64 65 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 Recyclable elastomers that rival environmentally persistent rubbers Earth Sciences & Environment – Chemistry – Materials Science – Organic Chemistry – Polymer Science Elastomers are indispensable to the automotive, healthcare and electronics industries. Most elastomers are petroleum-derived and lack viable recyclability or end-of-life degradation options thus contributing to the plastic waste problem. Current research to address the waste problem has developed more bio-based and potentially degradable alternatives, but these still fall far short of matching the performances of commercialised rubbers. A long-standing bottleneck in elastomer development has been designing for high tensile strength without compromising elasticity/stretchability and elastic recovery. Elastomers based on polycarbonate and polyester chemistries are attractive as 1) many monomers are bio-based, and 2) the polymer-monomer equilibria can be manipulated to recycle the products back to monomers or to ensure total chain degradation Pursuing high performance with sustainability, researchers at the UniversityofOxford investigatedblockco-polymersbasedonpoly(trimethylene carbonate) (PTMC) and zinc-ionomer polyesters. The soft, flexible, yet highly entangled chains of the polycarbonate (PTMC) appealed for stretchability; the harder zinc-ionomer polyesters would provide maximum tensile strength and excellent elastic recovery. Many elastomer properties emerge from the formation of physically cross-linked networks. ABA-type block co-polymers achieve the cross-linked networks through block microphase separation where A = hard rigid and B = soft flexible blocks. Small Angle X-ray Scattering (SAXS) measurements using the DL-SAXS instrument at Diamond allowed the researchers to probe the presence of this crucial phase separation behaviour with A = Zn-ionomer polyester and B = PTMC. Moreover, the mechanical performance of the polymer films can now be directly correlated to the precise morphology of the phase separation described by the SAXS patterns. The results from the University of Oxford and DL-SAXS, showed that the bio-based polyester/carbonate thermoplastics elastomers retained phase morphology on chemical functionalisation and endowed high-performance elastomer characteristics with spherical or cylindrical A-domains dispersed in a rubbery B-matrix. The elastomers match, or out-perform, commercial polyurethane and non-recyclable prevalent rubbers by combining high tensile strengths (60MPa) and extensibilities (>800%) with excellent elastic recovery (>95 %). Importantly, the elastomers do so whilst being re-processable, efficiently chemically recyclable back to monomer and/or fully degradable at end-of-life. The findings can be widely applied to polymer design strategies for adapting or enhancing material properties for innovative application areas or replacing commodity plastics. Notable is the small, yet efficient, quantities of polyester (< 20 wt%) and zinc (< 1 wt%) required with the PTMC polycarbonate to significantly enhance performance. Furthermore, the synthetic approach to making the materials is also highly generalisable to many available and bio-based monomers as it couples in one-pot controlled cyclic monomer ring-opening polymerisation and alternating epoxide/ anhydride ring-opening copolymerisation strategies. Related publication: Gregory, GL. et al. Block poly (carbonate‐ester) ionomers as high- performance and recyclable thermoplastic elastomers. Angewandte Chemie 134,47 : e202210748 (2022). DOI: 10.1002/anie.202210748 Funding acknowledgement: EPSRC: (EP/S018603/1; EP/R027129/1; EP/V003321/1) The Faraday Institute (FIRG026, SOLBAT) The Oxford Martin School (Future of Plastics) Corresponding authors: Dr Georgina L. Gregory, University of Oxford,
[email protected] Prof. Charlotte K. Williams, University of Oxford,
[email protected] Soft CondensedMatter Group DL-SAXS SAXS profiles measured of degradable polycarbonate-block-polyester films were used to assign block microphase separation behaviour for polymers differing in polyester (PE) content or overall molecular weight (P1-P3). This was then correlated to the stress—strain mechanical response. The impressive stress at break values of the materials is attributed to crystallites of the PTMC polycarbonate formed during stretching and reinforcement by interactions in the polyester segments. Targeting paediatric tumour cells with functionalised cubic phase nanoparticles Drug Delivery – Non Communicable Diseases – Health &Wellbeing – Cancer – Life Sciences & Biotech Focused delivery of chemotherapy drugs at tumour sites can increase the effectiveness of the treatments while reducing potential side effects. This long-standing challenge is being addressed using next-generation nanostructured liquid crystalline nanoparticles (NPs) called cubosomes. Cubosomes have high loading capacity, biocompatibility and thermostability, and have been shown to effectively deliver therapeutics to tumour sites in the patient’s body. Cubosomes can be designed for active targeting, to direct the therapeutics to the tumour cells, and protect healthy cells from systemic side-effects. Active targeting can be achieved by attaching antibodies, peptides or aptamers, that recognise cancer cells. Furthermore, cubosomes can be designed to respond to external stimuli such as magnetic fields, temperature or pH offering further control over drug delivery. Researchers from the University of Oxford evaluated an active tumour- targeting cubosome system directed towards rhabdomyosarcoma (RMS) cells. They employed a top-down synthesis approach to produce blank cubic phase NPs, which were subsequently functionalised with hyaluronic acid (HA), anti-CD221 half-sized antibodies (ha-Abs) and superparamagnetic iron oxide nanoparticles (SPIONs). These triple-functionalised cubosomes can be controlled via an external magnetic field. Small-Angle X-ray Scattering (SAXS) measurements on Diamond’s B21 beamline investigated the lipid lattice patterns and verified the formation of cubic phases. Both SAXS and cryo-Electron Microscopy (cryo-EM) performed at the Electron Bio-Imaging Centre (eBIC) played an important role in optimising the cubosome synthesis method and validating the structures throughout the investigation. The researchers found that all the cubic phase NPs possessed the primitive (Im3m) cubic phase, lattice parameters of 126-155 Å, and water channel diameters of 22-30 Å. The well-organised lattice patterns, however, were compromised by incorporating more than 3% SPIONs. The stability analysis showed that antibody-conjugated cubosomes were able to maintain the Im3m structure for 40 days under ambient conditions, while the integrity of triple-functionalised cubosomes was preserved for 30 days under the same conditions. The cubosome-based drug delivery platform constructed in this study can encapsulate large quantities of hydrophilic, lipophilic, or amphiphilic therapeutics and confine the chemotherapy to tumour tissues in an active manner. In addition, the cubosome synthesis and functionalisation procedures the team has established may also be useful in structural biology, vaccine, transfection, cosmetics, or biomedical imaging. Related publication: Mun, H. et al. CD44 and CD221 directed magnetic cubosomes for the targeted delivery of helenalin to rhabdomyosarcoma cells. Nano Research 16 , 2915–2926 (2023). DOI:10.1007/s12274-022-5037-4 Funding acknowledgement: PUST-UK scholarship TheWilliams Fund (Oxford Hospital Charity No. 0085) UK national electron bioimaging centre (No. NT32452) Corresponding authors: Helen E. Townley; University of Oxford;
[email protected] Nathan Cowieson; B21, Diamond Light Source;
[email protected] Soft CondensedMatter Group Beamline B21 (and eBIC from the Biological Cryo-Imaging Group) Structure and characteristics of functional cubosomes. (a) Schematic representation of functional cubosome structures and their active targeting towards tumour cells, (b) SAXS diffraction profiles of (i) empty cubosomes and (ii) drug-laden cubosomes, insets: the linear fit of the plot of vs , (c) Cryo-EM images of empty cubosomes and (ii) drug-laden cubosomes. 10.1007/s12274-022- 5037-4.