Mussel-inspired immobilization of vascular endothelial growth factor (VEGF) for enhanced endothelialization of vascular grafts

Mussel-inspired human gelatin nanocoating for creating biologically adhesive surfaces

Recombinant human gelatin was conjugated with dopamine using carbodiimide as a surface modifier. This dopamine-coupled human gelatin (D-rhG) was characterized by ¹H-nuclear magnetic resonance, mass spectroscopy, and circular dichroism. D-rhG-coated surface properties were analyzed by physicochemical methods. Additionally, cell attachment and growth on the modified surfaces was assessed using human umbilical endothelial cells. Binding of gelatin onto titanium was significantly enhanced by dopamine conjugation. The thickness of the D-rhG coating depended on the treatment pH; thicker layers were formed at higher pH values, with a maximum thickness of 30 nm. D-rhG enhanced the binding of collagen-binding vascular endothelial growth factor and cell adhesion as compared with gelatin alone, even at the same surface concentration. The D-rhG surface modifier enhanced substrate binding by creating an adhesive nanointerface that increased specific protein binding and cell attachment.

Mussel inspired coating of a biocompatible cyclodextrin based polymer onto CoCr vascular stents

During the past decade, drug-eluting stents (DES) have been widely used for the treatment of occlusive coronary artery diseases. They are supposed to reduce the incidence of early in-stent restenosis by the elution of highly hydrophobic antiproliferative drugs. Nevertheless, the absence of long-term activity of these devices is responsible for late acute thrombosis probably due to the delayed re-endothelialization of the arterial wall over the bare metallic stent struts. Thus, a new generation of DES with a sustained release of therapeutic agents is required to improve long-term results of these devices. In this article, we report an original functionalization of CoCr vascular devices with a hydrophilic, biocompatible and biodegradable cyclodextrins based polymer which acts as a reservoir for lipophilic drugs allowing the sustained release of antiproliferative drugs. In this setting, polydopamine (PDA), a strong adhesive biopolymer, was applied as a first coating layer onto the surface of the metallic CoCr device in order to promote the strong anchorage of a cyclodextrin polymer. This polymer was generated "in situ" from the methylated cyclodextrins and citric acid as a cross-linking agent through a polycondensation reaction. After optimization of the grafting process, the amount of cyclodextrin polymer coated onto the CoCr device was quantified by colorimetric titrations and the resulting film was characterized by scanning electron microscopy (SEM) investigations. The cytocompatibility of the resulting coated film was assessed by cell proliferation and vitality tests. Finally, the ability of this coated device to act as a drug-eluting system was evaluated with paclitaxel, a strong hydrophobic antiproliferative drug, a reference drug used in current vascular drug-eluting stents.

Effects of polydopamine functionalized titanium dioxide nanotubes on endothelial cell and smooth muscle cell

Previous investigations have demonstrated that TiO2 nanotubes (NTs) with particular structure cues could control the behavior of different types of cells, including endothelial cells (ECs) and smooth muscle cells (SMCs). Besides, polydopamine (PDA) modified surfaces were reported to be beneficial to increase the proliferation and viability of ECs and meanwhile could inhibit the proliferation of SMCs. The TiO2 nanotubes (NTs) were functionalized with polydopamine (PDA) (PDA/NTs) to study the synergetic effect of both nanotopography (NTs) and chemical cues (PDA) of TiO2 nanotubes on the regulation of cellular behavior of ECs and SMCs. The PDA-modified TiO2 nanotubes were subjected to field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and water contact angle (WCA) analysis. In vitro cell culture tests confirmed that, comparing with flat titanium (Ti) and TiO2 nanotubes, PDA/NTs surface synergistically promoted ECs attachment, proliferation, migration and release of nitric oxide (NO). Meanwhile, the PDA/NTs performed well in reducing SMCs adhesion and proliferation. This novel approach might provide a new platform to investigate the synergistic effect of local chemistry and topography, as well as the applications for the development of titanium-based implants for enhanced endothelialization.

Microfluidic generation of polydopamine gradients on hydrophobic surfaces

Engineered surface-bound molecular gradients are of great importance for a range of biological applications. In this paper, we fabricated a polydopamine gradient on a hydrophobic surface. A microfluidic device was used to generate a covalently conjugated gradient of polydopamine (PDA), which changed the wettabilty and the surface energy of the substrate. The gradient was subsequently used to enable the spatial deposition of adhesive proteins on the surface. When seeded with human adipose mesenchymal stem cells, the PDA-graded surface induced a gradient of cell adhesion and spreading. The PDA gradient developed in this study is a promising tool for controlling cellular behavior and may be useful in various biological applications.

Immobilization of bone morphogenetic protein on DOPA- or dopamine-treated titanium surfaces to enhance osseointegration

Titanium was treated with 3,4-dihydroxy-L-phenylalanine (DOPA) or dopamine to immobilize bone morphogenetic protein-2 (BMP2), a biomolecule. DOPA and dopamine solutions turned into suspensions, and precipitates were produced at high pH. Both treatments produced a brown surface on titanium that was thicker at high pH than low pH. Dopamine produced a thicker layer than DOPA. The hydrophobicity of the surfaces increased after treatment with dopamine independent of pH. Furthermore, there were more amino groups in the layers formed at pH 8.5 than pH 4.5 in both treatments. Dopamine treatment produced more amino groups in the layer than DOPA. BMP2 was immobilized on the treated surfaces via a coupling reaction using carbodiimide. More BMP2 was immobilized on surfaces treated at pH 8.5 than pH 4.5 in both treatments. The immobilized BMP induced specific signal transduction and alkali phosphatase, a differentiation marker. Thus, the present study demonstrates that titanium treated with DOPA or dopamine can become bioactive via the surface immobilization of BMP2, which induces specific signal transduction.

Superior in vivo compatibility of hydrophilic polymer coated prosthetic vascular grafts

PURPOSE

Protein adsorption, cell adhesion and graft patency was compared in hydrophilic versus hydrophobic polymer-coated prosthetic vascular grafts. We hypothesize that in vivo compatibility of hydrophilic polymer-coated prosthetic vascular grafts is superior to in vivo compatibility of hydrophobic grafts.

METHODS

A pairwise side-to-side common carotid artery interposition graft was placed eight female landrace goats (mean weight 55 kg). Protein adsorption was assessed using Western Blot in two hydrophilic and two hydrophobic grafts harvested after three days. Graft patency was monitored for 28 days in six goats with continuous wave Doppler ultrasonography. Adherence of endothelial cells, leukocytes and platelets was determined with ELISA and compared between the two graft types after 28 days.

RESULTS

After three days, more ApoA-I, albumin and VEGF and less fibrin adsorbed to hydrophilic grafts. After 28 days, compared to hydrophobic grafts, higher numbers of endothelial cells were present on hydrophilic grafts (P=0.016), and less thrombocytes and leukocytes (P=0.012 and 0.024, respectively). Two out of eight hydrophobic grafts lost patency, while none of the hydrophilic grafts failed (P=0.157).

CONCLUSIONS

Hydrophilic polymer-coated vascular grafts have superior in vivo compatibility when compared to hydrophobic grafts as characterized by reduced platelet and leukocyte adherence as well as higher endothelialization.

Polydopamine-assisted osteoinductive peptide immobilization of polymer scaffolds for enhanced bone regeneration by human adipose-derived stem cells

Immobilization of osteoinductive molecules, including growth factors or peptides, on polymer scaffolds is critical for improving stem cell-mediated bone tissue engineering. Such molecules provide osteogenesis-stimulating signals for stem cells. Typical methods used for polymeric scaffold modification (e.g., chemical conjugation or physical adsorption), however, have limitations (e.g., multistep, complicated procedures, material denaturation, batch-to-batch inconsistency, and inadequate conjugation) that diminish the overall efficiency of the process. Therefore, in this study, we report a biologically inspired strategy to prepare functional polymer scaffolds that efficiently regulate the osteogenic differentiation of human adipose-derived stem cells (hADSCs). Polymerization of dopamine (DA), a repeated motif observed in mussel adhesive protein, under alkaline pH conditions, allows for coating of a polydopamine (pDA) layer onto polymer scaffolds. Our study demonstrates that predeposition of a pDA layer facilitates highly efficient, simple immobilization of peptides derived from osteogenic growth factor (bone morphogenetic protein-2; BMP-2) on poly(lactic-co-glycolic acid) (PLGA) scaffolds via catechol chemistry. The BMP-2 peptide-immobilized PLGA scaffolds greatly enhanced in vitro osteogenic differentiation and calcium mineralization of hADSCs using either osteogenic medium or nonosteogenic medium. Furthermore, transplantation of hADSCs using pDA-BMP-2-PLGA scaffolds significantly promoted in vivo bone formation in critical-sized calvarial bone defects. Therefore, pDA-mediated catechol functionalization would be a simple and effective method for developing tissue engineering scaffolds exhibiting enhanced osteoinductivity. To the best of our knowledge, this is the first study demonstrating that pDA-mediated surface modification of polymer scaffolds potentiates the regenerative capacity of human stem cells for healing tissue defect in vivo.

Bio-orthogonal and combinatorial approaches for the design of binding growth factors

Merrifield chemistry enables the convenient synthesis of oligonucleotides and peptides, while recombinant DNA technology has facilitated protein engineering. Recently, protein engineering has been extended into bio-orthogonal protein engineering by the development of specific chemical or enzymatic modification technologies. The combinatorial approach of molecular evolutionary engineering (or in vitro selection) has also provided a new design tool for functional peptides. These methodologies have enabled the development of various new proteinaceous materials for biological and medical applications. Here, we will discuss recent progress in the molecular design of proteins with respect to the preparation of binding growth factors, which are of increasing importance in the biomaterials field.

Sustained delivery of siRNA from dopamine-coated stainless steel surfaces

Dopamine, an adhesive protein can be covalently deposited onto biomaterials. In this study, we evaluated the ability of dopamine-coated surfaces for small interfering RNA (siRNA) immobilization and release. Dopamine was deposited onto 316L stainless steel discs either as a monolayer at acidic pH or as polydopamine at alkaline pH, following which siRNA was immobilized onto these discs. To investigate the RNA interference ability of immobilized siRNA, reduction of luciferase expression in HeLa, and reduction of Egr-1 expression and cell proliferation in human aortic smooth muscle cells (HAoSMCs) were determined. Dopamine treatment of 316L stainless steel discs under both the acidic and alkaline conditions resulted in the deposition of amino (NH2) groups, which enabled electrostatic immobilization of siRNA. The immobilized siRNA was released from both types of coatings, and enhanced the percent suppression of firefly luciferase activity of HeLa significantly up to ~96.5% compared to HeLa on non-dopamine controls (18%). Both the release of siRNA and the percent suppression of firefly luciferase activity were sustained for at least 7 days. In another set of experiments, siRNA sequences targeting to inhibit the activity of the transcription factor Egr-1 were eluted from dopamine-coated surfaces to HAoSMCs. Egr-1 siRNA eluted from dopamine-coated surfaces, significantly reduced the proliferation of HAoSMCs and their protein expression of Egr-1. Therefore, this method of surface immobilization of siRNA onto dopamine-coated surfaces might be effective for nucleic acid delivery from stents.

Electrospun fibers immobilized with bone forming peptide-1 derived from BMP7 for guided bone regeneration

The development of ideal barrier membranes with appropriate porosity and bioactivity is essential for the guidance of new bone formation in orthopedic and craniomaxillofacial surgery. In this study, we developed bioactive electrospun fibers based on poly (lactide-co-glycolic acid) (PLGA) by immobilizing bone-forming peptide 1 (BFP1) derived from the immature region of bone morphogenetic protein 7 (BMP7). We exploited polydopamine chemistry for the immobilization of BFP1; polydopamine (PD) was coated on the electrospun PLGA fibers, on which BFP1 was subsequently immobilized under weakly basic conditions. The immobilization of BFP1 was verified by characterizing the surface chemical composition and quantitatively measured by fluorescamine assay. The immobilization of BPF1 on the electrospun fibers supported the compact distribution of collagen I and the spreading of human mesenchymal stem cells (hMSCs). SEM micrographs demonstrated the aggregation of globular mineral accretions, with significant increases in ALP activity and calcium deposition when hMSCs were cultured on fibers immobilized with BFP1 for 14 days. We then implanted the prepared fibers onto mouse calvarial defects and analyzed bone formation after 2 months. Semi-quantification of bone growth from representative X-ray images showed that the bone area was approximately 20% in the defect-only group, while the group implanted with PLGA fibers showed significant improvements of 44.27 ± 7.37% and 57.59 ± 15.24% in the groups implanted with PD-coated PLGA and with BFP1-coated PLGA, respectively. Based on these results, our approach may be a promising tool to develop clinically-applicable bioactive membranes for guided bone regeneration."

Strategies and techniques to enhance the in situ endothelialization of small-diameter biodegradable polymeric vascular grafts

Due to the lack of success in small-diameter (<6 mm) prosthetic vascular grafts, a variety of strategies have evolved utilizing a tissue-engineering approach. Much of this work has focused on enhancing the endothelialization of these grafts. A healthy, confluent endothelial layer provides dynamic control over homeo-stasis, influencing and preventing thrombosis and smooth muscle cell proliferation that can lead to intimal hyperplasia. Strategies to improve endothelialization of biodegradable polymeric grafts have encompassed both chemical and physical modifications to graft surfaces, many focusing on the recruitment of endothelial and endothelial progenitor cells. This review aims to provide a compilation of current and developing strategies that utilize in situ endothelialization to improve vascular graft outcomes, providing a context for the future directions of vascular tissue-engineering strategies that do not require preprocedural cell seeding.