Nanoporous membranes for medical and biological applications

Synthetic nanoporous materials have numerous potential biological and medical applications that involve sorting, sensing, isolating and releasing biological molecules. Nanoporous systems engineered to mimic natural filtration systems are actively being developed for use in smart implantable drug delivery systems, bioartificial organs, and other novel nano-enabled medical devices. Recent advances in nanoscience have made it possible to precisely control the morphology as well as physical and chemical properties of the pores in nanoporous materials that make them increasingly attractive for regulating and sensing transport at the molecular level. In this work, an overview of nanoporous membranes for biomedical applications is given. Various in vivo and in vitro membrane applications, including biosensing, biosorting, immunoisolation and drug delivery, are presented. Different types of nanoporous materials and their fabrication techniques are discussed with an emphasis on membranes with ordered pores. Desirable properties of membranes used in implantable devices, including biocompatibility and antibiofouling behavior, are discussed. The use of surface modification techniques to improve the function of nanoporous membranes is reviewed. Despite the extensive research carried out in fabrication, characterization, and modeling of nanoporous materials, there are still several challenges that must be overcome in order to create synthetic nanoporous systems that behave similarly to their biological counterparts

Atomic layer deposition-based functionalization of materials for medical and environmental health applications

Nanoporous alumina membranes exhibit high pore densities, well-controlled and uniform pore sizes, as well as straight pores. Owing to these unusual properties, nanoporous alumina membranes are currently being considered for use in implantable sensor membranes and water purification membranes. Atomic layer deposition is a thin-film growth process that may be used to modify the pore size in a nanoporous alumina membrane while retaining a narrow pore distribution. In addition, films deposited by means of atomic layer deposition may impart improved biological functionality to nanoporous alumina membranes. In this study, zinc oxide coatings and platinum coatings were deposited on nanoporous alumina membranes by means of atomic layer deposition. PEGylated nanoporous alumina membranes were prepared by self-assembly of 1-mercaptoundec-11-yl hexa(ethylene glycol) on platinum-coated nanoporous alumina membranes. The pores of the PEGylated nanoporous alumina membranes remained free of fouling after exposure to human platelet-rich plasma; protein adsorption, fibrin networks and platelet aggregation were not observed on the coated membrane surface. Zinc oxide-coated nanoporous alumina membranes demonstrated activity against two waterborne pathogens, Escherichia coli and Staphylococcus aureus. The results of this work indicate that nanoporous alumina membranes may be modified using atomic layer deposition for use in a variety of medical and environmental health applications

Stimuli-Responsive Polymer Brushes for Flow Control through Nanopores

Responsive polymers attached to the inside of nano/micro-pores have attracted great interest owing to the prospect of designing flow-control devices and signal responsive delivery systems. An intriguing possibility involves functionalizing nanoporous materials with smart polymers to modulate biomolecular transport in response to pH, temperature, ionic concentration, light or electric field. These efforts open up avenues to develop smart medical devices that respond to specific physiological conditions. In this work, an overview of nanoporous materials functionalized with responsive polymers is given. Various examples of pH, temperature and solvent responsive polymers are discussed. A theoretical treatment that accounts for polymer conformational change in response to a stimulus and the associated flow-control effect is presented

Chain-Amplified Photochemical Fragmentation of <i>N</i>‑Alkoxypyridinium Salts: Proposed Reaction of Alkoxyl Radicals with Pyridine Bases To Give Pyridinyl Radicals

Photoinduced electron transfer to <i>N</i>-alkoxypyridiniums, which leads to N–O bond cleavage and alkoxyl radical formation, is highly chain amplified in the presence of a pyridine base such as lutidine. Density functional theory calculations support a mechanism in which the alkoxyl radicals react with lutidine via proton-coupled electron transfer (PCET) to produce lutidinyl radicals (BH^•). A strong electron donor, BH^• is proposed to reduce another alkoxypyridinium cation, leading to chain amplification, with quantum yields approaching 200. Kinetic data and calculations support the formation of a second, stronger reducing agent: a hydrogen-bonded complex between BH^• and another base molecule (BH^•···B). Global fitting of the quantum yield data for the reactions of four pyridinium salts (4-phenyl and 4-cyano with <i>N</i>-methoxy and <i>N</i>-ethoxy substituents) led to a consistent set of kinetic parameters. The chain nature of the reaction allowed rate constants to be determined from steady-state kinetics and independently determined chain-termination rate constants. The rate constant of the reaction of CH₃O^• with lutidine to form BH^•, <i>k</i>₁, is ∼6 × 10⁶ M^–1 s^–1; that of CH₃CH₂O^• is ∼9 times larger. Reaction of CD₃O^• showed a deuterium isotope effect of ∼6.5. Replacing lutidine by 3-chloropyridine, a weaker base, decreases <i>k</i>₁ by a factor of ∼400

MoS₂ Quantum Dots: Effect of Hydrogenation on Surface Stability and H₂S Release

We employ density functional theory to investigate effects of hydrogenation on the energetic stability and electronic properties of triangular MoS₂ nanoclusters with S-edges. Excess edge sulfur atoms relative to the bulk stoichiometry along the edges are passivated by hydrogen atoms. We find that the hydrogen coverage for maximum stability can be calculated by (<i>n</i> – 2)/2­(<i>n</i> – 1), where <i>n</i> is the number of S atoms along an edge. The energetics reveal a preference for the zigzag arrangement of adsorbed hydrogen atoms on the edges. Our calculations show vanishing HOMO–LUMO gaps mainly due to the presence of dangling bonds at the edges and can be considered metal-like. We find that the activation energy required to release H₂S lies in between 0.47 and 0.62 eV, and this value is in good agreement with the recently reported experimental value

Empirical Relationship between Chemical Structure and Redox Properties: Mathematical Expressions Connecting Structural Features to Energies of Frontier Orbitals and Redox Potentials for Organic Molecules

A set of mathematical expressions to predict redox potentials and frontier orbital energy levels for organic molecules as a function of structural features is proposed. This is achieved by using the principal component regression method on reduction potential (<i>E</i>_red), oxidation potential (<i>E</i>_ox), highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) values calculated using density functional theory (DFT) on a training set consisting of 77 547 molecules from PubChem database. The first set of expressions allows prediction of <i>E</i>_red, <i>E</i>_ox, HOMO, and LUMO values using molecular fingerprints alone with <i>R</i>² of ca. 0.74, 0.82, 0.92, and 0.85, respectively, which can be used for preliminary screening of molecules before performing DFT calculations. In the second set of expressions, when we include DFT-calculated HOMO and LUMO values as additional descriptors, the <i>R</i>² values of <i>E</i>_ox and <i>E</i>_red predictions increase to 0.91 and 0.90, respectively. This more accurate approach for redox potential predictions is still significantly more computationally efficient compared to DFT calculations of redox potentials. The potential of these approaches is demonstrated by using the examples of polyacenes and quinoxaline family of molecules. These empirical relations are ideally suited for high-throughput screening for a variety of optoelectronic applications. The resultant tool, QSROAR, is made available at https://github.com/piyushtagade/qsroar_version2