Zhengwei Mao

Collagen/chitosan porous scaffolds with improved biostability for skin tissue engineering

Porous scaffolds for skin tissue engineering were fabricated by freeze-drying the mixture of collagen and chitosan solutions. Glutaraldehyde (GA) was used to treat the scaffolds to improve their biostability. Confocal laser scanning microscopy observation confirmed the even distribution of these two constituent materials in the scaffold. The GA concentrations have a slight effect on the cross-section morphology and the swelling ratios of the cross-linked scaffolds. The collagenase digestion test proved that the presence of chitosan can obviously improve the biostability of the collagen/chitosan scaffold under the GA treatment, where chitosan might function as a cross-linking bridge. A detail investigation found that a steady increase of the biostability of the collagen/chitosan scaffold was achieved when GA concentration was lower than 0.1%, then was less influenced at a still higher GA concentration up to 0.25%. In vitro culture of human dermal fibroblasts proved that the GA-treated scaffold could retain the original good cytocompatibility of collagen to effectively accelerate cell infiltration and proliferation. In vivo animal tests further revealed that the scaffold could sufficiently support and accelerate the fibroblasts infiltration from the surrounding tissue. Immunohistochemistry analysis of the scaffold embedded for 28 days indicated that the biodegradation of the 0.25% GA-treated scaffold is a long-term process. All these results suggest that collagen/chitosan scaffold cross-linked by GA is a potential candidate for dermal equivalent with enhanced biostability and good biocompatibility.

Pillar[6]arene/Paraquat Molecular Recognition in Water: High Binding Strength, pH-Responsiveness, and Application in Controllable Self-Assembly, Controlled Release, and Treatment of Paraquat Poisoning

The complexation between a water-soluble pillar[6]arene (WP6) and paraquat (G1) in water was investigated. They could form a stable 1:1 [2]pseudorotaxane with an extremely high association constant of (1.02 ± 0.10) × 10(8) M(-1) mainly driven by electrostatic interactions, hydrophobic interactions, and π-π stacking interactions. This molecular recognition has not only high binding strength but also pH-responsiveness. The threading and dethreading processes of this [2]pseudorotaxane could be reversibly controlled by changing the solution pH. This novel recognition motif was further used to control the aggregation of a complex between WP6 and an amphiphilic paraquat derivative (G2) in water. The reversible transformations between micelles based on G2 and vesicles based on WP6⊃G2 were realized by adjusting the solution pH due to the pH-responsiveness of WP6. The controlled release of water-soluble dye molecules from the vesicles could be achieved by the collapse of the vesicles into the micelles upon changing the solution pH to acidity. Additionally, the high binding affinity between WP6 and paraquat could be utilized to efficiently reduce the toxicity of paraquat. After the formation of a stable host-guest complex between WP6 and paraquat, less opportunity was available for paraquat to interact with the reducing agents in the cell, which made the generation of its radical cation more difficult, resulting in the efficient reduction of paraquat toxicity.

A Sugar-Functionalized Amphiphilic Pillar[5]arene: Synthesis, Self-Assembly in Water, and Application in Bacterial Cell Agglutination

A novel sugar-functionalized amphiphilic pillar[5]arene containing galactose groups as the hydrophlic part and alkyl chains as the hydrophobic part was designed and synthesized. It self-assembles in water to produce nanotubes as confirmed by TEM, SEM, and fluorescence microscopy. These nanotubes, showing low toxicity to both cancer and normal cells, can be utilized as excellent cell glues to agglutinate E. coli. The existence of galactoses on these nanotubes provides multivalent ligands that have high affinity for carbohydrate receptors on E. coli.

Colloidal particles for cellular uptake and delivery

Numerous colloidal particles have been designed for cellular uptake and intracellular delivery in biological systems. The different kinds of colloidal particle systems and the interactions between the particles and cells are highlighted, with a focus on the parameters governing cellular uptake. A perspective of the research is also proposed.

Chitosan-Based Biomaterials for Tissue Repair and Regeneration

Tissue repair and regeneration is an interdisciplinary field focusing on development of biological and bioactive substitutes. Chitosan is a natural polysaccharide exhibiting excellent biocompatibility, biodegradability, affinity to biomolecules, and wound-healing activity. It can also be easily modified via chemical and physical reactions to obtain derivatives of various structures, properties, functions, and applications. This paper focuses on chitosan and its derivatives as biomaterials for tissue repair and regeneration. Tuning the structure and properties such as biodegradability, mechanical strength, gelation property, and cell affinity can be achieved through chemical reaction, immobilization of specific ligands such as peptide and sugar molecules, combination with other biomaterials, and chemical or physical crosslinking. To obtain applicable three-dimensional scaffolding materials such as porous sponges, hydrogels, and rods, the formulation and stimuli-responsiveness of this material can also be modified. Moreover, chitosan and its derivatives can function as vectors for delivery of cell growth factors and particularly of functional genes encoding cell growth factors, which are easier to integrate with the formulated materials to obtain scaffolds of higher activity. Recent studies have shown that such scaffolds are of particular importance in mediating the proliferation, migration, and differentiation of stem cells. Finally, integration of chitosan with cell growth factors and associated genes and/or with cells (stem cells) produces chitosan-based biomaterials with applications in repair or regeneration of skin, cartilage, bone, and other tissue.

Gradient biomaterials and their influences on cell migration

Cell migration participates in a variety of physiological and pathological processes such as embryonic development, cancer metastasis, blood vessel formation and remoulding, tissue regeneration, immune surveillance and inflammation. The cells specifically migrate to destiny sites induced by the gradually varying concentration (gradient) of soluble signal factors and the ligands bound with the extracellular matrix in the body during a wound healing process. Therefore, regulation of the cell migration behaviours is of paramount importance in regenerative medicine. One important way is to create a microenvironment that mimics the in vivo cellular and tissue complexity by incorporating physical, chemical and biological signal gradients into engineered biomaterials. In this review, the gradients existing in vivo and their influences on cell migration are briefly described. Recent developments in the fabrication of gradient biomaterials for controlling cellular behaviours, especially the cell migration, are summarized, highlighting the importance of the intrinsic driving mechanism for tissue regeneration and the design principle of complicated and advanced tissue regenerative materials. The potential uses of the gradient biomaterials in regenerative medicine are introduced. The current and future trends in gradient biomaterials and programmed cell migration in terms of the long-term goals of tissue regeneration are prospected.

A pillararene-based ternary drug-delivery system with photocontrolled anticancer drug release.

A novel ternary drug delivery system (DDS) is constructed using a photodegradable anticancer prodrug (Py-Cbl), a water-soluble pillararene supramolecular container (WP6), and the diblock copolymer methoxy-poly(ethylene glycol)114 -block-poly(L -lysine hydrochloride)200. This DDS successfully addresses three important issues: enhancement of the water solubility of the anticancer prodrug; controlled release of the anticancer drug; accurate and quantitative measurement of the drug release.

Controlling the migration behaviors of vascular smooth muscle cells by methoxy poly(ethylene glycol) brushes of different molecular weight and density.

Cell migration is an important biological activity. Regulating the migration of vascular smooth muscle cells (VSMCs) is critical in tissue engineering and therapy of cardiovascular disease. In this work, methoxy poly(ethylene glycol) (mPEG) brushes of different molecular weight (Mw 2 kDa, 5 kDa and 10 kDa) and grafting mass (0-859 ng/cm(2)) were prepared on aldehyde-activated glass slides, and were characterized by X-ray photoelectron spectrometer (XPS) and quartz crystal microbalance with dissipation (QCM-d). Adhesion and migration processes of VSMCs were studied as a function of different mPEG Mw and grafting density. We found that these events were mainly regulated by the grafting mass of mPEG regardless of mPEG Mw and grafting density. The VSMCs migrated on the surfaces randomly without a preferential direction. Their migration rates increased initially and then decreased along with the increase of mPEG grafting mass. The fastest rates (~24 μm/h) appeared on the mPEG brushes with grafting mass of 300-500 ng/cm(2) depending on the Mw. Cell adhesion strength, arrangement of cytoskeleton, and gene and protein expression levels of adhesion related proteins were studied to unveil the intrinsic mechanism. It was found that the cell-substrate interaction controlled the cell mobility, and the highest migration rate was achieved on the surfaces with appropriate adhesion force.

Fabrication and physical and biological properties of fibrin gel derived from human plasma

The fast development of tissue engineering and regenerative medicine drives the old biomaterials, for example, fibrin glue, to find new applications in these areas. Aiming at developing a commercially available hydrogel for cell entrapment and delivery, in this study we optimized the fabrication and gelation conditions of fibrin gel. Fibrinogen was isolated from human plasma by a freeze-thaw circle. Gelation of the fibrinogen was accomplished by mixing with thrombin. Absorbance of the fibrinogen/thrombin mixture at 550 nm as a function of reaction time was monitored by UV-VIS spectroscopy. It was found that the clotting time is significantly influenced by the thrombin concentration and the temperature, while less influenced by the fibrinogen concentration. After freeze-drying, the fibrin gel was characterized by scanning electron microscopy (SEM), revealing fibrous microstructure. Thermal gravimetric analysis found that the degradation temperature of the crosslinked fibrin gel starts from 288 degrees C, which is about 30 degrees C higher than that of the fibrinogen. The hydrogel has an initial water-uptake ratio of approximately 50, decreased to 30-40 after incubation in water for 11 h depending on the thrombin concentration. The fibrin gels lost their weights in PBS very rapidly, while slowly in DMEM/fetal bovine serum and DMEM. In vitro cell culture found that human fibroblasts could normally proliferate in the fibrin gel with spreading morphology. In conclusion, the fibrin gel containing higher concentration of fibrinogen (20 mg ml(-1)) and thrombin (5 U ml(-1)) has suitable gelation time and handling properties, and thus is applicable as a delivery vehicle for cells such as fibroblasts.

Thermal dehydration treatment and glutaraldehyde cross-linking to increase the biostability of collagen–chitosan porous scaffolds used as dermal equivalent

A biodegradable scaffold for skin-tissue engineering was designed using collagen and chitosan, which are common materials for biomedical application. The scaffolds containing different amounts of chitosan were prepared by mixing the collagen and chitosan solutions followed by removal of the solvent using a freeze-drying method. The cross-linking treatment of these scaffolds was performed using the dehydrothermal treatment (DHT) method or glutaraldehyde (GA) to increase their biostability. The effect of the chitosan concentration and the cross-linking methods on the morphology of these scaffolds was studied by SEM. The water retention and the biodegradability in vitro of various collagen-chitosan scaffolds were investigated. Finally the biocompatibility of the collagen-chitosan (10 wt% chitosan) scaffold treated with different cross-linking methods was evaluated using a in vivo animal test. A mild inflammatory reaction could be detected in the early stages, and GA treatment can decrease the inflammatory reaction in a long-term implantation. After implantation for four weeks, all kinds of scaffolds, especially the GA-treated scaffolds (Col-GA) were filled with a large number of fibroblasts and were vascularized to a certain extent. These results suggest that the GA-treated scaffold has an increased biostability and excellent biocompatibility. It can be a potential candidate for skin-tissue engineering.