Adrian M. Kopacz

On the near-wall accumulation of injectable particles in the microcirculation: smaller is not better

Although most nanofabrication techniques can control nano/micro particle (NMP) size over a wide range, the majority of NMPs for biomedical applications exhibits a diameter of ~100 nm. Here, the vascular distribution of spherical particles, from 10 to 1,000 nm in diameter, is studied using intravital microscopy and computational modeling. Small NMPs (≤100 nm) are observed to move with Red Blood Cells (RBCs), presenting an uniform radial distribution and limited near-wall accumulation. Larger NMPs tend to preferentially accumulate next to the vessel walls, in a size-dependent manner (~70% for 1,000 nm NMPs). RBC-NMP geometrical interference only is responsible for this behavior. In a capillary flow, the effective radial dispersion coefficient of 1,000 nm particles is ~3-fold larger than Brownian diffusion. This suggests that sub-micron particles could deposit within diseased vascular districts more efficiently than conventional nanoparticles.

Quantifying uncertainties in the microvascular transport of nanoparticles

Abstract The character of nanoparticle dispersion in the microvasculature is a driving factor in nanoparticle-based therapeutics and bio-sensing. It is difficult, with current experimental and engineering capability, to understand dispersion of nanoparticles because their vascular system is more complex than mouse models and because nanoparticle dispersion is so sensitive to in vivo environments. Furthermore, uncertainty cannot be ignored due to the high variation of location-specific vessel characteristics as well as variation across patients. In this paper, a computational method that considers uncertainty is developed to predict nanoparticle dispersion and transport characteristics in the microvasculature with a three step process. First, a computer simulation method is developed to predict blood flow and the dispersion of nanoparticles in the microvessels. Second, experiments for nanoparticle dispersion coefficients are combined with results from the computer model to suggest the true values of its unknown and unmeasurable parameters—red blood cell deformability and red blood cell interaction—using the Bayesian statistical framework. Third, quantitative predictions for nanoparticle transport in the tumor microvasculature are made that consider uncertainty in the vessel diameter, flow velocity, and hematocrit. Our results show that nanoparticle transport is highly sensitive to the microvasculature.

Dielectrophoretic concentration of low-abundance nanoparticles using a nanostructured tip

Electric field-induced concentration has the potential for application in highly sensitive detection of nanoparticles (NPs) for disease diagnosis and drug discovery. Conventional two-dimensional planar electrodes, however, have shown limited sensitivity in NP concentration. In this paper, the dielectrophoretic (DEP) concentration of low-abundance NPs is studied using a nanostructured tip where a high electric field of 3 × 10(7) V m(-1) is generated. In experimental studies, individual 2, 10, and 100 nm Au NPs are concentrated to a nanotip using DEP concentration and are detected by scanning transmission and scanning electron microscopes. The DEP force on Au NPs near the end of a nanotip is computed according to the distance, and then compared with Brownian motion-induced force. The computational study shows qualitative agreement with the experimental results. When the experimental conditions for DEP concentration are optimized for 8 nm-long oligonucleotides, the sensitivity of a nanotip is 10 aM (10 attomolar; nine copies in a 1.5 μl sample volume). This DEP concentrator using a nanotip can be used for molecular detection without amplification.

Nanoscale sensor analysis using the immersed molecular electrokinetic finite element method

The concentration and detection of molecular biomarkers remain as a challenge to develop point-of-care diagnostic devices. An electric field induced concentration has been studied for such purposes but with limited success due to limited efficacy. This paper presents a computational study for investigating the molecular concentration and retention efficacy of single nanowire (SNW) and dendritic nanotip (DNT) sensors. Our computational results indicate that compared to a DNT, the SNW sensor produces higher dielectrophoretic (DEP) forces in the vicinity of the terminal end of the tip. Furthermore, the magnitude of the DEP force increases exponentially as the diameter of the SNW is decreased, resulting in a further improved retention efficacy of NPs. However, the SNW sensors concentration efficacy was not much improved for NPs smaller than 10 nm diameter when the nanowire diameter was reduced from 500 to 50 nm. Compared to the SNW, the DNT sensor showed improved concentration efficacy due to multiple points of electric field concentrations, which retard the exponential decay of the DEP force resulting in a greater widespread region where the DEP force dominates the Brownian motion forces. When oligonucleotides are used as a target particle, the DEP force can be used to elongate oligonucleotides to further enhance the concentration and retention efficacy.

Enhancing Endothelial Cell Retention on ePTFE Constructs by siRNA-Mediated SHP-1 Gene Silencing

Polymeric vascular grafts hold great promise for vascular reconstruction, but the lack of endothelial cells renders these grafts susceptible to intimal hyperplasia and restenosis, precluding widespread clinical applications. The purpose of this study is to establish a stable endothelium on expanded polytetrafluoroethylene (ePTFE) membrane by small interfering RNA (siRNA)-induced suppression of the cell adhesion inhibitor SH2 domain-containing protein tyrosine phosphatase-1 (SHP-1). Human umbilical vein endothelial cells (HUVECs) were treated with scrambled siRNA as a control or SHP-1 specific siRNA. Treated cells were seeded onto fibronectin-coated ePTFE scaffolds and exposed to a physiological range of pulsatile fluid shear stresses for 1 h in a variable-width parallel plate flow chamber. Retention of cells was measured and compared between various shear stress levels and between groups treated with scrambled siRNA and SHP-1 specific siRNA. HUVECs seeded on ePTFE membrane exhibited shear stress-dependent retention. Exposure to physiological shear stress (10 dyn/cm 2 ) induced a reduction in the retention of scrambled siRNA treated cells from 100% to 85% at 1 h. Increased shear stress (20 dyn/cm 2 ) further reduced retention of scrambled siRNA treated cells to 55% at 1 h. SHP-1 knockdown mediated by siRNA enhanced endothelial cell retention from approximately 60% to 85% after 1 h of exposure to average shear stresses in the range of 15―30 dyn/cm 2 . This study demonstrates that siRNA-mediated gene silencing may be an effective strategy for improving the retention of endothelial cells within vascular grafts.

Immersed Molecular Electrokinetic Finite Element Method for Nano-devices in Biotechnology and Gene Delivery

It has been demonstrated from recent research that modern uses of multiscale analysis, uncertainty quantification techniques, and validation experiments is essential for the design of nanodevices in biotechnology and medicine. The 3D immersed molecular electrokinetic finite element method (IMEFEM) will be presented for the modeling of micro fluidic electrokinetic assembly of nanowires, filaments and bio-molecules. This transformative bio-nanotechnology is being developed to enable gene delivery systems to achieve desired therapeutic effects and for the design and optimization of an electric field enabled nanotip DNA sensor. For the nanodiamond-based drug delivery device we will discuss the multiscale analysis, quantum and molecular mechanics, immersed molecular finite element and meshfree methods, uncertainty quantification, and validation experiments. In addition, we will describe the mathematical formulation of pH control interactions among chemically functionalized nanodiamonds, and their interactions with polymers. For the nanotip sensor, we will discuss the underlying mechanics and physical parameters influencing the bio-sensing efficiency, such as the threshold of applied electric field, biomolecule deformation, and nanoscale Brownian motion. Through multiscale analysis, we provide guidelines for nanodevice design, including fundamental mechanisms driving the system performance and optimization of distinct parameters.

Design and optimization of a nanotip sensor via immersed molecular electrokinetic finite element method

A critical challenge in the field of medicine is to develop a low cost sensor competent of detecting specific bacterial pathogens via a precise deoxyribonucleic acid (DNA) sequence. In order to identify such biological agents in a patient’s blood or other bodily fluids at the onset of infection, detection of specific pathogen genomic DNA is considered a reliable approach. Current techniques involving multiplex DNA/RNA detection arrays or immunoassays [1] require cumbersome sample preparation, aggressive nucleic acid amplification protocols and must be operated by trained personnel. To overcome the aforementioned obstacles, a time-dependent dielectrophoretic force driven sensor consisting of nanostructured tip is being developed.Copyright

Dielectrophoretic enrichment of low-abundance nanoparticles using a nanotip-concentrator for nanoengineered medicine and biology

Enrichment of low-concentration nanoparticles (NPs) is of great interest in medicine and biology. In particular, the enrichment of biomolecules such as DNA and protein can have broad impacts on disease diagnosis and drug discovery. Currently available methods utilize centrifugation or magnetic field. However, these methods are limited in cumbersome preparation steps and low sensitivity. Electric field-based methods have demonstrated potential for NP enrichment, but conventional planar electrodes trapping NPs are limited in sensitivity and imaging capability. Here, we present a nanotip-concentrator using dielectrophoresis (DEP) for NP enrichment. Unlike conventional planar electrodes, a nanostructured probe-tip can facilitate more sensitive detection of NPs because of high electric field strength. The NP enrichment mechanism is studied through numerical computation, and then validated through experiment using Au NPs. For optimized enrichment of NPs, 8 nm-long oligonucleotides are used to enrich through hybridization reactions, which shows the sensitivity at 10 aM (9 copies in a 1.5 μL sample). The nanotip-concentrator will offer a novel enrichment platform for highly sensitive NP detection and analysis.Copyright

Modeling of Endothelial Cell Adhesion Dynamics Modulated by Molecular Engineering

Vascular thrombosis, intimal hyperplasia, and atherosclerosis are common disorders affecting a very large portion of the human population. A potential reduction in these disorders will elicit a significant impact. It has been shown that endothelial cells play a critical role in protecting blood vessels against the formation of thrombosis and atherosclerosis. Hence, a successful endothelial cell lining of arterial constructs will prevent intimal hyperplasia in reconstructed arteries. However, in practice endothelial cells often detach from reconstructed arteries due to weak adhesion strength, hindering the effectiveness of endothelial cell lining.Copyright

Knockdown of SHP-1 enhances endothelial cell retention for vascular regeneration

Atherosclerosis is the leading cause of morbidity and mortality in the developed world. A common treatment option is arterial bypass surgery, which requires the use of a vascular graft. Autologous vein is the current gold standard for use as a vascular graft; however, donor site morbidity and inconsistent availability have provided an impetus to explore alternative graft sources.Copyright