- to meter-scale building Danijel
, 
, Martin
The construction industry will have to find new ways of building to accomplish radical reductions of pollution and waste. 
Nano
and biotechnology along with information technology have the potential
to constitute a new building paradigm. The paper describes the concept
of nano-
to meter-scale building, which is based on this potential. The concept
is not focused on the application of nanomaterials like nanosilica or
carbon nanotubes, but on a new way of building, which unfolds from the nano into the meter range. It is based on bionanorobots, producing building materials using carbon extracted from CO2
in the air. Criteria and requirements regarding relevant technologies
are defined and compared to the current research in the fields of
bioengineering, nanorobotics, and characteristics and production of
carbon nanotubes. The paper also presents a concept of a new building
technology that would enable control and monitoring of construction at
the nano
level, as well as requirements regarding design methods and tools
including the building information model that will become the only
human input to the automated nano- to meter-scale building process. The paper concludes with suggestions for further research and development.
►
A digital model of a building is projected to a production surface. ►
Bionanorobots, powered and controlled by projected light, interpret
wavelengths into instructions. ► Build 3D carbon nanotube structures. ►
Grows from nano- into meter-scale and forms the building.
Keywords: Nano- to meter-scale building; Automated building; Nanotechnology; Nanorobotics; Biotechnology; Building information modeling
Development of the core nano and biotechnologies is leading to results that are extremely interesting for the production of buildings on the nano level, growing them on site from the nano
into the meter range. Although areas like nanorobotics, molecular
nanotechnology, programmable materials, and programmable cells are
still considered to be speculative to some extent, their fast
development encouraged our systematic research of new ways for modeling
and construction of buildings using bio-nano-technologies. The main motivation, however, was the recognition that, if designed in a sustainable way, the new ways of nano-
to meter-scale building (n2mb) could significantly reduce the many
negative impacts of traditional construction and operation of buildings
on the environment. The cement industry itself produces about 5% of
global man-made CO2 emissions [1], and there are vast amounts of other materials such as steel and glass that have to be produced, transported, and installed.
The
“vision of buildings that build themselves” is not new. It has been
often expressed by visionaries, but only as some future technology, for
which we have to wait. Zhu et al. in [2] wrote: “One of the ultimate goals of nanotechnology is molecular manufacturing based on self-assembly or self-replicating nano-machines.
Though there is increasing evidence indicating that molecular
manufacturing is possible, full molecular nanotechnology capability is
unlikely to be developed for at least one or two decades. However,
extensive efforts toward that goal – in particularly studies in
biomimetics to better understand and replicate or mimic nature’s
version of molecular nanotechnology – will have huge potential for new
materials and processes applicable to construction in the next
10–15 years.” The same authors have also noticed that “nanotechnology
R&D in the broad area of construction and the built environment
lags behind other industrial sectors.” Our motivation to begin with
conceptual top-down design of a nano-
to meter-scale building system before nanotechnology delivers the
necessary basic technologies is to accelerate the process. By
formulating the requirements we intend to encourage researchers in bio
and nanotechnology to direct their bottom-up research towards
them. With the interdisciplinary top-down and bottom-up research we
want to develop test beds in which we will be able to study the
concepts and develop technologies that will help the construction
industry to reach the ultimate goal, the fully automated nano- to meter-scale building.
The
main aspect in the presented concept is, however, information. It is
the essence of the building information model, which becomes the full
recipe for the realization of a building and is the only direct product
of human activity in the process. It integrates the documentation of
the building design with the instructions and controls to construct the
building by organizing the flow of information from the 3D model to the
nano-production level, thus enabling the control of the production process from the nano- to the meter-scale.
Nanotechnology
is based on the study of the control of matter on an atomic and
molecular scale. It has the potential to create new materials and
devices with applications in medicine, electronics, energy production,
and also construction. Typically, an atom has a diameter of a few
Ångstroms (1 Å = 0.1 nm = 10−10 m), a molecule’s size is a
few nm, and clusters or nanoparticles formed by hundreds or thousands
of atoms have sizes of tens of nm. There is a large body of literature
giving an overview of nanotechnology (e.g. [3], [4] and [5]),
but the origin of this encompassing field is often attributed to
Richard Feynman and his now legendary talk “There’s Plenty of Room at
the Bottom” [6] where Feynman laid bare both the potentials and challenges of developing nano-scale technology. Several years later another landmark was set by Drexler with his paper on molecular manufacturing [7].
In this publication, Drexler established his own vision of molecular
manufacturing by integrating Feynman’s concepts with his ideas of
fabricating objects with atomic specifications using designed protein
molecules. Drexler states that molecular manufacturing and the
construction of “nano-machines”
is a product of an analogous relationship “between features of natural
macromolecules and components of existing machines.” He additionally
includes a table that outlines, by function, the molecular equivalents
to macroscopic technologies. Drexler in his controversial book Engines
of Creation [8]
went a step further in predicting self-replicating nanorobots:
“Molecular assemblers will bring a revolution without parallel since
the development of ribosomes, the primitive assemblers in the cell. The
resulting nanotechnology can help life spread beyond Earth – a step
without parallel since life spread beyond the seas; it can let our
minds renew and remake our bodies – a step without any parallel at
all.” Although his theories of “gray goo” and molecular manufacturing
were later criticized, Drexler’s work had a profound impact on the
establishment of nanotechnology as a scientific field. With the
invention of the Scanning Tunneling Microscope in 1981 and the Atomic
Force Microscope in 1986 nanotechnology started to be developed through
the scientific method rather than through the conceptual and thus
untestable visions. The study of carbon Buckyballs, discovered at Rice
University in 1985/1986, and the manipulation of individual xenon atoms
on a nickel surface to form the letters IBM by Eigler, directed further
trends in nanotechnology research and Drexler’s ideas were put aside
for some time [9].
Self-assembly and nanorobotic manufacturing did, however, never
disappear entirely from the agendas of researchers, and it seems that
the practical and the visionary research paths are beginning to merge.
Although today most of the research and development in nanotechnology
is focused on applications in electronics and medicine, it is growing
exponentially in all directions (a Roadmap is given in [10]).
Many predict it will change our lives in the coming decades. In the
following subsections we will focus on areas of nanotechnology that are
related to the idea of nano- to meter-scale building: carbon nanomaterials, nanorobotics, and nanomanufacturing.
One important reason to concentrate on materials consisting of carbon only is that carbon nanomaterials can be designed to have a range of extraordinary properties. The other reason is to avoid pollution caused by material production and transportation. Therefore we have based our concept on extracting carbon from CO2 from the air on site.
Carbon-based
materials have found many applications as high-performance materials
where high strength and low weight are key concerns such as in
aerospace, professional racing, and civil engineering. The higher
performing carbon materials contain a larger portion of graphite and a
more crystalline structure. However most of today’s commercially
available products utilize carbon fibers of varying characteristics. These can vary in physical dimensions, carbon content and crystalline structure [11].
The widespread use of carbon materials over the past decades has proven
their value as a structural material. Recent advances in carbon
materials, e.g. Fullerenes [12] and [13],
offer a promise of carbon materials with properties not realized by any
other material type. One material of interest to both complement and
potentially supersede current carbon fiber materials are atomically precise carbon nanotubes (CNT).
Since the discovery of CNT in the early 1990s [14] there has been a concerted effort to both characterize and control nanotube properties through careful preparation during synthesis. The predicted properties of atomically precise CNT lend themselves well to a wide range of applications in electronics, thermoelectric and structural materials, and while commercial quantities of defect-free tubes are not yet available, CNT are beginning to find use in materials today [15].
The impressive properties of CNT make them especially appealing in use as structural and mechanical materials. The tensile strength of CNT has been measured to be in the 10 s of GPa with a Young’s modulus on the order of a TPa [15]. CNT have been shown to be chemically stable due to their unique geometric structure [16]. The increased use of CNT in commercial applications will depend heavily on better production methods with an emphasis on the control of physical properties and producing bulk quantities. However CNT are employed in a wide range of nanomaterials today. Many of these materials are composite materials created by combining CNT with other more conventional structural materials to enhance strength and other performance-related characteristics. This is especially true in polymer-based composite materials where the focus of carbon nanotube research has taken place [17]. However CNT are now finding uses in ceramic and metal matrix composites. Kuzumaki et al. [16] has reported an increase in hardness and Young’s modulus of Ti/nanotube composites when compared with pure Ti, and Zhan et al. [17] report a threefold increase in toughness in alumina-based materials with further progress expected.
Nanorobotics is an emerging field of nanotechnology that deals with the controlled manipulation of nano-scale objects [18].
So far interactions with atomic- and molecular-sized objects are based
on several approaches. Industrial nanorobotics use complex microscopes
(AFM – Atomic Force Microscope, or SEM – Scanning Electron Microscope [19]; strategies of nanomanipulation under various microscopes are shown in [20]) to control and sense nanomanipulation. A Sandia report [21]
gives a good overview of research in the field. Bio-nanorobotics is
focused on bio-inspired mechanisms, actuators, sensors and robots
evolving in biological environments [22], inventing new design methods and tools [23].
Molecular biomimetic is an emerging field in which hybrid technologies
are developed by using the tools of molecular biology and
nanotechnology. Polypeptides can now be genetically engineered to
specifically bind to selected inorganic compounds for applications in nano- and biotechnology [24]. This
approach is seen as very promising in the near future as we are
learning from nature how to design highly efficient and powerful
artificial nano-machines
for complex operations in diverse realistic environments, leading to
practical nanoscale applications in the not so distant future [22]. Currently, bio-nanorobotics development focuses on applications in medicine [25] and [26].
There are two main approaches to nano-scale manufacturing. These have been labeled top-down and bottom-up by the nanotechnology community [27]. Top-down manufacturing methods consist of conventional micro-fabrication techniques including nano-lithography and chemical etching [27].
A common characteristic of top-down technologies is the removal of
material from bulk material to create the final product. In contrast,
bottom-up manufacturing is an assembly process [27].
Its goal is to create larger and more complex structures out of smaller
basic components. Within the bottom-up approach, there are two distinct
models. The first is the assembly of discrete blocks much like a brick
wall is assembled from individual bricks or a virus capsid is assembled
from individual protein blocks [28].
The concept here is that larger structures are built up from smaller
discrete component parts or building blocks. Often in nature, as in the
case of a virus, this is accomplished through methods of self-assembly.
As defined by Fryxell [29]:
“Self-assembly is the spontaneous aggregation of molecules (or
particles) to form ordered, organized arrays. This aggregation can be
driven by a number of different attractive forces, such as van der
Waal’s attractive forces, Coulombic attraction, dipole–dipole
interactions, hydrogen bonding, and acid–base interactions.
Self-assembly can be used to create sheets, ribbons, helixes and
complex three-dimensional architectures, based on the nature and
orientation of these intermolecular forces.” The second model is
analogous to the way a fingernail grows, new structural material is
added continually, in this case the protein keratin. The newly formed
material merges with the existing structure, pushing the nail further
out [30].
The continuous deposition of new material onto existing materials
offers a second model distinct from assembly of discrete units. This
process more resembles structural growth.
According to the Nanoforum report: Nanotechnology and Construction [31],
the use of nanotechnology in construction has so far been focused on
enhancing the characteristics of construction materials, including
concrete, steel, coatings and glass, leading to low maintenance
windows, long lasting scratch resistant floors, super strong structural
components, improved longer lasting facade paint, self-cleaning facades
and windows, antimicrobial steel surfaces, improved industrial building
maintenance, buildings with lower energy consumption, and better
durability. Two nano-sized particles that stand out in their application to construction materials are titanium dioxide (TiO2) and CNT. TiO2
is being used for its ability to break down dirt or pollution and then
allow it to be washed off by rain water on everything from concrete to
glass, and CNT are being used to strengthen and monitor concrete [31].
Envisaged gains of using nanomaterials in construction are thus to
allow product manufacturers to offer longer product warranties,
building owners to enjoy lower maintenance costs, and consumers to
expect houses that maintain themselves. But research and development of
nanotechnology in construction is not as extensive as in other areas.
According to the Nanoconex EU project report [32]
two factors severely impact research and technological development in
construction in general and on the exploitation of nanotechnology in
particular: (1) the inherently different nature of construction
compared with other sectors of manufacturing industry and (2)
historically very low levels of investment by the construction industry
into research.
In the Roadmap for development of nanotechnology in construction, Bartos [33] analyzes the current state and according to available resources plots the future development in this area. However he also points out the importance “to appreciate that the ‘routes/pathways’ shown in the charts are in many instances only now being formed or traced. Additional ones may develop in due course, and may not even exist as yet.” Bartos expects that the greatest impact on the construction industry and the economy within the timescale of the Roadmap (2004–2030+) is to come from an enhancement in performance of materials, which is a very strong driver of research and technological development in construction. The eventual total impact in construction is expected to be very substantial, due not necessarily to radical technological leaps forward but mainly to the massive quantities of basic (‘bulk’) construction materials used. According to Bartos the following aims and destinations are expected to be of significance for construction in the medium to long term:
nano-structures).• Bulk ‘traditional’ construction materials with a modified nano-structure (e.g., concrete, bitumen).
• New high performance structural materials (e.g., CNT, new fiber reinforcements, biomimetic materials, etc.).
• High performance new coatings, paints and thin films (e.g., wear-resistant coating, durable paints, self-cleaning/anti-bacteria coatings).
• New multi-functional materials and components (e.g., aerogel based insulating materials).
• New production techniques, tools and controls (e.g. more energy-efficient and environmental friendly production of materials and structures, novel processes with more intelligent and integrated control systems, etc.).
• Intelligent structures and use of micro/nanosensors (e.g., nano-electromechanical systems, biomimetic sensors, paint-on sensors).
• Integrated monitoring and diagnostic systems.
• Energy saving lighting, fuel cells and communication devices.
Furthermore,
papers presented at the 3rd Nanotechnology in Construction Conference
are showing the current research and technological development, which
includes nanotechnology and cementitious materials [34], concrete nanoscience and nanotechnology [35], application of nanofibers [36], and use of other nanomaterials to improve characteristics of building materials. There is, however, no discussion on nano-
to meter-scale building. Many barriers exist that prevent
nanomanufacturing on the meter scale, especially if we try to simply
scale-up the existing nanotechnology. The production processes
and characterization equipment to monitor parameters that impact
quality are inadequate. There is also a lack of scalable unit
operations as well as the inability to retain nanoparticle
functionality as the materials are incorporated into products [37]. Therefore we have to invent new concepts to scale-up nanoproduction of buildings.
One
specific technology that is close to our concept is 3D printing. In
general 3D printing is a process of depositing slices of material on
the desired area and gradually composing a 3D structure. 3D printing is
being considered for operation on a molecular level as described in the
Roadmap [38]. 3D nano-printing as well as 3D nano-lithography differ, however, significantly from the nano-
to meter-scale building concept as they require the building material
to exist on or be brought to the production surface. Both 3D nano-printing
methods are not expected to build products on the scale of a house. We
could not find any concept that would seriously consider using
nanomanufacturing on the meter scale.
There are, however, successful 3D printing attempts, which occur on a much larger scale. Shiro Studio printed a 3 × 3 m model of a pavilion using a new robotic building system called d_shape [39]. The material is produced using binder, “which transforms any kind of sand into a marble-like material (i.e., a mineral with microcrystalline characteristics) and with a resistance and traction much superior to Portland cement, so much so that there is no need to use iron to reinforce the structure.” d_shape products are limited to 6 × 6 m cubes.
Another system of automated production called Contour Crafting has been developed at the University of Southern California’s Center for Rapid Automated Fabrication Technologies. Concrete and gypsum are used as the basic material. Strain gauges and other “smart” components can be embedded within walls and the composition of structures can be varied by layering in different materials during construction. Metal reinforcement, plumbing, electrical systems, and tiling can also be automated [40].
d_shape and Contour Crafting use sophisticated equipment for production and need the building material to be transported to the building site in a conventional way. They do, however, represent an important contribution to more efficient, automated building.
Biotechnology refers to using organisms or biological substances to solve problems and make useful products. Biotechnology by itself is not something new and biotechnological products and processes have been used intentionally for millennia; we can even say that our civilization depends on biotechnology. In narrow terms we can recognize biotechnology in ancient procedures as using yeast in brewing beer or raising bread, and microorganisms in the fermentation of milk. In broader terms, agriculture is a fine example of biotechnology where plants are used to produce something useful, like drugs, food, fuels, building materials, etc.
Organisms used in biotechnological processes are only rarely used in their original forms. More often their genome was altered towards better yields, improved quality of products, physical properties, etc. Before the era of genetic engineering, processes like selection, crossing or induced mutations to produce new genes or combinations of them were used. All these processes are time-consuming and depend on chance and good luck, with the additional barrier of combining genes from unrelated organisms, which are reproductively isolated from each other. Many of the barriers are nowadays routinely crossed using tools from genetic engineering to modify existing genes of single organisms or transfer genes between organisms. Organisms like bacteria Escherichia coli produce insulin [41] or herbicide-tolerant crops [42] and are in commercial use. New genetically modified organisms are in testing phases or foreseen to be introduced in commercial use.
Even though the technologies for nano-
to meter-scale building do not yet exist in a synthetic,
human-controllable fashion, there are plenty of examples in nature and
in practice that suggest that a nano- to meter-scale building process may become a reality in the future.
nano to meter-scaleA
top-down concept has been developed following certain suppositions,
which are closely related to our motivation to reduce waste, pollution
and energy consumption caused by traditional building technologies. The
first supposition was to use materials that exist on site and can be
transformed into building materials at the nano
level. As discussed in the previous section, CNT have extraordinary
characteristics, which can be varied using today’s production
nanotechnologies. As carbon exists in nature in vast amounts, the next
supposition is to extract it from CO2 from the air. The
building process is to be executed at the nanolevel using active
nanodevices that shall be controlled extrinsically using a detailed
building information model (BIM) as the source of all necessary
information.
These suppositions suggest the following conceptual solution:
• building 3D carbon nanotube arrays with characteristics required for a specific area of the building (strength, conductivity, color, transparency, etc.).
2. Nanorobots are controlled and powered externally by light. Instructions are coded using specific wavelengths.
3. Light is emitted by a projector installed above the site. To avoid interference with light emitted by other sources, an adequate wavelength spectrum has to be chosen.
| Full-size image (25K) |
Projection of light-encoded instructions to the nanoproduction layer on the already built area.
5. Openings of the final model are temporarily filled with unstable carbon nanomaterial, which transforms back into CO2 after a specific time period (or under specific conditions), when its function as a supporting structure is fulfilled.
6. All utilities and coatings (if necessary) are built at the same time, together with the bearing structure (e.g. pipelines, power lines, communication lines), and are part of the building.
The building process consists of the following steps:
2. Site preparation (excavation, projector installation).
3. Deploying nanorobots onto the maximal extent of the building layout.
4. Starting the process by continuously emitting instructions (represented as specific light wavelengths) to build 3D CNT arrays with required characteristics, until the top of the building is reached.
5. After the light is off for a certain time, the nanorobots stop functioning permanently, thus preventing any unwanted activity after the process is finished.
The load
bearing material is placed as necessary during construction, therefore
any temporary supporting material can dissolve after the building is
finished. It out gases from the structure in the form of CO2
resulting in a habitable structure. Even windows could be “built-in”
during the process utilizing transparent CNT sheets, as well as
additional utilities. It is, however, too early to explore in great
detail all the effects of nano- to meter-scale building. Nevertheless, several of the key technologies that are required can already be specified.
From the presented concept we can derive the main required technologies. In this section we will elaborate on these technologies in more detail and compare them with existing technologies and trends in relevant research areas.
The following characteristics are required for the proposed nano- to meter-scale building material:
2. Conductive or insulating as required (for power and communication).
3. Chemically resistant (for coatings and pipes).
4. Able to adjust surface properties like color (for coatings).
5. Able to adjust transparency (for lighting).
6. Stable and inert at typical temperature ranges.
7. Assembly in all three dimensions.
8. Able to be self-decomposing (for decomposition of temporary supporting structures).
CNT possess many of the properties one would choose in designing an ideal structural material. They have a very high strength to weight ratio, are stable and inert at a wide range of temperatures, and can have varying degrees of conductivity based on their geometric properties. However, one challenge in utilizing CNT in meter-scale building is finding a natural configuration of nanotubes that allows for unlimited assembly in all three spatial dimensions while retaining the aforementioned properties. One very promising family of configurations can be found in Schwarzite structures, named so in honor of the mathematician H.A. Schwarz who first explored similar triply periodic minimal surfaces [43].
Schwarzite structures are a class of fullerenes that exhibit negative Gaussian curvature [44]. They are produced by the insertion of heptagonal and octagonal rings into the graphene lattice otherwise containing only hexagons [44]. It is these lattice deformities that produce the negative curvature necessary to create a structure that has symmetries in three spatial dimensions. In contrast, spherical fullerenes such as C60 contain pentagon rings that produce a positive curvature leading to a closed structure. The spatial symmetries of Schwarzite structures fulfill the necessary requirement of unlimited assembly in three dimensions. In addition, Schwarzite structures are stiff and can be either conductive or insulating depending on their topology [45]. Fig. 3 shows a possible nanotube configuration to be used as a nanoscale building block. The tube junctions are Schwarzite structures that have been connected by single-wall CNT of similar diameter.
| Full-size image (34K) |
Hydrogen terminated 3D carbon nanotube array; dimensions are 8 nm × 8 nm × 8 nm, density is 182 Kg/m3.
To get a rough comparison with a traditional building we have estimated the embodied energy for both approaches. Regarding traditional buildings, Suzuki et al. [46] applied basic sector classification input/output analysis to quantify the total energy consumption and CO2 emissions including direct and indirect effects due to the construction of various types of houses. As a result, energy consumption for construction is calculated as 8–10 GJ/m2 of floor area for multi-family steel reinforced concrete houses, 3 GJ for wooden single-family houses, and 4.5 GJ for lightweight steel structure single-family houses. CO2 emissions resulting from construction are 850, 250 and 400 kg/m2, respectively.
The energy required to obtain carbon from the atmosphere sufficient to synthesize 1 m3 of Schwarzite material is approximately 129 GJ. This energy is based on a maximum array density, i.e., Schwarzite junctions are connected directly without single-wall carbon nanotube spacers. This energy requirement would drop if the density of the building material is decreased and would be approximately 3.6 GJ for the material shown in Fig. 3. To compare with the required energy used for traditional buildings, we need to estimate the ratio between floor area of the building and the volume of the material built into it. In traditional buildings, this ratio is between 1 and 2, but for a CNT construction it can be estimated at least as high as 3 as its load-bearing capacity is much higher. In this case, the energy consumption for a square meter of a building built of 3D CNT array material (as shown in Fig. 3) would be around 1 GJ. In comparison, extensive bamboo growth utilizes approximately 1 GJ of energy (sun light) to produce a m3 of cellulose (a rough calculation was made by the authors taking into consideration average solar energy per m2, plant energy use efficiency, estimated area of leaves, and bamboo volumetric growth). Hence, it appears feasible, in most cases, from the perspective of energy availability to use energy sources that are locally available.
As stressed already, carbon, the raw material for producing CNT, should be extracted from the CO2 in the air. Our first consideration was whether it is possible to gain enough carbon from the air for the process to create a building in reasonable time. Calculations confirm that this indeed seems possible (note that growing trees do this as well). The CO2 quantity in the air is 0.00076626 kg/m3 or approximately 1 g/m3. The quantity of carbon is thus 0.0002088 kg/m3 or approx. 0.2 g/m3. Regarding the density of CNT, which is approximately 1400 kg/m3, for 1 m3 of CNT 6.7 × 106 m3 of air is needed. This quantity seems enormous, however, with the air speed of just 1 m/s, the quantity required for a 1 m high structure can be extracted in 78 days. A faster air flow would of course speed up the process in a linear way. The density of 3D CNT array is much lower. The structure shown in Fig. 3 has a density of 182 kg/m3, which reduces the calculated values by 87%. 8.7 × 105 m3 of air contains the adequate quantity of carbon to produce 1 m3 of such material.
As CO2 is heavier than other gases in the air, its molecules tend to fall to the Earth’s surface. So the CO2 molecules will always flow towards the ground and thus neutralize the effect of CO2 reduction through its decomposition. Capturing of carbon and production of CNT is the primary function of the bionanorobots.
For the extrinsically controlled nano- to meter-scale building process presented above the bionanorobots would have to be able to:
2. Transform light energy into working energy.
3. Extract CO2 molecules from the air and decompose them into C and O2.
4. Build 3D CNT arrays using C molecules.
In traditional buildings using natural biological sources (wood, bamboo, straw) the first phase is harvesting energy and materials produced in the process of photosynthesis. In photosynthesis, plants chemically bind carbon dioxide and water to produce sugars. These are a source of building blocks for other carbohydrates like starch or cellulose, as carbon is the backbone in combination with other minerals to produce a great number of molecules in a range from simple molecules, like formic acid, to multi-chain proteins, and as a source of chemical energy to power all these processes. In the second phase, the building materials produced by plants are processed (e.g., wood cut into logs) and transported to the building area. In the third phase, building materials are assembled by the workers and machines into a building, using information from design plans. To our knowledge, there exists no biotechnology at the moment, which would self-assemble any kind of building blocks into a meter-scale building. But research in the fields of synthetic biology (e.g. [47] and [41]) and biotechnology is promising and many concepts can be seen as forerunners for such a building process.
The first step is to provide the needed quantity of building materials and energy to drive the process. In nature, photosynthesis is the major source of organic materials, which are used as the building blocks of organisms, and as the storage of energy, using materials from the location where a photosynthetic organism (plant, bacteria) is living. So the first choice would be to search inside the plant or bacteria kingdoms. One problem we can foresee is that photosynthesis yields only less than 10% of available energy and is locally affected by the quantity and quality of light, weather conditions, latitude, shadows, etc. [48]. At the moment, different research groups are working on artificial photosynthesis [49] to improve energetic yield and to store light energy into something more appropriate to be used as fuel such as cellulose or starch; findings which could contribute to the n2mb concept.
After
the recognition that at the chemical level DNA is basically identical
in all organisms, and that all organisms share (with a few exceptions)
the same genetic code, it was only a matter of technology to change the
genetic sequence in one organism, or to cut a sequence (gene) from one
organism and insert it into another to produce something new and
useful. Many such organisms are already in use or are foreseen (e.g. [50], [51] and [52]). In such a manner, the ability of cells to build microtubules [53]
may be used to assemble CNT, and a technology once developed in one
organism transferred to others. On the other hand, cells are already
well able to produce cellulose. Therefore, homogenous wood-like
microbial cellulose could be an intermediate building material produced
by bionanorobots in the nano- to meter-scale building process.
Another issue is the control of assembling of building blocks, or the growth direction of such a building. In living organisms, basic principles, but not details, are well known and many internal or external regulatory mechanisms (e.g. [54] and [55]) are included in growing an organism from single cell stadium (e.g., fertilized egg, bud) toward a multi-cellular organism built from genetically identical, but phenotypically very different cells [56] and [57]. To assemble a building from a single dividing cell (nanorobot) its gene (information) sequence for such a building has to consist of a number of subsequences, which should be assembled in preferred order and with the possibility to be switched off/on when an action has to be stopped or the next step is to be taken (e.g., growing walls has to be stopped to build horizontal ceilings). Basu et al. [58] designed a synthetic multicellular system in which genetically engineered ‘receiver’ cells are programmed to form ring-like patterns of differentiation based on a chemical signal that is synthesized by the ‘sender’ cells.
Biotechnology is also able to modify bacteria to react to light in a required way. An E. coli bacterial system has been designed that is switched between different states by red light [59]. Tabor et al. [60] have genetically encoded an edge detection algorithm that programs an isogenic community of E. coli to sense an image of light, communicate to identify the light–dark edges, and visually present the result of the computation.
As a conclusion, we can optimistically search for engineering modules produced for different purposes in developing fields of synthetic biology and biotechnology to assemble them in a new sequence with a building as the end product.
nano- to meter-scale building equipmentIn the nano-
to meter-scale building process, the main human activity is to create a
detailed digital model of the building. BIM technology of today,
including detailed 3D geometry and material properties, perfectly fits
the requirements of nano- to meter-scale building. There are, however, some additional demands:
2. All utilities have to be designed together with the architectural elements in final details; they all become solid volumes with specific characteristics (conductivity, transparency, insulation, etc.).
3. Temporary supporting material has to be filled in all parts of the building, where any part of the structure exists on a higher vertical level (rooms, niches, pipes, etc.).
Existing BIM modeling tools can be used to design the digital model of the building, which includes architectural elements, electrical wiring, water pipes, plumbing, heating, ventilation and air conditioning (HVAC) and all other utility systems [61]. The model can be stored in a format, which supports the description of a BIM, as for example by using the Industry Foundation Classes (IFC) schema. The design process will not have to undergo any radical changes from the technical perspective, but it will have to be more collaborative and much more accurate, since a construction-ready building information model must be produced. On the other hand, changes could be made up to the moment before the projector instructs the bionanorobots to build CNT structures with particular characteristics in a particular location.
One important difference, however, is the structural sub model of the building. In the current BIM practice the structural model is derived from the architectural model by identifying the load bearing elements and defining their interconnections, and by adding data, which is essential for structural analysis. In case of n2m building all architectural elements, merged into a single homogenous structure, are load bearing. As the whole structure is of perfectly homogenous material finite element method based structural analysis software can be used directly to check the structural characteristics of the building. No optimization methods are required to minimize the dimensions of the structure as this does not affect the cost of the building, neither is it important for the weight of the structure as the n2mb CNT material is extremely light (see Fig. 3).
The next step in the n2mb process is to prepare the BIM model for production. First, all BIM structures with a defined geometry (e.g. HVAC shafts, water pipes and electrical wires within walls) are merged and transformed into a single solid geometry model (geometry consistency check can be performed in this step). CNT material code is added to each closed volume according to its function (load bearing, electrically conductive, etc.) Then the temporary supporting material is filled into all empty spaces below any part of the solid model (which is a much simpler case than today’s design, construction, and dismantling of temporary structures [62]). This includes filling HVAC shafts, water and plumbing pipes, etc. Generating the n2mb production model can be fully automated, as it does not require any human decisions. Existing geometric IFC structures can be used to represent this model.
In the final step of the process the n2mb solid model is sent to the projector, which continuously slices the 3D model into 2D sections and projects them onto the production plane. Fig. 4 illustrates the transformation of data in the information flow of the n2mb process.
The equipment that is to be used for the extrinsic control of the nano-
to meter-scale building process consists of a light projector with a
reliable power supply and stable geometrical position, which is crucial
for achieving the desired precision of all details of the building. The
projector also has to have a built-in computer that controls the light
projection and thus the whole process of nano-
to meter-scale building. It is connected to another computer on site,
which is used to enter data (to transmit the n2mb production model to
the projector) and to monitor the process. No other equipment is
required.
We are aware that the realization of nano-to-meter
scale automated building will require many more years of research in
the areas of biotechnology (bionanorobots), nanomaterials (3D CNT
arrays), physics (light projector), and construction informatics
(detailed and appropriate building information models and modeling
tools, building technology system). Intermediate results will probably
lead to useful applications (e.g. bionanorobots producing building
materials based on cellulose), and alternative concepts will surely
arise with different solutions for production of carbon nanomaterials
(e.g. nanomanufacturing based on self-assembly). Alternative approaches
to building control, like intrinsically controlled processes, where
bionanorobots would only follow internal programs and decide their
actions according to information exchanged with their neighbors and
data they would sense from their close surroundings might prove to be a
better way. Alternative ways will, however, open new questions. In the
intrinsic variation of the n2m building concept a new problem would
emerge on transforming an exact digital model of a building into local
bionanorobots models and programs. This could alter the presented
concepts in the future, but not the ecological goals that have been set
and which should bring the building industry to a clean and sustainable
way of future building, based entirely on the building information
model, information flow from the model to each bionanorobot, on the
nanotransformation of matter, and on the materials existing on site. If
this paper helps motivate researchers to focus their work to find
solutions for the required technologies, as well as the building
industry to believe in the need and the ability to change the building
production, it has achieved our first important goal.
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