The realization that blood-borne delivery systems must overcome a multiplicity of biological barriers has led to the fabrication of a multi-stage delivery system (MDS) designed to temporally release successive stages of particles or agents to conquer sequential barriers with a goal of enhancing delivery of therapeutic and diagnostic agents to the target site. In its simplest appearance, the MDS is comprised of stage one porous silicon microparticles that function as carriers of second stage nanoparticles. In this study, cellular uptake of non-targeted discoidal silicon microparticles by macrophages was confirmed by electron and atomic force microscopy (AFM). Using SPIONs as a model of secondary nanoparticles, successful loading of the porous matrix of silicon microparticles was achieved and retention of the nanoparticles was enhanced by aminosilylation of the loaded microparticle with 3-aminopropyltriethoxysilane. The impact of silane concentration and reaction time on the nature of the silane polymer on porous silicon was investigated by AFM and X-ray photoelectron microscopy. Tissue samples from mice intravenously administered the MDS supported co-localization of silicon microparticles and SPIONs across various tissues with enhanced SPION release in spleen, compared to liver and lungs, and enhanced retention of SPIONs following silane capping of the MDS. Phantom models of the SPION-loaded MDS displayed negative contrast in magnetic resonance images. In addition to forming a cap over the silicon pores, the silane polymer provided free amines for antibody conjugation to the microparticles, with both VEGFR-2 and PECAM specific antibodies leading to enhanced endothelial association. This study demonstrates assembly and cellular association of a multi-particle delivery system that is bio-molecularly targeted and has potential for applications in biological imaging.
Sidewall covalent functionalization of carbon nanotubes is necessary to achieve smaller bundles and individuals, link to other functional moieties, and aid in better dispersion in composites. In the present study, we developed a one-step functionalization method which uses fluorinated single wall carbon nanotubes (F-SWNTs) as starting materials in the reactions with urea, thiourea, or guanidine. Through these reactions, the derivatives with terminal amide and heteroamide groups on the nanotube sidewalls have been prepared. The nanotubes also contain some residual fluorine generating bifunctional derivatives. These derivatives were characterized by Raman spectroscopy, Fourier Transform infrared (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Compared to fluorinated nanotubes, the urea-functionalized SWNTs (U-F-SWNTs) have shown among the three derivatives the highest stability of their dispersions in DMF, water, and aqueous urea solutions, thereby creating new opportunities for biomedical applications with nanotubes. These bifunctional derivatives show improved dispersion in the epoxy system that should aid in creating an interface between the SWNTs and the polymers and result in much stronger composites. The three derivatives are efficiently synthesized, and the method can be easily scaled up for applications such as creating an integrated polymer network for stronger composites, coatings, and for use in biomedical applications and nanoelectronic devices.
Alignment of pristine carbon nanotubes (P-CNTs) and fluorinated carbon nanotubes (F-CNTs) in nylon-6 polymer composite fibers (PCFs) has been achieved using a single-screw extrusion method. CNTs have been used as filler reinforcements to enhance the mechanical and thermal properties of nylon-6 composite fibers. The composites were fabricated by dry mixing nylon-6 polymer powder with the CNTs as the first step, then followed by the melt extrusion process of fiber materials in a single-screw extruder. The extruded fibers were stretched to their maxima and stabilized using a godet set-up. Finally, fibers were wound on a Wayne filament winder machine and tested for their tensile and thermal properties. The tests have shown a remarkable change in mechanical and thermal properties of nylon-6 polymer fibers with the addition of 0.5 wt% F-CNTs and 1.0 wt% of P-CNTs. To draw a comparison between the improvements achieved, the same process has been repeated with neat nylon-6 polymer. As a result, tensile strength has been increased by 230% for PCFs made with 0.5% F-CNTs and 1% P-CNTs as additives. These fibers have been further characterized by DSC, Raman spectroscopy and SEM which confirm the alignment of CNTs and interfacial bonding to nylon-6 polymer matrix.
Carbon nanotubes (CNTs) have been used for a plethora of biomedical applications, including their use as delivery vehicles for drugs, imaging agents, proteins, DNA, and other materials. Here, we describe the synthesis and characterization of a new CNT-based contrast agent (CA) for X-ray computed tomography (CT) imaging. The CA is a hybrid material derived from ultrashort single-walled carbon nanotubes (20-80 nm long, US-tubes) and Bi(III) oxo-salicylate clusters with four Bi(III) ions per cluster (BiC). The element bismuth was chosen over iodine, which is the conventional element used for CT CAs in the clinic today due to its high X-ray attenuation capability and its low toxicity, which makes bismuth a more-promising element for new CT CA design. The new CA contains 20% by weight bismuth with no detectable release of bismuth after a 48 h challenge by various biological media at 37 °C, demonstrating the presence of a strong interaction between the two components of the hybrid material. The performance of the new BiC@US-tubes solid material as a CT CA has been assessed using a clinical scanner and found to possess an X-ray attenuation ability of >2000 Hounsfield units (HU).
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