Human umbilical vein endothelial cell culture on heparin-like microcarriers

Fn-HMGB1 Adsorption Behavior Initiates Early Immune Recognition and Subsequent Osteoinduction of Biomaterials

Implantable biomaterials are widely used in bone tissue engineering, but little is still known about how they initiate early immune recognition and the initial dynamics. Herein, the early immune recognition and subsequent osteoinduction of biphasic calcium phosphate (BCP) after implantation to the protein adsorption behavior is attributed. By liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis, the biomaterial-related molecular patterns (BAMPs) formed after BCP implantation are mapped, dominated by the highly expressed extracellular matrix protein fibronectin (Fn) and the high mobility group box 1 (HMGB1). Molecular dynamics simulations show that Fn has the ability to bind more readily to the BCP surface than HMGB1. The preferential binding of Fn provides a higher adsorption energy for HMGB1. Furthermore, multiple hydrogen bonding sites between HMGB1 and Fn are demonstrated using a molecular docking approach. Ultimately, the formation of BAMPs through HMGB1 antagonist glycyrrhizic acid (GA), resulting in impaired immune recognition of myeloid differentiation factor 88 (MYD88) mediated dendritic cells (DCs) and macrophages (Mφs), as well as failed osteoinduction processes is obstructed. This study introduces a mechanism for early immune recognition of implant materials based on protein adsorption, providing perspectives for future design and application of tissue engineering materials.

PolyNaSS grafting on titanium surfaces enhances osteoblast differentiation and inhibits Staphylococcus aureus adhesion

Titanium surface modifications to simultaneously prevent bacterial adhesion but promote bone-cell functions could be highly beneficial for improving implant osseointegration. In the present in vitro study, the effect of sulfonate groups on titanium surfaces was investigated with respect to both S. aureus adhesion and osteoblast functions pertinent to new bone formation. Commercial pure titanium (cpTi) squares were oxydized (Tiox), grafted with poly(sodium styrene sulfonate) groups (Tigraft) by covalent bonding using radical polymerization, and were characterized by infrared spectroscopy (HATR-FTIR) and colorimetry. Bacterial adhesion study showed that Tigraft exhibited high inhibition of S. aureus adhesion S at levels >90 %, when compared to cpTi (P < 0.05). In contrast osteoblasts adhesion was similar on all three titanium surfaces. While the kinetics of cell proliferation were similar on the three titanium surfaces, Alkaline phosphatase-specific activity of osteoblasts cultured on Tigraft surfaces was twofold higher than that observed on either on Tiox or cpTi surfaces (P < 0.01). More importantly, the amount and the distribution of calcium-containing nodules was different. The total area covered by calcium-containing nodules was 2.2-fold higher on the Tigraft as compared to either Tiox or cpTi surfaces (P < 0.01). These results provide evidence that poly(sodium styrene sulfonate) groups grafting on cpTi simultaneously inhibits bacteria adhesion but promote osteoblast function pertinent to new bone formation. Such modified titanium surfaces offer a promising strategy for preventing biofilm-related infections and enhancing osteointegration of implants in orthopaedic and dental applications.

The influence of biomaterials on endothelial cell thrombogenicity

Driven by tissue engineering and regenerative medicine, endothelial cells are being used in combination with biomaterials in a number of applications for the purpose of improving blood compatibility and host integration. Endothelialized vascular grafts are beginning to be used clinically with some success in some centers, while endothelial seeding is being explored as a means of creating a vasculature within engineered tissues. The underlying assumption of this strategy is that when cultured on artificial biomaterials, a confluent layer of endothelial cells maintain their non-thrombogenic phenotype. In this review the existing knowledge base of endothelial cell thrombogenicity cultured on a number of different biomaterials is summarized. The importance of selecting appropriate endpoint measures that are most reflective of overall surface thrombogenicity is the focus of this review. Endothelial cells inhibit thrombosis through three interconnected regulatory systems (1) the coagulation cascade, (2) the cellular components of the blood such as leukocytes and platelets and (3) the complement cascade, and also through effects on fibrinolysis and vascular tone, the latter which influences blood flow. Thus, in order to demonstrate the thrombogenic benefit of seeding a biomaterial with EC, the conditions under which EC surfaces are more likely to exhibit lower thrombogenicity than unseeded biomaterial surfaces need to be consistent with the experimental context. The endpoints selected should be appropriate for the dominant thrombotic process that occurs under the given experimental conditions.

Surface modification of silicone intraocular implants to inhibit cell proliferation

Photo-cross-linkable polymers bearing cinnamic, sulfonate, and carboxylate groups were synthesized by radical polymerization leading to randomly distributed copolymers. These polymers were used to coat silicone intraocular lenses in order to reduce posterior capsule opacification, also named "secondary cataract". We previously demonstrated that polymers containing both carboxylate and sulfonate groups inhibit cell proliferation, and formulations with the ratio R = COO-/(COO- + SO3-) equal to 0.64 provided the highest inhibitory effect. Ionic polymers with this formulation were synthesized to contain a monomer with pendant siloxane groups in order to get compatibility with the silicone matrix of the intraocular lenses. Anchorage of the ionic polymer at the surface of the silicone implant was achieved by a cycloaddition reaction of the photosensitive groups according to two options. These modified silicone surfaces grafted onto intraocular lenses were shown to inhibit cell proliferation to 60%.

Endothelial cell adhesion on RGD-containing methacrylate terpolymers

Hexyl methacrylate (HMA), methyl methacrylate (MMA), and methacrylic acid (MAA) were used as comonomers to produce a low glass transition temperature material, potentially useful in fabricating a small diameter vascular graft. Because it has been shown that grafts seeded with endothelial cells have better resistance to thrombosis, RGD-based peptide sequences were incorporated into the terpolymer. The two methods used for incorporating peptide sequences were a chain transfer reaction during polymerization, and a coupling reaction between the amine terminus of the peptide and the carboxyl groups of the MAA. Polymers were synthesized using the chain transfer reaction with peptide concentrations ranging from 1.7 to 7.0 micromol/g. Weight-average molecular weights decreased with increasing peptide concentration from 310,000 g/mol for the terpolymer without peptide, to 110,000 g/mol for a peptide concentration of 7.0 micromol/g. As a result, Young's modulus decreased with increasing peptide concentration. Terpolymers with peptides attached through a coupling reaction showed no decrease in molecular weight or mechanical properties. Confocal microscopy showed cells seeded on the RGD surfaces adhered and spread, while terpolymers with RGE sequences showed cells that were rounded and not spreading. Cell density on RGD surfaces increased with increasing peptide concentration up to a bulk peptide concentration of approximately 5 micromol/g and reached a plateau, which indicated the minimum peptide concentration necessary for maximum cell adhesion.

Modulating fibroblast cell proliferation with functionalized poly(methyl methacrylate) based copolymers: chemical composition and monomer distribution effect

Poly(methyl methacrylate)-based terpolymers bearing sulfonate and carboxylate groups have been synthesized by radical copolymerization leading to polymers with random distributions of ionic monomer units. Fibroblast cells were seeded on terpolymers of various molar compositions of ionic groups. Kinetics of the cell proliferation were examined and systematically compared to the nonfunctionalized control polymer, poly(methyl methacrylate). Modulation of cell proliferation was observed on 15% ionic monomer content copolymers of various compositions (R = COO(-)/(COO(-) + SO(3)(-)) and varies from 0 to 1). The inhibition percentage of cell proliferation calculated for each polymer by comparison to the cell proliferation on the control was plotted against R and gave a maximum value for R close to 0.55. Copolymers with ionic group contents higher or lower than 15% exhibit inhibition percentages fitting with those previously observed for the same R values, showing that the hydrophilic properties are not sufficient to explain the modulation effect of this material toward cells. Moreover, for each polymer tested, cells, even if inhibited in growth, were shown to be viable, indicating that the synthesized terpolymers exhibit cytostatic properties excluding any cytotoxic effect. Such polymers may be used for the fabrication of biocompatible intraocular lenses and prevent secondary cataract.

Randomness and biospecificity: random copolymers are capable of biospecific molecular recognition in living systems

Biospecific molecular recognition in living systems is known to be based on the lock and key principle as proposed by Emil Fischer. Based on this concept, biospecific polymers have been produced synthetically by attaching biospecific 'keys' to the polymer chain. We postulate that biospecificity can be achieved by alternative means, namely random substitution of a preformed polymer with suitable chemical groups or random copolymerization of suitable functional monomers. Such polymers, we suggest, will contain arrangements of the chemical functions which mimic natural biospecific sites and the probability of occurrence of such arrangements will depend on the average composition of the polymer. In support of this principle, we have developed several functional random copolymer systems which possess a variety of biological properties depending on the type of chemical function. Examples are: polymers possessing anticoagulant properties similar to those of heparin; polymers which interact specifically with components of the immune system; and polymers which, in contact with cells, affect their growth and metabolism. In the case of statistical copolymers possessing 'DNA-like' properties obtained by phosphorylation of hydroxylated polystyrene derivatives, Monte Carlo simulations were used to determine the distribution of phosphodiester (PDE) groups along the chains and to compute the probabilities of occurrence of particular arrangements of PDE found in the 'DNA-like' sites. The results showed that these sites are made up of PDE groups separated by distances that closely match those between the same groups along a generatrix of the DNA double-helix cylinder. These findings offer the prospect of manufacturing polymeric biomaterials endowed with biomimetic character. Moreover, they provide the basis for a hypothesis regarding the appearance of biospecificity at the origin of life, suggesting that biospecific structures may have evolved by natural selection from purely random copolymers. It is likely therefore that biospecificity is a continuous function of randomness, arising from purely statistical distributions of reactivity and evolving into precisely defined structures such as those involved in ligand-receptor interactions.

Adsorption of fibronectin and vitronectin onto Primaria and tissue culture polystyrene and relationship to the mechanism of initial attachment of human vein endothelial cells and BHK-21 fibroblasts

The two cell culture substrata, tissue culture polystyrene (TCPS) and Primaria, were compared in order to determine whether a nitrogen-containing surface such as Primaria attracts cells by a different mechanism to an oxygen-containing surface (TCPS). The amounts of vitronectin (Vn) and fibronectin (Fn) which adsorb from the fetal bovine serum (FBS) component of the culture medium onto Primaria and TCPS were determined. Primaria adsorbed two- to threefold more Fn than TCPS, but adsorbed similar amounts of Vn from medium containing FBS. The Fn and Vn binding sites on Primaria were distinct, as adsorption was non-competitive between these two proteins. The amounts of Fn and Vn that adsorbed onto the two surfaces were compared to the concentration dependence of the cell attachment activities of Fn and Vn. Whereas the amounts of Fn which adsorbed onto TCPS were suboptimal for cell attachment, Primaria adsorbed an Fn surface density that was supraoptimal for attachment of human vein endothelial cells and BHK-21 fibroblasts. We conclude that Primaria differs from TCPS in that both Fn and Vn mediate initial cell attachment to Primaria when the culture medium contains FBS, whereas cell attachment to TCPS is dependent upon Vn.

Conformational changes of fibronectin induced by polystyrene derivatives with a heparin-like function

It was previously reported that polystyrene substituted with the sulfonate group, PSSO3, which has anticoagulant heparin-like properties, and then coated with fibronectin supports the growth of human umbilical vein endothelial cells. On the other hand, polystyrene substituted with the amino acid sulfamide group, PSSO2-Asp, which has a higher anticoagulant activity, and then coated with fibronectin no longer supported the growth of endothelial cells. We report here that, while the affinity of fibronectin to either polymer is of the same order of magnitude, fibronectin is adsorbed onto the PSSO2-Asp polymer in a different conformation compared to the PSSO3 polymer. This was shown by a higher binding of polyclonal antifibronectin antibodies to fibronectin-coated PSSO2-Asp polymer, and by a decreased susceptibility of the coated fibronectin to proteolysis by thermolysin. This study provides evidence that a solid phase substrate with a strong heparin-like function may influence the conformation and biological properties of fibronectin.