Tal Dvir

Nanotechnological strategies for engineering complex tissues

Tissue engineering aims at developing functional substitutes for damaged tissues and organs. Before transplantation, cells are generally seeded on biomaterial scaffolds that recapitulate the extracellular matrix and provide cells with information that is important for tissue development. Here we review the nanocomposite nature of the extracellular matrix, describe the design considerations for different tissues and discuss the impact of nanostructures on the properties of scaffolds and their uses in monitoring the behaviour of engineered tissues. We also examine the different nanodevices used to trigger certain processes for tissue development, and offer our view on the principal challenges and prospects of applying nanotechnology in tissue engineering.

Remotely Triggerable Drug Delivery Systems

Triggerable drug delivery systems enable on-demand controlled release profiles that may enhance therapeutic effectiveness and reduce systemic toxicity. Recently, a number of new materials have been developed that exhibit sensitivity to visible light, near-infrared (NIR) light, ultrasound, or magnetic fields. This responsiveness can be triggered remotely to provide flexible control of dose magnitude and timing. Here we review triggerable materials that range in scale from nano to macro, and are activated by a range of stimuli.

Nanowired three-dimensional cardiac patches

Engineered cardiac patches for treating damaged heart tissues after a heart attack are normally produced by seeding heart cells within three-dimensional porous biomaterial scaffolds. These biomaterials, which are usually made of either biological polymers such as alginate or synthetic polymers such as poly(lactic acid) (PLA), help cells organize into functioning tissues, but poor conductivity of these materials limits the ability of the patch to contract strongly as a unit. Here, we show that incorporating gold nanowires within alginate scaffolds can bridge the electrically resistant pore walls of alginate and improve electrical communication between adjacent cardiac cells. Tissues grown on these composite matrices were thicker and better aligned than those grown on pristine alginate and when electrically stimulated, the cells in these tissues contracted synchronously. Furthermore, higher levels of the proteins involved in muscle contraction and electrical coupling are detected in the composite matrices. It is expected that the integration of conducting nanowires within three-dimensional scaffolds may improve the therapeutic value of current cardiac patches.

Prevascularization of cardiac patch on the omentum improves its therapeutic outcome

The recent progress made in the bioengineering of cardiac patches offers a new therapeutic modality for regenerating the myocardium after myocardial infarction (MI). We present here a strategy for the engineering of a cardiac patch with mature vasculature by heterotopic transplantation onto the omentum. The patch was constructed by seeding neonatal cardiac cells with a mixture of prosurvival and angiogenic factors into an alginate scaffold capable of factor binding and sustained release. After 48 h in culture, the patch was vascularized for 7 days on the omentum, then explanted and transplanted onto infarcted rat hearts, 7 days after MI induction. When evaluated 28 days later, the vascularized cardiac patch showed structural and electrical integration into host myocardium. Moreover, the vascularized patch induced thicker scars, prevented further dilatation of the chamber and ventricular dysfunction. Thus, our study provides evidence that grafting prevascularized cardiac patch into infarct can improve cardiac function after MI.

Nanoparticles targeting the infarcted heart.

We report a nanoparticulate system capable of targeting the heart after myocardial infarction (MI). Targeting is based on overexpression of angiotensin II type 1 (AT1) receptor in the infarcted heart. Liposomes 142 nm in diameter were conjugated with a ligand specific to AT1. The nanoparticles were able to specifically target cardiac cells in vitro, and in the infarcted heart after intravenous injection in vivo. This system may be useful for delivering therapeutic agents specifically to the infarcted heart.

The effect of immobilized RGD peptide in alginate scaffolds on cardiac tissue engineering.

Cardiac tissue engineering aims to regenerate damaged myocardial tissues by applying heart patches created in vitro. The present study was undertaken to explore the possible role of matrix-attached RGD peptide in the engineering of cardiac tissue within macroporous scaffolds. Neonatal rat cardiac cells were seeded into RGD-immobilized or unmodified alginate scaffolds. The immobilized RGD peptide promoted cell adherence to the matrix, prevented cell apoptosis and accelerated cardiac tissue regeneration. Within 6 days, the cardiomyocytes reorganized their myofibrils and reconstructed myofibers composed of multiple cardiomyocytes in a typical myofiber bundle. The nonmyocyte cell population, mainly cardiofibroblasts, benefited greatly from adhering to the RGD-alginate matrix and consequently supported the cardiomyocytes. They often surrounded bundles of cardiac myofibers in a manner similar to that of native cardiac tissue. The benefits of culturing the cardiac cells in RGD-immobilized alginate scaffolds were further substantiated by Western blotting, revealing that the relative expression levels of α-actinin, N-cadherin and connexin-43 were better maintained in cells cultured within these scaffolds. Collectively, the immobilization of RGD peptide into macroporous alginate scaffolds proved to be a key parameter in cardiac tissue engineering, contributing to the formation of functional cardiac muscle tissue and to a better preservation of the regenerated tissue in culture.

Photo-Targeted Nanoparticles

We report a novel and simple proof-of-concept of a nanoparticulate system that targets any tissue selectively upon illumination. Nanoparticles were covalently functionalized with the amino acid sequence YIGSR, which adheres to the beta1 integrins present on most cell surfaces. This peptide was masked with a caging group, rendering it biologically inert. Illumination with UV light released the caging group from the YIGSR, allowing binding to cells.

Engineered hybrid cardiac patches with multifunctional electronics for online monitoring and regulation of tissue function

In cardiac tissue engineering approaches to treat myocardial infarction, cardiac cells are seeded within three-dimensional porous scaffolds to create functional cardiac patches. However, current cardiac patches do not allow for online monitoring and reporting of engineered-tissue performance, and do not interfere to deliver signals for patch activation or to enable its integration with the host. Here, we report an engineered cardiac patch that integrates cardiac cells with flexible, free-standing electronics and a 3D nanocomposite scaffold. The patch exhibited robust electronic properties, enabling the recording of cellular electrical activities and the on-demand provision of electrical stimulation for synchronizing cell contraction. We also show that electroactive polymers containing biological factors can be deposited on designated electrodes to release drugs in the patch microenvironment on-demand. We expect that the integration of complex electronics within cardiac patches will eventually provide therapeutic control and regulation of cardiac function.

Gold nanoparticle-decellularized matrix hybrids for cardiac tissue engineering.

Decellularized matrices are valuable scaffolds for engineering functional cardiac patches for treating myocardial infarction. However, the lack of quick and efficient electrical coupling between adjacent cells may jeopardize the success of the treatment. To address this issue, we have deposited gold nanoparticles on fibrous decellularized omental matrices and investigated their morphology, conductivity, and degradation. We have shown that cardiac cells engineered within the hybrid scaffolds exhibited elongated and aligned morphology, massive striation, and organized connexin 43 electrical coupling proteins. Finally, we have shown that the hybrid patches demonstrated superior function as compared to pristine patches, including a stronger contraction force, lower excitation threshold, and faster calcium transients.

Targeting of polymeric nanoparticles to lung metastases by surface-attachment of YIGSR peptide from laminin.

Effective therapy for disseminated metastatic cancer is currently impossible because of low drug accumulation in target sites. Here, we aimed to enhance nanoparticle (NP) targeting to lung melanoma metastases via interactions with the laminin receptor, whose expression is upregulated in metastatic cells. To enable NP follow-up and a framework for targeting ligand binding, Estapor(®) fluorescent NPs (299 ± 6 nm in diameter) with surface carboxylic groups were employed and the laminin receptor binding peptide (YIGSR) was attached to their surface to facilitate targeting. In vitro uptake studies performed under medium flow conditions revealed that the uptake of YIGSR-attached NPs by monolayers of B16 melanoma cells was 2-fold higher compared to the uptake of scrambled peptide-NPs. In cultures of healthy lung cells, the uptake of YIGSR-NPs was low and similar to the uptake of scrambled peptide-NPs. Competition assays using cultured B16 melanoma cells pre-incubated with soluble laminin confirmed that the entry of the YIGSR-modified NPs was mediated via interaction with the laminin receptor. Following intravenous (i.v.) administration into B16 melanoma tumor-bearing mice, targeting of the tumor by the YIGSR-NPs was up to five-fold higher than the scrambled peptide-NPs, with no heart, liver or lung tropism. In an experimental lung metastases model, following i.v. administration the YIGSR-NPs targeted the cancerous metastatic cells in lungs, with nearly no targeting to the healthy lung cells. Collectively, the data indicate that YIGSR-targeted NPs have a potential to be used for systemic delivery of chemotherapeutic drugs for the treatment of metastatic lung cancer.