RESUMEN
BACKGROUND:The elastic modulus of traditional bone implants is large and does not match the elastic modulus of human bone,which will cause a stress shielding effect and lead to bone resorption.The trabecular scaffold of the triply periodic minimal surface with radial gradient has elastic modulus matching with human cancellous bone,and its yield strength is greater than that of human cortical bone,which provides a new choice for the design of bone scaffold. OBJECTIVE:Triply periodic minimal surface structure with radial gradient was constructed by the implicit surface method.The sample was manufactured by laser selective melting technology,and the quasi-static compression test was carried out to obtain trabecular scaffolds with mechanical properties matching human bones. METHODS:Four types of the trabecular scaffolds of the triply periodic minimal surface with a radial gradient of G,I,P and D were established by the implicit surface method.Samples were manufactured by laser selective melting technology.We observed the surface morphology of the molded sample,evaluated the molding quality,conducted a quasi-static compression test,and evaluated the mechanical properties of the samples. RESULTS AND CONCLUSION:The quasi-static compression test results showed that compared with the four triply periodic minimal surface scaffolds,the platform stress of the G scaffold had less fluctuation and no failure or fracture,indicating that the G scaffold had the best plasticity.The mechanical properties of the G scaffolds with 45%,55%and 65%porosities were analyzed.It was found that the elastic modulus of G scaffolds with 55%porosity was within the range of elastic modulus of human cancellous bone(0.022-3.7 GPa),and the yield strength was close to the maximum yield strength of human cortical bone(187.7-222.3 MPa).In conclusion,G triply periodic minimal surface scaffold with 55%porosity can reduce the stress shielding effect,bear a higher body load,improve the stability of the implant,and prolong the service life of the implant.
RESUMEN
Objective To develop a method for monitoring unconstrained sleep respiration suitable for daily use at home, so as to realize high precision screening of sleep apnea syndrome (SAS) or other respiratory diseases without affecting normal sleep. Methods A new unconstrained measurement method using sheet-type flexible pressure sensor was proposed. This method could obtain the information of respiratory motions of the chest and abdomen by measuring the pressure fluctuations of the chest and abdomen acting on the mattress. Experiments were conducted on ten healthy subjects to confirm effectiveness of the proposed method by comparing the result of the unconstrained measurement and those of respiratory inductance plethysmography (RIP) using band sensors, respectively. Results Sheet-type flexible pressure sensor could measure the pressure fluctuations of the chest and abdomen acting on the mattress during respiration and obtain respiratory waveform and respiratory rate. The respiratory rate measured with the sheet-type flexible pressure sensor agreed with those obtained by RIP. The gender and the lying position greatly affected whether the phases of the pressure fluctuations of the chest and abdomen measured with the flexible sensor differed from those obtained by RIP. The chest respiratory finite element model was established to analyze the phase difference of respiratory movement. Conclusions Sheet-type flexible pressure sensor is effective to monitor unconstrained sleep respiration, indicating the potential to identify the SAS types. But further researches of motion decoupling are required to identify the phase difference between the chest motion and the abdomen motion, which are coupled with each other.