Cell growth on poly(vinyl alcohol) hydrogel membranes containing biguanido groups

Development of a polyvinyl alcohol/sodium alginate hydrogel-based scaffold incorporating bFGF-encapsulated microspheres for accelerated wound healing

In the present study, a hybrid microsphere/hydrogel system, consisting of polyvinyl alcohol (PVA)/sodium alginate (SA) hydrogel incorporating PCL microspheres is introduced as a skin scaffold to accelerate wound healing. The hydrogel substrate was developed using the freeze-thawing method, and the proportion of the involved polymers in its structure was optimized based on the in-vitro assessments. The bFGF-encapsulated PCL microspheres were also fabricated utilizing the double-emulsion solvent evaporation technique. The achieved freeze-dried hybrid system was then characterized by in-vitro and in-vivo experiments. The results obtained from the optimization of the hydrogel showed that increasing the concentration of SA resulted in a more porous structure, and higher swelling ability, elasticity and degradation rate, but decreased the maximum strength and elongation at break. The embedding of PCL microspheres into the optimized hydrogel structure provided sustained and burst-free release kinetics of bFGF. Besides, the addition of drug-loaded microspheres led to no significant change in the degradation mechanism of the hydrogel substrate; however, it reduced its mechanical strength. Furthermore, the MTT assay represented no cytotoxic effect for the hybrid system. The in-vivo studies on a burn-wound rat model, including the evaluation of the wound closure mechanism, and histological analyses indicated that the fabricated scaffold efficiently contributed to promoting cell-induced tissue regeneration and burn-wound healing.

Evaluation of Cell Adhesion and Proliferation on a Novel Tissue Engineering Scaffold Containing Chitosan and Hydroxyapatite

Porous chitosan-hxdroxyapatite hybrids were developed by partial enzymatic degradation [14] of the chitin/chitosan surface using chitosanase and lysozyme. This article evaluates the influence of chitosan and hydroxyapatite components, substrate roughness, stability, as well as surface porosity produced by enzymatic hydrolysis to cell adhesion and proliferation. L929 mouse fibroblastic lung cells were cultured on enzymatic degraded porous chitosan-hydroxyapatite hybrids. The presence of hydroxyapatite and porosity produced by partial lysozyme hydrolysis enhance cell proliferation. Besides, cell adhesion and proliferation are primarily dependent on substrate roughness and stability.

Equilibrium and non-equilibrium charge-dependent quantification of endothelial cell hydrogel scaffolds

Using equilibrium swelling and non-equilibrium membrane potential measurements, this study assesses the charge density in two representative series of polyelectrolyte hydrogels and examines the morphological and proliferative responses of endothelial cells as a function of the prepared charge offset. The neutral monomers 2-hydroxyethylmethacrylate (HEMA) and poly(ethylene glycol) dimethacrylate (n = 1,000) (PEGDMA) were copolymerized with either the acidic monomer 2-sulfoethyl methacrylate (SEMA) or the basic monomer methacryloxy ethyltrimethylammonium chloride (MAETAC) to make membranes with pregelation charge offset concentrations varying from 0 to +/-200 mM. A thermodynamic analysis of swelling and membrane potential measurements quantified the hydrogel charge density state following equilibration at different ion strengths. Porcine pulmonary artery endothelial cells were seeded on samples of each HEMA and PEGDMA copolymer and the amount of cell coverage was measured over a 4-day period. Cellular attachment and proliferation increased with increasing proportions of charged monomers and showed a threshold pattern of attachment and growth on the positively charged HEMA-MAETAC copolymer hydrogels with increasing proportions of initially prepared charge. The series of PEGDMA copolymer hydrogels remained relatively resistant to cellular attachment and proliferation over the range of prepared charges considered in this study.

Albumin and urea production by hepatocytes cultured on extracellular matrix proteins-conjugated poly(vinyl alcohol) membranes

Production of albumin and urea by mouse hepatocytes on poly(vinylalcohol-co-ethylamine) (PVA-EA) membranes containing immobilized extracellular matrix (ECM) proteins was investigated for 7 days. The amount of ECM proteins (collagen, vitronectin and laminin) immobilized on PVA-EA and PVA-ECM membranes was determined to range from 1.09 microg/cm2 to 1.60 microg/cm2. Hepatocytes cultured on PVA-ECM membranes in serum-free media showed higher albumin production than those cultured on PVA-EA membranes after a 7-day incubation under the conditions in this study. Urea production by hepatocytes on PVA-ECM membranes was also determined to be higher than that on PVA-EA membranes up until day 5 of incubation in serum-free media, whereas no difference of urea production by hepatocytes on different PVA-ECM membranes and PVA-EA membranes was observed at 7 days of incubation. The effect of ECM proteins in PVA-ECM membranes on hepatocyte function (such as albumin and urea production) was observed in hepatocytes cultured in serum-free media up to day 5 of incubation. The ECM proteins immobilized on the PVA-ECM membranes contributed not only to the long-term stable production of albumin and urea by hepatocytes, but also the improved surviVal (viability) of hepatocytes on PVA-ECM membranes.

Surface-modified poly(lactide-co-glycolide) nanospheres for targeted bone imaging with enhanced labeling and delivery of radioisotope

Surface-modified nanospheres can be utilized for targeting drugs and diagnostic agents to the bone and bone marrow while extending their circulation time in the blood stream. The surface modification of poly(lactide-co-glycolide) (PLGA) nanospheres by radioisotope carrying poly(ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) triblock copolymers (Poloxamer 407) has been assessed by in vitro characterization and in vivo biodistribution studies after intravenous administration of the nanospheres to the mouse. A hydroxyphenylpropionic acid, a ligand for (125)I and (131)I labeling, was conjugated to the hydroxyl group of the Poloxamer 407 by using dicyclohexyl carbodiimide. The ligand-conjugated Poloxamer 407 was adsorbed onto the surface of PLGA nanospheres. Surface coating was confirmed by measuring both size distribution and the surface charge of the nanospheres. Besides, (125)I-labeling efficiency, radiolabeling stability, whole body imaging, and biodistribution of the radioisotope-labeled nanospheres were examined. Ligand-labeled, surface-modified PLGA nanospheres were in 100-nm size ranges, which may be adequate for long-circulation and further bone imaging. (125)I-labeling efficiency was >90% and was more stable at human serum for 24 h. A noticeable decrease in liver or spleen uptake was obtained by the surface-modified nanospheres. (125)I-labeled nanospheres showed higher blood maintenance and bone uptake compared with stannous colloid with the same size distribution. Therefore, a fully biodegradable, radioisotope-carrying, surface-modified nanosphere system has been developed as a promising tool for targeting bone and bone marrows.

Protein adsorption and smooth muscle cell adhesion on biodegradable agmatine-modified poly(propylene fumarate-co-ethylene glycol) hydrogels

We synthesized positively charged biodegradable hydrogels from poly(propylene fumarate-co-ethylene glycol) block copolymer and agmatine-modified poly(ethylene glycol)-tethered fumarate by radical crosslinking, and investigated the effect of the guanidino group of agmatine on vascular smooth muscle cell adhesion and protein adsorption to the hydrogels. In the presence of serum, the number of adherent smooth muscle cells per unit surface area increased dose-dependently from 15 to 75% of the initial seeding density at 20 h as the initial agmatine-modified monomer content increased from 0 to 200 mg/g. Cell spreading also depended on the initial monomer content. In the absence of serum, the number of adherent cells per unit surface area increased slightly from 10 to 17% of the initial seeding density as the initial monomer content increased from 0 to 200 mg/g. Cell adhesion increased significantly by adding exogenous vitronectin to serum-free medium, whereas exogenous fibronectin addition did not enhance cell adhesion. The enzyme-linked immunosorbent assay of fibronectin and vitronectin adsorbed onto the hydrogels revealed that the incorporation of positive charges into the hydrogels enhanced vitronectin, but not fibronectin, adsorption significantly. These results suggest that the guanidino group of agmatine enhanced cell adhesion by promoting the adsorption of serum components, and vitronectin may be one of the components.

Disulfide-crosslinked hyaluronan-gelatin hydrogel films: a covalent mimic of the extracellular matrix for in vitro cell growth

A new disulfide crosslinking method was developed for the preparation of blended hyaluronan (HA)-gelatin hydrogels to form a synthetic, covalently linked mimic of the extracellular matrix (ECM). The HA and gelatin were chemically modified using 3,3'-dithiobis(propionic hydrazide) (DTP). After reduction with dithiothreitol (DTT), the thiol derivatives of HA (HA-DTPH) and gelatin (gelatin-DTPH) were obtained and characterized. To minimize interference with biological function, the degree of substitution of HA-DTPH and gelatin-DTPH was kept below 50%. Solutions of HA-DTPH and gelatin-DTPH in varying blends (20%, 40%, 60%, 80% gelatin) were prepared in 1% w/v NaCl and crosslinked by disulfide bond formation in air. Hydrogel films were dried and further crosslinked with dilute hydrogen peroxide. Disulfide crosslinked HA-DTPH, gelatin-DTPH, and blends thereof, were degradable enzymatically by collagenase and by hyaluronidase (HAse). The rapid digestion of the crosslinked 100% gelatin-DTPH film by collagenase was significantly retarded by the presence of 20% or 40% HA-DTPH. Addition of at least 40% w/v gelatin into the 100% HA-DTPH films significantly improved the attachment and spreading of Balb/c 3T3 murine fibroblasts seeded on the surface of the hydrogel. These results demonstrate that disulfide-crosslinked HA-gelatin hydrogels, a new type of covalent synthetic ECM, constitute biocompatible and biodegradable substrata for cell culture in vitro.

Polyvinylalcohol three-dimensional matrices for improved long-term dynamic culture of hepatocytes

Rat hepatocytes were seeded on three-dimensional highly porous polyvinylalcohol (PVA) and aminoethyl-modified polyvinylalcohol (AE-PVA) matrices. Hepatocytes were cultured under static and dynamic conditions. The three-dimensional matrices offered an improved extracellular microenvironment for long-term (5 days) maintenance of hepatocytes, compared to reference monolayer cultures on collagen. Cellular adhesion exceeded 80% with a viability superior to 70%. The preservation of albumin secretion after 5 days of culture was two times higher for static cultures on three-dimensional matrices (18% on PVA, 13% on AE-PVA) and three times higher for dynamic three-dimensional cultures (25% PVA and AE-PVA), compared to the static two-dimensional culture on collagen film (8%). The biotransformation of ammonia into urea was also maintained throughout the culture period. The addition of the aminoethyl function demonstrated no toxicity for the hepatocyte cultures. This function could be suitable eventually to further improve the hepatocyte culture system by linking more specific adhesion molecules on the polymer surface. This study demonstrated the efficiency of polyvinylalcohol as a three-dimensional matrix coupled to a perfusion culture system, which improves extracellular conditions for hepatocyte survival and promotes preservation of long-term hepatospecific functions.

Substrate effects of gel surfaces on cell adhesion and disruption

Substrate effects of hydrogel surfaces prepared on hydrophilic and hydrophobic substrates on the cell adhesion and disruption were studied. The adhesion of tobacco protoplasts onto anionic hydrogels was strongly influenced by the substrates on which the gels were synthesized. In the case of anionic poly(2-acrylamido-2-methylpropanesulfonic acid) gel, more cells adhered on the gel surface prepared on hydrophobic substrates than that prepared on hydrophilic substrates. On the other hand, in the case of cationic quaternized poly-(dimethylaminopropylacrylamide) gel, cell disruption occurred in a few seconds accompanied with an intensive release of cellular contents on the gel surface prepared on the hydrophilic substrates, while the cationic gel synthesized on hydrophobic substrates induced no cell disruption. These different behaviors of the cell have been made in terms of different structures of gel surfaces associated with the presence of flexible dangling chains.

Attachment and growth of cultured fibroblast cells on PVA/chitosan-blended hydrogels

Hydrogels were prepared from poly(vinyl alcohol) and chitosan in various blend ratios. The water contents of the hydrogels were in the range of 65 to 75 wt %. The attachment and growth of fibroblast cells (L-929) on the hydrogels were studied with a cell culture method. On the hydrogels with more than 15 wt % chitosan content, the attached cells were able not only to remain viable but also to proliferate. The relative cell attachment after incubation for 30 h increased with increasing chitosan content in the hydrogels. Cell attachment and growth on the hydrogel with 40 wt % chitosan content exceeded those on collagen, a widely-used mammalian cell culture substrate. The morphology of the cells attached onto the hydrogels with a lower chitosan content was spherical, but in hydrogels with more than 15 wt % chitosan content, the number of spindle-shaped cells increased with increasing chitosan content.

Effect of the chemical modification of the arginyl residue in Bombyx mori silk fibroin on the attachment and growth of fibroblast cells

We prepared matrices of Bombyx mori silk fibroin (SF) with different degrees of modification of arginyl residues by reaction between 1,2-cyclohexanedione (CHD) and SF. Two kinds of SF, namely native SF (NSF), obtained from the silk gland of silkworm larvae, and regenerated SF (RSF), prepared from cocoons of the same silkworm, were used in this study because their amino acid compositions were slightly different from each other. The attachment and growth of mouse fibroblast (L-929) cells on the matrices of the NSF and RSF, in which half or almost all of the arginyl residues were modified (NSF50, RSF50, NSF100, and RSF100), were studied using a cell culture method. Both NSF50 and NSF100 exhibited higher cell attachment than did the unmodified NSF. While the cell growth on NSF50 was not significantly different from that on NSF and NSF100, the growth on NSF100 was higher than that on NSF. The cells attached to NSF50 and NSF100 were extensively spread out and their filopodia were visible by SEM. The cell attachment and growth on RSF were comparable to those on NSF100. Although RSF50 exhibited almost the same cell attachment as did the unmodified RSF, RSF100 exhibited a lower cell attachment than did the unmodified RSF and RSF50. There were no significant differences in the cell growth among RSF series. The cells attached to RSF50 and RSF100 aggregated to form masses, and their filopodia could not be found. The relationship of cell attachment to the basicity of the substrate is considered because the modification of the positively charged arginyl residue changed the basicity of the substrate and the cell attachment on the substrate.

Polysulphone inhibits final differentiation steps of osteogenesis in vitro

Biocompatibility is an important factor in the development of orthopedic implants as well as in the development of new tissue culture devices. Polysulphone has been used for orthopedic implants because of its mechanical properties, ease of sterilization, molding capacity, and biocompatibility. Therefore, polysulphone has been chosen as the prime material for the construction of tissue culture devices to be used for the cultivation of osteogenic cells (preosteoblast-like MN7 cells and primary bone marrow fragments), as well as complete fetal long bone explants under space flight conditions. Whereas polysulphone did not interfere with the proliferation in early stages of bone-forming cells, we show that leachable factors within the polysulphone polymer prevented the final steps of matrix formation as measured by collagen synthesis and matrix mineralization. These data argue against polysulphone as a material for orthopedic implants.