Rajeswari M. Kasi

Side-Chain Liquid Crystalline Polymer Networks: Exploiting Nanoscale Smectic Polymorphism To Design Shape-Memory Polymers

Herein, we investigate the influence of nanoscale smectic polymorphism within end-on fixed side-chain liquid crystalline polymer networks (SCLCNs) on macroscopic shape-memory and actuation properties. We have synthesized a series of SCLC-type linear (TP-n) and cross-linked random terpolymers (XL-TP-n) with varying length of flexible methylene spacers (n = 5, 10, and 15) between polynorbornene main-chain and cholesteryl ester side-chains. Thermal and mechanical analyses by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirm a glass transition (T(g)), a clearing temperature (T(cl)), and a network structure in the XL-TP-n. Detailed structural investigation conducted using wide-angle and small-angle X-ray scattering (WAXS and SAXS) at room temperature proves self-assembled smectic A (SmA) polymorphism of the XL-TP-n which evolves from non-interdigitated bilayer (SmA(2)) for n = 5 to mixed layers of monolayer-like highly interdigitated layer (SmA(1)) and SmA(2) for n = 10 and to SmA(1) for n = 15. In addition, TP10 at temperatures above 60 °C interestingly shows transformation of SmA structure from mixed layer (SmA(1) + SmA(2)) to interdigitated structure (SmA(d)). The SmA polymorphism developed in TP-n during shape-memory cycles (SMCs) significantly impacts the ultimate strain responses. A mechanism for the unique interdigitation-based thermostrictive behavior is proposed. More importantly, this new actuation mechanism observed in these XL-TP-n can be exploited to develop intelligent thermal actuators.

Polymers Comprising Cholesterol: Synthesis, Self-Assembly, and Applications

This article reviews the current status of self-assembling liquid crystalline polymers comprising cholesterol. This article will focus on synthesis, structure-property relationships and strategies to direct ordering and packing of meso- and nanostructures of cholesterol polymers in the neat- or melt state and in solution. The applications of these self-assembled structures will be presented.

Protein polymer conjugates: improving the stability of hemoglobin with poly(acrylic acid).

The synthesis, characterization, and evaluation of a novel polymer-protein conjugate are reported here. The covalent conjugation of high-molecular weight poly(acrylic acid) (PAA) to the lysine amino groups of met-hemoglobin (Hb) resulted in the covalent conjugation of Hb to PAA (Hb-PAA conjugate), as confirmed by dialysis and electrophoresis studies. The retention of native-like structure of Hb in Hb-PAA was established from Soret absorption, circular dichroism studies, and the redox activity of the iron center in Hb-PAA. The peroxidase-like activities of the Hb-PAA conjugate further confirmed the retention of Hb structure and biological activity. Thermal denaturation of the conjugate was investigated by differential scanning calorimetry and steam sterilization studies. The Hb-PAA conjugate indicated an improved denaturation temperature (T(d)) when compared to that of the unmodified Hb. One astonishing observation was that polymer conjugation significantly enhanced the Hb-PAA storage stability at room temperature. After 120 h of storage at room temperature in phosphate-buffered saline (PBS) at pH 7.4, for example, Hb-PAA retained 90% of its initial activity and unmodified Hb retained <60% of its original activity under identical conditions of buffer, pH, and temperature. Our conjugate demonstrates the key role of polymers in enhancing Hb stability via a very simple, efficient, general route. Water-swollen, lightly cross-linked, stable Hb-polymer nanogels of 100-200 nm were produced quickly and economically by this approach for a wide variety of applications.

Thermally Switchable Aligned Nanopores by Magnetic‐Field Directed Self‐Assembly of Block Copolymers

A scalable approach for developing large area polymer films, with stimuli responsive vertically aligned nanopores is reported. Magnetic fields are used to create highly aligned hexagonally packed block copolymer cylindrical microdomains with order parameters exceeding 0.95. Selective etch removal of material yields nanoporous films which demonstrate reversible pore closure on heating.

Long circulating self-assembled nanoparticles from cholesterol-containing brush-like block copolymers for improved drug delivery to tumors.

Amphiphilic brush-like block copolymers composed of polynorbonene-cholesterol/poly(ethylene glycol) (P(NBCh9-b-NBPEG)) self-assembled to form a long circulating nanostructure capable of encapsulating the anticancer drug doxorubicin (DOX) with high drug loading (22.1% w/w). The release of DOX from the DOX-loaded P(NBCh9-b-NBPEG) nanoparticles (DOX-NPs) was steady at less than 2% per day in PBS. DOX-NPs were effectively internalized by human cervical cancer cells (HeLa) and showed dose-dependent cytotoxicity, whereas blank nanoparticles were noncytotoxic. The DOX-NPs demonstrated a superior in vivo circulation time relative to that of free DOX. Tissue distribution and in vivo imaging studies showed that DOX-NPs preferentially accumulated in tumor tissue with markedly reduced accumulation in the heart and other vital organs. The DOX-NPs greatly improved survival and significantly inhibited tumor growth in tumor-bearing SCID mice compared to that for the untreated and free DOX-treated groups. The results indicated that self-assembled P(NBCh9-b-NBPEG) may be a useful carrier for improving tumor delivery of hydrophobic anticancer drugs.

Self-assembled nanoparticles from thiol functionalized liquid crystalline brush block copolymers for dual encapsulation of doxorubicin and gold nanoparticles

We synthesized new amphiphilic brush liquid crystalline block copolymers (brush-chol-BCP) comprised of polymethacrylates bearing polyethylene oxide (PEO) in one block and polymethacrylates bearing a cholesterol mesogen with a hemitelechelic thiol end group. Polymethacrylate bearing PEO (PMA-g-PEO) was first synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT) and used as a macro-chain transfer agent to prepare block copolymer (PMA-g-PEO)-b-PC5MA-thioester (brush-chol-BCP-thioester). Brush-chol-BCP-thiol was obtained by the reduction of a thioester to thiol in the presence of butylamine. Gold nanoparticles (AuNPs) were prepared in situ with the brush-chol-BCP-thiol template via the reduction of gold ions and were stabilized by directly anchoring to the brush-chol-BCP-thiol chains through the coordination bonds with the thiol groups in the copolymer. The hydrophobic anticancer drug doxorubicin (DOX) was successfully encapsulated into AuNP-templated brush-chol-BCP-thiol via physical entrapment to form dual-encapsulated NPs with a high drug loading of 21.4% (w/w) and a high encapsulation efficiency of 85.6%. The dual-encapsulated NPs had an average size of 157 nm, spherical shape, excellent stability, and a sustained drug release pattern. More importantly, the dual-encapsulated NPs could be effectively internalized by human cervical cancer cells (Hela) and showed dose-dependent cytotoxicity, while the blank nanoparticles were non-cytotoxic at the tested concentrations. The results indicate that the brush-chol-BCP-thiol and their nanoparticles are promising carriers for dual encapsulation and delivery of an anticancer drug and metal nanoparticles.

Ultra-stable hemoglobin–poly(acrylic acid) conjugates

Stabilization of proteins against thermal deactivation is a major challenge, and a simple, facile, novel chemical approach is described here to overcome this hurdle. We report here, for the first time, the successful synthesis of ultrastable protein nanoparticles consisting of met-hemoglobin (Hb) conjugated with low molecular weight polyacrylic acid (PAA, Mw 8000) to form discrete nanoparticles. Hb–PAA nanoparticles were not deactivated when subjected to prolonged thermal treatment such as steam sterilization conditions (122 °C, 40 minutes, 17–20 psi), while the unprotected Hb lost most of its activity when subjected to the same heating conditions. Several Hb–PAA derivatives which resist thermal inactivation, in a similar manner, are produced and characterized. Interestingly, the highest activity retention, after the above thermal treatment, was ∼100% for the untreated samples. This resistance to heat is attributed to the enhanced thermodynamic stability of the Hb–PAA conjugate and improved re-folding of the denatured state to the native form, facilitated by PAA conjugation to Hb. This is a unique approach to stabilize Hb against thermal inactivation, and it is a major breakthrough in the production of stable Hb-based nanomaterials that can be safely sterilized in an autoclave for biomedical/in vivo applications.

Redox-sensitive nanoparticles from amphiphilic cholesterol-based block copolymers for enhanced tumor intracellular release of doxorubicin.

UNLABELLED A novel amphiphilic cholesterol-based block copolymer comprised of a polymethacrylate bearing cholesterol block and a polyethylene glycol block with reducible disulfide bonds (PC5MA-SS-PEO) was synthesized and evaluated as a redox-sensitive nanoparticulate delivery system. The self-assembled PC5MA-SS-PEO nanoparticles (SS-NPs) encapsulated the anticancer drug doxorubicin (DOX) with high drug loading (18.2% w/w) and high encapsulation efficiency (94.9%). DOX-encapsulated PC5MA-SS-PEO self-assembled nanoparticles (DOX-encapsulated SS-NPs) showed excellent stability and exhibited a rapid DOX release in response to dithiothreitol reductive condition. Importantly, following internalization by lung cancer cells, the reducible DOX-encapsulated SS-NPs achieved higher cytotoxicity than the non-reducible thioester NPs whereas blank nanoparticles were non-cytotoxic. Furthermore, in vivo imaging studies in tumor-bearing severe combined immunodeficiency (SCID) mice showed that the nanoparticles preferentially accumulated in tumor tissue with remarkably reduced accumulation in the healthy non-target organs. The results indicated that the SS-NPs may be a promising platform for cancer-cell specific delivery of hydrophobic anticancer drugs. FROM THE CLINICAL EDITOR The use of nanocarriers for drug delivery against tumors has been under intense research. One problem of using carrier system is the drug release kinetics at tumor site. In this article, the authors continued their previous study in the development of an amphiphilic cholesterol-based block copolymer with redox-sensitive modification, so that the payload drug could be released in response to the microenvironment. The interesting results should provide a new direction for designing future novel nanocarrier systems.

Novel surface plasmon resonance sensor for the detection of heme at biological levels via highly selective recognition by apo-hemoglobin.

We have developed a novel surface plasmon resonance (SPR) biosensor for heme detection that utilizes the reconstitution of the heme cofactor with apohemoglobin (apoHb), hemoglobin from which the heme has been removed, as the sensing mechanism. The binding is highly specific, efficient and generated very strong SPR signals. This is the first report that uses immobilization of the apoprotein in a hydrophilic polymer matrix and senses the corresponding cofactor by SPR. This is also the first report of high sensitivity heme detection in real time by SPR and the sensing surface is re-generated many times without loss of sensitivity or selectivity. The sensing surface was fabricated by covalent immobilization of hemoglobin in a polyacrylic acid matrix in situ, which allowed for a high concentration of protein to be located in the plasmon detection range on the Au chip. Removal of the heme from the hemoglobin-polymer conjugate (Hb-PAA) resulted in a surface anchored apoHb-polymer conjugate. The limit of detection was approximately 2 μM or 1.30 μg/mL, which is relevant for biological heme levels (1-50 μM for hemolytic pathological conditions). This apoHb-polyacrylic acid system demonstrates a new concept in SPR detection with the use of protein cofactor binding pockets for analyte detection. The methodology that we developed here may be extended for the detection of a number of other cofactor molecules with high sensitivity, selectivity and low detection limits. In future, such sensors could be useful for the development of point-of-care devices to detect biologically important small molecules.

Reduced in vivo toxicity of doxorubicin by encapsulation in cholesterol-containing self-assembled nanoparticles.

We previously reported the development of an amphiphilic brush-like block copolymer composed of polynorbornene-cholesterol/polyethylene glycol (P(NBCh9-b-NBPEG)) that self-assembles in aqueous media to form long circulating nanostructures capable of encapsulating doxorubicin (DOX-NPs). Biodistribution studies showed that this formulation preferentially accumulates in tumor tissue with markedly reduced accumulation in the heart and other major organs. The aim of the current study was to evaluate the in vivo efficacy and toxicity of DOX containing self-assembled polymer nanoparticles in a mouse xenograft tumor model and compare its effects with the hydrochloride non-encapsulated form (free DOX). DOX-NPs significantly reduced the growth of tumors without inducing any apparent toxicity. Conversely, mice treated with free DOX exhibited significant weight loss, early toxic cardiomyopathy, acute toxic hepatopathy, reduced hematopoiesis and fatal toxicity. The improved safety profile of the polymeric DOX-NPs can be explained by the low circulating concentration of non-nanoparticle-associated drug as well as the reduced accumulation of DOX in non-target organs. These findings support the use of P(NBCh9-b-NBPEG) nanoparticles as delivery platforms for hydrophobic anticancer drugs intended to reduce the toxicity of conventional treatments.