A pinboard by
Fatemeh Karimi

PhD student, University of Melbourne


Marrying polymer design with advanced cell biology for application in improved vascular grafts

Cardiovascular disease remains a leading cause of death worldwide, with 31% of all deaths being attributed to cardiovascular disease. For blood vessels with medium and large diameter (>6 mm), synthetic polymers such as polyethylne terphethalate or dacron and expanded polytetrafluoroethylene are successfully used when there is high blood flow and therefore low flow resistance. Despite synthetic polymers already being used in the larger diameter blood vessels, the use of synthetic grafts for coronary bypass grafting, which involve small diameter vessels (<6 mm) is limited for long term applications. This is due to a lack of compatibility between the circulating blood and the polymeric small diameter vascular grafts implanted in the body which leads to the formation of blood clots on the biomaterial surfaces. The blood clot formation leads to occlusion of the vascular lumen and finally, life-threatening issues such as tissue ischemia or stroke occur. In addition to this important issue, there is an increasing worldwide demand for common blood-contacting cardiovascular devices with better performance.

An attractive strategy for improving blood compatibility is to generate polymeric biomaterials that foster a confluent and functioning endothelial cell layer- the cells that cover the surface of the cardiovascular system. Several strategies have been explored to improve endothelialization, but no blood compatible biomaterials have obtained commercial success as of yet. The lack of blood compatible interfaces is one of the most pressing challenges in the biomaterials field. My research project aims to design and develop blood-compatible polymeric biomaterials using nanotechnology; these will ultimately aid in the development of improved cardiovascular devices such as small diameter vascular grafts. As such, these polymeric biomaterials have great potential for commercialization and introduction into clinics as the next generation of polymeric platforms to could save the life of millions of people who are at risk of developing coronary heart disease in the near future.


RGD peptide and graphene oxide co-functionalized PLGA nanofiber scaffolds for vascular tissue engineering.

Abstract: In recent years, much research has been suggested and examined for the development of tissue engineering scaffolds to promote cellular behaviors. In our study, RGD peptide and graphene oxide (GO) co-functionalized poly(lactide-co-glycolide, PLGA) (RGD-GO-PLGA) nanofiber mats were fabricated via electrospinning, and their physicochemical and thermal properties were characterized to explore their potential as biofunctional scaffolds for vascular tissue engineering. Scanning electron microscopy images revealed that the RGD-GO-PLGA nanofiber mats were readily fabricated and composed of random-oriented electrospun nanofibers with average diameter of 558 nm. The successful co-functionalization of RGD peptide and GO into the PLGA nanofibers was confirmed by Fourier-transform infrared spectroscopic analysis. Moreover, the surface hydrophilicity of the nanofiber mats was markedly increased by co-functionalizing with RGD peptide and GO. It was found that the mats were thermally stable under the cell culture condition. Furthermore, the initial attachment and proliferation of primarily cultured vascular smooth muscle cells (VSMCs) on the RGD-GO-PLGA nanofiber mats were evaluated. It was revealed that the RGD-GO-PLGA nanofiber mats can effectively promote the growth of VSMCs. In conclusion, our findings suggest that the RGD-GO-PLGA nanofiber mats can be promising candidates for tissue engineering scaffolds effective for the regeneration of vascular smooth muscle.

Pub.: 26 Jul '17, Pinned: 28 Aug '17

Dual functionalization of poly(ε-caprolactone) film surface through supramolecular assembly with the aim of promoting in situ endothelial progenitor cell attachment on vascular grafts.

Abstract: In this study, we developed a method for the dual functionalization of a poly(ε-caprolactone) (PCL) surface by means of the supramolecular assembly technology. Polyethylene glycol (PEG), with resistance to protein adsorption, and TPSLEQRTVYAK (TPS) peptide, which can specifically bind endothelial progenitor cells (EPCs), were immobilized on the PCL surface through host-guest inclusion complexation. The chemical composition as well as the hydrophilic/hydrophobic property of the functionalized surface was characterized by X-ray photoelectron spectroscopy and water contact angle measurements. The relative composition of two functional molecules on the dually functionalized surface was further analyzed by fluorescence quantification. Finally, the fibrinogen adsorption, platelet adhesion and activation, and selective attachment of cells were systematically evaluated on the functionalized surface. The results show that the presence of PEG evidently inhibited the adsorption of plasma protein and platelet adhesion, thus reducing the possibility of thrombus formation on the functionalized surface. At the same time, the TPS-functionalized surface demonstrated enhanced attachment toward EPC compared with the surfaces in the absence of TPS functionalization. For the surface functionalized by both PEG and TPS, the functions provided by each component have been well demonstrated. The relative composition of the PEG and TPS could be further fine-tuned by adjusting the feeding ratio. All these results indicate that the dually functionalized surface developed in this study is a suitable candidate for vascular graft to induce and promote in situ endothelialization.

Pub.: 08 Oct '13, Pinned: 28 Aug '17

Engineering interaction between bone marrow derived endothelial cells and electrospun surfaces for artificial vascular graft applications.

Abstract: The aim of this investigation was to understand and engineer the interactions between endothelial cells and the electrospun (ES) polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) nanofiber surfaces and evaluate their potential for endothelialization. Elastomeric PVDF-HFP samples were electrospun to evaluate their potential use as small diameter artificial vascular graft scaffold (SDAVG) and compared with solvent cast (SC) PVDF-HFP films. We examined the consequences of fibrinogen adsorption onto the ES and SC samples for endothelialisation. Bone marrow derived endothelial cells (BMEC) of human origin were incubated with the test and control samples and their attachment, proliferation, and viability were examined. The nature of interaction of fibrinogen with SC and ES samples was investigated in detail using ELISA, XPS, and FTIR techniques. The pristine SC and ES PVDF-HFP samples displayed hydrophobic and ultrahydrophobic behavior and accordingly, exhibited minimal BMEC growth. Fibrinogen adsorbed SC samples did not significantly enhance endothelial cell binding or proliferation. In contrast, the fibrinogen adsorbed electrospun surfaces showed a clear ability to modulate endothelial cell behavior. This system also represents an ideal model system that enables us to understand the natural interaction between cells and their extracellular environment. The research reported shows potential of ES surfaces for artificial vascular graft applications.

Pub.: 26 Feb '14, Pinned: 28 Aug '17

Nanofibrous heparin and heparin-mimicking multilayers as highly effective endothelialization and antithrombogenic coatings.

Abstract: Combining the advantages of the fibrous nanostructure of carbon nanotubes (CNTs) and the bioactivities of heparin/heparin-mimicking polyanions, functional nanofibrous heparin or heparin-mimicking multilayers were constructed on PVDF membrane with highly promoted endothelialization and antithrombogenic activities. Oxidized CNT (oCNT) was first functionalized with water-soluble chitosan (polycation), then enwrapped with heparin or a typical sulfonated heparin-mimicking polymers (poly(sodium 4-styrenesulfonate-co-sodium methacrylate)) to construct the multilayers. Then, the surface-deposited multilayers were constructed via electrostatic layer-by-layer assembly of the functionalized oCNTs. The scanning electron microscope and atom force microscope images confirmed that the coated multilayers exhibited nanofibrous and porous structure. The live/dead cell staining and cell viability assay results indicated that the coated nanofibrous multilayers had excellent compatibility with endothelial cells. The cell morphology observation further confirmed the promotion ability of surface endothelialization due to the coated heparin/heparin-mimicking multilayers. Further systematical evaluation on blood compatibility revealed that the surface heparin/heparin-mimicking multilayer-coated membranes also had significantly improved blood compatibility including restrained platelet adhesion and activation, prolonged blood clotting times, and inhibited activation of coagulation and complement factors. In summary, the proposed nanofibrous multilayers integrated endothelialization and antithrombogenic properties; meanwhile, the heparin-mimicking coating validated comparable performances as heparin coating. Herein, it is expected that the surface coating of nanofibrous multilayers, especially the facilely constructed heparin-mimicking coating, may have great application potential in biomedical fields.

Pub.: 11 Feb '15, Pinned: 28 Aug '17

Endothelialization of Rationally Microtextured Surfaces with Minimal Cell Seeding Under Flow.

Abstract: The generation of a confluent and functional endothelium at the luminal surface of cardiovascular devices represents the ideal solution to avoid contact between blood and synthetic materials thus allowing the long-term body integration of the implants. Due to the foreseen paucity of source cells in cardiovascular patients, surface engineering strategies to achieve full endothelialization, while minimizing the amount of endothelial cells required to seed the surface leading to prompt and full coverage with an endothelium are necessary. A stable endothelialization is the result of the interplay between endothelial cells, the flow-generated walls shear stress and the substrate topography. Here a novel strategy is designed and validated based on the use of engineered surface textures combined with confined islands of seeded endothelial cells. Upon release of the confinement, the cell island populations are able to migrate on the texture and merge under physiological flow conditions to promptly generate a fully connected endothelium. The interaction between endothelial cells and surface textures supports the process of endothelialization through the stabilization of cell-to-substrate adhesions and cell-to-cell junctions. It is shown that with this approach, when ≈50% of a textured surface is initially covered with cell seeding, the time to full endothelialization compared to an untextured surface is almost halved, underpinning the viability and effectiveness of the method for the quick and stable coverage of cardiovascular implants.

Pub.: 28 Jun '16, Pinned: 28 Aug '17