Interaction of endothelial cells with methacrylic terpolymer biomaterials

Glass Transition in Crosslinked Nanocomposite Scaffolds of Gelatin/Chitosan/Hydroxyapatite

The development of biopolymeric scaffolds crosslinked with nanoparticles is an emerging field. Gelatin/chitosan scaffolds are gaining interest in medical areas, e.g., bone tissue engineering, given their suitability for nano-hydroxyapatite incorporation. The glass transition temperature is a thermodynamic property of polymer scaffolds that changes with crosslinker or nanofiller concentration. Here, we report the experimental change in glass transition temperature of gelatin/chitosan scaffolds modified by hydroxyapatite nanoparticles and crosslinker concentration. Our results show synergic effects between nanoparticles and crosslinking, which leads to a non-linear behavior of the glass transition temperature. Furthermore, a theoretical model to predict glass transition is proposed. This model can be used as a mathematical tool for the design of future scaffolds used in bone tissue engineering.

Improving cellular adhesion on scaffolds for transplantation: synthesising a poly(MMA-co-PEGM) network

Electrospun fibrous matrices prepared from methacrylate-based copolymers are investigated as a tool for retinal pigment epithelium (RPE) transplantation in the treatment of degenerative retinal diseases. Human RPE cells were used to probe the cell-surface interactions on these copolymer matrices. For the first time, simple changes in chemical functionality have been found to induce gel formation of these methacrylate backbone copolymers in vitro. This effect is shown to significantly improve RPE cell adhesion and survival.

Designing a gelatin/chitosan/hyaluronic acid biopolymer using a thermophysical approach for use in tissue engineering

Cell culture on biopolymeric scaffolds has provided treatments for tissue engineering. Biopolymeric mixtures based on gelatin (Ge), chitosan (Ch) and hyaluronic acid (Ha) have been used to make scaffolds for wound healing. Thermal and physical properties of scaffolds prepared with Ge, Ch and Ha were characterized. Thermal characterization was made by using differential scanning calorimetry (DSC), and physical characterization by gas pycnometry and scanning electron microscopy. The effects of Ge content and cross-linking on thermophysical properties were evaluated by means of a factorial experiment design (central composite face centered). Gelatin content was the main factor that affects the thermophysical properties (microstructure and thermal transitions) of the scaffold. The effect of Ge content of the scaffolds for tissue engineering was studied by seeding skin cells on the biopolymers. The cell attachment was not significantly modified at different Ge contents; however, the cell growth rate increased linearly with the decrease of the Ge content. This relationship together with the thermophysical characterization may be used to design scaffolds for tissue engineering.

Adhesion of endothelial cells and endothelial progenitor cells on peptide-linked polymers in shear flow

The initial adhesion of human umbilical vein endothelial cells (HUVECs), cord blood endothelial colony-forming cells (ECFCs), and human blood outgrowth endothelial cells (HBOECs) was studied under radial flow conditions. The surface of a variable shear-rate device was either coated with polymer films or covered by synthetic fibers. Spin-coating was applied to produce smooth polymer films, while fibrous scaffolds were generated by electrospinning. The polymer was composed of hexyl methacrylate, methyl methacrylate, poly(ethylene glycol) methacrylate (PEGMA), and CGRGDS peptide. The peptide was incorporated into the polymer system by coupling to an acrylate-PEG-N-hydroxysuccinimide comonomer. A shear-rate-dependent increase of the attached cells with time was observed with all cell types. The adhesion of ECs increased on RGD-linked polymer surfaces compared to polymers without adhesive peptides. The number of attached ECFCs and HBOECs are significantly higher than that of HUVECs within the entire shear-rate range and surfaces examined, especially on RGD-linked polymers at low shear rates. Their superior adhesion ability of endothelial progenitor cells under flow conditions suggests they are a promising source for in vivo seeding of vascular grafts and shows the potential to be used for self-endothelialized implants.

In vitro endothelialization of electrospun terpolymer scaffolds: evaluation of scaffold type and cell source

A family of methacrylic terpolymer biomaterials was electrospun into three-dimensional scaffolds. The glass transition temperature of the polymer correlates with the morphology of the resulting scaffold. Glassy materials produce scaffolds with discrete fibers and large pore areas (1531±1365 μm(2)), while rubbery materials produce scaffolds with fused fibers and smaller pore areas (154±110 μm(2)). Three different endothelial-like cell populations were seeded onto these scaffolds under static conditions: human umbilical vein endothelial cells (HUVECs), adult human peripheral blood-derived outgrowth endothelial cells, and umbilical cord blood-derived human blood outgrowth endothelial cells. Cellular behavior depended on both cell type and scaffold topography. Specifically, cord blood-derived outgrowth endothelial cells showed more robust adhesion and growth on all scaffolds in comparison to other cell types as measured by the density of adherent cells, the number of proliferative cells, and the enzymatic activity of the adherent cells. Peripheral blood-derived outgrowth cells exhibited less ability to inhabit the terpolymer interfaces in comparison to their cord blood-derived counterparts. HUVECs also exhibited less of a capacity to colonize the terpolymer interfaces in comparison to the cord blood-derived cells. However, the mature endothelial cells did show scaffold-dependent behavior. Specifically, we observed an increase in their ability to populate the low-porosity scaffolds. All cells maintained an endothelial phenotype after 1 week of culture on the electrospun scaffolds.

Design and characterization of sulfobetaine-containing terpolymer biomaterials

A methacrylic terpolymer system with non-fouling interfacial properties was synthesized by the random copolymerization of hexyl methacrylate, methyl methacrylate and sulfobetaine methacrylate (a monomer bearing a zwitterionic pendant group). Polymers were synthesized from feeds containing 0-15 mol.% of the zwitterion-containing methacrylate. Proton nuclear magnetic resonance verified the incorporation of sulfobetaine methacrylate into the polymer structure. Water absorption studies illustrate that the hydrophilicity of the material increases with increasing zwitterion concentration. The biological properties of the polymer were probed by fibrinogen adsorption, human umbilical vein endothelial cell adhesion and growth, and platelet adhesion. Strong resistance to protein adsorption and cell and platelet attachment was observed on materials synthesized from 15 mol.% sulfobetaine methacrylate. Results were compared to the non-fouling behavior of a PEGylated terpolymer formulation and it was observed that the poly(ethylene glycol)-containing materials were slightly more effective at resisting human umbilical vein endothelial cell adhesion and growth over a 7 day incubation period, but the zwitterion-containing materials were equally effective at resisting fibrinogen adsorption and platelet adhesion. The zwitterion-containing materials were electrospun into three-dimensional random fiber scaffolds. Materials synthesized from 15 mol.% of the zwitterion-containing monomer retained their non-fouling character after fabrication into scaffolds.

Endothelial cell adhesion and proliferation to PEGylated polymers with covalently linked RGD peptides

A nonfouling peptide grafted polymer was synthesized that can promote endothelial cell (EC) binding. The polymer was composed of hexyl methacrylate, methyl methacrylate, poly(ethylene glycol) methacrylate, and CGRGDS peptide. The peptide was incorporated into the polymer system either by a chain transfer reaction or by coupling to an acrylate-PEG-N-hydroxysuccinimide (NHS) comonomer. The introduction of PEG chains minimizes protein adsorption. Human umbilical vein ECs and endothelial colony forming cells were cultured on these surfaces in short term and long-term studies. A difference in number and morphology of ECs was observed depending on the method of peptide incorporation. Both cell types adhered better to polymer films containing NHS coupled RGD peptide after 2 h even in the presence of albumin but significant cell detachment occurred after 4 days. Polymer solutions were electrospun into fibrous scaffolds. Both nonfouling and peptide binding characteristics were retained after processing.

Next generation of electrosprayed fibers for tissue regeneration

Electrospinning is a widely established polymer-processing technology that allows generation of fibers (in nanometer to micrometer size) that can be collected to form nonwoven structures. By choosing suitable process parameters and appropriate solvent systems, fiber size can be controlled. Since the technology allows the possibility of tailoring the mechanical properties and biological properties, there has been a significant effort to adapt the technology in tissue regeneration and drug delivery. This review focuses on recent developments in adapting this technology for tissue regeneration applications. In particular, different configurations of nozzles and collector plates are summarized from the view of cell seeding and distribution. Further developments in obtaining thick layers of tissues and thin layered membranes are discussed. Recent advances in porous structure spatial architecture parameters such as pore size, fiber size, fiber stiffness, and matrix turnover are summarized. In addition, possibility of developing simple three-dimensional models using electrosprayed fibers that can be utilized in routine cell culture studies is described.

Design and characterization of PEGylated terpolymer biomaterials

A terpolymer copolymerized from hexyl methacrylate, methyl methacrylate, and poly(ethylene glycol) methacrylate (PEGMA) was synthesized. Polymers containing 0-25 mol % PEGMA were studied. As the mole fraction of PEGMA in the polymer chains increased, the material becomes more hydrophilic as observed by a decrease in the contact angle of water (81 degrees -68 degrees) and an increase in the equilibrium water absorption (0.7-237 wt %). Furthermore, the material shows nonfouling interfacial properties through resistance to protein adsorption and cellular attachment. A total of 1.2 microg/cm(2) fibrinogen, 18,000 HUVECs/cm(2), and 3,000,000 platelets/cm(2) adsorbed or adhered on non-PEGylated materials, whereas very low amounts of protein or cells were observed on materials containing >or=15 mol % PEGMA. Being thermoplastic, the polymer can be processed postsynthesis. To illustrate the processing capabilities of the material, polymer solutions were electrospun into nonwoven fibrous scaffold, which also retained their nonfouling character.

Electrospun scaffold topography affects endothelial cell proliferation, metabolic activity, and morphology

A family of methacrylic terpolymer biomaterials was electrospun into three-dimensional fibrous scaffolds. The glass transition temperature of the polymer correlates with the morphology of the resulting scaffold. Glassy materials produce scaffolds with discrete fibers and a high percent void space (84%) while the rubbery materials produced scaffolds with fused fibers and a much lower percent void space (18%). By electrospinning onto a rotating mandrel, aligned fiber scaffolds were fabricated, and it was shown that controlling the rotation speed of the collector allowed for control over the degree of fiber alignment. The electrospinning was shown to not degrade the number average molecular weight of the polymer chains. Human umbilical vein endothelial cells (HUVECs) were seeded onto the electrospun scaffolds under static conditions and it was found that the morphology of the scaffold controlled the cellular proliferation, the metabolic activity, and the morphology of adherent cells. In particular, HUVECs seeded onto low void space scaffolds exhibited enhanced cellular spreading, enzymatic activity, and proliferation. HUVECs seeded onto aligned fiber scaffolds did not demonstrate increased proliferation; however, the cells did organize themselves in the direction of fiber alignment resulting in cells with elongated morphology.