Why do humans go to space? A common question indeed. Because space always brings out the best in human beings. The moon race during the 70s inspired half-a-dozen nations to put flags on the moon after Armstrong took that significant step, initiating the golden age of technological improvements. Human beings have never stopped exploring, and the most important reason behind that is our curiosity.
Obstacles in Space Travels
Space traveling takes decades, so the resources that maintain space travelers’ living qualities may run out before they reach their destinations. Fortunately, synthetic biology can help! Recent studies have shown that engineered microorganisms can produce drugs[1], nutrients[2], building materials[3], or other resources in space, which have great potential to improve the quality of space travel.
Radiation Problem
However, there is a crucial problem: intense space radiation. What if the engineered microorganisms could not function due to space radiation? What if the grand space expedition ends earlier because of resource shortages due to disordered microorganisms?
What Can We Do?
NCKU_Tainan found a way to synthesize selenomelanin, a kind of melanin with greater radiation absorbance, in E. coli. According to research[4], NHEK (Normal Human Epidermal Keratinocytes) cells that produce selenomelanin can withstand up to 6 Gy X-ray irradiation, while 5 Gy can be lethal to humans. With this protective substance, synthetic biology applications in space can be achieved by humans. However, we cannot stop here. As we moved forward, we realized how important it is to connect to society.
References
[1] Romsdahl J, Blachowicz A, Chiang AJ, et al. International Space Station conditions alter genomics, proteomics, and metabolomics in Aspergillus nidulans. Applied Microbiology and Biotechnology. 2018;103(3):1363-1377. doi:10.1007/s00253-018-9525-0
[2] Vitug E. Space Synthetic Biology (SynBio). NASA. Published April 7, 2020. Accessed September 24, 2022. https://www.nasa.gov/directorates/spacetech/game_changing_development/projects/SynBio
[3] Volger R, Pettersson GM, Brouns SJJ, Rothschild LJ, Cowley A, Lehner BAE. Mining moon & mars with microbes: Biological approaches to extract iron from Lunar and Martian regolith. Planetary and Space Science. 2020;184:104850. doi:10.1016/j.pss.2020.104850
[4] Cao W, McCallum NC, Ni QZ, et al. Selenomelanin: An Abiotic Selenium Analogue of Pheomelanin. Journal of the American Chemical Society. 2020;142(29):12802-12810. doi:10.1021/jacs.0c05573
Human Practices
How Did We Start?
“Science and technology have the power to transform the future, that they are socially, ethically and politically entangled and that they can have potentially far-reaching, uncertain and unpredictable social consequences.” Responsible Research and Innovation (RRI) project official once said[1].
As scientists, to have a broader influence on the world, we need to think about not only experiment and research but also “how can our project connect to the world?”. So, we must explore further to realize its responsibility, ethicality, and inclusiveness. We wanted to integrate the thoughts of those strongly related to the topic, such as space travelers, synthetic biology scientists, space agencies, or even the general public who can benefit from space research. Thus, we held various activities, interviews, conferences, and surveys to communicate with people from different communities.
This year, the human practices team aims to ensure the value of our project, realize how our solution can be embraced by the world, and reach out to any communities influenced by this issue. Human Practices is an indispensable guide to our project. It makes the whole project more comprehensive and allows us to dig deeper and think about “project influence” and “how we can make the world a better place”.
Design
The concept of our project is futuristic but unfamiliar to the public. What comes along is uncertainty, which challenges scientific and technological decision-making in both public and private communities. Owing to its novelty, complexity, uncertainty, and publicity, it is vital that we proceed with more responsibility and deliberation. Therefore, we follow the Responsible Research and Innovation (RRI) framework: Anticipation, Reflection, Deliberation, and Responsiveness.
This framework was designed to evaluate research that engages various communities. Therefore, by this, we could conduct a more thorough deliberation and create a stronger connection with society.
This is the framework we followed, and how we designed to realize our human practices[2]:
[click each section to learn more about the framework]
In this step, we need to describe and analyze both intended and unintended impacts that might appear in economic, social, environmental, or other aspects because of our project.
In this step, we should reflect the underlying purposes, motivations, and potential impacts, to see what is known and what is unknown.
In this step, we should invite, communicate with, and listen to the public and multiple stakeholders to broaden our visions to a broader extent. During these communications, we can see our project from their perspectives, allowing us to integrate different points of view into our project and further reframe our approaches.
In response to the communication with the public, we need to integrate what we have received from the reflection and deliberation stages to adjust the direction of our project.
Our Solution
Anticipation and Reflection
By answering these questions[3] (Fig. 1), we can figure out the potential impacts and risks.
Fig. 1. Questions indicating the potential impacts of MerSe
Here are the answers:
I. The influencing and the influenced
Fig. 2. Stakeholder map related to MerSe
II. Potential impacts and risks
Amongst all these stakeholders, astronauts, space agencies, and the public are the most significant ones. Here, we analyzed how our project can impact these three communities (Fig. 3).
Fig. 3. Analysis of the benefits and risks that astronauts, space agencies, and the public might encounter
III. Responsibility of the society
After applying this innovative research in real life, it would be essential to figure out how to control the risks and benefits. Therefore, we believe that each social group is responsible for managing the risks and benefits in different aspects (Fig. 4).
Fig. 4. Analysis of the responsibility of different communities
Deliberation and Responsiveness
To widen our visions, we must communicate with the public, stakeholders, and potential customers (Fig. 5). Consequently, we have successfully integrated all the ideas and reframed our project step by step; moreover, we have increased people's understanding of this topic through reciprocity, flexibility, openness to learning, transparency, diversity, and inclusion (see Education & Communication and Integrated Human Practices page).
Fig. 5. Analysis of the communities we communicated with
References
[1] What is RRI? | RRI-Practice. www.rri-practice.eu. https://www.rri-practice.eu/about-rri-practice/what-is-rri/
[2] Owen R, Stilgoe J, Macnaghten P, Gorman M, Fisher E, Guston D. A Framework for Responsible Innovation. Responsible Innovation. Published online April 2, 2013:27-50. doi:10.1002/9781118551424.ch2
[3] Stilgoe J, Owen R, Macnaghten P. Developing a framework for responsible innovation. Research Policy. 2013;42(9):1568-1580. doi:10.1016/j.respol.2013.05.008
Integrated Human Practices
Overview
Space is a topic filled with uncertainty but novelty and potentiality. When conducting this research, we need to consider many things, including science, engineering, entrepreneurship, ethics, and society. On the path, we have received much help from experts and stakeholders in various fields. They taught us what we did not know, expanded our horizons, most importantly, allowed us to see what is possible and what is beyond our reach. Eventually, we were able to determine the value of our project.
Stage 1. Brainstorming
At the beginning of our project, we went through many brainstorming processes. We came up with different ideas about applying selenomelanin. Thus, we contacted experts from various fields and adjusted our direction based on their feedback.
Dr. Tzung-Fang Guo
What is the professional field of Dr. Tzung-Fang Guo?
Dr. Guo is a professor in the Department of Photonics, NCKU. He is an expert in the field of semiconductors. At first, we found a paper stating that melanin can be used to produce organic semiconductors. We thought maybe selenomelanin can have the same function. Moreover, should we succeed, this idea might improve space electronic application since space radiation can be converted into energy. Therefore, we met Dr. Guo to discuss the potentiality.
What is changed after the meeting?
Dr. Guo emphasized there are two obstacles. First, the manufacturing process of organic semiconductors is too complicated. Second, it would require high purity and quantity of selenomelanin, which is difficult to achieve for us. Besides this advice, he also helped us come up with other ideas for selenomelanin applications.
Our next step:
After some discussions, we realized that there are other opportunities for selenomelanin other than semiconductors. Moreover, from Dr. Guo’s advice, we learned that we should analyze the qualities of selenomelanin before using it on other devices.
Dr. Wei-Chen Tu
What is the professional field of Dr. Wei-Chen Tu?
Dr. Tu is a professor in the Department of Electrical Engineering, NCKU. We decided to make a UV intensity detector since we aimed to eliminate the harm of space radiation to humans. Therefore, we contacted Dr. Tu.
What is changed after the meeting?
Dr. Tu pointed out the difficulties we might encounter, such as lower competence compared to the commercial UV detector and the inaccurate measuring results.
Our next step:
After a thorough discussion, we found it difficult and unnecessary to continue trying to make a UV detector. However, after knowing more about UV light, we thought we could make a machine that is able to measure the effectiveness of selenomelanin by exposing it to UV light instead of detecting it.
Dr. Shu-Hui Chen
What is the professional field of Dr. Shu-Hui Chen?
Dr. Chen is the professor of the Department of Chemistry and the dean of College of Science in NCKU. Before we started building the experiment, we had to understand more about selenomelanin, regarding its chemical properties, the measuring methods, and its further applications. Therefore, we contacted Dr. Chen.
What is changed after the meeting?
As a chemist, she explained that “atomic number” is the key to determine the radiation absorbance ability of selenomelanin. In addition, she also gave us some advice on the methods we could use for analyzing selenomelanin, such as XPS, UV-Vis, and NMR. However, besides quantitative analysis, she recommended we do qualitative research. Last but not least, she also gave us some ideas about the chemical reactions, which allowed us to better understand how to adjust the experimental parameters.
Our next step:
We became more familiar with the property of selenomelanin by seeing it from the chemical perspective that Dr. Chen gave us. Moreover, we built up a clearer idea of how to measure our final product and optimized the original protocols for a higher yield of selenomelanin.
Dr. Chih-Hsun Lin (Part I)
What is the professional field of Dr. Chih-Hsun Lin?
Dr. Lin is a senior research scientist in the Institute of Physics, Academia Sinica and an expert conducting radiation tests. We held a meeting with him since he had participated in several cosmic rays and gamma-ray experiments in space.
What is changed after the meeting?
Our idea was to utilize selenomelanin as a shield of radiation protection in space. It can also reduce the launch cost of packages to space because of low weight. Dr. Lin suggested to us that the radiation (charged particles and gamma-rays) absorbance of a substance is strongly relative to its atomic weight and thickness. Therefore, take lead as a comparison, we might need the same or more amount of selenomelanin to reach the same radiation absorbance ability as lead. Therefore, it cannot reduce the launch cost by weight.
Our next step:
After the discussion, we understood that our original research direction was not realistic in the real situation. Consequently, our next step would be finding a new opportunity to take advantage of selenomelanin.
Dr. Ching-Gong Lin
What is the professional field of Dr. Ching-Gong Lin?
Dr. Lin is an Associate Professor in the Department of Cosmetic Science, CNU. We thought maybe we could mix selenomelanin with sunscreen as a preliminary protection for astronauts. Therefore, we came to Dr. Lin, who has conducted research about applying melanin to cosmetics.
What is changed after the meeting?
Dr. Lin has a rich experience in using synthetic biology to synthesize melanin, he kindly provided advice to our process and shared melanin UV resistance measuring methods. Moreover, Dr. Lin introduced Dr. Clay C. C. Wang to us, who is committed to study fungi that have the potential to produce pharmaceuticals in space.
Our next step:
We improved the process of melanin biosynthesis and built a platform for survival rate experiments. At that time, we were challenged that our production amount could hardly be enough for commercial use; furthermore, the effectiveness in sunscreen application is unknown. Therefore, after this meeting, we thought we could utilize selenomelanin to protect the bacteria themselves.
Dr. Clay C. C. Wang (Part I)
What is the professional field of Dr. Clay C. C. Wang?
Dr. Wang is a professor at the USC School of Pharmacy and chair of the Department of Pharmacology and Pharmaceutical Sciences. Before we contacted him, we had read a paper about utilizing microbes to produce pharmaceuticals during long-term space travels, and he was one of the authors. Fortunately, we came up with an idea. Since space radiation could be a threat to the microorganisms, it would be great if we can protect them with selenomelanin. To understand the problem and ensure this solution was viable, we contacted Dr. Wang, who is dedicated to this field and has rich experience in collaborating with NASA.
What is changed after the meeting?
After meeting with Dr. Wang, we had a better understanding of the potential of synthetic biology in space. Through his experience, he suggested that maybe we should utilize the proliferation ability of E. coli to produce selenomelanin sustainably. Moreover, since he was an expert in fungi research, he suggested that maybe we should apply the pathway in prokaryotes like E. coli instead of fungi. To have a more comprehensive idea, we should also contact other scientists who are conducting research about bacteria application in space.
Our next step:
In order to make the most of selenomelanin, our team decided to change our direction. We decided to utilize selenomelanin to protect those beneficial microorganisms in space so that we can improve the quality of space travel, maximizing its value in a broader aspect.
Stage 2. Determining the Value of the Problem
After consulting with many experts, we saw a universal possibility and built up a specific goal for our project. Before conducting, we ought to first determine three questions, making sure that our solution is responsible and good for the world. “Why do humans go to space?”, “Why do astronauts need engineered microorganisms to produce resources?”, and “Why do microorganisms need protection from radiation?”. To answer these questions, we did a lot of research, contacted many experts and conducted a public questionnaire.
Public questionnaire
Why did we conduct this questionnaire?
We conducted a public questionnaire to understand the public's thoughts about space, the space application of synthetic biology, and our project ideas.
How did it influence us?
Our respondents are from seven countries. They have an equal ratio of males and females, ranging from 18 to 50 years old, and include more than ten types of careers. There are a few noteworthy results. First, over half of them believed space research is essential. Second, four out of five thought "protecting the microbes in space from radiation for more synthetic biology application in space" is an important issue. For those who did not choose "yes," it was because they were unfamiliar with relevant topics. Last, over half of them were unfamiliar with the space application of synthetic biology.
Our next step:
Our goal is long-term and influential; therefore, convincing the public would be crucial to us. Through this questionnaire, we understood people's thoughts about space exploration. Moreover, we realized that education and communication would be necessary for the public to embrace this idea. Consequently, we should fulfill the anticipation and demands of the people and build a strong bond with them (see Inclusivity page).
Dr. Shih-Yun Kuo
What is the professional field of Dr. Shih-Yun Kuo?
It was important to figure out the decisive reasons why space research is significant to humans. At first, we thought it was because of climate change, pollution, or population explosion. Therefore, we contacted Dr. Kuo, a researcher in the Research Center for Environmental Changes. We thought that Dr. Kuo could offer us valuable advice on how our project can impact the world by increasing the chance to go to space.
What is changed after the meeting?
Dr. Kuo did not think immigrating to space would be the best choice for humans when we face climate change or pollution. First, climate change will not occur at the same time in all places on earth; thus, it is more likely that people will just migrate to other places that do not suffer from climate problems. Second, immigration to space would be too expensive for all humans; instead, people should utilize the budget to solve problems on earth such as eliminating carbon dioxide. Moreover, since she is also an expert in public communication, she gave us some suggestions on how to present this novel topic in order to attract audiences and how to exchange ideas with them.
Our next step:
After this meeting, we found out that the reasons we proposed were not that practical. The question we should answer was “Why do humans go to space now?” instead of “What are the things that force people to go to space in the future?”. Before this meeting, we thought that only if we utilize this technology when all humans can go to space will the public feel touched by our project. However, we then figured out that though this solution can only directly contribute to astronauts, it still can indirectly have a significant impact on the world.
iGEM World Environment Day
Image taken from recordings of iGEM World Environment Day Video link
What is changed after the event?
In this activity, some of our members participated in the Synbio and Space Explorations group. We shared our project ideas with the speakers Fan Yang and Xin Liu. They mentioned that there are actually a few biotechnology companies conducting research about utilizing Synbio in space. Currently, most of the experiments were conducted under conditions that astronauts could also stay at, which might not be lethal to the bacteria. Nevertheless, there were some research conducted directly in outer space, which the researchers planned to use organisms from harsh environments.
Our next step:
This event inspired us a lot. We realized that there are actually many people devoted to this field; moreover, by utilizing selenomelanin in E. coli, a widely used genetically engineered host, synthetic biology can have an even broader application!
After the event and further research, we realized that owing to the shipment budget and limited resources to bring to space, sending engineered microorganisms to space has great potential because they have less mass, less volume; thus, less power demand[1]. Maybe that is why there are many scientists so devoted to this field!
Dr. Timothy Hammond
What is the professional field of Dr. Timothy Hammond?
Dr. Hammond is a nephrology doctor who has been conducting research about utilizing microorganisms in space. He is the most suitable stakeholder and expert who clearly knows what the situation is in space.
What is changed after the meeting?
Dr. Hammond mentioned that ISS, where various space research was conducted at, is inside the Van Allen radiation belt; thus, the radiation level would not be lethal to both humans and microorganisms. Nevertheless, the radiation level beyond the Van Allen radiation belt would be high. He also told us about some problems astronauts might encounter. During long-time and long-distance space travel, travelers might encounter more severe diseases due to the harsh environment; moreover, the living resources are limited, so our solution would be necessary.
After the meeting, we also learned that there is some necessary equipment we would need in space experiments, such as PHAB, a sophisticated box which can contain toxic chemicals and biologicals. Also, since astronauts need a lot of time doing activities related to living, an automated system for the experiment is preferable. Last but not least, Dr. Hammond gave us some very helpful information about how we should really implement our project in space.
Our next step:
For our next step, we needed to figure out ways that really assist our project to get closer to space, which are automated systems, broader synthetic biology applications, and a specific business plan.
Stage 3. Designing Our Solution
During the previous stage, we received feedback and exchanged ideas from experts, the public, and the stakeholders who are closely related to the topic. To make further progress, we started to design our solutions with a more specific goal and solved problems step by step, in order to make our project more comprehensive.
Dr. Chih-Hsun Lin (Part II)
What is the professional field of Dr. Chih-Hsun Lin?
After figuring out a more specific plan, we visited Dr. Lin again at the Institute of Physics, Academia Sinica, hoping to receive some feedback from him.
What is changed after the meeting?
He suggested that we should specify how our engineered Se coli could have a better survival rate compared to the normal E. coli under the radiation environment. In addition, he also reminded us that all parameters must be well controlled and recorded when conducting experiments and tests.
Our next step:
After the discussion, we designed a more complete experimental plan. We were also planning to conduct experiments on growth curves of Se coli living under the space-environment simulation.
Abraham Tan
What is the professional field of Abraham Tan?
To mimic microgravity in space, we originally planned to design a clinostat, a device commonly used to assist the simulation of microgravity. Therefore, we contacted Abraham Tan, a postgraduate student in the Department of Physics, NCKU, who is also a student of Dr. Chopin Soo, an expert in the field of gravitation.
What is changed after the meeting?
After some research and discussion with Abraham Tan, we realized that microgravity conditions cannot be simulated by clinostats or any other hardware. Instead, the suspension of the sample results from the equally distributed force created by clinostats’ rotation.
Our next step:
Since true microgravity cannot be achieved on Earth, we decided to design a device that is capable of simulating the cell performance of bacteria that are cultured in space.
Dr. Chia-Hsien Hsu & Dr. Didem Rodoplu
What are the professional fields of Dr. Chia-Hsien Hsu & Dr. Didem Rodoplu?
After some research and discussion with experts, we decided to simulate the cell performance of E. coli cultured in space, which could be achieved by suspension culture of E. coli. We further found that Dr. Hsu, an investigator in the Institute of Biomedical Engineering and Nanomedicine of the National Research Institutes of Taiwan, is an expert in using microfluidic technology to produce suspended drops for cell culture, so we approached him for his help with our project.
What is changed after the meeting?
He provided us suggestions about the design, material, and fabrication method for making the E. coli culture chip. Specifically, he suggested we use PMMA as the main material of the chip because it is easy and inexpensive to fabricate. He also guided us to make chips that have different well sizes so that we could choose the best size for future experiments. Besides Dr. Hsu, we also like to thank his postdoctoral researcher Dr. Didem Rodoplu who helped a lot with the on-chip bacteria culture experiment.
Our next step:
Dr. Hsu helped us to start the microfluidic chip experiment which is significant to us. In the future, we could conduct more experiments by following the basic methods we learned from him, and even optimize the chip to fit our future project needs.
Chuan-Chieh Hsiang
What is the professional field of Chuan-Chieh Hsiang?
Chuan-Chieh Hsiang is a PhD student of Professor I-Son Ng. Regarding his numerous experience in the Taguchi methods, we discussed the experiment data and the application of the Taguchi methods with him for a higher yield of melanin.
What is changed after the meeting?
He kept reminding us why we used the Taguchi methods to analyze data. Eventually, we understood how to analyze the experimental data by Taguchi methods and efficiently optimized the culturing procedure.
Our next step:
With his suggestion and help, we were able to make further optimization for high-level melanin production.
Song-Yu Lu
What is the professional field of Song-Yu Lu?
Song-Yu Lu is a postgraduate student of Dr. Lung-Ming Fu, a professor in the Department of Engineering Science and an expert in microfluidic system analysis. Therefore, we decided to contact him for further improvement of our design: simulating the exchanging condition of the new and old cell culture medium.
What is changed after the meeting?
He taught us how to use Ansys Fluent, a fluid simulation software, to simulate the exchanging condition of the new and old cell culture medium.
Our next step:
However, owing to the time constraints, we decided to stop this model simulation after a thorough discussion.
Dr. Hsien-Hung Wei
What is the professional field of Dr. Hsien-Hung Wei?
When working on the modeling of bacteria aggregation and nutrient uptake processes in our microfluidic chip, we found Dr. Wei, a professor of the Department of Chemical Engineering in NCKU, to be extremely helpful. He is an expert in microfluidics and transport phenomena, and he provided a lot of useful advice to us.
What is changed after the meeting?
Dr. Wei suggested that we can take the well-known Keller-Segel equation for chemotaxis and modify it to simulate the processes mentioned above. Moreover, he also gave us very constructive feedback on how to better bridge the gap between our simulation results and actual experimental observations.
Vice President Kai Yang
What is the professional field of Vice President Kai Yang?
Kai Yang is the VP of product in Landing AI, a company providing software that enables reliable automated inspection for a wide range of applications in industrial automation and manufacturing. Since we decided to utilize image recognition for the automation system we planned to apply in space, we contacted Kai.
What is changed after the meeting?
At first, we did not know much about the application of AI; however, after a few meetings, we started to figure out how to make the most of AI and how it can make our project easier to be realized in space. Kai Yang has guided us through different stages of designing, regarding how to improve our data set, retrain our Model; until our Model performs at the desired level. Moreover, Landing AI provided us with a platform to utilize AI more efficiently and conveniently.
Our next step:
We started to have a clearer idea about AI applications. After receiving the help from Kai Yang and Landing AI, our AI project became more complete. We thought during the research phase, the complex experiment designs would require a great demand for manpower to conduct experiments. Therefore, we designed an AI system to let the system pick out the best colony in different experiment designs. However, owing to time limitations, through consideration, we decided to continue the project after iGEM.
Stage 4. Implementing Our Solution
With all our efforts and all the help from experts who helped us, we kept moving further and further. Eventually, we reached the final step - How will our project be implemented in the real world (see Future page).
Dr. Clay C. C. Wang (Part II)
What is the professional field of Dr. Clay C. C. Wang?
Through our efforts, our project became more complete. We thought maybe we should meet with Dr. Wang again and receive some feedback from him.
What is changed after the meeting?
Dr. Wang was optimistic about our project. He said that since we are in Taiwan, a country that does not invest many resources in the space industry, we could be a pioneer in this field; moreover, we might encourage other scientists in Taiwan to start exploring the possibility between synthetic biology and space. In addition to some suggestions about our project, Dr. Wang also gave us a lot of advice about how we can really send our research to space. He introduced some of his friends from space tango, NASA, or other well-known companies in this field to us.
Our next step:
With the help from Dr. Wang, we became more confident in the value and the impact of our research. Furthermore, we figured out a clear direction of entrepreneurship.
Chairman of GRAN SYSTEM, Mr. Ke
What is the professional field of Mr. Ke?
Mr. Ke is the chairman of GRAN SYSTEMS, which is a launch service provider to SpaceX, Nanoracks and other space companies, and they send experimental samples to ISS. We thought if we wanted to send our product to space, Mr. Ke is the best person to contact.
What is changed after the meeting?
Mr. Ke said that space experiments would have great potential since the development of various research would require space experiments for unexpected but significant discoveries. He was optimistic about our plan and provided helpful knowledge about the preparation before heading to space. He encouraged us that we should continue our project in the future, which would be highly possible to send our products to space for experiments. Most importantly, he told us the operation mechanism of how different companies ship their products. For instance, we can seek opportunities to join others’ projects. At the same time, we must make the most of the space in the spaceship, which means that we should minimize the volume and weight of our samples. Moreover, we had a clearer idea about the shipment price with a specific volume. Last, he also suggested how we could raise funds to support our project.
Our next step:
From the meetings, we became more certain about the direction we should head when making a business plan for sending our products to space. We are confident that this dream will surely come true.
References
[1] Menezes AA, Montague MG, Cumbers J, Hogan JA, Arkin AP. Grand challenges in space synthetic biology. Journal of The Royal Society Interface. 2015;12(113):20150803. doi:10.1098/rsif.2015.0803
