Effect of Physical Properties of Nanogel Particles on the Kinetic Constants of Multipoint Protein Recognition Process

Investigations on the influence of the structural flexibility of nanoliposomes on their properties

In the present study, nanoliposomes with tuneable structure elasticity were prepared by reverse-phase evaporation. Both Fluorescence Polarization and Fluorescence Resonance Energy Transfer was employed to characterize the structural elasticity of resultant nanoliposomes. Temozolomide, a kind of hydrophilic drug as the first-line treatment choice for glioblastoma, was encapsulated into nanoliposomes. The results showed that the flexibility of nanoliposomes gradually increased with sodium cholate, while decreasing with cholesterol, Labrafac CC and Labrafac PG adding. Furthermore, the structural flexibility of nanoliposomes was positively correlated with the encapsulation efficiency and release rate and cellular uptake. Our research reveals the structural flexibility of nanoliposomes could affect in vitro characteristics and thereafter in vivo behaviors of nanoliposomes.

A Biomimetic of Endogenous Tissue Inhibitors of Metalloproteinases: Inhibition Mechanism and Contribution of Composition, Polymer Size, and Shape to the Inhibitory Effect

A biomimetic of endogenous tissue inhibitors of metalloproteinases (TIMPs) was engineered by introducing three binding elements to a synthetic tetrapolymer. We evaluated the contribution of composition, size, and shape of the TIMP-mimicking polymers to the inhibition of BaP1, a P-I class snake venom metalloproteinase (SVMP). Inhibition was achieved when the size of the linear polymer (LP) was comparable to or greater than that of the enzyme, indicating the efficacy requires binding to a significant portion of the enzyme surface in the vicinity of the active site. The efficacy of a low cross-linked polymer hydrogel nanoparticle (NP) of substantially greater molecular weight was comparable to that of the LPs despite differences in size and shape, an important finding for in vivo applications. The abiotic TIMP was effective against two classes of SVMPs in whole snake venom. The results can serve as a design principle for biomimetic polymer inhibitors of enzymes.

Influence of Monomer Structures for Polymeric Multivalent Ligands: Consideration of the Molecular Mobility of Glycopolymers

Molecular mobility is important for interactions of biofunctional polymers with target molecules. Monomer structures for synthetic biofunctional polymers are usually selected based on their compatibility with polymerization systems, whereas the influence of monomer structures on the interaction with target molecules is hardly considered. In this report, we evaluate the correlation between the monomer structures of glycopolymers and their interactions with concanavalin A (ConA) with respect to the molecular mobility. Two types of glycopolymers bearing mannose are synthesized with acrylamide or acrylate monomers. Despite the similar structures, except for amide or ester bonds in the side chains, the acrylate-type glycopolymers exhibit stronger interaction with ConA both in the isothermal titration calorimetry measurement and in a hemagglutination inhibition assay. Characterization of the acrylate-type glycopolymers suggests that the higher binding constant arises from the higher molecular mobility of mannose units, which results from the rotational freedom of ester bonds in their side chains.

Switchable Adhesion of E. coli to Thermosensitive Carbohydrate-Presenting Microgel Layers: A Single-Cell Force Spectroscopy Study

Adhesion processes at the cellular scale are dominated by carbohydrate interactions, including the attachment and invasion of pathogens. Carbohydrate-presenting responsive polymers can bind pathogens and inhibit pathogen invasion by remote stimuli for the development of new antibiotic strategies. In this work, the adhesion forces of E. coli to monolayers composed of mannose-functionalized microgels with thermosensitive poly(N-isopropylacrylamide) (PNIPAM) and poly(oligo(ethylene glycol)) (PEG) networks are quantified using single-cell force spectroscopy (SCFS). When exceeding the microgels' lower critical solution temperature (LCST), the adhesion increases up to 2.5-fold depending on the polymer backbone and the mannose density. For similar mannose densities, the softer PNIPAM microgels show a significantly stronger adhesion increase when crossing the LCST as compared to the stiffer PEG microgels. This is explained by a stronger shift in swelling, mannose density, and surface roughness of the softer gels when crossing the LCST. When using nonbinding galactose instead of mannose, or when inhibiting bacterial receptors, a certain level of adhesion remains, indicating that also polymer-fimbria entanglements contribute to adhesion. The presented quantitative analysis provides insights into carbohydrate-mediated bacterial adhesion and the relation to material properties and shows the prospects and limitations of interactive polymer materials to control the attachment of bacteria.

Quantitative mechanistic model for ultrasmall nanoparticle-protein interactions

To date, extensive effort has been devoted toward the characterization of protein interactions with synthetic nanostructures. However, much remains to be understood, particularly concerning microscopic mechanisms of interactions. Here, we have conducted a detailed investigation of the kinetics of nanoparticle-protein complexation to gain deeper insights into the elementary steps and molecular events along the pathway for complex formation. Toward that end, the binding kinetics between p-mercaptobenzoic acid-coated ultrasmall gold nanoparticles (AuMBA) and fluorescently-labeled ubiquitin was investigated at millisecond time resolution using stopped-flow spectroscopy. It was found that both the association and dissociation kinetics consisted of multiple exponential phases, hence suggesting a complex, multi-step reaction mechanism. The results fit into a picture where complexation proceeds through the formation of a weakly-bound first-encounter complex with an apparent binding affinity (KD) of ∼9 μM. Encounter complex formation is followed by unimolecular tightening steps of partial desolvation/ion removal and conformational rearrangement, which, collectively, achieve an almost 100-fold increase in affinity of the final bound state (apparent KD ∼0.1 μM). The final state is found to be weakly stabilized, displaying an average lifetime in the range of seconds. Screening of the electrostatic forces at high ionic strength weakens the AuMBA-ubiquitin interactions by destabilizing the encounter complex, whereas the average lifetime of the final bound state remains largely unchanged. Overall, our rapid kinetics investigation has revealed novel quantitative insights into the molecular-level mechanisms of ultrasmall nanoparticle-protein interactions.

Hydrophobic Monomers Recognize Microenvironments in Hydrogel Microspheres during Free-Radical-Seeded Emulsion Polymerization

The three-dimensional structure of nanocomposite microgels was precisely determined by cryo-electron micrography. Several nanocomposite microgels that differ with respect to their nanocomposite structure, which were obtained from seeded emulsion polymerization in the presence of microgels, were used as model nanocomposite materials for cryo-electron micrography. The obtained three-dimensional segmentation images of these nanocomposite microgels provide important insights into the interactions between the hydrophobic monomers and the microgels, that is, hydrophobic styrene monomers recognize molecular-scale differences in polarity within the microgels during the emulsion polymerization. This result led to the formation of unprecedented multi-layered nanocomposite microgels, which promise substantial potential in colloidal applications.

Nanoparticle-supported temperature responsive polymer brushes for affinity separation of histidine-tagged recombinant proteins

We developed a modular approach for the preparation of nanoparticle-supported polymer brushes carrying repeating iminodiacetate units for affinity separation of histidine-tagged recombinant proteins. The nanoparticle-supported polymer brushes were prepared via the combination of surface-initiated atom transfer radical polymerization with Cu(I)-catalyzed azide-alkyne cycloaddition reaction. The nanocomposite materials were characterized to determine the particle size, morphology, organic content, densities of polymer chains and the affinity ligand. Protein binding assay illustrated that the iminodiacetate-rich polymer brushes enable to selectively bind histidine-tagged recombinant proteins in the presence of abundant interfering proteins. More importantly, the protein binding capacity can be tuned by adjusting the environmental temperature. STATEMENT OF SIGNIFICANCE: The nanoparticle core-polymer brush structure enables selective binding of histidine-tagged recombinant proteins via multiple metal-coordination interactions. The soft and flexible structure of the polymer brushes was found beneficial for lowering the steric hindrance in protein binding. Taking advantage of the conformational changes of the polymer brushes at different temperatures, it is possible to modulate the protein binding on the nanocomposite by adjusting the environmental temperature. In general, the iminodiacetate-rich core-brush nano adsorbents are attractive for purifying histidine-tagged recombinant proteins practically. The synthetic approach reported here may be expanded to develop other advanced functional materials for applications in various biomedical fields ranging from biosensors to drug delivery.

Design of Synthetic Polymer Nanoparticles Specifically Capturing Indole, a Small Toxic Molecule

Synthetic polymers are of interest as stable and cost-effective biomolecule-affinity reagents, since these polymers interact with target biomolecules both in vitro and in the bloodstream. However, little has been reported about orally administered polymers capable of capturing a target molecule and inhibiting its intestinal absorption. Here, we describe the design of synthetic polymer nanoparticles (NPs) specifically capturing indole, a major factor exacerbating chronic kidney disease, in the intestine. N-isopropylacrylamide-based NPs were prepared with various hydrophobic monomers. The amounts of indole captured by NPs depended on the structures and feed ratios of the hydrophobic monomers and the polymer density but not on the particle size. The combination of hydrophobic and quadrupole interaction was effective to enhance the affinity and specificity of NPs for indole. The optimized NPs specifically inhibited intestinal absorption of orally administered indole in mice. These results showed the potential of synthetic polymer NPs for inhibiting the intestinal absorption of a target molecule.

Polyquaternium-mediated delivery of morpholino oligonucleotides for exon-skipping in vitro and in mdx mice

Antisense oligonucleotide therapy for Duchenne muscular dystrophy has shown great potential in preclinical and clinical trials, but its therapeutic applications are still limited due to inefficient delivery. In this study, we investigated a few polyquaterniums (PQs) with different size and composition for their potential to improve delivery performance of an antisense phosphorodiamidate morpholino oligomer (PMO) both in vitro and in vivo. The results showed that LuviquatTM series, especially PQ-1 and PQ-3, promoted the exon-skipping efficiency comparable to Endoporter-mediated PMO delivery in vitro. Significant enhancement in skipping dystrophin exon 23 has also been achieved with PQ-3 up to seven-fold when compared to PMO alone in mdx mice. Cytotoxicity of the PQs was lower than Endoporter and PEI 25 K in vitro and muscle damage not clearly detected in vivo under the tested concentrations. These results together demonstrate that the optimization of PQ in molecular size, composition and distribution of positive charges is the key factor to achieve enhanced PMO exon-skipping efficiency. The higher efficiency and lower toxicity endow polyquaternium series as AO delivery enhancing agents for treating muscular dystrophy and other diseases.

Cationic polyelectrolyte-mediated delivery of antisense morpholino oligonucleotides for exon-skipping in vitro and in mdx mice

In this study, we investigated a series of cationic polyelectrolytes (PEs) with different size and composition for their potential to improve delivery of an antisense phosphorodiamidate morpholino oligomer (PMO) both in vitro and in vivo. The results showed that the poly(diallyldimethylammonium chloride) (PDDAC) polymer series, especially PE-3 and PE-4, improves the delivery efficiency of PMO, comparable with Endoporter-mediated PMO delivery in vitro. The enhanced PMO delivery and targeting to dystrophin exon 23 was further observed in mdx mice, up to fourfold with the PE-4, compared with PMO alone. The cytotoxicity of the PEs was lower than that of Endoporter and polyethylenimine 25,000 Da in vitro, and was not clearly detected in muscle in vivo under the tested concentrations. Together, these results demonstrate that optimization of PE molecular size, composition, and distribution of cationic charge are key factors to achieve enhanced PMO exon-skipping efficiency. The increased efficiency and lower toxicity show this PDDAC series to be capable gene/antisense oligonucleotide delivery-enhancing agents for treating muscular dystrophy and other diseases.

Design rationale of thermally responsive microgel particle films that reversibly absorb large amounts of CO2: fine tuning the pKa of ammonium ions in the particles

Fine-tuning of pK_a value of ammonium ions at both CO₂ capture and release temperature is found to be crucial for the design of the thermally responsive gel particle films that reversibly capture large amounts of CO₂.

Herein we revealed the design rationale of thermally responsive gel particle (GP) films that reversibly capture and release large amounts of CO₂ over a narrow temperature range (30–75 °C). The pK_a value of ammonium ions in the GPs at both the CO₂ capture temperature (30 °C) and release temperature (75 °C) is found to be the primary factor responsible for the stoichiometry of reversible CO₂ capture by the amines in the GP films. The pK_a values can be tuned by the properties of GPs such as volume phase transition temperature (VPTT), size, swelling ratio, and the imprinted microenvironment surrounding the amines. The optimal GP obtained according to the design rationale showed high capture capacity (68 mL CO₂ per g dry GPs, 3.0 mmol CO₂ per g dry GPs), although the regeneration temperature was as low as 75 °C. We anticipate that GP films that reversibly capture other acidic and basic gases in large amounts can also be achieved by the pK_a tuning procedures.

Generation of novel hybrid aptamer-molecularly imprinted polymeric nanoparticles

A strategy to exploit aptamers as recognition elements of molecularly imprinted polymeric nanoparticles (AptaMIP NPs) is presented, via modification of the chemical structure of the DNA. It is demonstrated that the introduction of this modified "aptamer monomer" results in an increase of the affinity of the produced MIP NPs, without altering their physical properties such as size, shape, or dispersibility.

Design of multi-functional linear polymers that capture and neutralize a toxic peptide: a comparison with cross-linked nanoparticles

In this paper, a library of multi-functional linear poly-N-isopropylacrylamide (pNIPAm) polymers having a range of molecular weights and functional groups were synthesized and their interaction with the hemolytic peptide, melittin, was examined.

Enzyme catalytic efficiency: a function of bio-nano interface reactions

Biocatalyst immobilization onto carbon-based nanosupports has been implemented in a variety of applications ranging from biosensing to biotransformation and from decontamination to energy storage. However, retaining enzyme functionality at carbon-based nanosupports was challenged by the non-specific attachment of the enzyme as well as by the enzyme-enzyme interactions at this interface shown to lead to loss of enzyme activity. Herein, we present a systematic study of the interplay reactions that take place upon immobilization of three pure enzymes namely soybean peroxidase, chloroperoxidase, and glucose oxidase at carbon-based nanosupport interfaces. The immobilization conditions involved both single and multipoint single-type enzyme attachment onto single and multi-walled carbon nanotubes and graphene oxide nanomaterials with properties determined by Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Our analysis showed that the different surface properties of the enzymes as determined by their molecular mapping and size work synergistically with the carbon-based nanosupports physico-chemical properties (i.e., surface chemistry, charge and aspect ratios) to influence enzyme catalytic behavior and activity at nanointerfaces. Knowledge gained from these studies can be used to optimize enzyme-nanosupport symbiotic reactions to provide robust enzyme-based systems with optimum functionality to be used for fermentation, biosensors, or biofuel applications.