Polymeric arsenicals as a platform for functional biomaterials

Arsenic exhibits diverse chemical reactivity depending upon its oxidation state. This distinctive reactivity has been largely overlooked in the field of polymer and biomaterials science, owing to concerns about the toxicity of arsenic. However, a recent clinical renaissance in the use of arsenicals suggests the possibility of broader acceptance and application. The aim of this work is to stimulate interest in and highlight the potential of polymeric arsenicals as a novel platform for functional and responsive biomaterials (Literature review discussed in Chapter 1). Cross-linking of polymers through pendent organic arsenic functional groups is demonstrated using three different chemistries: 1) reductive coupling forming arsine oligomers, As(I)n (Chapter 2) 2) forming arsenic-thiolate bonds with poly-thiol cross-linkers (Chapter 3) 3) polymerizing As(I) via the addition of acetylenes to form vinylene-acetylene bonds (Chapter 4). All three methods of cross-linking were able to cross-link thermally self-assembled NIPAm-PEG diblock copolymers with an arsenical acrylamide (AsAm) monomer incorporated in the NIPAm core. The first two were found to be responsive towards GSH and H2O2 under model physiological conditions. The stability of the particles can be finely tuned through varying the amounts of arsenic or varying the nature of the thiol-functional external cross-linker. The last form of cross-linking was found to be non-responsive towards the given stimuli however it enabled incorporation of further functionality to the nanoparticle, such as Rhodamine B, which helped determine the co-localization of the nanoparticle. Notably, in all three chemistries, the nanoparticles produced were not found to be toxic at 2 mg/ml by cell viability assays. Finally using the As(I)n cross-linking strategy, the formation of hydrogels (with DMA-AsAm copolymers made by FRP), was demonstrated which were responsive towards oxidation with H2O2. Synthesised hydrogels were responsive towards oxidation. 3D cell culturing of these gels were carried out by rehydration of dialyzed/lyophilized gels with trypsinized solution of cells. (Chapter 5). In addition to the investigation of polymeric arsenicals, synthesis of microscale multiblock copolymers are described (Appendix A). This enabled generation and characterisation of polymers at 2 μL scale, and procedure to synthesise Multi-block copolymers at 10 μL scale (DPn = 25, 5 blocks, 2 μL per block)

Self-assembly and dis-assembly of stimuli responsive tadpole-like single chain nanoparticles using a switchable hydrophilic/hydrophobic boronic acid cross-linker

Living systems are driven by molecular machines that are composed of folded polypeptide chains, which are assembled together to form multimeric complexes. Although replicating this type of system is a longstanding goal in polymer science, the complexity the structures impose is synthetically very challenging, and generating synthetic polymers to mimic the process of these assemblies appears to be a more appealing approach. To this end, we report a linear polymer programmable for stepwise folding and assembly to higher order structures. To achieve this, a diblock copolymer composed of 4-acryloylmorpholine and glycerol acrylate was synthesised with high precision via reversible addition fragmentation chain transfer polymerisation (Đ < 1.22). Both intramolecular folding and intermolecular assembly were driven by a pH responsive cross-linker, benzene-1,4-diboronic acid. The resulting intramolecular folded single chain nanoparticles were well defined (Đ < 1.16) and successfully assembled into a multimeric structure (Dh = 245 nm) at neutral pH with no chain entanglement. The assembled multimer was observed with a spherical morphology as confirmed by TEM and AFM. These structures were capable of unfolding and disassembling either at low pH or in the presence of sugar. This work offers a new perspective for the generation of adaptive smart materials

Functionalisation and stabilisation of polymeric arsenical nanoparticles prepared by sequential reductive and radical cross-linking

The chemical reactivity of arsenic is diverse and distinctive depending upon its interchangeable oxidation states. Alkyl and aryl arsines (As(I)) exist as oligomers, composed of labile and redox responsive As–As bonds which have been exploited to form reactive and responsive materials. Here, the lability and reactivity of As(I)-functional polymeric nanoparticles, derived from thermoresponsive polymers P(PEGA20-b-[NIPAm80-n-co-AsAmn]) (P1, n = 4; P2, n = 11; P3, n = 15; P4, n = 18), is elaborated by in situ reaction with functional acetylenes, resulting in the formation of vinylene–arsine cross-linked polymeric arsenical nanoparticles (NPV–As). Spherical particles with sizes <35 nm have been prepared, which are advantageous for potential drug-delivery (e.g. tumour accumulation) applications. Functional acetylenes enable the introduction of reactive amine, acid and alcohol functional groups into the particles, while the use of propargyl-O-rhodamine ester results in the formation of fluorescent nanoparticles. The vinylene–arsine cross-linking confers increased stability of the polymeric arsenical nanoparticles in model biological redox conditions (GSH, H2O2, 5 mM) compared to those reported previously, with nanoparticle structures retained over 7 days. The parent polymeric arsenicals and the resulting nanoparticles were all shown to exhibit limited cytotoxicity in vitro and cell uptake was confirmed by incubating fluorescent-labelled nanoparticles with PC3 cells. Furthermore, fluorescent confocal microscopy using the PC3 cell-line, confirmed that the nanoparticles were internalised by the cells with evidence of mitochondrial co-localisation, which supports a mitochondria-targeting of arsenic hypothesized based on work involving organoarsenical chemotherapeutics. Thus, this work demonstrates a novel strategy for the preparation of polymeric arsenical nanoparticles, with broad functional group tolerance, and expands our emerging understanding of the in vitro behaviour of this family of nanomaterials

Initial therapeutic results of atezolizumab plus bevacizumab for unresectable advanced hepatocellular carcinoma and the importance of hepatic functional reserve

Aim: We analyzed the association between the modified albumin–bilirubin (mALBI) grade and therapeutic efficacy of atezolizumab plus bevacizumab (Atezo+Bev) for the treatment of unresectable hepatocellular carcinoma (u-HCC). Methods: In this retrospective observational study, we included 71 u-HCC patients treated with Atezo+Bev between September 2020 and September 2021. Patients were grouped corresponding to the mALBI grade at the start of treatment (mALBI 1+2a or mALBI 2b+3) and analyzed for therapeutic effect and the transition rate to secondary treatment. Results: According to the Response Evaluation Criteria in Solid Tumors, the overall response rate was significantly higher for the mALBI 1+2a group, than for the mALBI 2b+3 group, with 26.2% and 3.4%, respectively. The progression-free survival (PFS) was significantly longer in the mALBI 1+2a group (10.5 months) than in the mALBI 2b+3 group (3.0 months). In the multivariate analysis, an mALBI of 1+2a was found to be an independent factor of PFS. The rate of second-line treatment with multi-targeted agents was also significantly higher in the mALBI 1+2a group. Conclusions: In real-world practice, Atezo+Bev treatment might have higher therapeutic efficacy in u-HCC patients with mALBI 1+2a

Evolution of Microphase Separation with Variations of Segments of Sequence-Controlled Multiblock Copolymers

Multiblock copolymers (MBCPs) are an emerging class of materials that are becoming more accessible in recent years. However, to date there is still a lack of fundamental understanding of their physical properties. In particular, the glass transition temperature (Tg) which is known to be affected by the phase separation has not been well characterized experimentally. To this end, we report the first experimental study on the evolution of the Tgs and the corresponding phase separation of linear MBCPs with increasing number of blocks while keeping the overall degree of polymerization (DP) constant (DP = 200). Ethylene glycol methyl ether acrylate (EGMEA) and tert-butyl acrylate (tBA) were chosen as monomers for reversible addition-fragmentation chain transfer polymerization to synthesize MBCPs. We found the Tgs (as measured by differential scanning calorimetry) of EGMEA and tBA segments within the MCBPs to converge with increasing number of blocks and decreasing block length, correlating with the loss of the heterogeneity as observed from small-angle X-ray scattering (SAXS) analysis. The Tgs of the multiblock copolymers were also compared to the Tgs of the polymer blends of the corresponding homopolymers, and we found that Tgs of the polymer blends were similar to those of the respective homopolymers, as expected. SAXS experiments further demonstrated microphase separation of multiblock copolymers. This work demonstrates the enormous potential of multiblock architectures to tune the physical properties of synthetic polymers, by changing their glass transition temperature and their morphologies obtained from microphase separation, with domain sizes reaching under 10 nm

Influence of grafting density and distribution on material properties using well-defined alkyl functional poly(styrene-co-maleic anhydride) architectures synthesized by RAFT

Poly(styrene-co-maleic anhydride) copolymers (PSMA) with controlled number and distribution of maleic anhydride (MAnh) units were synthesized by reversible addition–fragmentation chain transfer polymerization using chain-transfer agents (CTA) suitable for industrial scale processes. Linear- and star-shaped alternating PSMA polymers were prepared in a single-step synthesis, while a one-pot sequential chain-extension strategy was utilized to prepare diblock, multiblock, and multisite copolymer architectures. A library of grafted PSMAs with controlled density and distribution of side chains was achieved by the subsequent grafting of long aliphatic alcohol chains (C22) to the MAnh units. The influence of structure, composition, and long alkyl chain addition on PSMAs behavior in solution was studied with triple-detection size exclusion chromatography, while their thermal properties were examined by thermogravimetric analysis and differential scanning calorimetry. Overall, the side chain density and distribution did not impact the polymer conformations in solution (random coil); however, an effect on the molecular size (Rh) and structure density (intrinsic viscosity) were observed. The materials density was shown to be dependent on polymer architectures as lower intrinsic viscosity was observed for the star copolymer. All the materials had similar degradation points (400 °C), while the rate of degradation showed a dependence on the MAnh content and polymeric architecture. Ultimately, the grafting of long aliphatic side chains (crystalline) onto the PSMA backbone, even at low density, was shown to drastically change the microphase ordering, as all the grafted copolymers became semicrystalline. The difference of the crystallization temperature between low density multisite materials (Tc ≈ 8 °C) and the high density alternating material (Tc ≈ 40 °C) highlights the major importance of controlling copolymer composition and structure to tune material properties

Synthesis and optical properties of spirobi(dithienometallole)s and spirobi(dithienothiametalline)s

Spiro-condensed dithienometalloles (metal - Si, Ge) and dithienothiametallines (metal - Si, Ge, Sn) were prepared by the ring closure reactions of dilithiated bithiophene and dithienyl sulfide with metal tetrachlorides, and their optical properties were studied with respect to the UV absorption and emission spectra. The absorption and emission maxima of them moved to higher energies by increasing the size of the center metal from Si to Ge and Sn, and stepwise oxidation of the ring sulfur atom in the dithienothiasiline system forming sulfoxide and sulfone linkages, making the fine tuning of the electronic states possible

Tuning the structure, stability and responsivity of polymeric arsenical nanoparticles using polythiol cross-linkers

The use of organic arsenicals in polymer chemistry and biomaterials science is limited despite the distinctive and versatile chemistry of arsenic. The interchangeable oxidation states of arsenic and the subsequent changes in chemical properties make it a promising candidate for redox-responsive materials. Thus, reversible addition–fragmentation chain transfer (RAFT) polymerization has been employed for the first time to synthesize thermoresponsive organic arsenical containing block copolymers. The polymers undergo simultaneous self-assembly and cross-linking, via the organic arsenical pendant groups, under reductive conditions (to reduce As(V) to As(III)) in the presence of polythiol reagents as cross-linkers. The formation of As–S bonds stabilizes the nanoparticles formed (Dh = 19–29 nm) and enables the stability and responsivity to oxidative stress of the particles, in aqueous and model biological solutions, to be tuned as a function of the number of thiols in the cross-linker or the [SH]/[As] stoichiometric ratio. The parent block copolymers and nanoparticles are nontoxic in vitro, and the tunable responsivity of these nanoparticles and the (bio)chemical activity of organic arsenical reagents could be advantageous for targeted drug delivery and the other bio(nano)medical applications. To the best our knowledge, this is the first time that arsenic–thiolate (As–S) bonding has been employed for stimuli-responsive cross-linking of polymeric nanoparticles

Intraocular Pressure Readings Obtained through Soft Contact Lenses using Four Types of Tonometer

To compare the reliability and accuracy of intraocular pressure (IOP) measured while wearing soft contact lenses (SCLs) using a non-contact tonometer (NCT), Goldmann applanation tonometer (GAT), iCare rebound tonometer (RBT) and the Tono-Pen XL. Twenty-six healthy subjects were examined. The IOP was measured using NCT, GAT, RBT, and the Tono-Pen XL, while the subjects wore SCLs −5.00 D, −0.50 D and +5.00 D. Bland–Altman plots and a regression analysis were used to compare the IOPs obtained with those instruments and the IOPs of the naked eyes measured using GAT (the standard IOPs in this study). The IOPs obtained by the Tono-Pen XL while the subjects were wearing −5.00 D, −0.50 D, and +5.00 D SCLs were significantly higher than those of the naked eyes obtained using GAT. RBT showed that the IOPs were similar to the GAT standard IOPs under all conditions. The IOPs measured with NCT and GAT while the subjects were wearing −5.00 D and −0.50 D SCLs were similar to the GAT standard IOPs. The IOPs obtained with RBT and NCT while the subjects were wearing −5.00 D and −0.50 D SCLs exhibited a good correlation with the standard IOPs. The NCT and RBT are best when measuring IOP through hydrogel SCLs