Dynamic Non-Covalent Exchange Intrinsic Self-Healing at 20 °C Mechanism of Polyurethane Induced by Interactions among Polycarbonate Soft Segments

Two polyurethanes (PUs) were similarly synthesized by reacting a cycloaliphatic isocyanate with 1,4-butanediol and two polyols of different nature (polyester, polycarbonate diol) with molecular weights of 1000 Da. Only the PU synthesized with polycarbonate diol polyol (YCD) showed intrinsic self-healing at 20 °C. For assessing the mechanism of intrinsic self-healing of YCD, a structural characterization by molecular weights determination, infrared and X-ray photoelectronic spectroscopies, differential scanning calorimetry, X-ray diffraction, thermal gravimetric analysis, and dynamic mechanical thermal analysis was carried out. The experimental evidence concluded that the self-healing at 20 °C of YCD was due to dynamic non-covalent exchange interactions among the polycarbonate soft segments. Therefore, the chemical nature of the polyol played a key role in developing PUs with intrinsic self-healing at 20 °C.

The effect of chiral end groups on the assembly of supramolecular polyurethanes

We describe the generation of supramolecular polyurethanes and the positive effect that chirality has upon the physical properties of these materials.

A 3D printed drug delivery implant formed from a dynamic supramolecular polyurethane formulation

Prototype drug eluting implants have been 3D printed using a supramolecular polyurethane-PEG formulation. The implants are capable of releasing a pharmaceutical active with effective drug release over a period of up to 8.5 months.

In situ characterization of strain-induced crystallization of natural rubber by synchrotron radiation wide-angle X-ray diffraction: construction of a crystal network at low temperatures

Strain-induced crystallization (SIC) of natural rubber (NR) at descending temperatures as low as -60 °C is systematically investigated by in situ synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) measurement. The detailed structural evolution of NR during SIC is studied in the strain-temperature space, where up to four regions are defined depending on the SR-WAXD results. In region I, the molecular chains begin to be oriented under tensile loading. The onset of crystallization happens in the very beginning of region II, and the NR crystal acts as a new physical cross-linking point to form a crystal network, namely the series model. The further increment of crystallinity (> ca. 8%) leads to the transition of the crystal network from the series model to the parallel model in region III. The crystal network is finally accomplished in region IV, where the crystallinity remains almost constant. Interestingly, regions III and IV exist only in the intermediate-temperature zone II (-40 °C to -10 °C), which are missing in zones I (-10 °C to 25 °C) and III (-60 °C to -40 °C). This suggests that sufficient crystallinity (χ_II-III > ca. 8%) is required to form the parallel model. The new crystal network provides a deep understanding of SIC of NR considering the microscopic features, i.e. oriented amorphous component, the onset of crystallization and crystallinity evolution and its correlation with the macroscopic stress-strain curve.

Enhancement of microphase ordering and mechanical properties of supramolecular hydrogen-bonded polyurethane networks

Enhanced thermoreversible and mechanical properties in supramolecular polyurethanes have been realised by the incorporation of flexible DBDI derived hard segments.

3D Printing Polymers with Supramolecular Functionality for Biological Applications

Supramolecular chemistry continues to experience widespread growth, as fine-tuned chemical structures lead to well-defined bulk materials. Previous literature described the roles of hydrogen bonding, ionic aggregation, guest/host interactions, and π-π stacking to tune mechanical, viscoelastic, and processing performance. The versatility of reversible interactions enables the more facile manufacturing of molded parts with tailored hierarchical structures such as tissue engineered scaffolds for biological applications. Recently, supramolecular polymers and additive manufacturing processes merged to provide parts with control of the molecular, macromolecular, and feature length scales. Additive manufacturing, or 3D printing, generates customizable constructs desirable for many applications, and the introduction of supramolecular interactions will potentially increase production speed, offer a tunable surface structure for controlling cell/scaffold interactions, and impart desired mechanical properties through reinforcing interlayer adhesion and introducing gradients or self-assembled structures. This review details the synthesis and characterization of supramolecular polymers suitable for additive manufacture and biomedical applications as well as the use of supramolecular polymers in additive manufacturing for drug delivery and complex tissue scaffold formation. The effect of supramolecular assembly and its dynamic behavior offers potential for controlling the anisotropy of the printed objects with exquisite geometrical control. The potential for supramolecular polymers to generate well-defined parts, hierarchical structures, and scaffolds with gradient properties/tuned surfaces provides an avenue for developing next-generation biomedical devices and tissue scaffolds.

Rheology of nitrile rubber with hybrid crosslinked network composed of covalent bonding and hydrogen bonding

A hybrid crosslinked network composed of covalent bonding and non-covalent bonding was constructed in nitrile rubber (NBR) by using a compound crosslinking agents dicumyl peroxide (DCP) and N,N-methylenebis acrylamide (MBA).

An adhesive elastomeric supramolecular polyurethane healable at body temperature

In this paper, we report the synthesis and healing ability of a non-cytotoxic supramolecular polyurethane network whose mechanical properties can be recovered efficiently (>99%) at the temperature of the human body (37 °C). Rheological analysis revealed an acceleration in the drop of the storage modulus above 37 °C, on account of the dissociation of the supramolecular polyurethane network, and this decrease in viscosity enables the efficient recovery of the mechanical properties. Microscopic and mechanical characterisation has shown that this material is able to recover mechanical properties across a damage site with minimal contact required between the interfaces and also demonstrated that the mechanical properties improved when compared to other low temperature healing elastomers or gel-like materials. The supramolecular polyurethane was found to be non-toxic in a cytotoxicity assay carried out in human skin fibroblasts (cell viability > 94% and non-significantly different compared to the untreated control). This supramolecular network material also exhibited excellent adhesion to pig skin and could be healed completely in situ post damage indicating that biomedical applications could be targeted, such as artificial skin or wound dressings with supramolecular materials of this type.

3D Printing of Biocompatible Supramolecular Polymers and their Composites

A series of polymers capable of self-assembling into infinite networks via supramolecular interactions have been designed, synthesized, and characterized for use in 3D printing applications. The biocompatible polymers and their composites with silica nanoparticles were successfully utilized to deposit both simple cubic structures, as well as a more complex twisted pyramidal feature. The polymers were found to be not toxic to a chondrogenic cell line, according to ISO 10993-5 and 10993-12 standard tests and the cells attached to the supramolecular polymers as demonstrated by confocal microscopy. Silica nanoparticles were then dispersed within the polymer matrix, yielding a composite material which was optimized for inkjet printing. The hybrid material showed promise in preliminary tests to facilitate the 3D deposition of a more complex structure.

Microphase separation induced in the melt of Pluronic copolymers by blending with a hydrogen bonding urea-urethane end-capped supramolecular polymer

Blending with a hydrogen-bonding supramolecular polymer is shown to be a successful novel strategy to induce microphase-separation in the melt of a Pluronic polyether block copolymer. The supramolecular polymer is a polybutadiene derivative with urea-urethane end caps. Microphase separation is analysed using small-angle X-ray scattering and its influence on the macroscopic rheological properties is analysed. FTIR spectroscopy provides a detailed picture of the inter-molecular interactions between the polymer chains that induces conformational changes leading to microphase separation.

Incorporation of 1,4-cyclohexanedicarboxylic acid into poly(butylene terephthalate)-b-poly(tetramethylene glycol) to alter thermal properties without compromising tensile and elastic properties

Incorporation of 1,4-cyclohexanedicarboxylic acid to partially replace terephthalic acid results in a thermoplastic elastomer with decreased melting temperature and increased thermal stability while tensile and elastic properties remain unchanged.

Order-disorder transition in supramolecular polymers

In supramolecular polymers, directional interactions control the constituting units connectivity, but dispersion forces may conspire to make complex organizations. Here we report on the long-range order and order-disorder transition (ODT) of main-chain supramolecular polymers based on poly(propylene oxide) (PPO) spacers functionalized on both ends with thymine. Below the ODT temperature (T(ODT)), these compounds are semicrystalline with a lamellar structure, showing nanophase separation between crystallized thymine planes and amorphous PPO layers. Above T(ODT), they are amorphous and homogeneous even though their X-ray scattering spectrum reveals a peak. This peak is due to correlation hole effect resulting from contrast between end-functional groups and spacer. Macroscopically, the transition is accompanied by dramatic flow and mechanical properties changes.