WO2023217767A2 - Scaffold supported organoid farms for controlled high-throughput in vitro organoid aggregation and regional organoid patterning - Google Patents

Abstract

Methods and products for preparing organoids in regular arrays on scaffolds are proposed.

Description

SCAFFOLD SUPPORTED ORGANOID FARMS FOR CONTROLLED HIGH-THROUGHPUT IN VITRO ORGANOID AGGREGATION AND REGIONAL ORGANOID PATTERNING

Field of Invention

The present disclosure relates to methods and products for preparing organoids in regular arrays on scaffolds, in particular on lattice scaffolds.

Background

Conventionally grown organoids are initially aggregated in 96 well plates. Cells are seeded in each well. Media changes occur every 2 days in each well (typically hundreds of organoids are seeded at one time, involving multiple 96 well plates). The organoids usually grow spherical, and after about 10 to 13 days of culture, organoids are manually removed from their wells and embedded in Matrigel™ (which involves multiple steps of manually pipetting and treating each individual organoid). Organoids are then transferred to petri dishes, where they are free floating in the media and placed on an orbital shaker for long term culture.

Summary

The invention provides a lattice scaffold to guide organoid growth formed from strands comprising polymeric fibers. A lattice scaffold is provided that comprises strands made up from polymeric fibers. The fibers, which may comprise or consist of polycaprolactone, are arranged in layers to form strands. The lattice scaffold provides a platform for producing highly reproducible and high-throughput organoid arrays (e.g. Fig. 1). The lattice scaffold may comprise a lattice support (1), such a printed lattice support comprising a lattice holder (11) and scaffold clips (12), and one or more strands, e.g. held in place by scaffold clips (Fig. 11). A lattice scaffold can comprise a first set of strands which are substantially parallel, and a second overlapping set of strands which are substantially parallel lying in substantially the same plane and oriented in a second direction. The distance between the intersections between the first set of strands and the second set of strands of the lattice scaffold is much greater than the diameter of the strands, e.g. more than 10 times greater. The lattice scaffold can be coated to promote cell adherence, for example with hydrogels such as Matrigel™. The lattice scaffold can be patterned with growth factors or morphogens.

A method is provided for generating an array of organoids comprising culturing stem cells (e.g. pluripotent stem cells) on a scaffold which is a lattice (a lattice scaffold), thereby generating an array of organoids. The method comprises providing a lattice scaffold formed from strands comprising polymeric fibers, seeding stem cells on the lattice scaffold, and culturing the stem cells. The culturing vessel containing the lattice scaffold and the stem cells may be rocked. The lattice scaffold may be coated, e.g. with a hydrogel such as Matrigel™ prior to seeding. The lattice scaffold surface may be treated/coated with patterning molecules such as growth factors. The lattice scaffold may be lifted above the bottom surface of the culturing vessel during the culturing. The organoids may be brain organoids. When the method is used to culture cardiac cells on a lattice which is coated the method can produce cardiac tissue. Thus a method is provided for generating cardiac tissue comprising an array of nodes, the method comprising culturing stem cells (e.g. pluripotent stem cells) on a scaffold which is a lattice (a lattice scaffold), where the scaffold has been coated with a hydrogel such as Matrigel™, thereby generating cardiac tissue comprising an array of nodes.

In one embodiment the method generates an array of elongated organoids. The method comprises providing a polymeric lattice scaffold with a fixed structure of strands (an ‘elongated organoid lattice scaffold’), and culturing stem cells (e.g. pluripotent stem cells) on the polymeric lattice scaffold, thereby generating an array of elongated organoids. In this embodiment the stem cells are localized along the strands. The polymeric lattice scaffold may be coated with a hydrogel such as Matrigel™. The elongated organoids may be elongated brain organoids.

The method can guide the regional identity of an array of elongated organoids on a polymeric lattice scaffold. In one embodiment the method comprises patterning the lattice scaffold with signalling molecules such as growth factors. The method comprises providing a polymeric lattice scaffold which is surface-modified with a binding agent, such as heparin, and binding partners such as growth factors that bind heparin, e.g. with heparin-binding domains, incorporated in the surface of the scaffold. The surface chemistry can thus be modified to release growth factors to stimulate the growth of different brain regions. Alternatively, or in addition, the array of elongated organoids can be cultured in a culture chamber where the polymeric lattice scaffold is situated in culture medium and the composition of the culture medium varies depending on the position in the culture chamber. This can be facilitated using the microfluidic chip which incorporates a culture chamber which is described herein.

A microfluidics system is provided. The microfluidics system comprises a microfluidic chip. The microfluidics chip has at least a region with microchannels for diffusion-based mixing and a culture region comprising a culture chamber. The system can comprise a mount for positioning a scaffold within the culture chamber. The system can comprise a means for filling the microchannels. A process for printing and preparing a mold to make the chip is described. The microfluidics mold is printed using DLP 3D printing. Preparation of the mold (printed part) includes the following steps, in order: (i) washing in an organic solvent (e.g. sonication using ethanol or isopropanol); (ii) curing under UV light and optionally heat; (iii) soaking in an organic solvent (e.g. 30 - 60 min using ethanol or isopropanol); (iv) treatment using oxygen plasma (e.g. 100 W at 1 mBar O2 for 5 min); v) coating with a silane (e.g. vapour deposition of Trichloro(1 H,1 H,2H,2H-perfluorooctyl)silane); (v) incubation above room temperature (e.g. incubated at 60°C for at least 5 hours). The chip is cast with polydimethylsiloxane (PDMS) silicone. The culture chamber can house a lattice scaffold, for example one or more polymeric strands mounted on a lattice scaffold mount. The chip can provide a linear stable gradient, e.g. of growth factor, across the culture chamber and therefore along the one or more strands of the lattice scaffold. An elongated organoid can be grown on the lattice scaffold, inside the culture chamber. Figures

Figure 1. a). Graphic schematic of brain organoid growth on scaffolds. 1. Scaffold fabrication. 2. Scaffold geometry. 3. Cell seeding on scaffolds. 4. Organoid farms, b) Schematic to illustrate scaffold fixed on Cell Crown™ device, in 6 well plate, c) to f) Brain organoid growth on scaffolds: c) Scanning Electron Microscope (SEM) images of PCL scaffold fabricated by MEW, scale bar: left 10 pm, center 10 pm, right 50 pm. d) Brightfield images of PCL scaffold with different geometries. Strand separation from left to right: 250 micron; 500 micron; 800 micron; 1000 micron e) Brightfield images of brain organoids growing on scaffold compared to conventional and scaffold free method Scale bar: 500 pm. The top row shows day 9 and the bottom row shows day 17. f) Brightfield image of brain organoids forming an array growing on a single scaffold from one well in a six well plate.

Figure 2. Brightfield images of organoids growing on scaffolds on different scaffold geometries. Panel A: Organoids growing on Matrigel™ scaffolds on square grid lattice geometry (500 pm and 1000 pm spacing) and triangle grid geometry. Panel B: Organoids growing on non-treated scaffolds on square grid lattice geometry with 500 pm, 800 pm and 1000 pm spacing.

Figure 3. Characterisation of brain organoids on scaffolds, a) Immunostaining of day 20 brain organoids. Top, From LHS: 0-tubulin III; SOX2; Merge (all with scaffold); scaffold free; conventional. Bottom: From LHS: immunostaining of aPKCzeta, FOXG1 ; merge; scaffold free; conventional. Scale bar: 200 pm. b) Immunostaining of day 40 organoids. Top, From LHS: FOXG1 and PAX6 staining; Portion within dotted line from first panel blown up ; scaffold free; conventional. Bottom: Scale bar: 500 pm. From LHS: Stained with 0-tubulin III, PAX6 and DAPI. Portion within dotted line from first panel blown up ; scaffold free; conventional, c) Immunostaining of day 40 organoids. Scale bar: 100 pm. Top: TBR1 and PAX6. Scaffold; scaffold free; conventional. Bottom: GSX2 and DAPI. Scaffold; scaffold free; conventional.

Figure 4. Scaffold geometry guides lumen formation in human embryonic stem cells (hESCs). a-c: (a) square, (b) diamond (parallelogram) (c) triangle lattice scaffold geometry. For each lattice type, the figure shows: Cartoon schematic of scaffold geometry (Left); Brightfield image of hESCs growing on scaffold at day 5 (middle); IHC staining of ZO1 (apical marker) at day 5 (right). Scale bar in middle: 100 pm; scale bar on right side: 200 pm), d-h: 3D characterization of human pluripotent stem cell (hPSC) tissues on triangular scaffolds, d) Image gallery at day 5 showing single slice of scaffold and hESCs immunostained with SOX2 (grey) and ZO1 (light grey ) (left), 3D reconstruction from a confocal z stack, with the lumens segmented and pseudo coloured in light grey (middle) cross section of the confocal z stack showing a bisector slice through the lumens indicated by the white lines (right), scale bars correspond to 100 pm; e) Maximal cross-sectional lumen area (pm²) in small angles (S) (45° ± 9°) and large angles (L) (90° ± 5°); f) Lumen volume (pm³) in small angles (S) and large angles (L); g) Lumen circularity in small angles (S) and large angles (L); h) Total cell count in small angles (S) and large angles (L). P value of (****) <0.0001 as determined by Welch’s t-test. Figure 5. hESCs grow on scaffolds in a highly reproducible way and show stem cell identity a) Brightfield image timeline of hESCs growing on Matrigel™ coated PCL scaffolds, highlighting the emergence of the lumen b) overview image of a scaffold in a 6 well plate and zoomed in images at day 2 and day 5 c) Immunohistochemistry (IHC) staining demonstrates the early emergence of the lumen at day 2, and large luminal cavities around the scaffold at day 5 d) F-actin IHC stain, left: z projection of entire tissue around scaffold and right: cross-section of tissue in the xy planes e) IHC staining shows stem cell identity at day 5.

Figure 6. Cytoskeletal tissue dynamics and onset of lumenogenesis. SiR actin time lapse shows emergence of lumen a) Consecutive frames from live imaging of tissues stained with an F-actin probe, SiR-actin, from 24 h to 120 h (Day 1 to Day 5). SiR-actin time lapse shown at 24 hour intervals (i.e. at 24 hours, 48 hours, 72 hours, 96 hours, 120 hours). Top: fluorescent images of F-actin, showing F- actin expression in 2 emerging lumens in the scaffold corners (white solid arrowhead) and on the scaffold wall (white line arrowhead), bottom: brightfield images. Scale bar corresponds to 200 pm. b) Consecutive frames from live imaging of tissue stained with F-actin probe, SiR-actin, from 30 hours to 51 hours at 3 hour intervals during lumen emergence period. Top: fluorescent images of F-actin during lumenogenesis, displaying actin accumulation at the growing edge of the expanding tissue in the corner of the scaffold (white solid arrowhead), before accumulating inside the newly formed lumen (white line arrowheads). Bottom: brightfield images. Scale bar corresponds to 100 pm.

Figure 7. Brightfield image panel of organoid development on Matrigel™ coated square grid scaffolds day 3 to day 15 (D3-D15). From left hand side: Day 3; Day 5; Day 11 ; Day 15. b) IHC staining of brain organoids on day 20 (D20) (Left hand side panel, stained with (from the left): PAX6; FOXG1 ; FOXG1 and PAX6. Right hand side panel, stained with (from the left): Tuj1 ; SOX2; Tuj1 and SOX2) c) IHC of organoids day 15 showing ZO1 marker expression, left: 3D projection, right: cross-section of lumen in the xy planes.

Figure 8. Cardiac organoids growing on scaffolds, (a) Graphic schematic of cardiac organoids growing on scaffolds: (1) Scaffold fabrication (2) Scaffold geometry (3) Matrigel™ coating (4) Cell seeding (5) Cardiac organoids, (b) Brightfield images showing iPSCs grown on scaffolds (day 4) (Left hand side), and iPSC differentiation into cardiomyocytes (day 6, and day 10)( middle panel and right hand side respectively). Scale bar = 200pm.

(c) Immunostaining for cardiac troponin (mid grey) and connexin 43 (light grey). The connexin is particularly located on the strands indicated by the black arrows. The cardiac troponin is found in the round organoid (cardiac node) that has formed at the lattice intersection (lattice node). Scale bar: 100 pm. (d) Cardiac nodes numbered 1 to 8. (e) Representative fluorescence recording of Ca²⁺ transients from 8 cardiac organoids. [CA2+] I transients (a.u.) on Y-axis. Time in seconds on X axis (from 0 to 10). Recorded at locations 1 to 8 in panel (d). Figure 9. Elongated brain organoids growing on bioactive V2.0 PCL scaffolds, (a) Graphic schematic of elongated brain organoids growing on V2.0 bioactive scaffolds, b) SEM images of Matrigel™ coated scaffolds (right hand side) and uncoated scaffolds (left hand side). Scale bar: 10 pm. c) Brightfield images of elongated organoids growing on V2.0 scaffolds. Scale bar: 500 pm. From Left hand side: Day 2; Day 5; Day 10; Day 15. d) Bright field images of an elongated organoid at day 6 (top), day 11 (middle) and day 16 (bottom), e). Photographs of fixed organoid arrays at day 20 (left hand side) and day 40 (right hand side). Scale bar 3.5 cm.

Figure 10. Elongated organoids grown on SHH functionalised PCL scaffolds, a) Immunostaining for FOXG1 , MAP2 and DAPI on elongated organoids, grown in the absence of SHH. b) Immunostaining of SHH functionalised PCL scaffold, and non-functionalised scaffold. Scale bar: 500 pm. c) SHH release from PCL scaffolds over 7 days. d. Normalised cumulative release of SHH (%). Plotted against Time (Hours) (0 hours to 144 hours), e) Immunostaining for FOXA2, PAX6 and DAPI on elongated organoids on SHH bioactive scaffolds (with 200 nM SHH)(Top row and middle row) and on negative control without SHH (Bottom row). Scale bar: 200 pm. In order from Left Hand side: PAX6, FOXA2, DAPI, Merge (all three).

Figure 11. Microfluidics platform for perfusion of arrays, a) Schematic describing assembly of the microfluidics platform, whereby the custom cell crown (1) is assembled and inserted into the organoid culture region (6) in the microfluidics chip (2), which is then clamped between glass plates (3) using nuts (4) and bolts (5) to fully seal the chip. The microfluidic channels (7) have two entry points (9) which are ports, b). Close up view of the custom scaffold holder, showing the holder (11) and clips (12). c) Schematic view of the position of the elongated organoid on a PCL fiber positioned (6) within the microfluidic chip (2) under gradient perfusion conditions, with the dorsal region on the right hand side (R) and the ventral region on the left hand side (L). Includes schematic of different liquids being injected through ports (9) on left hand side (L) and right hand side (R) into the microchannels of chip (2) and view of organoid culture region (6) from above in the presence of a gradient, d) View of an assembled custom cell crown. A suture thread is used here as a surrogate PCL fiber and the cell crown is upside down to better visualise the placement of a scaffold strand. Scale bar 5mm. e) Fluorescent micrograph verifying diffusion-based mixing within the microfluidic channels creating a gradient from the left hand side (21) (L) to the right hand side (22) (R). Perfused fluid contains fluorescein sodium salt. Direction of flow is indicated with a black arrow. Scale abr 1 mm. f) Fluorescent micrograph verifying the presence of a concentration gradient generated from the microfluidics channels. Perfused fluid contains fluorescein sodium salt, g) Custom design features in the chip (2) to overcome challenges of the assembled custom cell-crown include Filleted edge at outlet (25) to prevent bubble trapping; flared outlet (23) from microfluidic channels (7) into growth chamber (6); tapered edges (24) in the growth chamber region (6).

Figure 12. An elongated organoid grown under perfusion without a gradient. Panel A provides a schematic of the experiment. Top of panel A: Day 5: Organoid (on custom scaffold holder (6)) placed in microfluidic chip (2). Day 5 - Day 10: Microfluidic perfusion. Culture chamber (6) is shown in expanded view with the scaffold (S) and the organoid (S). Media flow is indicated by the arrow along chip (2). Pumps feed the microchannels via ports (9). Day 10: Organoid placed in 6 well plate. Bottom of panel A: Shows medium changes over time. Day 5 - Day 12: Neural induction medium (diagonal hatching). Day 12 to Day 18. Improved -A medium + 2% Matrigel (vertical hatching). Day 18 - Day 20: Improved +A medium + 2% Matrigel (dotted hatching). Panel B shows immunostaining of elongated organoid grown under perfusion without a gradient between days 5 and 10 in a microfluidic chip, stained with apical marker aPKC (light grey), forebrain marker FOXG1 , dorsal marker PAX6 (mid grey) and DAPI (mid grey).

Figure 13. An elongated organoid grown under perfusion with a gradient. Figure 13 A provides a schematic of the experiment. Two syringe pumps provide medium for the culture chamber. Neural induction medium was used from day 5 (D5) to day 12 (D12), One syringe pump provides medium which also includes 200nM SAG + 2.5pM iWP2 from day 5 to day 10 (D10) (LHS, shown in black). The other pump just has the neural induction medium (shown in white). The microfluidic channels mix the medium output from the two syringes in such as way that a gradient of 200nM SAG + 2.5pM iWP2 is created across the culture chamber as shown in panel A and the elongated organoid is cultured in the presence of the gradient from Day 5 to Day 10. From Day 10 a gradient was no longer used and both syringe pumps provided the same medium: From day 10 to day 12 (D12), neural induction medium, without 200nM SAG + 2.5pM iWP2; From day 12 to day 15 (D15) Improved -A medium + 2% Matrigel; from day 18 (D18) to day 20 (D20) improved +A medium + 2% Matrigel. Culture chamber (6) is shown in expanded view with the scaffold (S) and the organoid (S) and a black triangle to indicate the dgradient from R to L. Bottom of panel A: Shows medium changes over time. Day 5 - Day 12: Neural induction medium (diagonal hatching). Day 5 to Day 10 (black) 200nM SAG + 2.5 pM iWP2.

Day 12 to Day 18. Improved -A medium + 2% Matrigel (vertical hatching). Day 18 - Day 20: Improved +A medium + 2% Matrigel (dotted hatching). Figure 13 B shows immunostaining of (a) an elongated organoid grown under perfusion with a gradient 200 nM SAG + 2.5 pM iWP2 between days 5 and 10 in a microfluidic chip (indicated by triangle with colouring in black as for Figure 12), stained with floor plate marker FOXA2, and Ventral MGE marker NKX2.1 and DAPI. (b) an elongated organoid grown under perfusion with a constant concentration of 200 nM SAG + 2.5 pM iWP2 between days 5 and 10 in a microfluidic chip (indicated by rectangle with colouring in black as for Figure 12), stained floor plate marker FOXA2, and Ventral medial ganglionic eminence (MGE) marker NKX2.1 and DAPI and c) an elongated organoid grown under perfusion in neural induction medium between days 5 and 10 in a microfluidic chip (indicated by rectangle in white to represent neural induction medium only) stained with floor plate marker FOXA2, and Ventral MGE marker NKX2.1 and DAPI.

Detailed description

The present invention provides a method of generating organoids in a high-throughput, reproducible manner on a controlled 3D matrix using a fibrous polymeric scaffold, e.g. poly(e-caprolactone) (PCL) (Fig. 1). A facile and highly adjustable fabrication system is provided, by way of direct-writing melt electrospinning. Electrospun fibers are deposited on a grounded collector plate using an extrusionbased printing technique with polymer melts. This yields highly defined fibrous lattice-structured scaffolds with micro-meter sized fibers (Fig. 1c, d). The lattice scaffold provides a structure for stem cells to settle on or around. As cells settle across the scaffold during cell seeding (e.g. after moving plate in a north south east west motion), groups of cells form clusters at the lattice intersections, forming a patterned arrangement of aggregated cells at the intersections (Fig. 1e). The organoids develop from the aggregated cells, and are tethered to the scaffold (Fig. 1e). A single scaffold structure can simultaneously grow hundreds of organoids. The whole array of organoids can be removed from the well plate for embedding steps or otherwise by manipulating the scaffold (Fig. 1). The scaffold can be inserted into a different well, which may be in multi-well plate, such as a 6-well plate (Fig. 1). 12, 24 or 48 well plates may also be used with appropriate lattice supports, e.g. CellCrown™ lattice supports. Lattice scaffolds with larger separation between the nodes (e.g. 1000 pm) can be used to grow organoids for longer before the individual organoids get too close to each other.

An array of organoids can be generated using a method which includes culturing stem cells (e.g. pluripotent stem cells) on a scaffold, such as a lattice scaffold. A lattice scaffold can be a lattice of printed strands. The strands may be polymeric, e.g. they may consist of or comprise polycaprolactone. The array of organoids can be generated by providing a lattice comprising strands comprising polymeric fibers, seeding stem cells on the lattice, and culturing the stem cells, thereby generating an array of organoids. The conditions used for culturing can support differentiation of the stem cells. Methods for culturing stem cells are known in the art. The culturing takes place in a culturing vessel. The culturing vessel may be rocked, preferably in a north-south-east-west direction (NSEW). The rocking can facilitate the stem cells congregating on the strands and/or at the nodes of the lattice. The stem cells can be pluripotent stem cells such as embryonic stem cells (ESC) or induced pluripotent stem cells (iPSC). The stem cells can be mammalian. The stem cells can be human.

The invention provides a lattice scaffold to guide organoid growth formed from strands comprising polymeric fibers. The organoids may be located at the ‘nodes’ in the lattice. A node is a location where the strands making up the lattice scaffold overlap (lattice intersections). A typical lattice scaffold may have greater than 2 nodes, greater than 4 nodes, greater than 9 nodes, greater than 50 nodes, preferably more than 100 nodes. The lattice scaffold can be printed in biocompatible and biodegradable polymers using melt electrospinning writing (MEW) fabrication, for example in poly(caprolactone) (PCL) or in mixtures containing poly(caprolactone). The lattice scaffold provides a platform for producing highly reproducible and high-throughput organoid arrays (E.g. Fig. 1). The lattice scaffold may comprise a lattice support (1), such a printed lattice support comprising a lattice holder (11) and scaffold clips (12), and one or more strands held in place by scaffold clips (Fig. 11). A construct is provided comprising a lattice scaffold formed from strands comprising polymeric fibers and organoids. The organoids may be located at the intersections between the strands of the lattice (also described herein as nodes). Each organoid may be located on a separate strand, and contact only one strand. The strand may be coated, e.g. to encourage stem cell attachment. The coating may be a hydrogel, for example an extracellular matrix (ECM) based hydrogel (e.g Matrigel™). The hydrogel may be a PEG-based hydrogel. Suitable hydrogels include basement membrane extracts and preparations. Possible coatings may include fibronectin and collagen. The coating may include a morphogen. The morphogen may be applied to the strand in predetermined locations. That is, the strand may be patterned with a morphogen.

The inventors have surprisingly found that culturing stem cells on fibrous lattice scaffolds provides a way to tether developing organoids on the scaffold in a fixed position, creating a matrix of organoids on a biomaterial scaffold, and providing the possibility for controlled growth factor release with spatiotemporal control directly to the organoid. The organoids are physically tethered to scaffold, which provides a fixed position on a 2D focal plane for experiments requiring positional control of organoids. The organoids are tethered on the same scaffold structure and as such can be treated en masse, for example, during Matrigel™ embedding steps, or when moving to a larger well plate. In addition, since each organoid within the array has a fixed position each organoid can be individually addressed. The lattice scaffold provides a way to deliver morphogens directly to the organoid core, with spatiotemporal control. Thus the invention relates to an improved method for organoid growth, on a structured bioengineered scaffold (Fig 1). This can provide several benefits, including generating a high-throughput method to grow organoids, tethering the organoids in a reproducible regular array, and providing multiple organoids that can manipulated en masse whilst keeping their spatial relationship by manipulating the scaffold they are attached to. Both the fact that the organoids can be produced or provided in a high-throughput format and the fact that individual organoids are tethered on a matrix in a fixed position provide benefits - improving the efficiency and usefulness of multiple different experiments, including live imaging experiments, drug screening, or optogenetic or electrical stimulation experiments. The methods provide improved organoid culture methods which facilitate high-throughput organoid culture for drug screening and toxicology applications. The methods described herein are improved methods which generate organoids such as brain organoids with less batch to batch variability. Further, the methods allow patterning of growth factors to generate polarized organoids, to correlate more closely with the in vivo configuration. The scaffold geometry can be modified to produce elongated organoids (e.g. elongated brain organoids), for example by increasing the distance between nodes. The surface chemistry can be modified to release signalling molecules such as growth factors in a time dependent and/or location dependent manner to stimulate the growth of different regions in the organ. The technology provides a valuable new approach to form human cell models for studying development, disease, and drug response.

Stem cells are seeded on the lattice scaffold in a culturing vessel, such as a single well in a 6 well plate, and a plurality of organoids are formed on a single lattice scaffold at once. The plurality of organoids are tethered to the fibrous scaffold. This means that it is only necessary to change the media in one big well (as opposed to one well per organoid). The scaffold can be manipulated, including being lifted and transferred to another plate, without disrupting or changing the position of the organoids. During subsequent processing such as a Matrigel™ embedding step, all of the organoids on the scaffold can be treated together, for example the entire lattice scaffold can be embedded in Matrigel™ rather than manually embedding individual organoids.

The lattice scaffold technology provides an in vitro system (cell culture platform) for the high- throughput generation of uniform and reproducible organoids, for example brain organoids. A method is provided to guide the regional identity of the cultured organoids by patterning the lattice scaffold surface with binding agents such as heparin, to allow the location of binding of molecules with a binding agent partner (e.g. molecules with a heparin binding function, for example signalling molecules such as growth factors) to be controlled. This can result in the controlled release of signalling proteins from the scaffold to organoid, in order to more closely mimic the anatomy on the in vivo developing organ, for example the brain. The invention provides a valuable new stem cell model for studying human organ development, disease and drug response.

The invention provides a method for generating high-throughput cardiac tissue. Thus 3D tissue culture efficiency and output is improved. The high-throughput cardiac tissue can be used for drug screening and toxicology. The methods of the invention can provide reproducible cardiac tissue to facilitate measurements of key functional properties.

Methods are provided to generate a 3D cardiac patch construct to deliver functionally active cardiac cells in vivo.

A method is provided to generate elongated organoids on a polymeric lattice scaffold. In this embodiment the lattice scaffold provides a fixed structure of one or more polymeric strands, e.g. one or more polymeric strands mounted on a lattice support, to grow stem cells (e.g. pluripotent stem cells) in an elongated arrangement. A polymeric lattice scaffold can be two or more polymeric strands mounted on a lattice support. A fixed structure of polymeric strands can be achieved by maintaining a constant separation between the strands in the lattice scaffold in a first direction, and varying the separation between the strands of the lattice scaffold in a second direction so that the separation between the strands at the edge of the lattice scaffold in the second direction is much less than the separation between the strands in the lattice scaffold in the first direction, and the separation between the strands in the middle of the lattice scaffold in the second direction is much greater than the separation between the strands in the lattice scaffold in the first direction (Fig. 9a). Alternatively one or more strands (such as polymeric strands comprising e.g. PCL) can be mounted on a lattice support (Fig. 11) to provide a lattice scaffold. The lattice scaffold can be coated in Matrigel™ prior to cell seeding to facilitate cell coverage along the linear fiber struts. A method is provided to guide the regional identity of an array of elongated organoids on a polymeric lattice scaffold, further comprising providing a lattice scaffold which is decorated in a binding agent and/ or an active substance (e.g. growth factors and/or morphogens such as SHH and FGF) in a specific spatial pattern. This can include providing a surface-modified polymeric lattice scaffold with heparin, and growth factors which bind heparin, incorporated in the surface of the scaffold. Surface modified scaffolds are prepared by layer-by-layer (LbL) deposition, based on the alternating adsorption via attractive electrostatic interaction of chitosan and heparin (Fig. 9). The scaffolds are prepared by dipping in heparin and chitosan after fabrication. Molecules with heparin-binding domains such as growth factors, for example sonic hedgehog (SHH) and/or fibroblast growth factor (FGF) can be incorporated into the heparin layers, for controlled release during organoid culture (Fig 10). Controlled release of growth factors during organoid growth specifies regional brain identity (Fig. 10).

Lattice Scaffold

A lattice scaffold can be formed from strands comprising polymeric fibers for generating an array of organoids, comprising a first set of strands which are substantially parallel with a first separation distance between adjacent strands, and a second set of strands which are substantially parallel lying in substantially the same plane, with a second separation distance between adjacent strands, and with the strand direction of the second set of strands orientated at a first angle to the strand direction of the first set of strands (Fig. 1). The polymer can be caprolactone (also described herein as poly(e- caprolactone or polycaprolactone (PCL)). The first separation distance and the second separation distance can be from 250 pm to 4000 pm. In some embodiments the lattice scaffold can be one or more strands, such as an array of parallel strands, held in position by a lattice scaffold mount (lattice support) (Fig. 11). The lattice scaffold can comprise a first set of strands which are substantially parallel with a first separation distance between adjacent strands, mounted on a lattice support.

The lattice scaffold can be printed using melt electrospinning writing (MEW) fabrication to print polymeric fibers. The polymeric fibers can be formed from a biocompatible and biodegradable polymer such as poly(e-caprolactone), also referred to herein as polycaprolactone and PCL. The polymer used to form the polymeric fibers may be provided at a molecular weight (MW) from 45 kDa to 80 kDa, or from 70 kDa to 80 kDa, e.g. such as polycaprolactone which is available from Sigma-Aldrich, for example with Mn 80,000. Polycaprolactone used to form the polymeric fibers may be used at a molecular weight of about 75 kDa. Apart from scaffolds composed of pure PCL, the fibers can also be prepared from: 1) PCL that has been physically blended with particle-based additives such as glass, e.g. bioglass, where the polymer used to form the polymeric fibers is provided at a molecular weight (MW) from 45 kDa to 80 kDa. Bioglass as used herein refers to any bioactive glass, e.g. Bioglass® which is Bioglass 45S5 or calcium sodium phosphosilicate, a bioactive glass specifically composed of 45 wt% SiO2, 24.5 wt% CaO, 24.5 wt% Na2O, and 6.0 wt% P2O5. Typically the blend comprises 5-50% of bioglass particles by weight. 2) PCL that has been chemically modified to give PCL conjugates such as hyaluronic acid binding peptide (HA-Bind peptide)-PCL (e.g. 5% HA-Bind peptide-PCL); cyclized Arg-Gly-Asp-Ser(RGDS) (cRGDS-PCL) (e.g. 5% cRGDS-PCL); ethyl a-bromoisobutyrate (EBIB)-PCL (E.g. 17% EBIB-PCL); oligo 3,4-ethylenedioxythiophene (EDOT)-PCL), 3) Other polymers that can be used independently without PCL, including Polyhydroxyalkanoate (PHA), poly(glycolic acid) (PGA), poly(lactic acid) (PLA), poly(lactide-co-glycolide), polyethylene glycol (PEG), polyethylene oxide (PEO) hydrogels, Polyvinyl alcohol and Polyuerethane containing materials or 4) natural polymers that can be used independently without PCL including: Proteins (Collagen, Silk fibroin, Gelatin, Fibrinogen, Elastin, Keratin), and Polysaccharides (Hyaluronic acid, Chrondoitin Sulfate, Chitosan, Alginates, Cellulose). The molecular weight (MW) referenced herein may be a weight average molecular weight (Mw) or a number average molecular weight (Mn). Preferably the molecular weight is a number average molecular weight (Mn). Molecular weights may be determined, for example, by size exclusion chromatography.

The lattice can be a square lattice, a rectangular lattice, a triangular lattice, a diamond lattice (which may also be called a rhombus lattice) or a hexagonal lattice (e.g. See Fig. 2, Fig. 4). The lattice provides intersection points, or nodes, where the strands intersect and therefore the cells aggregate. The distance between the nodes must be greater than the maximum diameter of the organoid to avoid confluence, thus the separation between the nodes must be longer to grow organoids for a longer time.

The lattice scaffold can be printed by laying down a first set of fibers in parallel lines with a first separation distance and a second set of fibers in parallel lines with a second separation distance, where there is a first angle between the direction of the first set of fibers and the direction of the second set of fibers (Fig. 1a). A strand is built up by layering more than one set of fibers (Fig. 1c). The separation distance between the fibers is approximately the same as the separation distance between the strands. The first separation distance and/or the second separation distance can be from 250 pm to 4000 pm. The separation distance and/or the second separation distance can be from 500 pm to 1000 pm. The first separation distance and the second separation distance can be the same, preferably wherein the angle is about 90°. The separation distance is preferably about 500 pm.

The diameter of a polymeric fiber can be from 2 pm to 100 pm, preferably from 2 pm to 20 pm, or from 3 pm to 10 pm, most preferably about 5 pm. A strand can be composed of from 1 to 50 layers of polymeric fibers, 2 to 20 layers, 5 to 15 layers of polymeric fibers, or preferably about 10 layers. The strands in the lattice scaffold can range in diameter from 2 pm to 200 pm, 2 pm to 100 pm, preferably 10 pm to 100 pm. The strand diameter can range from 30 pm to 70 pm. The strand diameter is preferably about 50 pm. A strand can comprise from 1 layer to 50 layers, from 2 to 20 layers, or from 5 layers to 15 layers of fibers, preferably from 8 layers to 12 layers. A strand can comprise about 2 layers, about 5 layers. A strand can comprise about 10 layers (Fig. 1).

The strands and/or the lattice scaffold can be coated, for example with a binding agent. Suitable reagents for coating the strands include binding agents, hydrogels (such as Matrigel™), fibronectin, heparin and collagen. The coating may be or may include a hydrogel, for example an extracellular matrix (ECM) based hydrogel (e.g Matrigel™). The hydrogel may be a PEG-based hydrogel. Suitable hydrogels include basement membrane extracts and preparations. Possible coatings may include fibronectin and collagen. The coating may include a morphogen. The morphogen may be applied to the strand in predetermined locations. That is, the strand may be patterned with a morphogen. The strands and/or lattice scaffold coating may include a growth factor, e.g. sonic hedgehog (SHH) or fibroblast growth factor (FGF). The growth factor and/or morphogen may be attached to a binding partner, such as a heparin binding domain, which can interact with a binding agent. The binding agent may be heparin.

The lattice can be a regular lattice made up from parallelograms. Where the separation between the nodes (intersections between opposing strands) is the same across the lattice, and the angle between the strands is 90°, the lattice is made up from repeating squares (a square lattice) (Fig. 1d).

A third set of fibers in parallel lines can be laid down. Where the third set of fibers intersects with the first and second set of fibers where the first and second set of fibers intersect, a network of triangles can be formed (Fig. 2, Fig. 4c). The lattice scaffold can further comprise a third set of strands lying in substantially the same plane which are substantially parallel with a third separation distance between adjacent strands, and with the strand direction of the third set of strands orientated at a second angle to the strand direction of the first set of strands. The separation distance between the third strands can be from 150 pm to 4000 pm. The separation distance between the third strands can be from 250 pm to 1500 pm. The second angle can be about 45°. The third set of strands may intersect the first set of strands at the same locations where the second set of strands intersects the first set of strands.

The separation distance between the fibers in the second set of fibers can be the same between each pair of adjacent strands (e.g. Fig. 1). The separation distance between the fibers in the second set of fibers can vary so that the distance between adjacent fibers is short at the beginning and the end of the set of fibers, and is much greater in the middle so that the separation between the strands at the edge of the lattice scaffold in the second direction is much less than the separation between the strands in the lattice scaffold in the first direction, and the separation between the strands in the middle of the lattice scaffold in the second direction is much greater than the separation between the strands in the lattice scaffold in the first direction (e.g. Fig. 9a, e). The strands in the lattice scaffold in the first direction thus provide a fixed structure of single linear fiber struts to grow stem cells in an elongated arrangement around the fibers. The separation distance can be about 300 pm, 400 pm, 500 pm, 600 pm, 700 pm, 800 pm, 900 pm, 1000 pm, 1500 pm, 2000 pm, 3000 pm or 4000 pm. The separation distance can be from 250 pm to 4000 pm, preferably from 500 pm to 1000 pm. A separation distance of 500pm is typically used for 20 day culture of brain organoids. A separation distance of about 1000 pm may be used for longer culture times, e.g. up to 70 days. This allows the organoids to grow to a larger size without interfering with each other on the lattice scaffold. The separation distance between the nodes depends on the separation distance between the strands. The separation distances between the nodes are equal to the separation distances between the strands in a square lattice and a rectangular lattice. The separation distance between the nodes can be about 300 pm, 400 pm, 500 pm, 600 pm, 700 pm, 800 pm, 900 pm, 1000 pm, 1500 pm, 2000 pm, 3000 pm or 4000 pm. The separation distance can be from 250 pm to 4000 pm, preferably from 500 pm to 1000 pm.

The features of the lattice scaffold described above apply to all the embodiments of the constructs and methods described herein.

Stem cells suitable for use in constructs and the methods of the invention include pluripotent stem cells, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (IPSCs). The stem cells may be multipotent or unipotent stem cells. The stem cells can be differentiated or undifferentiated. The stem cells may be human cells or non-human cells (e.g. mouse). Preferably the stem cells are human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hIPSCs).

Organoid systems that could be adapted to high throughput systems (growth on a lattice scaffold in an array) using this technology include cerebral, cardiac, lung, stomach, intestinal, prostate, optic cup, kidney, liver, blood vessel, pancreas, endometrium, and cancerous tumours (termed canceroids or tumeroids). The organoids that can be generated include one or more organoids selected from the following: brain organoid, cardiac organoid, lung organoid, stomach organoid, intestinal organoid, prostate organoid, optic cup organoid, kidney organoid, blood vessel organoid, pancreatic organoid, endometrial organoid, canceroid or tumeroid. The cells can be cultured using buffers and protocols known in the art (e.g. Lancaster et al. Nature Protocols 9, 2239-2340).

Scaffold matrix for organoid culture

The invention provides a method for generating high-throughput organoid growth in a single well plate. This is more efficient than a conventional cerebral organoid protocol where organoids are individually generated e.g. in 96-well plates and manually pipetted out for embedding or transferred to a new well plate which is time consuming, labour intensive, and introduces opportunity for error or contamination. The lattice scaffold fixes the position of each organoid, thereby creating an organised grid of organoids. In contrast, using conventional methods organoids are freely floating with the result that they are difficult to handle and manipulate. Maintaining organoids in a fixed position allows for greater ease of handling and control during a multitude of experiments, such as time lapse experiments, and stimulation or sensing experiments.

The invention provides a method to place the scaffold at any preferred distance from the bottom surface of the well. The lattice scaffold can be mounted on a support which fits within the culturing vessel, for example a cell within a multi-cell plate. The support holds the scaffold at an adjustable height above the bottom surface of the culturing vessel. The CellCrown™ device commercially available from Scaffdex can be used for this purpose. The mount and scaffold can easily be moved using forceps. This allows the scaffold to be raised as the organoids grow, preventing them from settling on the surface (Fig. 1). The lattice scaffold can be located at a first height substantially on the bottom surface of the culturing vessel when the seeding takes place. The lattice scaffold can be raised off the surface during the culturing step to a second height. The support is typically raised after the stem cells have aggregated around the nodes in the lattice scaffold and before the stem cells have become attached to the surface. The lattice scaffold may be raised to the second height at a time from at least 12 hours, such as 18 hours to 60 hours, at about 24 hours or from 24 hours to 48 hours after seeding. The lattice scaffold is typically raised at 12 to 24 hours after seeding. The lattice scaffold can be raised to a height where the organoid can grow in three dimensions without becoming attached to the surface of the culturing vessel. The lattice scaffold can be raised to a height from 1 mm to 20 mm, preferably from 3 mm to 8 mm, more preferably about 5 mm above the bottom surface of the culturing vessel.

Scaffold matrix allows control of lumen formation

The geometry of the scaffold guides where the lumen forms, and how big the lumen is. For example, on a triangle scaffold, larger lumens form at the smaller angles (due to increased surface curvature, and increased cell proliferation). The size of the angles influences the size of the lumen (Fig. 4). Scaffolds can be designed to control where lumens develop and/or how lumens develop. As lumens play a major role in early organogenesis for many organ systems, this is a powerful tool for engineering in vitro organ or organoid systems.

Scaffold matrix for cardiac tissue engineering

The scaffold technology can also be used to aggregate stem cells for the generation of 3D cardiac tissues, with applications for therapeutic delivery or disease modelling (Fig. 8). The method for generating 3D cardiac tissue (which is also referred to as array of cardiac organoids herein) in a culturing vessel comprises providing a lattice scaffold formed from strands comprising polymeric fibers, such as PCL, coating the lattice scaffold with Matrigel™; seeding stem cells on the lattice scaffold, culturing the stem cells, and thereby generating an array of cardiac organoids. Organoids (cardiac nodes) form at the lattice intersection (lattice node). The organoids can be linked (interconnected). The stem cells can be pluripotent stem cells, preferably human induced pluripotent stem cells (hiPSC).

A method is provided to generate cardiac organoids. The cardiac organoids may be linked to form 3D cardiac tissue. Thus a method is provided to generate 3D cardiac tissue. The 3D cardiac tissue has cardiac nodes that have a fixed position on a fibrous grid scaffold. The cardiac nodes are substantially coincident with the lattice nodes (Fig. 8). A method is provided to generate 3D cardiac tissue with multiple interconnected nodes. The 3D cardiac tissue can have functional network activity. The lattice scaffold facilitates controlled signal propagation between cardiac nodes (Fig. 8c, d), and can therefore be used as a platform to study key electrophysiological properties, network dynamics, and drug response. 3D cardiac tissue can be generated with functional activity across the entire lattice scaffold. Thus a method for controlled delivery of functional cardiomyocytes to large areas of injured myocardium is provided. The invention provides a facile method to move the entire lattice scaffold providing easy handling for further experiments or applications, which gives a huge amount of flexibility for the range of experiments and applications that may be undertaken such as time lapse experiments, stimulation or application as a cardiac patch. For example, moving the scaffold at critical time points to new well plates, or using the scaffold as a cardiac patch.

Scaffold guided elongated organoids

The present invention provides a method to generate high aspect ratio elongated organoids on a lattice scaffold (Fig. 9). The lattice scaffold provides axes to orient the developing organoids so that the resulting elongated structures more closely mimic the anatomy of the developing human brain. The PCL scaffold structure fabricated using direct-writing melt electrospinning provides a fixed structure of linear strands (‘Elongated organoid scaffolds’) to grow stem cells in an elongated arrangement around the strands. Elongated organoid scaffolds can be coated, e.g. with Matrigel™, prior to cell seeding to facilitate cell coverage along the strands (Fig. 9a). Stem cells are seeded onto the lattice scaffold and the cells cultured, in conditions where the culturing induces differentiation, resulting in elongated organoid structures which form around the single strands. The elongated organoid structures can form an array, with corresponding advantages to the organoid arrays where the organoids form on lattice nodes.

The invention uses a scaffold of linear strands to guide elongated organoid growth (Fig. 9). For embodiments with more than one strand, the strands oriented in a first direction are substantially parallel. The elongated organoids are high-aspect-ratio elongated organoids. Aspect ratio of the organoid is defined as the length of the organoid along the strand, divided by the width of the organoid. The aspect ratio of an elongated organoid is greater than 2:1 , typically at least 4:1 . Stem cells aggregate along the length of each strand forming a continuous elongated brain organoid structure. The elongated organoid is tethered to the fixed scaffold structure. This allows the organoid position to be manipulated with a high level of control by manipulating the lattice scaffold. A minimal lattice scaffold comprises a single strand mounted on a lattice support, so that it is tethered in a fixed position in relation to the lattice support.

Surface modified scaffolds guide the formation of different brain regions

Surface modified scaffolds can be prepared by layer-by-layer (LbL) deposition, for example, based on the alternating adsorption via attractive electrostatic interaction of chitosan and heparin (Fig. 9). The LbL deposition method is highly adaptable to a many different growth factors and cytokines through heparin-binding or attractive electrostatic interactions. The LbL deposition method enables temporal control of growth factor release. The invention is highly adaptable to different growth factors and cytokines. The ability to incorporate bioactive molecules in separate sets of layers enables time- controlled and position-dependent growth factor release, as well as the potential for sequential release of different growth factors. After fabrication the scaffolds are dip-coated in chitosan and heparin. The fiber is coated first with chitosan, followed by heparin. Multiple layers of heparin can be built up through electrostatic interactions with chitosan, growth factors, such as sonic hedgehog (SHH) and fibroblast growth factor (FGF), which bind heparin e.g. via heparin-binding domains, are incorporated into the heparin layers, for controlled release during organoid culture (Fig. 9 and Fig. 10). Controlled release of growth factors during organoid growth specifies regional brain identity. The invention offers a route to deliver morphogens directly to the organoid core with spatiotemporal control, for the guided differentiation of brain organoids. This enables organoid generation with the predictive, programmed development of multi-regional cerebral organoids, by the controlled release of morphogens from the scaffold to the organoid.

Microfluidics system for providing a culture chamber with a concentration gradient along the scaffold/ strands.

A microfluidics system is provided (Fig. 11). A microfluidics chip is provided comprising a region with microchannels for diffusion-based mixing (7) and a culturing region comprising a culture chamber (6). The microchannels have two entry points (9) which are ports. The fluidic channels have more than 2 outlets into the culture chamber (23). The fluidic channel outlet into the culture chamber has a greater cross-sectional area that the fluidic channel. The ratio between the cross sectional area of a fluidic channel to the cross-sectional area of the outlet is preferably greater than 1 :10. The ratio between the height of a fluidic channel at the outlet to the height of the growth chamber wall on which the outlet is located (‘height ratio’) is preferably between 1 :3 and 1 :5. A height ratio of 1 :4 works well for reducing turbulence. The total combined width of outlets when they enter the culture chamber is preferably greater than half of the width of the culture chamber at the point where they enter the culture chamber. The inventors have found that by increasing the size of the outlet into the culture chamber turbulence is reduced and there is less mixing between the adjacent channels. The concentration gradient across the culture chamber is therefore better preserved. A metered amount of liquid can be injected e.g. with a syringe. The same liquid can be injected in each port (Fig. 12) or a different liquid, e.g. a culture medium with varying concentrations of (or with and without) a component such as a morphogen can be injected in to each port (Fig. 13). The culture chamber preferably has a wide outlet region that spans the whole width of the culture chamber. The inventors have found that having a wide outlet region that tapers away from the chamber improves the passage of bubbles, e.g. that form on the scaffold support.

A process for printing and preparing a mold to make the chip is described. The microfluidics mold is printed using DLP 3D printing. The mold (i.e. printed part) is washed in an appropriate organic solvent such as 100% isopropanol or ethanol, e.g. for 10 minutes, with sonication. The mold is cured under UV, and optionally also heat (such as 60°C, for at least 2 hour). The mold is soaked in an organic solvent such as 100% isopropanol, e.g. for 30 -60 minutes. The mold is treated with oxygen plasma (e.g. 100 W at 1 mBar O2, for 5 minutes). The mold is coated with silane e.g. by treatment with vapour Trichloro-(1 H,1 H,2H,2H-perfluorooctyl)silane (PFOS, neat) under desiccator vacuum, e.g. for 4 hours. The mold is incubated above 25°C, e.g. at 60°C, for at least 5 hours. The chip is cast is a composition comprising polydimethylsiloxane (PDMS) silicone. The composition can comprise from 10% to 30% (w/v) crosslinker. Preferably the composition comprises 15% to 25% (w/v) crosslinker. More preferably the composition comprises about 20% (w/v) crosslinker. PDMS chips (comprising 6 and 7) can be plasma bonded onto a glass microscope slide (8) to enclose the channels by oxygen plasma treating both the glass and PDMS. The PDMS and glass interface may be further sealed using additional PDMS.

The culture chamber can house a lattice scaffold, for example mounted on a lattice scaffold mount. The chip can provide a linear stable gradient, e.g. of growth factor, across the culture chamber. An elongated organoid can be grown on the fiber scaffold, inside the culture chamber. The elongated organoid can be exposed to the gradient such as a morphogen gradient generated by the microfluidic mixing. This can induce organoid polarisation.

A method for generating an array of patterned organoids in a culturing vessel is provided comprising providing a lattice formed from strands comprising polymeric fibers, seeding stem cells (e.g. pluripotent stem cells) on the lattice, culturing the stem cells, and thereby generating an array of organoids, wherein (i) the strands are patterned with morphogen, and/or (ii) the culturing vessel is a culture chamber on a printed microfluidic chip, and/or (iii) the culturing is performed in a culturing vessel wherein the composition of the perfusing liquid varies according to position in the culturing vessel; and/or (iv) the culturing is performed in a culturing vessel wherein it is perfused with liquid having a concentration gradient with the first liquid at the highest concentration at a first end (21), and the second liquid at the highest concentration at a second end (22). The simplest form of array is generated on a single lattice strand mounted on a fiber scaffold mount. The array may comprise two or more strands comprising polymeric fibers. The strands may be oriented so that for each strand a first end of the strand is located at the first end of the culturing vessel, and the second end of the strand is located at the second end of the culturing vessel. The method typically includes culturing the stem cells on the lattice scaffold, e.g. for 1 to 7 days, such as 5 days, to generate an elongated organoid, before the lattice scaffold is transferred to a culture chamber or a culturing vessel wherein the composition of the perfusing liquid varies according to position in the culturing vessel. The developing organoid may be transferred out of the culture chamber or culturing vessel wherein the composition of the perfusing liquid varies according to position in the culturing vessel, e.g. to a culturing vessel such as a 6 well plate after a number of days, e.g. after 2 to 14 days, typically after 5 days.

The scaffold mount can comprise a scaffold holder, and clips, and can be configured to hold one or more lattice strands in position. The scaffold holder comprises a planar strand support with a hole (window), where in use the lattice strands lie substantially along the long axis of the scaffold holder and over the hole (window), and are held in position by a clip at each end of the hole. The scaffold support is configured so that the one or more lattice strands can be held firmly in place whilst allowing 3D growth of an organoid around the circumference of each strand. The scaffold mount can be oriented within a culture chamber so that the one or more lattice strands lie under the scaffold holder, and may be in contact with the bottom of the culture chamber. The scaffold mount can be oriented within a culture chamber so that the one or more lattice strands lie above the scaffold holder and are not in contact with the bottom of the culture chamber. The scaffold holder can be 3D printed, for example using a stereolithography apparatus (SLA) printer.

EXAMPLES

Example 1. Printing a lattice scaffold

Scaffold dimensions were written in G-code for 3D printing with poly(caprolactone) (PCL) melts via direct writing melt electrospinning, an extrusion-based printing technique (Fig. 1a). Pure polycaprolactone (PCL) (MW~ 75 000) was loaded into a 3cc polypropylene syringe (Nordson #7012074) and heated to 70 °C for 30 minutes. A 23G needle (Nordson #7018302) was installed, and the syringe was inserted into the spinneret. Scaffolds were printed using a 10 kV accelerating voltage, 10 mm collector distance, axis velocity of 1500 mm/min, feeding air pressure of 1 .0 Bar, and heating temperatures between 60 and 80 °C. Printing was controlled by MACH 3 CNC software (ARTSOFT, Livermore Falls, USA), and dimensions were specified by G-code, including lattice geometry with spacings of: 500 pm, 800 pm, 1000 pm and 4000 pm, triangle geometry, and single line fibers. Each scaffold consisted of 10 stacked layers with 40 mm x 40 mm dimensions. Scaffolds were detached from the collector plate using a drop of ethanol and moved to a petri-dish. For cell culture experiments, scaffolds were sterilized by cell culture-grade UV light irradiation for 30 minutes.

Highly defined fiber lattice scaffold structures with micro-meter sized fibers were produced, with grid dimensions typically between 500 pm and 1000 pm (Fig. 1c,d). Sterilisation was carried out by a combination of ethanol and UV exposure, and scaffolds were inserted on a mount, to fix them in place (e.g. Scaffdex CellCrown™, Tampere, Finland) (Fig. 1b). Scaffolds were then inserted into the culture vessel, e.g. low attachment 6-well plates (Fig. 1a, b).

Example 2. Preparing an array of organoids on a lattice scaffold.

Starting cells are typically stem cells, such as embryonic stem cells (ESCs) or human induced pluripotent stem cells (hiPSCs). H9 human embryonic stem cells (hESCs) were obtained from WiCell and maintained in feeder-free culture conditions with verified normal karyotype. Cells were cultured on hESC qualified Matrigel™ (Corning, cat. No 354277) coated 6-well cell culture plates with mTESRI (Stemcell Technologies) media. Cells were passaged every 4 - 5 days by EDTA treatment. Cells were routinely tested for mycoplasma and confirmed negative.

The cells were seeded in a single cell suspension on the scaffold (Fig. 1a), followed by moving the plate in a north-south-east-west direction (e.g. rocking) to promote an even distribution of cells across the scaffold. Once embryoid bodies formed at the scaffold grid intersections at about 24 hours, the cell crown was gently lifted up, to prevent cell-material interactions on the plate surface, and to facilitate 3D growth of the embryoid body (Fig. 1b).

Media changes were performed by aspirating media and replacing with new media in the 6-well plate.

In detail, PCL scaffolds were sterilized by UV exposure, before being inserted into a sterile 6-well CellCrown™ holder (Scaffdex CellCrown™, Tampere, Finland) (Fig. 1b). Scaffolds were placed in low attachment 6-well plates, or plates treated with anti-adherence rinsing solution (Stemcell Technologies) and pushed to the bottom of the plate. Prior to cell seeding, scaffolds were washed in PBS and soaked in mTESRI media for approximately 10 minutes. Optionally, scaffolds were incubated at 37°C and soaked in hESC qualified Matrigel™ (Corning) for 1-3 hours, then washed 3 x in PBS prior to cell seeding. For cell seeding, hESCs were counted and 100,000 cells were resuspended in mTESRI media containing 50 pM Rho-associated protein kinase (ROCK) inhibitor (Calbiochem) and 1% Antibiotic-Antimycotic (ThermoFisher). The cells were seeded directly on the scaffold followed by steady rocking of the plate in a north-south-east-west direction to promote an even distribution of cells across the scaffold. Once cells started to visibly cluster at the grid intersections, after 24 hours, the CellCrown™ was gently lifted up approximately 5 mm, to promote 3D growth and prevent cell-material interactions on the plate surface. At day 3, media was replaced with mTESRI without ROCK inhibitor or Antibiotic-Antimyocytic. At day 5, media was replaced with neural induction media (Nl). Media was replaced every day until day 10 - 13, when signs of optical clearing on the organoid borders was clearly present. Once that condition had been met, the scaffold was embedded in Matrigel™ or the media was supplemented with 2% Matrigel™. For Matrigel™ embedding the CellCrown™ insert with scaffold was removed from the well plate and placed on a strip of parafilm. 1 - 1 .5 mL of Matrigel™ was added to the scaffold organoids, until it covered the entire scaffold surface. The Matrigel™ was left to gel in the incubator at 37°C for 30 mins, and then placed in a 6 well-plate in Nl media, with the scaffold 5 mm from the bottom of the well plate. As an alternative to Matrigel™ embedding, the media can be supplemented with Matrigel™ to bring the concentration to 2% (and subsequently maintained at 2%, e.g. by supplementing media with 2% Matrigel™ for subsequent media changes). 2 - 3 days after Matrigel™ embedding or after the first addition of 2% Matrigel™, the media was changed to Improved-A media. For 3 days, 3 pM CHIR 99021 was also added. 4 days later, improved+A media was added, as previously described, and media was changed every other day. At day 20, CellCrown™ inserts and scaffolds were transferred to a 10 cm plate for longer-term culture.

The cells used to grow the organoids shown in Fig. 1e were human embryonic stem cells. Fig. 1e and Fig. 1f show brig htfield images of brain organoids growing on scaffold compared to conventional and scaffold free methods for organoid growth. Scale bar: 500 pm. As can be seen in the image at 17 days, individual brain organoids located at the nodes (intersection points) have formed (See also Fig. 2b). Fig. 1f shows brain organoids forming an array growing on a single scaffold from one well in a six well plate. Example 3. Scaffold geometries for organoid growth

A range of scaffold geometries have been tested using hESC culture for brain organoid generation, including lattice geometries with different spacings (500 pm, 800 pm, 1000 pm, 4000 pm), triangle geometry and single line fibers (mounted within a lattice scaffold) for elongated organoid growth. Fig.

2, top figure shows organoids growing on Matrigel™ scaffolds on square grid lattice geometry (500 pm and 1000 pm spacing) and triangle grid geometry. Fig. 2, bottom figure shows organoids growing on scaffolds not treated with Matrigel™ on square grid lattice geometry with 500 pm 800 pm and 1000 pm spacing.

on a lattice scaffold

The organoids grown on an array reach the same developmental checkpoints as those grown using a conventional techniques (Fig. 3). Characterisation by immunostaining shows that the developing scaffold brain organoids show expression of neural ectoderm markers and intact adherens junctions at the apical surface at day 20, comparable to control organoids (Fig. 3a). The developing scaffold brain organoids show regional co-expression of dorsal forebrain markers (Fig. 3b) and interspersed expression of deep layer subcortical dorsal markers and a ventral forebrain marker, comparable to control organoids (Fig. 3c). The adapted cell culture method typically generates smaller organoids then equivalent individual organoid culture methods. For example, at day 20: brain organoids grown in an array on a lattice scaffold have a typical diameter of 500 pm compared to a typical diameter of 2000 pm for individually cultivated organoids. In addition, organoids grown in an array on a lattice scaffold show less evidence of internal tissue necrosis due to improved oxygen diffusion across the organoid (Fig. 3). Necrosis in the organoid core is a limitation observed during conventional culture of cerebral organoids.

rown on Matrigel™ coated scaffolds

Fig. 4 shows scaffolds with different geometry and organoids growing on Matrigel™ coated scaffolds with those geometries. Fig. 4 shows that by varying the scaffold geometry, the emergence of the lumen can be controlled reproducibly. Lumens are a very common emergent organization during organogenesis of multiple different organ systems in vivo, such as the brain, heart, liver, kidney, lung and blood vessels. This technology allows highly specific control of lumen formation and morphology. hPSC tissue growth on triangular scaffolds was further characterized. Fig. 4d shows a single slice of a scaffold coated with Matrigel™, inoculated with hESCs, at 5 days. The images are immunostained with SOX2 (grey) and ZO1 (light grey). The right hand side shows a 3D reconstruction from a confocal z stack, with the lumens segmented and pseudo coloured in light grey (middle) cross section of the confocal z stack showing a bisector slice through the lumens indicated by the white lines (right), scale bars correspond to 100 pm. Measurements were made of the maximum cross sectional lumen area and lumen volume within the smaller angles and the larger angles, as well as the lumen circularity and the total cell count in the scaffold angles.

Fig. 5 shows that hESCs grow on scaffolds in a highly reproducible way and show stem cell identity, a) Brig htfield image timeline of hESCs growing on Matrigel™ coated PCL scaffolds, highlighting the emergence of the lumen; b) overview image of a scaffold in a 6 well plate and zoomed in images at day 2 and day 5; c) Immunohistochemistry (IHC) staining demonstrates the early emergence of the lumen at day 2, and large luminal cavities around the scaffold at day 5; d) F-actin IHC stain, left: z projection of entire tissue around scaffold and right: cross-section of tissue in the xy planes; e) IHC staining shows stem cell identity at day 5. Fig. 6 shows emergence of lumen via time lapse fluorescence imaging of cells stained with SiR actin. Images were taken daily from day 1 to day 5. For each time slot the upper panel shows a fluorescence image of the scaffold, with the actin visualised using SiR-actin, a probe specific for F-actin, and the lower panel shows the corresponding brightfield image. Fig. 7 shows characterisation of organoids grown in Matrigel™ coated scaffolds.

Example 6. Scaffold matrix for cardiac tissue engineering

The present invention provides a method of generating 3D cardiac tissue or ‘nodes’ in a reproducible manner on a controlled 3D matrix using a fibrous poly(e-caprolactone) (PCL) scaffold, comprising of the following steps (Fig. 8): Lattice scaffolds were prepared as described above and mounted on a support. Scaffolds were soaked in Matrigel™ and left at 37°C for a minimum of 1 hour. After soaking, scaffolds were transferred to low attachment 6-well plates.

The hiPSC cells were seeded in a single cell suspension on the scaffold, followed by steady rocking of the plate in a north-south-east-west direction to promote an even distribution of cells across the scaffold. Once cells attached to the lattice scaffold, after 12 - 48 hours, typically about 24 hours, the cell crown was gently lifted up, to prevent cell-material interactions on the plate surface, and to facilitate 3D growth of the embryoid body. Media changes were performed by aspirating media and replacing with new media in the 6 well plate. The scaffold structure enables highly reproducible patterns of interconnected growing cardiac tissue (Fig. 8b). Immunostaining revealed cardiomyocyte identity of cells on scaffold: Characterisation by immunostaining shows that the developing scaffold cardiac nodes show expression of cardiomyocyte markers (Fig. 8c). Widefield microscopy time-lapse videos have demonstrated spontaneous beating of cardiac nodes on scaffold. Synchronized network activity and signal propagation has been demonstrated via calcium imaging. For example, calcium recordings have demonstrated synchronised Ca²⁺ signal propagation in neighbouring cardiac tissue nodes (Fig. 8c, d).

Example 1. Generating an array of elongated organoids. Scaffolds dimensions were written in g-code for 3D printing with poly(caprolactone) (PCL) melts via direct writing melt electrospinning, an extrusion-based printing technique as described in Example 1. The PCL scaffold structure was fabricated using direct-writing melt electrospinning. The scaffold was coated with Matrigel™ prior to cell seeding as described previously e.g. in Example 1 . The ‘elongated organoid lattice scaffold’ provides a fixed structure of strands to grow pluripotent stem cells in an elongated arrangement around the strands (Fig. 9). Fig. 9b shows SEM images of Matrigel™ coated and uncoated scaffolds. Fig. 9c and d show brightfield images of elongated organoids growing on Matrigel™ coated scaffolds. Fig. 9e shows an array of elongated organoids growing on a scaffold at Day 20 and Day 40. Fig. 10a shows immunostaining for FOXG1 , MAP2 and DAPI on elongated organoids grown in the absence of morphogens such as SHH.

Example 8. Surface modified scaffolds guide the formation of different brain regions

Surface modified scaffolds have been used to guide the formation of different brain regions. Immunostaining data provide evidence that growth factor release from PCL fibers specifies organoid identity. Bioactive scaffolds were prepared by layer-by-layer (LbL) deposition, based on the alternating adsorption via attractive electrostatic interaction of chitosan and heparin (Fig. 9a). Growth factor sonic hedgehog (SHH), with a heparin-binding domains, was incorporated into the heparin layer (Fig. 9a). SHH functionalised scaffold and non-functionalised scaffold as a control was immunostained to visualise the SHH (Fig. 10b). SHH was released from PCL scaffolds over 7 days (Fig. 10c and d). Fig. 10e shows immunostaining on SHH functionalised PCL scaffold, and non-functionalised scaffold. Scale bar: 500 pm. Immunostaining for FOXA2 (red) PAX6 (green) and DAPI (blue) on elongated organoids on SHH bioactive scaffolds. Scale bar: 200 pm. FOXA2 marker is present in the +SHH sample. SHH is the morphogen used to pattern the organoids. FOXA2 is a floor plate marker, and is a target of SHH. This shows that by presenting SHH on the surface of the scaffold, FOXA2 expression is upregulated, indicating that there is floor plate identity in the organoids. -SHH sample is the negative control sample, and shows that without the morphogen, FOXA2 is not expressed in the organoid.

Example 9. A 3D printed microfluidics chip

CAD design of microfluidics chip mold was created printing. The resulting mold was post-processed according to the protocol below before casting with polydimethylsiloxane (PDMS) silicone to form the final microfluidics chip (Fig. 11 , (2)).

Main protocol steps:

(i) After printing is complete, the printed part ((6) and (7)) was washed in 100% isopropanol for 10 min via sonication.

(ii) The part was then post-cured under UV light and heat (60°C) for at least 2 hr.

(iii) The part was then soaked in 100% isopropanol for 1 hr.

(iv) The part was treated using oxygen plasma (100 W at 1 mBar O2 for 5 min). (v) The part was chemically coated with a silane by vapour deposition of trichloro(1 H,1 H,2H,2H- perfluorooctyl)silane for 4 hours under desiccator vacuum.

(vi) The part was incubated at 60°C for at least 5 hours before being used to cast PDMS.

This protocol has been successfully applied to molds made across different 3D printers from two different companies (Form 2, Formlabs and SL1S Speed, Prusa), and across four different 3D printing resins (proprietary formulations from the respective companies) including Clear V4 (Formlabs), Grey (Formlabs), Orange Tough (Prusa), and Orange Vibrant (Formlabs).

Microfluidic chip design features

Tapered edges in the culture chamber (22) facilitate fine tuning of height-position of the cell-crown without affect the fluidic flow path and avoid organoids resting on the bottom of the culture chamber. A major design challenge here was maintaining flow stability as the fluid transitioned between the microfluidic channels (200 pm) to the relatively larger culture chamber (20 mm). To address this, the opening of the fluidic channel outlet (21) was flared out to reduce fluidic turbulence that would otherwise affect preservation of gradients formed in the growth chamber (Fig. 11g). The channel width is flared from 200 pm to 1 .6 mm, and height is flared from 200 pm to 1 mm.

A second design challenge was that the presence of the custom cell crown resulted in regions within the growth chamber that were prone to trapping bubbles. The outlet region (23) has been designed so as to reduce risk of trapped bubbles.

20% (w/v) crosslinker was used for the PDMS casting, as opposed to the 10% (w/v) crosslinker that is typically used and recommended by the supplier. This increased stiffness of the overall chip, and decreased compliance within the channels (which may block the outlet channel or lead to bubble formation).

Microfluidics chip preparation and assembly

Once they have been cast, PDMS chips (comprising 6 and 7) are plasma bonded onto a glass microscope slide (8) to enclose the channels. This was done by oxygen plasma treating both the glass and PDMS (100 W at 1 mBar 02 for 1 min), followed by immediately bonding onto the glass.

The PDMS and glass interface was further sealed using additional PDMS. The PDMS microfluidic chips were autoclaved to sterilise, and to reduce hydrophobicity within the channels. This, in turn, prevents bubble formation within the channels during culture. Chips should be either kept in sterile PBS until use to keep the channel hydrophilicity or should be used directly after autoclave.

This chip (2, consisting of 6,7, and 8) is then assembled with the custom scaffold holder (1), and subsequently clamped between two glass plates (3) to fully seal the liquid-perfusable regions for long term culture. Fig. 11a provides a blown up illustration of the whole assembly (10) and its component parts.

Example 10. Microfluidics platform provides linear gradient across culture chamber A custom scaffold holder (1) (Fig. 11b) has been designed to affix one or more PCL scaffold ‘strands’. The scaffold holder was 3D printed using SLA printer, and post processing was carried out as described in Example 9, steps (i)-(iii). The scaffold holder (1) was sterilized by autoclave. PCL scaffold ‘strands’ were attached to the custom scaffold holder using forceps. Fig. 11b shows the placement of a single strand. Scaffold and holder (Shown in Fig. 11 b) were sterilized using 30-45 minutes of UV exposure. Scaffold and holder were placed in a 6 well plate, with the strand resting on the bottom of the plate. Scaffold was coated in hESC qualified Matrigel™ and left to incubate for 45 minutes.

Scaffold was washed in PBS, then placed in a low attachment 6 well plate. 1 million cells were seeded per well, and kept in mTESR stem cell media with Rock inhibitor. At day 3, scaffold holder was flipped, so that the strand was suspended in the well and not resting on the bottom of the plate, and media was changed to fresh mTESR (without rock inhibitor).

At day 5, scaffold + holders were transferred into the microfluidic chip culture chamber. 2 syringes were filled with 15 ml neural media each. Fig. 12 shows an elongated organoid grown under perfusion in neural induction medium between days 5 and 10 in a microfluidic chip, stained with apical marker aPKC, dorsal marker PAX6, forebrain marker FOXG1 and DAPI. At day 10 the scaffold and holder was transferred back to a low attachment 6 well plate. From day 12 the elongated organoid was cultured in improved -A medium with +2% Matrigel™. From Day 18 the elongated organoid was cultured in improved +A medium with +2% Matrigel™. The images were taken at day 20.

Example 11.

The method of Example 10 has been performed with different compositions in each syringe to create a gradient over the culture chamber. The sequential mixing of media from the two syringes in the microfluidic chip generates a stable gradient of morphogens (Fig. 11 e, f). To confirm the presence of a gradient in the culture chamber (6) one of the syringes was filled with fluorescein salt. Fig. 11f shows a fluorescence micrograph taken across the culture chamber (6) (L= left hand side, R= right hand side) where the gradient of light corresponds to the concentration gradient of the fluorescein.

For patterned growth, one syringe can contain patterning factors for organoid ventralisation, including SAG (smoothened agonist) and iWP2 (wnt inhibitor). Medium changing is done by replacing the syringes with 15 mL fresh medium at day 8. The scaffold holder is fixed in the microfluidic chip chamber such that the growing elongated organoid is suspended along the length of the culture chamber (Fig. 11, 13), thereby exposing the elongated organoid to the patterning factors in a linear gradient. After 5 days of microfluidic perfusion, the organoid can be taken out of the microfluidic chip and returned to a 6 well plate, where organoid culture resumes until the required timepoint.

Fig. 13 illustrates an experiment performed where the organoid was cultured under microfluidic perfusion in the presence of a gradient. The elongated organoid was prepared and cultured as described in Example 10 (method summarised in Fig. 13A). In panel a, the organoid was cultured under a gradient during the microfluidic perfusion. A gradient of 200 nM SAG + 2.5 pM iWP2 was created across the culture chamber by filling one syringe will neural induction medium, and filling one syringe with neural induction medium with 200 nM SAG + 2.5 pM iWP2. Fig. 13B shows, in panel a, an elongated organoid cultured with a gradient in this way. Fig 13B, panel a shows that being exposed to a morphogen gradient for 5 days, the organoids formed a distinct ventral domain on one side of the elongated organoid, marked by the expression of FOXA2 and NKX2.1 , indicating that the SAG gradient is translated into an SHH signalling gradient. These preliminary results indicate that using a microfluidic platform, a dorsoventral gradientcan be generated. Fig. 13B panel b is a positive control. An elongated organoid cultured with a constant concentration of 200 nM SAG + 2.5 pM iWP2 along the organoid shows ventralisation of most of the organoid. Fig. 13B panel c is a negative control. An elongated organoid cultured in the absence of 200nM SAG and 2.5 pM iWP2 shows no ventralisation.

Claims

Claims

1 . A method for generating an array of organoids comprising culturing stem cells on a scaffold wherein the scaffold is a lattice comprising polycaprolactone, thereby generating an array of organoids.

2. A method for generating an array of organoids in a culturing vessel comprising: a) providing a lattice comprising strands comprising polymeric fibers, b) seeding stem cells on the lattice, c) culturing the stem cells, thereby generating an array of organoids.

3. A method according to claim 1 or claim 2 further comprising mounting the lattice on a support configured to fit within a culturing vessel, wherein in use the height of the lattice above the bottom surface of the culturing vessel can be adjusted from a first height to a second height, preferably wherein the lattice is located at a first height substantially on the bottom surface of the culturing vessel when the seeding takes place and wherein the lattice is raised off the surface to a second height during the culturing step.

4. A method according to claim 3 wherein the lattice is raised to the second height at a time from 12 hours to 60 hours after seeding, preferably from 12 hours to 24 hours after seeding, and/or wherein the second height is from 1 mm to 20 mm, preferably from 3 mm to 8 mm, more preferably about 5 mm.

5. A method according to any previous claim wherein the culturing vessel is rocked, preferably in a north-south-east-west direction.

6. A method according to any of claim 1 to claim 5 wherein the stem cells are (a) pluripotent stem cells, such as embryonic stem cells (ESC) or induced pluripotent stem cells (IPSC), or (b) multipotent stem cells or (c) unipotent stem cells, preferably wherein the stem cells are human.

7. A construct comprising a lattice formed from strands comprising polymeric fibers and organoids wherein the organoids are located at the intersections between the strands of the lattice, or wherein the organoids are elongated and each organoid forms on an individual strand, optionally wherein the strand is coated.

8. A method according any one of claims 1 to 6 or a construct according to claim 7 wherein the lattice comprises a first set of strands which are substantially parallel with a first separation distance between adjacent strands, and a second set of strands which are substantially parallel lying in substantially the same plane, with a second separation distance between adjacent strands, and with the strand direction of the second set of strands orientated at a first angle to the strand direction of the first set of strands, or wherein the lattice comprises a first set of strands which are substantially parallel with a first separation distance between adjacent strands, mounted on a lattice support.

9. A method or a construct according to claim 8 wherein:

(i) the first separation distance and/or the second separation distance are from 250 pm to 4000 pm,

(ii) the first separation distance and/or the second separation distance are from 500 pm to 1000 pm, preferably wherein the separation distance is about 500 pm

(iii) wherein the first separation distance and the second separation distance are the same, preferably wherein the angle is about 90°.

10. A method or a construct according to any one of claim 7 to claim 9 wherein the lattice further comprises a third set of strands lying in substantially the same plane which are substantially parallel with a third separation distance between adjacent strands, and with the strand direction of the third set of strands orientated at a second angle to the strand direction of the first set of strands, optionally wherein the separation distance is from 250 pm to 1500 pm and/or wherein the second angle is about 45° and/or wherein the third set of strands intersects the first set of strands at the same locations where the second set of strands intersects the first set of strands.

11. A method or a construct according to any one of claim 7 to claim 9 wherein the separation between the strands at the edge of the lattice in the second direction is much less than the separation between the strands in the lattice in the first direction, and the separation between the strands in the middle of the lattice in the second direction is much greater than the separation between the strands in the lattice in the first direction, or wherein the lattice comprises a first set of strands which are substantially parallel with a first separation distance between adjacent strands, mounted on a lattice support.

12. A method according to any of claim 1 to claim 6 and claim 8 to claim 11 or a construct according to any one of claim 8 to claim 11 wherein the polymeric fibers comprise polycaprolactone, preferably wherein the polymeric fibers are polycaprolactone.

13. A method according to any of claim 1 to claim 6 and claim 8 to claim 12 or a construct according to any one of claim 7 to claim 12 wherein the polymeric fibers comprise one or more of: i) 45kDa - 80kDa polycaprolactone blends, or ii) bioglass particles, or iii) PCL conjugates comprising one or more of hyaluronic acid binding peptide, cyclized Arg-Gly-Asp- Ser(cRGDS), ethyl a-bromoisobutyrate, and 3,4-ethylenedioxythiophene (EDOT), or iv) polyhydroxyalkanoate (PHA).

14. A method according to any of claim 1 to claim 6 and claim 8 to claim 13 or a construct according to any one of claim 7 to claim 13 wherein the diameter of the polymeric fibers is from 2 pm to 100 pm, preferably wherein the diameter is from 5 pm to 20 pm.

15. A method according to any of claim 1 to claim 6 and claim 8 to claim 14 or a construct according to any one of claim 8 to claim 14 wherein a strand is composed of from 5 to 20 layers of polymeric fibers, preferably about 10 layers, and/or wherein the strand diameter is from 10 pm to 100 pm, preferably about 50 pm.

16. A method according to any of claim 1 to claim 6 and claim 8 to claim 15 or a construct according to any one of claim 8 to claim 15 wherein the lattice is coated, optionally wherein the lattice is coated with a hydrogel, preferably a gel comprising basement membrane extracts such as Matrigel™.

17. A method according to any of claim 1 to claim 6 and claim 8 to claim 16 or a construct according to any one of claim 8 to claim 16 wherein the lattice surface is patterned with a binding agent, optionally wherein the binding agent is heparin.

18. A method or a construct according to claim 17 wherein a binding partner is binding to the binding agent, optionally wherein the binding partner is attached to a growth factor or morphogen, optionally wherein the growth factor is sonic hedgehog (SHH) or fibroblast growth factor (FGF).

19. A method according to any of claim 1 to claim 6 and claim 8 to claim 18 wherein the organoid is a brain organoid, optionally wherein the stem cells are pluripotent stem cells, preferably wherein the stem cells are human embryonic stem cells (hESC), or a construct according to any one of claim 7 to claim 17 wherein the organoid is a brain organoid.

20. A method according to any of claim 1 to claim 6 and claim 8 to claim 18 wherein the array of organoids is 3D cardiac tissue, optionally wherein the stem cells are pluripotent stem cells, preferably wherein the pluripotent cells are human induced pluripotent cells (hIPSC), or a construct according to any one of claim 7 to claim 17 wherein the array of organoids is 3D cardiac tissue.

21. A method or a construct according to claim 11 wherein the organoid is an elongated organoid, optionally wherein the lattice surface is patterned with a growth factor and the organoid is a patterned organoid, further optionally wherein the organoid is a brain organoid and/or wherein the lattice is coated.

22. A lattice scaffold formed from strands comprising polymeric fibers for generating an array of organoids, comprising a first set of strands which are substantially parallel with a first separation distance between adjacent strands, and a second set of strands which are substantially parallel lying in substantially the same plane, with a second separation distance between adjacent strands, and with the strand direction of the second set of strands orientated at a first angle to the strand direction of the first set of strands, preferably wherein the polymer is polycaprolactone, optionally: wherein the first separation distance and the second separation distance are from 250 pm to 4000 pm; and/or wherein the diameter of the polymeric fibers is from 2 pm to 100 pm; and/or wherein a strand is composed of from 1 to 50 layers of polymeric fibers, preferably 5 to 20 layers of polymeric fibers, most preferably about 10 layers; and/or wherein the strand diameter is from 2 pm to 100 pm, preferably wherein the strand diameter is from 10 pm to 100 pm.

23. A microfluidic chip (2) for providing a culture chamber for perfusion of a lattice mounted on a support (1), wherein the microfluidic chip comprises: a culture chamber (6), a portion with microchannels for diffusion-based mixing (7), first and second entry ports for a first and a second liquid (9); configured so that in use the culture chamber is perfused with liquid having a concentration gradient with the first liquid at the highest concentration at a first end (21), and the second liquid at the highest concentration at a second end (22).

24. A printed lattice support (1) comprising a scaffold holder (11), and scaffold clips (12).

25. A method for generating an array of patterned organoids in a culturing vessel comprising: a) providing a lattice formed from strands comprising polymeric fibers, b) seeding stem cells on the lattice, c) culturing the stem cells, thereby generating an array of organoids, wherein

(i) the strands are patterned with morphogen, and/or

(ii) the culturing vessel is a culture chamber on a printed microfluidic chip, and/or

(iii) the culturing is performed in a culturing vessel wherein the composition of the perfusing liquid varies according to position in the culturing vessel; and/or

(iv) the culturing is performed in a culturing vessel wherein the culturing vessel is perfused with liquid having a concentration gradient with the first liquid at the highest concentration at a first end (21), and the second liquid at the highest concentration at a second end (22).