Preparation of antibacterial alginate microbubble structures by microfluidic system

Microbubbles produced with microfluidic systems have been used as contrast agents in ultrasound radiography for approximately 30 years. In recent years, it has been successfully used in different biomedical applications due to its simple, fast and reproducible production possibilities. These applications include drug delivery systems, gene therapy, intravenous oxygen transport agents, cancer therapy, blood-brain barrier targeted drug carriers, thrombolysis and focused ultrasound imaging. Microbubbles are also important structures in the production of 3-dimensional scaffolds with homogeneous pore distribution. Pore size, homogeneity and architecture cannot be fully controlled in structures produced by traditional methods (freeze drying, phase separation, gas foaming, particle removal, use of porogen) used in the preparation of porous structures, and variations are observed from production to production. In microfluidic systems, on the other hand, since a continuous flow production takes place, the microbubbles produced are stable, homogeneous and have a narrow pore size range. In this thesis, it was aimed to produce alginate/poly(vinyl alcohol)/polyethyleneimine (Alg-PVA-PEI) microbubbles using T-junction microfluidic systems, and to prepare 3-dimensional porous structures with antibacterial properties by adding silver nanoparticles (AgNP) to these structures. For this purpose, Alg-PVA-PEI microbubbles were produced using a T-junction microfluidic system and system parameters were optimized. During the production of microbubbles, the flow rate was optimized as 200 µL/min and the gas pressure as 9L/min, and microbubbles were produced in the size range of 90-175 µm depending on the sample group. On the other hand, AgNPs were synthesized to give antibacterial effect to these structures and the average hydrodynamic diameter distribution of AgNPs was 31.63±3.7nm, PDI value was 0.11 and surface charge zeta potential value was -21.7±9.1 mV. By adding the synthesized AgNPs to the Alg-PVA-PEI solution, antibacterial microbubbles (Alg-PVA-PEI/AgNP) were produced with microfluidic systems. The microbubbles produced are cross-linked with calcium chloride (CaCl2); 3-dimensional porous structures with 3-dimensional, homogeneous pores and high water holding capacity, stable, extended silver release, non-toxic effect and antibacterial activity were obtained. The water retention capacity of the obtained Alg-PVA-PEI/AgNP structures was found to be ~4000%. When the release profiles of AgNPs from 3-dimensional porous alginate microbubble structures were examined, it was observed that AgNPs exhibited burst effect in 24 hours and then prolonged release up to 72 hours. Alg-PVA-PEI1/AgNP0.05 samples showed 105% cell viability, while 2605 ppb AgNP release was detected after 72 hours. It was observed that the amount of AgNP above this value adversely affected cell viability. 3D-porous structures containing PEI and AgNP are highly antibacterial against gram-negative Escherichia coli (E. coli–ATCC 25922) and gram-positive Staphylococcus aureus (S. aureus-ATCC 29213), Methicillin Resistant Staphylococcus aureus ATCC 43300 (MRSA) bacterial strains. According to the results of the disk diffusion test; bacterial zone inhibition diameter in the control groups was observed in the range of 3-3.5 mm, while in the Alg-PVA-PEI1/AgNP0.05 sample group, it was 4 and 4.7 mm against gram-positive S. Aureus and MRSA bacteria, respectively, and against gram-negative E.coli bacteria. 3.7 mm zone inhibition diameter was determined. It has been concluded that 3-dimensional porous alginate microbubble structures can be a successful wound dressing material candidate for infected and exuding wounds, especially considering their long-term antibacterial activity with their high water retention capacity, cellular compatibility and controlled silver release. Keywords: T-Junction Microfluidic System, Microbubble, Alginate, Porous, Antibacterial, Silver Nanoparticle.