Engineering anisotropic cardiac monolayers on microelectrode arrays for non-invasive analyses of electrophysiological properties.

A standard culture of cardiac cells as unorganized monolayers on tissue culture plastic or glass does not recapitulate the architectural or the mechanical properties of native myocardium. We investigated the physical and protein cues from the extracellular matrix to engineer anisotropic cardiac tissues as highly aligned monolayers on top of the microelectrode array (MEA). The MEA platform allows non-invasive measurement of beating rate and conduction velocity. The effect of different extracellular proteins was tested by using the most common extracellular matrix proteins in the heart, fibronectin and gelatin, after aligning myocytes using a microcontact (µC) printing technique. Both proteins showed similar electrophysiological results before the monolayer began to delaminate after the sixth day of culture. Additionally, there were no significant differences on day 4 between the two microcontact printed proteins in terms of sarcomere alignment and gap junction expression. To test the effect of substrate stiffness, a micromolded (µM) gelatin hydrogel was fabricated in different concentrations (20% and 2%), corresponding to the elastic moduli of approximately 33 kPa and 0.7 kPa, respectively, to cover both spectra of the in vivo range of myocardium. Cardiac monolayers under micromolded conditions beat in a much more synchronized fashion, and exhibited conduction velocity that was close to the physiological value. Both concentrations of gelatin hydrogel conditions yielded similar sarcomere alignment and gap junction expression on day 4 of culture. Ultimately, the 3D micromolded gelatin hydrogel that recapitulated myocardial stiffness improved the synchronicity and conduction velocity of neonatal rat ventricular myocytes (NRVM) without any stimulation. Identifying such microenvironmental factors will lead to future efforts to design heart on a chip platforms that mimic in vivo environment and predict potential cardiotoxicity when testing new drugs.

Dentin Phosphoprotein Mimetic Peptide Nanofibers Promote Biomineralization.

Dentin phosphoprotein (DPP) is a major component of the dentin matrix playing crucial role in hydroxyapatite deposition during bone mineralization, making it a prime candidate for the design of novel materials for bone and tooth regeneration. The bioactivity of DPP-derived proteins is controlled by the phosphorylation and dephosphorylation of the serine residues. Here an enzyme-responsive peptide nanofiber system inducing biomineralization is demonstrated. It closely emulates the structural and functional properties of DPP and facilitates apatite-like mineral deposition. The DPP-mimetic peptide molecules self-assemble through dephosphorylation by alkaline phosphatase (ALP), an enzyme participating in tooth and bone matrix mineralization. Nanofiber network formation is also induced through addition of calcium ions. The gelation process following nanofiber formation produces a mineralized extracellular matrix like material, where scaffold properties and phosphate groups promote mineralization. It is demonstrated that the DPP-mimetic peptide nanofiber networks can be used for apatite-like mineral deposition for bone regeneration.

A glycosaminoglycan mimetic peptide nanofiber gel as an osteoinductive scaffold.

Biomineralization of the extracellular matrix (ECM) plays a crucial role in bone formation. Functional and structural biomimetic native bone ECM components can therefore be used to change the fate of stem cells and induce bone regeneration and mineralization. Glycosaminoglycan (GAG) mimetic peptide nanofibers can interact with several growth factors. These nanostructures are capable of enhancing the osteogenic activity and mineral deposition of osteoblastic cells, which is indicative of their potential application in bone tissue regeneration. In this study, we investigated the potential of GAG-mimetic peptide nanofibers to promote the osteogenic differentiation of rat mesenchymal stem cells (rMSCs) in vitro and enhance the bone regeneration and biomineralization process in vivo in a rabbit tibial bone defect model. Alkaline phosphatase (ALP) activity and Alizarin red staining results suggested that osteogenic differentiation is enhanced when rMSCs are cultured on GAG-mimetic peptide nanofibers. Moreover, osteogenic marker genes were shown to be upregulated in the presence of the peptide nanofiber system. Histological and micro-computed tomography (Micro-CT) observations of regenerated bone defects in rabbit tibia bone also suggested that the injection of a GAG-mimetic nanofiber gel supports cortical bone deposition by enhancing the secretion of an inorganic mineral matrix. The volume of the repaired cortical bone was higher in GAG-PA gel injected animals. The overall results indicate that GAG-mimetic peptide nanofibers can be utilized effectively as a new bioactive platform for bone regeneration.

Idarubicin-loaded folic acid conjugated magnetic nanoparticles as a targetable drug delivery system for breast cancer.

Conventional cancer chemotherapies cannot differentiate between healthy and cancer cells, and lead to severe side effects and systemic toxicity. Another major problem is the drug resistance development before or during the treatment. In the last decades, different kinds of controlled drug delivery systems have been developed to overcome these shortcomings. The studies aim targeted drug delivery to tumor site. Magnetic nanoparticles (MNP) are potentially important in cancer treatment since they can be targeted to tumor site by an externally applied magnetic field. In this study, MNPs were synthesized, covered with biocompatible polyethylene glycol (PEG) and conjugated with folic acid. Then, anti-cancer drug idarubicin was loaded onto the nanoparticles. Shape, size, crystal and chemical structures, and magnetic properties of synthesized nanoparticles were characterized. The characterization of synthesized nanoparticles was performed by dynamic light scattering (DLS), Fourier transform-infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) analyses. Internalization and accumulation of MNPs in MCF-7 cells were illustrated by light and confocal microscopy. Empty MNPs did not have any toxicity in the concentration ranges of 0-500µg/mL on MCF-7 cells, while drug-loaded nanoparticles led to significant toxicity in a concentration-dependent manner. Besides, idarubicin-loaded MNPs exhibited higher toxicity compared to free idarubicin. The results are promising for improvement in cancer chemotherapy.