Diblock copolymer microemulsions. A scaling model

Centrifugally spun poly(D,L-lactic acid)-alginate composite microbeads for drug delivery and tissue engineering

This work was based on medium-viscosity alginate as a minor constituent in composites with poly lactic acid (PLA) with the objective to prepare compositional variants through Forcespinning® (FS); for future medical applications. Composites within 0.08-0.25 wt% medium-viscosity alginate were used, at fixed PLA, 6.6 wt%, compared with a study using 0.17-0.48 wt% low-viscosity alginate (same PLA), starting from water-in-oil emulsions, before FS. The presence of alginate is proposed here to influence the high surface tension existing at the emulsion water/oil interface, reducing the total energy at this interface, and/or facilitating the particles in the amphiphilic blend to lie-flat (re-orient) for better fit to the PLA curvature. The study revealed a direct correlation of the inner-phase size (alginate/water ratio), to the change in the morphology and structure of the resultant composites before and after FS. The change in the alginate type, revealed characteristics better suited for medical applications by the medium-viscosity alginate. Composites at alginate- medium-viscosity; ≤0.25 wt%, and low-viscosity; ≤0.48 wt%, had fiber networks interwoven with micro-beads, with characteristics better suited for controlled-release drug delivery applications. Alternatively, each alginate type at 1.1 wt%, composites with PLA at 6.6 wt% could bring about homogenous fibrous materials better suited for wound dressing.

Centrifugally spun alginate-poly(lactic acid) microbeads: A promising carrier for drug delivery and tissue engineering

A facile and high yield centrifugal spinning technique known as Forcespinning® (FS) was used to develop unique microstructures consisting of PLA microbeads along alginate fibers. Morphological variation and structural features appeared in the field-emission scanning electron micrographs for the PLA-alginate composites and dried PLA-alginate films from precursor emulsions at constant PLA and varied alginate contents. Shrunk and deflated microbeads were observed for composites whilst spherical beads were evident for the PLA control. Furthermore, PLA was found surrounding the alginate when the alginate was present at 0.24 wt% or lower, while alginate (mushroom-like structures), were seen protruding through the PLA layer at ≥0.34 wt% alginate. Rheological characterization of the composite emulsions revealed that the filler (alginate) provided shear thinning properties including pseudoplasticity, desirable for printing and other related applications in contrast to the Newtonian flow shown by the PLA control. Along with infra-red spectroscopy, the nanocomposites were further characterized using thermal gravimetry and differential scanning calorimetry featuring reversible events influenced by heat capacity and irreversible kinetic/thermodynamic counterparts. The work provides a comprehensive investigation of biocompatible networks of PLA-alginate microbeads embedded in nano-sized fibers and the prospective application of these microbeads as a drug delivery system.

Tuning Supramolecular Polymers' Amphiphilicity via Host-Guest Interfacial Recognition for Stabilizing Multiple Pickering Emulsions

Supramolecular host-guest chemistry bridging the adjustable amphiphilicity and macromolecular self-assembly is well advanced in aqueous media. However, the interfacial self-assembled behaviors have not been further exploited. Herein, we designed a β-cyclodextrin-grafted alginate/azobenzene-functionalized dodecyl (Alg-β-CD/AzoC12) supra-amphiphilic system that possessed tunable amphiphilicity by host-guest interfacial self-assembly. Especially, supra-amphiphilic aggregates could be utilized as highly efficient soft colloidal emulsifiers for stabilizing water-in-oil-water (W/O/W) Pickering emulsions due to the excellent interfacial activity. Meanwhile, the assembled particle structures could be modulated by adjusting the oil-water ratio, resulting from the tunable aggregation behavior of supra-amphiphilic macromolecules. Additionally, the interfacial adsorption films could be partially destroyed/reconstructed upon ultraviolet/visible irradiation due to the stimuli-altering balance of amphiphilicity of Alg-β-CD/AzoC12 polymers, further constructing the stimulus-responsive Pickering emulsions. Therefore, the supramolecular interfacial self-assembly-mediated approach not only technologically advances the continued development of creative templates to construct multifunctional soft materials with anisotropic structures but also serves as a creative bridge between supramolecular host-guest chemistry, colloidal interface science, and soft material technology.

One-step formation of w/o/w multiple emulsions stabilized by single amphiphilic block copolymers

Multiple emulsions are complex polydispersed systems in which both oil-in-water (O/W) and water-in-oil (W/O) emulsion exists simultaneously. They are often prepared accroding to a two-step process and commonly stabilized using a combination of hydrophilic and hydrophobic surfactants. Recently, some reports have shown that multiple emulsions can also be produced through one-step method with simultaneous occurrence of catastrophic and transitional phase inversions. However, these reported multiple emulsions need surfactant blends and are usually described as transitory or temporary systems. Herein, we report a one-step phase inversion process to produce water-in-oil-in-water (W/O/W) multiple emulsions stabilized solely by a synthetic diblock copolymer. Unlike the use of small molecule surfactant combinations, block copolymer stabilized multiple emulsions are remarkably stable and show the ability to separately encapsulate both polar and nonpolar cargos. The importance of the conformation of the copolymer surfactant at the interfaces with regards to the stability of the multiple emulsions using the one-step method is discussed.

Structure of self-organized diblock copolymer solutions in partially miscible solvents

A diblock copolymer dissolved in a mixture of partially miscible solvents creates a self-organized microemulsion with a morphology that depends on the numerous parameters of the system. We discuss one particular case of spherical particles (containing the minority solvent) forming a hard gel with cubic structure and demonstrate using high-resolution synchrotron scattering experiments that the self-organized solution has a BCC structure. After fitting one- and two-dimensional form factors we extract from the data the one- and two-dimensional structure factors, S(q) and S(q,phi). The experimental S(q) corresponds almost quantitatively, up to the 9th order Bragg peak, to that calculated numerically for a randomly-oriented, finite-size BCC crystal. S(q,phi) contains a large number of reflections that allow the structure to be identified more exactly as a twin BCC morphology with some imperfections. Examination of the dependence of the structural parameters on polymer concentration reveals that the dilution law predicted theoretically for the center-to-center distance of the spheres is confirmed experimentally while the size of the spherical objects does not follow theoretical predictions due to chain extension with increasing concentration.

The structure of nanochannels formed by block copolymer solutions confined in nanotubes

Monte Carlo simulations are employed to obtain information about the radius and the roughness of the inner surface of the channels, which are generated by a family of block copolymer solutions confined in nanotubes. The fluctuations of the above quantities also have been calculated. The simulations have been carried out by varying the interactions between various kinds of segments and those between segments and the wall of the nanotubes, as well as the chemical structure of the copolymer and the nanotube diameter. The present simulations provide insight regarding the structure of ionic and water channels formed by protein in the phospholipid bilayers of the cell membrane.

Polymer brushes in cylindrical pores: simulation versus scaling theory

The structure of flexible polymers endgrafted in cylindrical pores of diameter D is studied as a function of chain length N and grafting density sigma, assuming good solvent conditions. A phenomenological scaling theory, describing the variation of the linear dimensions of the chains with sigma, is developed and tested by molecular dynamics simulations of a bead-spring model. Different regimes are identified, depending on the ratio of D to the size of a free polymer N(3/5). For D>N(3/5) a crossover occurs for sigma=sigma*=N(-6/5) from the "mushroom" behavior (R(gx)=R(gy)=R(gz)=N(35)) to the behavior of a flat brush (R(gz)=sigma(1/3)N,R(gx)=R(gy)=sigma(-1/12)N(1/2)), until at sigma**=(D/N)3 a crossover to a compressed state of the brush, [R(gz)=D,R(gx)=R(gy)=(N(3)D/4sigma)(1/8)<D], occurs. Here coordinates are chosen so that the y axis is parallel to the tube axis, and the z direction normal to the wall of the pore at the grafting site. For D<N(3/5), the coil structure in the dilute regime is a cigar of length R(gy)=ND(-2/3) along the tube axis. At sigma*=(ND(1/3))(-1) the structure crosses over to "compressed cigars," of size R(gy)=(sigmaD)(-1). While for ultrathin cylinders (D<N(1/4)) this regime extends up to the regime where the pore is filled densely (sigma=D/N), for N(1/4)<D<N(1/2) a further crossover occurs at sigma***=D(-9/7)N(-3/7) to a semidilute regime where R(gy)=(N(3)D/4sigma)(1/8) still exceeds D. For moderately wide tubes (N(1/2)<D<N(3/5)) a further crossover occurs at sigma****=N(3)D(-7), where all chain linear dimensions are equal, to the regime of compressed brush. These predictions are compared to the computer simulations. From the latter, extensive results on monomer density and free chain end distributions are also obtained, and a discussion of pertinent theories is given. In particular, it is shown that for large D the brush height is an increasing function of D(-1).