WO2025102014A1

WO2025102014A1 - Cylindrical printing attachment for additive manufacturing

Info

Publication number: WO2025102014A1
Application number: PCT/US2024/055286
Authority: WO
Inventors: Hansel HOBBIE; Paolo Maccarini; Aaron FRANKLIN
Original assignee: Duke University
Current assignee: Duke University
Priority date: 2023-11-09
Filing date: 2024-11-09
Publication date: 2025-05-15
Anticipated expiration: 2026-05-09

Abstract

Cylindrical motion control for an additive manufacturing system includes a cylindrical printing attachment. The cylindrical printing attachment can include a body having a platen-contacting surface for coupling to a platen of the additive manufacturing system, a rack surface, and an axle clamp track; a rack and pinion gear assembly, including a rack and a pinion, wherein the pinion rotatably engages with the rack, wherein the rack is coupled to the rack surface of the body; and an axle clamp structured to rotate along the axle clamp track of the body as the pinion rotates along the rack.

Description

CYLINDRICAL PRINTING ATTACHMENT FOR ADDITIVE MANUFACTURING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63/547,894, filed November 9, 2023, and U.S. Provisional Application Serial No. 63/663,352, filed June 24, 2024.

BACKGROUND

[0002] A challenge for additive manufacturing is uniform deposition of material onto a substrate that is not flat. Uniform deposition of material of a substrate is easiest when the angle of deposition is normal to the substrate. However, existing motion systems for additive manufacturing cannot maintain a normal angle of deposition when the substrate is not flat. As the print head moves around the substrate, steepness will be added to the angle of deposition. Also, existing motion control of motion systems for additive manufacturing that can deposit material on non-planar substrates can be complex and expensive to scale. Furthermore, existing motion systems for additive manufacturing encounter increased difficulty depositing material onto a non-flat substrate when the substrate is soft and/or flexible. Therefore, there is need for a motion system for additive manufacturing that maintains a normal angle of deposition, allows for efficient scalability, and is capable of uniform deposition of material onto soft and/or flexible substrates.

BRIEF SUMMARY

[0003] Cylindrical printing attachments for additive manufacturing are disclosed herein. The described cylindrical printing attachments can be used in existing planar substrate deposition systems. Advantageously, certain embodiments of an additive manufacturing system with cylindrical printing attachment as disclosed herein can maintain a normal angle of deposition onto nonplanar surfaces. Additionally, certain embodiments of the cylindrical printing attachment provide uniform deposition of material onto soft and/or flexible substrates.

[0004] In some aspects, the techniques described herein relate to a cylindrical printing attachment for an additive manufacturing system, including: a cylindrical coordinate conversion attachment, including: a body having: a platen-contacting surface for coupling to a platen of the additive manufacturing system; a rack surface: and an axle clamp track; and a rack and pinion gear assembly, including a rack and a pinion, wherein the pinion rotatably engages with the rack, wherein the rack is coupled to the rack surface of the body; and an axle clamp structured to rotate along the axle clamp track as the pinion rotates along the rack.

[0005] In some aspects, the techniques described herein relate to a computer readable storage medium having instructions stored thereon that when executed by a processor direct the processor to: obtain a diametric ratio of a substrate diameter of an object to a pinion diameter of a cylindrical printing attachment; perform length translation of 0- direction dimension values in a print file for the object having an axis of rotation of one dimension of the object based on the diametric ratio; and update each 0 -direction dimension values with a corresponding translated print length from the length translation. [0006] In some aspects, the techniques described herein relate to a cylindrical printing attachment for an additive manufacturing system, including: an axle, wherein the axle has a hollow region, wherein the axle includes: a fluid inlet at one end of the hollow region; and a fluid outlet for the hollow region and located at a position on the axle for mounting a flexible substrate; a fluid supply device coupled to the fluid inlet; and a suspension fixture having an axle support portion that supports the axle and a fixation portion that couples to a fixation point on the additive manufacturing system.

[0007] In some aspects, the techniques described herein relate to an additive manufacturing system, including: a material deposition device, including: a print head; a motion control system coupled to the print head; and a platen coupled to the motion control system and positioned beneath the print head; a cylindrical printing attachment coupled to the material deposition device, including: a cylindrical coordinate conversion attachment including: a body having: a platen-contacting surface coupled to the platen of the material deposition device: and a rotation control surface; and a rotation control device coupled to the rotation control surface of the body; an axle, wherein the axle has a hollow region, wherein the axle includes: a fluid inlet at one end of the hollow region; and a fluid outlet for the hollow region and located at a position on the axle for mounting a flexible substrate; a fluid supply device coupled to the fluid inlet; and a suspension fixture having an axle support portion that supports the axle and a fixation portion that couples to a fixation point on the additive manufacturing system, wherein the axle support portion is structured to allow the axle to rotate in place.

[0008] In a specific implementation, the described cylindrical printing attachment is used to print electronics on a catheter. [0009] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1A illustrates a cylindrical printing attachment for an additive manufacturing system.

[0011] Figure IB illustrates motion translation for a cylindrical printing attachment.

[0012] Figure 2 illustrates a method for adjusting values in a print file.

[0013] Figure 3 illustrates a cylindrical printing attachment for an additive manufacturing system.

[0014] Figure 4 illustrates an additive manufacturing system.

[0015] Figures 5A-5H illustrate views of an embodiment of a cylindrical printing attachment for additive manufacturing.

[0016] Figure 6 shows a fabrication process flow for printed CNT-TFTs on paper substrates on a 25 mm mandrel.

[0017] Figure 7(a-g) shows a variety of images illustrating printing of conformal electronics on complex substrates including concave and tapered substrates.

[0018] Figures 8A-8D show a diagram of the cylindrical printing attachment showing the pathway for pumped air to achieve on-axis catheter balloon inflation.

[0019] Figure 9 shows a fabrication process flow for a graphene sensor on a catheter balloon.

DETAILED DESCRIPTION

[0020] Cylindrical printing attachments for additive manufacturing are disclosed herein. The described cylindrical printing attachments can be used in existing planar substrate deposition systems. Advantageously, certain embodiments of an additive manufacturing system with cylindrical printing attachment as disclosed herein can maintain a normal angle of deposition onto nonplanar surfaces. Additionally, certain embodiments of the cylindrical printing attachment provide uniform deposition of material onto soft and/or flexible substrates.

[0021] With the growth of additive manufacturing, there has been increasing demand for fabricating conformal electronics that directly integrate with larger components to enable unique functionality. However, fabrication of conformal electronics is challenging because devices must merge with host substrates regardless of curvilinearity, topography, or substrate material. Existing planar substrate deposition systems for additive manufacturing include aerosol jet printers. Aerosol jet printers typically involve depositing a material onto a substrate on a platen where motion control utilizes a cartesian coordinate system.

[0022] As described herein, it is possible to mount flexible substrates and 3D objects on a rotating axis and print conformal electronics around the circumference of rotational bodies with 3D curvilinear surfaces through cylindrical coordinate motion while still utilizing existing planar substrate deposition systems.

[0023] Complex curvilinear surfaces are particularly challenging for conformal applications because they form 3D rotational bodies like cylinders, which require fully circumferential fabrication methods to access the entire surface. There are specific application needs for conformal electronics on rotational bodies that would benefit from a versatile additive manufacturing technique such as described herein, which is capable of conforming to the entire circumference of the substrate. For example, inflatable catheter balloons are used in surgical procedures throughout the body for purposes like endoscopy, angioplasty⁷, and elution-based drug delivery. The primary' function of inflatable catheter balloons is to facilitate the insertion of other probes; yet, the balloon surface itself provides the most direct contact with tissue and it would be invaluable to add functional electronics to these surfaces for additional monitoring during procedures. Through use of the described cylindrical printing capabilities, electronics can be printed on inflatable catheter balloons and other cylindrical or curved-shaped bodies. Example electronics that can be printed on inflatable catheter balloons through the described systems include tactile detection, temperature sensing, and aiding in ablative procedures.

[0024] Figure 1A illustrates a cylindrical printing attachment for an additive manufacturing system. Referring to Figure 1A, a cylindrical printing attachment 100 can include a body 102, a rack and pinion gear assembly 104, and an axle clamp 106. The body 102 and the rack and pinion gear assembly 104 can be considered part of a cylindrical coordinate conversion attachment according to certain embodiments. The body 102 includes a platen-contacting surface 108 that can be coupled to a platen 110 of an additive manufacturing system (not shown), a rack surface 112, and an axle clamp track 114.

[0025] A platen 110 of an additive manufacturing system typically moves in two orthogonal directions under computer control via x-y linear stages. Movement in a third direction (e.g., vertically) can be accomplished via the platen 110 or by control of a deposition flowhead, as examples. Accordingly, once the body 102 is coupled to a platen 110 at the platen-contacting surface 108, the body 102 can be moved by the control of a linear stage of the platen 110.

[0026] The rack and pinion gear assembly 104 includes a rack 116 coupled to the rack surface 112 and a pinion 118 that rotatably engages with the rack 116. Moving the rack 116 linearly, for example by movement of the platen 110, causes the pinion 118 to rotate. In this manner, rotation is controlled by the linear movement of the platen 110. As explained in more detail with respect to Figure IB, it is possible to print on a cylindrical or otherwise curved surface using a conventional x-y linear stage through motion translation. The axle clamp 106 can rotate along the axle clamp track 114 as the pinion 118 rotates along the rack 116.

[0027] The cylindrical printing attachment 100 can further include an axle 120 coupled to the pinion 118 and the axle clamp 106 to allow the pinion 118 to communicate rotational motion to the axle 120. The axle clamp 106 inhibits the axle 120 and pinion 118 from decoupling from the rack 116.

[0028] In some cases, the cylindrical printing attachment 100 further includes a suspension fixture 122. The suspension fixture 122 supports the axle 120 (and any substrate coupled to the axle 120) above the platen 110 so that the axle 120 can freely rotate. The suspension fixture 122 includes an axle support portion 124 that supports the axle 120 and a fixation portion 126 that couples to a fixation point (not shown), which can be on the additive manufacturing system (not shown). The axle support portion 124 is structured to allow the axle 120 to rotate in place. For example, the axle support portion 124 can include a tubular aperture through which the axle 120 can pass while permitting the axle 120 to freely rotate. As another example, the axle support portion 124 can include a trench or other holder that supports the axle 120 while permitting the axle 120 to freely rotate. In some cases, the suspension fixture 122 further includes a bearing 128 that couples to the axle support portion 124 and rotatably couples to the axle 120.

[0029] As mentioned above, control of rotation is based on translation of linear motion of the platen 110 (and thereby the rack 116 coupled to the platen 110 via the body 102). The diameter of a substrate coupled to the axle has an impact on the translation of linear motion control to rotational movement of the cylindrical printing attachment.

[0030] The ratio between the substrate diameter (Ds) and the pinion diameter (Dp), referred to as the diametric ratio (Ds/ Dp) can amplify or diminish the actual motion and print speed for the substrate under the nozzle. If the two diameters are equal, the x- and y- direction movement of the printer platen 110 is translated at a 1: 1 ratio with the 9- (circumferential) and z- (axial) direction movement of the rotating substrate. However, if the diameters are unequal then the translation of the x-direction platen movement to the 0-direction mandrel rotation will be multiplied by the diametric ratio, as illustrated in Figure IB. As a result, the true displacement (d) and print speed (v) of the rotating substrate in the 9- and z-directions will differ from the movement and print speed of the planar platen 110 according to the following equations:

V_Z = Vy

[0031] Although it is technically possible to choose pinions with the same diameter as a given substrate, that level of modularity is cost-inefficient and ineffective for substrates with varying diameter. It is much easier to acknowledge the difference in substrate and pinion diameters and select from commonly available pinions to achieve a diametric ratio as close to the ideal 1: 1 as possible.

[0032] Figure IB illustrates motion translation for a cylindrical printing attachment. Four pinions are shown with diameters of 7.5, 15, 25. and 50 mm to handle possible substrates up to 40 mm in diameter. To fully characterize the effect of the diametric ratio, the four available pinions were used to print traces onto a polyimide substrate wrapped around a 15 mm cylindrical mandrel. To account for the effect of the diametric ratio, the design file is adjusted by either elongating or shortening dimensions in the 0-direction to achieve the desired pattern. Referring to Figure IB, it can be seen that for the desired trace length in the 0-direction of 10 mm, the modified print lengths for each ratio are represented as follows:

[0033] The diametric ratio also affects the true rotational print speed. For the graphene traces, a linear print speed of 2 mm/s was set for the motorized platen, and the actual print speed of the rotating mandrel was determined simply by multiplying the set speed by the diametric ratio for the four example cases. As would be expected, for faster print speeds at higher diametric ratios the printed traces become thinner than when they are printed at lower diametric ratios with slower print speeds. Consequently, for the thicker traces printed with the lowest diametric ratios there is substantially less resistivity than for the relatively thinner traces produced at higher ratio values. This trend in resistivity is also expected, as the thicker traces contain a higher density of conductive material and thus exhibit lower resistivity than the thinner traces with less material.

[0034] These results highlight the importance of understanding and characterizing the effect of the diametric ratio on the aerosol jet printing so that appropriate design choices can be made. For example, while the diametric ratio of 1: 1 may be considered an ideal choice for length translation it is not always possible to achieve, especially for more complex shapes. In such a situation, a pinion that is larger than the substrate and that will yield a ratio below 1 : 1 throughout the print can be selected to avoid reducing the quality of the printed film. While it is also technically possible to adjust the linear print speed to account for the diametric ratio and achieve the correct rotational print speed at the substrate, this is relatively complicated to achieve especially during the dynamic print process. In tests, it was found that diametric ratios between 3: 10 and 2: 1 did not create a severe difference in speed between the modified rotational speed and the set speed of the printer platen.

[0035] Instructions for a software program, plug-in. or module can be provided that can adjust values in a print file having an object having an axis of rotation of one dimension of the object based on a relation between a circumference of the object and a circumference of a rotating component of a cylindrical coordinate conversion attachment.

[0036] Figure 2 illustrates a method for adjusting values in a print file. Referring to Figure 2, method 200 includes obtaining (210) a diametric ratio of a substrate diameter of an object to a pinion diameter of a cylindrical printing attachment; performing (220) length translation of ^-direction dimension values in a print file for the object having an axis of rotation of one dimension of the object based on the diametric ratio; and updating (230) each 9 -direction dimension values with a corresponding translated print length from the length translation. [0037] Accordingly, the instructions for a software program, plug-in, or module (which may be stored on a computer readable storage medium) can (when executed by a processor) perform method 200 by taking, as input, the print file and at least the diameter of the pinion/rotating component. In some cases, a diameter of the object in the print file can be received as input directly or indirectly (e.g., based on information in the print file). For obtaining (210) the diametric ratio, the instructions can either calculate the diametric ratio from the diameter of the pinion and the diameter of the object or can receive a diametric ratio as input. The instructions use the diametric ratio to perform (220) length translation, for example, by parsing or otherwise identifying from the print file for 6- direction dimension values and elongating or shortening the dimension values based on the diametric ratio. For example, a given 0-direction dimension value (e.g., print length) can be calculated as the substrate diameter divided by pinion diameter multiplied by the desired trace length in the ^-direction. The instructions can automatically adjust (230) the values in the print file according to the translated print length.

[0038] Once a print file has been adjusted to account for the diametric ratio, printing can be carried out by an additive manufacturing system having a cylindrical printing attachment.

[0039] In some cases, the adjustment to the print file can be carried out by a computing system associated with an additive manufacturing system that executes the instructions described above. In some cases, the adjustment to the print file can be carried out by the additive manufacturing system itself. In some cases, the adjustment to the print file can be carried out by a computing system on which design application(s) are executed and which may not be associated with any additive manufacturing system per se.

[0040] For scenarios in which the substrate being printed on is a catheter balloon or other flexible substrate, a fluid supply device can be included as a cylindrical printing attachment.

[0041] Figure 3 illustrates a cylindrical printing attachment for an additive manufacturing system. Referring to Figure 3, a cylindrical printing attachment 300 can enable printing on a flexible substrate through the inclusion of a fluid delivery system. The fluid delivery system of cylindrical printing attachment 300 includes a fluid supply device 304 and axle 302 having a fluidic ingress/egress. The axle 302 includes a hollow region 308, a fluid inlet 310 at one end 312 of the hollow region 308, and a fluid outlet 314 for the hollow region 308 and located at a position on the axle 302 for mounting, at region 350, a flexible substrate (not shown). The fluid supply device 304 can be coupled to the fluid inlet 310. The fluid supply device 304 can supply fluid to the fluid inlet 310 that can pass through the hollow region 308 of the axle 302 and through the fluid outlet 314 to inflate the flexible substrate (not shown). In some cases, the flexible substrate (not shown) is a catheter balloon. A suspension fixture 306 of the cylindrical printing attachment 300 has an axle support portion 316 that supports the axle 302 and a fixation portion 318 that couples to a fixation point on the additive manufacturing system (not shown). In some cases, the axle support portion 316 is structured to allow the axle 302 to rotate in place. The suspension fixture 306 may be disposed between the fluid supply device 304 and the region 350 on which a flexible substrate is mounted as shown in Figure 3 or may be disposed at a side of the fluid delivery system. In some cases, the fluid supply device 304 may be integrated with the suspension fixture 306.

[0042] In some cases, the cylindrical printing attachment 300 further includes a cylindrical coordinate conversion attachment 320, which may be implemented as described with respect to the cylindrical printing attachment, including rack and pinion gear assembly 104 of Figures 1A and IB. As an alternative to the cylindrical printing attachment such as described with respect to Figures 1A and IB, a separate motor may be used to rotate an axle supporting a substrate instead of using platen 110 to effectuate motion of the axle (e.g.. via the coupled body 102 and rack and pinion gear assembly 104) In some of such cases, the separate motor implementing cylindrical coordinate conversion attachment 320 includes a servo motor 322. The servo motor can be controlled by a separate controller or by a motion controller of an additive manufacturing system (e.g., instead of or in addition to any other stages for linear motion operation).

[0043] Figure 4 illustrates an additive manufacturing system having a cylindrical printing attachment. Referring to Figure 4, an additive manufacturing system 400 having a cylindrical printing attachment 404 includes a material deposition device 402, the cylindrical printing attachment 404, and a computing system 406.

[0044] The material deposition device 402 includes a print head 408, a motion control system 410 coupled to the print head 408, and a platen 412 positioned beneath the print head 408. Motion control system 410 controls the motion for the platen 412. The motion control system 410 can be a standalone system or part of computing system 406 as a motion control component. In some cases, the motion control component is a removable component of computing system 406, for example as a peripheral control card (e.g., that couples to a slot on a motherboard/printed circuit board (PCB) or via a connector to the motherboard/PCB). The control card can include an input/output interface, which can send signals to and receive signals from external components. For example, x-y linear stages and a z-axis component of material deposition device 402 can be controlled by the control card. In some cases, a digital signal processor or other external input/output component may be included. Control of material actuation and deposition components (e.g., including print head 408) may also be performed by the motion control card so as to time deposition events in coordination with motion.

[0045] The cylindrical printing attachment 404 includes a cylindrical coordinate conversion attachment 414, an axle 416, a fluid supply device 418, and a suspension fixture 420. The cylindrical coordinate conversion attachment 414 includes a body 422 and a rotation control device 424. The body 422 can be implemented as described with respect to body 102 of Figure 1A and the rotation control device 424 can be implemented as described with respect to rack and pinion gear assembly 104. Of course, in certain implementations, the cylindrical coordinate conversion attachment 414 may be implemented using a servo motor.

[0046] The axle 416 includes a hollow region 430, a fluid inlet 432 at one end 434 of the hollow region 430, and a fluid outlet 436 for the hollow region 430 and located at a position on the axle 416 for mounting a flexible substrate 438. The fluid supply device 418 is coupled to the fluid inlet 432. The fluid supply device 418 can supply fluid to the fluid inlet 432 that can pass through the hollow region 430 of the axle 416 and through the fluid outlet 436 to inflate the flexible substrate 438. In some cases, the flexible substrate 438 is a catheter balloon. The suspension fixture 420 has an axle support portion 440 that supports the axle 416 and a fixation portion 442 that couples to a fixation point 444 on the additive manufacturing system 400.

[0047] The computing system 406 can include a processor 446 and storage 448. Processor 446 can include one or more of any suitable processing devices (“processors”), such as a microprocessor, central processing unit (CPU), graphics processing unit (GPU), field programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), logic circuits, state machines, application-specific standard products (ASSPs), system-on- a-chip systems (SOCs), complex programmable logic devices (CPLDs), etc. Storage 448 can include any suitable storage media that can store instructions 450 and data. Suitable storage media for storage 448 includes random access memory, read only memory, magnetic disks, optical disks, CDs, DVDs, flash memory, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other suitable storage media. As used herein, “storage,” “memory storage,” and “storage media” do not consist of transitory’, propagating waves. Instead, these terms refer to non-transitory media. Instructions 450 can include those used as part of the motion control system 410 for the material deposition device 402. Instructions 450 can also include those used to adjust values in a print file having an object having an axis of rotation of one dimension of the object based on a relation between a circumference of the object and a circumference of a rotating component of a cylindrical coordinate conversion attachment as described above, for example, according to method 200. In some cases, instructions 450 include instructions to receive a file comprising motion control signals for the motion control system 410, adjust the motion control signals based on a relation between linear motion along a linear axis and rotational motion of the axle 416 along a rotational axis, and deliver the adjusted motion control signals to the motion control system 410.

[0048] Figures 5A-5H illustrate views of an embodiment of a cylindrical printing attachment for additive manufacturing. Referring to Figures 5A-5H, the cylindrical printing attachment 500 includes a body 502, a rack and pinion gear assembly 504, and an axle clamp 506. The body 502 includes a platen-contacting surface 508 coupled to a platen 510 of an additive manufacturing system (not shown), a rack surface 512, and an axle clamp track 514. The rack and pinion gear assembly 504 includes a rack 516 coupled to the rack surface 512 and a pinion 518 that rotatably meshes with the rack 516. The axle clamp 506 rotatably couples to the axle clamp track 514.

[0049] In some cases, the cylindrical printing attachment 500 further includes an axle 520 coupled to the pinion 518 and the axle clamp 506 to allow the pinion 518 to communicate rotational motion to the axle 520 and the axle clamp 506. The axle clamp 506 prevents the axle 520 and pinion 518 from decoupling from the rack 516. The axle allows a flexible substrate 522 to be mounted and rotated.

[0050] In some cases, the cylindrical printing attachment 500 further includes a suspension fixture 524. The suspension fixture 524 includes an axle support portion 526 that supports the axle 520 and a fixation portion 528 that couples to a fixation point (not shown) on the additive manufacturing system (not shown). The axle support portion 526 is structured to allow the axle 520 to rotate in place. In some cases, the axle support portion 526 includes a first axle support 530 coupled to the fixation portion 528 and a second axle support 532 that can be releasably coupled to the first axle support 530 such that a substrate may be mounted on the axle 520 at a region between the first axle support 530 and the second axle support 532. One or more support rods 540 coupling the first axle support 530 to the second axle support 532 can be used to support the second axle support 532 at the desired distance from the first axle support 530. The first axle support 530 can include a first bearing 534 that enables the axle 520 to freely rotate within the first axle support 530 and the second axle support 532 can include a second bearing 536 that enables the axle 520 to freely rotate within the second axle support 532.

[0051] Although not shown, a fluid supply device such as described with respect to Figure 3 can be included to provide fluid within the axle 520 so that the fluid can be applied in the region between the first axle support 530 and the second axle support 532, for example, to be output at fluid outlet 542.

[0052] Examples - conformal electronics on curved substrates

[0053] A prototype of the described cylindrical printing attachment was used to print electronics. To demonstrate conformal electronics fabricated with an additive manufacturing system with cylindrical printing attachment, electronic devices of resistive traces, capacitors, and thin-film transistors (TFTs) were printed onto substrate- wrapped cylindrical mandrels.

[0054] First, it was found that the resistance of infilled traces of printed graphene is dependent on the arc length (defined by the central angle and radius of the arc) and the infill direction, with axial infill yielding higher resistance at longer arc lengths. Resistance was measured in a two-terminal fashion by positioning micromanipulator probes at the ends of the long side of a trace. The two infill directions were tested by printing graphene traces along the circumference of a substrate-wrapped 15 mm diameter mandrel with different central angles of 5°, 15°, 45°, and 90° defining the arc lengths. These traces exhibited mostly similar values of resistance up to an arc length of 11.78 mm (central angle of 90°), where the resistance of the arc trace began to deviate from previous values. This deviation is due to the axial-infilled trace being printed perpendicular to the arc length direction, which uses more individual microstrip lines to form a given trace. In contrast, the circumferential-infilled trace used longer printed lines with increasing arc length, but the number of lines used to form the trace remained the same. Thus, the circumferential- infilled traces maintained a linear resistance across increasing arc lengths while the axial- infilled traces showed a jump to higher resistance for long arc lengths because it was composed of more individual lines than the circumferential infill. Therefore, the infill patterns for the materials throughout this work were chosen in accordance with having the fewest individual lines being printed for each geometry on a device layer to ensure consistent resistance. [0055] Next, resistive traces of varying arc length were printed along the circumferences of 15-and 25-mm diameter mandrels using a diametric ratio of 1: 1 and circumferential infill. Regardless of substrate diameter between the two mandrels, the resistance of the traces showed an expected trend of increasing resistance with arc length. These results indicate the reliable performance of the printing along increasing circumferential dimensions while also showing scalable application to substrates with different diameters. [0056] To demonstrate a three-layered carbon-based device, a two-plate capacitor of graphene contacts and cellulose nanocrystals (CNC) was fabricated on a paper substrate wrapped around a 15 mm diameter mandrel. The normalized capacitance across frequency for the capacitors of 0.81 mm² overlapping plate area decreases in a nonlinear fashion in accordance with the ionic nature of the CNC dielectric. Furthermore, under applied voltages of 0.5, 1, and 2 V, exponential behavior of the capacitor charging and discharging currents is observed with non-negligible leakage current for the 2 V case that diminishes for the lower voltages.

[0057] By expanding to four layers and using a top-gate transistor design that includes printed carbon nanotubes (CNTs) as the semiconducting layer, thin-film transistors (TFTs) were fully printed on paper in accordance with the process flow illustrated in Figure 6.

[0058] Figure 6 shows a fabrication process flow for printed CNT-TFTs on paper substrates on a 25 mm mandrel. Briefly, source and drain contacts of graphene along with fiducial marks were printed onto a paper substrate mounted on a 25 mm diameter cylindrical mandrel. Then, the CNT channel was printed to bridge the two contacts followed by the CNC gate dielectric and a graphene top gate, all of which utilize the fiducial marks for correct alignment between the four TFT layers. The switching characteristics of these TFTs were evaluated, wherein the drain current (ID) and gate current (Ig) were measured for applied gate voltages (VGS) from -1 to 1 V with a constant drain to source voltage (VDS) of -0.5 V. The measured CNT-TFT devices possess repeatable and consistent switching behavior with low' voltage requirements. As can be seen it is possible to produce electronic devices at the same quality as conventional planar aerosol jet printing but with the expansive capabilities of conformal electronics on nonpl anar surfaces.

[0059] From the demonstrations, it can be seen that it is possible to print conforming electronics onto cylindrical bodies and any curved 2D surface that has a uniform radius. It is also possible to print conformal electronics on a concave mandrel. [0060] Figure 7(a-g) shows a variety of images illustrating printing of conformal electronics on complex substrates including concave and tapered substrates. Figure 7(a) shows a picture of a print nozzle fixed at the focal point above a concave mandrel. By simply moving the shutter arm, it is possible to mount a concave mandrel with the tip of the deposition nozzle located at the focal point of the curvature, as shown in Figure 7(a) for a 15 mm diameter hollow half cylinder.

[0061] Figure 7(b) shows a picture of printed graphene in a meander line onto concave mandrel and Figure 7(c) shows a picture of printed graphene in parallel lines on concavely bent paper substrate. In Figures 7(b) and 7(c), example patterns of graphene were deposited onto this concave mandrel with and without a fixed substrate to show that it can also be used to print onto flexible substrates bent concavely.

[0062] Figure 7(d) shows a picture of a conical mandrel with printed AgNW traces. Figure 7(e) shows a picture of printing along the length of conical mandrel showing movement up the length of the cone after 5 seconds of printing. Because of the standoff distance and jet-stream deposition of aerosol jet printing, getting approximate uniformity in a printed trace is still possible for moderate angles of non-normal incidence. This tolerance of moderately non-normal incidence in conformal applications is demonstrated in Figures 7(d) and 7(e) by printing silver nanowires (AgNWs) onto a 3D-printed conical mandrel with a taper angle of 15°, resulting in a non-normal print incidence of 105° across the cone.

[0063] Figure 7(f) shows a picture of printing a graphene helix on 1000 pL pipette tip and Figure 7(g) shows a magnified view of graphene helix on the pipette tip. As an example, a 1000 pL pipette tip with a gradual taper of 7.5° was used as the substrate for a conformal graphene helix, which was printed spiraling down the length of the pipette tip from its narrow end as imaged in Figures 7(f) and 7(g).

[0064] Figures 8A-8D show a diagram of the cylindrical printing attachment showing the pathway for pumped air to achieve on-axis catheter balloon inflation (airflow pathway shown in Figure 8A). To enable the fabrication of conformal electronics onto catheters and catheter balloons, on-axis inflation is used that permits hollow and inflatable rotational bodies to be mounted on the lathe mechanism, as diagramed and pictured in Figures 8A- 8D; where Figure 8B shows a view of second axle support 532, Figure 8C shows an internal view of second axle support 532 with the axle passing through, including location of fluid outlet 542; Figure 8D is a close-up of Figure 8C. Support rods 540 are shown in the background. Since the on-axis inflation required no other modification to the lathe mechanism beyond the inclusion of a rotating air inlet, the system capabilities for printing onto any substrate less than 40 mm in diameter holds true, even for inflated catheters.

[0065] Figure 9 shows a fabrication process flow for a graphene sensor on a catheter balloon. A six-step fabrication process flow for printing onto the inflated catheter balloon is detailed in Figure 9. The first pretreatment step is critical for cleaning the balloon substrate and improving the surface adhesion properties of the polymeric material to ensure good print quality. Then, after mounting the catheter and printing graphene traces onto it, an encapsulating layer of polydimethylsiloxane (PDMS/silicone) is dripped over the printed material for a few reasons: to ensure printed films do not break off the surface during inflation/deflation, to provide a biocompatible coating over the chosen printed material, and also to reduce noise for printed sensors.

[0066] Using this fabrication process, a graphene meander line sensor was printed directly onto the surface of the inflated 14 mm TPU catheter balloon. Graphene was selected for this sensor demonstration because of the environmentally sensitive material properties it offers, which cause a resistive change in the printed graphene based on temperature, stress/strain, and humidity. Given that the graphene sensor is encapsulated by PDMS, humidity sensitivity is removed from the sensor leaving behind sensitivities to temperature and stress/strain. To demonstrate the value of having a functionalized catheter, the normalized resistive change of the graphene sensor was measured relative to temperature on the catheter balloon from 25 - 80 °C. The sensor provides clear resistive change across the entire temperature range with a sensitivity of 1.05 % change in normalized resistance per degree Celsius, and an R2 value of 0.987 when fitting the relationship to a simple polynomial. Furthermore, because the graphene sensor also exhibits a response to mechanical movement independent of temperature response, the sensor was used for the secondary function of detecting inflation and deflation of the catheter balloon in real time. When inflated, the graphene sensor on the catheter balloon is held taut in its originally printed position and shows little change from the initial resistance value. However, when the catheter balloon is deflated, the graphene sensor crumples up with the balloon surface and the sensor drops into a low-resistance state with a distinct 18% change from the initial resistive value. This inflation/deflation sensitivity is also shown to be repeatably detectable over time with negligible hysteresis and signal drift.

[0067] Both of these graphene sensor functions exemplify the potential utility of functionalized catheters with on-surface printed devices as they can provide real-time monitoring of important medical factors that are otherwise normally undetected. Advantageously, by printing using the described cylindrical printing attachment, it was possible to easily print this dual-function sensor directly onto the catheter balloon such that no secondary substrate or additional processing was required.

[0068] Although the subject matter has been described in language specific to structural features and/or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

Claims

CLAIMS What is claimed is:

1. An additive manufacturing system, comprising: a material deposition device, comprising: a print head; a motion control system coupled to the print head; and a platen coupled to the motion control system and positioned beneath the print head; a cylindrical printing attachment coupled to the material deposition device, comprising: a cylindrical coordinate conversion attachment comprising: a body having: a platen-contacting surface coupled to the platen of the material deposition device; and a rotation control surface; and a rotation control device coupled to the rotation control surface of the body; an axle, wherein the axle has a hollow region, wherein the axle comprises: a fluid inlet at one end of the hollow region; and a fluid outlet for the hollow' region and located at a position on the axle for mounting a flexible substrate; a fluid supply device coupled to the fluid inlet; and a suspension fixture having an axle support portion that supports the axle and a fixation portion that couples to a fixation point on the additive manufacturing system, wherein the axle support portion is structured to allow' the axle to rotate in place.

2. The additive manufacturing system of claim 1, wherein the rotation control device coupled to the rotation control surface of the body comprises a rack and pinion gear assembly comprising a rack and a pinion.

3. The additive manufacturing system of claim 2, further comprising: a computing system comprising a processor, storage, and instructions stored on the storage that when executed by the processor, cause the computing system to: obtain a diametric ratio of a substrate diameter of an object to a pinion diameter of the pinion; perform length translation of 0-direction dimension values in a print file for the object having an axis of rotation of one dimension of the object based on the diametric ratio; and update each 0-direction dimension values with a corresponding translated print length from the length translation, wherein the print file comprising the updated 0-direction dimension values is provided to motion control system coupled to the print head.

4. The additive manufacturing system of claim 1, further comprising: a computing system coupled to the material deposition device, comprising a processor, storage, and instructions stored on the storage that when executed by the processor, cause the computing system to: receive a file comprising motion control signals for the motion control system; adjust the motion control signals based on a relation between linear motion along a linear axis and rotational motion of the axle along a rotational axis; and deliver the adjusted motion control signals to the motion control system.

5. A cylindrical printing attachment for an additive manufacturing system, comprising: a cylindrical coordinate conversion attachment, comprising: a body having: a platen-contacting surface for coupling to a platen of the additive manufacturing system; a rack surface; and an axle clamp track; and a rack and pinion gear assembly, comprising a rack and a pinion, wherein the pinion rotatably engages with the rack, wherein the rack is coupled to the rack surface of the body; and an axle clamp structured to rotate along the axle clamp track as the pinion rotates along the rack.

6. The cylindrical printing attachment of claim 5. further comprising an axle coupled to the pinion and the axle clamp to allow the pinion to communicate rotational motion to the axle.

7. The cylindrical printing attachment of claim 6. further comprising a suspension fixture having an axle support portion that supports the axle and a fixation portion that couples to a fixation point on the additive manufacturing system, wherein the axle support portion is structured to allow the axle to rotate in place.

8. The cylindrical printing attachment of claim 7, wherein the suspension fixture further comprises a bearing that couples to the axle support portion and that rotatably couples to the axle.

9. A computer readable storage medium having instructions stored thereon that when executed by a processor direct the processor to: obtain a diametric ratio of a substrate diameter of an object to a pinion diameter of a cylindrical printing attachment; perform length translation of 0-direction dimension values in a print file for the object having an axis of rotation of one dimension of the object based on the diametric ratio; and update each 0 -direction dimension values with a corresponding translated print length from the length translation.

10. A cylindrical printing attachment for an additive manufacturing system, comprising: an axle, wherein the axle has a hollow region, wherein the axle comprises: a fluid inlet at one end of the hollow region; and a fluid outlet for the hollow region and located at a position on the axle for mounting a flexible substrate; a fluid supply device coupled to the fluid inlet: and a suspension fixture having an axle support portion that supports the axle and a fixation portion that couples to a fixation point on the additive manufacturing system.

11. The cylindrical printing attachment of claim 10. further comprising a cylindrical coordinate conversion attachment.

12. The cylindrical printing attachment of claim 11, wherein the cylindrical coordinate conversion attachment comprises a servo motor.

13. The cylindrical printing attachment of claim 11, wherein the cylindrical coordinate conversion attachment comprises: a body having: a platen- contacting surface coupled to a platen of the additive manufacturing system; a rack surface; and an axle clamp track; a rack and pinion gear assembly, comprising a rack and a pinion, wherein the pinion rotatably engages with the rack, wherein the rack is coupled to the rack surface of the body, wherein the pinion is coupled to the axle to allow the pinion to communicate rotational motion to the axle; and an axle clamp coupled to the axle and structured to rotate along the axle clamp track as the pinion rotates along the rack.

14. The cylindrical printing attachment of claim 10, wherein the flexible substrate comprises a catheter balloon.