| Biological materials are capable of producing highly efficient and flexible deformation behaviour with simple structures,such as pinta scales with differently oriented fibre-reinforced bilayer structures that can open or close in response to changes in environmental humidity.The human pinnate tissues harness changes in the angle of the muscle fibers to the muscle bundle to achieve modulation of actuation forces and deformations.Unlike artificial actuators,biological materials typically utilize an integrated internal structure for motion control instead of a mechanism.However,such integrated structural materials are difficult to achieve with conventional manufacturing methods.Additive manufacturing technology,often called 3D printing,is capable of producing ordered structures and complex geometries within materials that cannot be achieved by traditional manufacturing processes,providing a new means for manufacturing biomimetic materials.Smart materials with stimuli-responsive properties combined with 3D printing technology enable programmable changes in the shape and properties of printed materials,i.e.,4D printing,which provides a completely new way to bionic-driven materials.In this paper,the drive mode of typical biological materials and their internal structure are discussed in depth,the mechanism of biological materials using structural design to control the drive deformation are revealed,and a bilayer structure and two fiber-oriented biomimetic design methods are proposed.Water-swellable polyurethane(WPU)materials,fiber-reinforced WPU materials,heat-shrinkable materials,and prestressed shape-memory thermoplastic polyurethane(TPU)materials for 4D printing were prepared.Using self-developed direct ink writing(DIW)3D printing technology,fused deposition molding(FDM)3D printing process and material extrusion shear orientation mechanism,combined with mold casting process,the bilayer structure and ordered structure bionic-driven materials were 4D printed.The effects of printing path,structure parameters,material configuration and external stimuli on the deformation characteristics of bionic-driven materials were investigated,revealing the deformation control mechanism of bionic-driven materials,and proposing a new strategy to realize the design and manufacturing of the actuator using bionic principles and 4D printing technology.The main research of this paper is summarized as follows:(1)The deformation characteristics of typical biological tissues and their structural properties were analyzed.Then the mechanism of biological materials movement and deformation were revealed.Finally,the bionic-driven design methods were established.We carried out the design of bilayer structures and oriented fiber bionic-driven structures.For the two different bionic designs,the 3D printing preparation process of bilayer structure and oriented fiber composite was studied,and the 3D printing experimental device was built.A direct ink writing process was used to print the WPU material on a shape memory polymer(SMP)substrate to form a bilayer structure,which harnessed the strain mismatch between the deformation of the two layer material to achieve multiple morphological changes.Two process methods were designed to prepare oriented fiber-driven composites.One was to employ DIW process to print carbon fiber/WPU composites,which used the shear force formed by material extrusion to orient the fibers in the material.Then,through print path design,a variety of oriented fiber structures could be achieved.Another process was to use FDM to prepare oriented shape memory TPU fibers,which were then embedded in the silicone material body by casting method.The use of TPU fibers and the design of the long axis of the composite material pinch angle could achieve control of deformation.(2)A dual-response bilayer structure that can deform undergo both temperature and humidity stimuli was prepared by printing the WPU onto the SMP material by DIW printing process.This bilayer structure can not only produce non-uniform bending deformation in response to humidity alone,but also receive temperature stimulation alone to produce uniform bending or uniform spiral deformation,and also can produce non-uniform spiral deformation under the combined temperature and humidity stimuli.By designing the geometric parameters and material distribution patterns of the bilayer structure,we designed and printed a variety of non-uniformly distributed composite bilayer structures with dual response characteristics by harnessing the relationship between the degree of shrinkage of the shape memory material and the external excitation temperature,and the dependence between the degree of helical deformation and the printing angle.The shape changes of the composite structures under different stimuli were characterized,revealing the relationship between deformation and structure,demonstrating the feasibility of using external stimuli to program 4D printing.(3)Based on plant fiber reinforced material and plume-like muscle fiber structure,two bionic fiber-oriented driven materials were designed,which are divided into matrix driven and fiber driven deformable materials.Some deformable plant materials have directional fibers embedded in the water-swelling matrix material,where the matrix material expands when absorbing water,and the oriented fibers control the deformation mode of the overall material.Another strategy is adopted for human pinna fibers,where fiber contraction causes deformation of the muscle bundle,and the amount of deformation and driving force are controlled by the angle of the muscle fiber to the bundle.A mixture of WPU material and short-cut carbon fibers were selected as the material,and the fibers were subjected to shear forces to form a directional arrangement through the DIW printing process.The effect of fiber orientation angle on deformation characteristics was investigated,and the results showed that the deformation mode of oriented fiber materials could be controlled by fiber orientation design.TPU materials were used to print oriented fiber structures using FDM 3D printing technology.The printed oriented TPU structure was embedded in the silicone matrix to form a composite oriented fiber TPU-silicone driven material.The shape memory properties of TPU was utilized to deform the printed oriented fibers.The printed oriented TPU structure was extended by applying an external force above its glass transition temperature,followed by cooling down to remove the external force.When the TPU was heated again,the shape of the TPU was restored and deformed,thereby driving the overall deformation of the composite material.The effect of fiber orientation on the deformation was investigated,and the results demonstrated that the deformation pattern of the composite could be modulated by changing the fiber orientation.(4)Using numerical simulation,the deformation prediction and modeling research of 4D printing structure were carried out.In the study of 4D printing deformation characteristics,firstly,the theoretical knowledge related to its curvature in 2D and 3D space was thoroughly studied,and the characterization method of the deformation curvature in the 4D printing structure was determined.Image acquisition was performed for the deformation process of 4D printed WPU material,and the software was used to extract the set of feature points in the image to find out the curvature in2 D and 3D space.By fitting and graphing the experimental data,the corresponding expression of the deformation function was established,and finally the curvature was solved by using the corresponding calculation formula.Using the CF toolbox in Matlab software,a mathematical model for predicting the curvature of the curve was established,then the Weingarten transformation theorem was used to solve for the Gaussian curvature value,and the deformation prediction model was established by adjusting the Gaussian curvature value to the corresponding scatter value and fitting the function of the 3D surface.The prediction model of curvature is used to predict the deformation process of the material and its final deformation effect before printing,so as to achieve accurate prediction of the deformation effect of 4D printing,and the established model can be used for 4D printing structure design. |
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