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Potential Research Proposal January 2020 Raphael Kay Self-forming photo-sensing biomaterial fluid pockets in building skins for adaptive shading

Research Abstract Sea creatures like squid, krill, and pencilfish adaptively shade through the expansion and contraction of fluid-filled cells underneath their skin. Buildings, on the other hand, adaptively shade through the actuation of mostly rigid electro-mechanical components that tend to be costly, energy-intensive, and prone to failure over time. As buildings account for almost half of the energy footprint of the developed world, the design of climate-adaptive and energy-efficient building skins is vital. Accordingly, for my undergraduate thesis this year a colleague and I proposed to develop a bio-inspired architectural skin, modeled after pigment-cell activation within sea creatures. Since then, we have successfully engineered and automated an adaptive building membrane in which fluid pockets self-emerge and self-dissipate, activated locally by environmental sensors to regulate heat and light transmission into buildings. We observed interior temperature changes of 9 °C and light intensity changes of 27 Lux within minutes of fluid pocket activation in laboratory experiments. Building on this work, I propose to integrate photo-sensing biomaterials within this membrane to self-sense, self-activate, and self-power reversible fluid pocket formation for dynamic thermal and optical control. This will represent the first environmentally responsive photo-bioreactor facade, serving as a model for energy efficient and adaptive building envelope design.

Figure 1: The activation of chromatophore cells beneath the skin of pencilfish to change colour in response to increased ultraviolet radiation. Image: Tomlinson et al., 2009.


Background and Literature (Fluid Pocket Activation) The skin of buildings serves a similar function to the skin of animals – regulating the transmission of heat and light for internal operation; protecting against harmful radiation; and providing a medium by which to socially signal and communicate. Many taxa use the expansion and contraction of chromatophores – pigment-filled cells beneath the skin – to adaptively satisfy the above functionality (Figure 1). Some chromatophores, like those of cephalopods, are neuromuscular-activated (Messenger, 2001), while others, like those of crustaceans and fish, are endocrine-activated (Boyle and McNamara, 2015; Rao, 2001; Kwok et al., 2006). Because the activation of these pigment cells in animals is reversible, adaptive, and multifunctional, they serve as a model for dynamic building envelope design. Despite this, few engineered building skins have followed this biological precedent. There has been interest in embedding mammalian-inspired vein networks within building skins to facilitate heat flow for energy efficiency (Hatton et al., 2013; Alston and Barber, 2016; Alston, Pottgiesser, and Knaack, 2019). There has also been work to embed animal-skin-inspired light-refracting lenses within windows to control light transmission into buildings (Park et al., 2014). And, in my own previous research with Dr. Benjamin Hatton, we used the concepts of fluid migration beneath the skin of sea creatures to design colour-changing building membranes for thermal and optical control (Kay, Katrycz, and Hatton, 2020, manuscript in progress). These few examples, nonetheless, largely serve only one function (i.e., only regulating heat flow or light transmission), and are, for the most part, rigidly fabricated. Skins – of both animals and buildings – must be multifunctional and flexible. As such, for our independent thesis (Kay and Nitièma, 2019), and with the help of Doctoral candidate Charlie Katrycz, we used the Saffman-Taylor fluid instability – a fluidtunneling phenomenon brought about by viscosity differences between fluids – as a means of generating and dissipating chromatophore-inspired reversible fluid pockets within building skins (Figure 2-7). The fluid tunneling is initiated when a less viscous fluid is introduced with pressure into a more viscous fluid, producing a branched fractal pattern similar to the structure of mammalian tissue vascularity (Zamir, 2001), optimized for fluid flow, as well as the delivery and removal of heat (Bejan, 2001; Chen et al., 2010; Wu et al., 2010) (Figure 2-3). This instability has been used to tunnel channel networks into soft-polymers (Katrycz and Hatton, 2018) (Figure 4), and has been manipulated to show the potential for multiport fluid tunneling to define a network of webs (Islam and Gandhi, 2017). In no case, however, other than in our presented research, was the Saffman-Taylor instability utilized as an active agent for reversible fluid displacement, let alone along the surface of a building to adaptively shade, thermo-regulate, or change colour.

Figure 2: Saffman-Taylor instability demonstrated as air is introduced into soap, tunneling out a fractal network. This same fluidic phenomenon can be used to produce fluid pockets in building skins. Image: Kay and Nitièma, 2019.


Figure 3: Optimal flow pathway demonstrated, as the Saffman-Taylor instability (left) is contrasted against a naturally optimized river network in China (right) to demonstrate the optimal flow-network that is produced by the SaffmanTaylor instability. Left image: Kay and Nitièma, 2019. Right image: Beaty et al., 2018.

Figure 4: Saffman-Taylor instability demonstrated as air is introduced into silicon tunneling out a fractal network. Image and experiment conducted by a colleague, Charlie Katrycz.


Figure 5: Comparison between reversible chromatophore activation in krill (top), against reversible fluid pocket activation in a building membrane, demonstrated via the Saffman-Taylor instability (bottom). Top image: Auerswald et al., 2008. Bottom image: Kay and Nitièma, 2019.

Figure 6: Illustrating the generation of a fluid pocket (air) within a molasses-filled building skin, followed by its complete dissipation. The internal temperature beyond the displayed window along the surface of a metal rod was recorded to be 28 °C in image (a) and image (l) and 37 °C in image (f) and image (g). The internal light intensity beyond the displayed window was recorded to be 15 Lux in image (a) and image (l) and 42 Lux in image (f) and image (g). Image: Kay and Nitièma, 2019.

Figure 7: Illustrating the motion-activated fluid pocket formation and dissipation within a window skin. Image: Kay and Nitièma, 2019.


Background and Literature (Photo-Sensing Biomaterials) Photosynthetic biomaterials like microalgae sequester carbon dioxide, produce oxygen, and convert solar energy into productive biomass. Accordingly, in the context of architectural design, there has been interest in embedding photo-bioreactors (PBRs) within the skins of buildings. PBRs introduce the prospect of improved indoor air quality, improved psychological occupant wellbeing, useful biogas production, local agriculture and biomass production, and simultaneously sequester carbon dioxide from the local atmosphere. Centimeter-scale PBR screens, for example, were designed and tested as static shading devices inside buildings (Pagliolico et al., 2017; Pagliolico et al., 2019). An urban agricultural pavilion was built to provide solar shade; produce minerals, vegetable proteins, and oxygen; and take up carbon dioxide (ecoLogicStudio, 2015). And a large-scale PBR system was engineered as a building skin for the International Building Exhibition, producing year-round biomass and thermal energy, while sequestering local carbon dioxide (Wurm, 2014). The feasibility of PBR building skins has also been assessed, with research suggesting great thermal and optical performance potential (Kim, 2013; Elrayies, 2017). In almost all building-integrated PBRs, nonetheless, microalgae cells were static, creating a permanent thermal and optical barrier despite dynamic internal and external conditions. In some cases, only small variability in algal density occurred – and over prolonged and uncontrollable timescales – in response to changes in solar activity (Wurm, 2014). We have demonstrated, through our undergraduate thesis (Kay and Nitièma, 2019) the capability to use the Saffman-Taylor instability to displace fluids within building skins to generate fluid pockets for adaptive thermal and optical control. Building on this work, I propose to develop an adaptive building skin with carbon-sequestering and light-harvesting biomaterials as an internal medium. Beyond this capability, light-harvesting organisms have also been shown to produce electrical current when suspended within a bio-photovoltaic cell (McCormick et al., 2011) (Figure 9). In past research, it was observed that power outputs were correlated with light intensity (McCormick et al., 2011), meaning that there may exist the potential for light-harvesting biomaterials to be utilized as sensors – to communicate electrically when, and to what degree, fluid pockets should be generated based on solar input. Beyond this, the electrical power produced may have the potential to provide the small pumping power required for fluid pocket activation and dissipation. There is thus the potential, building on our previous research, for an entirely closed-loop, self-sensing, self-powering, and self-actuating adaptive window membrane.

Figure 8: A viscous microalgae bath in the lab of Professor David Sinton at the University of Toronto. Image: Raphael Kay.


Research Goals Through our past research, we have built and tested fluid-filled building skins in which fluid pockets reversibly emerge for dynamic thermal and optical control. Building on this previous work, I propose to develop an adaptive light-harvesting building skin, for which I will (1) produce a viscous bio-photo gel in which fluid pocket activation can occur, and (2) integrate bio-photovoltaic capability to utilize the solarsensing and current-generating potential of photo-sensing materials to drive activation and produce pumping power.

Experimental (1) Photo-sensing biomaterials can exist suspended in solutions with varying viscosities, and in particular cyanobacteria can exist in viscous gels. Fluid pocket activation based on the Saffman-Taylor instability (Figure 2-7) is largely governed by the difference in the viscosities between a displacing fluid and a displaced fluid. The objective for this research stage is to produce a viscous enough bio-photo gel such that fluid-tunneling can occur – whether by air, or by a non-viscous liquid solution. Experimentation with cyanobacteria gels, as well as displacing fluids, will be required. Potential limitations may be the degree to which these gels foul the surfaces of the cell. Experimentation with non-stick surfaces may be required. (2) Building on the work of McCormick et al., bio-photovoltaic cell components must be developed with fluid-tunneling capability (McCormick et al., 2011). From (1), a biofilm culture as a gel (viscous solution) must be developed. A line of tubing connected to a pump must also be integrated within the biofilm to control fluid pocket activation. A transparent cathode must also be integrated in order to allow optical variability. Almost certain limitations will be the degrees to which a gel biofilm, a line of tubing embedded within the biofilm, and regular fluid pocket activation each interfere with photosynthesis and power production – as the effect of these interventions has not been tested. Finally, an electrical component must be developed that reads an input electrical signal from the bio-photovoltaic unit and translates this into an output digital signal to a pump, in order to regulate fluid pocket activation appropriately. This must compliment a ‘brain’-like algorithm that determines when, and to what degree, fluid pockets should be generated depending on a range of external and internal inputs. A limitation may be scale. Figure 9 shows the design of a bio-photovoltaic unit, building on a device developed by McCormick et al. (McCormick et al., 2011).

Figure 9: Design of a bio-photovoltaic device to extract current from a viscous biofilm culture. Image: Raphael Kay, extracted from research by McCormick et al., 2011.


Importance A colleague and I have engineered a thermally and optically adaptive building skin modeled from chromatophore cell activation beneath the skin of sea creatures. This research represented the first fluidpocket-activated building skin with thermal and optical control. I propose, now, to build on this work, incorporating light-harvesting materials within a building skin. This will accordingly represent the first design of an adaptive and controllable building-integrated photo-bioreactor, able to sequester carbon, produce biomass and usable thermal energy, and control air quality, while importantly adapting to dynamic thermal and optical environments. With bio-photovoltaic integration, this will also represent the first entirely closed-loop, self-sensing, self-powering, and self-actuating adaptive window membrane – fuelled by the very material of which it is made. In the context of a changing climate, and one in which buildings make up a significant portion of our energy and carbon footprint, this building skin will serve as a climateadaptive, carbon negative, and energy-efficient model for future research.

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Profile for rafimkay

Research Proposal  

The research proposal for an entirely closed-loop, self-sensing, self-powering, and self-actuating adaptive window membrane – fuelled by the...

Research Proposal  

The research proposal for an entirely closed-loop, self-sensing, self-powering, and self-actuating adaptive window membrane – fuelled by the...

Profile for rafimkay
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