METHOD FOR MANUFACTURING LOW MODULUS ARTICLES

A method of manufacturing a three-dimensional (3D) article includes operating a print engine to fabricate a composite structure including the 3D article coupled to a support structure, removing the composite structure from the fluid tank, and peeling the inside surface of the sheath away from the outer surface of the article, peeling progressively breaks the plurality of strands. The support structure includes a conformal sheath having an inside surface that follows the outer surface of the 3D article with a gap between the inside surface of the sheath and the outer surface of the article, and a plurality of strands that span the gap and individually have opposed ends that are coupled to the inside surface of the sheath and the outer surface of the article to maintain the gap, the gap filled with the photocurable liquid ink.

FIELD OF THE INVENTION

The present disclosure concerns an apparatus and method for fabrication of solid three dimensional (3D) articles of manufacture from radiation curable (photocurable) inks. More particularly, the present disclosure concerns a method of supporting 3D articles that have a low modulus and are fragile.

BACKGROUND

Three dimensional (3D) printers are in rapidly increasing use. One class of 3D printers includes stereolithography printers having a general principle of operation including the selective curing and hardening of radiation curable (photocurable) liquid inks. A typical stereolithography system includes a liquid tank holding the photocurable ink, a movement mechanism coupled to a support surface, and a controllable light engine. The stereolithography system forms a three dimensional (3D) article of manufacture by selectively curing layers of the photocurable ink over the support surface.

One particular challenge is in forming 3D articles from fragile, low modulus materials such as hydrogels. One possible application is the printing of artificial tissue or bodily implants. Damage can occur during fabrication, post-processing, shipping and handling of the 3D article.

SUMMARY

An aspect of the disclosure is a method of manufacturing a three-dimensional (3D) article having an outer surface using a print engine having a fluid tank, a moveable build surface coupled to a movement mechanism, and a light engine. The method includes filling the fluid tank with a photocurable liquid ink, positioning the moveable build surface within the photocurable ink proximate to a build plane, operating the movement mechanism and the light engine to fabricate a composite structure including the 3D article coupled to a support structure, removing the composite structure from the fluid tank, and removing the sheath from the 3D article by peeling the inside surface of the sheath away from the outer surface of the article; peeling progressively breaks the plurality of strands. The support structure includes a conformal sheath having an inside surface that follows the outer surface of the 3D article with a gap between the inside surface of the sheath and the outer surface of the article, and a plurality of strands that span the gap and individually have opposed ends that are coupled to the inside surface of the sheath and the outer surface of the article to maintain the gap, the gap filled with the photocurable liquid ink.

This method has an advantage for a very low modulus and delicate 3D article such an article printed from a low modulus hydrogel material. The combination of the conformal sheath and the plurality of strands effectively supports the 3D article during manufacture and removal from the liquid tank. The peeling removal of the sheath from the article is easily and quickly performed manually. The low modulus strands, as they are broken, do not damage the delicate 3D article.

In one implementation the photocurable liquid ink contains water, a photopolymer, and a catalyst. The ink can include more than 30 weight percent water or more than 40 weight percent water. The photocurable liquid ink hardens in response to exposure to ultraviolet (UV), violet, and/or blue radiation.

In another implementation the photocurable liquid ink is a hydrogel formulation including, inter alia, water, natural or synthetic polymers, and a catalyst. Natural polymers for hydrogel preparation can include, inter alia, hyaluronic acid, chitosan, heparin, alginate, and fibrin.

In yet another implementation, the formed composite structure has an elastic modulus of less than five million pascals (MPa), less than two million pascals (MPa), less than one million pascals (MPa) or within a range of 50 to 500 thousand pascals (KPa).

In a further implementation, the gap can have a thickness of less than two millimeters (mm) or less than one millimeter (mm).

In a yet further implementation, the plurality of strands can include at least 25 strand, at least 50 strands, at least 100 strands, or at least 200 strands.

In another implementation, the plurality of strands can individually include a location of weakness within the gap at which they preferentially break when peeling the inside surface of the sheath away from the outer surface of the article.

In yet another implementation, the 3D article is one of a contact lens, an artificial bodily tissue construct, and a soft implant.

In a further implementation, the sheath can be left in place during post-processing and/or during transport. Post-processing can include cleaning, curing, coating, or otherwise treating the 3D article after fabrication. The sheath can be left on and then removed after transport to a site at which it is used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Unless the context indicates otherwise, it is specifically intended that the various features described herein can be used in any combination. Moreover, the disclosure also contemplates that in some embodiments, any feature or combination of features set forth herein can be excluded or omitted. To illustrate, if the specification states that a complex comprises components A, B, and C (or A, B, and/or C), it is specifically intended that any of A, B or C, or a combination thereof, can be omitted and disclaimed singularly or in any combination.

Unless explicitly indicated otherwise, all specified embodiments, features, and terms intend to include both the recited embodiment, feature, or term and biological equivalents thereof.

All numerical designations, e.g., pH, temperature, time, concentration, and molecular weight, including ranges, are approximations that can be varied (+) or (−) by increments of 1.0 or 0.1, as appropriate, or alternatively by a variation of +/−15%, or alternatively 10%, or alternatively 5%, or alternatively 2%. It is to be understood, although not always explicitly stated, that all numerical designations are preceded by the term “about”.

Definitions

The terms “substantially” and “about” are used herein to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. When used in conjunction with a numerical value, the terms can refer to a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. When referring to a first numerical value as “substantially” or “about” the same as a second numerical value, the terms can refer to the first numerical value being within a range of variation of less than or equal to ±10% of the second numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. The terms or “acceptable,” “effective,” or “sufficient” when used to describe the selection of any components, ranges, dose forms, etc. disclosed herein intend that said component, range, dose form, etc. is suitable for the disclosed purpose.

Preferably the ink is one that produces a low modulus article. The term “low modulus” as used herein means less than five megapascals (A/Pa). Even more preferably, the modulus is less than 2 MPa. Preferred inks include a soft hydrogel ink.

FIG.1is a schematic diagram of a three-dimensional (3D) printing system2for manufacturing a 3D article4. The 3D printing system2includes a fluid tank6, a build tray (e.g., a build tray, etc.)8coupled to a movement mechanism10, a light engine12, and a controller14. In describing the 3D printing system2, mutually orthogonal axes X, Y, and Z are used. Axes X and Y are lateral axes that are generally horizontal. The Z axis is generally vertical or generally aligned with a gravitational reference. When the term “generally” is used, it indicates that a direction or magnitude may not be exact but is within manufacturing tolerances. Thus, generally aligned indicates aligned to within manufacturing tolerances.

The fluid tank6includes upper and side walls16and a transparent sheet18. In the illustrated embodiment, the transparent sheet18is semipermeable and can therefore transmit an inhibitor such as oxygen from below the fluid tank6and to within the fluid tank6. The transparent sheet is a flexible polymer sheet and is generally transparent to ultraviolet (UV), violet, or blue light. The transparent sheet18may include one or more polymers such as polyvinylidene fluoride (PVDF), ethylenchlorotrifluoroethylene (ECTFE), ethyl enetetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF) or other materials known in the art. The transparent sheet18can include amorphous thermoplastic fluoropolymer films such as TEFLON AF 1600™ (trademark of Chemours Company of Wilmington, DE) or TEFLON AF 2400™. Other materials are possible. In an illustrative embodiment, the transparent sheet18can have a thickness of about 80 microns (one thousand microns equals one millimeter) although other thicknesses are possible.

The fluid tank6contains a photocurable liquid ink (e.g., ink, etc.)20. The photocurable liquid ink20hardens in response to exposure to ultraviolet (UV), violet, and/or blue radiation. In an illustrative embodiment, the ink20contains at least a photocurable liquid and a catalyst. The catalyst allows curing of the ink in response to radiation exposure. In a further illustrative embodiment, the ink contains a combination of water and a photopolymer that is miscible in the water.

In another illustrative embodiment, the ink is a hydrogel formulation that includes inter alia, water, natural or synthetic polymers, and a catalyst. The water is typically at or above 30 percent by weight. Natural polymers for hydrogel preparation can include, inter alia, hyaluronic acid, chitosan, heparin, alginate, and fibrin. Hydrogel bio-inks are known in the art for the printing of 3D articles such as soft artificial implants, contact lenses, and artificial tissue to name some examples.

In the illustrated embodiment, the build tray8has a downward facing lower face22for supporting the 3D article4. In other embodiments, the build tray8can have an upward facing surface (embodiment not shown) for supporting a 3D article4.

The movement mechanism10is a motorized device for vertically positioning the build tray8and outputting an encoder signal that is indicative of a vertical position of the build tray8. In an illustrative embodiment, the movement mechanism10includes a vertically fixed portion and a vertically moving portion. The vertically moving portion supports the build tray and includes a threaded bearing. The vertically fixed portion includes a motor coupled to a lead screw which is received within the threaded bearing. As the motor rotates the lead screw, the action upon the threaded bearing translates the build tray up or down, depending upon the rotational direction of the lead screw. The encoder can be a linear or rotational encoder and outputs a signal by which the controller14can determine and monitor a vertical position of the build tray8and hence by inference the lower face22of the build tray8.

Alternative embodiments of movement mechanisms10are possible. One alternative embodiment is a rack and pinion system. For such a system, the build tray8is coupled to a vertical gear (rack) with a vertical arrangement of gear teeth. A motor is coupled to a round pinion gear that engages the vertical arrangement of gear teeth. Rotation of the motor in turn translates the build tray8up and down. Yet another alternative is based upon a belt and pulley system. The belt is coupled to the build tray8and a motorized gear engages and translates the belt to vertically move the build tray8. With any of these mechanisms, the motor can be indirectly linked via a reduction gear train for improving precision and force of movement. Various movement mechanism10designs are known for 3D printing.

The light engine12is configured to project or transmit pixelated radiation up through the transparent sheet18. In one embodiment, the light engine12is a fixed projector that is based upon a radiation source, a spatial light modulator, and projection optics. Such light engines are known in the art for digital projectors that transmit visible or ultraviolet radiation for selectively curing resin for stereolithography. In a second embodiment, the light engine can include scanning light bar with a linear array of light emitting diodes. In a third embodiment, the light engine can include a laser and scanning optics. The scanning optics can include galvanometer mirrors for scanning a laser beam over the transparent sheet18. All such light engines are known in the field of stereolithography.

The controller14is coupled to the movement mechanism10, the light engine12, and other portions of the 3D printing system2. The controller14includes a processor24coupled to an information storage device26. The processor24can otherwise be referred to as a CPU (central processing unit) and is the electronic circuitry that executes software instructions. The information storage device26is non-transient storage device that stores the software instructions. When executed by the processor24, the software instructions control and monitor portions of the 3D printing system2.

To fabricate the article4, the controller14performs the following steps: (A) The movement mechanism10is operated to position the lower face22of the build tray (or later the 3D article4) at a build plane28which is just above the transparent sheet18. (B) The light engine12is operated to selectively irradiate the build plane28and to selectively harden and cure a layer of the ink20upon the lower face22of the build tray or 3D article4. (C) Steps A and B are repeated to complete fabrication of the 3D article4. As a note, support structures are also fabricated that provide support of the 3D article4to the build tray8. As will be seen infra, steps A-C are but a subset of the steps for manufacturing article4, which is the subject ofFIG.2.

FIG.2is a flowchart depicting an embodiment of a method30of manufacturing the 3D article4. According to32, 3D printing system2is provided including the fluid tank6, movement mechanism10, and light engine12. According to34, the fluid tank6is filled with photocurable liquid ink20. In an illustrative embodiment, the ink20is a photocurable hydrogel composition that includes water, a natural polymer, a synthetic polymer, and a catalyst. According to36, a support tray8is loaded onto the movement mechanism10.

According to38, the controller14operates the 3D printing system to fabricate a composite structure50according to steps A-C discussed supra. The composite structure50is illustrated inFIG.3attached to the support tray8. In the illustrated embodiment, the composite structure50includes the 3D article4and a support structure52that surrounds and supports the 3D article4. Support structure52includes three types of components including a conformal sheath (e.g., sheath)54, connecting strands56, and support columns58.

The 3D article4has an outer surface60which is outward facing. The conformal sheath54generally “follows” or conforms to the outer surface60. The conformal sheath54has an inner surface62that is in facing relation with the outer surface60with a fluid filled gap64therebetween. The fluid filled gap64is filled with the photocurable liquid ink20.

A plurality of the connecting strands56couple the outer surface60to the inner surface62. The connecting strands56serve to maintain the gap64between the outer60and inner62surfaces. The connecting strands control and maintain a magnitude of the gap64measured normal to the surfaces60and62. In a first illustrative embodiment, the magnitude of the gap64is less than two millimeters. In a second illustrative embodiment, the magnitude of the gap64is less than one millimeter. The connecting strands56individually have a thickness of less than two millimeters or less than a millimeter measured parallel to the outer60and inner62surfaces.

The support columns58couple the conformal sheath54to the lower face22of build tray8. Thickness or design of support columns58is selected to assure a stable coupling of the sheath54to the build tray8.

The composite structure50is generally a very low modulus material such as hydrogel. Typically the elastic modulus is less than five megapascals (MPa), less than two megapascals, or less than one megapascal. As a note: One million pascals equals one megapascal which equals one MPa.

Referring back toFIG.2—according to step40, the support tray8and composite structure50are removed from the fluid tank6. According to42, the composite structure50is separated from the build tray8.

According to44, the sheath54is peeled from the 3D article4. As the sheath54is peeled from the article4, the connecting strands56that span the gap64are broken. Compared to prior support methods, this removal of the support structure52can be performed quickly, easily, and with essentially no damage to the article4.

In some embodiments, a post-process and/or shipment can occur between steps42and44. The post-process can include one or more of cleaning, washing, surface treatment, surface coating, ultraviolet curing, and heat curing to name some examples. If shipment (transport by a carrier service including one or more of land transport, air transport, rail transport, and oceanic transport) is performed before step44, then the support structure52forms part of the packaging materials to avoid damage during transport.

FIG.4illustrates a first embodiment of a portion of the composite structure50with a first embodiment of connecting strands56. The connecting strands56individually have a pointed or low cross sectional area tip66for coupling to the outer surface60of the 3D article4. With this design, the tip has such a small cross sectional area that removal from the outer surface60requires very little force. Yet at the same time, the connecting strands56do provide a function of maintaining the fluid gap64.

FIG.5illustrates a second embodiment of a portion of the composite structure50with a second embodiment of connecting strands56. The connecting strands56individually have a location of weakness or side notch68. During the peeling process, the connecting strands56tend to break along the side notch68.

FIG.6illustrates a third embodiment of a portion of the composite structure50with a third embodiment of connecting strands56. The connecting strands56individually have a location of weakness or an annular notch70. During the peeling process, the connecting strands56tend to break along the annular notch70.

FIG.7illustrates a fourth embodiment of a portion of the composite structure50with a fourth embodiment of connecting strands56. The strands have a geometry that converges or narrows away from surfaces60and62to a location of weakness72. Other designs of connecting strands56are possible and may even combine more than one of the examples illustrated inFIGS.4-7.

Now referring generally toFIGS.8-16, is a support structure52and a 3D printed article4according to another embodiment. According to this embodiment, the build tray8is flat and mimics the outline of the 3D printed object4.

According to this embodiment, the support columns58extend vertically upward from build tray8in a gyroid-like design (e.g. infinitely connected) with gaps64. The support columns58are horizontally coupled such that each support column58is coupled to the adjacent support column58. The gaps64between the support columns58may be diamond shaped, or other various shapes.

The support structure52ofFIGS.8-16further includes the conformal sheath54. The sheath54is positioned on top of the support columns58. For example, the sheath54is positioned on the distal end of the support columns58relative to the build tray8.

The plurality of connecting strands56further include a plurality of touchpoints80. The touchpoints80extend through the sheath54. The touchpoints80are removeably coupled to the 3D printed object4. Placing the sheath54as close to the 3D printed object4as possible while maintaining a gap during printing will provide extra support. Uncured ink between the 3D printed article4and the sheath54leads to Stefan adhesion, which helps hold the 3D printed article4in place. The sheath54does not need to envelop the 3D printed article4completely, and thin cuts can be made in the support columns58to make removal easier as needed.

As shown inFIG.10-12, after the printing process is completed, the 3D printed object4is removed from the support structure52. The 3D printed object4is pulled away from the support structure52at an angle in a lift direction90. During the removal process, the touchpoints80between the 3D printed object4and the support structure52are broken.

Now referring toFIG.11, is a cross-sectional view of the embodiment of the support structure52and the 3D printed object4ofFIG.9. As shown inFIG.11, the 3D printed object202is coupled to the support structure52by small touchpoints80. The embodiment of the support structure52and the 3D printed4202further includes a space100. The space100is defined by the sheath54and a proximal side of the 3D printed object4.

The distance between touchpoints80varies. For example, the 3D printed structure4may include a body102and a flange104. The body102may be elongated and thicker, while the flange104may be thin and delicate. For example, the flange104may have more touchpoints80than the body102. Furthermore, the flange104may be coupled to more touchpoints80that are closer to each other. Instead, the body102may have less touchpoints80that are further spread apart. The flange104may require more touchpoints80because the flange104is a more delicate structure that may lack its own structural support prior to curing.

Now referring toFIG.13-14is a front and back perspective view, respectively, of the support structure52and the 3D printed object4. The support structure52may further includes a plurality of slits110. According to this embodiment, the support structure52surrounds the 3D printed object4. For example, the support structure52may support a portion of the 3D printed object4from below the 3D printed object4and from above. For example, this may be advantageous in supporting 3D printed objects4that have a hollow inner cavity.

According to this embodiment, the support structure52200includes an arched portion112that defines an inner cavity114for the 3D printed object4. The plurality of slits110are positioned on the arched portion112. For example the plurality of slits110may be a point of fracture for the support structure52during removal of the 3D object4. For example, when removing the 3D printed object4, the plurality of slits110may completely fracture the support structure52when the user peels the 3D printed object4from the support structure52.

FIG.15is a schematic illustrating the difference in gap size and density of touchpoints80. The difference in gap size and density of touchpoints80may vary based on the shape of the object being printed. Furthermore, varying the gap size and density of touchpoints80may make the removal of the 3D printed4object easier while still supporting the 3D printed object4during printing.

Now referring toFIG.16is a perspective view of a user20removing the 3D printed object4from the support structure52. As shown inFIG.16, the user200may use their finger (e.g. a thumb) to separate the 3D printed object4from the support structure52. For example, the user200may wedge their finger between the support structure52and the 3D printed object4and then peel the 3D printed object4away from the support structure52breaking any touchpoints80.

The specific embodiments and applications thereof described above are for illustrative purposes only and do not preclude modifications and variations encompassed by the scope of the following claims.

Other embodiments are set forth in the following claims.