Team:CUHKSZ/pages/material-engineering
Material Engineering
Pre-experiment (Protocol 1):
In this pre-experiment, we tested the ability for the water gel beads to form solid shape. The beads made with different concentrations of ingredients. Here we tested three main ingredients – polyvinyl acid (PVA), sodium algrinate (SA) and calsium bichloride (CaCl2). After consulting Professor Qi ZHANG from the Chinese University of Hong Kong, Shenzhen, School of Science and Engineering, as expected there should be differences in mass transfer efficiency, and mechanical strength of the water gel beads.
As the experiment carries on, we found difficulties in dealing with the measurment part: due to the lack of proper equipment, the beads can hardly form uniform balls as expected, and thus inabilities were met during physical property tests – we were not able to test the mass transfer rate with beads that have varied diameters, or test the mechanical strength without uniformly ball-shaped beads.
As consequences, some literature reviews were performed and we found that most tranfer-effective range of concentration (PVA:SA:CaCl2) = ([7%,9%]:[2%,4%]:[2%,4%]). Since this concentration range lies within the ‘formed’ interval of our experiment, further experiments (protocol 4) were then carried out with this range.
Ethanol degradation test (Protocol 2):
The same mixture from wet lab were added into the water gel beads for ethanol dagradation tests. The ingradients PVA-SA gel was selected to be midpoint concentration: (PVA:SA:CaCl2) = (8%, 3%, 3%) from the result in pre, while the E. coli and A. pasteurianus were balanced mixed and added into immobilization solution by 10%.
After cross linkage, the beads were washed with SPSS (0.9% NaCl solution) and then immersed in 5% alcohol solution, and shook inside 37 °C shaker for 48 hours. The ethanol measurment with handheld ethanol meter showed similar results as the parallel experiment the ethanol level rises for 1.67% in first 24 hours, and another 0.33% by 48 hours (see table 2).
• Permeability test (Protocol 3):
This experiment measures the permeability of E. coli and A. pasteurianus through the water gel beads. The formed beads were washed and cultivate in the corresponding cultural media. After 24 hours of cultivation, the spectrometer observes optical density of both cultural media to be around 0 (see table 3), and the increasing OD can be due to metabolites with similar absorbance number, or the equipment error. This result indicates that almost zero immobilized bacteria in our water gel beads can leak out. What’s more, the bacteria strains: the E. coli (Nissle 1917) and A. pasteurianus (CGMCC1.41) were labeled as nonpathogenic bacteria. Therefore, even if small number of bacteria is permeable, no food safety concern is needed.
