Material assembly from collective action of shape-changing polymers.

Some animals form transient, responsive and solid-like ensembles through dynamic structural interactions. These ensembles demonstrate emergent responses such as spontaneous self-assembly, which are difficult to achieve in synthetic soft matter. Here we use shape-morphing units comprising responsive polymers to create solids that self-assemble, modulate their volume and disassemble on demand. The ensemble is composed of a responsive hydrogel, liquid crystal elastomer or semicrystalline polymer ribbons that reversibly bend or twist. The dispersions of these ribbons mechanically interlock, inducing reversible aggregation. The aggregated liquid crystal elastomer ribbons have a 12-fold increase in the yield stress compared with cooled dispersion and contract by 34% on heating. Ribbon type, concentration and shape dictate the aggregation and govern the global mechanical properties of the solid that forms. Coating liquid crystal elastomer ribbons with a liquid metal begets photoresponsive and electrically conductive aggregates, whereas seeding cells on hydrogel ribbons enables self-assembling three-dimensional scaffolds, providing a versatile platform for the design of dynamic materials.

Chemical Modifications of Porous Shape Memory Polymers for Enhanced X-ray and MRI Visibility.

The goal of this work was to develop a shape memory polymer (SMP) foam with visibility under both X-ray and magnetic resonance imaging (MRI) modalities. A porous polymeric material with these properties is desirable in medical device development for applications requiring thermoresponsive tissue scaffolds with clinical imaging capabilities. Dual modality visibility was achieved by chemically incorporating monomers with X-ray visible iodine-motifs and MRI visible monomers with gadolinium content. Physical and thermomechanical characterization showed the effect of increased gadopentetic acid (GPA) on shape memory behavior. Multiple compositions showed brightening effects in pilot, T1-weighted MR imaging. There was a correlation between the polymeric density and X-ray visibility on expanded and compressed SMP foams. Additionally, extractions and indirect cytocompatibility studies were performed to address toxicity concerns of gadolinium-based contrast agents (GBCAs). This material platform has the potential to be used in a variety of medical devices.

Photopatterning Crystal Orientation in Shape-Morphing Polymers.

Shape-morphing polymers have gained particular attention due to their unique capability of shape transformation under numerous external stimuli such as light, pH, and temperature. Their shape-morphing properties can be used in various applications such as robotics, artificial muscles, and biomedical devices. To take advantage of the stimuli-responsive properties of the smart polymers in such applications, programming shape change precisely through a facile synthetic procedure is essential. Programmable shape-morphing is readily obtained in hydrogels and liquid crystal polymer networks, but shape programming of semicrystalline polymers usually relies on low-resolution mechanical deformation. In this paper, a semicrystalline shape-morphing polymer with a controlled shape programmability was developed via photopatterning crystal orientation using a spatially controlled photopolymerization technique. The semicrystalline polymer network forms aligned crystallites at the boundaries between dark and bright regions during photopolymerization using a projector, which introduces an anisotropic stimulus response in the films. The semicrystalline polymer films with photoaligned crystallites expand 9-15% in the direction perpendicular to the patterned lines when heated above the melting temperature. Furthermore, spatially patterning the crystal orientation enables the formation of various complex 3D structures including a helical coil, a coil with a handedness inversion, a cone, a saddle, and a twisting flower. Finally, the magnitude of the shape transformation was controlled by varying the polymerization temperatures, and the actuation temperature was tuned by changing the amount of crystallinity in the polymer films. The simplicity and ease of control of our approach to program complex 3D structures from 2D semicrystalline polymer films make it a promising system for the aforementioned applications.

Biodegradable shape memory polymer foams with appropriate thermal properties for hemostatic applications.

Shape memory polymer (SMP) foams are a promising material for hemostatic dressings due to their biocompatibility, high surface area, excellent shape recovery, and ability to quickly initiate blood clotting. Biodegradable SMP foams could eliminate the need for a secondary removal procedure of hemostatic material from the patients' wound, further facilitating wound healing. In this study, we developed hydrolytically and oxidatively biodegradable SMP foams by reacting polyols (triethanolamine or glycerol) with 6-aminocaproic acid or glycine to generate foaming monomers with degradable ester bonds. These monomers were used in foam synthesis to provide highly crosslinked SMP foam structures. The ester-containing foams showed clinically relevant thermal properties that were comparable to controls and excellent shape recovery within eight min. Triethanolamine-based ester-containing foams showed interconnected porous structure along with increased mechanical strength. Faster hydrolytic and oxidative biodegradation rates were achieved in ester-containing foams in comparison to controls. These biodegradable SMP foams with clinically applicable thermal properties possess great potential as an effective hemostatic device for use in hospitals or on battlefields.

Three-dimensional bioprinting of aneurysm-bearing tissue structure for endovascular deployment of embolization coils.

Various types of embolization devices have been developed for the treatment of cerebral aneurysms. However, it is challenging to properly evaluate device performance and train medical personnel for device deployment without the aid of functionally relevant models. Currentin vitroaneurysm models suffer from a lack of key functional and morphological features of brain vasculature that limit their applicability for these purposes. These features include the physiologically relevant mechanical properties and the dynamic cellular environment of blood vessels subjected to constant fluid flow. Herein, we developed three-dimensionally (3D) printed aneurysm-bearing vascularized tissue structures using gelatin-fibrin hydrogel of which the inner vessel walls were seeded with human cerebral microvascular endothelial cells (hCMECs). The hCMECs readily exhibited cellular attachment, spreading, and confluency all around the vessel walls, including the aneurysm walls. Additionally, thein vitroplatform was directly amenable to flow measurements via particle image velocimetry, enabling the direct assessment of the vascular flow dynamics for comparison to a 3D computational fluid dynamics model. Detachable coils were delivered into the printed aneurysm sac through the vessel using a microcatheter and static blood plasma clotting was monitored inside the aneurysm sac and around the coils. This biomimeticin vitroaneurysm model is a promising method for examining the biocompatibility and hemostatic efficiency of embolization devices and for providing hemodynamic information which would aid in predicting aneurysm rupture or healing response after treatment.

Electrically Conductive Polydopamine-Polypyrrole as High Performance Biomaterials for Cell Stimulation in Vitro and Electrical Signal Recording in Vivo.

Conductive polymers (CPs) such as polypyrrole (PPY) are emerging biomaterials for use as scaffolds and bioelectrodes which interact with biological systems electrically. Still, more electrically conductive and biologically interactive CPs are required to develop high performance biomaterials and medical devices. In this study, in situ electrochemical copolymerization of polydopamine (PDA) and PPY were performed for electrode modification. Their material and biological properties were characterized using multiple techniques. The electrical properties of electrodes coated with PDA/PPY were superior to electrodes coated with PPY alone. The growth and differentiation of C2C12 myoblasts and PC12 neuronal cells on PDA/PPY was enhanced compared to PPY. Electrical stimulation of PC12 cells on PDA/PPY further promoted neuritogenesis. In vivo electromyography signal measurements demonstrated more sensitive signals from tibia muscles when using PDA/PPY-coated electrodes than bare or PPY-coated electrodes, revealing PDA/PPY to be a high-performance biomaterial with potential for various biomedical applications.

Facile and controllable electrochemical fabrication of cell-adhesive polypyrrole electrodes using pyrrole-RGD peptides.

Electrically conductive polymers, such as polypyrrole (PPy), have been widely used for the fabrication of various biosensors and tissue engineering scaffolds. For their biologically relevant applications, conductive biomaterials capable of intimate cellular interactions are highly desired. However, conventional methods to incorporate biomolecules into conductive polymers do not offer fine and easy control over the surface density of the biomolecules and/or their stability. We present a novel method to electrochemically immobilize cell-adhesive Arg-Gly-Asp (RGD) ligands on PPy electrode surfaces with a simple control over the peptide surface density by varying the electrodeposition time. Synthesized pyrrole-GGGRGDS conjugates were electrochemically incorporated onto the surfaces of PPy-coated electrodes. The electrochemical impedances of the RGD-grafted PPy electrodes were not significantly different from the unmodified PPy films. Time-of-flight secondary-ion mass spectroscopy confirmed the presence of the RGD motif on the surface of the modified electrodes. In vitro studies with human mesenchymal stem cells (hMSCs) showed higher adhesion and faster proliferation of hMSCs on the PPy with a higher RGD density. This facile electrochemical modification of electrode surfaces allowed for a good control over the peptide surface density and cellular interactions and will benefit the fabrication of cell-interactive scaffolds or bio-electrodes.

Electrochemical deposition of dopamine-hyaluronic acid conjugates for anti-biofouling bioelectrodes.

Bioelectrodes have been widely used to effectively mediate electrical signals with biological systems for various biomedical applications, such as biosensors and prosthetic probes. However, the electrical properties of bioelectrodes are frequently degraded in the biological milieu due to biofouling of bioelectrode surfaces. Hence, the development of simple and effective strategies for bioelectrode surface modification is important for the mitigation of biofouling. To this end, we electrochemically modify electrodes with dopamine-conjugated hyaluronic acid (DA-HA); the modified electrodes exhibit highly hydrophilic surfaces. In addition, the electrochemical impedance of the DA-HA-modified electrodes remains similar to those of bare electrodes. The DA-HA-modified electrodes showed reduced non-specific protein adsorption and minimal adhesion of fibroblasts. Our novel electrochemical passivation of electrodes using DA-HA will contribute to the further development of fouling-resistant and biocompatible bioelectrodes. The electrodeposition of DA-HA can also be potentially applied for general surface modification of other metallic and conducting materials for various applications.

Electrochemical deposition of conductive and adhesive polypyrrole-dopamine films.

Electrode surfaces have been widely modified with electrically conductive polymers, including polypyrrole (PPY), to improve the performance of electrodes. To utilize conductive polymers for electrode modification, strong adhesion between the polymer films and electrode substrates should be ensured with high electrical/electrochemical activities. In this study, PPY films were electrochemically polymerized on electrodes (e.g., indium tin oxide (ITO)) with dopamine as a bio-inspired adhesive molecule. Efficient and fast PPY electrodeposition with dopamine (PDA/PPY) was found; the resultant PDA/PPY films exhibited greatly increased adhesion strengths of up to 3.7 ± 0.8 MPa and the modified electrodes had electrochemical impedances two to three orders of magnitude lower than that of an unmodified electrode. This electrochemical deposition of adhesive and conductive PDA/PPY offers a facile and versatile electrode modification for various applications, such as biosensors and batteries.