Reversible Electroaddressing of Self‐assembling Amino‐Acid Conjugates

The triggered assembly of organic and biological materials in response to imposed electrical signals (i.e., electroaddressing) provides interesting opportunities for applications in molecular electronics, biosensing and nanobiotechnology. Recent studies have shown that the conjugation of aromatic moieties to short peptides often yields hydrogelator compounds that can be triggered to self‐assemble over a hierarchy of length scales in response to a reduction in pH. Here, we examined the capabilities of fluorenyl‐9‐methoxycarbonyl‐phenylalanine (Fmoc‐Phe) to electrodeposit in response to an electrochemically‐induced pH gradient generated at the anode surface. We report that the electrodeposition of Fmoc‐Phe; is rapid (minutes), can be spatially controlled in normal and lateral directions, and can be reversed by applying a brief cathodic current. Further more, we show that Fmoc‐Phe can be simultaneously deposited on one electrode address (anode) while it is being cathodically stripped from a separate electrode address of the same chip. Finally, we demonstrate that these capabilities can be extended for electroaddressing within microfluidic channels. The reversible assembly/disassembly of molecular gelators (Fmoc‐amino acids and Fmoc‐peptides) in response to spatiotemporally imposed electrical signals offers unique opportunities for electroaddressing that should be especially valuable for lab‐on‐a‐chip applications.     

One‐Pot Template‐Free Synthesis of Monodisperse Hollow Hydrogel Microspheres and their Resulting Properties

Monodisperse poly(methacrylic acid/ethyleneglycoldimethacrylate) (MAA/EGDMA) hollow microcapsules, which exhibit pH‐responsive behavior, are prepared by diffusion of cationic surfactants and hydrophobic interaction. During the association of the negatively charged hydrogel microspheres and an oppositely charged surfactant (cetyltrimethylammonium bromide, CTA(+)B), the hydrophobic polymer‐surfactant complexes that form are separated from the internal water; consequently, a hollow structure can be formed. Confocal laser scanning microscopy, UV spectro­scopy and zeta potential are employed to study the formation of the hollow structure during the diffusion of the cationic surfactant. The controlled release behavior of methylene blue as a model drug from the as‐prepared poly(MAA/EGDMA) microcapsules with a hollow structure is investigated under different pH conditions. The hollow structure can be retained, even during repetitive pH changes.

     

Dextran‐Based Self‐Healing Hydrogels Formed by Reversible Diels–Alder Reaction under Physiological Conditions

A dextran‐based self‐healing hydrogel is prepared by reversible Diels–Alder reaction under physiological conditions. Cytocompatible fulvene‐modified dextran as main polymer chains and dichloromaleic‐acid‐modified poly(ethylene glycol) as cross‐linkers are used. Both macro‐ and microscopic observation as well as the rheological recovery test confirm the self‐healing property of the dextran‐l‐poly(ethylene glycol) hydrogels (“l” means “linked‐by”). In addition, scanning electrochemical microscopy is used to qualitatively and quantitatively in situ track the self‐healing process of the hydrogel for the first time. It is found that the longitudinal depth of scratch on hydrogel surface almost completely healed at 37 °C after 7 h. This work represents a facile approach for fabrication of polysaccharide self‐healing hydrogel, which can be potentially used in several biomedical fields.

     

Drying of PAAm Hydrogels at Various Temperatures: A Fluorescence Study

The steady‐state fluorescence (SSF) technique was employed for studying the drying of polyacrylamide (PAAm) hydrogels. Disc‐shaped hydrogels were prepared by free‐radical crosslinking copolymerization of acrylamide (AAm) with N,N′‐methylene bisacrylamide (BIS) as crosslinker in the presence of ammonium persulfate (APS) as an initiator. Pyranine (P) was introduced as a fluorescence probe and the intensity of pyranine was monitored during in situ drying at various temperatures. It was observed that the fluorescence intensity of pyranine increased during the drying process. A supporting, gravimetrical experiment was also performed. A phenomenological equation was introduced to determine the desorption coefficient, D, of water molecules from the drying hydrogels at various temperatures. The desorption activation energy, ΔE _d, values were measured for the drying processes and found to be 91.08 and 36.82 kJ mol^–1 by fluorescence and gravimetrical methods, respectively. This difference most probably originates from the origin of the techniques; the fluorescence technique measures the parameters at a molecular level, whereas the gravimetrical technique measures a parameter in the bulk.     

Synthesis and Properties of Polyacrylamide-Based Conducting Gels with Enhanced Mechanical Strength

A nanocomposite conducting hydrogel, polyacrylamide/MWNT/clay (abbreviated as PAM/MWNT/clay), prepared through in situ free radical aqueous polymerization and crosslinked by both clay, as a functional physical crosslinker, and N,N′-methylenebisacrylamide (MBA) as a chemical crosslinker, is reported. The morphology of the gels was characterized by scanning electron microscopy (SEM). The mechanical properties and electrical conductivity were also studied. The results show that the prepared hydrogels had the expected chemical components, with a highly porous structure, and the gels also showed high mechanical strength. The mechanical strength and electrical conductivity value increased with increasing content of multi-walled nanotube (MWNT), and decreased with increasing content of water.     

Prototype development and gait planning of biologically inspired multi-legged crablike robot

In order to investigate the walking gait of the legged robot with multiple redundant walking legs, the motion features of the biologic crab are studied. To study the motion property of multi-legged animals in depth, an event sequence analysis method is proposed, and employed to design the motion pattern of multi-legged robot. A low-consumption environmental self-adaptive bionic gait with its phase factor of 0.25 and duty factor of 0.454 is analyzed based on the analysis of pace order, gait parameters and single leg’s terminal trajectory on uneven terrain. According to the structures and motion patterns of biologic crab, a multi-legged crablike prototype with its experimental platform is developed. The contrast tests of environmental self-adaptive bionic gait and double tetrapod gait are experimented at the same velocity, and slope climbing tests are performed as well. The experimental results show that, although the double tetrapod gait enables four legs to support the robot’s body at any time, there exists halt or backward phenomena periodically. However, the robot using the new gait has lower gravity fluctuation in displacement and velocity without halt or backward problem, and the decreasing of motion speed leads to the increasing of the gravity fluctuation and the toe-force.     

Mussel Inspired Dynamic Cross‐Linking of Self‐Healing Peptide Nanofiber Network

A general drawback of supramolecular peptide networks is their weak mechanical properties. In order to overcome a similar challenge, mussels have adapted to a pH‐dependent iron complexation strategy for adhesion and curing. This strategy also provides successful stiffening and self‐healing properties. The present study is inspired by the mussel curing strategy to establish iron cross‐link points in self‐assembled peptide networks. The impact of peptide‐iron complexation on the morphology and secondary structure of the supramolecular nanofibers is characterized by scanning electron microscopy, circular dichroism and Fourier transform infrared spectroscopy. Mechanical properties of the cross‐linked network are probed by small angle oscillatory rheology and nanoindentation by atomic force microscopy. It is shown that iron complexation has no influence on self‐assembly and β‐sheet‐driven elongation of the nanofibers. On the other hand, the organic‐inorganic hybrid network of iron cross‐linked nanofibers demonstrates strong mechanical properties comparable to that of covalently cross‐linked network. Strikingly, iron cross‐linking does not inhibit intrinsic reversibility of supramolecular peptide polymers into disassembled building blocks and the self‐healing ability upon high shear load. The strategy described here could be extended to improve mechanical properties of a wide range of supramolecular polymer networks.     

Composite Three‐Dimensional Woven Scaffolds with Interpenetrating Network Hydrogels to Create Functional Synthetic Articular Cartilage

The development of synthetic biomaterials that possess mechanical properties mimicking those of native tissues remains an important challenge to the field of materials. In particular, articular cartilage is a complex nonlinear, viscoelastic, and anisotropic material that exhibits a very low coefficient of friction, allowing it to withstand millions of cycles of joint loading over decades of wear. Here, a three‐dimensionally woven fiber scaffold that is infiltrated with an interpenetrating network hydrogel can build a functional biomaterial that provides the load‐bearing and tribological properties of native cartilage. An interpenetrating dual‐network “tough‐gel” consisting of alginate and polyacrylamide was infused into a porous three‐dimensionally woven poly(?‐caprolactone) fiber scaffold, providing a versatile fiber‐reinforced composite structure as a potential acellular or cell‐based replacement for cartilage repair.     

Spatially Controlled Delivery of siRNAs to Stem Cells in Implants Generated by Multi‐Component Additive Manufacturing

Additive manufacturing is a promising technique in tissue engineering, as it enables truly individualized implants to be made to fit a particular defect. As previously shown, a feasible strategy to produce complex multicellular tissues is to deposit different small interfering RNA (siRNA) in porous implants that are subsequently sutured together. In this study, an additive manufacturing strategy to deposit carbohydrate hydrogels containing different siRNAs is applied into an implant, in a spatially controlled manner. When the obtained structures are seeded with mesenchymal stem (stromal) cells, the selected siRNAs are delivered to the cells and induces specific and localized gene silencing. Here, it is demonstrated how to replicate part of a patient's spinal cord from a computed tomography scan, using an additive manufacturing technique to produce an implant with compartmentalized siRNAs in the locations corresponding to distinct tissue. Hydrogel solutions loaded with different siRNA can be co‐printed together with polycaprolactone that acts as rigid mechanical support to the hydrogel. This study demonstrates a new route for the production of 3D functionalized, individualized implants which may provide great clinical benefit.