Biological MWCNT/chitosan composite coating with outstanding anti-corrosion property for implants.

Biocompatible coatings that can protect metal implants have great potential in tissue engineering. In this work, MWCNT/chitosan composite coatings with hydrophobic-hydrophilic asymmetric wettability were facilely prepared by one-step in situ electrodeposition. The resultant composite coating exhibits excellent thermal stability and mechanical strength (0.76 MPa), benefiting from the compact internal structure. The thickness of the coating can be controlled precisely by the amounts of transferred charges. The MWCNT/chitosan composite coating demonstrates a lower corrosion rate due to its hydrophobicity and compact internal structure. Compared with exposed 316 L stainless steel, its corrosion rate is reduced by two orders of magnitude from 3.004 × 10-1 mm/yr to 5.361 × 10-3 mm/yr. The content of iron released from 316 L stainless steel into the simulated body fluid drops to 0.1 mg/L under the protection of the composite coating. In addition, the composite coating enables efficient calcium enrichment from simulated body fluids and promotes the formation of bioapatite layers on the coating surface. This study contributes to furthering the practical application of chitosan-based coatings in implant anticorrosion.

Hollow chitosan hydrogel tube with controllable wrinkled pattern via film-to-tube fabrication.

Due to mechanical instability, surface wrinkles form spontaneously in plants, animals and human beings for propagation and enhanced surface functionality. However, there remains tremendous challenge in mimicking such exquisite structure at a micro/nanoscale in lab. Herein, we report an approach to converting an electrodeposited chitosan hydrogel film into a hollow tube with controllable wrinkle wavelength and amplitude via soaking the film in acidic sodium dodecyl sulfate (SDS). Notably, wrinkled pattern can be controlled by a self-design device through modulating the shrinkage ratio. The resultant wrinkled hydrogel tube with adjustable wall thickness, outer diameter shows excellent mechanical strength, anti-fatigue ability, recoverability and flexibility. It is demonstrated that 2D/3D complicated hollow framework with wrinkled pattern can be customized on demand. This facile strategy not only provides a feasible approach to preparing hydrogel tube with wrinkles, but also points to possible pathways for bioengineering more complicated materials from natural polymers.

Ion-responsive chitosan hydrogel actuator inspired by carrotwood seed pod.

Inspired by the gradient hygroscopic structure of carrotwood seed pod, patterned anisotropic structure was created in polysaccharide hydrogel by an anodic electrical writing process. Locally released Fe2+ was oxidized to Fe3+ and chelated with chitosan chains in the written area, resulting in a gradient structure in the hydrogel. The asymmetrical stress generated by the different swelling of the gradient structure enables the hydrogel to bend autonomously. The hydrogel shows opposite bending in deionized water and NaCl solution. The physicochemical properties of the hydrogel are characterized by tensile test, SEM, EDS, XRD, TGA, DTG and FT-IR. SEM and EDS show that the written hydrogel has a structural gradient and a concentration gradient of Fe3+ vertically. Moreover, anodic electrical writing increases the flexibility of chitosan hydrogel due to decreased crystallinity. This controllable electrical writing technique is convenient to create patterned anisotropic structure and provide a novel design concept for natural hydrogel actuators.