ratios were used for the synthesis of poly(VCL-co-SBMA) (P(VCL-co-SBMA)) copolymers via free radical solution polymerization. The P(VCL-co-SBMA) copolymers exhibited both a lower critical solution temperature (LCST) and an upper critical solution temperature (UCST) in aqueous solutions. Furthermore, both the UCST and LCST of the copolymer shift to higher temperatures with the increase of PSBMA segments, and they shift to lower temperatures with the increase of salt concentrations in the solution. Based on these results, P(VCL-co-SBMA) hydrogels were prepared using N,N′-methylenebisacrylamide (MBAA) as the crosslinker. Compared with the PVCL hydrogel, the P(VCL-co-SBMA) hydrogels exhibit better mechanical properties. Notably, the P(VCL-co-SBMA) hydrogel retained the temperature sensitivity of PVCL, and it could be modulated by varying the PVCL/PSBMA segment ratios. In addition, all the hydrogels exhibit good cytocompatibility. More importantly, the protein adsorption and cell adhesion of the hydrogel can be controlled by temperature. The non-specific protein adsorption was effectively suppressed at physiological temperatures. The switchable anti-biofouling nature of P(VCL-co-SBMA) hydrogel together with their temperature sensitivity can be potentially used in drug, cell or enzyme delivery.

Modulation of mesenchymal stem cells behaviors by chitosan/gelatin/pectin network films

In this article, the chitosan/gelatin/pectin (CGP) network films were prepared to build appropriate physicochemical and mechanical microenvironment for attachment, proliferation, and differentiation of mesenchymal stem cells (MSCs). Results suggested that the hydrophilicity and mechanical character of CGP composites films could be modulated via adjusting the pectin content in the composites. The investigations of attachment and proliferation behaviors of mesenchymal stem cells (MSCs) on the CGP films were carried out. The morphology of cells was observed with hematoxylin/eosin staining (HE) and scanning electron microscope (SEM). The osteogenic differentiation of MSCs was investigated via ALP and polymerase chain reaction (PCR). Results suggested that the CGP films have excellent biocompatibility. MSCs seeded on CGP (0.1) film show higher proliferation capacity compared with other samples. Moreover, osteogenic differentiation of MSCs also depends on the properties of the substrate. The MSCs seeded on CGP (0.5) expressed the highest ALP activity, osteogenic gene expression and mineral formation capacity. These results suggest that the composition of the CGP network films could effectively modulate their physicochemical and mechanical properties and further regulate the cell behaviors of MSCs.

Engineering pectin-based hollow nanocapsules for delivery of anticancer drug

Multifunctional capsules have great applications in biomedical fields. In this study, novel polysaccharide-based nanocapsules were prepared via a layer-by-layer technique using silica as the templates. The shell was constructed based on the electrostatic interactions between pectin and chitosan. The pectin-chitosan nanocapsules ((Pec/Cs)3Pec) could keep good colloidal stability within 96h in PBS solution and 48h in BSA solution. Meanwhile, the nanocapsules exhibited a high drug loading and pH-sensitive release property for doxorubicin hydrochloride. Moreover, (Pec/Cs)3Pec nanocapsules had no cytotoxicity to both human hepatocellular carcinoma cells (HepG2 cells) and mouse fibroblast cells (L929 cells). More importantly, (Pec/Cs)3Pec nanocapsules could be more easily uptaken by HepG2 cells when compared with L929 cells. In vitro anticancer activity tests indicated the carriers could effectively kill HepG2 cells. Overall, (Pec/Cs)3Pec nanocapsules have great potential as a novel anticancer drug carrier as a result of their pH-sensitivity, good colloidal stability and anticancer activity.

Alginate/PEG based microcarriers with cleavable crosslinkage for expansion and non-invasive harvest of human umbilical cord blood mesenchymal stem cells

Porous microcarriers are increasingly used to expand and harvest stem cells. Generally, the cells are harvested via proteolytic enzyme treatment, which always leads to damages to stem cells. To address this disadvantage, a series of alginate/PEG (AL/PEG) semi-interpenetrating network microcarriers are prepared in this study. In this AL/PEG system, the chemically cross-linked alginate networks are formed via the reaction between carboxylic acid group of alginate and di-terminated amine groups of cystamine. PEG is introduced to modulate the degradation of microcarriers, which does not participate in this cross-linked reaction, while it interpenetrates in alginate network via physical interactions. In addition, chitosan are coated on the surface of AL/PEG to improve the mechanical strength via the electrostatic interactions. Biocompatible fibronectin are also coated on these microcarriers to modulate the biological behaviors of cells seeded in microcarriers. Results suggest that the size of AL/PEG microcarriers can be modulated via adjusting the contents and molecular weight of PEG. Moreover, the microcarriers are designed to be degraded with cleavage of disulfide crosslinkage. By changing the type and concentration of reductant, the ratio of AL to PEG, and the magnitude of chitosan coating, the degradation ability of AL/PEG microcarriers can be well controlled. In addition, AL/PEG microcarriers can support the attachment and proliferation of human umbilical cord blood mesenchymal stem cells (hUCB-MSCs). More importantly, the expanded hUCB-MSCs can be detached from microcarriers after addition of reductant, which indeed reduce the cell damage caused by proteolytic enzyme treatment. Therefore, it is convinced that AL/PEG based microcarriers will be a promising candidate for large-scale expansion of hUCB-MSCs.

Chemically crosslinked alginate porous microcarriers modified with bioactive molecule for expansion of human hepatocellular carcinoma cells.

Microcarrier is an essential matrix for the large-scale culture of anchorage-dependent cells. In this study, chemical cross-linked alginate porous microcarriers (AMC) were prepared using microemulsion and freeze-drying technology. Moreover, chitosan was coated on the surface of microcarriers (AMC-CS) via electrostatic interactions to improve the mechanical strength. The size of AMC can be modulated through adjusting the concentration of alginate, amount of dispersant and stirring rate. The surface chemical characteristics and morphology of AMC-CS were evaluated by Fourier transformed infrared, X-ray photoelectron spectroscopy, and scanning electron microscope. Fibronectin (Fn) or heparin/basic fibroblast growth factor (bFGF) was then immobilized on the surface of microcarriers via layer-by-layer technology to improve the cytocompatibility. Our data suggested that the size of AMC can be accurately modulated from 90 μm to 900 μm with a narrow size distribution. Micropore structures of AMC-CS were relatively disordered and the pore size ranged between 20 μm and 100 μm. Using AMC after modified with Fn or bFGF as the cell expansion microcarriers, we showed that the proliferation rates of HepG2 cells increased significantly, reaching to more than 30-fold of cell expansion after 10 days of culture, with minor cellular damage caused by the microcarriers. Moreover, the AMC microcarriers modified with Fn or bFGF can increase albumin secretion of HepG2. We suggest that our new modified AMC-based microcarriers will be an attractive candidate for the large-scale cell culture of therapeutic cells.

Degradation in vitro and in vivo of β-TCP/MCPM-based premixed calcium phosphate cement

Premixed calcium phosphate cements (CPCs) have been developed to shorten the surgical time of conventional CPCs. However, there is lack of investigation on degradation behavior of premixed CPCs in vitro and in vivo. In this study, the premixed CPCs are prepared by mixing glycerol or polyethylene glycol (PEG) with the CPC power (β-tricalcium phosphate (β-TCP) and monocalcium phosphate monohydrate (MCPM)), and their degradation performances including the microstructure, chemical composition and mechanical properties are systematically evaluated both in vitro and in vivo (subcutaneous implantations in rabbits). When the premixed CPCs aged in PBS or FBS, results show weight loss of the specimens, decreased pH value and increased calcium ion concentration of aging media. Meanwhile, the setting products convert from dicalcium phosphate dihydrate (DCPD) to dicalcium phosphate anhydrous (DCPA), and no hydroxyapatite deposit. The specimen size and the molecular weight of non-aqueous solvent can modulate the setting product of premixed CPCs. For the larger specimens, DCPA is the main setting product, for the smaller ones, the composite contained DCPD and DCPA. With the decrease of the molecular weight of the non-aqueous solvent PEG, the setting product change from both DCPD and DCPA to DCPA due to the quicker exchange rate of PEG with water. After a period of subcutaneous implantation, the surface of the grafts obviously disintegrated with the formation of porous structures, but their internal morphology do not obviously change.