Role of nanotopography in the development of tissue engineered 3D organs and tissues using mesenchymal stem cells

Table 1 Classification of various types of nanotopography (nanofabrication) methods

Energy source	Method	Mechanism and final outcome	Processable polymers
Thermal	Replica modelling	Creating negative shape of the mold by thermal cross-linking of cavity-filled pre-polymer	Thermocurable polymers, e.g., poly(dimethyl siloxane)
	Nanoimprint lithography	Creating negative shape of the mold by plastic deformation of polymer above Tg	Thermoplastic, e.g., polystyrene, poly(lactic acid), and conductive polymers, e.g., polyaniline and polypyrrole
	Block copolymer lithography	Creating nanoscale hole, line and lamellar structures by microphase separation of two immiscible polymers	Block copolymer, e.g., polystyrene-block-poly(methyl methacrylate), styrenebutadiene-styrene
Optical	Photolithography	Depending on mask design and selective UV exposure, solubility is changed	Photo curable polymers, e.g., photoresist, polyurethane-based
	E-beam lithography	Formation of arbitrary patterns using different electron beam pathways and selective irradiation of focused electron beams to change solubility	E-beam sensitive polymers, e.g., polymethyl methacrylate
	Direct laser writing	Formation of arbitrary patterns by selective cross-linking of the polymer by laser irradiation	Photo-curable polymers
Chemical	Microcontact printing	Creating extruded patterns of elastomeric stamp using relative surface energy difference needed for transferring materials	Proteins and self-assembled monolayers
	Dip-pen lithography	Formation of arbitrary patterns by direct writing of molecules with a sharp tip	Self-assembled monolayers
	Salt leaching/gas foaming	Formation of a block of polymer with voids by dissolution of salt particles (salt leaching) and/or bubble formation in the polymer block (gas foaming)	Solvent soluble polymers, e.g., thermoplastic and conductive ones
Electrical	Electrochemical deposition	Forming negatively shaped molds by electrochemical reduction of the polymer	Conductive polymers
	Electrospinning	Drawing a three dimensional nanofibrous mesh from the polymer solution using an electric field	Solvent soluble polymers
Physical	Capillary force lithography	Formation of partially filed negative shape of the mold by capillary rise of thermoplastic polymer above Tg	Thermoplastic and solvent soluble polymers
	Micromolding in capillaries	Creating a negative shape of the mold by capillary-driven microchannel filling	Solvent soluble polymers
	Wrinkle	Formation of random or aligned micro- or nanolines using mechanical buckling Mechanical buckling between elastic substrate and rigid film	Elastomeric polymers, e.g., polydimethylsiloxane
	Crack	Formation of aligned or inter-crossing line patterns by mechanical fracturing of the stiff film adhered onto elastic substrate	Elastomeric polymers

Adapted from Kim et al[3].

Table 2 Significant studies on nanotopography and mesenchymal stem cells for developing 3D bone, cartilage and skin

Tissue/organ	Nanotopographical cues	Description	Outcome	Ref.
Bone	Nano-ridges, and nanogrooves nanotopography surfaces	The effect of nanotopographic ridges and grooves on MSCs morphology, proliferation and differentiation to osteoblast cells were investigated	Osteogenic differentiation can be controlled and directed using specific size scale of topographic cues with or without osteogenic agents	Watari et al[54]
	Implementing nanostructures of different sizes	The effect of titanium-coated hemisphere-like topographic nanostructures of various sizes (50, 100, and 200 nm) on hMSCs cellular behaviour towards osteoblast lineage was investigated	Osteogenic differentiation of hMSCs is dependent on the size of the underlying nanotopographical structures. Colloidal lithography combined with coating technologies can have great potentials for fabricating nanoscale topography on scaffolds	de Peppo et al[64]
	Bioactive calcium phosphate thin films sputter deposited onto a polycrystalline titanium nanostructured surface	Calcium phosphate thin films were used to study the cellular response of hMSCs to nanostructured titanium surfaces with the aim of directing them towards osteogenic differentiation	Various in vitro studies revealed that the use of nanostructured titanium surfaces and the bioactive calcium phosphate coatings could allow for directed and controlled differentiation of hMSCs towards osteogenic lineage. The combination of the two materials together showed higher rate of osteogenic differentiation compared to that of each of these materials on their own	McCafferty et al[63]
	Polished Ti surfaces chemically treated with H2SO4/H2O2 to create nanotopography	Chemically treated Ti surfaces with nanotopography and seeded with rat MSCs were used to investigate their osteoinductive potentials compared to untreated surfaces. Signalling pathways responsible for osteoinductive effect of nanotopography on MSCs were also investigated	Ti surfaces with nanotopography exhibited increased cell proliferation and alkaline phosphate activity. Gene expression of key bone markers was upregulated on nanotopography surfaces, under non-osteogenic conditions, compared to control	Rosa et al[66]
Cartilage	A biomimetic microfluidic device embedded with aligned nanofibers consisting of microchambers of different angle	A device was developed to create a microenvironment that integrates nanotopography and flow stimulus of the ECM of natural cartilage for the purpose of investigating the effect of microfluidic and nanotopography on the cellular behaviour and fibrochondrogenesis of MSCs	The angle of flow direction, in relation to the aligned nanofibers, affects MSCs behaviour. Fibrochondrogenesis of MSCs was evident when the flow direction was perpendicular to the aligned nanofibers	Zhang et al[75]
	Nanowire nanotopographic surfaces	Polycaprolactone nanowires surfaces were fabricated using a solvent-free gravimetric template technique to investigate their nanotopographical effects on the adhesion, proliferation, differentiation and ECM synthesis of adipose-derived MSCs	The results demonstrated that adhesion and proliferation of adipose-derived MSCs were enhanced on nanowire surfaces compared to the control. Nanowires also effected the morphology of these cells Interestingly, it was shown that nanowires supported adipogenic differentiation of these cells rather than chondrogenic differentiation	Trujillo et al[73]
	Nano-pillar, nano-hole and nano-grill nanotopography surfaces	Nano-pillar, nano-hole and nano-grill structures were formed on polycaprolactone surface using thermal nanoimprinting to investigate their effect on chondrogenic differentiation of hMSCs	Nanotopographical patterns have the ability to induce changes in MSC morphology and cytoskeletal structure towards a specific lineage, in this case chondrocyte cells. Delayed chondrogenesis was observed on nanogrill topography compared to nano-pillar and nano-hole topography, which enhance MSC chondrogenesis	Wu et al[55]
Skin	Electrospun nanofibrous scaffolds	Electrospun Coll/PLLCL and PLLCL nanofibrous scaffolds were prepared to investigate the proliferation and differentiation of MSCs to epidermal lineages	Cell proliferation was significantly higher on Coll/PLLCL nanofibrous scaffolds compared to PLLCL scaffolds. MSC morphology was also different on Coll/PLLCL nanofibrous scaffolds compared to control. Electrospun Coll/PLLCL exhibited similar properties to the native skin ECM	Jin et al[85]
	Nanotopographically variable grooved matrices	Nanotopographically variable grooved matrices, using UV assisted capillary force lithography, with curable PUA polymer were fabricated and then coated with gelatine to investigate the effect of nanotopographical density on hMSC migration and proliferation for wound healing purposes	As the density of the nanogrooved matrices increased, the speed of hMSCs migration increased proportionally. It was shown that hMSC proliferation was not significantly different on nanogrooved matrices, compared to flat control. Therefore, suggesting that proliferation of hMSCs may not be influenced by the nanogrooves	Kim et al[82]

PUA: Polyurethane acrylate; Coll/PLLCL: Collagen/poly(llactic acid)-co-poly(3-caprolactone); Ti: Titanium; hMSCs: Human mesenchymal stem cells.