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Papers by Jonathan Gilbert

Bulletin of the American Physical Society, Mar 3, 2015

We demonstrate that non-covalent ion-pair interactions in solution can be employed at a solid-liq... more We demonstrate that non-covalent ion-pair interactions in solution can be employed at a solid-liquid interface, to control the lateral spacing of thiols in a self-assembled monolayer (SAM) on gold. Ion-pairs formed between the carboxylate tail-group of 16-mercaptohexadecanoic acid (MHA) and tetralkylammonium (TAA+) hydroxide salts of various alkyl side-chain lengths remain intact during self-assembled monolayer formation and result in a loose packing of chemisorbed MHA chains on the surface, despite the strong tendency of thiols to organize into a tightly-packed monolayer at the gold-solution interface. The ion-pair film can be converted into a loosely-packed MHA monolayer, by rinsing the SAM with a solution of potassium perchlorate, which releases the TAA+ from the surface. Contact angle measurements confirm that the ion-pair SAMs do not resemble fully-packed pure MHA SAMs and appear to have a mixture of methylene and methyl groups exposed at the surface due to the presence of TAA+...

Targeted delivery of drugs and imaging agents to inflamed tissues, as in the cases of cancer, Alz... more Targeted delivery of drugs and imaging agents to inflamed tissues, as in the cases of cancer, Alzheimer’s, Parkinson’s disease, and arthritis, represents one of the major challenges facing nanomedicine. Recent studies have utilized the unique abilities of circulatory mammalian cells to control the in vivo fate of polymeric drug carriers. Monocytes, in particular, routinely target and penetrate deep into sites of inflammation, unlike all clinically approved nanomedicines. Here, we describe an approach to take advantage of the natural ability of monocytes to target inflammation by attaching a flat polymeric particle, dubbed a “Cellular Backpack”, that attaches strongly to monocytes through specific antibody interactions. We show that monocytes with backpacks attached retain two important cellular functions, transmigration through endothelial layers and differentiation into macrophages, which are essential for targeting the backpack to desirable tissues. Backpack-laden monocytes exhibi...

Advances in drug delivery have been enabled by modifying the surface chemistry and, more recently... more Advances in drug delivery have been enabled by modifying the surface chemistry and, more recently, the shape of particles to target delivery of therapeutics to diseased sites. Recent studies have utilized the unique ability of certain mammalian cells to target and home to sites of inflammation, or disease, by conjugating drug carrying particles directly to the surface of these cells for targeted delivery to these diseased sites(1). The synergism between particle and cell has great potential to increase the efficiency of drug delivery in the future. In this work we have developed a polymeric particle termed a backpack that conjugates strongly to monocytes through specific antibody interactions and has many applications in cell-mediated delivery. The backpacks are anisotropic, stratified polymeric thin films that are hundreds of nanometers thick and microns wide. We will discuss the fabrication and applications of backpacks in monocyte-mediated drug delivery. Since the backpack leaves...

Langmuir : the ACS journal of surfaces and colloids, Jan 24, 2015

In this work, it is demonstrated that poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH... more In this work, it is demonstrated that poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/SPS) multilayer films can be successfully tailored for the capture and detection of small biomolecules in dilute concentrations. Based on in vitro results, these films could be potentially applied for rapid and high-throughput diagnosis of dilute biomarkers in serum or tissue. PAH presents functional amino groups that can be further reacted with desired chemistries in order to create customizable and specific surfaces for biomolecule capture. A variety of film assembly characteristics were tested (pH, molecular weight of PAH, and ionic strength) to tune the biotinylation and swelling behavior of these films to maximize detection capabilities. The resultant optimized biotinylated PAH/SPS 9.3/9.3 system was utilized in conjunction with quantum dots (Qdots) to capture and detect a dilute biomarker for prostate cancer, prostate-specific antigen (PSA). Compared to previous work, our system p...

ACS nano, Jan 27, 2015

X-ray photoelectron spectroscopy (XPS) depth profiling with C60(+) sputtering was used to resolve... more X-ray photoelectron spectroscopy (XPS) depth profiling with C60(+) sputtering was used to resolve the lithium-ion distribution in the nanometer-scale domain structures of block polymer electrolyte thin films. The electrolytes of interest are mixtures of lithium trifluoromethanesulfonate and lamellar-forming polystyrene-poly(oligo(oxyethylene)methacrylate) (PS-POEM) copolymer. XPS depth profiling results showed that the lithium-ion concentration was directly correlated with the POEM concentration. Furthermore, chemical state and atomic composition of the film were analyzed through the deconvolution of the C1s signal, indicating that the lithium ions appear to be uniformly distributed in the POEM domains. Overall, the unique capabilities of C60(+) depth profiling XPS provide a powerful tool for the analysis of nanostructured polymer thin films in applications ranging from energy storage and generation to surface coatings and nanoscale templates.

Journal of Controlled Release, 2015

Proceedings of the National Academy of Sciences, 2013

Functional organic thin films often demand precise control over the nanometer-level structure. In... more Functional organic thin films often demand precise control over the nanometer-level structure. Interlayer diffusion of materials may destroy this precise structure; therefore, a better understanding of when interlayer diffusion occurs and how to control it is needed. Xray photoelectron spectroscopy paired with C 60 + cluster ion sputtering enables high-resolution analysis of the atomic composition and chemical state of organic thin films with depth. Using this technique, we explore issues common to the polyelectrolyte multilayer field, such as the competition between hydrogen bonding and electrostatic interactions in multilayers, blocking interlayer diffusion of polymers, the exchange of film components with a surrounding solution, and the extent and kinetics of interlayer diffusion. The diffusion coefficient of chitosan (M = ∼100 kDa) in swollen hydrogenbonded poly(ethylene oxide)/poly(acrylic acid) multilayer films was examined and determined to be 1.4*10 −12 cm 2 /s. Using the highresolution data, we show that upon chitosan diffusion into the hydrogen-bonded region, poly(ethylene oxide) is displaced from the film. Under the conditions tested, a single layer of poly(allylamine hydrochloride) completely stops chitosan diffusion. We expect our results to enhance the understanding of how to control polyelectrolyte multilayer structure, what chemical compositional changes occur with diffusion, and under what conditions polymers in the film exchange with the solution. XPS depth profiling | layer-by-layer films | interdiffusion

Langmuir, 2009

We demonstrate that noncovalent ion-pair interactions in solution can be employed to control the ... more We demonstrate that noncovalent ion-pair interactions in solution can be employed to control the molecular spacing of thiols in a self-assembled monolayer (SAM) on gold. Ion-pairs formed between the carboxylate tail-group of 16-mercaptohexadecanoic acid (MHA) and tetraalkylammonium (TAA + ) hydroxide salts of various alkyl side-chain lengths remain intact during chemisorption of the thiol on gold. The resulting ion-pair SAMs exhibit a 1:1 molar ratio of MHA:TAA + on the surface and are covalently bound to the gold surface through the thiol headgroup of MHA. We hypothesize that the incorporation of the bulky TAA + group competes with the strong tendency of the thiols to organize into an ordered monolayer, which highlights the strength of the ion-pair complexes. The ion-pair films can be converted into a loosely packed MHA monolayer by rinsing the SAM with a solution of potassium perchlorate, which releases the TAA + from the surface. Contact angle measurements and X-ray spectroscopy (XPS) confirm the stoichiometry and covalent attachment of the monolayers. XPS analysis and contact angle measurements indicate that the surface density of bound MHA decreases with increasing size of the TAA + cation. These results suggest that steric hindrance created by the bulky side-chains of the TAA + cation dictates the lateral spacing of MHA chains on the surface.

Biomacromolecules, 2010

Cellular "backpacks" are a new type of anisotropic, nanoscale thickness microparticle that may be... more Cellular "backpacks" are a new type of anisotropic, nanoscale thickness microparticle that may be attached to the surface of living cells creating a "bio-hybrid" material. Previous work has shown that these backpacks do not impair cell viability or native functions such as migration in a B and T cell line, respectively. In the current work, we show that backpacks, when added to a cell suspension, assemble cells into aggregates of reproducible size. We investigate the efficiency of backpack-cell binding using flow cytometry and laser diffraction, examine the influence of backpack diameter on aggregate size, and show that even when cell-backpack complexes are forced through small pores, backpacks are not removed from the surfaces of cells.

Advanced Materials, 2011

Macrophages, ubiquitous phagocytic cells in the human immune system, play a key role in homeostat... more Macrophages, ubiquitous phagocytic cells in the human immune system, play a key role in homeostatic, immunological, and infl ammatory processes. Macrophages are widely distributed in various tissues and play a central role in clearing invading pathogens, dead cells, and foreign entities through phagocytosis. Their wide presence in various organs and tissues makes them particularly suited to provide an immediate defense against invading threats. Moreover, macrophages are rapidly recruited to the diseased site by signaling molecules such as cytokines. Hence, macrophages are involved in a wide range of pathological conditions including cancer, atherosclerosis, various infl ammatory diseases such as vasculitis and asthma, and many others.

We demonstrate a reduction in the measured inner wall shear stress in moderately turbulent Taylor... more We demonstrate a reduction in the measured inner wall shear stress in moderately turbulent Taylor-Couette flows by depositing sprayable superhydrophobic microstructures on the inner rotor surface. The magnitude of reduction becomes progressively larger as the Reynolds number increases up to a value of 22% at Re=8.0×10^{4}. We show that the mean skin friction coefficient C_{f} in the presence of the superhydrophobic coating can be fitted to a modified Prandtl-von Kármán-type relationship of the form (C_{f}/2)^{-1/2}=Mln (Re(C_{f}/2)^{1/2})+N+(b/Δr)Re(C_{f}/2)^{1/2} from which we extract an effective slip length of b≈19 μm. The dimensionless effective slip length b^{+}=b/δ_{ν}, where δ_{ν} is the viscous length scale, is the key parameter that governs the drag reduction and is shown to scale as b^{+}∼Re^{1/2} in the limit of high Re.