Xiudong Liu

Synthesis and Characterization of Amphiphilic Glycidol-Chitosan-Deoxycholic Acid Nanoparticles as a Drug Carrier for Doxorubicin

Novel amphiphilic chitosan derivatives (glycidol-chitosan-deoxycholic acid, G-CS-DCA) were synthesized by grafting hydrophobic moieties, deoxycholic acid (DCA), and hydrophilic moieties, glycidol, with the purpose of preparing carriers for poorly soluble drugs. Based on self-assembly, G-CS-DCA can form nanoparticles with size ranging from 160 to 210 nm, and G-CS-DCA nanoparticles maintained stable structure for about 3 months when stored in PBS (pH 7.4) at room temperature. The critical aggregation concentration decreased from 0.043 mg/mL to 0.013 mg/mL with the increase of degree of substitution (DS) of DCA. Doxorubicin (DOX) could be easily encapsulated into G-CS-DCA nanoparticles and keep a sustained release manner without burst release when exposed to PBS (pH 7.4) at 37 °C. Antitumor efficacy results showed that DOX-G-CS-DCA have significant antitumor activity when MCF-7 cells were incubated with different concentration of DOX-G-CS-DCA nanoparticles. The fluorescence imaging results indicated DOX-G-CS-DCA nanoparticles could easily be uptaken by MCF-7 cells. These results suggested that G-CS-DCA nanoparticles may be a promising carrier for DOX delivery in cancer therapy.

Microencapsulated probiotics using emulsification technique coupled with internal or external gelation process

Alginate-chitosan microcapsules containing probiotics (Yeast, Y235) were prepared by emulsification/external gelation and emulsification/internal gelation techniques respectively. The gel beads by external gelation showed asymmetrical structure, but those by internal gelation showed symmetrical structure in morphology. The cell viability was approximately 80% for these two techniques. However, during cell culture process, emulsification/internal gelation microcapsules showed higher cell growth and lower cell leakage. Moreover, the survival rate of entrapped low density cells with culture (ELDCwc) increased obviously than that directly entrapped high density cells (dEHDC) and free cells when keeping in simulated gastrointestinal conditions. It indicated the growth process of cells in microcapsule was important and beneficial to keep enough active probiotics under harmful environment stress. Therefore, the emulsification/internal gelation technique was the preferred method for application in food or biotechnological industries.

In Vitro and in Vivo characterization of alginate-chitosan-alginate artificial microcapsules for therapeutic oral delivery of live bacterial cells

Oral administration of artificial cell microcapsules entrapping live bacterial cells is a promising approach in disease therapy. However, the current technology of microcapsules limits this approach. In this study, alginate-chitosan-alginate (ACA) microcapsules entrapping live bacterial cells were prepared with the purpose of oral delivery for therapy, and their in vitro and in vivo properties were investigated. Genetically engineered Escherichia coli DH5 were used as the model bacterial strain. ACA microcapsules remained intact and stable in simulated gastrointestinal fluid and the entrapped bacteria cells survived and grew normally. Moreover, ACA microcapsules were more stable than alginate-polylysine-alginate microcapsules in the rat gastrointestinal tract, which was attributed to the enhanced resistance of the ACA microcapsules to enzymatic digestion. Therefore, these results reinforce the potential of ACA microcapsules for the therapeutic oral delivery of live bacterial cells.

Enhancement of Surface Graft Density of MPEG on Alginate/Chitosan Hydrogel Microcapsules for Protein Repellency

Alginate/chitosan/alginate (ACA) hydrogel microcapsules were modified with methoxy poly(ethylene glycol) (MPEG) to improve protein repellency and biocompatibility. Increased MPEG surface graft density (n(S)) on hydrogel microcapsules was achieved by controlling the grafting parameters including the buffer layer substrate, membrane thickness, and grafting method. X-ray photoelectron spectroscopy (XPS) model was employed to quantitatively analyze n(S) on this three-dimensional (3D) hydrogel network structure. Our results indicated that neutralizing with alginate, increasing membrane thickness, and in situ covalent grafting could increase n(S) effectively. ACAC(PEG) was more promising than ACC(PEG) in protein repellency because alginate supplied more -COO(-) negative binding sites and prevented MPEG from diffusing. The n(S) increased with membrane thickness, showing better protein repellency. Moreover, the in situ covalent grafting provided an effective way to enhance n(S), and 1.00 ± 0.03 chains/nm(2) was achieved, exhibiting almost complete immunity to protein adsorption. This antifouling hydrogel biomaterial is expected to be useful in transplantation in vivo.

Improving Stability and Biocompatibility of Alginate/Chitosan Microcapsule by Fabricating Bi‐Functional Membrane

Cell encapsulation technology holds promise for the cell-based therapy. But poor mechanical strength and biocompatibility of microcapsule membrane are still obstacles for the clinical applications. A novel strategy is presented to prepare AC₁ C₂ A microcapsules with bi-functional membrane (that is, both desirable biocompatibility and membrane stability) by sequentially complexing chitosans with higher deacetylation degree (C₁) and lower deacetylation degree (C₂) on alginate (A) gel beads. Both in vitro and in vivo evaluation of AC₁C₂ A microcapsules demonstrate higher membrane stability and less cell adhesion, because the introduction of C₂ increases membrane strength and decreases surface roughness. Moreover, diffusion test of AC₁C₂ A microcapsules displays no inward permeation of IgG protein suggesting good immunoisolation function. The results demonstrate that AC₁C₂ A microcapsules with bi-functional membrane could be a promising candidate for microencapsulated cell implantation with cost effective usage of naturally biocompatible polysaccharides.

Injectable in situ forming chitosan-based hydrogels for curcumin delivery

AbstractIn this paper, a series of injectable in situ forming chitosan-based hydrogels were prepared by chemical crosslinking of chitosan and genipin with the cooperation of ionic bonds between chitosan and sodium salts at room temperature. Four hydrogels (A, B, C, and D) were obtained by mixing chitosan, genipin and a sodium salt of trisodium phosphate (Na3PO4·12H2O), sodium sulfate (Na2SO4), sodium sulfite (Na2SO3), or sodium bicarbonate (NaHCO3) and examined for their characteristics, morphology, and rheological properties. Their cell viability assays exhibited low toxicity and the localized in situ gel formation was detected after subcutaneous injections in rat. Curcumin which possesses many pharmaceutical potentials but has low bioavailability, was chosen as a drug model. In vitro curcumin release profiles exhibit sustained release properties with initial burst release for all hydrogels with about 3 to 6 times higher cumulative release than other gel controls. The results of this study demonstrate that our hydrogels have a potential as local curcumin carriers.

Culture of low density E. coli cells in alginate–chitosan microcapsules facilitates stress resistance by up-regulating luxS/AI-2 system

Entrapped low density cells with culture (ELDCwc) have been proved as a more effective way than direct entrapped high density cells (dEHDC) and free cells to protect probiotics from harsh environment, that is, to improve their stress resistance. The aim of this study was to investigate whether bacterial quorum sensing (QS) facilitated the stress resistance of Escherichia coli in microcapsules by detecting the expression of luxS/AI-2 system. As a result, both the expression of luxS gene and the concentration of autoinducer-2 (AI-2, QS signal molecule) have been discovered higher in ELDCwc than in dEHDC and free cells. Besides that, the luxS mutant E. coli strain was used as a negative control of QS to verify the influence of QS on bacterial stress resistance in microcapsules. The significantly decreased viability of luxS mutant strain in simulated gastric fluid also indicated that the QS played a critical role in protecting microorganisms from severe environment.

A crucial role for spatial distribution in bacterial quorum sensing.

Quorum sensing (QS) is a process that enables bacteria to communicate using secreted signaling molecules, and then makes a population of bacteria to regulate gene expression collectively and control behavior on a community-wide scale. Theoretical studies of efficiency sensing have suggested that both mass-transfer performance in the local environment and the spatial distribution of cells are key factors affecting QS. Here, an experimental model based on hydrogel microcapsules with a three-dimensional structure was established to investigate the influence of the spatial distribution of cells on bacterial QS. Vibrio harveyi cells formed different spatial distributions in the microcapsules, i.e., they formed cell aggregates with different structures and sizes. The cell aggregates displayed stronger QS than did unaggregated cells even when equal numbers of cells were present. Large aggregates (LA) of cells, with a size of approximately 25 μm, restricted many more autoinducers (AIs) than did small aggregates (SA), with a size of approximately 10 μm, thus demonstrating that aggregate size significantly affects QS. These findings provide a powerful demonstration of the fact that the spatial distribution of cells plays a crucial role in bacterial QS.

Improved probiotic viability in stress environments with post-culture of alginate-chitosan microencapsulated low density cells.

In this study, probiotics (Saccharomyces cerevisiae Y235) were entrapped in alginate-chitosan microcapsules by emulsification/internal gelation technique. Two different encapsulation patterns were established as directly entrapped high density cells (dEHDC) and entrapped low density cells with culture (ELDCwc). The performance of microencapsulated cells, with free cells (FC) as control, was investigated against sequential stress environments of freeze-drying, storage, and simulated gastrointestinal fluids. After being freeze-dried without cryoprotectant, the survival rate of ELDCwc (14.33%) was significantly higher than 10.00% of dEHDC, and 0.05% of FC. The lower temperature (-20°C) and ELDCwc pattern were beneficial for keeping viable cells at 7.00 logCFU g(-1) after 6 months. Furthermore, the ELDCwc microcapsule maintained viable cells of 6.29 logCFU g(-1) after incubation in SGF and SIF. These studies demonstrated that the pattern of entrapped low density cells with culture was an effective and superior technique of resisting harmful stress environments.

An improved pH-responsive carrier based on EDTA-Ca-alginate for oral delivery of Lactobacillus rhamnosus ATCC 53103.

A pH-responsive carrier based on an ethylenediaminetetraacetic-calcium-alginate (EDTA-Ca-Alg) system was developed by controlling the release of Ca2+. The system remained in the solution state at neutral pH since EDTA completely chelated the Ca2+. In contrast, a hydrogel immediately formed when the pH was below 4.0, which triggered the in situ release of Ca2+ from the EDTA-Ca compound and led to alginate-Ca binding. Taking advantage of the pH sensitivity, we prepared hydrogel microspheres with uniform size to entrap Lactobacillus rhamnosus ATCC 53103 through emulsification. In an acidic environment, the hydrogel structure remained compact with negligible pores to protect L. rhamnosus ATCC 53103. However, in a neutral intestinal environment, the hydrogel structure gradually disassembled because of the Ca2+ release from the hydrogel, which caused cell release. Therefore, a pH-responsive carrier was developed for the protection and the controlled release of cells in gastrointestinal tract, thus providing potential for oral delivery of probiotics.