Cross-linked Core Research Articles

Design and Synthesis of Core–Shell Microgels with One‐Step Clickable Crosslinked Cores and Ultralow Crosslinked Shells

AbstractThe present study is conducted to explore the engineering of core–shell microgels such that the core can be rapidly labeled with a variety of fluorophores, while the shell retains the softness needed in specific biomedical applications. Azide containing crosslinked core particles based on a crosslinked poly(N‐isopropylacrylamide) particle, using a one‐pot, multistep polymerization is synthesized. A core–shell microgel is then synthesized by growing a crosslinker‐free poly(N‐isopropylacrylamide)‐co‐acrylic acid (ULC10AAc) shell through a two‐step seed and feed polymerization. A simple “click” reaction between the azide present on the core and dibenzocyclooctyne containing fluorophores to make dyed core–shell microgels is further demonstrated. This approach toward dyed core–shell microgels eliminates the difficulty of crossreactivity between shell‐localized chemoligation sites and the core‐localized functionalities. The use of strained‐ring systems to achieve the click reaction eliminates the use of cytotoxic catalysts common in traditional click chemistry. This approach allows not only to label the microgel core with different fluorophores but also to synthesize multiprobe core–shell microgel by simultaneously labeling a microgel core with multiple different fluorophores.

Ketal core cross-linked micelles for pH-triggered release of doxorubicin

A ketal core cross-linked (CCL) micelle system of block copolymers of poly(oligo(ethylene glycol) methyl ether methacrylate)-b-poly(styrene-alt-maleic anhydride)-b-poly(styrene) (POEGMA-b-PSMA-b-PS) was prepared by the combination of the reversible addition-fragmentation chain transfer (RAFT) polymerization and amidation process. Doxorubincin (DOX), a model anticancer drug, was loaded into block copolymer micelles with POEGMA segment as hydrophilic corona and PSMA-b-PS block as hydrophobic core. Then core cross-linking was carried out by amidation reaction between maleic anhydride moiety and difunctional amino cross-linker bearing an acid cleavable bond (ketal). The ketal CCL micelles illustrated good stability under physiological condition but disassociated rapidly under acidic pH conditions. TEM images presented spherical shape of CCL micelles with average hydrodynamic diameter at around 45 nm. The DOX release experiments demonstrated a rapid DOX release at pH 5.0 compared to pH 7.4.

Diselenide Core Cross-Linked Micelles of Poly(Ethylene Oxide)-b-Poly(Glycidyl Methacrylate) Prepared through Alkyne-Azide Click Chemistry as a Near-Infrared Controlled Drug Delivery System.

In this article, a drug delivery system with a near-infrared (NIR) light-responsive feature was successfully prepared using a block copolymer poly(ethylene oxide)-b-poly(glycidyl methacrylate)-azide (PEO-b-PGMA-N3) and a cross-linker containing a Se-Se bond through “click” chemistry. Doxorubicin (DOX) was loaded into the core-cross-linked (CCL) micelles of the block copolymer along with indocyanine green (ICG) as a generator of reactive oxygen species (ROS). During NIR light exposure, ROS were generated by ICG and attacked the Se-Se bond of the cross-linker, leading to de-crosslinking of the CCL micelles. After NIR irradiation, the CCL micelles were continuously disrupted, which can be a good indication for effective drug release. Photothermal analysis showed that the temperature elevation during NIR exposure was negligible, thus safe for normal cells. In vitro drug release tests demonstrated that the drug release from diselenide CCL micelles could be controlled by NIR irradiation and affected by the acidity of the environment.

Fabrication of Core Crosslinked Polymeric Micelles as Nanocarriers for Doxorubicin Delivery: Self-Assembly, In Situ Diselenide Metathesis and Redox-Responsive Drug Release.

Polymeric micelles (PMs) have been used to improve the poor aqueous solubility, slow absorption and non-selective biodistribution of chemotherapeutic agents (CAs), albeit, they suffer from disassembly and premature release of payloads in the bloodstream. To alleviate the thermodynamic instability of PMs, different core crosslinking approaches were employed. Herein, we synthesized the poly(ethylene oxide)-b-poly((2-aminoethyl)diselanyl)ethyl l-aspartamide)-b-polycaprolactone (mPEG-P(LA-DSeDEA)-PCL) copolymer which self-assembled into monodispersed nanoscale, 156.57 ± 4.42 nm, core crosslinked micelles (CCMs) through visible light-induced diselenide metathesis reaction between the pendant selenocystamine moieties. The CCMs demonstrated desirable doxorubicin (DOX)-loading content (7.31%) and encapsulation efficiency (42.73%). Both blank and DOX-loaded CCMs (DOX@CCMs) established appreciable colloidal stability in the presence of bovine serum albumin (BSA). The DOX@CCMs showed redox-responsive drug releasing behavior when treated with 5 and 10 mM reduced glutathione (GSH) and 0.1% H2O2. Unlike the DOX-loaded non-crosslinked micelles (DOX@NCMs) which exhibited initial burst release, DOX@CCMs demonstrated a sustained release profile in vitro where 71.7% of the encapsulated DOX was released within 72 h. In addition, the in vitro fluorescent microscope images and flow cytometry analysis confirmed the efficient cellular internalization of DOX@CCMs. The in vitro cytotoxicity test on HaCaT, MDCK, and HeLa cell lines reiterated the cytocompatibility (≥82% cell viability) of the mPEG-P(LA-DSeDEA)-PCL copolymer and DOX@CCMs selectively inhibit the viabilities of 48.85% of HeLa cells as compared to 15.75% of HaCaT and 7.85% of MDCK cells at a maximum dose of 10 µg/mL. Overall, all these appealing attributes make CCMs desirable as nanocarriers for the delivery and controlled release of DOX in tumor cells.

Molecularly Imprinted Polymeric Receptors with Interfacial Hydrogen Bonds for Peptide Recognition in Water

Protein receptors bind their peptide ligands by a combination of hydrophobic and hydrogen-bonding interactions to achieve high affinity and selectivity. Construction of synthetic receptors for peptides by the same principle, however, is challenging because of the complexity of the guest molecules and subtle structural differences among closely related sequences. Molecular imprinting of peptides in surface–core doubly-cross-linked micelles yielded hydrophobic pockets complementary to the hydrophobic side chains of peptides. Amide-functionalized bis­(acrylamide) cross-linkers such as N,N′-methylene­bis­(acrylamide) (MBAm) used in the core cross-linking installed a layer of hydrogen bonds at the surfactant/water interface and was found to enhance the molecular recognition of peptides in water, particularly hydrophilic ones rich in polar residues. An extremely strong imprinting effect was obtained, with the imprinted/nonimprinted ratio ranging from 3000 to 10000 for model tripeptides. These hydrogen bonds allowed distinction of closely related peptide sequences and enabled a general, simple, one-pot preparation of highly selective receptors for binding complex hydrophilic peptides with <200 nM affinity in aqueous buffer.

Computer simulation of the core-shell microgels synthesis via precipitation polymerization

In this work we presented a novel computational model of precipitation polymerization allowing one to obtain core-shell microgels via a realistic cross-linking process based on the experimental procedure. We showed that the cross-linker–monomer reactivity ratios r are responsible for the microgel internal structure. Values of r lower than 1 correspond to the case when alternating sequences occur at the early reaction stages; this leads to the formation of microgels with pronounced core-shell structure. The distribution of dangling ends for small values of r becomes bimodal with two well-distinguished peaks, which correspond to the core (short dangling ends) and corona (long dangling ends) regions. The density profiles confirm the existence of two distinct regions for small r: a densely cross-linked core and a loose corona entirely consisting of dangling ends with no cross-linker. The consumption of the cross-linker in the course in the microgel formation was found to be in a perfect agreement with the predictions of Monte Carlo (MC) model in the sequence space.

Dynamic core crosslinked camptothecin prodrug micelles with reduction sensitivity and boronic acid-mediated enhanced endocytosis: An intelligent tumor-targeted delivery nanoplatform.

The physicochemical properties of camptothecin (CPT) limit its clinical application. To maximize drug efficacy, a novel intelligent prodrug delivery nanoplatform with a tumor microenvironment-cleavable core crosslinking strategy was proposed based on a phenylboronic acid (PBA) modified polyethylene glycol (PEG)-polyglutamic acid (PGlu) polymer with disulfide-bonded CPT, called PBA-PEG-P(Glu-co-GlussCPT). The fabricated nanoplatform was a spherical micelle that could withstand dilution and carry a large number of therapeutic molecules to the tumor tissues, thereby minimizing premature drug release. Moreover, the nanoplatform release 6.2±0.62, 12.4±1.8, 46.7±0.33, and 79.2±1.58% of CPT after incubation in 0.02, 1, 5, and 10mM dithiothreitol for 24h, respectively, exhibiting good reduction-sensitivity. Moreover, the nanoplatform exhibited significant antiproliferative activity against tumor cells. In addition, with PBA modification, the nanoplatform demonstrated enhanced endocytosis efficiency. This prodrug nanoplatform also exhibited significant in vivo antitumor efficacy on both murine and human hepatoma xenograft models, without showing significant systemic toxicity but demonstrating good biocompatibility. In other words, this novel intelligent prodrug delivery nanoplatform with tumor microenvironment-cleavable core crosslinking strategy and active targeting strategy based on prodrug polymer PBA-PEG-P(Glu-co-GlussCPT) demonstrated multiple functions and significant potential for antitumor drug delivery.

Deswelling studies of pH and temperature-sensitive ultra-low cross-linked microgels with cross-linked cores

Microgels prepared without exogenous crosslinker have recently been explored for diverse applications in biotechnology. However, our fundamental understanding of structure-property relationships for this class of materials is still lacking, especially in the context of more complex structures such as core-shell particles. In this article, core-shell microgels were prepared by seed-mediated, surfactant-free emulsion polymerization using a N,N′-methylenebis (acrylamide) (BIS) cross-linked poly(N-isopropylacrylamide) (pNIPAm) microgel core upon which a crosslinker-free poly(N-isopropylacrylamide)-co-acrylic acid (ULC10AAc) shell was synthesized. Dynamic light scattering (DLS) and phase analysis light scattering (PALS) measurements show that the hydrodynamic radius and electrophoretic mobility of the core-shell microgels increase significantly with increasing pH due to the pH responsive ULC10AAc shell, while the temperature sensitivity of the microgels is also strongly pH dependent. The turbidity and the temperature-dependent scattering intensity plots of microgels at different pH also provide insight into the charged state of the microgels under the studied conditions. For example, we observe multiple temperature-induced transitions when the pH is either 4.5 or 6.5, illustrating that the core and shell domains, while remaining mechanically connected, are only partially coupled thermodynamically. These studies provide insight into the perturbation of ULC microgel behavior that might be brought about due to the presence of a higher density core region. Complex architectures such as these are relevant in biotechnology applications where the soft, deformable ULC shell is advantageous to control the polymer-biology interface, but a denser core region might be required to obtain a higher loading of encapsulated therapeutics, tracking dyes, or oligonucleotides. Thus, it is important to understand the synthetic conditions that allow a ULC shell to remain “ULC-like” despite the presence of a denser core.

Influence of Core Cross-Linking and Shell Composition of Polymeric Micelles on Immune Response and Their Interaction with Human Monocytes.

Block copolymer micelles have received increasing attention in the last decades, in particular for their appealing properties in nanomedicine. However, systematic investigations of the interaction between polymeric micelles and immune cells are still rare. Therefore, broader studies comparing the structural effects remain inevitable for a comprehensive understanding of the immune response and for the design of efficient, nonimmunogenic delivery systems. Here, we present novel block copolymer micelles with the same hydrophobic core, based on a copolymer of BA and VDM, and various hydrophilic shells ranging from common PEG derivatives to morpholine-based materials. The influence of these shells on innate immune responses was studied in detail. In addition, we investigated the impact of micelle stability by varying the cross-linking density in the micellar core. Surprisingly, whereas different shells had only a minor impact on immune response, micelles with reduced cross-linking density considerably enhanced the release of cytokines from isolated human monocytes. Moreover, the uptake of non-cross-linked micelles by monocytes was significantly higher as compared to cross-linked materials. Our study emphasizes the importance of the micellar stability on the interaction with the immune system, which is the key for any stealth properties in vivo. Polymers based on morpholines result in a similar low response as the PEG derivative and may represent an interesting alternative to the common PEGylation.

Poly(ethylene glycol) shell-sheddable TAT-modified core cross-linked nano-micelles: TAT-enhanced cellular uptake and lysosomal pH-triggered doxorubicin release

This study aimed to develop sheddable polyethylene glycol (PEG) shells with TAT-modified core cross-linked nanomicelles as drug-delivery carriers of doxorubicin (DOX) to establish a programmed response against the tumor microenvironment, enhanced endocytosis, and lysosomal pH-triggered DOX release. First, poly(L-succinimide) (PSI) underwent a ring-opening reaction with ethylenediamine to generate poly(N-(2-aminoethyl)-l-aspartamide) (P(ae-Asp)). Next, the thiolytic cleavable PEG, 3,4-dihydroxyphenylacetic acid, and TAT were grafted onto P(ae-Asp) to synthesize the amphiphilic graft copolymer of mPEG-SS-g-P(ae-Asp)-MCA-DA-TAT. In aqueous solution, the amphiphilic polymer self-assembled into nanomicelles, encapsulating DOX into the hydrophobic core of micelles. TAT was shielded by the PEG corona during circulation to avoid non-specific transmembrane interaction with normal cells, while the tumor redox environment-responsive shedding of PEG could expose TAT to promote internalization of tumor cells. In order to improve the stability of nanomicelles and achieve pH-triggered drug release, a core cross-linking strategy based on the coordination of catechol and Fe3+ was adopted. In vitro studies demonstrated that core cross-linked nanomicelles maintained the nanostructure in 100 times dilution in pH 7.4 phosphate-buffered saline (PBS). Moreover, DOX release from DOX-loaded core cross-linked nanomicelles (DOX-TAT-CCLMs) was favored at simulated lysosomal conditions over simulated plasma conditions, indicating that these nanomicelles demonstrate characteristics of pH-triggered DOX release. The TAT modification considerably enhanced the mean fluorescence intensity of the nanomicelles endocytosed by MCF-7/ADR cells by 8 times, compared with DOX·HCl after 8 h of incubation. Notably, the IC50 value of nanomicelles (11.61 ± 0.95 μg/mL) was nearly 4 times lower than that of DOX·HCl against MCF-7/ADR cells, implying that the nanomicelles could overcome drug resistance observed in MCF-7/ADR cells. Furthermore, the DOX-TAT-CCLMs reported superior tumor growth suppression in a 4T1 tumor-bearing mouse model. Thus, the redox- and pH- stimuli stepwise-responsive novel nanomicelles fabricated from the mPEG-SS-g-P(ae-Asp)-MCA-DA-TAT graft copolymer exhibited multifunctionality and displayed great potential for drug delivery.

Conversion of an Injectable MMP-Degradable Hydrogel into Core-Cross-Linked Micelles.

In this study, a new type of injectable hydrogel called “HyMic” that can convert into core cross-linked (CCL) micelles upon exposure to matrix metalloproteinases (MMP’s), was designed and developed for drug delivery applications. HyMic is composed of CCL micelles connected via an enzyme cleavable linker. To this end, two complementary ABA block copolymers with polyethylene glycol (PEG) as B block were synthesized using atom transfer radical polymerization (ATRP). The A blocks were composed of a random copolymer of N-isopropylacrylamide (NIPAM) and either N-(2-hydroxypropyl)methacrylamide-cysteine (HPMA-Cys) or N-(2-hydroxypropyl) methacrylamide-ethylthioglycolate succinic acid (HPMA-ETSA). Mixing the aqueous solutions of the obtained polymers and rising the temperature above the cloud point of the PNIPAM block resulted in the self-assembly of these polymers into flower-like micelles composed of a hydrophilic PEG shell and hydrophobic core. The micellar core was cross-linked by native chemical ligation between the cysteine (in HPMA-Cys) and thioester (in HPMA-ETSA) functionalities. A slight excess of thioester to cysteine groups (molar ratio 3:2) was used to allow further chemical reactions exploiting the unreacted thioester groups. The obtained micelles displayed a Z-average diameter of 80 ± 1 nm (PDI 0.1), and ζ-potential of −4.2 ± 0.4 mV and were linked using two types of pentablock copolymers of P(NIPAM-co-HPMA-Cys)-PEG-peptide-PEG-P(NIPAM-co-HPMA-Cys) (Pep-NC) to yield hydrogels. The pentablock copolymers were synthesized using a PEG-peptide-PEG ATRP macroinitiator and the peptide midblock (lysine-glycine-proline-glutamine-isoleucine-phenylalanine-glycine-glutamine-lysine (Lys-Gly-Pro-Gln-Gly-Ile-Phe-Gly-Gln-Lys)) consisted of either l- or d-amino acids (l-Pep-NC or d-Pep-NC), of which the l-amino acid sequence is a substrate for matrix metalloproteases 2 and 9 (MMPs 2 and 9). Upon mixing of the CCL micelles and the linker (l/d-Pep-NC), the cysteine functionalities of the l/d-Pep-NC reacted with remaining thioester moieties in the micellar core via native chemical ligation yielding a hydrogel within 160 min as demonstrated by rheological measurements. As anticipated, the gel cross-linked with l-Pep-NC was degraded in 7–45 days upon exposure to metalloproteases in a concentration-dependent manner, while the gel cross-linked with the d-Pep-NC remained intact even after 2 months. Dynamic light scattering analysis of the release medium revealed the presence of nanoparticles with a Z-average diameter of ∼120 nm (PDI < 0.3) and ζ-potential of ∼−3 mV, indicating release of core cross-linked micelles upon HyMic exposure to metalloproteases. An in vitro study demonstrated that the released CCL micelles were taken up by HeLa cells. Therefore, HyMic as an injectable and enzyme degradable hydrogel displaying controlled and on-demand release of CCL micelles has potential for intracellular drug delivery in tissues with upregulation of MMPs, for example, in cancer tissues.

Novel Organic/Inorganic Hybrid Star Polymer Surface-Crosslinked with Polyhedral Oligomeric Silsesquioxane

Novel organic/inorganic hybrid star polymer was prepared dually crosslinked within inner-core via divinylbenzene (DVB) and outer-surface via octafunctional polyhedral oligomeric silsesquioxane (POSS). Core cross-linked star polymers bearing dialkynyl-terminated polystyrene arms, (dialkynyl-PS)n-CCL, were synthesized at first by the atom transfer radical polymerization (ATRP) of DVB using α,α-dialkynyl-terminated PS macroinitiator, followed by the subsequent fractionation. Under high dilution conditions, (dialkynyl-PS)n-CCL was subjected to surface cross-linking with octa(3-azidopropyl) polyhedral oligomeric silsesquioxane, POSS-(N3)8, via click reaction, affording POSS-functionalized hybrid polymer doubly cross-linked within core and surface regions, SCL-(PS)n-CCL. FT-IR, 1H NMR, GPC, and elemental analysis results revealed that on average, the obtained hybrid polymer possesses a cross-linked PDVB inner core, ∼14 linear PS arms (the Mw per arm of 5.1 kDa), and ∼4-5 POSS moieties at outer surface. Differential scanning calorimetry (DSC) thermograms and thermogravimetric analysis (TGA) revealed that after surface cross-linking the thermal stability of SCL-(PS)n-CCL is considerably improved. This work provides a proof-of-concept example for the preparation of dually cross-linked hybrid star polymer, which represents a novel category of organic/inorganic composite materials with unique chain architectures.

Effect of Core Cross-linking on the Physical Properties of Poly(dimethylsiloxane)-Based Diblock Copolymer Worms Prepared in Silicone Oil

A trithiocarbonate-capped poly(dimethylsiloxane) (PDMS) precursor is chain-extended via reversible addition–fragmentation chain transfer dispersion polymerization of 2-(dimethylamino)ethyl methacrylate (DMA) in decamethylcyclopentasiloxane (D5) silicone oil at 90 °C. For a fixed mean degree of polymerization (DP) of 66 for the PDMS steric stabilizer block, targeting core-forming PDMA block DPs of between 105 and 190 enables the preparation of either well-defined worms or vesicles at a copolymer concentration of 25% w/w. The as-synthesized linear PDMS66–PDMA100 worms exhibit thermoresponsive behavior in D5, undergoing a worm-to-sphere transition on heating to 100 °C. Variable temperature 1H NMR spectroscopy indicates that this thermal transition is driven by reversible solvent plasticization of the PDMA cores. This change in copolymer morphology is characterized by transmission electron microscopy (TEM) studies, variable temperature dynamic light scattering and small-angle X-ray scattering experiments. Oscillatory rheology studies indicate that degelation occurs at 32 °C, but shear-induced polarized light imaging measurements suggest that full conversion of worms into spheres requires significantly higher temperatures (∼110 °C). 1,2-Bis(2-iodoethoxy)ethane (BIEE) is evaluated as a cross-linker for PDMS66–PDMAx diblock copolymer nano-objects in D5. This bifunctional reagent quaternizes the tertiary amine groups on the DMA residues within the worm cores, introducing cross-links via the Menshutkin reaction. TEM studies confirm that such covalently-stabilized worms no longer undergo a worm-to-sphere transition when heated to 100 °C. Kinetic studies performed on PDMS66–PDMA176 vesicles suggest that cross-linking requires approximately 13 h at 20 °C to ensure that these nano-objects remain intact when dispersed in chloroform, which is a good solvent for both blocks. Oscillatory rheology studies of a PDMS66–PDMA100 worm gel indicated that covalent stabilization using a BIEE/DMA molar ratio of 0.15 increased its dynamic elastic modulus (G′) by almost two orders of magnitude. Furthermore, such cross-linked worms exhibit a much lower critical gelation concentration (∼2% w/w) compared to that of the linear precursor worms (∼12% w/w).

Triple-Responsive Pickering Emulsion Stabilized by Core Cross-linked Supramolecular Polymer Particles.

It is significant to explore multiresponsive Pickering emulsions because of their flexibility in terms of demulsification in comparison with the single stimuli-responsive systems. In this study, we described a triple-responsive oil-in-water Pickering emulsion that was stabilized by amphiphilic core cross-linked supramolecular polymer particles (CCSPs). For this purpose, β-cyclodextrin-terminated poly(N-isopropylacrylamide) (PNIPAM-β-CD) and azobenzene-capped poly(4-vinylpyridine) (P4VP-azo) were separately synthesized by reversible addition-fragmentation chain transfer polymerization. By virtue of the inclusion interaction between the β-CD host and the azobenzene guest in dimethyl sulfoxide, the amphiphilic supramolecular block copolymer, poly(4-vinylpyridine)-b-poly(N-isopropylacrylamide) (P4VP-b-PNIPAM), was formed. CCSPs were prepared through the combination of the self-assembly of P4VP-b-PNIPAM in the selective solvent, water, and the cross-linking of the P4VP core with 1,4-dibromobutane. Due to thermoresponsiveness of PNIPAM shells and the supramolecular linkages between the cross-linked hydrophobic P4VP core and hydrophilic PNIPAM shells, the as-prepared CCSPs exhibited temperature-, light-, and amantadine hydrochloride guest-triggered morphological transitions. Such triple-responsive morphological transitions gifted CCSPs stabilized oil-in-water Pickering emulsion with flexible demulsification in response to various factors, such as thermo, light, and amantadine hydrochloride or their combinations. Such triple-responsive oil-in-water Pickering emulsion also provided an ideal platform for heterogeneous reactions conducted at the oil-water interface. A large interfacial area and responsive demulsification allowed the reaction to be performed with an efficient and sustainable pattern.

Synthesis of high-molecular-weight star-shaped cyclopoymers of divinyl ethers and their network membranes via controlled cationic cyclopolymerization

Star-shaped cyclopolymers were first synthesized on the basis of living cationic cyclopolymerization of divinyl ethers bearing a variety of bulky substituents, including cyclohexene, norbornene, norbornane, cyclic acetal, and adamantane groups. All the obtained cyclopolymers exhibited a high degree of cyclization, as high as ~97%, judging from the contents of residual pendant vinyl ether double bonds in the polymers. The glass transition temperatures (Tgs) of both the linear and star-shaped cyclopolymers were in the range of 145−229 °C depending on the pendant substituents. Methacrylate-terminated end-functionalized star-shaped cyclopolymers were synthesized by the functionalized initiator-based living cationic cyclopolymerization of divinyl ethers. The subsequent cross-linked core formation occurred via the reaction of the growing tail termini, whereas the methacrylate head terminals remained intact. The obtained end-functionalized star-shaped cyclopolymers were subjected to a thermal cross-linking reaction to yield star-shaped cyclopolymer networks with film-forming ability. Controlled cationic cyclopolymerizations of divinyl ethers with cyclohexene, norbornene, norbornane, cyclic acetal, or adamantane moiety were carried out. High-molecular-weight star-shaped cyclopolymers were synthesized by the reaction of the formed living cyclopolymers with a small amount of divinyl ether crosslinking agent. Glass transition temperatures (Tg’s) of both the cyclopolymers and star-shaped cyclopolymers were as high as 145−229 oC. Methacrylate-terminated end-functionalized star-shaped cyclopolymers were synthesized by the functionalized initiator-based living cationic cyclopolymerization of divinyl ethers followed by the chain linking reactions among the formed living cyclopolymers with divinyl ether crosslinker. The obtained end-functionalized star-shaped cyclopolymers were subjected to thermal crosslinking reaction to give star-shaped cyclopolymer networks with film-forming ability.

Bioinspired nanoplatform for enhanced delivery efficiency of doxorubicin into nucleus with fast endocytosis, lysosomal pH-triggered drug release, and reduced efflux

A novel bioinspired nanoplatform capable of fast endocytosis, lysosomal pH-triggered drug release, and reduced drug efflux based on PBA-PEG-b-P(Glu-co-GluDA) copolymer was developed in this study. The synthesized copolymer could facilitate doxorubicin encapsulation with relatively high drug-loading content and efficiency. Inspired by mussel byssal threads, a core crosslinking strategy based on the coordination between catechol and ferric ions was introduced to improve the stability of nanomicelles and realize lysosomal pH-controlled drug release. This nanoplatform could maintain integrity even after being dissolved in a good solvent, demonstrating its the potential to withstand infinite dilution of plasma after intravenous injection. Moreover, this nanoplatform demonstrated lysosomal pH-triggered drug release, and the cumulative release amount of doxorubicin under a simulated lysosomal condition was 13 times higher than that under a simulated plasma condition. Moreover, as a result of the high binding capacity between phenylboronic acid (PBA) and sialic acid on the surface of human hepatoma cell line (HepG2), the fast and enhanced endocytosis in addition to lysosomal pH-triggered release property and significantly low efflux, this nanoplatform exhibits improved delivery efficiency of doxorubicin into the nucleus and notably outstanding antiproliferative effects compared with doxorubicin. Furthermore, the PBA modification remarkably increased the mean fluorescence intensity of this nanoplatform endocytosed by HepG2 cells to twice that of doxorubicin after one hour of incubation. The nanoplatform exhibited an inhibition rate of 70% against tumor growth. Thus, this novel nanoplatform based on PBA-PEG-b-P(Glu-co-GluDA) copolymer displayed multifunctionality and exhibited great potential as an intelligent nanoplatform for antitumor drug delivery.

Cationic versus anionic core-shell nanogels for transport of cisplatin to lung cancer cells

Stimuli-responsive polymeric nanogels have been proposed as nanocarriers of cisplatin to maximize its effect for cancer treatment. In this work, a comparative study between anionic core nanogels (ACN) and cationic core nanogels (CCN), both with PEGylated shells, has been performed. The nanogels were synthesized with different cross-linked cores: CCN with poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA) and ACN with poly(2-methacryloyloxi benzoic acid) (P2MBA). Cisplatin chelate formation with carboxylic acids (ACN) or metal coordination with the amine groups (CCN) leads to a high loading of cisplatin into the nanocarriers. The nanocarriers ability to contain and modulate the supply of cisplatin was tested according to the pH of the medium, in which ACN efficiently released the drug at a typical pH value of a tumor tissue (pH = 6.8) while CCN only releases the drug at more acidic, endosome like, conditions (pH = 5). The effect of drug-free nanogels on cell lines NCI-H1437 (non-small cell lung carcinoma) was evaluated, showing biocompatibility at all concentrations studied (30–400 μg/mL) for both ACN and CCN. However, the survival percentage of the cells in contact with cisplatin-loaded nanogels were dependent on the dose, the time of contact and the type of nanogel. Cisplatin loaded CCN induced lower cell viability after 48 h of contact. Fluorescence microscopy showed a viable internalization of the CCN nanogels, this was confirmed by flow cytometry in which 37.8% of cells contained drug loaded CCNs after 30 min of contact, representing a more effective nanocarrier for cisplatin to this cell-line.

Understanding the Phase and Morphological Behavior of Dispersions of Synergistic Dual-Stimuli-Responsive Poly(N-isopropylacrylamide) Nanogels.

This work represents a detailed investigation into the phase and morphological behavior of synergistic dual-stimuli-responsive poly(N-isopropylacrylamide) nanogels, a material that is of considerable interest as a matrix for in situ forming implants. Nanogels were synthesized with four different diameters (65, 160, 310, and 450 nm) as monodispersed particles. These different samples were then prepared and characterized as both dilute (0.1 wt %) and concentrated dispersions (2–22 wt %). In the dilute form, all of the nanogels had the same response to the triggers of the physiological temperature and ionic strength. In water, the nanogels would deswell when heated above 32 °C, while they would aggregate if heated above this temperature at the physiological ionic strength. In the concentrated form, the nanogels exhibited a wide range of morphological changes, with liquid, swollen gel, shrunken gel, and aggregate structures all possible. The occurrence of these structures was dependent on many factors such as the temperature, ionic strength of the solvent, size and ζ-potential of the nanogel, and dispersion concentration. We explored these factors in detail with techniques such as visual studies, rheology, effective volume fraction, and shape factor measurement. The different-sized nanogels displayed differing phase and morphological behavior, but generally higher concentrations of the nanogels (>7 wt %) yielded gels in water with the transitions depending on the temperature. The smallest nanogel (65 nm diameter) exhibited the most unique behavior; it did not form a swollen gel at any concentration tested. Shape factor measurement for the nanogel samples showed that two of the larger three samples (160 and 310 nm) had core–shell structures with denser core cross-linking, while the smallest nanogel sample displayed a homogeneous cross-linked structure. We hypothesize that the smallest nanogels are able to undergo more extensive interpenetration compared to the larger nanogels, which meant that the smallest nanogel was not able to form a swollen gel. In the presence of salt at 12 wt %, all of the nanogels formed aggregates when heated above 35 °C due to the screening of the electrostatic stabilization by the salt. This work revealed unique behavior of the smallest nanogel with a homogeneous cross-linked structure; its phase and morphological behavior were unlike a particle dispersion, rather these were more similar to those of a branched polymer solution. In total, these findings can be used to provide information about the design of poly(N-isopropylacrylamide) nanogel dispersions for different applications where highly specific spatiotemporal control of morphology is required, for example, in the formation of in situ forming implants or for pore blocking behavior.

Low degree of polymerization xylooligosaccharides production from almond shell using immobilized nano-biocatalyst

In this work, the effect of particle size on alkali pretreatment of the almond shell was evaluated for recovery of hemicellulose. Further, endoxylanase from Thermomyces lanuginosus was immobilized on Fe-based magnetic nanoparticles to enable reuse of enzyme. Reduction in particle size significantly influences the recovery of hemicellulose as particle size below 120 μm enable recovery of 97% available hemicellulose in 1 h at 121 °C with 2 M alkali. The enzyme could retain 93.3% of enzymatic activity upon immobilization onto magnetic support using glutaraldehyde (25 mM) and was at par with the free enzyme in terms of pH and temperature profile. The measurement of reaction kinetics (Km and Vmax) indicates similar values for free and immobilized enzyme. The structural and morphological analysis indicates presence near spherical magnetic core and successful cross-linking of the enzyme without alteration of the magnetic core. The immobilized enzyme was able to hydrolyze hemicellulose to produce XOS, the yield equivalent to 67.4% of that obtained using free enzyme at 50 °C. The comparison of XOS production ability at 50 and 60 °C, suggests that the immobilized enzyme retains activity as similar yield was obtained at both temperatures, whereas, the yield for free enzyme decreases significantly. The XOS yield on recycling of immobilized enzyme for three successive cycles was found to reduce to 41% of the initial cycle. However, in all cycles of enzymatic hydrolysis, the percentage of xylobiose was found to be above 90%.

Glucose-responsive complex micelles for self-regulated delivery of insulin with effective protection of insulin and enhanced hypoglycemic activity in vivo

Large amounts of insulin-loaded glucose-responsive micelles based on poly(amino acid)s have been developed for diabetes treatment over last decades, but most of them could not effectively protect insulin from enzymatic degradation in vivo because the micellar core was biodegradable and lacked protective structure for insulin, which would lower the efficacy of insulin to a large extent. In this study, we fabricated a new type of insulin-loaded glucose-responsive complex micelles (CMs), which were self-assembled by a phenylboronic acid (PBA)-modified block copolymer PEG-b-P(Asp-co-AspPBA) and a glucosamine (GA)/nitrilotriacetic acid (NTA)-functionalized block copolymer PNIPAM-b-P(Asp-co-AspGA-co-AspNTA), for self-regulated delivery of insulin with effective protection of insulin and enhanced hypoglycemic activity in vivo. The CMs possessed mixed shell of PEG/PNIPAM and cross-linked core of PBA/GA complex, which could be disintegrated under the condition of high glucose concentration (5 g/L) while maintaining stable at low glucose concentration (1 g/L). The NTA groups of CMs greatly improved the loading content of insulin by specifically bind insulin via the chelated zinc ions. More importantly, PNIPAM chains in the mixed shell would collapse under 37 °C and form hydrophobic domains around the micellar core, which could significantly protect the micellar core as well as the encapsulated insulin from attacking by external proteases. In a murine model of type 1 diabetes, the CMs with insulin chelated by NTA showed a long hypoglycemic effect, which is superior to insulin-loaded simple micelles without PNIPAM and insulin in PBS buffer (pH 7.4). Therefore, this kind of CMs could be a potential candidate for insulin delivery in diabetes therapy.