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Kulak, Renewable Materials and Nanotechnology Research Group

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Abstract Bachelor project 1 FBT 2021-2022: Glycyrrhizine more than candy

The wound healing world is booming in the last decades. Glycyrrhizine was used by the Chinese in the Early ages to treat wounds. In this research different activities of glycyrrhizine are further explored. The wound healing application that was investigated is a hydrogel. Glycyrrhizine is the gelator of this gel but not only that, it also has beneficial wound healing properties. In previous research there was searched for a pH range in which a stable glycyrrhizine gel was formed. This project takes this pH range as a template to check the pH of new gels to see if they are in this determent range. As the first part of this bachelor project involved the analysis of wounds, furthermore new formulation based on glycyrrhizine were tested. This to expand the possibilities of applications in which the glycyrrhizine hydrogel can be used. These formulation were made and optimized within this project and the phase diagrams of the different combinations will be used for future research. The gel loaded with active compounds was furthermore tested to see its antifungal properties against Candida Albicans. The gel kills off or inhibits the grow of Candida Albicans on a yeast extract peptone dextrose medium. To conclude, glycyrrhizine hydrogels and its combination are very promising applications for not only wound healing but also eradication of fungi (Candida Albicans). In the future rheology testing can be done on the formulations to have an idea of how strong the gels are and the length of the strains.

Abstract Bachelor project 2 FBT 2021-2022: Optimization of glycyrrhizin hydrogels with active components against vulvovaginal candidiasis

This project consists of the optimization of hydrogels for various human applications, here the focus is on vulvovaginal candidiasis. Two active compounds were added to a glycyrrhizin based hydrogel to counteract the fungal infection caused by the Candida yeast.

The aim of this project is to commercialize a gel against this common infection affecting a large part of the female population.

Several methods were used to optimize the protocol. First, the synthesis of gels on lab scale was investigated. During the synthesis of the gel, precipitations occurred. This was a big problem, because the concentration of the gels dropped. These were measured on the FT-IR to investigate what they were and how the precipitation could be avoided. It appeared that one active compound and glycyrrhizin form a complex and precipitate. When the precipitation was no longer a problem, multiple tests could be done to investigate this gel further. This by changing gel variables, for example changing the concentrations of the gelator and active compounds. Next the importance of the order of addition was investigated. Rheology tests were performed to confirm the gelation and to check the reproducibility of the additional compounds and gelation. A second method was trying to keep the gelated structure by changing the pH.

As this is an early-stage research, the technology level is too low to sell this gel against vulvovaginal candidiasis. There are still multiple experiments to be done and clinical trials need to be conducted before this product can be sold. But a lot can already be concluded. An optimal protocol for hydrogels containing these active compounds has been found. But a way has yet to be found to automate this protocol so that it is possible to produce this gel in large quantities.

Abstract Bachelor project 2020-2021: Modification of cellulose with amino acids and derivatives to flocculate microalgae

Microalgae are a new source of biomass with many possibilities such as the synthesis of chemicals, nutrients, and biofuels. Currently many applications of microalgae are not exploited since it is too expensive to grow and harvest the microalgae. It is possible to reduce the cost of harvesting of microalgae by using flocculants. These flocculants can aggregate several microalgae in a suspension so a bigger mass that will sink to the bottom is formed. When using flocculants, the need for expensive separation methods during the harvesting of microalgae is lowered.  

This research attempts to synthesize new flocculants for microalgae which can make the harvesting of the microalgae cheaper.

The flocculants are produced by first hydrolyzing cellulose with an acid. After the hydrolysis, the produced cellulose nanocrystals (CNCs) are modified with amino acids or derivatives so that they are given a positive charge. During the modification, an ester should be formed between the CNCs and the amino acids or derivatives. The positive charge given to the CNCs enables them to interact with the negatively charged cell wall of the microalgae. In this research the modification is attempted in HCl vapors, dry sulfolane and dry pyridine for several amino acids and derivatives.

Neither the modification in dry sulfolane nor in HCl vapors was successful, but there was some success with the modification in dry pyridine. In a pyridine solution the CNCs were successfully modified with betaine HCl and N,N-dimethylglycine HCl. Unfortunately, only the CNCs modified with betaine HCl were able to flocculate the tested microalgae. The modifications in pyridine with other amino acids and derivatives such as N-methylglycine, arginine and histidine did not result in an ester. The CNCs modified with these compounds are not given a positive charge. During the modification with glycine and lysine amides were formed. It is possible that along with the amides esters were formed, but in such a small quantity that they are not easily detected. Because of this modification it is possible to build chains of amino acids on the CNCs. There is a chance that this modification also occurs when using histidine however these results are not yet clear.

Currently only CNCs modified with betaine HCl in a pyridine solution can be used to flocculate microalgae. This method might also prove useful with the glycine derivative N,N-dimethylglycine after some more research. When using this method with the amino acids glycine and lysine it is possible to build polymers of amino acids on the CNCs. This modification might also be possible when using histidine.  

Abstract Bachelor project 2017-2018: Synthesis and characterization of functionalized nanocellulose for the flocculation of microalgae

With the world population growing exponentially, the global demand for biomass is expected to increase in the future. Several studies have shown that microalgae could be considered as a promising new sources of biomass. The biomass of algae can been seen as a possible way to solve the food and energy crisis. But a major challenge is separating the microalgae from their growth medium. Methods available today are still not on point, because they need too much energy, contaminate the harvested biomass and/or are very expensive. Therefore new low-cost methods are needed.

The aim of this study is the production of positive charged nanocellulose as new kind of flocculants, which can be used to harvest microalgae. Acid hydrolysis treatment of cotton wool results in cellulose nanocrystals (CNCs). Nanocellulose, covered with hydroxyl groups, provide an ideal platform for modification. During modification, hydroxyl groups are being replaced by positive chemical groups. The resulting positive charged nanocellulose is able to interact with the negative surface of microalgae to form flocs and are allowed to sediment. In this work, modification is performed by adding betaine (HCl) or imidazole on the surfaces of nanocellulose.

To achieve optimal flocculants, modification protocols needs optimization, by experimenting with parameters such as the temperature, time and stoichiometry of the chemicals. The flocculants are analyzed with several techniques like the Fourier-Transform infrared spectroscopy, thermal gravimetric analysis, element analyzer and zeta-potential. The quantification of modification is presented in terms of degree of substitution (DS). A flocculant is expected better when modified CNCs have a large DS, without damaging the structure. Finally, all flocculants were tested for flocculation of the fresh water microalgae Chlorella vulgaris.

CNCs with betaine (HCl) on the surface were positive charged and were independent of the pH. Imidazole grafted CNCs were shown to have a pH dependent surface charge which was in general positive below pH 7.5 and negative above pH 9. The best betaine grafted CNC had a maximum flocculation of 95.12 % with a dose of 40 mg/L. The flocculation efficiency of imidazole grafted CNCS was also tested, but the maximum flocculation was very low.

Both types of modified CNCs were successfully synthesized, but didn’t have a large DS. It seems that highly charged CNCs are excellent flocculants for Chlorella vulgaris. The DS turns out to have an influence on the flocculation. An increase of DS results in a decrease in dosage. The main of future experiments is the improvement in level of modification, repeat the flocculation test of imidazole grafted CNCs, remove imidazole grafted CNCs out of the harvested biomass.


E. Sabbelaan


Traineeship supervisor
Maarten Mees
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