Increasing surface hydrophilicity with biopolymers: a combined single bubble collision, QCM-D and AFM study.

HYPOTHESIS: Naturally extracted polysaccharides, such as guar gum, are promising candidates for environmentally friendly flotation reagents. It is hypothesized that the kinetics of collision of sub- to millimeter gas bubbles with a hydrophobic graphite surface, and the stability of thin liquid film formed between the bubble and surface is affected by an adsorbed layer of guar gum. EXPERIMENTS: A combination of gravimetric (quartz crystal microbalance with dissipation) and imaging (atomic force microscopy) techniques was used to investigate the adsorption of guar gum on graphite surface, while high-speed camera imaging allowed for direct observation of the bubble collision process with guar gum-modified graphite surfaces with millisecond resolution. FINDINGS: Atomic force microscope topography images revealed a guar gum concentration-dependent interconnected network of guar gum molecules adsorbed at graphite surface. These adsorbed molecules at low surface coverage, changed the wettability of the graphite surface, resulting in a film drainage time longer by an order of magnitude, while at higher surface coverage successfully prevented bubble attachment to the graphite surface. Most importantly, the adsorbed layer changed the strength of the bubble's bouncing off the graphite surface. This enhanced bubble bouncing can be correlated with the film drainage time and used to predict a successful bubble-particle attachment.

Teaching an Old Dog New Tricks: A Global Approach to Enhancing the Cytotoxicity of Drug-Loaded, Non-responsive Micelles Using Oligoelectrolytes.

Polymeric micelles have been extensively studied as vectors for the delivery of hydrophobic drugs for the treatment of cancers and other diseases. Despite intensive research, few formulations provide significant benefits, and even fewer have been clinically approved. While many traditional non-responsive micelles have excellent safety profiles, they lack the ability to respond to the intracellular environment and release their cargo in a spatiotemporally defined manner to effectively deliver large doses of cytotoxic drugs into the cytosol of cells that overwhelm efflux pumps. As a novel and adaptable strategy, we hypothesized that well-established non-responsive polymeric micelles could be augmented with a pH-trigger via the co-encapsulation of cytocompatible oligoelectrolytes, which would allow rapid cargo release in the endosome, leading to increased cytotoxicity. Herein, we demonstrate how this strategy can be applied to render non-responsive micelles pH-responsive, resulting in abrupt cargo release at specific and tunable pH values compatible with endosomal delivery, which significantly increased their cytotoxicity up to 3-fold in an ovarian adenocarcinoma (SKOV-3) cell line compared to non-responsive micelles. In comparison, the oligoelectrolyte-loaded micelles were significantly less toxic to healthy 3T3 fibroblasts, indicating a selective cargo release in cancer cell lines. Oligoelectrolytes can be co-encapsulated in the micelles along with drugs at high encapsulation efficiency percentages, which are both ejected from the micelle core upon oligoelectrolyte ionization. Mechanistically, the increase in cytotoxicity appears to also result from the accelerated endosomal escape of the cargo caused by disruption of the endosomal membrane by the simultaneous release of the oligoelectrolytes from the micelles. Furthermore, we show how this approach is broadly applicable to non-responsive micelles regardless of their composition and various classes of hydrophobic chemotherapeutics. The preliminary studies presented here reveal the versatility and wide scope of oligoelectrolyte-mediated, pH-triggered drug release as a compelling and powerful strategy to enhance the cytotoxicity of non-responsive polymeric micelles.

Influence of Lyophilization and Cryoprotection on the Stability and Morphology of Drug-Loaded Poly(ethylene glycol-b-ε-caprolactone) Micelles.

Polymeric micelles are promising carriers for the delivery of poorly water-soluble drugs, providing enhanced drug solubility, blood circulation times, and bioavailability. Nevertheless, the storage and long-term stability of micelles in solution present challenges requiring the lyophilization and storage of formulations in the solid state, with reconstitution immediately prior to application. Therefore, it is important to understand the effects of lyophilization/reconstitution on micelles, particularly their drug-loaded counterparts. Herein, we investigated the use of ß-cyclodextrin (ß-CD) as a cryoprotectant for the lyophilization/reconstitution of a library of poly(ethylene glycol-b-ε-caprolactone) (PEG-b-PCL) copolymer micelles and their drug-loaded counterparts, as well as the effect of the physiochemical properties of different drugs (phloretin and gossypol). The critical aggregation concentration (CAC) of the copolymers decreased with increasing weight fraction of the PCL block (fPCL), plateauing at ~1 mg/L when the fPCL was >0.45. The blank (empty) and drug-loaded micelles were lyophilized/reconstituted in the absence and presence of ß-CD (9% w/w) and analyzed via dynamic light scattering (DLS) and synchrotron small-angle X-ray scattering (SAXS) to assess for changes in aggregate size (hydrodynamic diameter, Dh) and morphology, respectively. Regardless of the PEG-b-PCL copolymer or the use of ß-CD, the blank micelles displayed poor redispersibility (<10% relative to the initial concentration), while the fraction that redispersed displayed similar Dh to the as-prepared micelles, increasing in Dh as the fPCL of the PEG-b-PCL copolymer increased. While most blank micelles displayed discrete morphologies, the addition of ß-CD or lyophilization/reconstitution generally resulted in the formation of poorly defined aggregates. Similar results were also obtained for drug-loaded micelles, with the exception of several that retained their primary morphology following lyophilization/reconstitution, although no obvious trends were noted between the microstructure of the copolymers or the physicochemical properties of the drugs and their successful redispersion.

pH-Responsive Poly(ethylene glycol)-b-poly(2-vinylpyridine) Micelles for the Triggered Release of Therapeutics.

The use of pH-responsive polymeric micelles is a promising approach to afford the targeted, pH-mediated delivery of hydrophobic drugs within the low-pH tumour milieu and intracellular organelles of cancer cells. However, even for a common pH-responsive polymeric micelle system-e.g., those utilising poly(ethylene glycol)-b-poly(2-vinylpyridine) (PEG-b-PVP) diblock copolymers-there is a lack of available data describing the compatibility of hydrophobic drugs, as well as the relationships between copolymer microstructure and drug compatibility. Furthermore, synthesis of the constituent pH-responsive copolymers generally requires complex temperature control or degassing procedures that limit their accessibility. Herein we report the facile synthesis of a series of diblock copolymers via visible-light-mediated photocontrolled reversible addition-fragmentation chain-transfer polymerisation, with a constant PEG block length (90 repeat units (RUs)) and varying PVP block lengths (46-235 RUs). All copolymers exhibited narrow dispersity values (D ≤ 1.23) and formed polymeric micelles with low polydispersity index (PDI) values (typically <0.20) at physiological pH (7.4), within a suitable size range for passive tumour targeting (<130 nm). The encapsulation and release of three hydrophobic drugs (cyclin-dependent kinase inhibitor (CDKI)-73, gossypol, and doxorubicin) were investigated in vitro at pH 7.4-4.5 to simulate drug release within the tumour milieu and cancer cell endosome. Marked differences in drug encapsulation and release were observed when the PVP block length was increased from 86 to 235 RUs. With a PVP block length of 235 RUs, the micelles exhibited differing encapsulation and release properties for each drug. Minimal release was observed for doxorubicin (10%, pH 4.5) and CDKI-73 exhibited moderate release (77%, pH 4.5), whereas gossypol exhibited the best combination of encapsulation efficiency (83%) and release (91% pH 4.5) overall. These data demonstrate the drug selectivity of the PVP core, where both the block molecular weight and hydrophobicity of the core (and accordingly the hydrophobicity of the drug) have a significant effect on drug encapsulation and release. These systems remain a promising means of achieving targeted, pH-responsive drug delivery-albeit for select, compatible hydrophobic drugs-which warrants their further investigation to develop and evaluate clinically relevant micelle systems.

Composition-Property Relationships of pH-Responsive Poly[(2-vinylpyridine)-co-(butyl methacrylate)] Copolymers for Reverse Enteric Coatings.

The taste-masking of bitter-tasting active pharmaceutical ingredients is key to ensuring patient compliance when producing oral pharmaceutical formulations. This is generally achieved via the incorporation of pH-responsive, reverse enteric polymers, that prevent the dissolution of the formulation in the oral environment, but rapidly mediate it within the gastric environment. Reverse enteric polymers are commonly applied as coatings on oral dosage forms via spray atomisation (e.g., fluidised-bed spray coating), and generally exhibit the most efficient taste-masking. However, currently used reverse enteric coatings require high mass gains (% w/w) during coating to mediate taste-masking, and thereby exhibit delayed release within the gastric environment. Therefore, there remains a need for the development of new reverse enteric coatings, that can efficiently taste-mask at low mass gains and maintain rapid release characteristics within the gastric environment. Herein we report the synthesis and evaluation of a series of addition copolymers of 2-vinylpyridine and butyl methacrylate, methyl methacrylate and isobornyl methacrylate. The thermal, solubility, and water absorption properties of the copolymers were effectively tuned by altering the mol% fraction of the constitutive monomers. Based on their physical properties, selected copolymers were preliminarily evaluated for their compatibility with fluidised-bed spray coating, and effectiveness as taste-masking reverse enteric coatings. The copolymers poly[(2-vinylpyridine)-co-(butyl methacrylate)] (mol% ratio 40:60) and poly[(2-vinylpyridine)-co-(butyl methacrylate)-co-(methyl methacrylate)] (mol% ratio 40:50:10) were found to exhibit excellent taste-masking properties following fluidised-bed spray coating onto Suglets® sugar spheres. Suglets® bearing a film coating of either copolymer (5.2-6.5% w/w mass gain) were found to effectively impede the release of a model drug formulation for up to 72 h in a simulated salivary environment, and rapidly release it (<10 min) within a simulated gastric environment. The results demonstrated the potential of poly[(2-vinylpyridine)-co-(butyl methacrylate)] copolymers to form effectively taste-masked, reverse enteric dosage forms, and suggested that these copolymers may provide improved performance compared to currently available polymers.

pH-Responsive Polymer Implants for the Protection of Native Mammals: Assessment of Material Properties and Poison Incorporation on Performance.

Efforts to mitigate the effects of feral cats through the management of remnant or reintroduced populations of threatened species, are often unsuccessful due to predation by control-averse feral cats, or 'problem individuals'. In order to target these animals, we have developed the Population Protecting Implant (PPI). PPIs are designed to be implanted subcutaneously in a native animal. If the animal is preyed upon, and the implant ingested by a feral cat, release of a toxic payload is triggered in the acidic stomach environment and the problem individual is eliminated. We introduce the first toxic implant incorporating the poison sodium fluoroacetate. Manufactured via fluidised-bed spray coating, toxic implants exhibited uniform reverse enteric coatings and low intra-batch variation. Toxic implants were found to exhibit favourable stability at subcutaneous pH in vitro, and rapidly release their toxic payload in vitro at gastric pH. However, limited stability was demonstrated in rats in vivo (~39-230 d), due to the use of a filament scaffold to enable coating and was likely exacerbated by metachromatic interactions caused by 1080. This work highlights that future development of the PPIs should primarily focus on removal of the filament scaffold, to afford implants with increased in vivo stability.

Microstructure-Thermal Property Relationships of Poly (Ethylene Glycol-b-Caprolactone) Copolymers and Their Micelles.

The crystallinity of polymers strongly affects their properties. For block copolymers, whereby two crystallisable blocks are covalently tethered to one another, the molecular weight of the individual blocks and their relative weight fraction are important structural parameters that control their crystallisation. In the case of block copolymer micelles, these parameters can influence the crystallinity of the core, which has implications for drug encapsulation and release. Therefore, in this study, we aimed to determine how the microstructure of poly(ethylene glycol-b-caprolactone) (PEG-b-PCL) copolymers contributes to the crystallinity of their hydrophobic PCL micelle cores. Using a library of PEG-b-PCL copolymers with PEG number-average molecular weight (Mn) values of 2, 5, and 10 kDa and weight fractions of PCL (fPCL) ranging from 0.11 to 0.67, the thermal behaviour and morphology were studied in blends, bulk, and micelles using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WXRD), and Synchrotron wide-angle X-ray scattering (WAXS). Compared to PEG and PCL homopolymers, the block copolymers displayed reduced crystallinity in the bulk phase and the individual blocks had a large influence on the crystallisation of one another. The fPCL was determined to be the dominant contributor to the extent and order of crystallisation of the two blocks. When fPCL < 0.35, the initial crystallisation of PEG led to an amorphous PCL phase. At fPCL values between 0.35 and 0.65, PEG crystallisation was followed by PCL crystallisation, whereas this behaviour was reversed when fPCL > 0.65. For lyophilised PEG-b-PCL micelles, the crystallinity of the core increased with increasing fPCL, although the core was predominately amorphous for micelles with fPCL < 0.35. These findings contribute to understanding the relationships between copolymer microstructure and micelle core crystallinity that are important for the design and performance of micellar drug delivery systems, and the broader application of polymer micelles.

Exploring the versatility of pentafulvene-maleimide cycloaddition as a ligation strategy: buffer and pH effects.

Ligation chemistries are often required to perform under stringent conditions that preserve the integrity and function of (bio)conjugates, including specific biological buffers. To explore the versatility of the pentafulvene-maleimide ligation for (bio)conjugations, we studied the stability of the coupling partners and their Diels-Alder cycloaddition (DAC) in buffers used commonly in biological assays, protein chemistry and bioconjugates. The stability of 6,6-dialkylpentafulvene and maleimide derivatives to a panel of buffers with pH values between 3.7 and 10.1 was monitored via1H NMR spectroscopy. While the pentafulvene displayed excellent stability, hydrolysis of the maleimide was observed in several cases, although the extent of hydrolysis did not correlate with pH. For almost all buffers the pentafulvene-maleimide DAC proceeded efficiently and at a significantly faster rate than maleimide hydrolysis under the conditions studied. The buffer composition nor pH appeared to have a significant effect on the kinetics of the DAC with second-order rate constants (k2) ranging from 0.14 to 0.33 M-1 s-1 (23 ± 1 °C). This study highlights the versatility of the pentafulvene-maleimide ligation to proceed under a wide range of conditions relevant for (bio)conjugations and that maleimide hydrolysis in aqueous system may be promoted or inhibited by certain buffers.

A europium metal-organic framework for dual Fe3+ ion and pH sensing.

Metal-organic frameworks (MOFs) with ratiometric sensing properties are desirable for many applications due to their intrinsic self-calibration. We report the re-assessment of the sensing properties of a MOF, originally reported as containing europium(III) and 2-hydroxyterephtalic acid, and having fluorescent ratiometric iron(III) sensing properties. Synchrotron single-crystal X-ray diffraction and proton nuclear magnetic resonance (1H NMR) spectroscopy revealed that the MOF is composed of 2-methoxyterephthalate, not 2-hydroxyterephthalate as originally reported. We found that the MOF exhibits a sensor turn-off response towards Fe3+ ion concentrations in the range 0.5-3.7 ppm (band 425 nm), and a turn-on response towards a decrease of pH from 5.4 to 3.0 (band 375 nm), both resulting from the addition of acidic Fe3+ salt solution to a MOF suspension. Thus, the ratiometric sensing properties and the originally proposed mechanism no longer apply; our work reveals a dynamic quenching mechanism for the fluorescence turn-off response due to the presence of Fe3+ ions, and a ligand protonation mechanism for the turn-on response to a decrease in pH. Our work highlights the importance of a thorough investigation of the structure of any newly synthesized MOF, and, in the case of potential sensors, their selectivity and any environmental effects on their sensing behavior.

Using GPCRs as Molecular Beacons to Target Ovarian Cancer with Nanomedicines.

The five-year survival rate for women with ovarian cancer is very poor despite radical cytoreductive surgery and chemotherapy. Although most patients initially respond to platinum-based chemotherapy, the majority experience recurrence and ultimately develop chemoresistance, resulting in fatal outcomes. The current administration of cytotoxic compounds is hampered by dose-limiting severe adverse effects. There is an unmet clinical need for targeted drug delivery systems that transport chemotherapeutics selectively to tumor cells while minimizing off-target toxicity. G protein-coupled receptors (GPCRs) are the largest family of membrane receptors, and many are overexpressed in solid tumors, including ovarian cancer. This review summarizes the progress in engineered nanoparticle research for drug delivery for ovarian cancer and discusses the potential use of GPCRs as molecular entry points to deliver anti-cancer compounds into ovarian cancer cells. A newly emerging treatment paradigm could be the personalized design of nanomedicines on a case-by-case basis.

Injectable Diels-Alder cycloaddition hydrogels with tuneable gelation, stiffness and degradation for the sustained release of T-lymphocytes.

Engineered T-cell therapies have proven highly efficacious for the treatment of haematological cancers, but translation of this success to solid tumours has been limited, in part, due to difficulties in maintaining high doses at specific target sites. Hydrogel delivery systems that provide a sustained release of T-cells at the target site are emerging as a promising strategy. Therefore, in this study we aimed to develop an injectable hydrogel that gels in situ via efficient Diels-Alder cycloaddition (DAC) chemistry and provides a sustained release of T-cells through gradual hydrolysis of the hydrogel matrix. Hydrogels were prepared via the DAC between fulvene and maleimide functionalised poly(ethylene glycol) (PEG) derivatives. By adjusting the concentration and molecular weight of the functionalised PEGs in the hydrogel formulation the in vitro gelation time (Tgel), initial Young's modulus (E) and degradation time (Td) could be tailored from 15-150 min, 5-179 kPa and 7-114 h, respectively. Prior to gelation, the formulations could be readily injected through narrow gauge (26 G) needles with the working time correlating closely with the Tgel. A 5 wt% hydrogel formation with conjugated cyclic RGD motif was found to be optimal for the encapsulation and release of CD3+ T-cells with a near linear release profile and >70% cell viability over the first 4 d and release continuing out to 7 d. With their tuneable Tgel, Td and stiffness, the DAC hydrogels provide the opportunity to control the release period and profile of encapsulated cells.

Interrogating the relationship between the microstructure of amphiphilic poly(ethylene glycol-b-caprolactone) copolymers and their colloidal assemblies using non-interfering techniques.

Understanding the microstructural parameters of amphiphilic copolymers that control the formation and structure of aggregated colloids (e.g., micelles) is essential for the rational design of hierarchically structured systems for applications in nanomedicine, personal care and food formulations. Although many analytical techniques have been employed to study such systems, in this investigation we adopted an integrated approach using non-interfering techniques - diffusion nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS) and synchrotron small-angle X-ray scattering (SAXS) - to probe the relationship between the microstructure of poly(ethylene glycol-b-caprolactone) (PEG-b-PCL) copolymers [e.g., block molecular weight (MW) and the mass fraction of PCL (fPCL)] and the structure of their aggregates. Systematic trends in the self-assembly behaviour were determined using a large family of well-defined block copolymers with variable PEG and PCL block lengths (number-average molecular weights (Mn) between 2 and 10 and 0.5-15 kDa, respectively) and narrow dispersity (Ð < 1.12). For all of the copolymers, a clear transition in the aggregate structure was observed when the hydrophobic fPCL was increased at a constant PEG block Mn, although the nature of this transition is also dependent on the PEG block Mn. Copolymers with low Mn PEG blocks (2 kDa) were observed to transition from unimers and loosely associated unimers to metastable aggregates and finally, to cylindrical micelles as the fPCL was increased. In comparison, copolymers with PEG block Mn of between 5 and 10 kDa transitioned from heterogenous metastable aggregates to cylindrical micelles and finally, well-defined ellipsoidal micelles (of decreasing aspect ratios) as the fPCL was increased. In all cases, the diffusion NMR spectroscopy, DLS and synchrotron SAXS results provided complementary information and the grounds for a phase diagram relating copolymer microstructure to aggregation behaviour and structure. Importantly, the absence of commonly depicted spherical micelles has implications for applications where properties may be governed by shape, such as, cellular uptake of nanomedicine formulations.

Retro Diels-Alder Fragmentation of Fulvene-Maleimide Bioconjugates for Mass Spectrometric Detection of Biomolecules.

Diels-Alder chemistry is a well-explored avenue for the synthesis of bioactive materials; however, its potential applications have recently expanded following the development of reactions that can be performed in buffered aqueous environments at low temperatures, including fulvene-maleimide [4 + 2] cycloadditions. In this study, we synthesized two novel amine-reactive fulvene linkers to demonstrate the application of this chemistry for generating mass spectrometry-cleavable labels ("mass tags"), which can be used for the labeling and detection of proteins. Successful conjugation of these linkers to maleimide-labeled peptides was observed at low temperatures in phosphate-buffered saline, allowing the non-destructive modification of proteins with such mass tags. The labile nature of fulvene-maleimide adducts in the gas phase also makes them suitable for both matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrometric analysis. Unlike previous examples of MALDI mass tags, we show that fulvene-maleimide cycloaddition adducts fragment predictably upon gas-phase activation without the need for bulky photocleavable groups. Further exploration of this chemistry could therefore lead to new approaches for mass spectrometry-based bioassays.

Pentafulvene-Maleimide Cycloaddition for Bioorthogonal Ligation.

The applications of bioconjugation chemistry are rapidly expanding, and the addition of new strategies to the bioconjugation and ligation toolbox will further advance progress in this field. Herein, we present a detailed study of the Diels-Alder cycloaddition (DAC) reaction between pentafulvenes and maleimides in aqueous solutions and investigate the reaction as an emerging bioconjugation strategy. The DAC reactions were found to proceed efficiently, quantitatively yielding cycloadducts with reaction rates ranging up to ∼0.7 M-1 s-1 for a series of maleimides, including maleimide-derivatized peptides and proteins. The absence of cross-reactivity of the pentafulvene with a large panel of functional (bio)molecules and biological media further demonstrated the bioorthogonality of this approach. The utility of the DAC reaction for bioorthogonal bioconjugation applications was further demonstrated in the presence of biological media and proteins, as well as through protein derivatization and labeling, which was comparable to the widely employed sulfhydryl-maleimide coupling chemistry.

Recycling of Selective Laser Sintering Waste Nylon Powders into Fused Filament Fabrication Parts Reinforced with Mg Particles.

This paper presents recycling of selective laser sintering (SLS) waste nylon into printable filaments and parts reinforced with Mg particles. Waste nylon and waste-Mg powder mixture with 2%, 4%, and 8% Mg to nylon were extruded into the filaments. Moisture absorption, differential scanning calorimetry, and melt flow index experiments were conducted to determine the thermal characteristics, while tensile and flexural tests were conducted to evaluate mechanical properties and failure mechanisms. The results were compared with off-the-self (OTS) nylon. Waste powder was found to be extrudable and printable as FFF filament. Waste filament diameter closely matched standard filament size, while exhibiting reduced moisture absorption. High melting and crystallisation temperature for the waste nylon demonstrated a degradation of the plastic during the SLS process. Young's modulus and ultimate tensile strength for the waste filament increased by 1.6-fold compared to that for OTS, while Mg-composite filament surpassed the waste and OTS. Waste and Mg composite dog bone results showed an increase in strength and stiffness, but the ductility deteriorated. Both flexural strength and modulus for the waste nylon increased by 13% and 26%, respectively, over OTS, and the addition of Mg enhanced flexural strength by up to 5-fold at 8% Mg over the waste. Printed surface topography demonstrated that the waste and Mg composite filaments can print the parts with desired geometric shapes and acceptable surface texture. The findings showed that recycling waste SLS powder into FFF prints would be a viable and useful alternative to disposal, given its abundance.

A Facile Strategy for the High Yielding, Quantitative Conversion of Polyglycol End-Groups to Amines.

Amino end-group functionalised polyglycols are important intermediates in the synthesis of sophisticated polymeric architectures and biomaterials. Herein, we report a facile strategy for the end-group conversion of hydroxyl-terminated polyglycols to amino-terminated polyglycols in high isolated yields and with excellent end-group fidelity. Following traditional conversion of polyglycol hydroxyl end-groups to azides via the corresponding mesylate, reduction with zinc in the presence of ammonium chloride afforded a range of amino end-group functionalised poly(ethylene glycol) and poly(propylene glycol) homopolymers and copolymers with isolated yields of 82-99% and end-group conversions of >99% as determined by NMR spectroscopy and MALDI ToF MS. Furthermore, this process is applicable to a sequential reagent addition approach without intermediate polymer isolation steps with only a slight reduction in yield and end-group conversion (95%). Importantly, a simple work-up procedure provides access to high purity polyglycols without contamination from other reagents.

Pharmaceutical Development of 5-Fluorouracil-Eluting Stents for the Potential Treatment of Gastrointestinal Cancers and Related Obstructions.

BACKGROUND: Drug-eluting gastrointestinal (GI) stents are emerging as promising platforms for the treatment of GI cancers and provide the combined advantages of mechanical support to prevent lumen occlusion and as a reservoir for localized drug delivery to tumors. Therefore, in this work we present a detailed quality assurance study of 5-fluorouracil (5FU) drug-eluting stents (DESs) as potential candidates for the treatment of obstructive GI cancers. METHODS: The 5FU DESs were fabricated via a simple two-step sequential dip-coating process of commercial GI self-expanding nitinol stents with a 5FU-loaded polyurethane basecoat and a drug-free protective poly(ethylene-co-vinyl acetate) topcoat. The drug loading, content uniformity and drug stability were determined using a validated high-performance liquid chromatography (HPLC) method, which is also recommended in the United States Pharmacopeia. In vitro drug release studies were performed in phosphate buffered saline to determine the drug releasing properties of the two 5FU-loaded stents. Gas chromatography (GC) and HPLC were employed to determine total residual tetrahydrofuran and N,N-dimethylformamide in the stents remaining from the manufacturing process. Sterilization of the stents was performed using gamma radiation and stability testing was carried out for 3 months. RESULTS: The drug loading analysis revealed excellent uniformity in the distribution of 5FU between and within individual stents. Determination of drug stability in the biorelevant release media confirmed that 5FU remains stable over 100 d. In vitro drug release studies from the stents revealed sustained release of 5FU across two different time scales (161 and 30 d), and mathematical modeling of drug release profiles revealed a diffusion-controlled mechanism for the sustained 5FU release. GC and HPLC analysis revealed that the daily residual solvent leached from the stents was below the United States (US) Food and Drug Administration (FDA) guidelines, and therefore, unlikely to cause localized/systemic toxicities. Sterilization of the stents with gamma radiation and accelerated stability tests over a period of 3 months revealed no significant effect on the stability or in vitro release of 5FU. CONCLUSION: Our results demonstrate that the 5FU DESs meet relevant quality standards and display favourable drug release characteristics for the potential treatment of GI cancers and related obstructions.

Drug-Loaded, Polyurethane Coated Nitinol Stents for the Controlled Release of Docetaxel for the Treatment of Oesophageal Cancer.

For several decades, self-expanding metal stents (SEMSs) have shown significant clinical success in the palliation of obstructive metastatic oesophageal cancer. However, these conventional oesophageal stents can suffer from stent blockage caused by malignant tumour cell growth. To overcome this challenge, there is growing interest in drug-releasing stents that, in addition to palliation, provide a sustained and localized release of anticancer drugs to minimise tumour growth. Therefore, in this study we prepared and evaluated an oesophageal stent-based drug delivery platform to provide the sustained release of docetaxel (DTX) for the treatment of oesophageal cancer-related obstructions. The DTX-loaded oesophageal stents were fabricated via dip-coating of bare nitinol stents with DTX-polyurethane (PU) solutions to provide PU coated stents with DTX loadings of 1.92 and 2.79% w/w. Mechanical testing of the DTX-PU coated stents revealed that an increase in the drug loading resulted in a reduction in the ultimate tensile strength, toughness and Young's modulus. In vitro release studies showed a sustained release of DTX, with ~80-90% released over a period of 33 days. While the DTX-loaded stents exhibited good stability to gamma radiation sterilisation, UV sterilisation or accelerated storage at elevated temperatures (40 °C) resulted in significant DTX degradation. Cell proliferation, apoptosis and Western blotting assays revealed that the DTX released from the stents had comparable anticancer activity to pure DTX against oesophageal cancer cells (KYSE-30). This research demonstrates that the dip-coating technique can be considered as a promising approach for the fabrication of drug-eluting stents (DESs) for oesophageal cancer treatment.

Strategies for the Development of pH-Responsive Synthetic Polypeptides and Polymer-Peptide Hybrids: Recent Advancements.

Synthetic polypeptides and polymer-peptide hybrid materials have been successfully implemented in an array of biomedical applications owing to their biocompatibility, biodegradability and ability to mimic natural proteins. In addition, these materials have the capacity to form complex supramolecular structures, facilitate specific biological interactions, and incorporate a diverse selection of functional groups that can be used as the basis for further synthetic modification. Like conventional synthetic polymers, polypeptide-based materials can be designed to respond to external stimuli (e.g., light and temperature) or changes in the environmental conditions (e.g., redox reactions and pH). In particular, pH-responsive polypeptide-based systems represent an interesting avenue for the preparation of novel drug delivery systems that can exploit physiological or pathological pH variations within the body, such as those that arise in the extracellular tumour microenvironment, intracellularly within endosomes/lysosomes, or during tissue inflammation. Here, we review the significant progress made in advancing pH-responsive polypeptides and polymer-peptide hybrid materials during the last five years, with a particular emphasis on the manipulation of ionisable functional groups, pH-labile linkages, pH-sensitive changes to secondary structure, and supramolecular interactions.

Thermoresponsive polysaccharides with tunable thermoresponsive properties via functionalisation with alkylamide groups.

Polysaccharides have been used widely in many industries, from food technology and mining to cosmetics and biomedical applications. Over recent years there has been growing interest in the development of responsive polysaccharides with unique and switchable properties, particularly systems that display lower-critical solution temperatures (LCSTs). Therefore, in this study we aimed to investigate a novel strategy that would allow the conversion of non-responsive polysaccharides into thermoresponsive polysaccharides with tuneable LCSTs. Through the functionalisation of dextran with alkylamide groups (isopropyl amide, diethyl amide, piperidinyl and diisobutyl amide) using a carbodiimide coupling approach in conjunction with amic acid derivatives, we prepared a library of novel dextrans with various degrees of substitution (DS), which were characterised via nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The alkylamide-functionalised dextrans were found to have good solubility in aqueous solutions, with the exception of those having a high DS of large hydrophobic substituents. Determination of the thermoresponsive characteristics of the polymer solutions via UV-vis spectroscopy revealed that the LCST of the alkylamide-functionalised dextrans was highly dependent on the type of alkylamide group and the DS and could be tuned over a large range (5-35 °C). Above the LCST, all of the thermoresponsive alkylamide-functionalised dextrans formed colloidal dispersions with particles sizes ranging from 400 -600 nm, as determined by dynamic light scattering (DLS). In addition, the polymers were found to exhibit a fast and reversible phase transition in solution with narrow hysteresis (∼ 1-5 °C). Finally, the injectability and biocompatibility of the novel thermoresponsive dextrans was confirmed in vivo via subcutaneous and intracranial ventricle injections, with no local or systemic toxicity noted over a 14 d period. Overall, the alkylamide-functionalised dextrans display interesting thermoresponsive properties and trends that may make them useful in biomedical applications, such as drug-delivery.