Institute of Fundamental Technological Research

This paper studies the interrelationships between the molecular weight, rheology, crystallinity, and tackiness of three types of commercial thermoplastic hot melt adhesives. The hot melt adhesives employed here differ in their compositions and molecular weights, even though all are copolyesters primarily based on poly(butylene terephthalate). Differences in the composition were found to influence the adhesives’ crystallization and melting behavior. These structural variations can translate into different thermal responses and processing characteristics relevant for tailoring adhesive selection to application requirements. Furthermore, adhesives with higher molecular weight were observed to possess larger elasticity, leading to significantly enhanced tackiness properties, as evidenced by the higher values of tensile modulus, peak stress, and work of debonding. This elevated tackiness was linked to the increased fibrillation process observed in polymers with higher molecular weights. Additionally, all tested adhesives exhibited storage moduli below the Dahlquist threshold (G′ < 3.3 × 105 Pa), which supports their ability to achieve measurable tackiness during the initial bonding process. The results presented in this study underscore the diversity among hot melt adhesives and the critical properties that should be considered when selecting adhesives for specific applications.

Hot melt adhesives, copolyester, polybutylene terephthalate, tack properties, rheology, crystallinity

Fused Deposition Modelling (FDM) technique has been widely utilized in fabrication of 3D porous scaffolds for tissue engineering (TE) applications. Surprisingly, although there are many publications devoted to the architectural features of the 3D scaffolds fabricated by the FDM, none of them give us evident information about the impact of the diameter of the fibres on material properties. Therefore, the aim of this study was to investigate, for the first time, the effect of the diameter of 3D-printed PCL fibres on variations in their microstructure and resulting mechanical behaviour. The fibres made of poly(ε-caprolactone) (PCL) were extruded through commonly used types of nozzles (inner diameter ranging from 0.18 mm to 1.07 mm) by means of FDM technique. Static tensile test and atomic force microscopy working in force spectroscopy mode revealed strong decrease in the Young's modulus and yield strength with increasing fibre diameter in the investigated range. To explain this phenomenon, we conducted differential scanning calorimetry, wide-angle X-ray-scattering, Fourier-transform infrared spectroscopy, infrared and polarized light microscopy imaging. The obtained results clearly showed that the most prominent effect on the obtained microstructures and mechanical properties had different cooling and shear rates during fabrication process causing changes in supramolecular interactions of PCL. The observed fibre size-dependent formation of hydrogen bonds affected the crystalline structure and its stability. Summarising, this study clearly demonstrates that the diameter of 3D-printed fibres has a strong effect on obtained microstructure and mechanical properties, therefore should be taken into consideration during design of the 3D TE scaffolds.

fused deposition modelling, polycaprolactone, mechanical properties, hydrogen bonds, microstructure

Biodegradable 3D-printed polycaprolactone scaffolds for bone tissue engineering applications have been extensively studied as they can provide an attractive porous architecture mimicking natural bone, with tunable physical and mechanical properties enhancing positive cellular response. The main drawbacks of polycaprolactone-based scaffolds, limiting their applications in tissue engineering are: their hydrophobic nature, low bioactivity and poor mechanical properties compared to native bone tissue. To overcome these issues, the surface of scaffolds is usually modified and covered with a ceramic layer. However, a detailed description of the adhesion forces of ceramic particles to the polymer surface of the scaffolds is still lacking. Our present work is focused on obtaining PCL-based composite scaffolds to strengthen the architecture of the final product. In this manuscript, we report qualitative and quantitative evaluation of low temperature plasma modification followed by detailed studies of the adhesion forces between chemically attached ceramic layer and the surface of polycaprolactone-nanohydroxyapatite composite 3D-printed scaffolds. The results suggest modification-dependent alteration of the internal structure and morphology, as well as mechanical and physical scaffold properties recorded with atomic force microscopy. Moreover, changes in the material surface were followed by enhanced adhesion forces binding the ceramic layer to polymer-based scaffolds.

surface modification, low temperature plasma, atomic force microscopy, bone tissue engineering