Design and Preparation of Stretchable Semiconductors Through Polymer Blending

A new strategy for influencing the solid-state morphology of conjugated polymers was developed through physical blending with a low molecular weight branched polyethylene (BPE). This non-toxic and low boiling point additive was blended with a high charge mobility diketopyrrolopyrrole (DPP)-based conjugated polymer and a detailed investigation of both electronic (Chapter III) and mechanical (Chapter IV) properties was performed. The new blended materials were characterized by various techniques, including X-ray diffraction, UV-Vis spectroscopy and atomic force microscopy (AFM). Interestingly, the branched additive was shown to reduce the crystallinity of the conjugated polymer, while promoting aggregation and phase separation in the solid-state. The performance of the new branched polyethylene/conjugated polymer blends was also investigated in organic field-effect transistors, which showed a stable charge mobility, independent of the blending ratio. Furthermore, by using the new BPE additive, the amount of conjugated polymer required for the fabrication of organic field-effect transistor devices was reduced down to 0.05 wt.%, without affecting charge transport, which is very promising in a large-scale fabrication of organic-field effect transistors (OFET) devices. Moreover, BPE additive acts as a plasticizer, thus drastically decreasing the crystallinity of conjugated polymers which is beneficial for the development of stretchable and flexible electronic devices. The incorporation of BPE amount to the conjugated polymer leads to an increase of the crack onset strain of polymer blends and decrease in the number of cracks, as well as their width. Our results demonstrate that the physical blending of conjugated polymer with non-toxic, low-molecular weight BPE is a promising strategy for the modification and fine-tuning of the solid-state morphology of conjugated polymers without sacrificing their charge transport properties, thus creating new opportunities for the large-scale processing of organic semiconductor

Effect of Branched Polyethylene on the Mechanical and Electronic Properties of Semiconducting Polymers

With the rise of portable and implantable electronics, where objects and human are constantly connected, there is a need for materials that can used in electronic devices that have a good charge transport and eco-friendly properties while also being stable in various conditions. Directly inspired by biological tissues, next generation electronics have to be capable of being molded in different shapes and forms and, more importantly, being utilized directly on (or inside) the human body to enhance our connectivity to the environment. This means that the components required to design and fabricate the next generation electronics need to be electronically and mechanically robust, while possessing properties similar to that of our body. To address this challenge, our research exploits a combination of a DPP-based conjugated polymer with a low-molecular-weight and low boiling point branched polyethylene (BPE) that are physically blended to improve the mechanical properties of the semiconducting polymers. Using various characterization methods such as atomic-force microscopy, UV-vis spectroscopy and X-ray diffraction, we evaluated the effect of the branched polyethylene additive on the mechanical properties of the polymers. Interestingly, this additive was shown to reduce Young’s modulus, decrease crack propagation, reduce crystallinity, promote aggregation, and increase crack onset strain. Our new materials were used to fabricate organic field-effect transistors, critical components of modern circuits. This presentation will discuss the preparation and characterization of new conjugated polymer and soft materials blends, and will highlight the potential of our new materials for the preparation of next generation electronics and sensors

Gold-enhanced brachytherapy by a nanoparticle-releasing hydrogel and 3d-printed subcutaneous radioactive implant approach

Brachytherapy (BT) is a widely used clinical procedure for localized cervical cancer treatment. In addition, gold nanoparticles (AuNPs) have been demonstrated as powerful radiosensitizers in BT procedures. Prior to irradiation by a BT device, their delivery to tumors can enhance the radiation effect by generating low-energy photons and electrons, leading to reactive oxygen species (ROS) production, lethal to cells. No efficient delivery system has been proposed until now for AuNP topical delivery to localized cervical cancer in the context of BT. This article reports an original approach developed to accelerate the preclinical studies of AuNP-enhanced BT procedures. First, a AuNP-containing hydrogel (Pluronic F127, alginate) is developed and tested in mice for degradation, AuNP release, and biocompatibility. Then, custom-made 3D-printed radioactive BT inserts covered with a AuNP-containing hydrogel cushion are designed and administered by surgery in mice (HeLa xenografts), which allows measuring AuNP penetration in tumors (~100 m), co-registered with the presence of ROS produced through the interactions of radiation and AuNPs. Overall, the application of a biocompatible AuNPs-releasing hydrogel in the vicinity of cervical cancer prior to BT could decrease the total amount of radiation needed per BT treatment, with benefits on the preservation of healthy tissues surrounding cancer

A 3D-printable hydrogel formulation for the local delivery of therapeutic nanoparticles to cervical cancer

Cervical cancer is the fourth most common malignancy among women. Compared to other types of cancer, therapeutic agents can be administrated locally at the mucosal vaginal membrane. Thermosensitive gels have been developed over the years for contraception, or for the treatment of bacterial, fungal, and sexually transmitted infections. These formulations often carry therapeutic nanoparticles and are now being considered in the arsenal of tools for oncology. They can also be 3D-printed for a better geometrical adjustment to the anatomy of the patient, thus enhancing the local delivery treatment. In this study, a localized delivery system composed of a Pluronic F127-alginate hydrogel with efficient nanoparticle (NP) release properties was prepared for intravaginal application procedures. The kinetics of hydrogel degradation and its NP releasing properties were demonstrated with ultra-small gold nanoparticles (~80% of encapsulated AuNPs released in 48 h). The mucoadhesive properties of the hydrogel formulation were assayed by the periodic acid/Schiff’s reagent staining, which revealed that 19% of mucins were adsorbed on the gel’s surface. The hydrogel formulation was tested for cytocompatibility in three cell lines (HeLa, CRL 2616, and BT-474; no sign of cytotoxicity revealed). The release of AuNPs from the hydrogel and their accumulation in vaginal membranes were quantitatively measured in vitro/ex vivo with positron emission tomography (PET), a highly sensitive imaging modality allowing real-time imaging of nanoparticle diffusion (lag time to start of permeation 3.3 h, 47% of AuNPs accumulated in the mucosa after 42 h). Finally, the potential of the AuNPs-containing Pluronic F127-alginate hydrogel for 3D-printing was demonstrated, and the geometrical precision of the 3D-printed systems was measured by magnetic resonance imaging (MRI, <0.5 mm precision; deviation from the design values <2.5%). In summary, this study demonstrates the potential of Pluronic F127-alginate formulations for the topical administration of NP-releasing gels applied to vaginal wall therapy. This technology could open new possibilities for photothermal and radiosensitizing oncology applications

Branched Polyethylene as a Plasticizing Additive to Modulate the Mechanical Properties of π-Conjugated Polymers

A new approach for improving the mechanical properties of semiconducting polymers was established via physical combination of a diketopyrrolopyrrole-based conjugated polymer with a low-molecular-weight branched polyethylene (BPE). The influence of the BPE additive on the stretchability and mechanical properties of the conjugated polymer was studied at different scales, using various characterization techniques, including atomic force microscopy, UV–vis spectroscopy, and grazing incidence X-ray diffraction. At the micron scale, the BPE additive acts as a plasticizer and significantly reduces Young’s modulus of the conjugated polymer and increases the crack onset strain, reaching a maximum of a 75% strain elongation when 90 wt % of BPE is blended with the conjugated polymer. The introduction of BPE to the blended systems decreases the crack propagation of polymer thin films, making them softer and more ductile, with Young’s modulus of 112 MPa at 25 wt % of BPE before thermal annealing. At the nanoscale, the improvement of stretchability is shown by the reduction of the crack size under a 100% strain, going from 3100 to 600 nm at 0 and 90 wt % of BPE, respectively. The results obtained in this investigation confirm that an improvement in the mechanical properties and a modulation of the solid-state morphology of the semiconducting materials can be enabled by the physical mixing of conjugated polymers with a nontoxic, low-molecular-weight branched polyethylene, particularly favorable for the solution deposition of organic semiconductors

Influence of Amide-Containing Side Chains of the Mechanical Properties of Diketopyrrolopyrrole-Based Polymers

An efficient strategy to modulate the mechanical properties of conjugated polymers has been developed through the incorporation of amide-containing alkyl chains in diketopyrrolopyrrole-based conjugated polymers. The side-chain engineering performed with hydrogen bonding moieties (up to 20 mol% of amide-containing side-chains) was found to reduce the crystallinity of the conjugated polymers in the solid state. Interestingly, this reduction in crystallinity drastically influenced the mechanical properties of the new DPP-polymers, by promoting their stretching ability, reducing the elastic modulus of the polymers, and facilitating the molecular alignment after stretch. The resulting polymers with 10% hydrogen bonding side chains showed a maximum stretchability of 75% elongation, without the appearance of nanoscale cracks, and a detailed investigation of the mechanical properties was performed by a combination of morphological characterization tools, including grazing-incidence X-ray diffraction, polarized UV-Vis spectroscopy and optical/atomic force microscopy to support our finding. Additionally, incorporation of amide-containing side-chains also enabled the regeneration of the conjugated polymer morphology after damage. Our results demonstrate that the introduction of amide-containing alkyl chains is an effective strategy to enhance the mechanical properties of π-conjugated polymers without disrupting the π-conjugation, and to enable new properties such as morphological healing

Toward the Prediction and Control of Glass Transition Temperature For Donor-Acceptor Polymers

Semiconducting donor–acceptor (D–A) polymers have attracted considerable attention toward the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for advanced applications. Here, polydiketopyrrolopyrrole (PDPP)‐based D–A polymers with varied alkyl side‐chain lengths and backbone moieties are systematically designed, followed by investigating their thermal and thin film mechanical responses. The experimental results show a reduction in both elastic modulus and glass transition temperature (T g) with increasing side‐chain length, which is further verified through coarse‐grained molecular dynamics simulations. Informed from experimental results, a mass‐per‐flexible bond model is developed to capture such observation through a linear correlation between T g and polymer chain flexibility. Using this model, a wide range of backbone T g over 80 °C and elastic modulus over 400 MPa can be predicted for PDPP‐based polymers. This study highlights the important role of side‐chain structure in influencing the thermomechanical performance of conjugated polymers, and provides an effective strategy to design and predict T g and elastic modulus of future new D–A polymers