Multi-membrane alginate water capsule: An eco-friendly method of sustainable water supply for agricultural fields

Summary

Drought is an increasingly threatening problem in agriculture all around the world. The biggest problem is that most methods of watering crops waste large amounts of water, resulting in inefficient water usage. Currently, attempts to tackle this problem exist: drip irrigation and mulching are iconic. However, these attempts fail to consider equally important factors such as price and pollution of the terrain.

Our project not only conserves water but is sustainable, eco-friendly and affordable. Alginate, the key substance of our invention, is extracted from brown algae. It is extremely cheap and eco-friendly.

Alginate forms a gel with divalent cations. It is from this property we get our concept: multi-membrane water capsules made with alginate gel. When we plant these capsules in the ground with the roots, we observed that water seeps out through the membrane quite steadily. We use ice to make the capsules. We cover a spherical ice block with the cation solution and dip that in the alginate solution to form a gel. We can make multi-membrane capsules by freezing a capsule in a bigger ice block and making a capsule out of it.

We considered three main variables to test our project: the thickness of the membrane, the composition of the membrane and how it affects a real plant.

We learned that:

More layers lead to steadier output;

calcium ions are the best fit;

adding agarose and chitosan significantly steadies the discharge.

We confirmed that customization of our capsules is possible, meaning potential application in the field.

 

Question / Proposal

The conventional method of farming requires phenomenal amounts of water; water is sprayed towards the farm, and large proportions of that water never reach the roots. Thus, not only do we waste thousands of gallons of water from farming each year, but also if a drought strikes, farms and their crops will be devastatingly affected.

Our project will help resolve that problem. The goal of our project is to create eco-friendly, low-cost methods that can conserve water in agriculture.

Our first idea originated from a startup in London that aimed to develop alternatives to plastic bottles by making edible water capsules. They used alginate, a substance extracted from seaweeds, to make the packaging edible and biodegradable; we thought we could apply this in agriculture.

With the use of alginate, we hoped to create a capsule that is able to control its water-release rate in order to minimize evaporation. Through the incorporation of capsule-in-a-capsule structures, we thought we could release water through a controlled amount of time, providing a temporary solution for droughts. 

We hope to see,

1. The construction of a capsule-in-a-capsule model to control the water discharge rate.

2. The change of the stiffness and water permeability of the capsule by changing the alginate membrane structure by using different crosslinking ions.

3. Increased stability of the capsule for practical applications by adding different encapsulating substances such as chitosan and agarose to the composition.

 

 

 

Research

There are various methods of water conservation in agriculture. Drip irrigation used with mulching is one of the common methods that is being used to preserve water: plants are watered slowly through a pipe near the roots while a substance like plastic vinyl covers the ground. This direct method of watering prevents large evaporation. However, the disadvantage is that the installment is costly and can be harmful to the environment by plastic degradation; one can see a lot of black vinyl littered in the rural areas of Korea. A method that is more eco-friendly, low-cost, and customizable compared to drip irrigation for small fields is required. 

Thus we researched environment-friendly materials, and we came across a substance called alginate. Alginate is a polysaccharide located in brown algaes. It can be easily extracted from algaes like seaweeds which is not only biodegradable but also cheap due to the abundance of algaes and seaweed wasts; in Goheung, Korea alone, there were 50,000 tons of seaweed waste! The price of alginate is about six dollars per kg; since our project requires very small amount of alginate per capsule, it can be mass produced.

Alginate forms a gel, a membrane, when interacted with cations via ionic interactions. Ions that are able to crosslink with alginate are divalent cations such as copper, strontium, calcium, cobalt, and etc. Previous studies have shown that alginate crosslinked membranes show different traits for each type: some ions result in stronger bonds and membranes, while other ions such as magnesium will not even form membranes. Also, the SEM photos of these membranes show that each membrane has different size micropores, which is an important factor that affects the water discharge profile.

Alginate’s ability to form a gel and to absorb and contain water had led its use in various fields such as food preservation and biomedical fields. Alginate’s use in drug delivery system has given us many ideas. Medical researchers has used alginate to create microbeads in size of 100~1000μm in order to convey medicine and microorganisms. There were also other researches that had used additional substances such as chitosan to reduce the permeability of the alginate membrane. These researches provided us factors to control the water discharge rate and the stability of our capsules.

However, these researches were only done on small-size alginate beads. Research on larger scale alginate beads, or capsules, were limited. Also, its applications on agricultural fields were rarely done. Thus, we had to experiment and test various alginate membranes with different composition and find different methods to create large capsules that would be applicable to agricultural fields.

Method / Testing and Redesign

1. The Formation of Alginate gel according to the 2+ cation

We prepared 8 1% cation solutions(Mg2+, Ca2+, Sr2+, Cu2+, Mn2+, Co2+, Fe2+, Ni2+) and mixed each with 20ml of 1% alginate solutions, and observed the formation of gel.

2. Measuring the strength and stiffness of alginate gels

To measure the Young’s modulus of each type of gel, we made samples by pouring 10ml of 5% solutions of each cation on a dish with alginate and waited 1 minute. We cut the formed gel into a rectangular shape and measured its dimensions using a caliper. With one end of the gel fixed to the table, we pulled the other end with a laundry tong connected to a force gauge. Once measuring the elongated length and the force used to do it, we used the formula for the Young’s Modulus to obtain the modulus for all gels.

In order to get accurate results, we repeated the above process with 10 samples and incorporated the arithmetic average value for each type of gels.

3. Producing Multi-membrane alginate capsules

We dipped a spherical piece of ice(diameter 25mm) coated in 2% CaCl2 solution in a 1% alginate solution and waited 1 minute to form the gel on the outside. Repeating this process, we could enforce the alginate membrane with layers. We then inserted the made 25mm capsule in a 50mm diameter ice tray and made ice spheres with capsules inside.

Repeating the previous steps with the bigger ice piece, we made multi-membrane alginate capsules. Note that we can mix the alginate solution with an agarose solution to include agarose in the membrane.

To make chitosan membranes, we mixed the CaCl2 solution with citric acid and chitosan to make a 2% chitosan solution. The citric acid is essential for the chitosan to dissolve.

4. The change of the capsules in the air

We placed the capsules on a petri dish in room conditions and observed the process of water drying out of the capsule.

5. Measuring the water discharged from the alginate capsules

Differing the number of layers and composition, we put the capsules in sealed containers and measured the amount of water discharged every day using a pipet.

6. Confirming the effect of the capsules on a real plant environment

We planted mustard plants in transparent pots with various capsules near the roots. For the control group, we poured the same amount of water directly on the soil. We observed the growth of the plant and the humidity of the soil.

 

Results

1. The Formation and Stiffness of Alginate Gel According to the Type of Cation and Concentration of Alginate

(1) The Formation of gel according to the type of cation

The gel formed better in the order of copper, calcium, and strontium, and the gel became stiffer with more time in the solution. Manganese, cobalt, and nickel all took more than 30 minutes and made irregular shapes. Iron and Magnesium ions couldn't produce gels.

(2) Measuring the Stiffness of the Membrane

We first compared the Young's Modulus of membranes with different cross-linking ions and membranes with agarose. Copper was stiffest among the different ions, with calcium, strontium, and cobalt following. 

When we mixed the 0.5% agarose and 2% 1:1, the stiffness of the membrane was almost identical to that of 100% alginate membranes, but the stiffness increased as the proportion of agarose in the membrane increased. Next, we compared the Young's Modulus of capsules made with solutions with different alginate concentrations and capsules stored in various conditions. Capsules made with 1% or 2% alginate solutions had similar stiffness, both much stiffer than ones made with a 0.5% solution. We then left capsules made with 2% alginate in KCl solutions, CaCl2 solutions, and water for 24 hours and measured the Young's Modulus of the resultant membrane. The membrane stored in the KCl solution was extremely brittle. The ones stored in water kept their initial stiffness while the ones in CaCl2 solution were 1.5 times stiffer.

2. The Effect of the Number of Layers and the Use of Chitosan and Agarose on the Water Discharge Profile

 

(1) Number of layers(Single Membrane)

This graph shows the daily water discharge of single capsules with 2, 4, and 6 layers. It shows that the more layers, the slower the discharge rate.

(2) Chitosan and Agarose(Single Membrane)

This graph shows the discharge profile of single capsules with chitosan or agarose. The supplementary substances make the water discharge substantially slower and steadier. 

(3) Double Membrane 

Similar to the single capsules, more layers lead to a slower discharge rate, but the double capsules are characterized by a peak in the graph. It can be intuitively inferred that the inner capsule starts to discharge water at this peak.

The next graph shows that by increasing the number of layers of the enclosed smaller capsule, the position of that peak can be controlled.

(5) Chitosan and Agarose(Double Membrane)

The last graph is another representation of the effects of chitosan or agarose. One can visibly notice that both significantly delays the water discharge.

5. Observation with Plants

We conducted an experiment using mustard plants. While the plants in the control group died within 3 days, plants with a capsule lasted much longer, up to a week. Also, plants with the double capsule lasted longer than the ones with the equivalent amount of single capsules. Ones with agarose capsules seemed to last much longer until all the other trials were near death.

 

Conclusion

Our capsule has many factors that make it customizable for each crop and situations.

Our creation of the capsule-in-a-capsule model had led us to control and customize the capsule's water discharge profile. Differentiation in the number of outer layers and inner layers will be the primary way to control the duration of the capsule: more layers will prolong the time of discharge. As water discharges from the outer capsule, it will create a 'peak' when the inner capsule starts to discharge, prolonging the discharge time compared to mono-capsules. Also customizing the number of layers in each outer and inner membranes will allow us to move that peak as we want, manipulating when and how much water is discharged. (we find controlling the number of layers more effective than changing the thickness of the membrane)

Changing the cross-linking ion also changed the water permeability of the membrane, affecting the creation of the capsule and its effectiveness. While copper ions showed the best gel capabilities, we decided to use calcium, which had similar capabilities, due to copper's detrimental effect on the environment. 

Addition of other substances such as agarose or chitosan had changed the water discharge rate significantly; chitosan and agarose would fill the micropores of the alginate membrane, significantly reducing the initial water discharge, making it more practical for real-life installations. However, it failed to increase the stability of our capsule, in a macro-scale, which was our initial hypothesis. Researches on medical microbeads show increased stability; however, we concluded that it did not produce a tangible effect on macro-scale capsules.

We have proved that our multi-membrane capsule can release water through a controlled amount of time and have seen its effects on mustard plants. Since the capsule is customizable, it can be used for plants that can stand without water for a longer period of time. For example, beans or cabbage requires less water per lifetime; here, we can increase the number of layers with the coating of chitosan to minimize the water discharge. For a plant that requires a larger amount of water per day, we can simply decrease the number of layers.

The main objective of our project is to create a method that conserves water in an eco-friendly, low-cost way. From our results, we could conclude that by using substances like chitosan and agarose, it is possible to lengthen the lifespan of plants with minimal amounts of water and that we can control when how much of a what nutrition is discharged.

Our study lacks a more extensive investigation of the effects of chitosan and agarose on alginate. Also, more verification is required with more real plant tests and methods for installments. With such further research, we are positive that our project will bring answers to a lot of water problems around the world.

About me

We attend the Korean Minjok Leadership Academy, a lonely high school located in the deepest mountains of Gangwon province, South Korea. Our school was founded under two goals: to recognize the talented and to train future leaders of our nation and the world. Our founder believed that talented students should learn to sacrifice for the welfare of others, much like how a candle burns itself to brighten its surroundings. That is why there is a candle in our school logo, and why we recite such motto every week.

We, as wannabe scientists and engineers, believe that science and creativity are key to achieve such values. 

 

Minseok "Joseph" Kim

Fields of Interest: Biology, Chemistry, Medicine, Neuroscience


Jaihyun Kim

Fields of Interest: Physics, Mechanical & Aerospace Engineering

 

Interesting fact: Despite what our last names suggest, we are not related to each other.

 

Winning this competition will not be limited to a certificate and a prize; it will be worldwide recognition that our efforts are paying off, and motivation to continue our endeavor to aid humanity.

 

Health & Safety

Laboratory Safety Guidelines (School Lab)

Korean Minjok Leadership Academy Chemistry Lab,

Manager Mr. Shin Seung Keun

 

1. Do not taste any chemical or smell any chemical directly.

2. When using fire, clear the surroundings of any chemical or object.

3. Wear gloves and use tongs when handling hot objects.

4. Do not use any glass equipment that is cracked or broken.

5. When a chemical touches bare skin or goes into an eye, immediately cleanse with clean water and seek appropriate measures.

6. Never handle electronic equipment with wet hands.

7. Deal with used chemicals according to the supervisor's instructions.

8. Clean all used equipment and return them to their original location.

9. Wash hands after using the lab.

Bibliography, references, and acknowledgements

References

Blandino, A., Macías, M., & Cantero, D. (1999). Formation of calcium alginate gel capsules: Influence of sodium alginate and CaCl2 concentration on gelation kinetics. Journal of Bioscience and Bioengineering, 88(6), 686–689. https://doi.org/10.1016/S1389-1723(00)87103-0

Lee, K. Y., & Mooney, D. J. (2012). Alginate: Properties and biomedical applications. Progress in Polymer Science (Oxford), 37(1), 106–126. https://doi.org/10.1016/j.progpolymsci.2011.06.003

Mørch, Ý. a., Donati, I., & Strand, B. L. (2006). Effect of Ca 2+ , Ba 2+ , and Sr 2+ on Alginate Microbeads. Biomacromolecules, 7(5), 1471–1480. https://doi.org/10.1021/bm060010d

Pathak, T. S., Yun, J. H., Lee, J., & Paeng, K. J. (2010). Effect of calcium ion (cross-linker) concentration on porosity, surface morphology and thermal behavior of calcium alginates prepared from algae (Undaria pinnatifida). Carbohydrate Polymers, 81(3), 633–639. https://doi.org/10.1016/j.carbpol.2010.03.025

Teoh, P. L., Mirhosseini, H., Mustafa, S., Hussin, A. S. M., & Manap, M. Y. A. (2011). Recent approaches in the development of encapsulated delivery systems for probiotics. Food Biotechnology, 25(1), 77–101. https://doi.org/10.1080/08905436.2011.547332

Tønnesen, H. H., & Karlsen, J. (2002). Alginate in drug delivery systems. Drug Development and Industrial Pharmacy, 28(6), 621–630. https://doi.org/10.1081/DDC-120003853

 

 

 

Acknowledgments

Mr. Shin Seung Keun, for supervising the entire process and giving us access to the school lab.

Our parents, for giving us the opportunity to participate in such meaningful activities.