Structural Design And Properties Of 4D Printed Shape Memory Orbital Stent

Shape memory polymers（SMPs）can transform temporary shapes into permanent shapes under external stimuli.4D printing structures based on SMPs can be changed forms or properties,which is significant for achieving minimally invasive surgery and personalized treatment in biomedical applications.Shape memory polyurethane（SMPU）,with controllable transition temperature(T_trans),adjustable mechanical properties and biocompatibility,is one of the promising implant materials in the biomedical field.For the disease of endophthalmos,the current treatments is using implants to fill the internal subsidence to recover volume,but there ar e many problems of the implant such as no development,no degradation,large wound,and inaccurate appearance.Based on SMPU,various 4D printed biological composites with controllable and functional properties were designed and prepared in this paper.Then,the melt extrusion process is predicted to optimize the printing process based on the analytical results and the constitutive model.Finally,based on the prepared composite and printing process,personalized orbital stents were designed and prepared for treating endophthalmos.In this paper,a series of SMPU samples with T_trans near body temperature were prepared by solution prepolymerization using Hexamethylene diisocyanate（HDI）and 1,4-butanediol（BDO）as hard segments and polycaprolactone diol（PC D）as soft segments.The SMPU had good biocompatibility,mechanical properties and shape memory.A series of light-driven shape memory composites（AuNPs/PU,AP）were prepared by introducing AuNPs into SMPU matrix to achieve remotely and precisely controlled biological structures.AP can not only achieve shape recovery function through light-thermal effect,but also achieve cancer hyperthermia.In order to broaden the application scenarios of SMPU in the biological field,the composite（nHA/PU,HP）with excellent mechanical properties and satisfactory biological and shape memory properties was prepared by hydrogen bonding between the surface of nano-hydroxyapatite（nHA）and SMPU matrix.AuNPs has good X-ray attenuation characteristics,and the density of nHA is three times that of human soft tissue.A composite material（AuNPs/nHA/PU,AHP）with the characteristics of both composites and CT development was prepared by combining AP and HP composites.In vitro CT scan showed that the gray value of AHP composites met the needs of visualization in vivo.Based on the rheological behavior of AP and HP melts,the print ed temperature ranges were determined and the viscosity constitutive relationships were established.By inputting the constitutive equation into FLUENT software,the velocity and pressure field distribution in printing process were simulated to predict the appropriate printing parameters.The optimal printed parameters of the actual extrusion process were close to the simulated values,indicating that it was of great significance to predict the melt extrusion process by analyzing the rheological behavior of melt and establishing the melt constitutive model.Based on the designed printed parameters of AP melt,a series of 4D printed AP structures with different shapes and good printing quality were produced,and can fully recover under light,which was of great significance for remote control to grasp and release objects.Based on the designed HP melt printing parameters,a bionic cartilage scaffold inspired by mangrove structure was manufactured,which provided an idea for manufactur ing customized 4D printed cartilage scaffolds.Aiming at the disease of enophthalmos,a 4D printed orbital stent with good CT developability and biodegradable was fabricated based on the AHP composite.According to the simulation results in ABAQUS software,the bionic honeycomb pore structure was introduced to reduce the deformation and strain energy of the orbital stent subjected to ocular tissue tension.Combined with the defect profile obtained by the CT reconstruction,an orbital stent model matching the defect was designed and established.Based on the designed printed parameters,the 4D printing orbit stent was fabricated.Based on the constitutive equation of SMP,the viscoe lastic parameters of AHP were calculated,which can effectively predict the tensile modulus and shape memory cycle of the 4D printed orbital stent.Based on the creep test curve of AHP composites,the power-law creep model was established.The experimental and simulation results showed that the orbital scaffolds had sufficient mechanical strength to support the orbital tissues.The orbital stent compressed into a flat temporary shape can be easily implanted into the upper orbital wall and the orbital cavity behind and above the eyeball.The collected postoperative CT images clearly showed that the volume filling capacity of the 4D printing stent was 150%higher than that of the two commercial implants when the implant volume was the same.After 3 months of follow-up,the postoperative effect was good.4D printed orbital stent is expected to be a promising and effective personalized medical device for the treatment of enophthalmos.