Enhanced mass transport during the high temperature processing of ceramics by microwave heating, generally known as the 'microwave effect', has been observed by many researchers and some hypotheses have been proposed to explain it. However it is still a controversial issue, centring on temperature measurement accuracy. The primary goal for the present work was to achieve definitive evidence of the microwave effect via the microwave hybrid processing of ceramics using accurate temperature measurement.


Three temperature measurement techniques, viz. thermocouple, pyrometer and optical fibre thermometer, have been investigated to determine their accuracy during the hybrid microwave heating of ceramic materials. The experimental results, obtained from melting point measurement on vanadium pentoxide and the heating of three other materials with different loss factors and thermal conductivities, showed that the optical fibre thermometer was the best choice. An accuracy of ±2oC was obtained,
provided the probe had been calibrated and was protected from stray radiation from conventional heating elements.


Direct evidence for the microwave effect was sought from experiments involving the sintering and annealing of ceramics at different microwave power levels but using an identical temperature I time profile in each case. Sample temperature was monitored using optical fibre thermometry and sample size, composition and precursor powder size were all varied. Specifically, four main ceramics with different loss factors were investigated, viz. zinc oxide (very lossy), yttria stabilised zirconia (intermediate loss) and alumina and silica (low loss).


The results from the experiments showed that an increase in final density was observed for the samples that saw the highest microwave power level compared to


I
 
those sintered using pure conventional heating, nearly 25% in the largest case for zinc oxide with the highest loss factor among the four investigated materials. This was equivalent to an effective temperature increase of approximately 1OOoC. For the low
loss alumina samples, the increase was extremely small, with the yttria stabilised zirconia intermediate between the two. In addition, during annealing of fully dense ZnO ceramic pellets, enhanced grain growth was observed during hybrid heating compared to pure conventional heating. Temperature gradients within the samples, a major potential cause of the effect, were assessed using two different approaches and found to be

Evidence for the microwave effect during hybrid sintering and annealing of ceramics

Conventional drugs used for antibacterial therapy display several limitations. This is not due to antibiotics being ineffective, but rather due to their low bioavailability, limited penetration to sites of infection and the rise of drug-resistant bacteria. Although new delivery systems (e.g., nanoparticles) that are loaded with antibacterial drugs have been designed to overcome these limitations, therapeutic efficacy does not seem to have improved. Against this backdrop, stimuli-responsive antibiotic-loaded nanoparticles and materials with antimicrobial properties (nanoantibiotics) present the ability to enhance therapeutic efficacy, while also reducing drug resistance and side effects. These stimuli can either be exogenous (e.g., light, ultrasound) or endogenous (e.g., pH, variation in redox gradient, enzymes). This promising therapeutic approach relies on advances in materials science and increased knowledge of microorganism growth and biofilm formation. This review provides an overview in the field of antibacterial drug-delivery systems and nanoantibiotics that benefit from a response to specific triggers, and also presents a number of future prospects.

https://www.mdpi.com/1420-3049/24/10/1991/pdf

Recent Developments in Antibacterial Therapy: Focus on Stimuli-Responsive Drug-Delivery Systems and Therapeutic Nanoparticles

Hydroxyapatite (HAp) has significant biological activity, degradability, and osteoconductivity. In recent decades, it has been widely used in dentistry, anti-tumour drug carriers, and orthopaedic repair. However, hydroxyapatite has limit features which are poor mechanical properties for directly inducing tooth enamel remineralization, particle size and morphology issues on drug delivery and brittleness for bone transplantation. This article summarizes the problems encountered in the preparation, application, and modification of hydroxyapatite in the above-mentioned fields and the current research progress, combining theory with experiment. Therefore, the greatest significance of this review is to comprehensively integrate and argue the forms and effects of nHA-based biomaterials, which provides a theoretical basis for the application of this material and help readers have clear insights into future research.

Recent advances in biomedical engineering of nano-hydroxyapatite including dentistry, cancer treatment and bone repair

Electrospinning is a quite consolidated technique to produce polymer nanofibrous matrices whose nanostructured morphology received great interest for application in the biomedical field i.e. in manufacturing matrices for tissue regeneration. Purpose of the work to design electrospun matrices made of Poly- l -lactide-co-poly-e-caprolactone (PLA-PCL) 70:30 M ratio and their thoroughly physico-chemical and functional characterization. The ultimate goal of the research work is to obtain electrospun matrices suitable for circular substitution of esophageal defects. However the paper deals with very preliminary investigation mainly on electrospinning process and physical-chemical characterization of the electrospun matrices. The investigation on electrospinning process conditions involves polymer starting solution concentration between 20% w/v and 25% w/v, viscosity and surface tension, but also process parameters of electrospinning apparatus in order to optimize them at achieving homogeneous and reproducible nanofibers. The optimized electrospun matrices are characterized for their cytocompatibility, morphology (SEM analysis), polymer molecular structure in the solid state (FT-IR analysis) and thermal behavior (DSC analysis) and mechanical properties. In vitro degradation test is performed to evaluate electrospun matrix biodegradability. Results show good cytocompatibility for all polymer concentrations and electrospinning times. Moreover, the electrospun matrices biodegradation is slower with respect to matrices made by solvent casting method. The behavior is related to modifications in the polymer solid state and to polymer chains structure.

Design of copolymer PLA-PCL electrospun matrix for biomedical applications

Tissue engineering is an emergent and very interesting research field, providing potential solutions for a myriad of challenges in healthcare. Fibrous scaffolds specifically have shown promise as an effective tissue engineering method, as their high length-to-width ratio mimics that of extracellular matrix components, which in turn guides tissue formation, promotes cellular adhesion and improves mechanical properties. In this review paper, we discuss in detail both the importance of fibrous scaffolds for the promotion of tissue growth and the different methods to produce fibrous biomaterials to possess favorable and unique characteristics. Here, we focus on the pressing need to develop biomimetic structures that promote an ideal environment to encourage tissue formation. In addition, we discuss different biomedical applications in which fibrous scaffolds can be useful, identifying their importance, relevant aspects, and remaining significant challenges. In conclusion, we provide comments on the future direction of fibrous scaffolds and the best way to produce them, proposed in light of recent technological advances and the newest and most promising fabrication techniques.

Nanofibrous scaffolds for biomedical applications

The fabrication process of ceramic yttria-stabilized zirconia (YSZ) and nickel oxide nanofibers by electrospinning is reported. The preparation of hollow YSZ nanofibers and aligned nanofiber arrays is also demonstrated. The influence of the process parameters of the electrospinning process, the physicochemical properties of the spinning solutions, and the thermal treatment procedure on spinnability and final microstructure of the ceramic fibers was determined. The fiber diameter can be varied from hundreds of nanometers to more than a micrometer by controlling the solution properties of the electrospinning process, while the grain size and surface roughness of the resulting fibers are mainly controlled via the final thermal annealing process. Although most observed phenomena are in qualitative agreement with previous studies on the electrospinning of polymeric nanofibers, one of the main differences is the high ionic strength of ceramic precursor solutions, which may hamper the spinnability. A strategy to control the effective ionic strength of precursor solutions is also presented.

https://ris.utwente.nl/ws/files/6942942/nanomaterials-07-00016.pdf

Vera Smulders

Papers

Influence of Solution Properties and Process Parameters on the Formation and Morphology of YSZ and NiO Ceramic Nanofibers by Electrospinning