No abstract

This study was conducted on different models of biodegradable SMP (shape-memory polymer) scaffolds. A comparison was conducted utilizing a basic FDM (fused deposition modeling)/MEX (material extrusion) printer with a standard printing technique and a novel, modified, four-axis printing method with a PLA (poly lactic acid) polymer as the printing material. This way of making the 4D-printed BVS (biodegradable vascular stent) made it possible to achieve high-quality surfaces due to the difference in printing directions and improved mechanical properties—tensile testing showed a doubling in the elongation at break when using the four-axis-printed specimen compared to the regular printing, of 8.15 mm and 3.92 mm, respectfully. Furthermore, the supports created using this method exhibited a significant level of shape recovery following thermomechanical programming. In order to test the shape-memory effect, after the thermomechanical programming, two approaches were applied: one approach was to heat up the specimen after unloading it inside temperature chamber, and the other was to heat it in a warm bath. Both approaches led to an average recovery of the original height of 99.7%, while the in-chamber recovery time was longer (120 s) than the warm-bath recovery (~3 s) due to the more direct specimen heating in the latter case. This shows that 4D printing using the newly proposed four-axis printing is an effective, promising technique that can be used in the future to make biodegradable structures from SMP.

No abstract

No abstract

No abstract

No abstract

Исследовались особенности трения образцов из полилактической кислоты (PLA), полученных по технологии FDM 3D печати при различных значениях заполнения внутренней структуры. Трибологические испытания проводились на нанотрибометре при нагрузках в диапазоне 5-15 мН по схеме шар/плоскость при вращении образца. Сравнивались данные, полученные при трении в направлении вдоль и перпендикулярно направлению печати. Установлено, что меньший коэффициент трения наблюдается при трении по направлению печати. Образцы с 20 % наполнением внутренней структуры имели значительно больший коэффициент трения, чем образцы со 100 % наполнением. Более высокий коэффициент износа зарегистрирован в случае 100 % заполнение. Показано, что при увеличении нагрузки наблюдается локальный минимум значений износа для всех образцов. Коэффициент износа исследованных образцов не превышал 10 -3 мм 3 /(Н⋅м).

Introduction. Between 6 and 15% of the adult population throughout the world faces with the fear of dentists. Fear of dentists directly correlates with the pain experienced during previous visits to the dentist. Objective. The aim of the study was to assess the validity, reliability and factor structure of the Serbian version of the Dental Fear Survey on a sample of university and high school students. Method. Two hundred and fifty students and high school students participated in the study and completed the Serbian version of the Dental Fear Survey. Results. This study's sample showed excellent internal consistency (Cronbach's alpha = 0.98). Descriptive statis