pH-Responsive Polymer Microspheres: Rapid Release of Encapsulated Material within the Range of Intracellular pH

A pH-sensitive near-infrared fluorescent probe with alkaline pKa for chronic wound monitoring in diabetic mice

An alkaline pH-sensitive near-infrared fluorescent probe can monitor pH changes in the course of chronic wound development in mice.

Chaotropic-anion-induced supramolecular self-assembly of ionic polymeric micelles

Traditional micelle self-assembly is driven by the association of hydrophobic segments of amphiphilic molecules forming distinctive core-shell nanostructures in water. Here we report a surprising chaotropic-anion-induced micellization of cationic ammonium-containing block copolymers. The resulting micelle nanoparticle consists of a large number of ion pairs (≈60,000) in each hydrophobic core. Unlike chaotropic anions (e.g. ClO4(-)), kosmotropic anions (e.g. SO4(2-)) were not able to induce micelle formation. A positive cooperativity was observed during micellization, for which only a three-fold increase in ClO4(-) concentration was necessary for micelle formation, similar to our previously reported ultra-pH-responsive behavior. This unique ion-pair-containing micelle provides a useful model system to study the complex interplay of noncovalent interactions (e.g. electrostatic, van der Waals, and hydrophobic forces) during micelle self-assembly.

Microcarriers designed for cell culture and tissue engineering of bone

Microspherical particulates have been an attractive form of biomaterials that find usefulness in cell delivery and tissue engineering. A variety of compositions, including bioactive ceramics, degradable polymers, and their composites, have been developed into a microsphere form and have demonstrated the potential to fill defective bone and to populate tissue cells on curved matrices. To enhance the capacity of cell delivery, the conventional solid form of spheres is engineered to have either a porous structure to hold cells or a thin shell to in-situ encapsulate cells within the structure. Microcarriers can also be a potential reservoir system of bioactive molecules that have therapeutic effects in regulating cell behaviors. Due to their specific form, advanced technologies to culture cell-loaded microcarriers are required, such as simple agitation or shaking, spinner flask, and rotating chamber system. Here, we review systematically, from material design to culture technology, the microspherical carriers used for the delivery of cells and tissue engineering, particularly of bone.

Responsive polymer welds via solution casting for stabilized self-assembly

We present a simple solution casting technique to apply polymer welds to stabilize capillary-force directed self-assembled systems including arrays of pillars and microbeads. The strength of the polymer welds can be enhanced by increasing either the polymer concentration or molecular weight. The use of responsive polymers to form the welds allow for the fabrication of hierarchical structures that actuate in response to external stimuli. For example, temperature-responsive and pH-responsive microstructures can be formed by solution casting poly(vinyl methyl ether) and poly(methacrylic acid), respectively. We demonstrate that polymer welds formed using biocompatible alginate allows for controllable release of microbeads in microfluidic channels, which has potential applications in drug delivery.

Amphoteric core-shell microgels: contraphilic two-compartment colloidal particles

pH-responsive amphoteric core-shell microgel particles were synthesized by emulsion copolymerization of the appropriate functional monomers with ethylene glycol dimethacrylate as the cross-linker. 2-(Diethylamino)ethyl methacrylate (DEA) was used as the ionizable basic monomer, and tert-butyl methacrylate served as the hydrophobic monomer precursor, which gave the methacrylic acid (MAA) moieties following acid hydrolysis of the ester groups. The core of the polyampholyte microgels comprised a cross-linked poly(2-(diethylamino)ethyl methacrylate) (PDEA) or poly(methacrylic acid) (PMAA) network surrounded by a cross-linked PMAA or PDEA shell, respectively. A polyampholyte random copolymer microgel with the DEA and MAA units randomly distributed within the gel phase was also prepared. Scanning electron microscopy studies showed spherical particles of a narrow size distribution, and transmission electron microscopy verified the core-shell topology of the particles. Potentiometric titration curves revealed two plateau regions for the polyampholyte core-shell microgels attributed to the independent ionization process of the core and the shell of the particles, in contrast to the random copolymer microgel particles that exhibited a single plateau region as a result of the simultaneous protonation/deprotonation process of the basic and acidic moieties of the microgels. The core and the shell of the particles were found to swell independently upon ionization of the DEA or MAA moieties at low or high pH, respectively, whereas collapsed latex particles were obtained in the intermediate pH range when both the core and the shell of the particles were neutral, in agreement with the potentiometric titration data. These core-shell microgels comprise novel two-compartment nanostructures that exhibit contraphilic properties in the core and the shell of the particles in response to a single external stimulus.

Fluorogenic 1,3-Dipolar Cycloaddition within the Hydrophobic Core of a Shell Cross-Linked Nanoparticle

Using either nitroxide mediated polymerization (NMP) or reversible addition fragmentation transfer (RAFT) techniques, novel block copolymers that present terminal acetylenes, in the side chain of the styrenic block, were obtained with narrow polydispersities and targeted molecular weights. For the conversion of these acetylene-functionalized polymers to amphiphilic block copolymers, RAFT techniques were preferred. Mild protection/deprotection chemistries were employed which were compatible with the incorporation of the acetylene functionality in the hydrophobic segment. These acetylene-functionalized, Click-readied amphiphilic block copolymers were then self-assembled and cross-linked to afford shell cross-linked knedel-like (SCK) nanoparticles that contained acetylene groups in the core domain. The hydrodynamic diameters (D(h)) of the block copolymer micelles and nanoparticles were determined by dynamic light scattering (DLS), and the dimensions of the nanoparticles were characterized using tapping-mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). The chemical availability of the Click functionality within the core domain of the SCKs was investigated using the copper(I)-catalyzed 1,3-dipolar fluorogenic cycloaddition with a non-fluorescent 3-azidocoumarin profluorophore to afford intensely fluorescent nanoparticles.