Abstract

Dynamical oil-water systems such as droplets display lifelike properties and may lend themselves to chemical programming to perform useful work, specifically with respect to the built environment. We present Bütschli water-in-oil droplets as a model for further investigation into the development of a technology with living properties. Otto Bütschli first described the system in 1898, when he used alkaline water droplets in olive oil to initiate a saponification reaction. This simple recipe produced structures that moved and exhibited characteristics that resembled, at least superficially, the amoeba. We reconstructed the Bütschli system and observed its life span under a light microscope, observing chemical patterns and droplet behaviors in nearly three hundred replicate experiments. Self-organizing patterns were observed, and during this dynamic, embodied phase the droplets provided a means of introducing temporal and spatial order in the system with the potential for chemical programmability. The authors propose that the discrete formation of dynamic droplets, characterized by their lifelike behavior patterns, during a variable window of time (from 30 s to 30 min after the addition of alkaline water to the oil phase), qualify this system as an example of living technology. The analysis of the Bütschli droplets suggests that a set of conditions may precede the emergence of lifelike characteristics and exemplifies the richness of this rudimentary chemical system, not only for artificial life investigations but also for possible real-world applications in architectural practice.

1 Introduction

Living technology refers to a broad spectrum of interventions with differing relationships to the phenomenology of life, which include: being integrated as functional components within a living thing that do not possess an innate agency (e.g., hip implants), actively participating within a living system to create designed outputs (e.g., genetic engineering, reproductive technologies, stem cells), and reproducing phenomena that are arguably lifelike, yet do not share the same materiality as biological systems (e.g., the Internet, artificial intelligence, domestic robots, lifelike chemical systems). This article aims to describe a system compatible with the living technology portfolio, which is a non-biological chemistry that exhibits lifelike behavior and creates outputs that potentially can be designed and engineered with particular relevance to the built environment.

The principles of self-organizing chemistry can be observed in the complex, diverse range of pattern formation in nature. This occurs at many different scales that all follow the same rules of physics and chemistry, from cosmic phenomena to the structure of microorganisms and down to the nano scale. Throughout the ages architects have drawn upon the patterns and phenomena of nature for design inspiration and physical solutions to address real-world challenges. Whereas R. Buckminster Fuller supposed that these drivers were mathematical and looked to digital computing to explore generative forces, Antonio Gaudi explored the physical and chemical imperatives of materials that underpin biological systems, through his unique architectural style. To conduct his experiments, Gaudi created a set of unique and individually crafted elemental forms by suspending clay in hanging cloths during the construction of La Sagrada Familia, and let the forces of gravity shape the material. These material self-organizing imperatives were then used to generate his unique style of “organic” design. Unlike most architecture, which normally follows a top-down blueprint, Gaudi controversially assembled the architectural components using a bottom-up approach. He allowed the rules of gravity to generate the cathedral's design rather than impose his own personal inclinations. This technique created a completely different look and feel to his architecture, which designers from all disciplines are still trying to reproduce today [3].

Growing interest in the field of architectural sustainability has created interest in the application of dynamic materials that can respond in real time to environmental changes [5]. Bottom-up approaches, such as Gaudi's, based on the local interactions of materials and simple, self-organizing chemical systems to solve complex design challenges, are now routinely used. Frei Otto's 1972 design for the canopy structure of the Munich Olympic stadium [6] was produced by using wire frames and soap bubbles to create an instant experimental answer to this challenging mathematical problem. However, the study of form and pattern alone is not sufficient for addressing changing environmental conditions, and there is a need for added functionality in the application of bottom-up solutions in architectural practice that venture beyond structural geometry and exploit the functional aspects of other lifelike strategies, such as metabolism, movement, growth, and repair [4].

The Bütschli system comprises a pattern progression that exhibits features of interest to the living technology portfolio that may offer the kind of design and engineering solution that architects are searching for. At a critical stage within the evolution of the system, droplets appear that can act as a dynamic container in which materials can be distributed in time and space. This is in keeping with the current interest in more environmentally compatible design and engineering solutions as an adjunct and possible alternative to industrial, machine-based practices. In an appropriate context, programmed dynamic droplets might address challenges in the built environment that are not readily amenable to mechanical solutions and represent a systems science approach to architectural design, which blurs the distinction between artificial and natural living systems and, by implication, the boundary between the built environment and the landscape [2]. The solutions of particular interest are time and space based and engage challenges such as sequestration of pollutants, or growth and self-repair of building materials. Although such materials do not yet exist in practice, basic scientific research suggests that these approaches may be possible [18]. The Bütschli system was identified as a model system that warranted further investigation, to take the first set of next steps regarding potential applications of lifelike chemical systems toward the design and engineering of living technologies, with possible real-world applications in the built environment.

2 The Dynamic Bütschli Droplet System

In 1898 Otto Bütschli first described a dynamic water-in-oil droplet system using potash and olive oil as reactants, in which he observed the genesis of an artificial amoeba with pseudopodia (cytoplasmic extensions) that behaved in a lifelike manner [11]. His aim was to make a simplified experimental model to explain the plasticity of body morphology and movement, purely on the basis of physical and chemical processes such as fluid dynamics and surface tension [10]. Bütschli's original experiment was documented with hand drawings. Although various research groups are investigating other dynamic chemical systems that use amphiphiles such as reverse micelles (water-in-oil droplets stabilized by a surfactant) [30, 31] and the behavior of oil droplets in aqueous media [19, 33], no photographic documentation of the Bütschli system of droplets appears to exist in the contemporary literature. Although man-made, and in that sense artificial, the lifelike performance of the Bütschli system provides an opportunity to consider the emergent characteristics as a subset of living qualities in order to achieve a more thorough understanding of the system as a whole. However, there is no classification system to characterize dynamic lifelike chemistries, although Carl Linnaeus [24], in Systema natura (1735), imposed an order on natural systems, which included three domains—animal, vegetable, and mineral—and which therefore embraced both living and nonliving materials and facilitated a comparative understanding of these systems by appreciating similarities and differences. Of interest is Linnaeus' taxonomy of stones, which he asserted possessed some of the properties of living things. In particular, Linnaeus asserted that stones grew by way of an accretion process, such as when sand aggregated and became sandstone or when the apparent clumping of clay particles formed limestone. He also included the formation of quartz in his classification system, which he proposed was due to a “parasitic” mechanism. However, minerals were dropped from taxonomic classification during the eighteenth century and are absent from Lamarck's 1809 classification scheme Zoological philosophy [21], which focuses exclusively on the cataloging of animals. Additionally, Ernst Haeckel's famous 1866 “tree of life” [16] based on Charles Darwin's taxonomic diagram [13], equated phylogeny with the story of evolution. Minerals were not considered as part of that story, and therefore are not featured in subsequent phylogenetic ordering systems. The authors of this article speculate that the omission of minerals from a scientific ordering of the natural world may also have been, at least in part, influenced by the popularization of Louis Pasteur's germ theory [29], which refuted a widespread belief in spontaneous generation, whereby life was thought to be created directly from inert matter.

The approach taken in reporting our observations bears relevance to current systems of classification used in biology and natural history that may help relate nonliving phenomena to biological systems through a description of the pattern morphology. There is much to be learned through comparative analysis, and the results in this document are an attempt to construct an understanding of the lifelike properties of the Bütschli system as the basis for further study. An examination of this system also aims to establish some guiding features and principles that identify its potential for development toward living technology.

3 Method

The experimental design followed was a modern version of Bütschli's original ingredients (potash and fresh olive oil). A 0.2-mL drop of 3 M sodium hydroxide was added to olive oil in a 3-cm-diameter Petri dish, which was filled to a depth of 0.5 cm with extra virgin olive oil. This initiates a saponification reaction, in which the triglycerides of the olive oil are cleaved to produce free fatty acids and glycerol. The main ingredient of olive oil is oleic acid, which constitutes 61.09% to 72.78%, depending on the source [25]. The same brand of oil, Monini extra virgin from Spoleto, Italy, was used exclusively in this experiment, but it is not known whether different bottles came from the same production batch. All ingredients were used at room temperature. Over three hundred replicate experiments were performed under these standard conditions. Systems that included a titration of NaOH were also performed.

Controls included adding a 0.2-mL drop of water to a 3-cm-diameter Petri dish filled 0.5 cm deep with olive oil, and also adding 0.2 mL of 3 M sodium hydroxide to a 3-cm-diameter glass bottom Petri dish filled 0.5 cm deep with canola oil (rapeseed), from Cargill Oil Packers, which is around 85% oleic acid [35].

The behavior of the system was characterized in detail using a Nikon Eclipse TE2000-S inverted microscope with Photometrics Cascade II 512 camera and in-house software.

4 Results and Observations

The breaking up of the alkaline droplet in the oil could be clearly seen with the naked eye (Figures 1 and 2 within Table 1), producing smaller droplets whose diameters varied between a millimeter and a centimeter and producing turbid deposits of soap in the dish. In the case of the water-in-olive-oil control, no breaking up of the droplet was observed, and in the case of adding 3 M sodium hydroxide to olive oil, the alkali droplet dispersed into smaller droplets but did not show the pattern progression, dynamism, or production of material observed in the Bütschli system.

Table 1. 

High-energy, chaotic phase: Birth phase from 0 s to 5 min following addition of sodium hydroxide droplet to olive oil.

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Additional experiments were also carried out under the same conditions to establish the concentration range of sodium hydroxide that would produce the characteristic Bütschli pattern formation, which was established to lie within the 3 to 5 M range. At concentrations less than 3 M the droplets possessed little dynamism or visible crystal formation, although the droplet gradually broke up over the course of several minutes (around 3–10 min) to form droplets. The characteristic sequence of patterns typically observed at higher molarity was not observed. At concentrations greater than 5 M the system quickly became inert and instantly formed a crystal layer at the oil-water interface, quenching the reaction and preventing the appearance of dynamic patterns.

When canola oil was used as the medium for sodium hydroxide in the active range for pattern production seen in the Bütschli system (3–5 M), the activating droplet broke up immediately into smaller, regular droplets in the oil field, but neither was sequential, organizing activity observed, nor was any formation of product visible.

In the study group of experiments (0.2 mL of 3 M sodium hydroxide added to extra virgin olive oil), the Bütschli system demonstrated a repeatable sequence of events with identifiable characteristics, recorded in still photography and movies. The Bütschli droplets were observed and studied in a similar manner to the one that is currently used to study and report on single-celled organisms such as protozoa or bacteria. No staining was necessary to observe the Bütschli droplets, due to their refractive index, and they ranged from the micro scale to around a centimeter in diameter. The authors consider the lifelike qualities of the Bütschli system as being sufficiently striking to justify using a method of observation normally applied in a natural history context for the study of the living characteristics of a system, with the intention to consider experimentally what kinds of organizing principles appear to be at work in the transition from inert to living matter. The findings are described in figures and movies that are organized into different phases of pattern progression in Tables 1,2345.

Table 2. 

Organization and droplets: primary morphologies. Life phase (0–30-s time interval following addition of 0.2-mL droplet of sodium hydroxide to oil).

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Table 3. 

Organization and droplets: primary behaviors. Life phase (0–30-s time interval following addition of 0.2-mL droplet of sodium hydroxide to oil).

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Table 4. 

Quiescence: Death phase (0–30-s time interval following addition of 0.2-mL droplet of sodium hydroxide to oil).

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Table 5. 

Secondary metabolism—internal programming: metabolic phase (continuous).

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4.1 Context (Habitat)

Bütschli droplets are entirely artificial and exist only in a laboratory when specific agents, olive oil and strong alkali, are combined in a process of saponification. They have not been reported in nature.

4.2 Primary Characteristics (Based on the Primary Metabolism of the Droplet)

Bütschli droplets possess a primary metabolism saponification, which spontaneously occurs at the interface where strongly alkaline water and olive oil meet. This reaction releases both energy and products in the form of surfactants that modify the oil-water interface. It is responsible for both the lowering of surface tension, allowing the droplet to deform, and the flow of liquid, which results in morphological fluctuations, movement, and splitting of the droplet. As the droplets move through their environment, they can consume the olive oil, processing it by the saponification reaction. In addition they use the alkali reactant within the droplet as fuel. Bütschli droplet movements last from several seconds to around 20 min. The activity of any particular droplet is not predictable, and success in creating the system is variable and possibly dependent on the quality of ingredients, with additives or degradation products in the olive oil decreasing the reactivity of the system. As the active droplet system progresses in time, the activity of the system slows as it approaches chemical equilibrium. Due to both the accumulation of inhibitory products and the consumption of fuel, the droplet eventually becomes inactive.

Typically water droplets in oil self-assemble and do not dissipate, due to the hydrophobic effect. However, in the Bütschli system, once the saponification reaction begins at the interface between the oil and water, the tension holding the droplet intact relaxes considerably, and the droplet begins to distort and spread with increasing surface area. The droplets contain enough energy to split up into smaller droplets, which are then able to move about in the olive oil environment (Figure 1, Figure 2, and movie S1 in Table 1). Notably, a control with water at neutral pH produces a spherical droplet in the olive oil that does not react, spread, split, or behave like the alkaline droplet, and an alkaline droplet in canola oil splits into smaller droplets but without pattern formation.

In the reactive system, the chemical potential is combined with physical instabilities and fluid dynamics to result in the movement of droplets associated with the production of a soapy crystalline deposit that spontaneously forms at the oil-water interface. Distinct phases characterize the progression of the ingredients from a highly energetic dissipative system to one that has reached equilibrium. During this progression, mass interactions are observed in the system as emergent phenomena, wherein droplets and populations of droplets typically exhibit lifelike behavior such as movement and the production of microstructures. Even when baseline conditions are uniform (temperature, pressure), these agents show a range of distinct characteristics that lend themselves to classification through distinct morphological and behavioral types that emerge from the self-organizing field (see movie S2 in Table 1).

4.3 Stages

Osmotic growths like living things may be said to have an evolutionary existence, the analogy holding good down to the smallest detail. In their early youth, at the beginning of life, the phenomena of exchange, of growth, and of organization are very intense. As they grow older, these exchanges gradually slow down, and growth is arrested. With age the exchanges still continue, but more slowly, and these then gradually fail and are finally completely arrested. The osmotic growth is dead, and little by little it decays, losing its structure and its form. [22, p. 151]

In 1911, Stephane Leduc studied the behavior of chemical solutions mixed together. He noted that they produced strikingly lifelike results, which he described as “evolutionary,” and he likened their behavior to that of living systems, using terminology that is normally associated with the life cycle of an organism. This article builds on Leduc's analogy and proposes a progression of events in the Bütschli system that suggests possible consideration and reflection on natural phenomena.

The stages of the lifespan of Bütschli droplets are:

  • (a) High energy, chaotic [birth] (0–5 min)

  • (b) Organization, droplets [life] (30 s–30 min)

  • (c) Quiescent, crystalline osmotic structures [death] (0–30 min)

4.3.1 High-Energy Chaotic Stage

4.3.1.1 Field of Fire and Ice

When the alkaline droplet first breaks up in the oil field, it self-organizes into a polarized, dynamic field with a characteristic appearance. The active, leading front end of the field moves outward, away from the point at which the water droplet entered the oil field, and produces ripples as it moves through the oil medium, producing a flamelike appearance. The leading edge is where oil molecules are consumed in the metabolism of the droplet. The trailing back end accumulates the product soap crystals, which are swept backward by the movement of the system and, in the case of sodium oleate, appear like ice crystals. In this initial dynamic and energetic stage, smaller droplets can break off of the moving front and then continue to display the same reactive motion. In the initial phase of self-organization these fields look like a moving island of fire and ice, and it is possible to determine which direction the field is moving by its morphology. See Figure 3 and movie S3 in Table 1.

4.3.1.2 Shells

As the polarized field of self-organizing activity progresses, it starts to break up due to lowered surface tension and fluid dynamics as a consequence of saponification and the presence of soap crystals. The first recognizable structures that appear are turbulent, shell-like ones and probably represent dissipative structures that are throwing away energy to remain stable (Figure 4 in Table 1). These kinds of nonequilibrium phenomena were noted by the chemist Ilya Prigogine [15, 28], who observed their occurrence in nature in structures such as snowflakes and vortices (cyclones and whirlpools); they are also found in living systems. Video footage suggests that the droplet shells are manifolds, rather than chaotic spheres of activity, which burst out of themselves like Russian dolls; it also suggests that these droplets are in a high energy state, as shown in movie S5 (Table 2). Some of the shells suddenly collapse and form crystalline deposits. Others eventually stop splitting and bursting out of themselves and enter a new phase of organization as lifelike droplets. It is not possible to predict which shell-like formations will occur, or say from these initial experiments what proportion of them will become self-organizing droplets, as their distribution is outside the field of view of the microscope and they cannot be identified with the naked eye.

4.3.2 Organizing Droplets

After the chaotic formation phase, the resulting droplets are able to move around, sense their environment, modify their surroundings, produce complex structures, and even interact with each other. The interactions and systems are complex, and it is not possible to predict the outcomes of the various droplet types. Yet, there are definite patterns of behavior and interactions that offer a pedagogical view of the system.

These characteristics will be discussed as:

  • (a) Primary morphologies—structural characteristics encapsulating the state of the system: droplets, droplets with product, droplets with extended osmotic crystalline structures, polyps, compound structures.

  • (b) Primary behaviors—dynamic interactions that lead to more complex phenomena: interfacing, mirroring, population dynamics.

4.3.2.1 Primary Morphologies

Droplet: The first form that an organized protocell adopts is a polarized, free-moving droplet, like the one shown in Figure 5 (within Table 2), which possesses a fundamental direction partially conferred by its original position in the primary field of fire and ice. Propelled by its primary metabolism, the droplet moves in a trajectory away from where the original droplet met the oil field, influenced by inhibitors or attractants in the medium, as shown in movie S5 (Table 2). It appears that protocells modify their surroundings as they pass through a medium [17, 20] and create chemical changes in the field that the protocell senses. The identification of these substances is under characterization for the Bütschli system.

Droplet with Product: Depending on the speed of the chemical reaction and the environmental conditions, a small deposit of crystals appears at the trailing end of the active droplet as the metabolism progresses (see Figure 6 and movie S6 in Table 2). The physical properties of the crystals cause downstream effects on the body of the droplet that influence its locomotion, and ripples can be observed as the gradually increasing load is dragged behind the active front. This gives rise to jellyfishlike or wormlike morphologies and different kinds of movement such as peristalsis-like locomotion.

Droplet with Extended Osmotic Crystalline Deposit: Bütschli droplets undergo progressive physical changes as they continue to consume their primary metabolism and interact with environmental cues, resulting in the production of osmotic microstructures that grow at the trailing end as the droplet moves around the environment (see Figure 7 and movie S7 in Table 2). These extended products consist of soap deposits with an inner core of aqueous medium, which is visible with fluorescence microscopy on adding a hydrophilic dye (0.25 percent fluorescein by weight) to the droplet.

Stephane Leduc described similar forms that he was able to produce by the mixing of various solutions, as osmotic structures, in his 1911 publication The mechanism of life [22, pp. 123–146].

As Bütschli droplets perform their primary metabolism, soap crystals travel to the back end of the droplet and accumulate at such a speed and density that they form a tubular, taillike extension of material (see Figure 8 and movie S8 in Table 2). Bütschli droplets can combine to make compound osmotic microstructures when droplets fuse.

Polyps: Under very highly alkaline conditions such as 4–5 M solutions of sodium hydroxide, the Bütschli droplets respond in a characteristic way in the oil field by producing long, thin tubes of crystalline product that create a scaffolding that closely follows the movement of the droplet and is intimately linked to and shaped by its movement (see Figure 9 and movie S9 in Table 2).

Compound Structures: The sequential movie stills in Figures 10 and 11 (Table 2) were taken from movie S10 at the moment when two Bütschli droplets fused to produce a new growth point. The short osmotic structure of one droplet meets a longer branched one to produce a complex microstructure, which is just out of focus. A spiral structure is also clearly visible, which has most likely been formed by another droplet passing through the oil field, twisting and advancing simultaneously.

4.3.2.2 Primary Behaviors

Interfacing: Bütschli droplets are attracted to each other, and when they meet they do not usually fuse, but instead align their interfaces, producing a very dynamic, oscillating, yet loose relationship between the oil-water boundaries of adjacent droplets, so that they appear to be holding a chemical interaction with each other. Dynamic interface connections seem to influence droplet behavior and generate different outcomes depending on the number of participating agents. It was not possible to determine the exact number of participating agents that constitute a systemically different kind of interaction between small and larger groups in these experiments, and it is not known if there are specific thresholds for the emergence of different patterns of interaction. More research is needed to further characterize the observed effects. Perhaps a more precise delivery system for the production of discrete numbers of droplets will be to be useful.

Different kinds of interfacing behaviors are observed:

  • (a) Between individuals (2)

  • (b) In small groups (more than 2, less than 6)

  • (c) With larger populations (6 or more)

Individual droplets moving independently can collect together, forming a shared contact area. Over time this zone of contact fluctuates, and the droplets distort themselves as they reach for a point of contact and then retract repeatedly. As shown in Figure 12 and movie S11 (within Table 3), a small Bütschli droplet is situated between two larger ones, where an active interface exchange is constructed between them. There is another point of contact between the two larger droplets below the small one. In general, Bütschli droplets appear to make multiple points of contact in an interface zone. It is not clear if any material is exchanged during this process, but the intensity of the contact decreases as product builds up and the metabolism, which provides the energy for interaction, runs down.

Mirroring: Bütschli droplets that establish an early connection with each other have been observed to mirror each other's appearance and behavior. In Figure 13 within Table 3), two agents have established an active interface connection and have produced similar broad-based osmotic structures that anchor them. Smaller droplets appear to be attracted to this site of intense activity, and a second site of interfacing has been established between the two large droplets by a smaller one (see movie S12, Table 3).

Population Dynamics: Bütschli droplets appear to be attracted toward sites of intense metabolism. It is likely that a product of the primary metabolism is acting as a chemical attractant, though this has not been scientifically verified. Large droplets appear to be able to strongly attract smaller ones, resulting in a commonly observed satellite phenomenon where smaller agents frequently orbit larger ones (see Figure 14 and movie S13 in Table 3).

Chains of interfacing Bütschli droplets are frequently the first formations that can be seen in the early self-organization process. This occurs where individual droplets have stopped traveling but are engaged in intense activity at their interfaces with neighboring droplets. These chains appear to stimulate the metabolism of participating droplets and rapidly encase the active interfaces with crystals, as shown in Figures 15 and 16 and also in movies S14 and S15 (within Table 3).

As Bütschli droplets are drawn toward each other, they form larger populations. They then undergo a range of interactions that change both the behavior of the individual agents and their appearance. Behavioral changes are likely to occur as the result of metabolic products that attract and/or repel individual droplets, as well as the accumulation of product that progressively reduces the area that the droplets have available as an active interface, as shown in Figure 17 and movie S16 (within Table 3). It is likely that a product created by the metabolism causes droplets to be attracted to each other and may be responsible for characteristic emergent behavioral differences observed between small populations (two to six interacting droplets) and larger groups (more than six droplets). These numbers are a guideline based on observation and familiarity due to working with the constantly changing system. They are estimated from the frequency of observation of transient, multiple formations of interacting droplets during the life cycle of the Bütschli system. Even if the delivery of the reagents becomes more precise, finer control of delivery itself is unlikely to create specificity within the constantly changing system until the Bütschli system itself has been better characterized.

Bütschli droplets appear to possess both attractants (stimulants) and inhibitors (repellents) of droplet activity. Synchronous group behavior has been occasionally observed that results from the recruitment of a number of droplets in proximity. In larger groups a different, emergent quality has been observed several times that is characterized by sudden group behaviors such as scattering, as shown in Figure 18 and movie S17 (Table 3). These group interactions may be likened to quorum sensing [27] in certain species of bacteria when, at a threshold number of communicating bacteria, a signal is passed between members that causes a change in the products expressed by the colony.

4.3.3 Quiescence

As the metabolism of the Bütschli droplets consumes their bodies and surroundings, it leaves skins of crystalline materials behind, breaking free of the structures when they produce too much drag. Over time the metabolism is less vigorous, the droplet moves more slowly, and more crystals accumulate over a larger region of the oil-water interface, partially occluding it and reducing the amount of product produced. The droplet enters a stage of chemical oscillations, where it appears to pulse until it finally stops moving when the area available for chemical exchange is occluded entirely by crystals.

4.3.3.1 Chemical Death

When a Bütschli droplet is incarcerated by its product, the active interface is blocked, preventing the metabolic processes from working and rendering the system quiescent. This amounts to a chemical form of death, as shown in Figures 19 and 20 and also in movies S18 and S19 (within Table 4).

4.4 Secondary Characteristics

Bütschli droplets can be designed to create a range of different products by chemically programming them with a second metabolism delivered into their surroundings. The droplet of aqueous inorganic salt is contained in the olive oil field and responds to the passage of Bütschli droplets in a manner depending on their contact with alkali in time and space. In this way the Bütschli droplets can be engineered to make secondary forms such as shells, using different kinds of ingredients. This programming is a different process from the fundamental chemical reaction that exists at the oil-water interface and confers additional properties on the droplets, such as the ability to deposit magnetite as shown in Figure 21 (Table 5). The resultant materials produced are the consequence of environmental interactions (the oil field contains the inorganic matter spatially and temporally, and only interacts should a droplet with a primary metabolism pass through the reservoir of material) as well as intrinsic interactions (inorganic chemistry), and because of their environmental contingency they can produce a wide range of forms depending on the distribution, their chemical programming, and the environmental context.

4.4.1 Secondary Forms

4.4.1.1 Magnetite-Producing Droplets

In this preparation, alkaline water droplets are added to an oil medium at the same time as droplets of ferrous and ferric salts prepared according to an aqueous ferrofluid recipe with a molar ratio Fe3+:Fe2+ of 2:1 [9], which produces magnetite when the iron solutions come into contact with alkali. The alkali oxidizes the iron salts on contact and produces a layer of magnetite, a form of iron oxide that is black and magnetic. In this particular case the movement of the droplets through the oil medium and their subsequent interactions have produced a sculptural form of magnetite as shown in Figure 21 (within Table 5).

4.4.2 Secondary Behaviors

4.4.2.1 Locomotion

The Bütschli system is sensitive to its environment and changes its morphology and behavior in space and time and according to the nature of its metabolism. In this way the drivers behind the Bütschli patterns are different from those behind the formation of bubbles, whose patterns emerge as a consequence of the amphiphilic bilayer interface being supported by internal air pressure and are not fueled by a specific chemistry. Over their active life span, Bütschli agents can undergo a wide range of changes where form and movement are intertwined. The specific changes are different for each agent, as Bütschli droplets operate according to complex interactions and in the context of an equally complex environment. However, the Bütschli system exhibits a minimum complexity, and it has been possible to observe repeatable patterns appearing when the two complex systems interact with each other. In movie S6 (Table 2), an individual Bütschli droplet changes its appearance as it grows a crystalline skin at the posterior pole. This causes drag and causes the agent to alter its form of locomotion as it crawls over the bottom of the Petri dish, dragging the weight of the crystalline osmotic structure behind it. The degree of plasticity and behavioral change in this system is remarkable, as it does not require any central programming from an organizational molecule such as DNA to initiate the state change. This behavior suggests that rapid morphological changes without DNA not only are possible but may occur rapidly (compared with the time scales associated with more complex biological systems) in systems that possess only a few interacting chemistries.

4.4.2.2 Self-Replication

The Bütschli system does not replicate, and although droplets are observed to divide and fuse, they cannot pass any specific information to other droplets, as they do not have a specific chemical program as nucleotide polymers do. This adds more intrigue to the indeterminate status of Bütschli droplets between living and nonliving, as they have a very low degree of autonomy.

5 Discussion

The ongoing search for increasingly lifelike materials for use in the built environment raises new opportunities for the development of the living technology portfolio. Materials that can deal with ongoing real-time changes in their surroundings by harnessing living properties, without needing to be preprogrammed with an all-embracing palette of future possibilities, raises the potential for new paradigms in practice for the design, planning, and engineering of our homes and cities. The advent of these desirable solutions is accompanied by new technological challenges that require an understanding of how it is possible to design with emergent phenomena. The Bütschli system and other lifelike chemistries, which have been observed since the nineteenth century by researchers such as Frederic Ferdinand Runge [32], Mortiz Traube [34], Raphael E. Liesegang [23], Boris Pavlovich Belousov [8], Vladimir Yevgenyevich Zhabotinsky [36], and more recently by Lee Cronin and colleagues [12], provide new platforms for exploring how design and engineering principles can be meaningfully applied to self-organizing, material systems.

These findings are not only of interest to the architectural community, but also of increasing relevance to the scientific community in understanding the nature of life. The Bütschli system, possessing only some of the hallmarks of living systems, is not alive [7], but an analysis of the analogies between the Bütschli system and biology may assist in further understanding the nature of the transition between living and nonliving matter. It may help identify systems and conditions in which lifelike phenomena could occur. While no unequivocal definition of life exists, it is possible to create a nonliving system that appears lifelike. We may eventually understand what we mean by life through creation and further reflection, and Bütschli droplets offer a model for research in that they can be thought of as being minimal agents for lifelike behaviors that are irreducibly complex. In this article the various morphologies and behaviors of the Bütschli system indicate that self-assembly alone is not enough for lifelike behavior [18], that is, for the appearance of persistent, dynamic morphology and behavior. Livingness may be a different phenomenon from life, or one part of a continuum of phenomena. Attempting to define livingness may assist in identifying new systems that may be explored in a design and engineering context for the production of living technology. Also, there may be value in establishing a basis for classifying chemical living phenomena to characterize the kinds of possible platforms available for design and engineering purposes. We propose that livingness (as opposed to life) may be characterized by:

  • (a) A persistent interface in an open system (for the transfer of energy to take place across)

  • (b) Metabolism (linked to any mechanism to keep the system away from equilibrium)

  • (c) Architecture (internally structured spatial/temporal distribution)

  • (d) Environment (external structure)

The above criteria that establish conditions for livingness are consistent with those put forth by the National Research Council [26], where the circumstances necessary for life are stated to be an open nonequilibrium environment, solvents in liquid form, and the capability of forming covalent chemical bonds. However, we make a further clarification with respect to their relevance for identifying potential new chemical living technologies in that they engage with the phenomenology of biological life. This clarification is made with respect to their internal versus external structure and internal mechanisms that allow the system to escape or at least delay equilibrium. We explore the mechanism of self-movement in this article, but another potential mechanism for escape from equilibrium is reproduction. Our criteria are necessarily more general than the frequently used container, metabolism, and information model derived from the chemoton model [14], which is used to characterize life, as our criteria propose to assist in identifying a broader range of conditions through which new kinds of chemical living technology could be identified, or be used in design and engineering.

The self-organizing Bütschli system exhibits a recognizable series of chemical patterns that result from the process of saponification and that are visible to the naked eye. Closer examination under the microscope provides further information about the morphology of the chemical waves. During the evolution of the pattern (the lifelike phase ranging from 30 s to 30 min after formation), the system produces dynamic droplets that exhibit technological potential, since they are enclosed in a discrete boundary and could be used as a container for the spatial and temporal distribution of specific chemistries, or metabolisms. These droplets produce microstructures at the oil-water interface and are sensitive to chemical and physical fluctuations in their surroundings. When Bütschli droplets come into contact with discrete chemistries such as aqueous ferrofluids, they can produce spatially distributed mineral deposits with sculptural qualities. It is anticipated that applying precision-guided devices, such as 3D modeling software coupled to 3D printing devices, will provide opportunities to design and engineer with bottom-up chemical solutions to provide a development platform for dynamic, chemistry-based living technologies with potential architectural applications. Yet, Bütschli droplets are not autonomous. They can be orchestrated by manipulating flows of chemical information and instructed to consume or produce selectively in a given environment, as shown with other droplet systems [19].

Bütschli droplets also exhibit population-scale behavior and resist fusing with adjacent droplets through dynamic boundary interactions. This study suggests that interacting droplets exhibit as yet uncharacterized chemical periodicity of attraction and repulsion at the oil-water interface between droplets. This appears to prevent even densely packed arrangements from fusing and maintaining the self. The periodic interfacing between Bütschli droplets enables them to remain mobile, yet in the vicinity of each another. This prolonged (lasting from 30 s to 30 min), sensitive, dynamic mobile interaction with neighboring droplets creates an opportunity for performing complex material calculations. These kinds of dynamic technological interactions are in keeping with the principles being applied to alternative forms of computing [1], which are also of interest for creating the built environment. Bütschli droplets may have future real-world applications, for example, by functioning as potential lifelike “hardware,” they can serve as containers. They may have applications in the new field of unconventional computing [1] as a lifelike vehicle to distribute second-order chemical systems in response to environmental stimuli. As a technology, Bütschli droplets not only respond spontaneously to their context, but can also be programmed to behave in ways that are directly related to the applications designed by humans. The Bütschli droplets also constitute a chemical programming platform and can be designed for use in a range of situations. For example, Bütschli droplets could be used as a delivery system for environmental pharmaceuticals such as smart paints, or surface coatings with the potential to fix carbon dioxide into inorganic carbonate in response to environmental cues [4]. The design and engineering of chemical systems that exhibit lifelike behavior create a platform for the potential development of new kinds of technology that can integrate living, nonliving, and technological systems and may provide new opportunities in addressing environmental challenges [3].

Potential applications of the Bütschli system are also relevant to the practice of science and include use in origins-of-life research as models for lifelike systems that operate without the help of sophisticated nucleic acid information-function systems. This system has the advantage of being able to respond directly to environmental changes without needing to interpret the observations using genetic mechanisms. Although Bütschli droplets are complex entities and characteristically behave in ways that cannot be predicted, their outcomes are constrained within the chemistry and the physics of their system and demonstrate a range of recognizable patterns for observers to report and discuss. The Bütschli system therefore may provide a model that can serve as a counterpart against which contemporary explanations of cellular responsiveness and regulation may be tested.

Here we have presented an established system for creating artificial lifelike structures that has been analyzed by microscopy. Certainly there are many aspects of the Bütschli droplet system that have little to do with the structure, behavior, and evolution of extant life, but we highlighted all phenomena observed in this system, noting patterns both similar and dissimilar to living systems. By creating and observing systems and noting lifelike properties, we may be able to deepen our understanding of living systems. Additionally the Bütschli droplet system provides an emerging model technology that provides an opportunity to test principles of design and engineering with emergence. At the same time we may gain a better understanding of the design of new lifelike technologies. Certainly a greater understanding of complexity, living phenomena, and how these can be classified and described is necessary. The Bütschli system provides one model that can help further investigation of these fundamental issues to develop the necessary tools, methods, and approaches for creating new ways of problem solving, which complement and may ultimately replace the object-centered, industrial approaches that are in use today.

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Author notes

Contact author.

∗∗

School of Architecture & Construction, University of Greenwich, Avery Hill Campus, Mansion Site, Bexley Road, Eltham, London, UK SE9 2PQ. E-mail: grayanat@yahoo.co.nz

Institute of Physics, Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark. E-mail: martin@ifk.sdu.dk