Bionic 4D Printing Of Polylactic Acid/polycaprolactone Composite

4D printing is a technology that upgrades 3D printing with intelligent materials and time dimension to achieve specific functions by programming the geometric shape,material structure,and structure configuration of intelligent materials.Owing to its powerful influence,it has attracted increasing attention of researchers and has become a hot topic in various fields in recent years.In order to adapt to their environment,organisms have certain stimulus response behaviors,such as the touch-induced deformation of the Mimosa plant,the colorchanging ability of octopuses,the intelligent opening and closing of pine cones,and the self-spiraling deformation of pea pods.These dynamic characteristics of natural organisms provide inspiration for 4D printing technology based on biomaterials.Biomimetic 4D printing technology uses the tissue construction methods and perception decision response principles of biological materials to program and design the material structure,and uses biomimetic 3D printing technology to prepare intelligent material systems with perception,decision-making,and response characteristics.Although researchers have extensively studied biomimetic 4D printing in recent years,there are still certain limitations.First,the forming process often uses the melting deposition forming process,which results in thermal history of the material.Second,the influence of printing parameters on the structure and performance of the printed material is often ignored.Finally,the shaping process mostly uses mold shaping,which is difficult to precisely control.Inspired by biological deformation behavior,this article designs a biomimetic deformation structure for studying thermal engine performance and shape memory performance.Polylactic acid(PLA)is a commonly used shape memory polymer,and its deformation behavior can be mimicked by programming the printing parameters during the printing process.This article systematically studies the dynamic thermal engine performance and shape memory performance of PLA under different scanning conditions.By using a self-developed direct writing printer to precisely control the internal structure of the printed samples and studying the influence of printing parameters on the thermal response and shape memory performance of PLA,the programming and control of the shape memory behavior of the printed samples are achieved.The thermal driving 4D printing behavior of the printed samples is realized by programming and controlling the high-temperature shaping and low-temperature fixing shaping of the printed samples using a dynamic thermal analyzer’s stretching fixture.To enhance the tensile deformation of the printing material,this article modifies the PLA matrix material by adding polycaprolactone(PCL)to prepare a PLA/PCL flexible composite material.The self-developed multi-material direct writing printer and software control system are used to print the PLA/PCL composite material,and the printed samples are analyzed and characterized.The influence of PCL content,external applied stress,shaping temperature on the shape memory performance of the PLA/PCL composite material is studied,and the performance influencing factors are analyzed using artificial intelligence neural network algorithms.The main research contents are as follows:(1)A multi-material direct writing 3D printer and software control system for composite material printing is self-developed.The direct writing device consists of an air pump,air pressure controller,solenoid valve,printing substrate,etc.The software control system slices the model to be printed and imports the sliced code into the printing device for printing process control.(2)The dynamic thermal and shape memory performance of PLA is studied.The linear viscoelastic range,glass transition temperature range,frequency scan characteristics,temperature scan characteristics,and fatigue resistance characteristics of PLA molecules are studied using a dynamic thermal analyzer system.The shape memory performance of PLA is also studied,and the influence of four printing parameters(layer height,printing speed,infill angle,and infill pattern)on the shape recovery rate,fixation rate,and recovery speed of PLA is investigated.(3)A PLA/PCL composite material for direct writing printing is prepared.The printability,cold crystallization temperature,glass transition temperature,melting temperature,thermal stability,microstructure,and chemical composition of the composite material are characterized using a rheometer,differential scanning calorimeter,thermogravimetric analyzer,fluorescence microscope,and infrared spectrometer.The influence of different mass ratios,external stress,and heating temperature on the shape memory performance of the composite material is studied using a dynamic thermal analyzer,and the experimental results are optimized using artificial intelligence neural network algorithms.The optimal combination obtained after optimization is compared with the original combination to determine a reasonable material ratio and preparation process.