Bioinspired Natural Shellac Dressing for Rapid Wound Sealing and Healing.

Developing safe and effective wound dressings that address the complexities of wound healing is an ongoing goal in biomaterials research. Inspired by the shield used to protect lac insects, we have designed and developed a type of bioactive shellac-based wound dressing in this paper. The dressing exhibited a high adhesion energy of 146.6 J·m-2 in porcine skin and showed a reversible binding due to its pH sensitivity. Meanwhile, a novel "shellac-like" compound, n-octacosanol gallate ester, has been synthesized and added to the dressing to improve its antibacterial and blood coagulation properties. The novel shellac-based dressing could be sprayed to form a sticky film within 70 s for rapid hemostasis and wound sealing, which could be conveniently applied to various wounds on extensible body parts. In addition, the shellac-based dressing can actively promote the healing of a full-thickness wound in the skin of mice. We also used molecular dynamics simulations to investigate the interactions between the shellac molecule and the phospholipid bilayer and attempted to show that the shellac molecule was beneficial for wound healing. This work provides a novel and practical bioinspired wound dressing with significant properties, facile preparation, and ease of use, which is an interesting alternative to its traditional counterparts.

Simulations and Experiments on the Vibrational Characteristics of Cylindrical Resonators with First Three Harmonic Errors.

A cylindrical resonator gyroscope is a kind of Coriolis gyroscope, which measures angular velocity or angle via processing of the standing wave. The symmetry of a cylindrical resonator is destroyed by different degrees of geometric nonuniformity and structural damage in the machining process. The uneven mass distribution caused by the asymmetry of the resonator can be expressed in the form of a Fourier series. The first three harmonics will reduce the anti-interference ability of the resonator to the external vibration, as well as increase the angular random walk and zero-bias drift of the gyroscope. In this paper, the frequency split of different modes caused by the first three harmonic errors and the displacement of the center of the cylindrical resonator bottom plate are obtained by simulation, and the relationship between them is explored. The experimental results on five fused silica cylindrical resonators are consistent with the simulation, confirming the linear relationship between the n = 1 frequency split and second harmonic error. A method for evaluating the first three harmonic errors of fused silica cylindrical resonators is provided.

A High-Precision Method of Stiffness Axes Identification for Axisymmetric Resonator Gyroscopes.

Axisymmetric resonators are key elements of Coriolis vibratory gyroscopes (CVGs). The performance of a CVG is closely related to the stiffness and damping symmetry of its resonator. The stiffness symmetry of a resonator can be effectively improved by electrostatic tuning or mechanical trimming, both of which need an accurate knowledge of the azimuth angles of the two stiffness axes of the resonator. Considering that the motion of a non-ideal axisymmetric resonator can be decomposed as two principal oscillations with two different natural frequencies along two orthogonal stiffness axes, this paper introduces a novel high-precision method of stiffness axes identification. The method is based on measurements of the phase difference between the signals detected at two orthogonal sensing electrodes when an axisymmetric resonator is released from all the control forces of the force-to-rebalance mode and from different initial pattern angles. Except for simplicity, our method works with the eight-electrodes configuration, in no need of additional electrodes or detectors. Furthermore, the method is insensitive to the variation of natural frequencies and operates properly in the cases of either large or small frequency splits. The introduced method is tested on a resonator gyroscope, and two stiffness axes azimuth angles are obtained with a resolution better than 0.1°. A comparison of the experimental results and theoretical model simulations confirmed the validity of our method.

Experimental Study on Variation of Surface Roughness and Q Factors of Fused Silica Cylindrical Resonators with Different Grinding Speeds.

For the axisymmetric shell resonator gyroscopes, the quality factor (Q factor) of the resonator is one of the core parameters limiting their performances. Surface loss is one of the dominating losses, which is related to the subsurface damage (SSD) that is influenced by the grinding parameters. This paper experimentally studies the surface roughness and Q factor variation of six resonators ground by three different grinding speeds. The results suggest that the removal of the SSD cannot improve the Q factor continuously, and the variation of surface roughness is not the dominant reason to affect the Q factor. The measurement results indicate that an appropriate increase in the grinding speed can significantly improve the surface quality and Q factor. This study also demonstrates that a 20 million Q factor for fused silica cylindrical resonators is achievable using appropriate manufacturing processes combined with post-processing etching, which offers possibilities for developing high-precision and low-cost cylindrical resonator gyroscopes.

A Novel Method for Estimating and Balancing the Second Harmonic Error of Cylindrical Fused Silica Resonators.

The cylindrical resonator gyroscope (CRG) is a type of Coriolis vibratory gyroscope which measures the angular velocity or angle through the precession of the elastic wave of the cylindrical resonator. The cylindrical fused silica resonator is an essential component of the CRG, the symmetry of which determines the bias drift and vibration stability of the gyroscope. The manufacturing errors breaking the symmetry of the resonator are usually described by Fourier series, and most studies are only focusing on analyzing and reducing the fourth harmonic error, the main error source of bias drift. The second harmonic error also is one of the obstacles for CRG towards high precision. Therefore, this paper provides a chemical method to evaluate and balance the second harmonic error of cylindrical fused silica resonators. The relation between the frequency split of the n = 1 mode and the second harmonic error of the resonator is obtained. Simulations are performed to analyze the effects of the first three harmonic errors on the frequency splits. The relation between the location of the low-frequency axis of n = 1 mode and the heavy axis of the second harmonic error is also analyzed by simulation. Chemical balancing experiments on two fused silica resonators demonstrate the feasibility of this balancing procedure, and show good consistency with theoretical and simulation analysis. The second harmonic error of the two resonators is reduced by 86.6% and 79.8%, respectively.

Trimming of Imperfect Cylindrical Fused Silica Resonators by Chemical Etching.

The cylindrical resonator gyroscope (CRG) is a kind of solid-state gyroscope with a wide application market. The cylindrical resonator is the key component of CRG, whose quality factor and symmetry will directly affect the performance of the gyroscope. Due to the material properties and fabrication limitations, the actual resonator always has some defects. Therefore, frequency trimming, i.e., altering the local mass or stiffness distribution by certain methods, is needed to improve the overall symmetry of the resonator. In this paper, we made further derivation based on the chemical trimming theory proposed by Basarab et al. We built up the relation between the frequency split and the balanced mass to determine the mass to be removed. Chemical trimming experiments were conducted on three cylindrical fused silica resonators. The frequency splits of the three resonators were around 0.05 Hz after chemical trimming. The relation between frequency split and balanced mass established from experimental data was consistent with the theoretical calculation. Therefore, frequency split can be reduced to lower than 0.05 Hz under rigorous theoretical calculation and optimized chemical trimming parameters.

Biocompatible and acid-cleavable poly(ε-caprolactone)-acetal-poly(ethylene glycol)-acetal-poly(ε-caprolactone) triblock copolymers: synthesis, characterization and pH-triggered doxorubicin delivery.

A series of acid-cleavable ABA-type triblock copolymers, namely poly(ε-caprolactone)-acetal-poly(ethylene glycol)-acetal-poly(ε-caprolactone) (PCL-a-PEG-a-PCL), were synthesized via a combination of ring-opening polymerization (ROP) of ε-caprolactone initiated by propargyl alcohol and subsequent "CuAAC" click reaction with azide terminated acetal-containing poly(ethylene glycol). The chemical composition and structures of the copolymers were characterized by 1H NMR and FT-IR spectroscopy, while their molecular weights and molecular weight distributions were measured by gel permeation chromatography (GPC). The critical aggregation concentration (CAC), size parameters and morphologies of micelles self-assembled from PCL-a-PEG-a-PCL were determined by fluorescence probing, dynamic light scattering (DLS), and transmission electron microscopy (TEM), respectively. Since the acetal groups are unstable in weak acidic media, it is anticipated that this class of triblock copolymer micelles can be dissociated in an intracellular environment. This was confirmed by monitoring the size change of micelles with the increase of degradation time under acidic conditions, as well as the molecular weights of degradation products. The pH-triggered release of doxorubicin (DOX) from PCL-a-PEG-a-PCL micelles was studied and compared with a pH-insensitive PCL-b-PEG-b-PCL system without acetal groups, demonstrating that the cleavage of acetal linkages was responsible for the pH-responsive drug release profiles. In vitro cytotoxicity tests against HeLa and L929 cells by MTT assays indicated that the self-assembled micelles displayed very low cytotoxicity. In addition, the intracellular drug release against HeLa cells was further investigated by a live cell imaging system using free DOX as a control. This work provides a facile strategy for the preparation of a new type of biodegradable amphiphilic copolymer as a highly promising intracellular delivery system for hydrophobic drugs.