Kaiqin Xiong

A biocompatible and functional adhesive amine-rich coating based on dopamine polymerization

Amine groups physiologically play an important role in regulating the growth behavior of cells and they have technological advantages for the conjugation of biomolecules. In this work, we present a method to deposit a copolymerized coating of dopamine and hexamethylendiamine (HD) (PDAM/HD) rich in amine groups onto a target substrate. This method only consists of a simple dip-coating step of the substrate in an aqueous solution consisting of dopamine and HD. Using the technique of PDAM/HD coating, a high density of amine groups of about 30 nmol cm-2 was obtained on the target substrate surface. The PDAM/HD coating showed a high cross-linking degree that is robust enough to resist hydrolysis and swelling. As a vascular stent coating, the PDAM/HD presented good adhesion strength to the substrate and resistance to the deformation behavior of compression and expansion of a stent. Meanwhile, the PDAM/HD coating exhibited good biocompatibility and attenuated the tissue response compared with 316L stainless steel (SS). The primary amine groups of the PDAM/HD coating could be used to effectively immobilize biomolecules containing carboxylic groups such as heparin. These data suggested the promising potential of this PDAM/HD coating for application in the surface modification of biomedical devices.

A simple one-step modification of various materials for introducing effective multi-functional groups

Covalent immobilization of various biomolecules is a desired strategy for bio-multifunctional surface modification. Multi-functionalization of a material surface is considered to be the premise of immobilizing a variety of biomolecules. However, currently adopted methods, used to introduce proper reactive functional groups on material surfaces, mostly are hard to be carried out and frequently can only introduce insufficient functional groups. In this work, we successfully develop the films (GAHD films) prepared via the simple copolymerization of gallic acid (GA) and hexamethylenediamine (HD), which can be deposited on different kinds of material surfaces including metals, ceramics and polymers by a one-step dip-coating method. Moreover, these copolymerized GAHD films possess high concentration of multi-functional groups like carboxyl (COOH), primary amine (-NH2) and quinone groups on the surfaces. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) results prove either the occurrence of Michael addition reaction, Schiff base reaction in the film-forming process, or the existence of COOH, NH2 and quinone groups on the surfaces. The maximum contents of carboxyl and amine on the GAHD film are 24.9 nmol/cm(2) and 31.7 nmol/cm(2) respectively. After dynamical immersion for 30 days, slight swellings can be observed, which reveals that the GAHD films possess good stability. Moreover, Heparin (Hep), fibronectin (Fn) and laminin (Ln) are successfully immobilized on the GAHD film surfaces. The results of cell counting kit-8 (CCK-8) and rhodamine fluorescence photograph indicate that the 1:1.62 GAHD film has good cytocompatibility.

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.

Guidance of Stem Cells to a Target Destination in Vivo by Magnetic Nanoparticles in a Magnetic Field

Stem cells contribute to physiological processes such as postischemic neovascularization and vascular re-endothelialization, which help regenerate myocardial defects or repair vascular injury. However, therapeutic efficacy of stem cell transplantation is often limited by inefficient homing of systemically administered cells, which results in a low number of cells accumulating at sites of pathology. In this study, anti-CD34 antibody-coated magnetic nanoparticles (Fe3O4@PEG-CD34) are shown to have high affinity to stem cells. The results of hemolysis rate and activated partial thromboplastin time (APTT) tests indicate that such nanoparticle may be used safely in the blood system. In vitro studies showed that a nanoparticle concentration of 100 μg/mL gives rise to a significant increase in cell retention using an applicable permanent magnet, exerting minimal negative effect on cell viability and migration. Subsequent in vivo studies indicate that nanopartical can specifically bind stem cells with good magnetic response. Anti-CD34 antibody coated magnetic nanoparticle may be used to help deliver stem cells to a lesion site in the body for better treatment.

Gallic Acid Tailoring Surface Functionalities of Plasma-Polymerized Allylamine-Coated 316L SS to Selectively Direct Vascular Endothelial and Smooth Muscle Cell Fate for Enhanced Endothelialization

The creation of a platform for enhanced vascular endothelia cell (VEC) growth while suppressing vascular smooth muscle cell (VSMC) proliferation offers possibility for advanced coatings of vascular stents. Gallic acid (GA), a chemically unique phenolic acid with important biological functions, presents benefits to the cardiovascular disease therapy because of its superior antioxidant effect and a selectivity to support the growth of ECs more than SMCs. In this study, GA was explored to tailor such a multifunctional stent surface combined with plasma polymerization technique. On the basis of the chemical coupling reaction, GA was bound to an amine-group-rich plasma-polymerized allylamine (PPAam) coating. The GA-functionalized PPAam (GA-PPAam) surface created a favorable microenvironment to obtain high ECs and SMCs selectivity. The GA-PPAam coating showed remarkable enhancement in the adhesion, viability, proliferation, migration, and release of nitric oxide (NO) of human umbilical vein endothelial cells (HUVECs). The GA-PPAam coating also resulted in remarkable inhibition effect on human umbilical artery smooth muscle cell (HUASMC) adhesion and proliferation. These striking findings may provide a guide for designing the new generation of multifunctional vascular devices.

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.

Facile immobilization of vascular endothelial growth factor on a tannic acid-functionalized plasma-polymerized allylamine coating rich in quinone groups

Biomolecules with thiol or amine groups can easily be covalently immobilized onto a substrate equipped with quinone groups in a mild alkali buffer solution based on Schiff base or Michael addition reactions. In this study, we reported a simple two-step approach to creating a functional coating with abundant quinone groups for facile immobilization of vascular endothelial growth factor (VEGF) in mild phosphate buffered saline (PBS, pH 7.4). This approach initially involved the deposition of an amine-bearing plasma-polymerized allylamine (PPAam) coating. Tannic acid (TA) was subsequently used for introducing phenolic hydroxylic hydroxyl/quinone groups. The results of water contact angles (WCAs), Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis (XPS) revealed the effective conjugation of TA to PPAam, as well as the immobilization of VEGF to TA-functionalized PPAam (TA-PPAam). The result of a quartz crystal microbalance with dissipation (QCM-D) showed that 158 ± 13 ng cm−2 of VEGF was successfully immobilized onto the TA-PPAam surface. TA-PPAam bound with VEGF significantly enhanced human umbilical vein endothelial cell (HUVEC) proliferation, indicating the good retention of the bioactivity of VEGF. The TA-PPAam functional coating provided a novel, facile strategy for the covalent immobilization of biomolecules, especially growth factors, under mild reaction conditions.

Proliferation and functionality of human umbilical vein endothelial cells on angiopoietin-1 immobilized 316L stainless steel

Angiopoietin-1 (Ang-1), a vascular-specific growth factor secreted from periendothelial cells, has drawn increasing attention in clinical applications because it can promote the reconstruction of blood vessels and has an anti-inflammatory effect compared with vascular endothelial growth factor (VEGF). In this study, Ang-1 was firstly covalently conjugated onto polydopamine (PDA) coated 316L stainless steel (SS), aiming at developing an Ang-l modified surface for endothelialization. The results of Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) measurements confirmed the successful immobilization of Ang-1. Quartz crystal microbalance with dissipation (QCM-D) studies demonstrated that ∼154 ng cm-2 of Ang-1 were bonded onto the PDA surface. To confirm its functionality, the effects of the Ang-1-modified coating on the growth behavior of human umbilical vein endothelial cells (HUVECs) were studied. As a result, the Ang-1 functionalized surface significantly enhanced endothelial cell adhesion, proliferation and migration. It was also found the Ang-1 functionalized coating could promote the release of nitric oxide (NO), secretion of prostacyclin-2 (PGI2) and inhibit the apoptosis of HUVECs. These data effectively suggested angiopoietin-1 could potentially be applied not only in neovascularization such as ischemic reperfusion and vascularization of tissue engineering scaffolds, but also in surface modification of cardiovascular implant materials for re-endothelialization.

Multifunctional coating based on EPC-specific peptide and phospholipid polymers for potential applications in cardiovascular implants fate

Surface biofunctional modification of cardiovascular implants via the conjugation of biomolecules to prevent thrombosis and restenosis formation and to accelerate endothelialization has attracted considerable research interest. In this study, we aimed to develop a multifunctional surface that could exhibit good hemocompatibility and function well in inducing desirable vascular cell-material interactions. The multifunctional coating (PCDLOPTPT@Ti), containing phosphorylcholine groups and endothelial progenitor cell (EPC)-specific peptides (PT), was prepared on titanium (Ti) surfaces via chemical conjugation. The results of platelet adhesion, activation, fibrinogen denaturation, and whole blood dynamic adhesion testing indicated that the PCDLOPTPT@Ti coating presented a better hemocompatibility when compared with bare Ti and other control samples. In vitro EPC and smooth muscle cell (SMC) cultures showed that the PCDLOPTPT@Ti coating significantly promoted the adhesion and proliferation of EPCs and inhibited the attachment and proliferation of SMCs. In vivo animal tests further confirmed that the PCDLOPTPT@Ti coating effectively inhibited thrombus formation and intimal hyperplasia while supporting endothelium regeneration. These results effectively suggest that the PCDLOPTPT@Ti coating may be promising as a coating on cardiovascular implants.

Biocompatibility studies of poly(ethylene glycol)–modified titanium for cardiovascular devices

The rapid protein adsorption on a material surface causes blood coagulation, platelet activation, and complement system activation, which poses a risk for failure of cardiovascular devices. In this study, a chemically hydroxylated titanium surface was aminosilanized and covalently grafted with poly(ethylene glycol). The reaction conditions on the grafted quantity were studied by the respective amine and carboxyl densities. The blood compatibility of the PEGylated surfaces with different poly(ethylene glycol) densities and chain lengths was evaluated; the PEGylated surfaces with higher grafted density and longer chain length had less fibrinogen adsorption, less fibrinogen γ-chain exposed, less adherent platelets, and lower activation of the adherent platelets. In addition to the influence on blood, the longer chain PEGylated surfaces resisted, not only smooth muscle cell attachment and proliferation, but also macrophage attachment and death. This method is a good candidate for improving cardiovascular implant surfaces.