No abstract

Liposomes (nontoxic/nonantigenic vesicles derived from phospholipids) have long been utilized in numerous biotechnology and pharmaceutical applications to improve therapeutic indices and enhance cellular uptake.1 Their structural stability, however, is dependent upon many intrinsic and environmental parameters that often serve to compromise their efficacy.2 Polymersomes (polymer vesicles formed from a wide variety of fully synthetic amphiphiles) 3 -5 have similar utility to their lipid counterparts but possess several advantageous properties including vastly superior stability6 and diverse functionality afforded by tuning material chemistries through polymer synthesis. Recently, there has been considerable interest in the development of degradable polymersomes suitable for in vivo drug delivery. Here, we present the generation of self-assembled vesicles comprised entirely of an amphiphilic diblock copolymer of poly(ethylene oxide) (PEO) and polycaprolactone (PCL), two previously FDAapproved polymers. Unlike degradable polymersomes formed from blending bioinert and hydrolyzable components,7 , 8 PEO-b-PCL-based vesicles promise to be fully bioresorbable, 9 leaving no potentially toxic byproducts upon their degradation. Moreover, unlike published reports of other degradable (peptide-, polyester-, or polyanhydride-based) polymersomes, 10-12 these bioresorbable vesicles are formed through spontaneous self-assembly of their pure component amphiphile.Poly(ethylene oxide) was chosen as the hydrophilic block as it imparts to the vesicle's surface biocompatibility and prolonged blood circulation times.13 -15 Polycaprolactone constitutes the vesicles' hydrophobic membrane portion. PCL is degraded by hydrolysis of its ester linkages in physiological conditions (such as in the human body) and has therefore received a great deal of attention for use as an implantable biomaterial in drug delivery devices, bioresorbable sutures, adhesion barriers, and scaffolds for injury repair via tissue engineering. 16 -19 Compared to other biodegradable aliphatic polyesters, PCL has several advantageous properties, including (1) high permeability to small drug molecules, (2) NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript neutral pH environment upon degradation, (3) facility in forming blends with other polymers, and (4) suitability for long-term delivery afforded by slow erosion kinetics as compared to polylactide (PLA), polyglycolide (PGA), and polylactic-co-glycolic acid (PLGA). 17 Utilization of PCL as the hydrophobic block in our formulations promises that the resultant polymersomes should have safe and complete in vivo degradation.Amphiphilic poly(ethylene oxide)-b-polycaprolactone was generated via ring-opening polymerization of cyclic ∊-caprolactone (CL) in the presence of stannous(II) octoate (SnOct) and monocyano-or monomethoxypoly(ethylene oxide) (PEO, 0.75K, 1.1K, 1.5K, 2K, 5K, 5.5K, 5.8K; Polymer Source, Dorval, Canada). 20 The reactions yielded PEO-b-PCL copolymers with varying PCL block size (betwe...

No abstract

Dendritic cells (DCs) play a pivotal role in both immune tolerance and the initiation of immunological responses. The ability to track DCs in vivo is imperative for the development of DC-based cellular therapies and to advance our understanding of DC function and pathophysiology. Here, we conjugate a cell permeable peptide, Tat, to near-infrared (NIR) emissive polymersomes in order to enable efficient intracellular delivery for future DC tracking with these optical probes. NIR imaging allows quantitative, repetitive, in vivo detection of fluorophore-laden cells, at centimeter tissue depths without disturbing cellular function. Flow cytometry and confocal microscopy results indicate that Tat-mediated polymersome delivery to DCs is concentration and time dependent, resulting in punctate intracellular localization. Further, loading cells with Tat NIR emissive polymersomes does not interfere with cytokine-induced DC maturation and has modest effects on DC viability, but has a significant effect on mature DC-induced activation of naive T cells. We observe significant uptake of NIR emissive polymersomes when conjugated to the peptide, with a lower detection limit of 5000 labeled DCs. The extent of polymersome delivery is estimated as 70 000 +/- 10 000 vesicles/cell, equivalent to 0.7 +/- 0.1 fmol of NIR fluorophore. Our studies will enable future in vivo tracking of ex vivo labeled DCs by NIR fluorescence based imaging.

Nanoparticles formed from diblock copolymers of FDA approved PEO and PCL have generated considerable interest as in vivo drug delivery vehicles. Herein, we report the synthesis of the most extensive family PEO-b-PCL copolymers that vary over the largest range of number-average molecular weights (Mn: 3.6 – 57K), PEO weight fractions (fPEO: 0.08 – 0.33), and PEO chain lengths (0.75–5.8K) reported to date. These polymers were synthesized in order to establish the full range of aqueous phase behaviours of these diblock copolymers and to specifically identify formulations that were able to generate bilayered vesicles (polymersomes). Cryogenic transmission electron microscopy (cryo-TEM) was utilized in order to visualize the morphology of these structures upon aqueous self-assembly of dry polymer films. Nanoscale polymersomes were formed from PEO-b-PCL copolymers over a wide range of PEO weight fractions (fPEO: 0.14 – 0.27) and PEO molecular weights (0.75 – 3.8K) after extrusion of aqueous suspensions. Comparative morphology diagrams, which describe the nature of self-assembled structures as a function of diblock copolymer molecular weight and PEO weight fraction, show that in contrast to micron-scale polymersomes, which form only from a limited range of PEO-b-PCL diblock copolymer compositions, a multiplicity of PEO-b-PCL diblock copolymer compositions are able to give rise to nanoscale vesicles. These data underscore that PEO-b-PCL compositions that spontaneously form micron-sized polymersomes, as well as those that have previously been reported to form polymersomes via a cosolvent fabrication system, provide only limited insights into the distribution of PEO-b-PCL diblocks that give rise to nanoscale vesicles. The broad range of polymersome-forming PEO-b-PCL compositions described herein suggest the ability to construct extensive families of nanoscale vesicles of varied bilayer thickness, providing the ability to tune the timescales of vesicle degradation and encapsulant release based on the intended in vivo application.

Cyanate ester (PT-15, Lonza Corp.) composites containing the blended polyhedral oligomeric silsesquioxane (POSS), TriSilanolPhenyl-POSS (C 42 H 38 O 12 Si 7 ), were prepared containing PT-15/POSS 99/1, 97/3, 95/5, 90/10, and 85/15 w/w ratios. The composites were characterized by FT-TR, X-ray diffraction (XRD), small-angle neutron scattering (SANS), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (X-EDS), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA), and three-point bending flexural tests. TriSilanolPhenyl-POSS was throughly dispersed into uncured liquid PT-15 resin. After curing, XRD, SANS, and X-EDS measurements were consistent with partial molecular dispersion of a portion of the POSS units in the continuous matrix phase while the remainder forms POSS aggregates. Larger aggregates are formed at higher loadings. SANS, SEM, and TEM show that POSS-enriched nanoparticles are present in the PT-15/POSS composites. The storage bending moduli, E′, and the glass transition temperatures, T g , of PT-15/POSS 99/1, 97/3, and 95/5 composites are higher than those of the pure PT-15 over the temperature range from 35 to 350 °C. The E′ values for all these composites (except for the 15 wt % POSS sample) are significantly greater than that of the pure resin at T > T g . Therefore, small amounts (e5 wt %) of TriSilanolPhenyl-POSS incorporated into cyanate ester resin PT-15 can improve the storage modulus and the hightemperature properties of these cyanate ester composites versus the pure PT-15 resin. The flexural strength and flexural modulus are also raised by POSS incorporation.

The incorporation of both monofunctional and multifunctional polyhedral oligomeric silsesquioxane (POSS) derivatives into crosslinked resins has been conducted as a route to synthesize hybrid organic/inorganic nanocomposites. The central cores of POSS molecules contain an inorganic cage with (SiO1.5)n stoichiometry where n=8,10 and 12. Each Si atom is capped with one H or R function giving an organic outer shell surrounding the nanometer‐sized inorganic inner cage. By including polymerizable functions on the R groups, a hybrid organic/inorganic macromer is obtained which can be copolymerized with organic monomers to create thermoplastic or thermoset systems. We have focused on incorporating POSS derivatives into crosslinking resins of the following types: (1) dicyclopentadiene (2) epoxies (3) vinyl esters (4) styrene‐DVB (5) MMA/1,4‐butane dimethacrylate (6) phenolics and (7) cyanate esters. One goal has been to determine if molecular dispersion of the POSS macromers has been achieved or if various degrees of aggregation occur during crosslinked resin formation. As network formation proceeds, a kinetic race between POSS molecular incorporation into the network versus phase separation into POSS‐rich regions (which then polymerize) occurs. Ultimately, we hope to determine the effects of such microstructural features on properties. Combustion of these hybrids creates a SiO2‐like surface layer that retards flame spread. Dynamic mechanical properties have been studied.

Cyanate ester (PT‐15, Lonza Corp) composites containing the inorganic–organic hybrid polyhedral oligomeric silsesquioxane (POSS) octaaminophenyl(T8)POSS [1; (C6H4NH2)8(SiO1.5)8] were synthesized. These PT‐15/POSS‐1 composites (99/1, 97/3, and 95/5 w/w) were characterized by X‐ray diffraction (XRD), transmission election microscopy (TEM), dynamic mechanical thermal analysis, solvent extraction, and Fourier transform infrared. The glass‐transition temperatures (Tg's) of the composite with 1 wt % 1 increased sharply versus the neat PT‐15, but 3 and 5 wt % 1 in these cyanate ester composites depressed Tg. All the PT‐15/POSS composites exhibited higher storage modulus (E′) values (temperature > Tg) than the parent resin, but these values decreased from 1 to 5 wt % POSS. The loss factor peak intensities decreased and their widths broadened upon the incorporation of POSS. XRD, TEM, and IR data were all consistent with the molecular dispersion of 1 due to the chemical bonding of the octaamino POSS‐1 macromer into the continuous cyanate ester network phase. The amino groups of 1 reacted with cyanate ester functions at lower temperatures than those at which cyanate ester curing by cyclotrimerization occurred. In contrast to 1, 3‐cyanopropylheptacyclopentyl(T8)POSS [2; (C5H9)7(SiO1.5)8CH2CH2CH2CN] had low solubility in PT‐15 and did not react with the resin below or at the cure temperature. Thus, phase‐separated aggregates of 2 were found in samples containing 1–10 wt % 2. Nevertheless, the Tg and E′ values (temperature > 285 °C) of these composites increased regularly with an increase in 2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3887–3898, 2005