Living paint

Abstract

A living paint comprises a living photosynthetic microorganism, binder, growth medium, and water. The microorganism may comprise algae, cyanobacteria, or lichens. The binder may be composed of primary

Description

Field of the Invention The present invention provides living paint compositions, methods of making such compositions and methods of applying the compositions to a substrate, as well as painted substrates coated with the paint compositions. In particular, the invention provides living paint compositions which comprise a living photosynthetic microorganism. Background to the Invention Carbon dioxide (CO2) emissions have a major impact on climate change since carbon dioxide contributes to the “greenhouse effect”, wherein thermal radiation emitted e.g. by the Earth’s surface is absorbed by greenhouse gases (such as carbon dioxide). This slows the rate at which heat escapes the Earth’s atmosphere, resulting in gradual increases in global temperatures. Carbon sequestration, i.e. removing carbon dioxide from the atmosphere, is one way of mitigating the negative effects of carbon dioxide emissions. One particular implementation of this approach is reforestation or afforestation, which involves the planting of trees and forests. Trees and other photosynthetic organisms are known to be effective carbon sinks by virtue of their photosynthetic ability to convert carbon dioxide into organic compounds such as sugars, which can act to sequester carbon in the form of organic matter. The process of photosynthesis involves a first light-dependent stage, wherein light energy (photons) is absorbed by a photosynthetic pigment, located within a protein complex called Photosystem II (PSII). This photon absorption causes the pigment to lose an electron which is then passed into an electron transport chain, culminating in the reduction of hydrogen carrier molecules such as NADP to form NADPH. PSII replenishes lost electrons through the photolysis of water, which also releases protons to provide a proton gradient which is utilised to drive the generation of ATP. The light-independent reactions, predominantly the Calvin cycle, form the next stage of photosynthesis. Here, the enzyme RuBisCO captures CO2 from the atmosphere and uses it to synthesise three-carbon sugars (which can be further converted into carbohydrate products), using the NADPH and ATP. New applications for photosynthetic organisms have been explored in order to increase carbon dioxide sequestration from the atmosphere in more populated areas. For instance, so-called “living walls”, where plant species are integrated into external building surfaces, are gaining popularity. However, such constructions require potentially complex structures and irrigation systems to support their planting and survival, as well as ongoing maintenance. Concrete-based materials to support plant life have also been developed. However, their weight makes them unsuitable for many applications, they are opaque and can involve complex application procedures. Thus, there is a need for environmentally-friendly, sustainable and resilient materials that can provide a suitable environment for the growth of carbon-sequestering photosynthetic organisms and which can be readily applied to numerous surfaces. This need is met by the present invention. Summary of the Invention The present invention is based on the surprising discovery that living photosynthetic microorganisms can be incorporated to prepare a stable paint which can be applied to a surface, while still providing a suitable growth environment to allow the microorganisms to survive and photosynthesise. In this way the paint, and any surfaces to which it is applied, are able to act as effective carbon sinks by virtue of the photosynthetic activity of the living microorganisms contained therein. Thus, in one aspect, the present invention provides a living paint composition for application to a surface, comprising a living photosynthetic microorganism; a binder; a growth medium; and water. In another aspect, the present invention is directed to a method of making a living paint composition, comprising the steps of: incorporating a living photosynthetic microorganism into a composition comprising water and a binder which is at least partially set such that the living photosynthetic microorganism is dispersed throughout the composition to form a living paint, wherein a growth medium is either present in the composition used in this step or is incorporated during or after this step. In a further aspect, the present invention provides a method of painting a substrate, said method comprising coating a substrate with the living paint composition according to the invention to form a coating layer. In a yet further aspect, the present invention provides a method for increasing the carbon dioxide absorption capacity of a substrate, said method comprising coating a substrate with the living paint composition according to the invention to form a coating layer. The present invention also provides a use of a living paint composition of the present invention for increasing the carbon dioxide absorption capacity of a substrate. Also provided is a painted substrate which comprises a substrate, and the living paint of the present invention coated thereon. Description of the Figures Figure 1 is a graph showing the effect of agar percentage on the moisture content of paint compositions according to the present invention. Figure 2 is a graph showing the growth of the photosynthetic microorganism over time in a paint composition according to the present invention. Figure 3 is a chart showing the effect of the concentration of sodium alginate in a paint composition according to the present invention on the growth of the photosynthetic microorganism. Figure 4 is a graph showing the effect of the agar’s boiling time on the moisture content of paint compositions according to the present invention. Figure 5 is a graph showing the effect of glycerol on the moisture content of paint compositions according to the present invention. Figure 6 is a chart showing the effect of different humectants on the moisture content of paint compositions according to the present invention. Figure 7 is a chart showing the effect of different humectants, and their combination, on the moisture content of paint compositions according to the present invention. Figure 8 is a chart showing the effect of different amounts of humectants in a combination on the moisture content of paint compositions according to the present invention. Figure 9 is a graph showing the growth of the photosynthetic microorganism over time in a paint composition according to the present invention. Figure 10 is a graph showing the ability of the paint compositions according to the present invention to sequester carbon dioxide. Detailed Description The present invention relates to living paint compositions and substrates coated with these living paint compositions, as well as methods of making and applying the living paint compositions. Living paint composition In one aspect, the present invention is directed towards a living paint composition. As used herein, a paint composition refers to a material or mixture which, when applied to the surface of a substrate, can adhere to it to form a coating layer, for instance by the drying of the composition. Paints are typically slurries of solid particles (often pigments) in a liquid medium. Paints are typically intended to provide a colour to a surface for decorative purposes, although they can also serve to protect the surface of the substrate from elemental and / or physical damage, or to provide other benefits. In particular, the living paint compositions of the present invention are pourable at room temperature. Thus, a living paint composition refers to a paint composition, as defined above, which comprises a living component, i.e. an organism which is alive and capable of surviving within compositions of the present invention for extended periods. For instance, the living component should be able to survive within the living paint composition, when applied to a suitable surface, for a period of at least a month, preferably at least a year, and more preferably at least three years. Specifically, the paint compositions of the present invention comprise a living photosynthetic microorganism as a living component. It will be appreciated that paint compositions such as those described in the present application can exist in a number of states depending on whether or not the composition has been applied to a surface, and depending on the extent of any drying that has occurred subsequent to such application. Unless otherwise specified, references herein to living paint compositions are intended to refer to the compositions before application to a substrate. Similarly, unless otherwise specified, in discussions pertaining to the paint compositions of the present invention the terms “living paint compositions”, “paint compositions” and “compositions” are intended to each refer to the living paint compositions of the present invention. A living paint composition is fluid, meaning that it is able to flow, i.e. it undergoes a continuous change in shape when subjected to a shear stress. Notably, the living paint composition is fluid at room temperature (25 °C). Therefore, the living paint composition may have a viscosity of up to 2000 mPas, preferably up to 1000 mPas, and more preferably upto 750 mPas. The paint composition may have a viscosity of at least 100 mPas, preferably at least 200 mPas, and more preferably at least 250 mPa s. Thus, the living paint composition may have a viscosity in the range of from 100 to 2000 mPas, preferably from 200 to 1000 mPas, and more preferably from 250 to 750 mPa s. Viscosities in these ranges have been found to provide a good consistency that is still sprayable onto substrates. Alternatively, although less preferred, the paint composition may have a viscosity of up to 1000 mPa s, such as up to 500 mPa s, or such as up to 100 mPa s. The living paint composition may have a viscosity of at least 0.1 mPa s, such as at least 0.5 mPa s, or such as at least 1 mPa s. Thus, the living paint composition may have a viscosity in the range of from 0.1 to 1000 mPa s, such as from 0.5 to 500 mPa s, or such as from 1 to 100 mPa s. Viscosity may be measured using a falling-ball type viscometer, using a metal ball of radius 0.65 cm and density of 7337 kg / m3 and a measuring cylinder, using the formula: Viscosity = 2(ps-pi)ga2] / 9v, where ps is the density of the metal ball, pi is the density of the liquid composition, g is the gravitational constant, a is the radius of the ball, and v is the velocity of the sphere which is determined by measuring the time taken for the ball to travel a certain distance through the liquid composition. The paint composition is preferably a fluid gel, i.e. a suspension of gelled particles dispersed in a non-gelled continuous medium, such as may be formed by the application of shear to the binder solution undergoing (or having finished) gelation. Living photosynthetic microorganism The living paint compositions of the present invention comprise a living photosynthetic microorganism. As denoted by the term “photosynthetic”, the microorganisms present in the paint compositions are able to transform light energy into chemical energy, and in particular are able to convert carbon dioxide into organic compounds. The presence of photosynthetic microorganisms in paint compositions of the present invention enables it to act as an effective method of carbon capture. As used herein, a microorganism refers to an organism of microscopic size. The microorganism may be a prokaryotic microorganism, such as from the kingdoms Bacteria and Archaea, or a eukaryotic microorganism from the kingdoms Protozoa, Chromista, Plantae or Fungi. Preferably, the living photosynthetic microorganism is an algae, a cyanobacteria or a lichen. Photosynthetic microorganisms of the types described herein tend to absorb carbon dioxide at higher rates than other photosynthetic organisms like Spermatophyte plants. Any references herein to “living photosynthetic microorganism”, “photosynthetic microorganism” and “microorganism” are, unless otherwise indicated, intended to refer to the living photosynthetic microorganisms comprised in the present compositions. The living photosynthetic microorganism may be unicellular, may tend to form colonial aggregates, or may form multicellular structures. For instance, filamentous cyanobacteria often exist as elongate hair-like structures typically composed of hundreds or thousands of cells, although they are capable of surviving as discrete cells rather than as part of such structures. It will be appreciated that where the microorganism is multicellular, the living paint composition may only comprise individual cells ora subset of cells of the multicellular structure. Once the paint composition is applied to a substrate and the photosynthetic microorganisms can begin to grow, their multicellular structures may then begin to form. For instance, the living photosynthetic microorganism may be an algae, in particular an algae selected from the genera Polysiphonia, Chondrus, Ectocarpus, Cephaleuros, Oedogonium, Spirogyra, Desmococcus such as Desmococcus olivaceus, Coelastrella such as Coelastrella oocystiformis, Neochlorosarcina such as Neochlorosarcina negevensis and Trebouxia such as Trebouxia decolorans. The living photosynthetic microorganism may also be a cyanobacteria, such as those of the genera Anabaena; Schizotrichaceae such as Schizothrix calcicole; Chalicogloea such as Chalicogloea cavernicola; Oscillatoria; Calothrix; Cyanothece; Anabaenopsis; Nostoc such as Nostoc flagelliforme; Synechococcus such as Synechococcus elongatus 3222; Mycrocystis; Gloebacter such as Gloeobacter violaceus; Synechocystis such as Synechosystis sp. PCC6803; Aphanocapsa; Gleocapsa; Microcoelus; and Chroococcidiopsis such as Chroococcidiopsis cubana PCC 7433, and Tolypothrichaceae. The living photosynthetic microorganism may also be a lichen. Lichens are symbioses of a fungal species (the “mycobiont”) and a photosynthetic partner (the “photobiont”) which lives among its hyphae, the photobiont typically being cyanobacteria or algae. For instance, the lichen may be selected from the genera Trentepohlia; Pseudocyphellaria such as Pseudocyphellaria rainierensis; Flavoparmelia such as Flavoparmelia caperata; and Chloroidium such as Chloroidium lichinum. Preferably, the living photosynthetic microorganism is selected from: a Coelastrella which is preferably Coelastrella oocystiformis; a Desmococcus which is preferably Desmococcus olivaceus; a Nostoc which is preferably Nostoc flagelliforme; a Neochlorosarcina which is preferably Neochlorosarcina negevensis; an Oscillatoria; an Oedgogonium; a Synechococcus which is preferably Synechococcus elongatus 3222; a Spirogyra; or a Tolypothrichaceae. These photosynthetic microorganisms have been found to be able to grow well under a variety of environmental conditions. In addition to a photosynthetic microorganism as described above, the living paint composition may further comprise a plant, such as: an angiosperm of the genera Utricularia such as Utricularia nephrophylla; a fern of the genera Asplenium such as Asplenium sandersonii; or a moss, i.e. a non-vascular plant of the division Bryophyta. Where the composition further comprises a plant, this is preferably a moss, for instance of the genera Bryum such as Bryum capillare and Bryum argenteum; Rhynchostegium such as Rhynchostegium confertum; Brachythecium such as Brachythecium rutabulum; Plagiomnium such as Plagiomnium cuspidatum; Leucobryum such as Leucobryum glaucum; and Splachnum such as Splachnum rubrum, or any combinations thereof. Preferably, the moss is selected from a Bryum, a Rhynchostegium or a Leucobryum, and more preferably is selected from Bryum capillare, Rhynchostegium confertum or Leucobryum glaucum. The moss may be present in the composition in the form of cuttings or spores. The paint composition may comprise the living photosynthetic microorganism in an amount of up to 2x109 cells, such as up to 1x109 cells, or such as up to 8x108 cells per litre of the paint composition. The living paint composition may comprise at least 1x107 cells, such as at least 5x107 cells, or such as at least 1x108 cells per litre of the paint composition. Thus, the paint composition may comprise the living photosynthetic microorganism in an amount in the range of from 1x107to 2x109 cells, such as from 5x107 to 1x109 cells, or such as from 1x108to 8x108 cells per litre of the paint composition. It has been found that at least this amount of photosynthetic microorganism provides a beneficial combination of survivability of the microorganism and suitable pigmentation for the paint composition. Where greater pigmentation of the paint compositions initially is desirable, the paint composition may comprise the living photosynthetic microorganism in a higher amount, such as in an amount of up to 1x1012 cells, preferably up to 5x1011 cells, and more preferably up to 2.5x1011 cells per litre of the paint composition. In these instances, the paint composition may comprise the living photosynthetic microorganism in an amount of at least 1x109 cells, preferably at least 5x109 cells, and more preferably at least 1x1010 cells. Thus, the paint composition may comprise the living photosynthetic microorganism in an amount in the range of from 1x109 to 1x1012 cells, preferably from 5x109 to 5x1011 cells, and more preferably from 1x1010 to 2.5x1011 cells per litre of the paint composition. Where the composition further comprises a moss, the moss may be present in an amount of up to 200 g / l, preferably up to 150 g / l, and more preferably up to 100 g / l of the composition. The paint composition may comprise moss in an amount of at least 10 g / l, more preferably at least 50 g / l, and more preferably at least 75 g / l of the composition. Thus, the paint composition may comprise moss in an amount in the range of from 10 to 200 g / l, preferably from 50 to 150 g / l, and more preferably from 75 to 100 g / l. The living photosynthetic microorganism is present in at least a portion of the paint composition. For instance, the composition may comprise a living photosynthetic microorganism in an upper portion of the composition, such that an outer surface of the upper portion of the composition is exposed to the atmosphere when the paint composition is applied to a substrate. Preferably, however, the living photosynthetic microorganism is dispersed throughout the paint composition. This means that the photosynthetic microorganisms are, on average, distributed uniformly within the composition such that a first portion of the composition comprises about the same number of cells of the microorganism as a second portion having the same portion. This is also true, where present, of any moss that may be present in the composition. Therefore, the paint composition preferably comprises a living photosynthetic microorganism at an average density in the range of from 1x104to 2x106 cells, such as from 5x104 to 1x106 cells, or such as from 1x105to 8x105 cells per ml of the paint composition. Alternatively, where greater pigmentation of the paint compositions initially is desirable, the paint composition may comprise the living photosynthetic microorganism at an average density in the range of from 1x106 to 1x109 cells, preferably from 5x106 to 5x108 cells, and more preferably from 1x107 to 2.5x108 cells per ml of the paint composition. Binder The paint composition also comprises a binder. As used herein, a binder refers to a substance that promotes the adhesion of the composition to a substrate, as well as providing structure to suspend the photosynthetic microorganisms which are present. In order for the paint composition to be suitably ecologically friendly and have low ecotoxicity, it is preferred that the binder is a biopolymer or a derivative thereof. As used herein, a biopolymer refers to a polymer that is produced by living organisms. A biopolymer derivative may be a biopolymer which has been chemically modified, for instance by addition of a chemical group to the backbone and / or sidechain of a polymer. Examples of biopolymer derivatives include modified celluloses such as methylcellulose and hydroxypropyl methylcellulose. The binder used in the paint composition is preferably a polymer. For instance, although less preferred, the binder may be a resin such as an epoxy resin, an alkyd resin, an acrylic resin, a polyurethane resin, a fluorocarbon resin, a phenolic resin, a nitrocellulose resin, an amino resin, a vinyl resin, or a natural resin such as amber, balm of gilead, balsam, copal, and dammar gum, or any combinations thereof. Preferably, the polymer is a gelling agent, in that it is capable of forming a gel (i.e. a semi-rigid colloidal suspension of a solid dispersed in a liquid). More preferably, the binder is a polymer which is capable of forming a hydrogel, such that the paint composition comprises a binder in the form of a hydrogel. Therefore, the binder may be a polysaccharide such as: agar; agarose; cellulose and derivatives thereof, such as methylcellulose, hydroxypropyl methylcellulose and hydroxyethyl cellulose; carrageenans such as kappa, iota and lambda carrageenan; gellan gum; locust bean gum; guar gum; xanthan gum; alginates such as sodium alginate; pectin; starch such as corn starch, tapioca starch, potato starch; chitosan; or any combinations thereof; or a polyamide such as collagens such as gelatin; or a synthetic polymer such as poly(vinyl alcohol), poly(ethylene glycol), poly(ethylene oxide), poly(2-hydroxyethyl methacrylate), polyacrylates such as poly(acrylic acid), and polyacrylamide, or any combinations thereof. However, it is preferred that the paint composition does not comprise a poly(acrylic acid). The binder being capable of forming a hydrogel is particularly preferred, since hydrogels are able to swell and retain water, making it better able to help regulate the moisture content of the paint composition if e.g. it is subjected to periods of relative drought. Additionally, the porosity of hydrogels provides breathable compositions which can promote the exchange of metabolites (such as carbon dioxide) and water - for instance, it can allow the paint composition to better absorb moisture from the environment to which it is exposed. These features further assist in promoting the survivability of the living photosynthetic microorganisms which are also comprised in the paint compositions. As binders, cellulose and derivatives thereof have been found to be able to provide the advantageous combination of high moisture retention and favourable adhesion and growth properties, whilst also having an improved stability and viscosity across a wide range of temperatures to which the paint composition is likely to be exposed when in use. Therefore, it is most preferred that the binder comprises a cellulose or a derivative thereof. For instance, the composition may comprise a cellulose, preferably a methylcellulose such as methylcellulose, hydroxypropyl methylcellulose, or an ethylcellulose such as hydroxyethyl cellulose, and more preferably comprises hydroxypropyl methylcellulose. As mentioned, the composition may comprise a combination of binders, each being of one of the types described above. Where a combination of binders is present, it is preferred that each of the binders in the composition is a polysaccharide binder. In such instances, the composition may comprise a primary binder and one or more secondary binders different from the primary binder. The primary binder may be a polysaccharide as described above, and preferably is a cellulose or a derivative thereof, and more preferably is a methylcellulose such as hydroxypropyl methylcellulose. The one or more secondary binders may be other polysaccharides as described above, preferably comprising a starch, agar and / or an alginate, and more preferably comprising an alginate. Thus, the combination of binders preferably comprises a cellulose or a derivative thereof (as the primary binder), an alginate (as a secondary binder) and optionally a starch and / or agar (as a further secondary binder). Such combinations have been found to exhibit further improved moisture retentive properties in the paint compositions. The paint composition may comprise the binder in an amount of up to 15 %, preferably up to 12.5 %, and more preferably up to 10 % by weight of the composition. The paint composition may comprise the binder in an amount of binder of at least 1 %, preferably at least 1.5 %, and more preferably at least 2% by weight of the composition. Thus, the paint composition may comprise the binder in the range of from 1 to 15%, preferably from 1.5 to 12.5%, and more preferably from 2.0 to 10% by weight of the composition. Where more than one binder is used, these values represent the total amount of binder that is present in the composition. Where the composition comprises a primary and secondary binder, the primary binder may be present in an amount of up to 7 %, preferably up to 6 %, and more preferably up to 5 % by weight of the composition. The primary binder may be present in an amount of at least 1 %, preferably at least 1.5 %, and more preferably at least 2 % by weight of the composition. Thus, the primary binder may be present in an amount in the range of from 1 to 7 %, preferably from 1.5 to 6 %, and more preferably from 2 to 5 % by weight of the composition. Amounts of the binder in these amounts have been found to promote water retention and assist in providing viscosities in the range suitable for paint applications. Where the paint composition comprises only one binder, these amounts may represent the total amount of binder present in the paint composition. Where a secondary binder is provided, each secondary binder may be present in an amount of up to 4 %, preferably up to 3.5 %, and more preferably up to 3 % by weight of the composition. Each secondary binder may be present in an amount of at least 0.1 %, preferably at least 0.2 %, and more preferably at least 0.3 % by weight of the composition. Thus, each secondary binder may be present in an amount in the range of from 0.1 to 4 %, preferably from 0.2 to 3.5 %, and more preferably from 0.3 to 3 % by weight of the composition. Although less preferred, and especially when the binder is agar, the binder may alternatively be present in the paint composition in an amount of up to 3%, such as up to 2%, or such as up to 1% by weight of the paint composition. The binder may be present in an amount of at least 0.1%, such as at least 0.25%, or such as at least 0.5% by weight of the composition. Thus, the binder may be present in an amount of from 0.1 to 3%, such as from 0.25 to 2%, or such as from 0.5 to 1% by weight of the composition. The binder may be present in the paint composition in an amount of up to 50 mmol / l, preferably up to 40 mmol / l, and more preferably up to 30 mmol / l. The binder may be present in an amount of at least 10 mmol / l, preferably at least 15 mmol / l, and more preferably at least 20 mmol / l. Thus, the binder may be present in an amount of from 10 to 50 mmol / l, preferably from 15 to 40 mmol / l, and more preferably from 20 to 30 mmol / l. Where the binder is a polymer, it will be appreciated that this refers to the number of moles of monomer units present in the polymer. Growth medium In order to promote the survival and growth of the photosynthetic microorganisms within the paint composition, the composition also comprises a growth medium. It will be appreciated that a growth medium refers to a mixture designed to support the growth of a microorganism (of the sort present in the paint composition) by comprising one or more of the nutrients required fortheir growth, typically in an aqueous solution. The growth medium, in particular the constituent nutrients thereof, is preferably dispersed throughout the composition. The nutrients which the growth medium may comprise may be any one or more of: a phosphate source such as K2HPO4; a nitrogen source such as an ammonium salt, urea or preferably a nitrate such as NaNCh; a magnesium source such as MgSO4; a calcium source such as CaCh; acids such as citric acid; a boronic acid such as H3BO3; a manganese salt such as MnCh; a zinc salt such as ZnSO4; a molybdenum salt such as Na2MoO4; a copper salt such as CUSO4; and a cobalt salt such as Co(NO3)2, or any combinations thereof. Preferably, the growth medium comprises at least a phosphate source and a nitrogen source, and more preferably comprises a compound (such as those listed) from each of the groups. Most preferably, in orderto promote long term survival and growth of the microorganisms within the composition, the paint composition may comprise the nutrients of the growth medium in a total amount of up to 15 g, preferably up to 13 g, and more preferably up to 12 g per litre of the paint composition. The paint composition may comprise the nutrients in a total amount of at least 5 g, preferably at least 7.5 g, and more preferably at least 10 g per litre of the paint composition. Thus, the paint composition may comprise the nutrients of the growth medium in a total amount in the range of from 5 to 15 g, preferably from 7.5 to 13 g, and more preferably from 10 to 12 g per litre of the paint composition. Alternatively, although less preferred, the paint composition may comprise the nutrients of the growth medium in a total amount of up to 2 g, such as up to 1 g, or such as up to 0.8 g per litre of the paint composition. The paint composition may comprise the nutrients in a total amount of at least 0.1 g, such as at least 0.5 g, or such as preferably at least 0.7 g per litre of the paint composition. Thus, the paint composition may comprise the nutrients of the growth medium in a total amount in the range of from 0.1 to 2 g, such as from 0.5 to 1 g, and or such as from 0.7 to 0.8 g per litre of the composition. As will be discussed further on, the growth medium is typically added as part of the paint composition as a solution comprising one or more of the nutrients. Therefore, the paint composition may comprise these nutrients in an amount which is proportional to the amount of growth medium used therein - for example, if a growth medium comprising nutrients is added at 45% by volume of the composition, then the composition will comprise said nutrients in an amount of 45% of that present in the growth medium. Therefore, the paint composition (rather than the growth medium) preferably comprises one or more, and preferably all, of: a phosphate source in an amount of at least 0.001 moles per litre, and / or in an amount of up to 0.04, preferably up to 0.03, and more preferably up to 0.027 moles per litre; a nitrate source in an amount of at least 0.001 moles per litre, and / or in an amount of upto 0.03 moles, preferably upto 0.025 moles, and more preferably upto 0.018 moles per litre; a magnesium source in an amount of at least 0.001 moles per litre, and / or in an amount of up to about 0.03 moles, preferably up to about 0.02 moles, and more preferably up to about 0.0175 moles per litre; a calcium source in an amount of at least 0.001 moles per litre, and / or in an amount of up to about 0.025 moles, preferably up to about 0.02 moles, and more preferably up to 0.015 moles per litre; an acid in an amount of at least 0.01 mmol per litre, and / or in an amount in an amount of up to 3 mmol, preferably up to about 2 mmol, and more preferably up to about 1.75 mmol per litre; a boronic acid in an amount of at least 0.001 mmol per litre, and / or in an amount of up to about 0.06 mmol, preferably up to about 0.05 mmol, and more preferably up to about 0.0475 mmol per litre; a manganese salt in an amount of at least 0.1 nmol per litre, and / or in an amount of up to about 3.5 nmol, preferably up to about 3 nmol, and more preferably up to about 2.25 nmol per litre; a zinc salt in an amount of at least 0.001 mmol per litre, and / or in an amount of up to about 0.09 mmol, preferably up to about 0.085 mmol, and more preferably up to about 0.08 mmol per litre; a molybdenum salt in an amount of at least 0.01 nmol per litre, and / or in an amount of up to about 6 nmol, preferably up to about 5 nmol, and more preferably up to about 5 nmol per litre; a copper salt in an amount of at least 0.0001 nmol per litre, and / or in an amount of up to about 0.01 nmol, preferably up to about 0.009 nmol, and more preferably up to about 0.008 nmol per litre; and a cobalt salt in an amount of at least 0.001 nmol per litre, and / or in an amount of up to about 0.05 nmol, preferably up to about 0.04 nmol, and more preferably up to about 0.035 nmol per litre. Alternatively, although less preferred, the paint composition may comprise one or more, and preferably all, of: a phosphate source in an amount in the range of from around 0.05 to 0.15 mmol / l; a nitrate source in an amount in the range of from around 8 to 12 mmol / l; a sulfate source in an amount in the range of from around 0.1 to 0.2 mmol / l; a calcium source in an amount in the range of from 0.1 to 0.2 mmol / l; an acid in an amount in the range of from around 0.01 to 0.02 mmol / l; a boronic acid in the amount in the range of from about 0.015 to 0.025 mmol / l; a manganese salt in an amount in the range of from about 3 to 5 nmol / l; a zinc salt in an amount in the range of from about 0.25 to 0.45 nmol / l; a molybdenum salt in an amount in the range of from about 0.5 to 0.7 nmol / l; a copper salt in an amount in the range of from about 0.1 to 0.2 nmol / l; and a cobalt salt in an amount in the range of from 0.06 to 0.08 nmol / l, or any combination thereof. As mentioned above, the concentration of nutrients in the paint composition will be less than the concentration of nutrients in the growth medium. Thus, the growth medium may comprise one or more, and preferably all, of: a phosphate source in an amount in the range of from around 0.2 to 0.3 mmol / l; a nitrate source in an amount in the range of from around 17 to 18 mmol / l; a sulfate source in an amount in the range of from around 0.25 to 0.35 mmol / l; a calcium source such as CaCI2 in an amount in the range of from around 0.2 to 0.35 mmol / l; an acid in an amount in the range of from around 0.025 to 0.035 mmol / l; a boronic acid in the amount in the range of from about 0.04 to 0.05 mmol / l; a manganese salt in an amount in the range of from about 0.009 to 0.01 mmol / l; a zinc salt in an amount in the range of from about 0.75 to 0.85 nmol / l; a molybdenum salt in an amount in the range of from about 0.001 to 0.002 mmol / l; a copper salt in an amount in the range of from about 0.3 to 0.4 nmol / l; and a cobalt salt in an amount in the range of from 0.15 to 0.25 nmol / l, or any combination thereof. The paint composition may comprise the growth medium in an amount of up to 60%, preferably up to 55%, and more preferably up to 50% by weight of the composition. It may comprise the growth medium in an amount of at least 25%, preferably at least 30%, and more preferably at least 40% by weight of the composition. Thus, the paint composition may comprise the growth medium in the range of from 25 to 60%, preferably from 30 to 55%, and more preferably from 40 to 50% by weight of the composition. Where the growth medium comprises multiple nutrients, it will be appreciated that these amounts refer to the total amount of growth medium (for instance, the amount added when formulating the composition) ratherthan ofthe individual nutrients it contains. It will be appreciated that the growth medium, and in particular the nutrients and amounts thereof, may be tailored to best suit the requirements of different photosynthetic microorganisms by methods well known to the person skilled in the art. Water Living paint compositions ofthe present invention also comprise water. For instance, the paint composition may comprise water in an amount of up to 98%, preferably up to 90%, and more preferably up to 85%, such as up to 80%, by weight ofthe composition. The paint composition may comprise water in an amount of at least 40%, preferably at least 42.5%, and more preferably at least 45%, such as at least 50%, by weight ofthe composition. Thus, the paint composition may comprise water in an amount in the range of from 40% to 98%, preferably from 42.5% to 90%, and more preferably from 45% to 85% by weight ofthe composition. Further optional ingredients In addition to the components described above, the paint composition may comprise additional components in order to impart or improve particular properties ofthe composition. Preferably, the paint composition comprises a humectant, for the purpose of improving its hygroscopicity and thereby further promoting the microorganism’s growth. Suitable humectants include sugar alcohols such as glycerol, sorbitol, xylitol, and maltitol; diols such as propylene glycol, hexylene glycol and butylene glycol; mono- and di-saccharides such as glucose, fructose, mannose, galactose, sucrose, lactose, trehalose, and maltose, in particular a corn syrup comprising glucose; oligosaccharides, preferably as part of a corn syrup; alphahydroxy acids such as lactic acid; aloe barbadensis leaf juice; jojoba oil; and hyaluronic acid. Preferably, the humectant comprises a sugar alcohol or a mono- and / or di-saccharide, and more preferably comprises sorbitol and / or corn syrup. It is most preferred that the paint composition comprises a combination of humectants. For instance, the composition may comprise a sugar alcohol, such as sorbitol, and a further humectant. Preferably, the further humectant comprises a mono- or di-saccharide such as glucose and / or fructose, for instance as a corn syrup. Such combinations have been found to provide improved moisture retention in the paint compositions, especially in the set paint compositions e.g. having been applied to a substrate. It has also been found that combining a sugar alcohol, a mono- or di-saccharide such as glucose and / or fructose (such as a corn syrup) and a polysaccharide binder such as an alginate leads to surprisingly improved moisture retention. Thus, the composition may comprise a sugar alcohol, a mono- or di-saccharide such as glucose and / or fructose (for instance as part of a corn syrup) and a polysaccharide binder such as an alginate. In this instance, these compounds may be present in the composition in a total combined amount of at least 1%, preferably at least 1.25%, and more preferably at least 1.5% by weight of the composition. More generally, humectants may be present in the paint composition in an amount of up to 6%, preferably up to 5 %, and more preferably up to 4% by weight of the composition. The paint composition may comprise humectants in an amount of at least 0.1%, preferably at least 0.2%, and more preferably at least 0.25% by weight of the composition. Thus, the paint composition may comprise humectants in an amount in the range of from 0.1 to 6%, preferably from 0.2 to 5%, and more preferably from 0.25 to 4% by weight of the composition. Where a combination of humectants is present, these amounts may represent the total amount of humectant present in the composition. Alternatively, although less preferred, the composition may comprise humectants in an amount of up to 12%, such as up to 10%, or such as up to 9% by weight of the composition. The paint composition may comprise humectants in an amount of at least 1%, such as at least 3%, or such as at least 5% by weight of the composition. Thus, the paint composition may comprise a humectant in an amount in the range of from 1 to 12%, such as from 3 to 10%, or such as from 5 to 9 % by weight of the composition. In certain cases, higher amounts of humectant can be detrimental to growth of the photosynthetic microorganism. In terms of molarity, the paint composition may comprise a humectant in an amount of up to 1 mol / l, preferably up to 0.5 mol / l, and more preferably up to 0.25 mol / l. The paint composition may comprise a humectant in an amount of at least 0.005 mol / l, preferably at least 0.01 mol / l, and more preferably at least 0.015 mol / l. Thus, the paint composition may comprise the humectant in an amount in the range of from 0.005 to 1 mol / l, preferably from 0.01 to 0.5 mol / l, and more preferably from 0.015 to 0.25 mol / l. Alternatively, although less preferred, the composition may comprise a humectant in an amount of up to 1.1 mol / l, such as up to 0.9 mol / l, or such as up to 0.8 mol / l. It may comprise a humectant in an amount of at least 0.1 mol / l, such as at least 0.3 mol / l, or such as at least 0.5 mol / l. Thus, the paint composition may comprise a humectant in an amount in the range of from 0.1 to 1.1 mol / l, such as from 0.3 to 0.9 mol / l, or such as from 0.5 to 0.8 mol / l. Another ingredient which may be included is an acid. Acids have been found to increase the growth rate of the photosynthetic microorganism, particularly during the first few days following the composition’s formulation. Any suitable acid may be used in order to provide a composition at a suitable pH, which may be in the range of from pH 7 to 8, preferably from pH 7 to 7.5, and more preferably around pH 7.1. Preferably, the acid is an organic acid such as formic acid, acetic acid, citric acid, lactic acid, oxalic acid, uric acid, malic acid, tartaric acid, butyric acid and folic acid. More preferably the acid is citric acid, for instance wherein the citric acid is provided to the composition in the form of lemon zest. Where lemon zest is added to the composition in order to provide the citric acid, the lemon zest may be added in an amount of up to 10g, preferably up to 5g, and more preferably up to 4g per litre of the composition. Lemon zest may be added in an amount of at least 1g, preferably at least 2g, and more preferably at least 3g per litre of the paint composition. Thus, the lemon zest may be added in an amount of from 1 to 10g, preferably from 2 to 5g, and more preferably from 3 to 4g per litre of the paint composition. The paint composition may also include a thickener, i.e. a substance able to increase the viscosity of the composition. For instance, the paint composition may comprise psyllium husk, beeswax. The paint composition may also include a colourant additive, in order to improve the aesthetics of the composition, for instance by reducing translucency. The colourant additive may be a clay, such as French green clay, French pink clay, red clay, Rhassoul clay, French yellow clay, Brazilian purple clay, or white clay such as bentonite and kaolin clays. Preferably, the colourant additive is a montmorillonite clay, and more preferably is French green clay. Where country names are provided in the list of clays above, it will be appreciated that these are not intended to limit the subject-matter to clays specifically derived from such countries, but merely represent the common names used to describe these clays. The paint composition may comprise the colourant additive in an amount of up to 2%, preferably up to 1 %, and more preferably up to 0.25% by weight of the paint composition. The colourant additive may be used in an amount of at least 0.05%, preferably at least 0.1%, and more preferably at least 0.15% by weight of the paint composition. Thus, the paint composition may comprise the colourant additive in an amount in the range of from 0.05% to 2%, preferably from 0.1% to 1%, and more preferably from 0.15% to 0.25% by weight of the paint composition. In some instances, a clay may be added in significantly higher amounts than would be required simply for use as a colourant additive. In these higher amounts, the clay can act as a porous filler material, which has been found to promote gas exchange within the composition. Suitable clays for this purpose include phyllosilicates such as halloysite, kaolinite, pyrophyllite, bentonite, montmorillonite, talc, illite, chlorite, vermiculite, antigorite, chrysotile, lizardite. Preferably, the clay comprises kaolinite. The clay may be present in an amount of up to 40%, preferably up to 35%, and more preferably up to 30% by weight of the paint composition. The paint composition may comprise the clay in an amount of at least 10%, preferably at least 15%, and more preferably at least 20% by weight of the composition. Thus, the paint composition may comprise the clay in an amount in the range of from 10 to 40%, preferably from 15 to 35%, and more preferably from 20 to 30% by weight of the composition. The paint composition may also comprise a UV protectant, i.e. a compound which is able to absorb UV radiation, in order to promote the survival of the photosynthetic microorganisms. For instance, the paint composition may comprise an inorganic UV protectant such as calcium carbonate and titanium dioxide, or an organic UV protectant which does not compromise the ability of the photosynthetic microorganisms to grow, such as benzophenones, salicylates, benzotriazoles, cinnamates, p-aminobenzoates, triazines and camphors. Preferably, the UV protectant is an inorganic UV protectant, and more preferably is calcium carbonate. The paint composition may comprise the UV protectant in an amount of up to 10%, preferably up to 8%, and more preferably up to 7% by weight of the composition. The composition may comprise a UV protectant in an amount of at least 0.5%, preferably at least 1%, and more preferably at least 2.5% by weight of the composition. Thus, the paint composition may comprise a UV protectant in an amount in the range of from 0.5 to 10%, preferably from 1 to 8%, and more preferably 2.5 to 7% by weight of the composition. Preferably, the composition will comprise at least a humectant and a clay filler of the types described herein, and more preferably will comprise a humectant, a clay filler and a UV protectant. Method of making a living paint composition In another aspect, the present invention relates to a method for making a living paint composition as described above. This method comprises a step i) of incorporating a living photosynthetic microorganism into a composition comprising water and a binder which is at least partially set such that the living photosynthetic microorganism is dispersed throughout the composition to form a living paint. Incorporation of the photosynthetic microorganism may be performed by any suitable mixing means, such as a mechanical stirrer, agitator or vortexer. Preferably, the incorporation of the photosynthetic microorganism is performed using low shear mixing, in particular when the binder is not an agar. Compared to using higher shear conditions, this may result in improved structural integrity of the resulting composition. For instance, the incorporation of the photosynthetic microorganism may be performed using a stirrer at up to 5000 rpm, preferably up to 3500 rpm, and more preferably up to 2000 rpm. In the incorporation, it is preferred that sharp blades are avoided, for instance by using a paddle stirrer, Z blade mixer, a folding mixer or a tumbling mixer. Where the method comprises the incorporation of further ingredients, e.g. as discussed below, it is preferred that each of these further ingredients is incorporated using low shear mixing as described above. The photosynthetic microorganism may be incorporated in an amount of up to 2x109 cells, such as up to 1x109 cells, or such as up to 8x108 cells per litre of the paint composition. The living paint composition may comprise at least 1x107 cells, such as at least 5x107 cells, or such as at least 1x108 cells per litre of the paint composition. Thus, the paint composition may comprise the living photosynthetic microorganism in an amount in the range of from 1x107 to 2x109 cells, such as from 5x107 to 1x109 cells, or such as from 1x108to 8x108 cells per litre of the paint composition. Where greater pigmentation of the paint compositions initially is desirable, the paint composition may comprise the living photosynthetic microorganism in a higher amount, such as in an amount of up to 1x1012 cells, preferably up to 5x1011 cells, and more preferably up to 2.5x1011 cells per litre of the paint composition. In these instances, the paint composition may comprise the living photosynthetic microorganism in an amount of at least 1x109 cells, preferably at least 5x109 cells, and more preferably at least 1x1010 cells. Thus, the paint composition may comprise the living photosynthetic microorganism in an amount in the range of from 1x109 to 1x1012 cells, preferably from 5x109 to 5x1011 cells, and more preferably from 1x1010 to 2.5x1011 cells per litre of the paint composition. For instance, the photosynthetic microorganism is preferably incorporated into the composition as an aqueous mixture. The aqueous mixture may have an optical density (OD600) of up to 10, preferably up to 5, and more preferably up to 3. It may have an optical density (OD600) of at least 0.1, preferably at least 1, and more preferably at least 2. Thus, the photosynthetic organism may be incorporated as an aqueous mixture having an optical density (OD600) in the range of from 0.1 to 10, preferably in the range of from 1 to 5, and more preferably in the range of from 2 to 3. As such, the photosynthetic organism may be incorporated as an aqueous mixture having a cell density in the range of from 1x105 to 1x108 cells, preferably from 1x106 to 1x107 cells, and more preferably from 5x106 to 8x106 cells per ml of the aqueous mixture. Alternatively, where greater pigmentation of the paint compositions initially is desirable, the aqueous mixture may have an optical density (OD600) of up to 25, preferably up to 20, and more preferably up to 15. It may have an optical density of at least 5, preferably at least 7.5, and more preferably at least 10. Thus, the photosynthetic organism may be incorporated as an aqueous mixture having an optical density (OD600) in the range of from 10 to 25, preferably in the range of from 7.5 to 20, and more preferably in the range of from 10 to 15. Where this greater pigmentation is desirable, the paint composition may comprise the living photosynthetic microorganism at an average density in the range of from 1x106 to 1x109 cells, preferably from 5x106 to 5x108 cells, and more preferably from 1x107 to 2.5x108 cells per ml of the paint composition. Optical density of an aqueous solution of cells may be measured using a spectrophotometer at a wavelength of 600nm, using a sample of the cell solution in a cuvette having a path length of 1 cm. Serial dilutions were used for optical density values greater than about 1. Where the photosynthetic microorganism is incorporated into the composition as an aqueous mixture having the described optical density properties, the aqueous mixture may be incorporated in an amount of up to 200 ml / l, preferably up to 150 ml / l, more preferably up to 100 ml / l, and most preferably up to 50 ml / l of the composition. The aqueous mixture may be incorporated in an amount of at least 10 ml / l, preferably at least 20 ml / l, more preferably at least 25 ml / l, and most preferably at least 30 ml / l, such as at least 50 ml / l or at least 75 ml / l of the composition. Thus, the aqueous mixture may be incorporated in an amount in the range of from 10 to 200 ml / l, preferably from 20 to 150 ml / l, more preferably from 25 to 100 ml / l, and most preferably from 30 to 50 ml / l of the composition. A relatively high concentration of photosynthetic microorganism, from which appropriate aqueous mixtures can be prepared, may be achieved by methods known to the skilled person, for instance by using centrifugation or, for larger volumes, by flocculation. Alternatively, although less preferred, the method may further comprise a blending step before step i), wherein a composition comprising water and a binder which is at least partially set is blended to reduce its viscosity and form a blended composition, this blended composition being used as the composition into which the living photosynthetic microorganism is incorporated in step i). This blending step is, however, preferred where the binder comprises agar, and especially where a combination of binders is present where agar is e.g. a secondary binder in an amount at least equal to the amount of primary binder. As mentioned, the composition which is used in step i) of the method, and in the blending step (where present) comprises water and a binder, wherein the binder is at least partially set. A binder being at least partially set means that the process of gelation ( / .e. the formation of a three-dimensional network by cross-linking of the binder) has at least begun to occur before or during the step, and thus that the composition has a higher viscosity than it did immediately following the addition of the binder. In methods where a blending step is present, it is preferred that the composition has fully set before the blending process occurs. As used herein, blending refers to the application of a stress, preferably a shear stress, on the composition. This may be achieved using e.g. a stirrer, a rotary mixer, a rotor / stator mixer, a blender or a homogeniser, and preferably using a blender. Where used, the process of blending the composition produces a blended composition. Blending the composition may serve to modify its microstructure; for instance, where the binder is a gelling agent (as is preferred), blending may reduce the extent of cross-linking within the composition such that the distance spanned, on average, by the cross-linked network is lower than in a quiescent gel (i.e. a gel which is formed without the application of shear). As such, the blended composition may be a fluid gel, i.e. a suspension of gelled particles dispersed in a non-gelled continuous medium, formed by the application of shear to the binder solution undergoing (or having finished) gelation. It will be appreciated that cross-linking need not refer solely to covalent bonds, and that cross-linking in e.g. agar can arise from ionic and hydrogenbonding interactions. The viscosity of the blended composition is lower than that of the composition before it was blended, rendering it suitable to act as a paint composition. For instance, the viscosity of the blended composition is preferably substantially the same as that for the paint composition, as described above. Preferably, the blended composition does not contain any lumps visible to the naked eye; in other words, it is smooth. The binder present in the composition used in step i) or, where present, the blending step, is the same as already described in relation to the paint composition itself. Similarly, the composition which is used in step i) or, where present, the blending step, comprises the binder and water in substantially the same amounts as described earlier in relation to these constituents in the paint composition itself. Intervening steps may take place between the formation of the blended composition in the blending step and the incorporation of a living photosynthetic microorganism in step i). Preferably, however, the blended composition is used directly in step i). A growth medium is either present in the composition used in step i) or is incorporated during or after step i). Where the growth medium is incorporated during step i), the growth medium may be added at the same or an overlapping time as the photosynthetic microorganism (i.e. while the microorganism is being incorporated). Alternatively, the growth medium may be incorporated after the incorporation of the microorganism, or before the incorporation of the microorganism. Preferably, however, the growth medium is already present in the composition that is used in step i), such that this composition comprises water, a binder which is at least partially set, and the growth medium. For instance, this may mean that the growth medium is present in the composition used in the blending step, where present. The growth medium is the same as already described in relation to the paint composition itself. Similarly, the growth medium is comprised in the composition used in step i) or the blending step, or is incorporated after step i), in the same amounts as described earlier in relation to the presence of the growth medium in the paint compositions itself. Similarly, a humectant may either be present in the composition used in step i) or is incorporated during or after step i). Where the humectant is incorporated during step i), it may be added at the same or an overlapping time as the photosynthetic microorganism (i.e. while the microorganism is being incorporated). Alternatively, the growth medium may be incorporated after the incorporation of the microorganism, or before the incorporation of the microorganism. Preferably, however, the humectant is present in the composition used in step i), such that this composition comprises at least water, a binder which is at least partially set, and a humectant. It is also preferred that the binder is allowed to at least partially set before the humectant is introduced. The composition formed by incorporating the photosynthetic microorganism in step i) is preferably the final paint composition, although further steps may also be performed afterwards to arrive at a final paint composition. Further steps The method of making a living paint composition preferably further comprises a prior step of preparing the composition that is used in step i), or the composition used in the blending step (where present). Where the binder comprises agar, this preparation step involves heating the composition of binder and water. Otherwise, the preparation step involves combining the binder with water which is at a temperature greater than room temperature, to form, the composition of binder and water. It will be appreciated that this composition of binder and water are the same constituents as are present in the composition to be used in step i) or the blending step. In the preparation step, the temperature of the water that is combined with the binder may be at least 50°C, preferably at least 80°C, and more preferably at least 90°C. Following addition of the water at an elevated temperature, the mixture may then be stirred under low shear conditions to provide a smooth gel. In the preparation step involving heating where the binder is agar, the binder and water are preferably already intermixed, although they may be mixed together as part of the preparation step. As part of this preparation step, the composition comprising binder and water may be heated to an elevated temperature. This is preferred where the binder comprises agar. As used herein, an elevated temperature refers to a temperature sufficient to convert a portion of the water in the composition into gaseous form, such that the overall weight of the composition is reduced. For instance, the temperature may be at least 50°C, preferably at least 80°C, and more preferably at least 90°C. In particular, the composition comprising binder and water may be boiled, i.e. held at a temperature of at least 90% or higher, preferably 100%, of the composition’s boiling point. For the compositions described herein, which comprise water, the boiling point will be around 100°C, although it will be understood that this may vary depending upon the external pressure. The composition may be heated to an elevated temperature fora period of at least 50 seconds, preferably at least 100 seconds, and more preferably at least 180 seconds. These heating times have been found to result in higher levels of moisture retention in the paint composition once painted onto a substrate. It is believed that such properties may result from the presence of larger pores and reduced fibrosity in the microstructure of the binder. As a result of the heating, the weight of the composition comprising binder and water may decrease by at least 5%, preferably at least 10%, and more preferably at least 15%. The weight of the composition may decrease by up to 40%, preferably up to 30%, and more preferably up to 25%. Thus, by heating the composition comprising binder and water at an elevated temperature as part of the preparation step, the weight of the composition may decrease by an amount in the range of from 5 to 40%, preferably from 10 to 30%, and more preferably from 15 to 25%. The composition comprising binder and water used in the preparation step may comprise a binder in an amount of up to 60 g / l, preferably up to 50 g / l, and more preferably up to 40 g / l of water. The composition may comprise a binder in an amount of at least 10 g / l, preferably at least 20 g / l, and more preferably at least 30 g / l of water. Thus, the composition may comprise a binder in an amount in the range of from 10 to 60 g / l, preferably from 20 to 50 g / l, and more preferably from 30 to 40 g / l. The composition comprising binder and water used in the preparation step may comprise a binder in an amount of up to 0.2 mol / l, preferably up to 0.15 mol / l, and more preferably up to 0.12 mol / l. The composition may comprise the binder in an amount of at least 0.03 mol / l, preferably at least 0.06 mol / l, and more preferably at least 0.08 mol / l. Thus, the composition may comprise the binder in an amount in the range of from 0.03 to 0.2 mol / l, preferably from 0.06 to 0.15 mol / l, and more preferably from 0.08 to 0.12 mol / l. In the situation where the growth medium is not added during step i), the growth medium is preferably added after the composition has been boiled, i.e. once heat has been removed, or afterthe binder and water have been combined. In this case, the growth medium is preferably added as an aqueous solution comprising the growth medium in an amount of up to 50 ml / l, preferably up to 35 ml / l, and more preferably up to 25 ml / l. The solution may comprise the growth medium in an amount of at least 1 ml / l, preferably at least 10 ml / l, and more preferably at least 15 ml / l. Thus, the solution may comprise the growth medium in an amount in the range of from 1 to 50 ml / l, preferably from 10 to 35 ml / l, and more preferably from 15 to 25 ml / l. The method may further comprise a cooling step after step i). The cooling step can assist the composition in retaining its consistency during extended periods of storage before application to a substrate. This cooling step may comprise cooling the composition at a temperature in the range of from 1 to 5°C for up to 10 minutes, preferably for up to 8 minutes, and more preferably for up to 5 minutes. However, it will be understood that the composition may still set at higher temperatures, for instance at room temperature. The method may also comprise a step of adding an acid, of the type and in the amount as described earlier in relation to the composition itself. Preferably, the addition of an acid occurs at the same time as the addition of the growth medium, more preferably wherein the acid is mixed into the growth medium. The method preferably comprises a step of adding a humectant. The humectant may be added prior to, or during, step i). Method of painting a substrate In a further aspect, the present invention relates to a method of painting a substrate using a paint composition of the present invention. Specifically, the method comprises coating a substrate with a living paint composition of the present invention, to form a coating layer. By applying a living paint composition as described to a substrate, the photosynthetic microorganisms contained therein are provided onto the substrate in a composition which can sustain their survival and facilitate their photosynthetic activity. Since photosynthesis utilises carbon dioxide, which would be present in the atmosphere surrounding the substrate, this photosynthetic activity will reduce the level of carbon dioxide. Therefore, in another aspect this method provides a method of increasing the carbon dioxide absorption capacity of a substrate, comprising coating a substrate with the living paint compositions of the present invention to form a coating layer. Increasing carbon dioxide absorption of a substrate refers to its ability to remove carbon dioxide from its surrounding environment. Specifically, this method provides a substrate with a coating layer that can remove more carbon dioxide from its environment, as compared to the substrate without said coating layer. Carbon dioxide concentration can be measured using e.g. an infra-red gas analyser. A substrate refers to a solid material upon which a paint composition may be painted. Preferably, the substrate is a construction material, i.e. a material which is commonly used in construction, such as a building material, and more preferably the substrate is a material which is typically used to form an exterior surface of a building or other outdoor installation. Suitable building materials include: ceramics such as fired bricks and tiles; cement; concrete; fabrics; glass; metal; plastic; stone; and wood. Preferably, the substrate is ceramic, concrete, metal or plastic, as these materials have low water absorbency. In these methods, coating of the substrate may be performed with any known means for applying paint. For instance, the paint composition may be coated onto the substrate using a paintbrush, a paint roller or as a spray paint, wherein applying the coating composition as a spray paint preferably comprises applying more than one layer of the paint composition in order to form the coating layer. Coating the substrate with the paint composition forms a coating layer of the paint composition on the substrate. It will be understood that the coating layer need not completely cover all surfaces of a substrate or even fully cover the whole of one constituent surface of the substrate; therefore, the coating layer covers at least a portion of a surface of the substrate, but preferably covers the majority of a surface of the substrate, and more preferably covers the whole of a surface of the substrate. As used herein, a surface refers to an outer face of the substrate, for instance one face of the six faces of a cube would be a surface. The coating layer may have a thickness of up to 5 cm, preferably up to 4 cm, more preferably up to 3 cm, and most preferably up to 1.5 cm. The thickness of the coating layer may be at least 1 mm, preferably at least 5 mm, more preferably at least 7 mm, and most preferably at least 9 mm. Thus, the thickness of the coating layer may be in the range of from 1 mm to 5 cm, preferably from 5 mm to 4 cm, more preferably from 7 mm to 3 cm, and most preferably from 9 mm to 1.5 cm. It will be appreciated that the thicknesses of layers referred to herein represent the average minimum and maximum thicknesses the layer may have, i.e. a thickness of from A to B means that the minimum thickness of the layer is at least A and the maximum thickness of the layer is up to B. The thickness of the coating layer may be measured using scanning electron microscopy. Specifically, scanning electron microscopy may be used to generate images of this layer, with the thickness preferably determined using a computer program. The coating layer may be applied to an area on the substrate of at least 0.5 m2, preferably at least 1 m2 and more preferably at least 5 m2. The coating layer refers to the layer of paint composition which has recently been applied to the substrate and has not set. Preferably, these methods comprise a further step of setting the coating layer to form a set coating layer. Setting, as used herein in relation to coating layers, refers to a process whereby the moisture level of the coating layer is reduced, for instance by standard drying processes. At temperatures in the range of from 25-35°C, setting may take approximately 24-48 hours. The set coating layer may have a moisture level of up to 35%, preferably up 30%, and more preferably up to 25% by weight. The set coating layer may have a moisture level of at least 1%, preferably at least 5%, and more preferably at least 10% by weight. Thus, the set coating layer may have a moisture level in the range of from 1% to 35%, preferably from 5% to 30%, and more preferably from 10% to 25% by weight. Moisture levels may be measured using thermogravimetric analysis. The set coating layer is thinner than the coating layer immediately following its application onto the substrate. For instance, the set coating layer may have a thickness of up to 5 mm, preferably up to 3 mm, and more preferably up to 1 mm. It may have a thickness of at least 0.1 mm, preferably at least 0.2 mm, and more preferably at least 0.5 mm. Thus, the set coating layer may have a thickness in the range of from 0.1 mm to 5 mm, preferably from 0.2 mm to 3 mm, and more preferably from 0.5 mm to 1 mm. At a temperature of around 30°C, setting of the coating layer may take up to 60 hours, preferably up to 55 hours, and more preferably up to 48 hours. Setting may take at least 15 hours, preferably at least 20 hours, and more preferably at least 24 hours. Thus, setting of the coating layer may take in the range of from 15 to 60 hours, preferably from 20 to 55 hours, and more preferably from 24 to 48 hours. However, it will be appreciated that these times may vary depending on external factors, such as temperature. For instance, at around 34°C the average setting time may be in the range of from 20-30 hours. Painted substrate In another aspect, the present invention provides a painted substrate which comprises a substrate and the living paint composition, as described herein, coated thereon. The substrate is a substrate as already described herein. Where the paint composition has not yet set, it may form a fresh coating layer on the substrate. The fresh coating layer corresponds to the coating layer as already described herein in relation to the method of painting a substrate, for instance with regard to its thickness. Preferably, however, the living paint coated on the substrate forms a set coating layer, said set coating layer being as already described in relation to the method of painting a substrate, for instance as regards its thickness and moisture content. Examples The invention will now be described with reference to the following non-limiting examples. Example 1A: Ingredients to make a sample of a living paint composition Ingredient % w / w Cellulose binder 2.50% Sodium alginate 1.0% Corn syrup 0.30% Sorbitol 0.30% Agar 0.50% Photosynthetic microorganism1 2.0% Water inc. growth medium2 93.2% 1Optical density of 2.75; 2Growth medium nutrients in amounts up to those listed in Example 3 To provide a 50 ml batch of this composition, the hydroxypropylmethylcellulose (approx. 1.25 g of dry powder), sodium alginate (0.5 g), agar (0.25 g) and corn syrup (0.15 g) were combined before 10 ml of boiling water was added, and the resulting solution stirred to form a smooth gel base. Approximately 25 ml of cold water comprising nutrients (as the growth medium) was then added gradually while maintaining the stirring. The resulting gel was refrigerated overnight, after which a 5 ml solution containing sorbitol (0.15 g) was added and mixed into the gel. Finally, a solution of concentrated photosynthetic microorganisms was added. This mixture was gently mixed to ensure a homogenous distribution, and additional water added as appropriate to arrive at a 50 ml batch having a desired consistency. Example 1B: Ingredients to make a further sample of a living paint composition Ingredient % w / w Photosynthetic microorganism1 2.0% Cellulose binder 2.5-4% Water inc. growth medium2 56.2-57.7% Sodium alginate 1.0% Corn starch 3.0% Corn syrup 0.3% Sorbitol 0.3% Kaolin clay 25.0% Calcium carbonate 5.0% Diatomaceous earth 3.0% 1Optical density of 2.75 2Growth medium nutrients in amounts up to those listed in Example 3 To provide a 50 ml batch of this composition, a cellulose binder (approx. 1.25 to 2 g), sodium alginate (0.5 g), corn starch (1.5 g) and corn syrup (0.15 g) were combined before 10 ml of boiling water was added, and the resulting solution stirred to form a smooth gel base. Approximately 25 ml of cold water comprising nutrients (as the growth medium) was then added gradually while maintaining the stirring. The resulting gel was refrigerated overnight, after which a 5 ml solution containing sorbitol (0.15 g) was added and mixed into the gel. A dry mixture of kaolin clay (12.5 g), calcium carbonate (2.5 g) and diatomaceous earth (1.5 g) was prepared, and subsequently incorporated slowly into the gel. Finally, a solution of the concentrated photosynthetic microorganisms was added. This mixture was gently mixed to ensure homogenous distribution, and additional water added as required to arrive at a 50 ml batch having a desired consistency. Example 1C: Ingredients to make an approx. 55ml sample of a living paint composition Ingredient Amount Synechosystis PCC68031 5 ml Agar agar 0.4 g De-ionised water 25 ml Lemon zest 0.2 g Growth medium2 25 ml 1 Optical density of 2.75 2 BG-11 available from Sigma-Aldrich. As used here, contains (per 1L): NaNOs: 1.5g; K2HPO4: 0.04g; MgSO4'7H2O: 0.075g; CaCl2'2H2O: 0.036g; Citric acid: 0.006g; Ferric ammonium citrate: 0.006 g; EDTA (disodium salt): 0.001g; Na2COs: 0.02g; Trace metal mix3: 1.0 ml. 3 Trace metal mix contains (per 1L): H3BO3: 2.86g; MnCl2'4H2O: 1.81g; ZnSO4'7H2O: 0.222g; NaMoO4'2H2O: 0.39g; CuSO4'5H2O: 0.079g; Co(NO3)2-6H2O: 49.4mg. Example 2: Manufacture of a living paint composition according to Example 1C 25 ml of deionised water was mixed with 0.5 ml of growth medium, followed by the addition of 0.2g of lemon zest. The resulting mixture was agitated for 30 seconds. Separately, 0.4g of agar agar powder was mixed with 25 ml of deionised water and agitated 10 for30 seconds, before being heated to boiling point and boiled fora period of 2 minutes. The agar mixture is then removed from the heat, and stirred while adding the previously prepared mixture of growth medium and lemon zest. Following this, the resulting mixture was left to cool and set for at least 10 minutes. A cyanobacteria (Synechosystis PCC6803) sample was prepared by centrifuging a 50ml 15 sample of de-concentrated cyanobacteria for 15 minutes at 4000 rpm, and removing the water fraction to produce a 5ml concentrated sample. The concentration was checked, and adjusted as required, to an optical density of 2.75 using a spectrophotometer measured at 600nm with a 1 cm path length cuvette. Once the agar mixture has at least partially set, it was blended until no lumps were visible to 20 the naked eye. The 5ml sample of cyanobacteria at an optical density of 2.75 was then stirred into the blended composition, to form a living paint composition. Example 3: Growth medium nutrients Experiments were performed to determine the amounts of certain nutrients in the growth medium that sustained good levels of growth in the photosynthetic microorganisms. An exemplary composition, showing the total amount of each nutrient present in the paint 5 composition, is shown in Table 1 below. It will be appreciated, however, that the paint composition may still comprise these nutrients, or selections thereof, in amounts different to these, for instance as discussed above. Table 1 Nutrient Final concentration in paint composition (g / L) NaNO3 15 K2HPO4 4.568504884 MgSO4 (anhydrous) 1.83 CaCl2'2H2O 1.8 Citric acid 0.3 Ferric ammonium citrate 0.01 EDTA (disodium salt) 0.0376 Na2COs 1 Trace metals (as indicated below) Trace metals ZnSO4-7H2O 0.02199326332 CuSO4-5H2O 0.000001964196917 MnCl2'4H2O 0.0004322646128 Co(NO3)2'6H2O 0.00000988 NaMoO4-2H2O 0.001141084908 H3BO3 0.002860057201 10 Example 5: Effect of agar binder on moisture content Compositions were formulated comprising various amounts of binder, which in these tests was agar, and tested fortheir moisture content when set. Aside from the varied amounts of binder, as described below, the compositions each comprised: 5ml of photosynthetic microorganism (Spirulina) at an optical density (OD600) of 2.75, 50ml of deionised water, and 50ml of growth medium. During the synthesis, the agar and water mixture was boiled for 120 seconds before addition of the growth medium and photosynthetic microorganism. Once synthesised, the compositions were poured onto a substrate to form a layer, the moisture of which was tested when set. The results are shown in Table 2, below, and are illustrated in Figure 1. As can be seen, below a certain threshold increasing the agar binder content results in an increase in moisture content in the set coating layer. Table 2 Agar content (wt.%) 0.36 0.48 0.55 0.76 0.95 1.9 Moisture Content (wt.%) 4.9 6.6 7.9 9.3 8.6 6.4 Example 6: Influence of binder A representative paint composition comprising 4 wt.% of a cellulose binder (hydroxypropyl methylcellulose), a growth medium and a photosynthetic microorganism was tested by application to a substrate, to demonstrate that the cellulose binder provided an excellent growth environment. The results are shown in Figure 2, which depicts a metric indicative of the content of microorganism biomass of the compositions over time, and demonstrates that the compositions using a cellulose binder are effective at promoting and sustaining growth of the microorganisms. Other cellulose binders (methylcellulose and hydroxyethyl cellulose) were also tested. While these binders still provided effective paint compositions, hydroxypropyl methylcellulose provided higher viscosities and formed a more favourable gel structure. As a comparison, acrylic acid-based binders were also examined in paint compositions according to the present invention. However, these compositions, once applied to a substrate, proved to be unsuitable for sustaining the photosynthetic microorganisms, leading to death of the microorganisms and bleaching of the paint composition. It is believed that degradation products from weathered acrylics {e.g., mono- / dicarboxylic acids) can be toxic, reducing biomass and photosynthesis rates. The weathered acrylics may also form hydrophobic surfaces which reduce permeability significantly, thereby impeding gaseous diffusion. Example 7: Effect of presence of secondary binder The presence of a secondary binder, in this instance a sodium alginate binder, was also examined to determine its influence on the growth of the photosynthetic microorganisms. A control composition comprising 3 wt.% of a cellulose binder, the photosynthetic microorganism and a growth medium was compared with equivalent compositions further comprising 0.5 wt.%, 0.75 wt.%, and 1 wt.% of sodium alginate. As shown in Figure 3, after 12 days the total biomass of the paint compositions that comprised sodium alginate were each higher than the control sample, but the samples comprising 0.75 wt.% and 1 wt.% demonstrated particular increases in growth. It is believed that the secondary binder, especially an alginate, helps to improve porosity of the binder structure and can increase moisture retention in the paint compositions, which may account at least in part for these results. Example 8: Effect of boiling time on moisture content Where the binder is agar, a preferred part of the method of manufacturing a living paint composition is a step of boiling the agar binder composition. Variations in this boiling time were tested fortheir impact on the moisture content of the resulting paint composition when set. For these experiments, samples of 50ml of deionised water with 1g of agar binder were boiled for varying amounts of time. After boiling was completed, 50 ml of growth medium was added and the composition was then refrigerated at 4 Celsius for 5 minutes, after which time the 5ml of photosynthetic microorganism at an optical density (OD600) of 2.75 was added while the composition was blended. Once synthesised, the compositions were poured onto a substrate to form a layer, the moisture of which was tested after 1 week. The results are shown in Table 3, below, and are illustrated in Figure 4 in graphical form. Table 3 Boiling time (s) 15 33 60 90 120 180 Moisture Content (wt.%) 0 7.8 9.4 8.7 11.6 14.9 Example 9A: Effect of a glycerol humectant on moisture content Compositions were formulated with different amounts of glycerol present, and tested fortheir moisture content when set. For these experiments, the composition used comprised: 5ml of photosynthetic microorganism at an optical density (OD600) of 2.75, 0.5g of agar, 25ml of deionised water, and 25ml of growth medium, using a boil time of 120 seconds. The results are shown in Table 4, below, and are illustrated in Figure 5. Table 4 Glycerol content (g) 0.62 1.72 2.29 4 8.36 Moisture Content (wt.%) 11.7 12.3 13.3 14.6 14.9 Example 9B: Effect of further humectants on moisture content Moisture content of the paint compositions can be an important factor in promoting survival and growth of the living photosynthetic microorganisms. For instance, moisture contents of above about 10-20% have been found particularly suitable for survival of certain microorganisms (such as Synechocystis spp. PCC6803), with higher moisture contents being associated with higher growth rates. Compositions were formulated with varying amounts (0.5 wt.%, 1 wt.%, 1.5 wt.% and 2 wt.%) of sorbitol and corn syrup, and tested for their moisture content immediately following their production, and after one week following coating onto a substrate. For each composition, one sample was tested under open air conditions, and another was tested under higher humidity conditions (approximately 90% humidity). The composition used for these experiments comprised 3 wt.% methylcellulose, a growth medium and 2 wt.% of a solution of photosynthetic microorganism at an OD600 of 2.75, as well as the humectant. The control experiment did not comprise any humectant. Moisture content of the compositions was measured using a pintype moisture meter. The results of these experiments are shown in Figure 6, which depicts the moisture content of the resulting compositions. For the avoidance of doubt, for each composition (moving from left to right) the leftmost bar represents the moisture content immediately after production in open air conditions, the next bar represents the moisture content after 1 week in open air conditions, the next bar represents the moisture content immediately after production in higher humidity conditions, and the rightmost bar represents the moisture content after 1 week in higher humidity conditions. As can be seen from Figure 6, the inclusion of a humectant resulted in all cases in higher moisture retention after 1 week in higher humidity conditions as compared to the control composition. For instance, the presence of sorbitol led to moisture contents ranging from about 29% (at 1.5% sorbitol) to about 39% (at 1 % sorbitol), while the presence of corn syrup resulted in moisture contents ranging from about 12% (at 1 % corn syrup) to about 17% (at 1.5% corn syrup). Improvements in moisture content after 1 week in open air conditions were also typically found. For instance, sorbitol at 0.5% resulted in a moisture content of about 19% and corn syrup at 1.5% resulted in a moisture content of about 7%. These results at about 0.5% sorbitol and about 1.5% corn syrup therefore represented particularly favourable combinations using relatively low amounts of additive and exhibiting increased moisture retention. Example 9C: Combinations of humectants Paint compositions comprising combinations of humectants were also examined for their moisture content. In a first experiment, the results of which are shown in Figure 7, a base composition comprising 3 wt.% methylcellulose binder, a growth medium and 2 wt.% of a solution of photosynthetic microorganism at an OD600 of 2.75 was tested with 0.5 wt.% corn syrup, glycerin, sorbitol ora combination of sorbitol / corn syrup / sodium alginate. The moisture content of the resulting solutions after 1 week are shown in Figure 7. While each of the humectants provided higher moisture content at both amount levels, the combination of sorbitol / corn syrup / sodium alginate proved the most efficacious. It is believed that the inclusion of a polysaccharide secondary binder such as sodium alginate, in combination with a humectant, further enhances the moisture retentive properties of the compositions. Combinations of sodium alginate, sorbitol and corn syrup in this same base composition were further examined for their moisture content. As can be seen in Figure 8, while both compositions comprising 1 wt.% sodium alginate and 0.5 wt.% or 0.3 wt.% of each of sorbitol and corn syrup provided higher moisture contents after 1 week, the combination of 1 wt.% sodium alginate with 0.3 wt.% sorbitol and 0.3 wt.% corn syrup provided the highest moisture content in the composition, at about 12%. Example 10: Microorganism survival Living paint compositions were refrigerated at 4°C in the absence of light for a period of six months. Throughout this period, the samples retained their pigmentation, moisture and consistency. Samples of the living paint composition were also reviewed to determine whether growth of the photosynthetic microorganisms was only occurring on the outer level. All samples showed growth within the paint throughout their 2cm thickness. This indicates that the paint compositions are breathable, allowing suitable penetration of nutrients into even the deepest portions of the compositions. Figure 9 illustrates the results of a multi-sample analysis of the growth of photosynthetic microorganisms in the paint compositions, showing changes in a metric indicative of the 5 biomass of the photosynthetic microorganism overthe course of 60 days. As can be seen, the paint composition, in this instance using an agar binder, was able to sustain the living photosynthetic microorganisms and promote their continued growth over this period. Example 11: CO2 sequestration by living paint compositions Figure 10, showing changes in the carbon dioxide concentration in a sealed environment 10 containing a substrate coated with a paint composition, demonstrates that the paint compositions are able to effectively remove carbon dioxide from the environment. Specifically, overthe course of 250 hours, the carbon dioxide concentration fell from over 700 ppm to about 600 ppm. In comparison, a control experiment in the absence of the paint composition showed no change in concentration over the same time period. To enable higher accuracy of the 15 carbon dioxide sensor being used, the carbon dioxide concentration used in this test was slightly higher than atmospheric carbon dioxide levels.

Claims

1. A living paint composition for application to a surface, comprising:a) a living photosynthetic microorganism;b) a binder;c) a growth medium; andd) water.

2. The paint composition of Claim 1, wherein the composition has a viscosity in the range of from 0.1 to 1000 mPa s, 0.5 to 500 mPa s, preferably in the range of from 1 to 100 mPa s; orwherein the composition has a viscosity in the range of from 100 to 2000 mPa s, preferably from 200 to 1000 mPa s, and more preferably from 250 to 750 mPa s.

3. The paint composition of any preceding claim, wherein the living photosynthetic microorganism is dispersed throughout the composition.

4. The paint composition of any preceding claim, wherein the living photosynthetic microorganism is selected from: algae such as Polysiphonia, Chondrus, Ectocarpus, Cephaleuros, Oedogonium, Spirogyra, Desmococcus such as Desmococcus olivaceus, Coelastrella such as Coelastrella oocystiformis, Neochlorosarcina such as Neochlorosarcina negevensis and Trebouxia decolorans; cyanobacteria such as those of the genera Anabaena, Schizotrichaceae such as Schizothrix calcicole, Chalicogloea such as Chalicogloea cavernicola, Oscillatoria, Calothrix, Cyanothece, Anabaenopsis, Nostoc such as Nostoc flagelliforme; Synechococcus such as Synechococcus elongatus 3222, Mycrocystis, Gloebacter such as Gloeobacter violaceus, Synechocystis such as Synechosystis sp. PCC6803, Aphanocapsa, Gleocapsa, Microcoelus and Chroococcidiopsis such as Chroococcidiopsis cubana PCC 7433, and Tolypothrichaceae; and lichens such as Trentepohlia, Pseudocyphellaria rainierensis, Flavoparmelia caperata, and Chloroidium lichinum, or any combination thereof, and is preferably selected from a Coelastrella which is preferably Coelastrella oocystiformis; a Desmococcus which is preferably Desmococcus olivaceus; a Nostoc which is preferably Nostoc flagelliforme; a Neochlorosarcina which is preferably Neochlorosarcina negevensis; an Oscillatoria; an Oedgogonium; a Synechococcus which is preferably Synechococcus elongatus 3222; a Spirogyra; or a Tolypothrichaceae.

5. The paint composition of any preceding claim, wherein the composition comprises the living photosynthetic microorganism in an amount in the range of from 1x107to 2x109cells, preferably from 5x107to 1x109 cells, more preferably from 1x108to 8x108 cells per litre of the paint composition; orwherein the composition comprises the living photosynthetic microorganism in an amount in the range of from 5x109 to 1x1012 cells, preferably from 1x1010 to 5x1011 cells, and more preferably from 5x1010 to 2.5x1011 cells per litre of the paint composition.

6. The paint composition of any preceding claim, wherein the binder is selected from polysaccharides such as agar, cellulose and derivatives thereof such as methylcellulose, hydroxypropyl methylcellulose and hydroxyethyl cellulose;, carrageenans such as kappa, iota and lambda carrageenan, gellan gum, locust bean gum, guar gum, xanthan gum, alginates, pectin, starch such as corn starch, sodium alginate or any combinations thereof, preferably selected from a cellulose, more preferably a methylcellulose such as methylcellulose, hydroxypropyl methylcellulose, or an ethylcellulose such as hydroxyethyl cellulose, and most preferably hydroxypropyl methylcellulose.

7. The paint composition of any preceding claim, wherein the composition comprises a primary binder and one or more secondary binders different from the primary binder, preferably wherein:the primary binder is a polysaccharide, and preferably is a cellulose or a derivative thereof, and more preferably is a methylcellulose such as hydroxypropyl methylcellulose; and / orthe one or more secondary binders are each a polysaccharide, preferably comprising a starch, agar and / or an alginate, and more preferably wherein the one or more secondary binders comprises an alginate.

8. The paint composition of any preceding claim, wherein the binder is present in an amount in the range of from 1 to 7 %, preferably from 1.5 to 6 %, and more preferably from 2 to 5 % by weight of the composition.

9. The paint composition of any preceding claim, wherein the growth medium comprises one or more of: a phosphate such as K2HPO4; a nitrate such as NaNCh; a magnesium salt such as MgSO4; acids such as citric acid; a boronic acid such as H3BO3; a manganese salt such as MnCh; a zinc salt such as ZnSO4; a molybdenum salt such as NaMoO4; a copper salt such as CUSO4; and a cobalt salt such as Co(NO3)2, or any combinations thereof, preferably wherein the growth medium comprises a compound from each of these groups; and / orwherein the composition comprises water in an amount in the range of from 40 to 98%, preferably from 42.5 to 90%, and more preferably from 45 to 85% by weight of the composition.

10. The paint composition of any preceding claim, wherein the composition further comprises:a humectant, such as sugar alcohols such as glycerol, sorbitol, xylitol, and maltitol; diols such as propylene glycol, hexylene glycol and butylene glycol; mono- and di-saccharides such as glucose, fructose, mannose, galactose, sucrose, lactose, trehalose, and maltose; oligosaccharides, preferably as part of a corn syrup; alpha-hydroxy acids such as lactic acid; aloe barbadensis leaf juice; jojoba oil; and hyaluronic acid,preferably wherein the humectant is present in an amount in the range of from 0.1 to 6%, preferably from 0.2 to 5%, and more preferably from 0.25 to 4% by weight.

11. The paint composition of Claim 10, wherein the humectant comprises a sugar alcohol and / or a mono- and / or di-saccharide, and more preferably comprises sorbitol and / or corn syrup.

12. The paint composition of any preceding claim, wherein the composition further comprises:a colourant additive, which is preferably montmorillonite; and / ora thickener such as psyllium husk, or beeswax; and / ora moss such as Bryum capillare, Rhynchostegium confertum, Bryum argenteum, Brachythecium rutabulum, Plagiomnium cuspidatum, Leucobryum glaucum, Utricularia nephrophylla, Asplenium sandersonii, and Splachnum rubrum, or any combinations thereof; and / oran acid, such as biological acids such as citric acid, acetic acid and pyruvic acid, preferably wherein the acid is citric acid, and more preferably the citric acid is provided in the form of lemon zest.

13. A method of making the living paint composition of any preceding claim, comprising the steps of:i) incorporating a living photosynthetic microorganism into a composition comprising water and a binder which is at least partially set such that the living photosynthetic microorganism is dispersed throughout the composition to form a living paint,wherein a growth medium is either present in the composition used in step i) or is incorporated during or after step i).

14. The method of Claim 13, wherein the step i) of incorporating the photosynthetic microorganism is performed using low shear mixing, optionally by mixing at up to 5000 rpm, preferably up to 3500 rpm, and more preferably up to 2000 rpm.

15. The method of Claim 13, wherein the method further comprises a blending step before step i), wherein a composition comprising water and a binder which is at least partially set is blended to reduce its viscosity and form a blended composition, this blended composition being used as the composition into which the living photosynthetic microorganism is incorporated in step i).

16. The method of Claims 13 to 16, wherein the method comprises preparing the composition used in step i) or the composition used in the blending step of Claim 16 by heating the binder and waterto a temperature sufficient to convert a portion of the water in the composition into gaseous form, fora period of at least 50 seconds, preferably at least 100 seconds, and more preferably at least 180 seconds; and / or wherein the method further comprises a cooling step after step i), wherein the composition is preferably cooled at temperatures in the range of from 1 to 5°C for up to 10 minutes, preferably for up to 8 minutes, and more preferably for up to 5 minutes.

17. A method of painting a substrate, said method comprising coating a substrate with the living paint composition of any of Claims 1 to 12 to form a coating layer.

18. A method for increasing the carbon dioxide absorption capacity of a substrate, said method comprising coating a substrate with the living paint composition of any of Claims 1 to 12 to form a coating layer.

19. The method of Claims 17 or 18, wherein the paint composition is applied using a paintbrush, paint roller or as a spray paint, wherein applying the coating composition as a spray paint preferably comprises applying more than one layer of the paint composition.

20. The method of any of Claims 17 to 19, wherein the thickness of the coating layer is in the range of from 1 mm to 5 cm, preferably from 5 mm to 4 cm, more preferably from 7 mm to 3 cm, and most preferably from 9 mm to 1.5 cm; and / or wherein the method further comprises a step of setting the coating layer to form a set coated layer, wherein the thickness of the set coated layer is up to 5 mm, preferably up to 3 mm, and more preferably up to 1 mm.

21. The method of any of Claims 17 to 20, wherein the substrate is a construction material, such as a building material, preferably an exterior surface of a building or other outdoor installation.

22. Use of a living paint composition as defined in any of Claims 1 to 12 for increasing the carbon dioxide absorption capacity of a substrate.

23. A painted substrate which comprises: a substrate; and the living paint of any Claims 1 to 12 coated thereon.

24. The painted substrate of Claim 23, wherein:the living paint forms a fresh coating layer having a thickness of up to 5 cm, preferably up to 3 cm, and more preferably up to 1 cm; orthe living paint forms a set coating layer having a thickness of up to 5 mm, preferably up to 3 mm, and more preferably up to 1 mm.

25. The painted substrate of Claim 24, wherein the living paint has a moisture level in the range of from 1% to 35%, preferably from 5% to 30%, and more preferably from 10% to 25%.IntellectualPropertyOfficeApplication GB2511730.0Search report under Section 17 of the Patents Act 1977Date search completed: 22 August 2025Claims searched: 1-25International classificationSubclass and subgroup Valid from C09D101 / 28 01 / 01 / 2006 C09D105 / 12 01 / 01 / 2006 C09D5 / 00 01 / 01 / 2006 C09D7 / 40 01 / 01 / 2018Field of searchWorldwide search of patent documents classified in the following areas of the IPC:C09DDatabases used in the preparation of this search report:SEARCH-NPL; SEARCH-PATENTDocuments considered to be relevantPatent literatureRelevant claims Document of relevanceCategoryX 1,3,4,6,9,12,13,15 19,21-23 at least JP 06136293 A (KAJIMA), see particularly paragraphs [0011] &[0021]. X 1,3,12,17-19,21 23 at least JP 08183914 A (OKABE et al), see whole document. X 1,3,17-24 at least JP 03111460 A (SUMITOMO CEMENT), see particularly Example 5.Non-patent literatureCategory Relevant claims Document of relevance X 1,3,4,17,18,22,23 Microbiology Spectrum, Vol. 11, No. 5, 25 / 09 / 2023, KRINGS et al, “Oxygen evolution from extremophilic cyanobacteria confined in hard biocoatings”, pages 1-19, see particularly pages 1-2 &14.Categories Letter or symbol Description X Document indicating lack of novelty or inventive step. Y Document indicating lack of inventive step, if combined with another document of the same category. & Member of the same patent family. A Document indicating technological background. P Document published on or after the priority date but before the fling date of the present application. E Earlier application published on or after the filing date of the present application.

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