Predictive Molecular Design and Structure-Property Validation of Novel Terpene-Based, Sustainably Sourced Bacterial Biofilm-Resistant Materials.

Presented in this work is the use of a molecular descriptor, termed the α parameter, to aid in the design of a series of novel, terpene-based, and sustainable polymers that were resistant to biofilm formation by the model bacterial pathogen Pseudomonas aeruginosa. To achieve this, the potential of a range of recently reported, terpene-derived monomers to deliver biofilm resistance when polymerized was both predicted and ranked by the application of the α parameter to key features in their molecular structures. These monomers were derived from commercially available terpenes (i.e., α-pinene, ß-pinene, and carvone), and the prediction of the biofilm resistance properties of the resultant novel (meth)acrylate polymers was confirmed using a combination of high-throughput polymerization screening (in a microarray format) and in vitro testing. Furthermore, monomers, which both exhibited the highest predicted biofilm anti-biofilm behavior and required less than two synthetic stages to be generated, were scaled-up and successfully printed using an inkjet "valve-based" 3D printer. Also, these materials were used to produce polymeric surfactants that were successfully used in microfluidic processing to create microparticles that possessed bio-instructive surfaces. As part of the up-scaling process, a novel rearrangement was observed in a proposed single-step synthesis of α-terpinyl methacrylate via methacryloxylation, which resulted in isolation of an isobornyl-bornyl methacrylate monomer mixture, and the resultant copolymer was also shown to be bacterial attachment-resistant. As there has been great interest in the current literature upon the adoption of these novel terpene-based polymers as green replacements for petrochemical-derived plastics, these observations have significant potential to produce new bio-resistant coatings, packaging materials, fibers, medical devices, etc.

Droplet Microfluidic Optimisation Using Micropipette Characterisation of Bio-Instructive Polymeric Surfactants.

Droplet microfluidics can produce highly tailored microparticles whilst retaining monodispersity. However, these systems often require lengthy optimisation, commonly based on a trial-and-error approach, particularly when using bio-instructive, polymeric surfactants. Here, micropipette manipulation methods were used to optimise the concentration of bespoke polymeric surfactants to produce biodegradable (poly(d,l-lactic acid) (PDLLA)) microparticles with unique, bio-instructive surface chemistries. The effect of these three-dimensional surfactants on the interfacial tension of the system was analysed. It was determined that to provide adequate stabilisation, a low level (0.1% (w/v)) of poly(vinyl acetate-co-alcohol) (PVA) was required. Optimisation of the PVA concentration was informed by micropipette manipulation. As a result, successful, monodisperse particles were produced that maintained the desired bio-instructive surface chemistry.

Extrusion 3D Printing of Paracetamol Tablets from a Single Formulation with Tunable Release Profiles Through Control of Tablet Geometry.

An extrusion-based 3D printer was used to fabricate paracetamol tablets with different geometries (mesh, ring and solid) from a single paste-based formulation formed from standard pharmaceutical ingredients. The tablets demonstrate that tunable drug release profiles can be achieved from this single formulation even with high drug loading (> 80% w/w). The tablets were evaluated for drug release using a USP dissolution testing type I apparatus. The tablets showed well-defined release profiles (from immediate to sustained release) controlled by their different geometries. The dissolution results showed dependency of drug release on the surface area/volume (SA/V) ratio and the SA of the different tablets. The tablets with larger SA/V ratios and SA had faster drug release. The 3D printed tablets were also evaluated for physical and mechanical properties including tablet dimension, drug content, weight variation and breaking force and were within acceptable range as defined by the international standards stated in the US Pharmacopoeia. X-ray powder diffraction, differential scanning calorimetry and attenuated total reflectance Fourier transform infrared spectroscopy were used to identify the physical form of the active and to assess possible drug-excipient interactions. These data again showed that the tablets meet USP requirement. These results clearly demonstrate the potential of 3D printing to create unique pharmaceutical manufacturing, and potentially clinical, opportunities. The ability to use a single unmodified formulation to achieve defined release profiles could allow, for example, relatively straightforward personalization of medicines for individuals with different metabolism rates for certain drugs and hence could offer significant development and clinical opportunities.

Selective molecular annealing: in situ small angle X-ray scattering study of microwave-assisted annealing of block copolymers.

Microwave annealing has emerged as an alternative to traditional thermal annealing approaches for optimising block copolymer self-assembly. A novel sample environment enabling small angle X-ray scattering to be performed in situ during microwave annealing is demonstrated, which has enabled, for the first time, the direct study of the effects of microwave annealing upon the self-assembly behavior of a model, commercial triblock copolymer system [polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene]. Results show that the block copolymer is a poor microwave absorber, resulting in no change in the block copolymer morphology upon application of microwave energy. The block copolymer species may only indirectly interact with the microwave energy when a small molecule microwave-interactive species [diethylene glycol dibenzoate (DEGDB)] is incorporated directly into the polymer matrix. Then significant morphological development is observed at DEGDB loadings ≥6 wt%. Through spatial localisation of the microwave-interactive species, we demonstrate targeted annealing of specific regions of a multi-component system, opening routes for the development of "smart" manufacturing methodologies.

Molecular Design of Squalene/Squalane Countertypes via the Controlled Oligomerization of Isoprene and Evaluation of Vaccine Adjuvant Applications.

The potential to replace shark-derived squalene in vaccine adjuvant applications with synthetic squalene/poly(isoprene) oligomers, synthesized by the controlled oligomerization of isoprene is demonstrated. Following on from our previous work regarding the synthesis of poly(isoprene) oligomers, we demonstrate the ability to tune the molecular weight of the synthetic poly(isoprene) material beyond that of natural squalene, while retaining a final backbone structure that contained a minimum of 75% of 1,4 addition product and an acceptable polydispersity. The synthesis was successfully scaled from the 2 g to the 40 g scale both in the bulk (i.e., solvent free) and with the aid of additional solvent by utilizing catalytic chain transfer polymerization (CCTP) as the control method, such that the target molecular weight, acceptable dispersity levels, and the desired level of 1,4 addition in the backbone structure and an acceptable yield (∼60%) are achieved. Moreover, the stability and in vitro bioactivity of nanoemulsion adjuvant formulations manufactured with the synthetic poly(isoprene) material are evaluated in comparison to emulsions made with shark-derived squalene. Emulsions containing the synthetic poly(isoprene) achieved smaller particle size and equivalent or enhanced bioactivity (stimulation of cytokine production in human whole blood) compared to corresponding shark squalene emulsions. However, as opposed to the shark squalene-based emulsions, the poly(isoprene) emulsions demonstrated reduced long-term size stability and induced hemolysis at high concentrations. Finally, we demonstrate that the synthetic oligomeric poly(isoprene) material could successfully be hydrogenated such that >95% of the double bonds were successfully removed to give a representative poly(isoprene)-derived squalane mimic.

Application of Targeted Molecular and Material Property Optimization to Bacterial Attachment-Resistant (Meth)acrylate Polymers.

Developing medical devices that resist bacterial attachment and subsequent biofilm formation is highly desirable. In this paper, we report the optimization of the molecular structure and thus material properties of a range of (meth)acrylate copolymers which contain monomers reported to deliver bacterial resistance to surfaces. This optimization allows such monomers to be employed within novel coatings to reduce bacterial attachment to silicone urinary catheters. We show that the flexibility of copolymers can be tuned to match that of the silicone catheter substrate, by copolymerizing these polymers with a lower Tg monomer such that it passes the flexing fatigue tests as coatings upon catheters, that the homopolymers failed. Furthermore, the Tg values of the copolymers are shown to be readily estimated by the Fox equation. The bacterial resistance performance of these copolymers were typically found to be better than the neat silicone or a commercial silver containing hydrogel surface, when the monomer feed contained only 25 v% of the "hit" monomer. The method of initiation (either photo or thermal) was shown not to affect the bacterial resistance of the copolymers. Optimized synthesis conditions to ensure that the correct copolymer composition and to prevent the onset of gelation are detailed.

Facile Determination of Molecular Structure Trends in Amphiphilic Core Corona Star Polymer Synthesis via Dielectric Property Measurement.

The use of dielectric property measurements to define specific trends in the molecular structures of poly(caprolactone) containing star polymers and/or the interbatch repeatability of the synthetic procedures used to generate them is demonstrated. The magnitude of the dielectric property value is shown to accurately reflect: (a) the number of functional groups within a series of materials with similar molecular size when no additional intermolecular order is present in the medium, (b) the polymer molecular size for a series of materials containing a fixed core material and so functional group number, and/or (c) the batch to batch repeatability of the synthesis method. The dielectric measurements are validated by comparison to spectroscopic/chromatographic data.

Molecular Differentiated Initiator Reactivity in the Synthesis of Poly(caprolactone)-Based Hydrophobic Homopolymer and Amphiphilic Core Corona Star Polymers.

Macromolecules that possess three-dimensional, branched molecular structures are of great interest because they exhibit significantly differentiated application performance compared to conventional linear (straight chain) polymers. This paper reports the synthesis of 3- and 4-arm star branched polymers via ring opening polymerisation (ROP) utilising multi-functional hydroxyl initiators and Sn(Oct)2 as precatalyst. The structures produced include mono-functional hydrophobic and multi-functional amphiphilic core corona stars. The characteristics of the synthetic process were shown to be principally dependent upon the physical/dielectric properties of the initiators used. ROP's using initiators that were more available to become directly involved with the Sn(Oct)2 in the "in-situ" formation of the true catalytic species were observed to require shorter reaction times. Use of microwave heating (MWH) in homopolymer star synthesis reduced reaction times compared to conventional heating (CH) equivalents, this was attributed to an increased rate of "in-situ" catalyst formation. However, in amphiphilic core corona star formation, the MWH polymerisations exhibited slower propagation rates than CH equivalents. This was attributed to macro-structuring within the reaction medium, which reduced the potential for reaction. It was concluded that CH experiments were less affected by this macro-structuring because it was disrupted by the thermal currents/gradients caused by the conductive/convective heating mechanisms. These gradients are much reduced/absent with MWH because it selectively heats specific species simultaneously throughout the entire volume of the reaction medium. These partitioning problems were overcome by introducing additional quantities of the species that had been determined to selectively heat.

An effective route to the additive manufacturing of a mechanically gradient supramolecular polymer nanocomposite structure.

3D Printing techniques are additive methods of fabricating parts directly from computer-aided designs. Whilst the clearest benefit is the realisation of geometrical freedom, multi-material printing allows the introduction of compositional variation and highly tailored product functionality. The paper reports a proof-of-concept additive manufacturing study to deposit a supramolecular polymer and a complementary organic filler to form composites with gradient composition to enable spatial distribution of mechanical properties and functionality by tuning the number of supramolecular interactions. We use a dual-feed extrusion 3D printing process, with feed stocks based on the supramolecular polymer and its organic composite, delivered at ratios predetermined. This allows for production of a graded specimen with varying filler concentration that dictates the mechanical properties. The printed specimen was inspected under dynamic load in a tensile test using digital image correlation to produce full-field deformation maps, which showed clear differences in deformation in regions with varying compositions, corresponding to the designed-in variations. This approach affords a novel method for printing material with graded mechanical properties which are not currently commercially available or easily accessible, however, the method can potentially be directly translated to the generation of biomaterial-based composites featuring gradients of mechanical properties.

Ring opening polymerisation of ɛ-caprolactone with novel microwave magnetic heating and cyto-compatible catalyst.

We report on the ring-opening polymerization of ɛ-caprolactone incorporated with a magnetic susceptible catalyst, FeCl3, via the use of microwave magnetic heating (HH) which primarily heats the bulk with a magnetic field (H-field) from an electromagnetic field (EMF). Such a process was compared to more commonly used heating methods, such as conventional heating (CH), i.e., oil bath, and microwave electric heating (EH), which is also referred to as microwave heating that primarily heats the bulk with an electric field (E-field). We identified that the catalyst is susceptible to both the E-field and H-field heating, and promoted the heating of the bulk. Which, we noticed such promotion was a lot more significant in the HH heating experiment. Further investigating the impact of such observed effects in the ROP of ɛ-caprolactone, we found that the HH experiments showed a more significant improvement in both the product Mwt and yield as the input power increased. However, when the catalyst concentration was reduced from 400:1 to 1600:1 (Monomer:Catalyst molar ratio), the observed differentiation in the Mwt and yield between the EH and the HH heating methods diminished, which we hypothesized to be due to the limited species available that were susceptible to microwave magnetic heating. But comparable product results between the HH and EH heating methods suggest that the HH heating method along with a magnetic susceptible catalyst could be an alternative solution to overcome the penetration depth problem associated with the EH heating methods. The cytotoxicity of the produced polymer was investigated to identify its potential application as biomaterials.

Discovery of a polymer resistant to bacterial biofilm, swarming, and encrustation.

Innovative approaches to prevent catheter-associated urinary tract infections (CAUTIs) are urgently required. Here, we describe the discovery of an acrylate copolymer capable of resisting single- and multispecies bacterial biofilm formation, swarming, encrustation, and host protein deposition, which are major challenges associated with preventing CAUTIs. After screening ~400 acrylate polymers, poly(tert-butyl cyclohexyl acrylate) was selected for its biofilm- and encrustation-resistant properties. When combined with the swarming inhibitory poly(2-hydroxy-3-phenoxypropyl acrylate), the copolymer retained the bioinstructive properties of the respective homopolymers when challenged with Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. Urinary tract catheterization causes the release of host proteins that are exploited by pathogens to colonize catheters. After preconditioning the copolymer with urine collected from patients before and after catheterization, reduced host fibrinogen deposition was observed, and resistance to diverse uropathogens was maintained. These data highlight the potential of the copolymer as a urinary catheter coating for preventing CAUTIs.

A potential alternative to fungicides using actives-free (meth)acrylate polymers for protection of wheat crops from fungal attachment and infection.

Fungicidal compounds are actives widely used for crop protection from fungal infection, but they can also kill beneficial organisms, enter the food chain and promote resistant pathogen strains from overuse. Here we report the first field crop trial of homopolymer materials that prevent fungal attachment, showing successful crop protection via an actives-free approach. In the trial, formulations containing two candidate polymers were applied to young wheat plants that were subject to natural infection with the wheat pathogen Zymoseptoria tritici. A formulation containing one of the candidate polymers, poly(di(ethylene glycol) ethyl ether acrylate) (abbreviated DEGEEA), produced a significant reduction (26%) in infection of the crop by Z. tritici, delivering protection against fungal infection that compared favourably with three different commercially established fungicide programmes tested in parallel. Furthermore, the sprayed polymers did not negatively affect wheat growth. The two lead polymer candidates were initially identified by bio-performance testing using in vitro microplate- and leaf-based assays and were taken forward successfully into a programme to optimize and scale-up their synthesis and compound them into a spray formulation. Therefore, the positive field trial outcome has also established the validity of the smaller-scale, laboratory-based bioassay data and scale-up methodologies used. Because fungal attachment to plant surfaces is a first step in many crop infections, this non-eluting polymer: (i) now offers significant potential to deliver protection against fungal attack, while (ii) addressing the fourth and aligning with the eleventh principles of green chemistry by using chemical products designed to preserve efficacy of function while reducing toxicity. A future focus should be to develop the material properties for this and other applications including other fungal pathogens.

Screening of Oligomeric (Meth)acrylate Vaccine Adjuvants Synthesized via Catalytic Chain Transfer Polymerization.

This report details the first systematic screening of free-radical-produced methacrylate oligomer reaction mixtures as alternative vaccine adjuvant components to replace the current benchmark compound squalene, which is unsustainably sourced from shark livers. Homo-/co-oligomer mixtures of methyl, butyl, lauryl, and stearyl methacrylate were successfully synthesized using catalytic chain transfer control, where the use of microwave heating was shown to promote propagation over chain transfer. Controlling the mixture material properties allowed the correct viscosity to be achieved, enabling the mixtures to be effectively used in vaccine formulations. Emulsions of selected oligomers stimulated comparable cytokine levels to squalene emulsion when incubated with human whole blood and elicited an antigen-specific cellular immune response when administered with an inactivated influenza vaccine, indicating the potential utility of the compounds as vaccine adjuvant components. Furthermore, the oligomers' molecular sizes were demonstrated to be large enough to enable greater emulsion stability than squalene, especially at high temperatures, but are predicted to be small enough to allow for rapid clearance from the body.

Developing Echogenic Materials as Catheters for Use with Ultrasound.

Patients with peripherally inserted central catheters (PICCs) are routinely discharged with the catheters in place. These patients experience complications due to undetected thrombosis or accidental dislodgement, with tracking through limited X-ray imaging. Developing catheters with the capability to be tracked without the need for X-ray imaging would greatly benefit these patients by decreasing patient stress, reducing time to diagnosis, and increasing nursing home capabilities. This study reports on the incorporation of echogenic microspheres into catheters to produce bulk echogenic effects for developments in the field of real-time ultrasound tracking of polymeric medical devices. The impact on elastic modulus, ultrasound contrast, and cytocompatibility of the polymer was analyzed when incorporating up to 10 wt % glass microspheres. Up to this loading level, the elastic modulus was found to remain constant. However, at 10 wt %, extrusion defects due to agglomeration, air bubbles, and shearing were numerous and deemed detrimental to ultrasound imaging. Successful, defect-free samples were produced with 5 wt % microsphere loading and when embedded in a soft tissue phantom revealed a significant increase in the signal-to-noise ratio as compared to the polymer alone. Preliminary results have shown a successful increase in polymer's echogenic properties, without undermining its mechanical and cytocompatibility properties.

Facile Synthesis of Functionalised Hyperbranched Polymers for Application as Novel, Low Viscosity Lubricant Formulation Components.

A novel, previously unreported, method for synthesising hyperbranched (HB) materials is detailed. Their use as additives to produce lubricant formulations that exhibit enhanced levels of wear protection and improved low-temperature oil viscosity and flow is also reported. The lubricant formulations containing HB additives were found to exhibit both significantly lower viscosities and improved in-use film-forming properties than the current industry standard formulations. To achieve this, alkyl methacrylate oligomers (predominantly dimers and trimers) were synthesised using catalytic chain transfer polymerisation. These were then used as functional chain transfer agents (CTA) to control the polymerisation of divinyl benzene (DVB) monomers to generate highly soluble, high polydispersity HB polymers. The level of dimer/trimer purification applied was varied to define its influence on both these HB resultant structures and the resultant HB additives' performance as a lubricant additive. It was shown that, while the DVB acted as the backbone of the HB, the base oil solubility of the additive was imparted by the presence of the alkyl chains included in the structure via the use of the oligomeric CTAs.

Microparticles Decorated with Cell-Instructive Surface Chemistries Actively Promote Wound Healing.

Wound healing is a complex biological process involving close crosstalk between various cell types. Dysregulation in any of these processes, such as in diabetic wounds, results in chronic nonhealing wounds. Fibroblasts are a critical cell type involved in the formation of granulation tissue, essential for effective wound healing. 315 different polymer surfaces are screened to identify candidates which actively drive fibroblasts toward either pro- or antiproliferative functional phenotypes. Fibroblast-instructive chemistries are identified, which are synthesized into surfactants to fabricate easy to administer microparticles for direct application to diabetic wounds. The pro-proliferative microfluidic derived particles are able to successfully promote neovascularization, granulation tissue formation, and wound closure after a single application to the wound bed. These active novel bio-instructive microparticles show great potential as a route to reducing the burden of chronic wounds.

Ink-jet 3D printing as a strategy for developing bespoke non-eluting biofilm resistant medical devices.

Chronic infection as a result of bacterial biofilm formation on implanted medical devices is a major global healthcare problem requiring new biocompatible, biofilm-resistant materials. Here we demonstrate how bespoke devices can be manufactured through ink-jet-based 3D printing using bacterial biofilm inhibiting formulations without the need for eluting antibiotics or coatings. Candidate monomers were formulated and their processability and reliability demonstrated. Formulations for in vivo evaluation of the 3D printed structures were selected on the basis of their in vitro bacterial biofilm inhibitory properties and lack of mammalian cell cytotoxicity. In vivo in a mouse implant infection model, Pseudomonas aeruginosa biofilm formation on poly-TCDMDA was reduced by ∼99% when compared with medical grade silicone. Whole mouse bioluminescence imaging and tissue immunohistochemistry revealed the ability of the printed device to modulate host immune responses as well as preventing biofilm formation on the device and infection of the surrounding tissues. Since 3D printing can be used to manufacture devices for both prototyping and clinical use, the versatility of ink-jet based 3D-printing to create personalised functional medical devices is demonstrated by the biofilm resistance of both a finger joint prosthetic and a prostatic stent printed in poly-TCDMDA towards P. aeruginosa and Staphylococcus aureus.

Discovery of a Novel Polymer for Xeno-Free, Long-Term Culture of Human Pluripotent Stem Cell Expansion.

Human pluripotent stem cells (hPSCs) can be expanded and differentiated in vitro into almost any adult tissue cell type, and thus have great potential as a source for cell therapies with biomedical application. In this study, a fully-defined polymer synthetic substrate is identified for hPSC culture in completely defined, xenogenic (xeno)-free conditions. This system can overcome the cost, scalability, and reproducibility limitations of current hPSC culture strategies, and facilitate large-scale production. A high-throughput, multi-generational polymer microarray platform approach is used to test over 600 unique polymers and rapidly assess hPSC-polymer interactions in combination with the fully defined xeno-free medium, Essential 8 (E8). This study identifies a novel nanoscale phase separated blend of poly(tricyclodecane-dimethanol diacrylate) and poly(butyl acrylate) (2:1 v/v), which supports long-term expansion of hPSCs and can be readily coated onto standard cultureware. Analysis of cell-polymer interface interactions through mass spectrometry and integrin blocking studies provides novel mechanistic insight into the role of the E8 proteins in promoting integrin-mediated hPSC attachment and maintaining hPSC signaling, including ability to undergo multi-lineage differentiation. This study therefore identifies a novel substrate for long-term serial passaging of hPSCs in serum-free, commercial chemically-defined E8, which provides a promising and economic hPSC expansion platform for clinical-scale application.

Synthesis of water-soluble surfactants using catalysed condensation polymerisation in green reaction media.

Sustainable and biobased surfactants are required for a wide range of everyday applications. Key drivers are cost, activity and efficiency of production. Polycondensation is an excellent route to build surfactant chains from bio-sourced monomers, but this typically requires high processing temperatures (≥200 °C) to remove the condensate and to lower viscosity of the polymer melt. In addition, high temperatures also increase the degree of branching and cause discolouration through the degradation of sensitive co-initiators and monomers. Here we report the synthesis of novel surface-active polymers from temperature sensitive renewable building blocks such as dicarboxylic acids, polyols (d-sorbitol) and fatty acids. We demonstrate that the products have the potential to be key components in renewable surfactant design, but only if the syntheses are optimised to ensure linear chains with hydrophilic character. The choice of catalyst is key to this control and we have assessed three different approaches. Additionally, we also demonstrate that use of supercritical carbon dioxide (scCO2) can dramatically improve conversion by reducing reaction viscosity, lowering reaction temperature, and driving condensate removal. We also evaluate the performance of the new biobased surfactants, focussing upon surface tension, and critical micelle concentration.

Bespoke 3D-Printed Polydrug Implants Created via Microstructural Control of Oligomers.

Controlling the microstructure of materials by means of phase separation is a versatile tool for optimizing material properties. Phase separation has been exploited to fabricate intricate microstructures in many fields including cell biology, tissue engineering, optics, and electronics. The aim of this study was to use phase separation to tailor the spatial location of drugs and thereby generate release profiles of drug payload over periods ranging from 1 week to months by exploiting different mechanisms: polymer degradation, polymer diluent dissolution, and control of microstructure. To achieve this, we used drop-on-demand inkjet three-dimensional (3D) printing. We predicted the microstructure resulting from phase separation using high-throughput screening combined with a model based on the Flory-Huggins interaction parameter and were able to show that drug release from 3D-printed objects can be predicted from observations based on single drops of mixtures. We demonstrated for the first time that inkjet 3D printing yields controllable phase separation using picoliter droplets of blended photoreactive oligomers/monomers. This new understanding gives us hierarchical compositional control, from droplet to device, allowing release to be "dialled up" without manipulation of device geometry. We exemplify this approach by fabricating a biodegradable, long-term, multiactive drug delivery subdermal implant ("polyimplant") for combination therapy and personalized treatment of coronary heart disease. This is an important advance for implants that need to be delivered by cannula, where the shape is highly constrained and thus the usual geometrical freedoms associated with 3D printing cannot be easily exploited, which brings a hitherto unseen level of understanding to emergent material properties of 3D printing.