pH-Mediated Mucus Penetration of Zwitterionic Polydopamine-Modified Silica Nanoparticles.

Zwitterionic polymers have emerged as promising trans-mucus nanocarriers due to their superior antifouling properties. However, for pH-sensitive zwitterionic polymers, the effect of the pH microenvironment on their trans-mucus fate remains unclear. In this work, we prepared a library of zwitterionic polydopamine-modified silica nanoparticles (SiNPs-PDA) with an isoelectric point of 5.6. Multiple-particle tracking showed that diffusion of SiNPs-PDA in mucus with a pH value of 5.6 was 3 times faster than that in mucus with pH value 3.0 or 7.0. Biophysical analysis found that the trans-mucus behavior of SiNPs-PDA was mediated by hydrophobic and electrostatic interactions and hydrogen bonding between mucin and the particles. Furthermore, the particle distribution in the stomach, intestine, and lung demonstrated the pH-mediated mucus penetration behavior of the SiNPs-PDA. This study reveals the pH-mediated mucus penetration behavior of zwitterionic nanomaterials, which provides rational design strategies for zwitterionic polymers as nanocarriers in various mucus microenvironments.

Protein adsorption mechanisms determine the efficiency of thermally controlled cell adhesion on poly(N-isopropyl acrylamide) brushes.

This study investigated the impact of the protein adsorption mechanism(s) on the efficiency of thermally controlled cell adhesion and release from poly(N-isopropyl acrylamide) brushes. Large format polymer gradients were used to screen for grafting densities and substrate chemistries that alter both cell adhesion at 37 °C and rapid cell release at 25 °C. In particular, the grafting conditions investigated allowed protein adsorption to the underlying substrate, penetration of the brush only, or adsorption to the outer edge of the film. At an average molecular weight of 30 kDa (degree of polymerization N ∼ 270), the results show that robust protein adsorption to polymer brushes impairs rapid cell release below the lower critical solution temperature. Conversely, grafting conditions that permit protein penetration of the brush but block strong adsorption to the underlying substrate support cell adhesion above the transition temperature and ensure efficient cell recovery at lower temperature. These findings demonstrate the impact of protein adsorption mechanisms, surface chemistry, and polymer properties on thermally controlled cell capture and release.

Protein adsorption on poly(N-isopropylacrylamide) brushes: dependence on grafting density and chain collapse.

The protein resistance of poly(N-isopropylacrylamide) brushes grafted from silicon wafers was investigated as a function of the chain molecular weight, grafting density, and temperature. Above the lower critical solution temperature (LCST) of 32 °C, the collapse of the water-swollen chains, determined by ellipsometry, depends on the grafting density and molecular weight. Ellipsometry, radio assay, and fluorescence imaging demonstrated that, below the lower critical solution temperature, the brushes repel protein as effectively as oligoethylene oxide-terminated monolayers. Above 32 °C, very low levels of protein adsorb on densely grafted brushes, and the amounts of adsorbed protein increase with decreasing brush-grafting-densities. Brushes that do not exhibit a collapse transition also bind protein, even though the chains remain extended above the LCST. These findings suggest possible mechanisms underlying protein interactions with end-grafted poly(N-isopropyl acrylamide) brushes.

Engineered Hydroxyapatite Nanoadjuvants with Controlled Shape and Aspect Ratios Reveal Their Immunomodulatory Potentials.

Hydroxyapatite (HAP) has been formulated as adjuvants in vaccines for human use. However, the optimal properties required for HAP nanoparticles to elicit adjuvanticity and the underlying immunopotentiation mechanisms have not been fully elucidated. Herein, a library of HAP nanorods and nanospheres was synthesized to explore the effect of the particle shape and aspect ratio on the immune responses in vitro and adjuvanticity in vivo. It was demonstrated that long aspect ratio HAP nanorods induced a higher degree of cell membrane depolarization and subsequent uptake, and the internalized particles elicited cathepsin B release and mitochondrial reactive oxygen species generation, which further led to pro-inflammatory responses. Furthermore, the physicochemical property-dependent immunostimulation capacities were correlated with their humoral responses in a murine hepatitis B surface antigen immunization model, with long aspect ratio HAP nanorods inducing higher antigen-specific antibody productions. Importantly, HAP nanorods significantly up-regulated the IFN-γ secretion and CD107α expression on CD8+ T cells in immunized mice. Further mechanistic studies demonstrated that HAP nanorods with defined properties exerted immunomodulatory effects by enhanced antigen persistence and immune cell recruitments. Our study provides a rational design strategy for engineered nanomaterial-based vaccine adjuvants.

UV-defined flat PDMS stamps suitable for microcontact printing.

We report a simple method of creating well-defined micropatterns on the surface of a flat PDMS stamp, making it suitable for microcontact printing of proteins. This method only requires a UV lamp (254 nm) and a TEM grid (as a photomask) to modify the surface of PDMS for creating desired micropatterns. By using the UV-modified stamp, a printed protein micropattern that resembles the original TEM grid can be obtained. Surprisingly, unlike the oxygen-plasma-treated PDMS, the UV-modified flat stamp is also long-lasting (>1 week). The method reported herein is very economical for microcontact printing applications because expensive silicon masters and microstructured PDMS are no longer required.

Complex dynamic substrate control: dual-tone hydrogel photoresists allow double-dissociation of topography and modulus.

Complex substrate control is demonstrated with a dual-tone hydrogel photoresist. By exposing a photodegradable hydrogel to UV light through a photomask, both swollen and eroded micropatterns with a decreased modulus can be created on the surface under different exposure conditions. This provides an important tool for investigating the synergistic effects of spatially heterogeneous mechanical and topological cues on cell behavior.

A method of printing uniform protein lines by using flat PDMS stamps.

In this paper, we report a method of printing uniform protein lines on glass slides by using UV-treated flat PDMS stamps. Unlike traditional microcontact printing (µCP) which requires microstructured PDMS stamps, this µCP method only requires a flat PDMS stamp, an UV lamp and a number of straight needles. Our results show that lines of bovine serum albumin (BSA), immunoglobin (IgG), anti-biotin, anti-human IgG and anti-mouse IgG can be printed evenly on glass slides by using this µCP method. We also demonstrate that the printed protein lines are suitable for applications such as microfluidic immunoassays.

Minimizing nonspecific protein adsorption in liquid crystal immunoassays by using surfactants.

In this paper, we report the role of surfactants in minimizing nonspecific protein adsorption in liquid crystal (LC)-based immunoassays in which LC is used as a readout system. Among all surfactants tested, only nonionic surfactant such as Tween 20 can effectively reduce the nonspecific protein adsorption, while maintaining the selectivity of the LC-based immunoassay. We also show that to minimize nonspecific protein adsorption, Tween 20 can be added directly into the antibody solution to a final concentration of 0.8 mM. After the addition of Tween 20, better correlations between the antibody concentrations and the interference colors of LCs can therefore be obtained. For example, when Cy3 antibiotin was used, black, yellow, red, and green interference colors correspond to a concentration of 5, 25, 50, and 100 µg/mL, respectively. This feature gives LC immunoassay a unique advantage over the fluorescence-based immunoassay.

Controlling and manipulating supported phospholipid monolayers as soft resist layers for fabricating chemically micropatterned surfaces.

Chemically micropatterned surfaces have broad applications in many fields. In this paper, we report a new method for preparing chemically micropatterned surfaces by controlling and manipulating supported phospholipid monolayers as soft resist layers with molecular-level precision. First, we introduce self-assembled supported phospholipid monolayers on solid surfaces and use a microcontact lift-up process to create micropatterned phospholipid monolayers (with micrometer resolution) on the surface. Next, the micropatterned phospholipid monolayers can function as "soft" resist layers to protect underlying solid substrates and create either positive or negative chemically micropatterned surfaces during subsequent treatments. Unlike traditional "hard" resist layers which can only be removed by using harsh chemical treatments, this novel soft resist layer only comprises a single layer of compact phospholipid; therefore, it can be easily removed by water rinsing after the preparation of micropatterns. This method is also versatile. It can be applied to prepare a protein microarray or silver patterns on solid substrates.