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Biomedical subjects

Changyou Gao

Publications and source records attributed to Changyou Gao.

At least 37 records · Page 2Linked to original sources
PubMed2005

Cartilage tissue engineering PLLA scaffold with surface immobilized collagen and basic fibroblast growth factor.

A previously reported "grafting and coating" method (J. Biomed. Mater. Res. (Appl. Biomater.) 63 (2002) 838) was modified and used to introduce stable collagen layer and incorporate basic fibroblast growth factor (bFGF) on PLLA scaffold surface to prepare tissue engineering scaffold with improved biocompatibility. To make the modification of the 3-D porous PLLA scaffold possible, grafting of polymethacrylic acid (PMAA) onto the PLLA surface was initiated by the -OOH/Fe2+ system instead of the UV light used in the former method. Water soluble carbodimmide chemistry was applied to graft collagen onto the PLLA scaffold surface, followed by physical coating of the collagen solution with or without basic fibroblast growth factor (bFGF). Surface modification of 2-D PLLA membrane was also done for fundamental understanding of the modification. The -COOH density on/in the PMAA grafted PLLA membrane/scaffold was measured by colorimetric method and the collagen content on/in the collagen immobilized PLLA membrane/scaffold was measured by ninhydrin method. Chondrocyte culturing on the collagen immobilized PLLA surfaces showed significantly improved cell spreading and growth. Incorporation of fibroblast growth factors in the collagen layer further enhanced the cell growth. This convenient and effective method can be used to prepare bioactive scaffolds with extra cellular matrix (ECM)-mimic composition for tissue engineering.

Animals↗
PubMed2005

Collagen-coated polylactide microspheres as chondrocyte microcarriers.

Polylactide (PLA) microspheres were coated with collagen for cell culture and injectable cell carriers. Utilizing a method of emulsion-solvent evaporation, PLA microspheres with diameter ranging from 180 to 280 microm were prepared, followed with aminolysis in hexanediamine/n-propanol solution to introduce free amino groups on their surfaces. After the amino groups were transferred into aldehyde groups by a treatment of glutaraldehyde, collagen type I was covalently coupled via Schiff base formation between the aldehyde groups and the amino groups on collagen molecules. Meanwhile, physically entangled collagen molecules were retained following a grafting-coating protocol to yield microspheres coated with larger amount of collagen. Aminolysis resulted in weight loss of the microspheres following a linear relationship with the aminolysis time. The NH2 and collagen contents existed on the microsphere surface were quantitatively determined by ninhydrin and hydroproline (Hyp) analyses, respectively. Larger amount of collagen was immobilized on the microspheres with higher content of NH2. In vitro chondrocyte culture revealed that the cells could attach, proliferate and spread on these PLA microspheres, in particular on the ones having higher content of collagen. These results show that the collagen-coated PLA microspheres are promising candidate as cell microcarriers.

Animals↗
PubMed2005

[Primary study on histocompatibility of three kinds of collagen-chitosan porous scaffolds].

OBJECTIVE: To construct three kinds of collagen-chitosan porous scaffolds with enhanced bio-stability and to investigate the histocompatibility of the scaffolds in vivo. METHODS: Collagen-chitosan porous scaffolds were fabricated by freeze-drying method, cross-linked using dehydrothermal treatment and glutaraldehyde, respectively. The morphology of the uncross-linked scaffold (scaffold 1), dehydrothermal cross-linked scaffold (scaffold 2) and glutaraldehyde cross-linked scaffold (scaffold 3) was studied by scanning electron microscopy. Three kinds of scaffolds were embedded subcutaneously on dorsal surface of 12 rabbit ears. The general and local responses were recorded daily. The bio-stability and histocompatibility of the scaffolds were observed by using HE staining after 3, 7, 14 and 28 days of operation. RESULTS: The scaffolds had three-dimensional porous structures with a porosity of more than 90%, and possessed pore sizes of 120 +/- 10 microm, 80 +/- 15 microm and 170 +/- 20 microm, respectively. All experimental rabbits survived with good general condition during the study. All skin incisions healed well without obvious reactive red or swelling. Histological study showed that scaffold 1 was degraded rapidly with obvious inflammation. The degradation of scaffold 2 was slower than that of scaffold 1 and the inflammation of scaffold 2 was also milder than that of scaffold 1. Scaffold 3 possessed slow degradation property with slight inflammatory reaction, and rapid tissue regeneration. CONCLUSION: The collagen-chitosan porous scaffolds have three-dimensional porous structures that are suitable for tissue regeneration. The bio-stability and histocompatibility of the scaffolds are enhanced after cross-linked. Glutaraldehyde cross-linked is better than dehydrothermal cross-linked, which can facilitate dermal tissue reconstruction.

Animals↗
PubMed2004

Biodegradability and cell-mediated contraction of porous collagen scaffolds: the effect of lysine as a novel crosslinking bridge.

A novel crosslinking method was adopted to modify the porous collagen scaffolds by using a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDAC) and N-hydroxysuccinimide (NHS) in the presence of lysine, which functions as a crosslinking bridge. In vitro biodegradation tests proved that in the presence of lysine the biostability of the EDAC crosslinked scaffolds was greatly enhanced. The biostability of the resultant scaffolds was also elucidated as a function of the concentrations of lysine and EDAC/NHS. Compared to the Col-DHT, the ability of the Col-EDAC and the Col/Lys to resist cell-mediated contraction (CMC) was greatly enhanced. Yet no obvious difference between the Col-EDAC and the Col/Lys was found with respect to CMC. SEM observations showed that the microstructure of the crosslinked scaffolds could be largely preserved after fibroblast seeding. As a result, MTT assays proved that the fibroblasts in the Col/Lys scaffolds proliferated faster compared to the DHT-treated one on the assumption that the cell viability was preserved to a similar level. Histological section results indicated that the Col/Lys scaffolds had the ability to accelerate the cell infiltration and proliferation. All these results demonstrated that this novel crosslinking method is an effective way to achieve a collagen scaffold with improved biostability and a more stable structure, which can resist cell-mediated contraction. (c) 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 334-342, 2004.

Animals↗
PubMed2004

A novel process for inking the stamp with biomacromolecule solution used in reactive microcontact printing.

This paper describes a novel process for inking the stamp with biomacromolecule solution used in reactive microcontact printing. The stamp was first coated with biomacromolecule solution such as bovine serum albumin (BSA) solution for 20 min, and then dried by soft nitrogen flow. After cooling the stamp below the dew point for 1 min and incubated at room temperature for 10 s, a thin layer of condensed water was formed on the stamp surface. Then, an aldehyde functionalized glass slide was pressed immediately onto the stamp for certain time, yielding the covalently patterning of the biomacromolecules on the aldehyde-containing surface. A notable feature of this process is that the biomacromolecule solution can be inked onto the stamp at a controlled state, neither too "dry" nor too "wet". As a result, the covalently grafting reaction can occur at a comparable speed with those in solution, while avoiding the contamination caused by dispersal of excessive solvent.

Biopolymers↗
PubMed2004

Endothelial cell functions in vitro cultured on poly(L-lactic acid) membranes modified with different methods.

We recently developed several methods to enhance the cell-polymer interactions. Optimal conditions for each method have been revealed separately by in vitro cell culture. As a practical consideration for construction of tissue-engineered organs, it is necessary to consider which is the most suitable and convenient in clinical applications. To compare the efficiency of these methods with respect to cell functions, poly-L-lactic acid (PLLA) was selected as matrix being modified by 1) aminolysis (PLLA-NH(2)), 2) collagen immobilization with GA (PLLA-GA-Col), 3) chondroitin sulfate (CS)/collagen layer-by-layer (LBL) assembly (PLLA-CS/Col), 4) photo-induced grafting copolymerization of hydrophilic methacrylic acid (MAA) (PLLA-g-PMAA), and 5) further immobilization of collagen with 1-ethyl-3-(3-dimethylamino propyl) carbodiimide hydrochloride (EDAC) (PLLA-g-PMAA-Col). The surface wettability of the modified PLLA was determined by water contact angle measurements. The cell response to the modified PLLA was quantitatively assessed and compared by using human umbilical endothelial cells (HUVECs) culture. Our results indicate that all the modifications can improve the cytocompatibility of PLLA (e.g., cells can attach with spreading morphology, proliferate and secret vWF and 6-keto-PGF(1 alpha)). All the collagen-modified PLLA showed more positive cell response than those purely aminolyzed or PMAA grafted. Among all the methods, collagen immobilization by LBL assembly or GA bridging after aminolysis is more acceptable for the convenience and applicability to scaffolds.

Biocompatible Materials↗
PubMed2004

Enhanced biological stability of collagen porous scaffolds by using amino acids as novel cross-linking bridges.

Collagen porous scaffolds have been widely employed as a dermal equivalent to induce fibroblasts infiltration and dermal regeneration. To eliminate the disadvantageous drawback of the fast degradation speed, a cross-linking method was adopted by using a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDAC) and N-hydroxysuccinimide (NHS) in the presence of amino acids (glycin, glutamic acid or lysine), which function as cross-linking bridge between collagen molecular chains. In vitro assessment of the biological stability of the cross-linked collagen scaffolds found that the collagenase biodegradation degree was greatly decreased when lysine was added, resulting in a more biological stable scaffold. On the other hand, the biodegradation degree was accelerated compared with the purely cross-linked when glutamic acid was added, while less influenced by glycin addition. By comparing the biodegradation degree of the scaffolds added with amino acids and their model compounds, i.e. adipic acid and hexane diamine, the key factor influencing the biological stability was further investigated. The results indicated that the crucial factor is dependent on the ratio of amino groups to carboxyl groups in the cross-linking system. At optimal ratio the lowest biodegradation degree is achieved. Scanning electron microscopy measurements prove that the three-dimensional structure of the scaffolds was largely preserved. Preliminary in vitro culture of fibroblasts in the collagen scaffold cross-linked with EDAC/NHS in the presence of lysine has shown that the original good cytocompatibility of collagen was retained.

Amino Acids↗
PubMed2004

Endothelium regeneration on luminal surface of polyurethane vascular scaffold modified with diamine and covalently grafted with gelatin.

Using the recently developed surface modification technique, free amino groups have been introduced onto polyester-type polyurethane (PU) scaffolds. The introduction of these free amino groups increases the surface energy and provides a convenient way to further immobilize bioactive species such as gelatin, collagen or chitosan, etc. on the scaffold surface by employing glutaraldehyde as a coupling agent. These modifications are advantageous to enhance cell-material interaction. The culture of human umbilical vein endothelial cells (HUVECs) in vitro proved that the cell proliferation ratio of both the aminolyzed and the biomacromolecules-immobilized PU membranes was improved greatly comparing with the control PU. Scanning electron microscopy and confocal laser scanning microscopy observations displayed that the gelatin-immobilized PU vascular scaffold had formed a monolayer of endothelial intima on its luminal surface after HUVECs were cultured for 6 d. Therefore, the aminolysis and the following biomacromolecule immobilization is a promising way to enhance the cell-PU interaction that can accelerate the endothelium regeneration, which is crucial for blood vessel tissue engineering.

Biocompatible Materials↗
PubMed2004

Promoting the cytocompatibility of polyurethane scaffolds via surface photo-grafting polymerization of acrylamide.

Polyurethane (PU) porous scaffolds were modified by grafting polymerization of acrylamide (AAm) initiated under UV light. A pre-adsorbing-monomer method was used beforehand. FTIR-ATR spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements confirmed the presence of grafted PAAm on PU scaffolds. The measurement of water adsorption demonstrated the improvement of hydrophilicity after PU scaffolds were grafted with polyacrylamide (PAAm). The PAAm grafting degree related to the amount of AAm adsorbed, average pore diameter, and the degree of porosity. This study shows that higher degree of porosity and bigger porous areas yielded larger amounts of absorbed AAm and higher grafting degrees. In vitro human endothelial cell cultures of PU scaffolds modified with hydrophilic PAAm showed better cytocompatibility than the control matrix.

Acrylic Resins↗
PubMed2004

[Factors controlling the microstructure of collagen-based dermis regeneration scaffold].

The factors controlling the microstructure and properties of collagen-based bioactive artificial dermis are reviewed. The second component, the pore diameter and porosity, the thickness of scaffold, the bioactive factors as well as the cross-linking density that are important parameters of artificial dermis should be carefully researched and designed. Experiment methods controlling these parameters are suggested.

Biocompatible Materials↗
PubMed2003

Engineering porous polyurethane scaffolds by photografting polymerization of methacrylic acid for improved endothelial cell compatibility.

Using a preadsorbing-monomer method, polyurethane (PU) porous scaffolds were modified by grafting polymerization of methacrylic acid (MAA) initiated under UV light. Fourier transform infrared-attenuated total reflection spectroscopy and X-ray photoelectron spectroscopy characterizations confirmed the occurrence of the grafting polymerization of poly(methacrylic acid) (PMAA) on PU scaffolds and the measurement of water adsorption also demonstrated enhanced hydrophilicity. The PMAA grafting degree correlated to the amount of MAA adsorbed, the pore average diameter, and the porosity. It was verified that the higher porosity the scaffold has, the larger porous area (or the larger contact area with MAA) it has, and therefore the higher amount of MAA adsorbed and higher grafting degree obtained. The results of human endothelial cells cultured in vitro showed that the PU scaffolds modified with the hydrophilic PMAA had more improved cell compatibility than the control matrix.

Cell Adhesion↗
PubMed2003

Paraffin spheres as porogen to fabricate poly(L-lactic acid) scaffolds with improved cytocompatibility for cartilage tissue engineering.

Three-dimensional poly(L-lactic acid) (PLLA) scaffolds with high porosity and pore size ranging from 150 to 700 microm were conveniently prepared with paraffin spheres used as porogen. PLLA/1,4-dioxane solution containing a given amount of paraffin spheres was frozen at -25 degrees C to obtain a solidified mixture, followed with freeze drying and subsequent leaching with hexane to remove the 1,4-dioxane and paraffin spheres, respectively. The fabricated PLLA scaffolds were highly porous with evenly distributed and interconnected pores. The microstructures of the PLLA scaffolds as a function of paraffin-sphere size, paraffin-sphere dosage, and PLLA concentration were characterized by confocal laser scanning microscopy (CLSM) and scanning-electronic microscopy (SEM). To improve the cytocompatibility of the bioinert material, a hybrid PLLA scaffold containing Type I collagen was prepared by pressing the collagen solution into the scaffold under reduced pressure. The amounts of the collagen introduced in the scaffolds were detected by ninhydrin method. The distribution of the collagen in the scaffolds was studied with CLSM. Finally, in vitro cell culture was performed by injecting a chondrocyte suspension into the scaffolds. The results showed that the chondrocytes were more evenly distributed and more spread out in the collagen-modified PLLA scaffolds than in the unmodified ones.

Animals↗
PubMed2003

Swelling and shrinking of polyelectrolyte microcapsules in response to changes in temperature and ionic strength.

Swelling and shrinking of polyelectrolyte microcapsules consisting of poly(styrene sulfonate, sodium salt) (PSS) and poly(diallyldimethyl ammonium) chloride (PDADMAC) multilayers have been observed in response to temperature and electrolyte exposure, respectively. Heat-induced capsule swelling and capsule wall volume reduction were observed by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). On the other hand, pronounced shrinking in diameter induced by exposure to an electrolyte was observed in parallel to increases in the thickness of the capsule wall. The estimated wall volume was reduced to two thirds of the control for the salt-exposed capsules and one half for the salt-exposed and simultaneously annealed capsules. This reduction in volume was supposedly mainly caused by the compression of the capsule wall due to the ionic screening from the electrolyte. The highly porous microstructure of the multilayers and loosely bound PSS/PDADMAC complex are thought to be responsible for the structure of the PSS/PDADMAC capsules being easily modulated upon annealing and salt-exposure.

Journal Article↗
PubMed2003

Chondrocyte behaviors on poly-L-lactic acid (PLLA) membranes containing hydroxyl, amide or carboxyl groups.

Hydrophilic groups, i.e. hydroxyl (-OH), carboxyl (-COOH) or amide (-CONH(2)) were introduced onto the poly-L-lactic acid (PLLA) membrane surfaces via the photo-induced grafting copolymerization of the corresponding monomers, i.e. hydroxyethyl methacrylate, methacrylic acid or acrylamide, respectively. Chondrocyte culture was used to study the correlation between the cell behaviors and the hydrophilic functional groups. The results showed that the cytocompatibility of the PLLA membranes with hydroxyl or amide groups on the surface was greatly improved compared to that of the original PLLA membrane. However, the PLLA membrane with carboxyl groups on the surface had even worse cytocompatibility though possessed a similar hydrophilicity.

Animals↗
PubMed2003

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.

Animals↗
PubMed2003

Photografting of poly(hydroxylethyl acrylate) onto porous polyurethane scaffolds to improve their endothelial cell compatibility.

In order to improve the cytocompatibility of polyurethane (PU) porous scaffolds obtained by thermally-induced phase separation, poly(hydroxylethyl acrylate) (PHEA) was covalently immobilized by grafting copolymerization of HEA by photo-oxidation of the scaffolds and initiation of UV light. FT-IR-ATR spectroscopy and X-ray photoelectron spectroscopy (XPS) characterizations confirmed the occurrence of the grafting co-polymerization of HEA on the porous PU scaffolds. The measurement of water absorption demonstrated the improvement of the hydrophilicity after grafting with PHEA. The results obtained in a human umbilical vein endothelial cell (HUVEC) culture proved that the porous PU scaffold modified with the hydrophilic PHEA had better cytocompatibility than the control. The influence of surface pore size on the HUVEC growth behavior was assessed regarding cell anchorage, proliferation and viability, as well as morphology. An overall increase of cell number and viability with the decrease of the surface pore size was found.

Absorption↗
PubMed2003

Surface modification of poly-L-lactic acid (PLLA) membrane by grafting acrylamide: an effective way to improve cytocompatibility for chondrocytes.

Poly-L-lactic acid (PLLA) membranes were photo-oxidized in hydrogen peroxide solution under ultraviolet light (UV) to introduce hydroperoxide groups onto the PLLA membrane surfaces. The photo-oxidized membranes were then immersed in acrylamide (AAm) solution containing Fe2+ to graft polyacrylamide (PAAm) onto the PLLA membrane surfaces. The density of the hydroperoxide groups introduced on the PLLA membrane surfaces varied with the temperature and the photo-oxidization time. The occurrence of grafting was verified by X-ray photoelectron spectroscopy (XPS). The degree of grafting increased with the monomer concentration and the polymerization time. Water contact angle measurements showed that the wettability of the modified PLLA membranes had improved. Chondrocytes proliferated more rapidly and were more spread out on the modified membrane than on the control PLLA membrane, indicating that the PAAm-grafted PLLA membrane has better cytocompatibility for chondrocytes.

Acrylamide↗