Most cited article - PubMed ID 35161043
Biodegradable Thermoplastic Starch/Polycaprolactone Blends with Co-Continuous Morphology Suitable for Local Release of Antibiotics
We modified native wheat starch using 15, 30, and 60 min of acid hydrolysis (AH). The non-modified and AH-modified starches were converted to highly homogeneous thermoplastic starches (TPSs) using our two-step preparation protocol consisting of solution casting and melt mixing. Our main objective was to verify if AH can decrease the processing temperature of TPS. All samples were characterized in detail by microscopic, spectroscopic, diffraction, thermomechanical, rheological, and micromechanical methods, including in situ measurements of torque and temperature during the final melt mixing step. The experimental results showed that (i) AH decreased the average molecular weight preferentially in the amorphous regions, (ii) the lower-viscosity matrix in the AH-treated starches resulted in slightly higher crystallinity, and (iii) all AH-modified TPSs with a less viscous amorphous phase and higher content of crystalline phase exhibited similar properties. The effect of the higher crystallinity predominated at a laboratory temperature and low deformations, resulting in slightly stiffer material. The effect of the lower viscosity dominated during the melt mixing, where the shorter molecules acted as a lubricant and decreased the in situ measured processing temperature. The AH-induced decrease in the processing temperature could be beneficial for energy savings and/or possible temperature-sensitive admixtures for TPS systems.
- Keywords
- low viscosity, melt mixing, processing temperature, thermoplastic starch,
- Publication type
- Journal Article MeSH
This work describes the preparation of highly homogeneous thermoplastic starches (TPS's) with the addition of 0, 5, or 10 wt.% of maltodextrin (MD) and 0 or 3 wt.% of TiO2 nanoparticles. The TPS preparation was based on a two-step preparation protocol, which consisted in solution casting (SC) followed by melt mixing (MM). Rheology measurements at the typical starch processing temperature (120 °C) demonstrated that maltodextrin acted as a lubricating agent, which decreased the viscosity of the system. Consequently, the in situ measurement during the MM confirmed that the torque moments and real processing temperatures of all TPS/MD systems decreased in comparison with the pure TPS. The detailed characterization of morphology, thermomechanical properties, and local mechanical properties revealed that the viscosity decrease was accompanied by a slight decrease in the system homogeneity. The changes in the real processing temperatures might be quite moderate (ca 2-3 °C), but maltodextrin is a cheap and easy-to-add modifier, and the milder processing conditions are advantageous for both technical applications (energy savings) and biomedical applications (beneficial for temperature-sensitive additives, such as antibiotics).
- Keywords
- lower processing temperature, lower viscosity, maltodextrin modification, thermoplastic starch,
- Publication type
- Journal Article MeSH
Morphology, macro-, and micromechanical properties of novel poly(urethane-urea)/silica nanocomposites were analyzed by electron microscopy, dynamic mechanical thermal analysis, and microindentation. The studied nanocomposites were based on a poly(urethane-urea) (PUU) matrix filled by nanosilica, and were prepared from waterborne dispersions of PUU (latex) and SiO2. The loading of nano-SiO2 was varied between 0 (neat matrix) and 40 wt% in the dry nanocomposite. The prepared materials were all formally in the rubbery state at room temperature, but they displayed complex elastoviscoplastic behavior, spanning from stiffer elastomeric type to semi-glassy. Because of the employed rigid and highly uniform spherical nanofiller, the materials are of great interest for model microindentation studies. Additionally, because of the polycarbonate-type elastic chains of the PUU matrix, hydrogen bonding in the studied nanocomposites was expected to be rich and diverse, ranging from very strong to weak. In micro- and macromechanical tests, all the elasticity-related properties correlated very strongly. The relations among the properties that related to energy dissipation were complex, and were highly affected by the existence of hydrogen bonding of broadly varied strength, by the distribution patterns of the fine nanofiller, as well as by the eventual locally endured larger deformations during the tests, and the tendency of the materials to cold flow.
- Keywords
- aqueous polyurethane dispersion, mechanical properties, microindentation, nanocomposites, polyurethanes, silica,
- Publication type
- Journal Article MeSH
This contribution lays the foundation for the European database of explanted UHMWPE liners from total joint replacements. Three EU countries (Czech Republic, Italy and Spain) have joined their datasets containing anonymized patient data (such as age and BMI), manufacturer data (such as information on UHMWPE crosslinking, thermal treatment and sterilization), orthopedic evaluation (such as total duration of the implant in vivo and reasons for its revision) and material characterization (such as oxidative degradation and micromechanical properties). The joined database contains more than 500 entries, exhibiting gradual growth, and it is beginning to show interesting trends, which are discussed in our contribution, including (i) strong correlations between UHMWPE oxidative degradation, degree of crystallinity and microhardness; (ii) statistically significant differences between UHMWPE liners with different types of sterilization; (iii) realistic correlations between the extent of oxidative degradation and the observed reasons for total joint replacement failures. Our final objective and task for the future is to continuously expand the database, involving researchers from other European countries, in order to create a robust tool that will contribute to the better understanding of structure-properties-performance relationships in the field of arthroplasty implants.
