Quanli Li

Endothelial Cell and Platelet Behavior on Titanium Modified with a Mutilayer of Polyelectrolytes

Endothelial cell seeding, a promising method for improving the performance of vascular grafts, often requires immobilizing biological molecules on the surface of the substrate material. In this study, chitosan (CS) and sulfated chitosan (SCS) multilayers were coated on pure titanium using a layer-by-layer self-assembly technique. The CS—SCS multilayer growth was carried out by first depositing a single layer of positively charged poly(L-lysine) (PLL) on the NaOHtreated titanium substrate, followed by alternate deposition of negatively charged SCS and positively charged CS, and terminated by an outermost layer of SCS. Platelet-rich plasma (PRP) and endothelial cells were seeded on NaOH treated titanium and CS—SCS coated titanium samples, respectively, to evaluate the adhesion and activation of platelets and the behavior of endothelial cells in vitro. The multilayer processed surfaces displayed reduced platelet adhesion and activation, and promoted endothelial cell attachment and growth in vitro. This approach may be used for the fabrication of titanium-based vascular implant surfaces for endothelial promotion.

Anticoagulant surface modification of titanium via layer‐by‐layer assembly of collagen and sulfated chitosan multilayers

Extracellular matrix (ECM)-like biomimetic surface modification of cardiovascular implants is a promising method for improving hemocompatibility. In the present work, collagen (Col) and sulfated chitosan (SCS) multilayers were coated on pure titanium using a layer-by-layer (LBL) self-assembly technique. The Col-SCS multilayer growth was carried out by first depositing a single layer of positively charged poly-L-lysine (PLL) on the NaOH-treated titanium substrate (negatively charged surface), followed by alternate deposition of negatively charged SCS and positively charged Col, and terminated by an outermost layer of SCS. Platelet adhesion in vitro, partial activated thromboplastin time (APTT) and prothrombin time (PT) assays were used to evaluate the hemocompatibility of the Col-SCS multilayer coated titanium. The multilayer processed surfaces displayed reduced platelet adhesion and activation, and prolonged clotting time of APTT and PT compared with untreated titanium. Thus, the approach described here may provide a basis for the preparation of modified titanium surfaces for application in cardiovascular implants.

Biofunctionalization of titanium with PEG and anti-CD34 for hemocompatibility and stimulated endothelialization

Thrombosis and restenosis are the main causes of failure of cardiovascular and other blood-contacting biomedical devices. It is recognized that rapid endothelialization is a promising method for preventing these complications. Convincing evidence in vivo has further emerged that the vascular homing of endothelial progenitor cells (EPCs) contributes to rapid endothelial regeneration. This study deals with improving the hemocompatibility and enhancing EPC colonization of titanium by covalently bonding PEG(600) or PEG(4000), then end-grafting of an anti-CD34 antibody. For this, a chemically hydroxylated titanium surface was aminosilanized, which was further used for covalent grafting of polyethylene glycol and the antibody. The grafting efficiency was verified in each step. In vitro platelet adhesion analysis confirmed superior hemocompatibility of the modified surface over the control. Affinity of EPC to the surface and inhibition of smooth muscle cell adhesion, two prerequisites for endothelialization, are demonstrated in in vitro cell culture. While the coating selectively stimulates EPC adhesion, its antifouling properties prevent formation of an extracellular matrix and proliferation of the cells. Additional affinity for matrix proteins in the coating is considered for further studies. Potent inhibitory effect on macrophage activation and the relative stability of the coating render this technique applicable.

Oriented immobilization of anti-CD34 antibody on titanium surface for self-endothelialization induction.

Inducing spontaneous endothelialization of synthetic cardiovascular implant in vivo is thought to be a promising approach to solve the surface-induced thrombosis and restenosis problem. In the present study, anti-CD34 antibody, a kind of special marker of EPC, was oriented immobilized on titanium surface by means of a layer-by-layer self-assembly coating technique. The multilayer coating was prepared by first depositing one layer of avidin on the NaOH-treated titanium substrate, then depositing a layer of biotinylated protein A binding to the avidin, and finally anti-CD34 antibody was oriented immobilized by protein A binding to the Fc fragment (COOH-terminal of a antibody molecule, which has no antigen binding sites) of the anti-CD34 antibody with its antigen binding fragment (Fab) away from the titanium surface. The coated titanium was exposed to EPC derived from mouse bone marrow in vitro, and implanted into dog femoral arteries. The results suggested that the anti-CD34 antibody immobilized surfaces could increase EPC attachment and capture, and induce rapid complete endothelialization of the lumenal surface of the implant in vivo. It suggests that the approach described here may be used for fabrication of titanium-based vascular implant surfaces for inducing endothelialization in vivo.

An extracellular matrix–like surface modification on titanium improves implant endothelialization through the reduction of platelet adhesion and the capture of endothelial progenitor cells

To address the problem of surface-induced thrombosis and restenosis, an extracellular matrix–like biological membrane was constructed from collagen, heparin, vascular endothelial growth factor, and an anti-CD34 antibody. This membrane was assembled on a titanium surface using a layer-by-layer self-assembly technique and induced the spontaneous endothelialization of synthetic cardiovascular implants in vivo. The multilayer growth process was carried out by first depositing a single layer of positively charged poly-L-lysine on the negatively charged NaOH-treated titanium substrate. This was followed by alternating depositions of negatively charged heparin, containing vascular endothelial growth factor and an anti-CD34 antibody and positively charged collagen, terminating with an outermost layer of heparin containing vascular endothelial growth factor and the anti-CD34 antibody. The uncoated and coated titanium samples were exposed to platelet-rich plasma and endothelial progenitor cells, respectively, under static and flow conditions in vitro. Then, the samples were implanted into dog femoral arteries. The results suggest that the multilayering process led to reduced platelet adhesion and activation, promoted the attachment and growth of endothelial progenitor cells in vitro, and induced the rapid and complete endothelialization of the lumenal surface of the implant. Thus, the approach described here may be used in the fabrication of titanium-based vascular implant surfaces to induce endothelialization in vivo.