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[Katsuhiko Ariga](https://orcid.org/0000-0002-2445-2955), [Jingwen Song](https://orcid.org/0000-0003-1910-9287), [Kohsaku Kawakami](https://orcid.org/0000-0002-3466-9365)

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[Layer-by-layer designer nanoarchitectonics for physical and chemical communications in functional materials](https://mdr.nims.go.jp/datasets/dd33a5e1-96bb-4ed8-8fe6-1274fc5ec9ac)

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Layer-by-layer designer nanoarchitectonics for physical and chemical communications in functional materials2152 |  Chem. Commun., 2024, 60, 2152–2167 This journal is © The Royal Society of Chemistry 2024Cite this: Chem. Commun., 2024,60, 2152Layer-by-layer designer nanoarchitectonics forphysical and chemical communications infunctional materialsKatsuhiko Ariga, *ab Jingwen Songc and Kohsaku Kawakami cdNanoarchitectonics, as a post-nanotechnology concept, constructs functional materials and structuresusing nanounits of atoms, molecules, and nanomaterials as materials. With the concept ofnanoarchitectonics, asymmetric structures, and hierarchical organization, rather than mere assembly andorganization of structures, can be produced, where rational physical and chemical communications willlead to the development of more advanced functional materials. Layer-by-layer assembly can be apowerful tool for this purpose, as exemplified in this feature paper. This feature article explores thepossibility of constructing advanced functional systems based on recent examples of layer-by-layerassembly. We will illustrate both the development of more basic methods and more advancednanoarchitectonics systems aiming towards practical applications. Specifically, the following sections willprovide examples of (i) advancement in basics and methods, (ii) physico-chemical aspects andapplications, (iii) bio-chemical aspects and applications, and (iv) bio-medical applications. It can beconcluded that materials nanoarchitectonics based on layer-by-layer assembly is a useful method forassembling asymmetric structures and hierarchical organization, and is a powerful technique fordeveloping functions through physical and chemical communication.1. IntroductionThe development of humankind has been accompanied by theprogress of materials science. The development of new func-tional materials has enriched human life. In particular, thechemistry has made a significant contribution in the past fewdecades. For example, organic chemistry,1 inorganicchemistry,2 polymer chemistry,3 supramolecular chemistry,4coordination chemistry,5 biochemistry,6 and other materialsa Research Center for Materials Nanoarchitectonics, National Institute for MaterialsScience (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan.E-mail: ARIGA.Katsuhiko@nims.go.jpb Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa 277-8561, Japanc Research Center for Functional Materials, National Institute for Materials Science(NIMS), 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japand Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1Tennodai, Tsukuba 305-8577, Ibaraki, JapanKatsuhiko ArigaKatsuhiko Ariga received his PhDdegree from the Tokyo Institute ofTechnology in 1990. He joined theNational Institute for MaterialsScience (NIMS) in 2004 and iscurrently the leader of the Sup-ermolecules Group and principalinvestigator of the World PremierInternational (WPI) Research Cen-tre for Materials Nanoarchitectonics(MANA), NIMS. He is alsoappointed as a professor in TheUniversity of Tokyo. Jingwen SongJingwen Song received her PhDdegree from The University ofTokyo under the guidance of Prof-essor Katsuhiko Ariga in 2021. Shealso studied in the SupermoleculesGroup at the World Premier Inter-national (WPI) Research Centrefor Materials Nanoarchitectonics(MANA), National Institute forMaterials Science (NIMS) from2018 to 2021. She is currently apostdoctoral researcher in theMedical Soft Matter group, NIMS.Received 8th October 2023,Accepted 18th January 2024DOI: 10.1039/d3cc04952crsc.li/chemcommChemCommFEATURE ARTICLEhttps://orcid.org/0000-0002-2445-2955https://orcid.org/0000-0002-3466-9365http://crossmark.crossref.org/dialog/?doi=10.1039/d3cc04952c&domain=pdf&date_stamp=2024-01-30https://rsc.li/chemcommThis journal is © The Royal Society of Chemistry 2024 Chem. Commun., 2024, 60, 2152–2167 |  2153chemistry7 have continuously developed new functional mate-rials. Physics has also made a significant contribution. Physics-based analysis has revealed that the quality of functionalitydepends not on the material itself but on its structure (espe-cially its internal structure).8 The biggest turning point was therise of nanotechnology. Nanotechnology, proposed by RichardFeynman,9 has made the direct observation, manipulation, andcharacterization of structures down to the atomic and molecu-lar level possible.10 As a post-nanotechnology,11 nanoarchitec-tonics was founded by Masakazu Aono.12 Based on theknowledge and techniques obtained from nanotechnology,nanoarchitectonics architects functional materials and struc-tures using nano-units of atoms, molecules, and nanomaterials(Fig. 1).13Rather than creating a new and novel field, nanoarchitectonicscan be thought as the integration of many areas of materialsscience with a focus on nanotechnology.14 In nanoarchitectonicsapproaches, the architecture of functional materials from nano-units is achieved through selection and combination of opera-tions, such as atomic and molecular manipulation and theirphysical and chemical transformations, organizational processessuch as self-assembly/self-organization and orientation and align-ment by external forces and fields, and more advanced nano/microfabrication and biochemical processes.15 This methodologyis not bound by material or application objectives and can beapplied to a wide variety of objects. In fact, recent papersadvocating nanoarchitectonics include multiple topics rangingfrom material synthesis,16 structure control,17 fundamentalphysical phenomena,18 and biochemistry-related research19 toapplications such as catalysts,20 sensors,21 devices,22 energy,23environment,24 and biomedical research.25 Since materials areoriginally formed from atoms and molecules, nanoarchitectonics,which architects functional materials from atoms and molecules,can be applied to all materials. It may correspond to the theory ofeverything,26 which could be the super unification theory (SUT) inthe world of physics. Nanoarchitectonics can be a method foreverything in materials science.27 In order to construct materialsfrom atoms and molecules, it is necessary to deal with phenom-ena specifically. In particular, it is necessary to bridge the sciencespecific to the nanoscale with the properties of the macroscale.These processes require the integration of many methodologiesthat have been developed to date. Nanoarchitectonics aims toestablish such an integrated discipline.In nanoarchitectonics, several processes are combined toform functional materials and structures, which are moresuitable for forming asymmetric and hierarchical structures.28Compared to self-assembly based on simple equilibrium, it ismore suitable for forming hierarchical structures by multipleprocesses, including nonequilibrium processes. In addition,the nanoscale phenomena and interactions underlying nano-architectonics involve uncertainty and complexity. Comparedto macroscopic phenomena, uncertainties such as thermalfluctuations, stochastic distributions, and quantum effectsare difficult to ignore in the nanoscopic regime. Therefore,rather than simply integrating various interactions andresponses, the overall response of the material or functionalsystem is demonstrated in a harmonized way.29 This mode offunctional expression in which various effects are harmonizedunder a hierarchical structure is common in biologicalsystems.30 In other words, the creation of functional materialsby nanoarchitectonics has the potential to realize advancedfunctional systems such as those found in living organisms.31In biological systems, a number of functional units are hier-archically organized in a field such as a biological membrane,widely employed in photosynthesis and signal transductionsystems.32 The coordination of these interactions results insophisticated functions. The essence of these functions is seenin the rational physical and chemical communications of signals,energy, and molecules. In living systems, membrane tissues suchas biomembranes are successfully used as a medium for thesefunctions. In order to artificially mimic this, it is beneficial toapply methods to fabricate thin films with ideal controllablestructures. The Langmuir–Blodgett method33 and layer-by-layerassembly34 are useful as such techniques. These two methods arealso powerful tools for the fabrication of functional structures thatcan be taken to good use in nanoarchitectonics.35Fig. 1 Outline of the nanoarchitectonics concept.Kohsaku KawakamiKohsaku Kawakami received hisPhD in Chemical Engineering in2000 from Kyoto University. Afterworking for pharmaceutical comp-anies including Shionogi and Merck,he joined National Institute forMaterials Science in 2006. He iscurrently a group leader of theMedical Soft Matter group and adirector of the Material Open Plat-form for Pharmaceutical Science. Healso serves as a professor atUniversity of Tsukuba.Feature Article ChemComm2154 |  Chem. Commun., 2024, 60, 2152–2167 This journal is © The Royal Society of Chemistry 2024The Langmuir–Blodgett method is a technique for creatinghighly oriented monolayers at the liquid interface and buildingthem up in layers on a solid substrate.36 Generally speaking,this method is easy to obtain denser and more controlled thin-film structures, but it is not necessarily applicable to manytypes of materials. The layer-by-layer assembly method is amethod to obtain multilayer thin films by sequentially adsorb-ing components into a film based on interactions between thematerials.37 A typical method is as follows. A thin film is madeby adsorbing a substance with opposite charge on a solidsubstrate. In this process, the surface charge is inverted so thatanother substance with an opposite charge can be adsorbed asa thin film. Using the principle of charge inversion, multilayersof various substances can be produced in any number oflayers and any desired sequence. Since there are an extremelylarge number of substances with charge, many substancescan be applied to this technique. The interactions arenot limited to electrostatic interactions, but can be hydrogenbonds,38 coordination,39 charge transfer interactions,40 stereo-complexation,41 supramolecular inclusion,42 biospecificrecognition,43 and many other interactions.44 Thereby, manymaterials ranging from various polymers45 to quantummaterials,46 colloidal particles,47 two-dimensional materials,48biomolecules,49 and viral particles50 can be applied in layer-by-layer assembly. In addition to the usual dipping method,51engineering techniques such as spin-coating52 and spraying53are also applied. In addition, layer-by-layer assembly on micro-scopic particles as well as layer-by-layer assembly fabrication ofhollow capsules are widely used.54Thus, layer-by-layer assembly is a promising method fororganizing multi-components and constructing systems thatcontrol the physical and chemical communications betweenthem. Layer-by-layer assembly is also an easy method to combinewith other processes to create hierarchical structures. In thefabrication shown in Fig. 2, mesoporous silica capsules created bymolecular assembly and template synthesis can be stacked togetherwith other nanoparticles in a layer-by-layer organization.55 In thiscase, a hierarchical structure is built up, with nanometer-levelmesopore structures and microcapsule spaces, which are built upmacroscopically in layers. The layer-by-layer structure of the asso-ciated mesoporous materials can perform functions specific to thehierarchical structure, such as sensor functions that can be adjustedin various ways56 and automatic on/off material release functions.57Nanoarchitectonics has the potential to architect highlyfunctional systems such as living organisms. A key to this isthe realization of physical and chemical communications ofsignals, energy, and matter in structures with properties suchas asymmetry, hierarchy, and so on. Layer-by-layer assembly is apromising structure fabrication method for this purpose. Basedon this background, this feature article explores the possibilityof constructing advanced functional systems based on recentexamples of layer-by-layer assembly. In the following sections,we will illustrate the development of more basic methods andthe development of nanoarchitectonics systems that bringabout functional expression from structural understanding.Specifically, the following sections will provide examples of(i) advancement in basics and methods, (ii) physico-chemicalaspects and applications, (iii) bio-chemical aspects and appli-cations, and (iv) bio-medical applications.2. Advancement in basics and methodIn order to reasonably communicate physically and chemicallyin functional structures, precise structures must be controlledand evaluated. As mentioned above, a promising method fornanoarchitectonics of materials with such functional proper-ties is the layer-by-layer method described above. Compositenanoarchitectures can be fabricated from a wide variety ofmaterials, ranging from quantum inorganic objects to organicpolymers and biomaterials. It is also an environmentallyfriendly, simple, and economical method of fabrication. Incontrast to the high potential of the layer-by-layer method,there is still much room for further study on how to analyzethe nanoscopic structure. In the development of devices involvingphysical and chemical communications, prediction and under-standing of their performance are important keys.Gutfreund et al. used neutron scattering to study the averageconformation of polymer chains in layer-by-layer film structuresconsisting of deuterated polyelectrolyte chains.58 Layer-by-layerfilms of poly(sodium 4-styrenesulfonate) and poly(allylaminehydrochloride) were prepared by dipping, spray, and spin-assisted methods and compared. The three-dimensionalFig. 2 Layer-by-layer organization of mesoporous silica capsules togetherwith other nanoparticles as a hierarchical structure with nanometer-levelmesopore structures and microcapsule spaces. Reproduced with permis-sion from ref. 55. Copyright 2008 American Chemical Society.ChemComm Feature ArticleThis journal is © The Royal Society of Chemistry 2024 Chem. Commun., 2024, 60, 2152–2167 |  2155nanostructure of the layer-by-layer assembled polyelectrolytemultilayers was determined under various conditions. The out-of-plane radius of rotation of layer-by-layer films preparedat different salt concentrations was compared, and the lowerthe salt concentration, the less equilibrated the structure. Thestructure of the resulting solid-state polyelectrolyte multilayerstrongly depends on the deposition process, in the followingorder: spin-assisted method 4 spray-assisted method 4 dippingmethod, which affected the asymmetry. Off-specular neutronreflectometry revealed that complexation at the polyanion/poly-cation interface occurs at the molecular level, not at the mono-mer level. The poly(sodium 4-styrenesulfonate) chain exhibits aflattened coil structure with an asymmetry coefficient of about 7.Despite being a non-equilibrium polymer chain, its densityprofile follows a Gaussian distribution occupying approximatelythe same volume as the bulk complex. The deformation of thechain is equal on all length scales, preserving the Gaussiannature of the segmental density. Such an analytical approachprovides a better understanding of the formation of layer-by-layer multilayers composed of polyelectrolytes, their internalstructures, and the properties they confer. Tuning of thesestructural details affects the efficiency and anisotropy of physicaland scientific communications. Varying layer-by-layer assemblymethods can be viewed as a well-stocked toolbox for fine-tuningto meet the needs of specific applications.Decher and co-workers reported a very simple method tocreate anisotropic layer-by-layer films (Fig. 3).59 This is a spraylayer-by-layer method by controlling the angle between thespray jet and the surface in a grazing incidence spray. This isa simple and efficient method for spray-assisted orientation ofnanofibrils in layer-by-layer assembly of cellulose nanofibrils.Spraying at an angle of 901 to the deposition surface producesfilms with uniform in-plane orientation. On the other hand,spraying at a smaller angle produces a macroscopic directionalsurface flow of liquid on the receiving surface of the spray. As aresult, films with in-plane anisotropy are obtained. Cellulosenanofibrils are oriented parallel to the spray direction. Further-more, the orientation order depends on the distance of thedeposition surface from the spray nozzle. In a layer-by-layermultilayer film nanoarchitected in this way, the apparentrefractive index of the film has a minimum in the orientationdirection and a maximum in the direction perpendicular to theorientation direction. This technique provides a simple methodfor creating optically birefringent films over a large surfacearea. This method utilizes shear alignment when depositinglayer-by-layer collective films. This method of forming highlyanisotropic structures by spray alignment, combined with theability to form further layered structures by further layer-by-layer methods, may yield materials with a higher degree ofanisotropy and hierarchical structure. With grazing incidencespraying, the orientation direction in individual layers can beeasily selected. Different chemical compounds can be used fordifferent layers. As a result, it is possible to prepare materialswith a hierarchical structure with more complex anisotropythan one direction of orientation.The nanoarchitectonics of artificial layer-by-layer structureswill also lead to the development of materials that mimicnatural layered structures and exhibit higher functionality.For example, certain biomaterials are known to exhibit superiorstrength, modulus, and toughness due to mechanical commu-nication in their layered structures.60 Mechanical communica-tion of inorganic reinforced nanofillers within a ductile organicmatrix leads to such properties. In particular, the two-dimensional nanosheets and nanoplatelets are attributed tothe elaborate formation of layered microstructures. Liu and co-workers reported a method for nanoarchitectonics of nanocom-posite materials with highly ordered layered structures.61 Thisstrategy exploits the shear flow-induced orientation of two-dimensional nanosheets at the interface between the immisci-ble hydrogel and oil. This can be thought of as the fabricationof bulk artificial pearl layers using graphene oxide, clay, andcarbon nanotubes. Layered nanocomposites based on gra-phene oxide and clay nanosheets yielded high strength, suchas 9.0 times the tensile strength and 2.8 times the Young’smodulus equivalent of natural mother-of-pearl. When claynanosheets were used, nanocomposites exhibiting 20.4 timesthe toughness of natural mother-of-pearl were obtained. Suchcritical interfaces have a very high regime for crack formationand propagation under high tensile stress. In particular, thesmall aspect ratio of the clay nanosheets allows the transitionof the deformation mode from nanosheet fracture to nanosheetpullout. The method is a layered nanoarchitectonic based onsuper-diffusive shear flow-induced orientation of nanosheets atthe immiscible hydrogel/oil interface. It is a scalable layeringmethod that can be universally applied to many materials. Itwill be a simple methodology to fabricate layered nanocompo-site films from a wide range of polymers and two-dimensionalinorganic materials that can encapsulate mechanical commu-nication. It is a promising nanoarchitectonics method for thedevelopment of advanced layered nanocomposites for practicalapplications.The nanoarchitectonics of laminated membranes oftentakes place at stable interfaces between immiscible solvents.Using interfaces between immiscible solvents, Zhao and co-workers reported spontaneous water-on-water diffusion andFig. 3 Simple and efficient method for spray-assisted orientation ofnanofibrils in layer-by-layer assembly of cellulose nanofibrils: less orientedfilm (top); anisotropic films fabricated with a grazing incidence spray(bottom). Reproduced from ref. 59, under the terms of the CC BY.Feature Article ChemComm2156 |  Chem. Commun., 2024, 60, 2152–2167 This journal is © The Royal Society of Chemistry 2024self-assembly of polyelectrolyte membranes (Fig. 4).62 This is anexample of water-on-water diffusion applied to materials engi-neering and other fields. In this example, the process of spread-ing an aqueous solution mixture containing poly(ethyleneimine)and poly(sodium 4-styrenesulfonate) over acidic water is used tocreate a hierarchical porous membrane. The decrease in surfacetension of the polyelectrolyte mixture solution promotes surfacediffusion. Complexation of the polyelectrolytes at the interface,caused by the low pH of the water, moderates water–watermixing. In this design, poly(sodium 4-styrenesulfonate) givesthe mixed solution a lower surface tension than water. This isthe driving force behind surface diffusion. Poly(ethyleneimine)is a weak polyelectrolyte that takes on a positive charge underacidic conditions, leading to complexation. This synergisticapproach of surface tension and pH-dependent complex for-mation does not require surfactants or sophisticated equipment.It does not require small droplets or complex techniques, andcan be easily manipulated using a pipette at room temperature.It is also applicable to various polyelectrolytes and nanomater-ials, and can be a general methodology for functional materialsengineering.Efforts are also being devoted to the nanoarchitectonics oftwo-dimensional structures that form the cornerstone oflayered structures. Beyond Staudinger’s concept based on poly-mers on linear chains, sheet polymers with long-range orderingalong two orthogonal directions are attracting attention as two-dimensional polymers.63 Methodologies for nanoarchitectonicsof reliable structures of new classes of organic two-dimensionalmaterials, rather than inorganic two-dimensional materials suchas graphene, are needed. Kaiser, Zheng, Feng, and co-workersreported surfactant-monolayer-assisted interface synthesis.64 Itis a controlled synthesis of few-layer two-dimensional polymercrystals with high crystallinity and domain sizes of a fewmicrometers. In this method, rigid and symmetric monomerarrangements and two-dimensional polymerization wereachieved using surfactant monolayers on the water surface.The thickness of the nanoarchitectonized two-dimensional poly-imide nanosheets is about 2 nm, which corresponds to about5 layers. The average crystalline domain size is about 3.5 mm2.This surfactant monolayer-assisted interfacial synthesis strategyhas also been extended to polycondensation reactions to developcrystalline few-layer two-dimensional polyamides with adouble-pore lattice structure. These methods are strategies forthe synthesis of two-dimensional polymer crystals, two-dimen-sional polyimides and two-dimensional polyamides, underambient temperature conditions. Extensions to other two-dimensional polymerizations involving reversible or irreversiblecovalent bonds are expected.Similarly, nanoarchitectonics has also been investigatedthrough the self-assembly of peptides and other molecules onsurfaces. Understanding the mechanisms by which short pep-tides self-assemble into two- and three-dimensional structuresis of great interest in the formation of crystalline biomolecularsystems and their practical applications. Yurtsever, Sun,Sarikaya, and co-workers used graphite-bound dodecapeptidesfor a highly oriented self-assembly process in aqueous solutionobserved in situ using frequency-modulated atomic forcemicroscopy.65 The main observations suggest that the firstlayer forms homogeneously and produces self-assembled crys-tals with a lattice structure in contact with the underlyinggraphite. In detail, peptide crystals formed on the surface havea chiral crystallographic orientation relationship with theunderlying graphite lattice, forming a six-fold symmetricdomain. Thus, molecular surface self-assembly nanoarchitec-tonics depends on a series of molecular interactions, includingconformational states, molecule–substrate and intermolecularinteractions. These studies are helpful in the scientific under-standing and construction of coherent bio/nano hybrid inter-faces through the surface behavior of short peptides on solids.Detailed computational modelling studies, such as controlledmolecular dynamics, should be performed in hierarchicaldimensions, through which peptides are likely to take onvarious conformational structures while behaving at the surfaceand folding as they form various two-dimensional molecularcrystals at the surface. This provides quantitative guidelines forthe elucidation of molecular mechanisms of self-assembly. It isalso a fundamental guideline for designing nanostructures forhybrid surface technologies such as biomolecular logic devices.Materials nanoarchitectonics based on the layer-by-layermethod has been widely studied because of its simplicity andwide range of applications. It is an easy method to assembleasymmetric structures and hierarchical organization, and is apowerful technique for developing functions through physicaland chemical communications. However, not everything hasbeen clarified by such a popular method, and research con-tinues to analyze basic issues such as the average conformationof polymer chains in layer-by-layer membrane structures. Onthe other hand, the fabrication of highly oriented layer-by-layerfilm structures by spraying from low angles and the creation ofFig. 4 Spontaneous water-on-water diffusion and self-assembly of poly-electrolyte membranes: the process of spreading of an aqueous solutionmixture containing poly(ethyleneimine) and poly(sodium 4-styrene-sulfonate) over acidic water to create a hierarchical porous membrane.Reproduced from ref. 62, under the terms of the CC BY.ChemComm Feature ArticleThis journal is © The Royal Society of Chemistry 2024 Chem. Commun., 2024, 60, 2152–2167 |  2157spontaneous multilayer films using miscible and immiscibleinterfaces are also being investigated. Two-dimensionalmaterials and aggregate structures, which are also the basicstructures of layered structures, are also being investigated.The analysis and exploration of nanoscopic structures areconsidered to be key to predicting and understanding theirperformance in device development involving physical andchemical communications.3. Physico-chemical aspects andapplicationsThe cleverly designed layer-by-layer structure creates physicaland chemical communications of signals and properties. Thisleads to more advanced functionality. Various studies are beingpromoted from this perspective. These functional structuresare often done with various application developments in mind.Wang and co-workers developed a material in which highlyeffective heat transmission can be controlled by a layer-by-layerstructure.66 They nanoarchitectonized sodium silicate-derivedsilica aerogels by a one-pot, continuous and natural solventevaporation method of hydrophobization, solvent exchange,sodium purification, and atmospheric pressure drying (Fig. 5).Using inexpensive sodium silicate as the silica precursor, acontinuous and spontaneous progressive hierarchical sub-sensorial alignment was obtained. Silica aerogels with highcontact angle, high specific surface area, low density, and lowthermal conductivity were synthesized by this one-pot nanoarch-itectonics approach. A layer-by-layer structure containing thissilica aerogel layer and an additional phase change materiallayer was designed. Experimental and simulation results showthat this layer-by-layer structure has dual-function thermoregu-latory performance to control thermal communication andpostpone the time to reach equilibrium in both severe coldand hot environments. It has been shown that when the outsidetemperature is �30 1C, the internal temperature can be main-tained above 20 1C for extended periods, and when the outsidetemperature is 70 1C, the internal temperature can be main-tained at 30 1C. A proof-of-concept experimental setup simulat-ing sunlight exposure was performed. It was proven that a modelcar protected by a layer-by-layer structure can maintain aninterior temperature of 28 1C or lower, even when the outsidetemperature is 70 1C. Through layer-by-layer nanoarchitectonics,thermal communication in both harsh hot and cold environ-ments can be controlled, enabling the development of robustdual-function personal thermal management systems forthermoregulation.Technologies such as 5G communication, electric vehicles,and wearable electronics are developing. Accordingly, commu-nication of electromagnetic radiation has become more andmore important. For example, ultra-high performance and cost-effective shielding materials are required to avoid potentiallyharmful effects of electromagnetic interference on the humanbody. Kim and co-workers have shown that layer-by-layerassembly using copper nanosheets can be a practical andpromising electromagnetic interference shielding technology(Fig. 6).67 In this study, hierarchical porous copper foils withlayer-by-layer assembly of single-crystal, nanometer-thick, andmicrometer-long copper nanosheets were nanoarchitectoni-cally investigated for their use in electromagnetic interferenceshielding. Layer-by-layer assembly of Cu nanosheets can beused for multilayer stacking, two-dimensional networking, andlayer-by-layer sheet void structures, and hierarchically struc-tured porous Cu films can be formed. Large metal sheets can bevertically stacked to form multilayer two-dimensional struc-tures and sheet-like voids simultaneously. The layer-by-layerstructure of porous Cu foil fabricated in this way exhibitedsuperior electromagnetic interference shielding performancecompared to dense copper and other materials of the samethickness. The layer-by-layer layering inside the Cu nanosheetand its interaction with the incoming electromagnetic radiationis responsible for this strong absorption of radiation. Con-trolled electromagnetic communication through hierarchicallayer-by-layer structures has numerous advantages, includinglight weight, thinness, mechanical softness, low cost, ease ofsynthesis, and ease of fabrication. It would be useful forperformance in a wide range of electronic applications.It can also control the physicochemical properties of sub-stances that have been widely distributed since ancient times.Cotton and its blends are among the most commonly usedfabrics. However, cotton is known to be highly flammable. Lvovand co-workers have dramatically restricted the flammability ofthose materials by coating them with a flame retardant layer-by-layer process (Fig. 7).68 Flame retardancy was imparted by layer-Fig. 5 A layer-by-layer structure containing this silica aerogel layer and anadditional phase change material layer with dual-function thermoregula-tory performance to control thermal communication and postpone thetime to reach equilibrium in both severe cold and hot environments.Reproduced with permission from ref. 66. Copyright 2021 AmericanChemical Society.Feature Article ChemComm2158 |  Chem. Commun., 2024, 60, 2152–2167 This journal is © The Royal Society of Chemistry 2024by-layer assembly of cationic polyethyleneimine and anionichalloysite clay nanotubes on the raw cotton as a nanoarchitec-tural structure of organic/inorganic coating. From the overallstructure, only two layers of polyethyleneimine/halloysite claynanotube layer-by-layer coating with a weight ratio of approxi-mately 7% were needed to give the processed cotton an optimallevel of flame retardancy. The flame retardant properties aresuch that the flame would self-extinguish when burned. Thehalloysite clay nanotubes used in the coating have a hollowstructure with a diameter of 50 nm, composed of biocompatibleSiO2/Al2O3. Chemical substances can be held in this nanospace,which guarantees the addition of various functionalities andsafe interaction with living organisms. For instance, color-enhancing dyes, antimicrobial chloramphenicol or silver canbe loaded in the halloysite clay nanotubes. They can also bearchitectural coatings with complex functionality. Halloysiteclay nanotube/polyethyleneimine layer-by-layer multilayershave been shown to withstand multiple washings. The nanos-tructural design of integrated nano-, micro-, and macrostruc-tural composites is a promising nano-architectonics methodfor practical fabric material development.Communication of physical information by reflection oflight rays depends on the design of the mirror. Conventionalmirrors invert the circular polarization handedness duringreflection. Pauly and co-workers fabricated chiral mirrors bylayer-by-layer assembly of oriented silver nanowire layers fabri-cated using the aforementioned grazing incidence method on asemi-reflective silver layer (Fig. 8).69 The chiral mirror functionis achieved by the formation of twisted Ag nanowire super-structures on a reflective metal surface. By tuning the numberof oriented Ag nanowire layers and the spacing between thelayers, optical properties such as total reflectance, differentialreflectance, and spectral shape can be tuned. The nanoarchi-tected chiral metasurfaces exhibit structure-dependent differ-ential reflectance for circularly polarized light over a widewavelength range in the UV, visible, and near-infrared regions.They also have extremely high merit indices. Most chiralmirrors created by conventional techniques are fabricated bytop-down techniques such as electron beam lithography. Thisconventional technique is very costly and difficult to scale up tomacroscopic devices. In contrast, the method presented hereonly uses aqueous suspensions/solutions of commercially avail-able nanowires and polymers and is based on wet chemistry labtechniques, which are very inexpensive and easy compared tovacuum-based lithography processes. Layer-by-layer nanoarch-itectonically oriented nanowire layers not only have sufficientoptical quality but also benefit from low cost and simplicity.They can also be created on the surface of various opticalelements. Such large-area chiral mirrors have many potentialapplications, including optics, sensing, and chiral light-matterinteractions. Adding another chiral mirror on top of the chiralsuperstructure could result in a closed chiral resonator, gen-erating tunable chiral resonator modes. Alternatively, it wouldFig. 6 A layer-by-layer assembly of single-crystal, nanometer-thick,and micrometer-long copper nanosheets for promising electromagneticinterference shielding technology: design (top) and image (bottom).Reproduced with permission from ref. 67. Copyright 2021 AmericanChemical Society.Fig. 7 Flame retardancy imparted by layer-by-layer assembly of cationicpolyethyleneimine and anionic halloysite clay nanotubes on the rawcotton as a nanoarchitectural structure of organic/inorganic coating.Reproduced with permission from ref. 68. Copyright 2023 Wiley-VCH.ChemComm Feature ArticleThis journal is © The Royal Society of Chemistry 2024 Chem. Commun., 2024, 60, 2152–2167 |  2159contribute to chiral catalytic reactions and enantioselectivesynthesis.Important examples of physical property conversion andfunctional communication can be found in the design of variousenergy-related devices. For example, solution-processed organicsolar cells have become an extremely promising methodologyfor inexpensive and sustainable light-energy conversion withincreasing photovoltaic efficiency.70 However, in many cases, theefficiency of large-scale organic solar cell modules fabricated bythe donor–acceptor bulk heterojunction strategy is not alwayssatisfactory. Focusing on the excellent physical dynamics andgood surface uniformity of layer-by-layer blends, Min and co-workers applied layer-by-layer nanoarchitectonics to the fabrica-tion of organic photovoltaic modules with larger active areas(Fig. 9).71 A layer-by-layer approach was introduced to the fabrica-tion of organic solar cells by blade-coating and demonstrated toobtain higher photovoltaic performance compared to bulk hetero-junctions. The layer-by-layer fabrication strategy can significantlyreduce the scaling gap. Printing techniques that process photo-active layers by a layer-by-layer strategy have proven to be usefulfor large-scale production and industrial application of high-performance organic solar cells.Layer-by-layer methods are used for coating micro- andnanoparticles and fabricating hollow capsules,72 as well as forcoating surfaces with flat multilayers. Cui, Caruso, and co-workers proposed the coordination of metal ions to quinonesvia metal-acetylacetone coordination bonds to design structurallytunable, universally adhesive, hydrophilic, and pH-degradablecapsules and other materials (Fig. 10).73 A library of metal-quinone networks is formed from nine metal ions and five pairedmodel quinone ligands. The structures to be nanoarchitectonizedare diverse, including particles, tubes, capsules, and films. Thenetworks can also serve as reactive platforms for functionalizationwith molecules that can improve fluorescence, enzyme catalysis,and colloidal stability. The result is a network in which physical,chemical, and biological functions can communicate. A notableproperty of this network is that it exhibits bidirectional pH-responsive degradation in acidic and alkaline solutions. Quinoneligands mediate the degradation kinetics, allowing temporal andspatial control of the release of multiple components through themultilayer metal-quinone network. Since quinones are themselvesfunctional molecules, they can be used as prodrugs for cancertherapy. High drug-loading metal-quinone network prodrugs havebeen designed using doxorubicin for anticancer therapy andshikonin for inhibition of the major protease of the SARS-CoV-2virus. Metal-quinone networks, as hydrophilic coatings on a widerange of substrates, are beneficial structures for the creation ofcomplex and tunable stimuli-responsive organometallic films andparticles for a variety of applications.As shown in some of the examples above, cleverly designedlayer-by-layer structures create various types of physical andchemical communication. Controlling thermal exchange allowsmaterials to block external temperature changes and to behighly flame retardant. Similarly, materials that block electro-magnetic interference have been developed. Layer-by-layerstructures aimed at controlling optical management will giverise to new materials called chiral mirrors and highly efficientlight-energy conversion devices. Thus, nanoarchitectonics withlayer-by-layer structures are useful for controlling the commu-nication of physical and chemical signals. New strategies suchas multilayer metal-quinone networks have been proposed tocomplement layer-by-layer structures, and the exploration ofphysical functions through hierarchical and oriented layeredstructures will continue to be active.4. Bio-chemical aspects andapplicationsThe advantages of forming orientational, anisotropic, andhierarchical nanostructures of layer-by-layer assembly gobeyond bringing about modulation of physical propertiesFig. 8 Fabrication of chiral mirrors by layer-by-layer assembly of orientedsilver nanowire layers fabricated using the grazing incidence method on asemi-reflective silver layer. Reproduced from ref. 69, under the terms ofthe CC BY.Fig. 9 Layer-by-layer nanoarchitectonics to the fabrication of organicphotovoltaic modules with larger active areas by blade-coating to obtainhigher photovoltaic performance compared to bulk heterojunctions.Reproduced with permission from ref. 71. Copyright 2020 Elsevier.Feature Article ChemComm2160 |  Chem. Commun., 2024, 60, 2152–2167 This journal is © The Royal Society of Chemistry 2024through physical and chemical interactions. It is also possibleto control biological events through chemical stimulus ofsignals and molecules. Originally, sophisticated functions inliving organisms are due to vectorial and oriented transporta-tion of signals and substances. This is brought about by thehierarchical organization of functional components. The hier-archical and anisotropic arrangement of functional unitsallows for rational and efficient communication of signals,energy, and chemicals. In layer-by-layer nanoarchitectonics,the formation of anisotropic and hierarchical structures alsoleads to the regulation of biochemical phenomena throughefficient chemical communication.Artificial nanoarchitectonics of highly organized skeletalmuscle tissue is promising for a variety of bioapplications,e.g., treatment of muscle damage and muscle diseases, alter-native medicine, or pharmacological research. To this end,myoblasts must differentiate into parallel-oriented myotubesand form aligned myofibers. Boulmedais and co-workers devel-oped hydrogen-bonded tannic acid/collagen layer-by-layernanofilms by the brushing method as a substrate to inducesuch a tissue structure.74 The brushed tannic acid/collagenfilms were highly oriented compared to films obtained byconventional dipping. An orientation of collagen fibers with adiameter of 60 nm was observed along the brushing direction.Human myoblasts were cultured on oriented tannic acid/col-lagen films terminated with collagen. This aligned tannic acid/collagen nanofilm improves adhesion to the substrate. Cellbehavior is regulated by its effects on cell morphology, alignment,and differentiation. When cultured in a differentiation mediumwithout other supplements, human myoblasts aligned on brushedtannic acid/collagen films. Differentiation into long-aligned myo-tubes was induced by two properties: collagen fiber orientation,which induces myoblast alignment, and tannic acid release, whichpromotes differentiation. The oriented structures generated bylayer-by-layer nanoarchitectonics with the brushing method canmimic complex in vivo states by taking advantage of topographiccues and strong cell/collagen interconnections. This methodologyholds promise for designing model tissues for anisotropic tissueregeneration, injury and disease treatment, and pharmacologicalresearch.When nanoparticles are exposed to serum or plasma, pro-teins from the blood adsorb onto the nanoparticle surface toform a protein corona. Chan and co-workers have investigatedthe basic organization and binding function of these adsorbedproteins based on a layer-by-layer structure.75 This study pro-vides detailed functional and structural insights into the pro-tein corona on nanomaterials and clues to strategies for coronato control interactions with biological systems. Fig. 11 proposesa mechanism for the structure and function of the proteincorona. This is a layer-by-layer structure based on protein–protein–protein interactions in which this is a three-layerstructure. When nanoparticles are exposed to serum or plasma,the interaction between the protein and the nanoparticlecauses the protein to adsorb to the surface. This forms theunderlying layer. The chemical composition and surface chem-istry of the nanoparticles may determine the specific serumprotein that is adsorbed. Based on further protein–proteininteractions, an aggregation layer is formed that is bound tothe protein base layer. The functional proteins of the finalbound layer will determine the interaction function of thenanoparticle protein corona with the cellular receptor. Success-ful control of this structure makes it possible to tailor theprotein corona. It can be used to design precoated coronas withvarious biological identities in nanomaterials.The nanoarchitectonics of nanoparticles with proper inter-action with biofilms is also important in terms of antimicrobialdrug development.76 Microorganisms that are established inbiofilms tolerate high concentrations of antibiotics because ofthe viscous extracellular matrix that encapsulates their antimi-crobial activity. Compared to such free drugs alone,nanoparticle-based therapeutics achieve higher local concentra-tions in the biofilm, thereby increasing their efficacy. In parti-cular, positively charged nanoparticles bind multivalently toanionic biofilm components, enhancing their penetration intothe biofilm. Unfortunately, cationic particles are toxic and arerapidly expelled from the circulation in vivo, limiting their use.Fig. 10 Fabrication of a metal-quinone network upon coordination ofmetal ions to quinones via metal-acetylacetone coordination bonds todesign structurally tunable materials including particles, tubes, capsules,and films from a library of nine metal ions and five paired model quinoneligands. Reproduced from ref. 73, under the terms of the CC BY.ChemComm Feature ArticleThis journal is © The Royal Society of Chemistry 2024 Chem. Commun., 2024, 60, 2152–2167 |  2161Hammond and co-workers have developed pH-responsivenanoparticles that change their surface charge from negative topositive in response to a decrease in the pH microenvironmentof the biofilm nanoarchitectonics (Fig. 12).77 Four pH-dependenthydrolysable polymers were synthesized and biocompatiblenanoparticles were prepared using a layer-by-layer electrostaticassembly method. These polymers differ in the hydrophilicity oftheir backbones and the flexibility of their side chains. Accord-ingly, each resulted in a different and predictable charge reversalrate. This reversal rate determines penetration and permeationinto the biofilm. The rates ranged from several hours to unde-tectable within the experimental time frame. Tobramycin, anantibiotic known to be trapped by anionic biofilm components,was loaded into the final layer of layer-by-layer nanoparticles.By loading tobramycin, a clinically relevant antibiotic that isattenuated in the biofilm matrix, onto the nanoparticle surface,the increased accumulation of nanoparticles due to the surfacecharge reversal rate leads to more effective drug delivery. Thefastest charge-converting nanoparticles resulted in a 3.2-foldreduction in bacterial colony-forming units compared to freetobramycin. State communication, i.e., the layer-by-layer struc-ture change over time and return of charge state, led to theelimination of biofilm-based infections. This will be useful inproviding structure-function guidance for future design ofrelated pH-responsive nanocarriers.In a biofunctional system, various functional units areorganized to perform sophisticated functions through directedchemical communication. As an artificial construct of such asystem, Dong, Li, and co-workers developed a supramolecularassembly of bacteriorhodopsin and ATP synthase co-assembledin an artificial biomimetic system (Fig. 13).78 This system allowscascade reactions and ATP synthesis under illumination. Thedirected transport of protons is used to generate a high protongradient, which facilitates energy conversion under illumination.First, oriented bacteriorhodopsin is constructed by layer-by-layerassembly in a polyelectrolyte-based microcapsule. Bacteriorho-dopsin maintains a highly uniform orientation due to its highloading capacity and accelerated phosphorylation. Proteolipo-somes then introduce FoF1-ATPase onto the microcapsules byfusion. Bacteriorhodopsin in the microcapsules pumps protonsfrom the inside to the outside only under light irradiation. Aproton gradient is formed in the proteoliposome and FoF1-ATPase is activated sequentially to synthesize ATP. To furtherpromote photosynthetic activity, CdSe/ZnS quantum dots wereintroduced. The introduction of optically matched quantum dotssignificantly enhanced the light-induced phosphorylation andfurther improved the ATP production. Rational nanoarchitec-tonics of tissue bodies using layer-by-layer assembly enabledmultiple functional communications in favor of light tochemical energy.Advanced functions in living organisms depend on vectorialand oriented communication of signals and substances. Inlayer-by-layer nanoarchitectonics, anisotropic and hierarchicalstructures are formed to regulate biochemical phenomenathrough efficient chemical communication. For example, theoriented structure of hydrogen-bonded tannic acid/collagenlayer-by-layer nanofilms by the brushing method can mimiccomplex states in vivo by using topographic cues and strongcell/collagen interactions. The structure of the biofilms can beFig. 11 An organization model of the adsorbed proteins based on a layer-by-layer structure to provide detailed functional and structural insights intothe protein corona on nanomaterials and clues to strategies for corona tocontrol interactions with biological systems. Reproduced with permissionfrom ref. 75. Copyright 2020 American Chemical Society.Fig. 12 pH-Responsive nanoparticles that change their surface chargefrom negative to positive in response to a decrease in the pH microenvir-onment of the biofilms. Reproduced with permission from ref. 77. Copy-right 2023 American Chemical Society.Feature Article ChemComm2162 |  Chem. Commun., 2024, 60, 2152–2167 This journal is © The Royal Society of Chemistry 2024analyzed based on a layer-by-layer structure to devise strategies forcorona control to control interactions with biological systems, andnanoarchitectonics of pH-responsive nanoparticles that changetheir surface charge from negative to positive in response to adecrease in the pH microenvironment of the biofilm, and enhan-cing antimicrobial activity. In this nanoarchitectonics of supra-molecular assembly, bacteriorhodopsin and ATP synthase areco-assembled in an artificial biomimetic system, enabling cascadereactions and ATP synthesis under illumination. In the lattersystem, multiple species of functional units are organized in layer-by-layer nanoarchitectonics, and the conversion of light energyinto chemical energy is achieved by facilitating functional com-munication among them. The above example shows that thedevelopment of chemical communication by layer-by-layernanoarchitectonics is also useful for mimicking biologicalfunctions.5. Biomedical applicationsAs emphasized in the previous section, asymmetric or hier-archical organization through layer-by-layer nanoarchitectonicsallows for the expression of functions through controlledchemical communication. The effect is more suitable formimicry and application of various biological functions. Suchan approach is useful not only in basic biochemistry, but alsoin applicable biomedical fields such as drug delivery.For example, layer-by-layer assemblies based on nano-particles can be important tools in the field of drug delivery.79Applications include the delivery of chemotherapeutic agents,small molecule inhibitors, and nucleic acids. Potentially usefulis the ability to encapsulate multiple functional units. Nanoarch-itectonics of nanocarriers, such as the stepwise achievement ofcomplex combination therapies, will be possible. Comparedto the already well-established planar film-type layer-by-layerassemblies, the multi-step process of organizing a series offunctional units into a nanoscopic template is inherentlycomplex. The nanoarchitectonics of these materials requiresappropriate conditions for each synthesis step and adsorbedmaterial. Hammond and co-workers examined the requirementsfor a reliable method for the synthesis of layer-by-layer liposomescontaining nucleic acids: the influence of solution conditionssuch as pH, ionic strength, salt composition, and valence on thepreparation of layer-by-layer nanoparticles.80 The results revealedthe importance of optimizing the parameters for the selection ofsolution conditions to control the degree of ionization andelectrostatic screening length suitable for the adsorption ofnucleic acids and synthetic polypeptides. Moreover, the amountof nucleic acids in layer-by-layer liposomes was improved byabout 8-fold. It was shown that the optimization of the solutionconditions for the preparation of layer-by-layer nanoparticles fortherapeutic use is actually a fundamental part of the preparation.Despite the above example being a fundamental study, it isobvious that the functionalization of liposomes is a practicaland important matter, with layer-by-layer membranes to extendtheir biomedical applications, because liposomes are importantdrug delivery entities. Layer-by-layer nanoarchitectonics also sug-gests that optimization of practicality must go back to basics.Nanoarchitectonics of biosynthetic bioparts in artificial cell-like hollow structures is very useful to advance research in biomo-lecular synthesis, biosensing, and biomedical applications.81 As aprovider of such a venue, microcapsules nanoarchitectonized bytemplated layer-by-layer assembly using natural polymers are apowerful tool. In one such attempt, Drachuk et al. immobilizedDNA templates encoding translationally activated riboswitches andRNA aptamers in layer-by-layer microcapsules prepared from regen-erated silk fibroin protein (Fig. 14).82 To successfully meet theappropriate biocompatibility and semipermeability, several impor-tant parameters were controlled, including the presence of polymerprimers, the concentration of silk protein, and the amount of DNAin each layer during assembly. The properties of the material,regenerated silk fibroin protein, were also successfully used.Acute treatment with methanol induced a transition in thesecondary structure of silk. The use of organic solvents facili-tated the formation of b-sheets in the shell structure of theprotein, allowing stacking through multiple hydrogen bondsand hydrophobic interactions. The resulting microcapsuleswere DNA immobilized, uniformly sized, and robust. Thecapsule shell was further functionalized by modifying it withgold nanoparticles and IgG antibodies. This organizes a micro-compartmentalized nanoarchitecture with sensing elementsfor remote sensing and targeted delivery. Such a design couldpotentially be used as a target cell-specific biosensor. Further-more, the incorporation of various RNA sensors could lead tothe design of multiplexed biosensors that track multiple bio-markers in complex media.Fig. 13 Supramolecular assembly of bacteriorhodopsin and ATP synthasein an artificial biomimetic system to allow cascade reactions and ATPsynthesis under illumination. Reproduced with permission from ref. 78.Copyright 2022 Wiley-VCH.ChemComm Feature ArticleThis journal is © The Royal Society of Chemistry 2024 Chem. Commun., 2024, 60, 2152–2167 |  2163Polyelectrolyte complex hydrogels, such as biopolymers,have shown promise as therapeutic agents and cell carriers.83The nanoarchitectonics of these polyelectrolyte complex hydro-gels in the form of microcapsules and others have been inves-tigated for their potential application as drug and cell carriers.Duan and co-workers used sodium alginate and poly-L ornithineas polyanions and polycations, and tailored polyelectrolyte com-posite hydrogels based on their electrostatic interactions. Inparticular, poly-L-ornithine, a positively charged synthetic aminoacid, promotes cell adhesion.84 It also improves the stability ofalginate chelated with polyvalent cations. Poly-L-ornithine has aweaker immune response and better biocompatibility than otherpolycations, e.g., poly-L-lysine. Furthermore, they can efficientlyencapsulate enzymes and nano-sized therapeutic agents. Basedon this property, a sustained release of at least 21 days wasachieved. Alginate/poly-L-ornithine fibers have suitable mechan-ical properties and self-healing behavior. They are a favorablemedium for cell growth and differentiation. The nanoarchitec-tonics of these bio-polyelectrolyte composite hydrogels isexpected to make a significant contribution to biomedicalapplications as therapeutic agents and cell carriers.Various nanomaterials have been used both in vitro andin vivo to facilitate intracellular delivery of small interferingRNA (siRNA) to induce post-transcriptional gene silencing viaRNA interference.85 However, in many cases silencing efficiency ishampered by poor intracellular and nuclear delivery. Ahlenstiel andco-workers have delivered siRNA into the nucleus of HIV-1 infectedcells to silence HIV-1 transcribed genes by layer-by-layer capsules(Fig. 15).86 The siRNA was complexed with multilayer particlesformed by a layer-by-layer assembly of poly(styrenesulfonate) andpoly(arginine). siRNA was incubated with HIV-infected cell types tostudy its action. This layer-by-layer capsule system mediates thenuclear delivery of siPromA to gene promoter sites and induces areduction in viral RNA and protein levels. Viral RNA and proteinwere measured and functional viral silencing by siRNA deliveredwith the particles was confirmed after 16 days of treatment. Theseresults pave the way for future studies on particle-delivered siRNAfor efficient transcriptional gene silencing of various diseases andinfections, including HIV. It provides a non-viral particle platformfor nuclear-targeted siRNA delivery as well. More importantly, itbrought the fundamental knowledge for research to achieve epige-netic silencing of genes involved in disease.Structural formation by layer-by-layer nanoarchitectonics isbeneficial for organizing diverse functional units, includingvarious bio-components, into the same system. In particular,biomedical applications require complex biological andchemical communications among many units, and layer-by-layer assemblies that can be adapted to a variety of situationscan meet the demand. Layer-by-layer assembly can be effectivein dealing with diseases that do not fit into a simple frame-work. It is useful for biomedical applications such as efficientdrug delivery, gene delivery and gene silencing.6. Short summary and perspectivesThe concept of nanoarchitectonics universally applies to atoms,molecules, and nano-units for architecting functional materialsystems. Asymmetric structures and hierarchical organization,Fig. 14 A layer-by-layer microcapsule immobilized with DNA templatesencoding translationally activated riboswitches and RNA aptamers tosuccessfully meet the appropriate biocompatibility and semipermeability.Reproduced with permission from ref. 82. Copyright 2020 AmericanChemical Society.Fig. 15 Delivery of siRNA into the nucleus of HIV-1 infected cells tosilencing HIV-1 transcribed genes by layer-by-layer capsules ofpoly(styrenesulfonate) and poly(arginine). Reproduced with permissionfrom ref. 86. Copyright 2023 American Chemical Society.Feature Article ChemComm2164 |  Chem. Commun., 2024, 60, 2152–2167 This journal is © The Royal Society of Chemistry 2024rather than mere assembly and organization of structures, andrational physical and chemical communications will lead to thedevelopment of more advanced functional materials. Layer-by-layer assembly can be a powerful tool for this purpose, asexemplified in this feature paper. Cleverly organized layer-by-layer structures produce various types of physical and chemicalcommunications. They contribute to functions related to thecontrol of thermal communication, optical communication, andchemical signal communication. Hierarchical and directed layer-by-layer structures also serve to control biological functions. Layer-by-layer nanofilm oriented structures can mimic the complexstates found in real living organisms based on topographic cuesand cell interactions. Alternatively, nanoarchitectonics of supra-molecular assemblies that create communication between func-tional units not found in living organisms and co-assemblebacteriorhodopsin and ATP synthase in an artificial biomimeticsystem, which enables the conversion of light energy intochemical energy. Furthermore, layer-by-layer organization is use-ful for biomedical applications such as efficient drug delivery,gene delivery and gene silencing. On the other hand, the meth-odology of layer-by-layer assembly itself is still being pioneered.For example, highly oriented layer-by-layer membrane structuresare being fabricated by spraying from low angles, and sponta-neous multilayer creation using miscible and immiscible inter-faces is also being investigated. New strategies such as multilayermetal-quinone networks that complement layer-by-layer struc-tures have also been proposed. It can be concluded that materialnanoarchitectonics based on the layer-by-layer method is an easymethod to assemble asymmetric structures and hierarchicalorganization, and is a powerful technique for developing func-tions through physical and chemical communications.Finally, as a simple future perspective, we considered thedevelopment of functional materials from a broader perspec-tive. The interaction of chemical substances dispersed insolution can be considered as the basic functional expression.On the other hand, the most developed system at the oppositeend of the spectrum is a rational, hierarchically organizedfunctional system, such as that found in biological systems.These systems are created through processes such as self-organization against the thermodynamic fate of increasingentropy. This artful organization, which living systems haveachieved for billions of years, is what humanity is trying toachieve in a few decades of history. Much effort has beenexpended and much has been accomplished through self-assembly by supramolecular chemistry.87 Nanoarchitectonics,an integrated technology, goes beyond supramolecular chem-istry to more deliberate and multifaceted construction of func-tional systems.88 The greatest functional construction isthrough the control of physical and chemical communications.Layer-by-layer assembly is a rational technology for buildingsuch structures. The greatest advantage of the layer-by-layermethod is that it can be applied to a wide variety of materials.This characteristic is advantageous in assembling complex tissuesystems such as biological systems, which are composed ofmany components. However, most current research examplestend to be individualistic functional studies using individualcomponents. Contrary to such a tendency, it is possible toconstruct more advanced functional systems by assembling alarge number of functional units in a layer-by-layer assembly. Itmay be difficult to construct such complex systems using con-ventional approaches. However, current layer-by-layer nanoarch-itectonics does not seem to be fully utilizing its great potential.Fortunately, mankind has developed new methodologies ofmachine learning89 and material informatics90 using artificialintelligence. The introduction of this concept may enable thedevelopment of organized structures composed of morecomplex components. Conceptual fusion of nanoarchitectonicsand material informatics is proposed for the development offunctional nanoporous materials.91 This conceptual fusion isworth introducing to layer-by-layer assembly, which hasachieved diverse applications. If this can be done, it may bepossible to artificially assemble the functional systems withrationally integrated organization as found in biological sys-tems. Humans will be able to develop the functional systemsthat nature has achieved over billions of years of evolutionwithin a short time span that we can experience.Finally, we summarize the main messages of this review. Inmaterials with organized functional components, physical andchemical communications of energy, electrons, signals, andmolecules between unit structures is necessary for functionalexpression. This is essential for response behavior to externalstimuli, as well as for energy accumulation, signal transduction,and other functions. For such communication, what is realisticand immediately achievable is nanoarchitectonics of controlledlayered structures. The most useful approach for this is layer-by-layer assembly. This nanoarchitectonics strategy would develophighly functional systems like living organisms. To achieve this,it is essential to take into account factors such as operating outof equilibrium, metabolism, compartmentalization, and recipro-cal interaction with the environment, which have been difficultin the conventional self-assembly approach. In this case, it willbe necessary to further develop layer-by-layer nanoarchitectonicsand go beyond it. It will also be necessary to integrate nanoarch-itectonics with new concepts such as materials informatics.Author contributionsKatsuhiko Ariga: conceptualization, writing – original draftwriting – review & editing, funding acquisition. Jingwen Song:conceptualization, review & editing. Kohsaku Kawakami: pro-ject administration, review & editing.Conflicts of interestThere are no conflicts to declare.AcknowledgementsThis study was partially supported by the Japan Society for thePromotion of Science KAKENHI (Grant Numbers JP20H00392and JP23H05459).ChemComm Feature ArticleThis journal is © The Royal Society of Chemistry 2024 Chem. 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