Abstract:The crystallization behavior of poly(ε-caprolactone) (PCL) in a poly(vinylidene fluoride) (PVDF)/PCL blend as well as on a highly orientated PVDF substrate was studied by means of POM, DSC and TEM. The results show that the miscibility of the PVDF/PCL blend and the spherulitic morphology of PVDF varies with the blend ratio. For all the compositions, the pre-existing PVDF crystals accelerated the crystallization of PCL because the PVDF exhibits very strong nucleation ability toward PCL as reflected by the occurrence of heteroepitaxy and the transcrystallization of PBA on the PVDF substrate. This is associated with the perfect lattice matching between the PBA and PVDF crystals.

To investigate the influence of stress Lode angle on frozen soil, a series of directional shear tests was conducted on artificial frozen clay at three temperatures (–6, –10, and –15 °C) and five stress Lode angles (θσ = –30°, –16.1°, 0°, 16.1°, and 30°) using a hollow cylindrical apparatus. An elliptical function was proposed according to the strength envelope evaluation with the mean principal stress (p) in the p–q plane. In addition, generalized nonlinear strength theory (GNST) was introduced in the π plane to describe the evolution of the strength envelope with increasing mean principal stress. Then a strength criterion for frozen clay in three-dimensional principal stress space was proposed by combining strength functions in the p–q and π planes. The temperature effect was also introduced into the strength criterion. The proposed strength criterion can predict the multi-axial strength characteristics of frozen clay and reveal the influence of the stress Lode angle.

Bacterial infections and limited surface lubrication are the two key challenges for bioimplants in dynamic contact with tissues. However, the simultaneous lubricating and antibacterial properties of the bioimplants have rarely been investigated. In this work, we successfully developed a multifunctional coating with simultaneous antibacterial and lubricating properties for surface functionalization of bioimplant materials. The multifunctional coating was fabricated on a polyurethane (PU) substrate via polydopamine (PDA)-assisted multicomponent codeposition, containing polyethyleneimine (PEI) and trace amounts of copper (Cu) as synergistic antibacterial components and zwitterionic poly­(2-methacryloyloxyethyl phosphorylcholine) (PMPC) as the lubricating component. The obtained PDA­(Cu)/PEI/PMPC coating showed excellent antibacterial activity (antibacterial efficiency: ∼99%) to both Escherichia coli and Staphylococcus aureus compared with bare PU. The excellent antibacterial properties were attributed to the combined effect of anti-adhesion capability of hydrophilic PMPC and PEI and bactericidal activity of Cu in the coating. Meanwhile, the coefficient of friction of the coating was significantly decreased by ∼52% compared with bare PU owing to the high hydration feature of PMPC, suggesting the superior lubricating property. Furthermore, the PDA­(Cu)/PEI/PMPC coating was highly biocompatible toward human umbilical vein endothelial cells demonstrated by in vitro cytotoxicity tests. This study not only contributes to the chemistry of PDA-assisted multicomponent codeposition but also provides a facile and practical way for rational design of multifunctional coatings for medical devices.