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New nonstandard method for measuring physical properties of homemade polymer filaments for ffd 3d printing
(Society of Physicists of Macedonia, 2021-09)
Popeski-Dimovski, Riste
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Veliu, Arta
The large advance in fused filament deposition (FFD) 3D printing technology is becoming a challenge for the introduction of new materials used in the process. The standard destructive mechanical testing of materials uses large amount of raw filament. As desktop FFD 3D printing becomes an everyday occurrence and 3D printing filament extrusion, a DIY makers practice, stablishing a method for physical characterization of parts using only small amounts of homemade filament is of interest. This research is focused on introducing a new nonstandard method for evaluation of 3D printing filament with samples of less than 50 mg material. In this work we test the new method by comparison the results acquired for standard everyday 3D printing filaments. It was found out that the results obtained with this method are in correlation with the results from the standard tests used in everyday practice. This is of interest because it allows fast characterization of exotic filament blends with very small amount of material for research purposes, reducing the costs of production, and the possibility to implement fast changes in the filament blends
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SN-38 loading capacity of hydrophobic polymer blend nanoparticles: formulation, optimization and efficacy evaluation
(Informa UK Limited, 2017-03)
Dimchevska, Simona
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Geskovski, Nikola
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Petruševski, Gjorgji
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Chacorovska, Marina
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Popeski-Dimovski, Riste
One of the most important problems in nanoencapsulation of extremely hydrophobic drugs is poor drug loading due to rapid drug crystallization outside the polymer core. The effort to use nanoprecipitation, as a simple one-step procedure with good reproducibility and FDA approved polymers like Poly(lactic-co-glycolic acid) (PLGA) and Polycaprolactone (PCL), will only potentiate this issue. Considering that drug loading is one of the key defining characteristics, in this study we attempted to examine whether the nanoparticle (NP) core composed of two hydrophobic polymers will provide increased drug loading for 7-Ethyl-10-hydroxy-camptothecin (SN-38), relative to NPs prepared using individual polymers. D-optimal design was applied to optimize PLGA/PCL ratio in the polymer blend and the mode of addition of the amphiphilic copolymer Lutrol®F127 in order to maximize SN-38 loading and obtain NPs with acceptable size for passive tumor targeting. Drug/polymer and polymer/polymer interaction analysis pointed to high degree of compatibility and miscibility among both hydrophobic polymers, providing core configuration with higher drug loading capacity. Toxicity studies outlined the biocompatibility of the blank NPs. Increased in vitro efficacy of drug-loaded NPs compared to the free drug was confirmed by growth inhibition studies using SW-480 cell line. Additionally, the optimized NP formulation showed very promising blood circulation profile with elimination half-time of 7.4 h.
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Effect of vegetable fat on the texture, colour and sensory properties of Macedonian white brined cheese
(Croatian Dairy Union, 2020-12-14)
Sulejmani, Erhan
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Beqiri, Lavdrim
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Popeski-Dimovski, Riste
<jats:p>This study aimed to investigate the influence of substitution of milk fat with palm fat on the composition, yield and technological quality of White cheese, a Macedonian traditional cheese. In this study, full-fat white brined cheese was used as a control sample (WC), while experimental cheeses were prepared from cow milk with vegetable fat (WV) addition and low-fat cheese (WL), respectively. The cheeses have been analysed for physicochemical (acidity, pH, fat, fat acidity, protein), instrumental texture and colour properties (L, a, b) as well as the sensory properties after 1, 20 and 60 days. WV cheeses showed a significantly (P<0.05) lower degree of pH and higher titratable acidity than the WC and WL cheese samples. Cheese that contained vegetable fat showed lower degrees of lipolysis, as assessed by the acid-degree value and received significantly (P<0.05) better appearance, highest hardness value (5226.98 N) and cheese yield scores compared to other samples.</jats:p>
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Tunable high-Q resonator by general impedance converter
(AIP Publishing, 2021-02-01)
Mifune, Toshiro
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Mishonov, Todor M.
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Serafimov, Nikola S.
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Dimitrova, Iglika M.
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Popeski-Dimovski, Riste
<jats:p>A tunable high-Q resonator is performed in the schematics of the General Impedance Converter (GIC). In the framework of frequency dependent open-loop gain of operational amplifiers, a general formula of the frequency dependence of the impedance of GIC is derived. The explicit formulas for the resonance frequency and Q-factor include as an immanent parameter the crossover frequency of the operational amplifier. Voltage measurements of GIC with a lock-in amplifier perfectly agree with the derived formulas.</jats:p>

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