Fiber-reinforced viscoelastic INKS for direct ink writing
Patent Information
- Application Number
- PCT/US2026/018592
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-10
- Filing Date
- 2026-03-10
- Publication Date
- 2026-09-17
Smart Images
Figure US2026018592_17092026_PF_FP_ABST
Abstract
Description
FILED MARCH 10, 2026 P2974PC01 (2025-041)FIBER-REINFORCED VISCOELASTIC INKS FOR DIRECT INK WRITING RELATED APPLICATIONS
[0001] This application claims the benefit of United States Provisional Patent Application Serial No. 63 / 769,578 filed March 10, 2025 entitled, “Direct Ink Writing of Hexagonal Honeycomb Carbon Fiber-Reinforced Epoxy Composites,'’ the disclosure of which is herein incorporated by reference as if fully set forth herein.BACKGROUND
[0002] Computer-controlled material extrusion additive manufacturing techniques have revolutionized the manufacturing of complex architectures and material compositions at the meso-, micro-, and nano-scales. These advanced manufacturing techniques can manufacture specimens with high precision, production efficiency, and cost-savings. These advancements in additive manufacturing are highly dependent upon the feedstock used to create two-dimensional (“2D’') and three-dimensional (“3D”) architectures.
[0003] Various additive manufacturing techniques have been explored to create 2D and 3D architectures, such as fused filament fabrication (“FFF”). digital light processing (“DLP”), stereolithography (“SLA”), powder bed fusion (“PBF”), and direct ink writing (“DIW”). However, these techniques face unique challenges, due at least in part to the feedstock used in generating 2D and 3D architectures. For example, FFF suffers from fabrication-induced defects such as shrinkage and warping and weak filler-matrix bonding; DLP and SLA face challenges with filler dispersion and uniform curing; and PBF struggles with homogeneous filler dispersion in powders.
[0004] DIW is a versatile, computer-controlled, selective multi-material ink deposition technique that enables the use of micro- and nano-sized filler particles. DIW provides precise geometric control across macro-, meso-, and micro-scale levels. DIW may be used to create unique multi -material specimens with unique architectures. DIW with pneumatic control extrusion enables multi-stroke print paths thus avoiding print overlapping as seen in standard 3D printing, which facilitates the creation of unique geometries. Thereby, Direct Ink Writing (DIW) typically generates less material waste than conventional 3D printing methods, thereby improving material usage and sustainability.
[0005] Although DIW offers many advantages over other additive manufacturing techniques, DIW requires specialized inks to create specimens. DIW ink must have unique shear-thinning, viscoelastic properties that allow the ink to transition between low and high viscosity states depending on the application of external stress and shear. The current inks used in DIW sufferFILED MARCH 10, 2026 P2974PC01 (2025-041)from deficiencies that include post-cure shrinkage, warping and insufficient fiber volume content in fiber-reinforced epoxy inks. These deficiencies may result in compromised loadbearing capabilities, reduced print accuracy, and inadequate mechanical performance of printed specimens. There is, therefore, a need for improved DIW inks to address these and other shortcomings of the prior art.BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more implementations described herein and, together with the description, explain these implementations. The drawings are not intended to be draw n to scale, and certain features and certain views of the figures may be show n exaggerated, to scale or in schematic in the interest of clarity and conciseness. Not every component may be labeled in every drawing. Like reference numerals in the figures may represent and refer to the same or similar element or function.
[0007] FIG. 1 presents log-log plots of viscosity as a function of shear rate for fiber-reinforced viscoelastic inks formulated in accordance with exemplary embodiments and compared to analytical expectations based on the Herschel-Bulkley fluid model.
[0008] FIG. 2 presents log-log plots of storage and loss moduli as a function of oscillatory shear stress of fiber-reinforced viscoelastic inks formulated in accordance with exemplary embodiments.
[0009] FIG. 3 is a process flow chart for an exemplary method of creating a fiber-reinforced viscoelastic ink.
[0010] FIG. 4 is a process flow' chart for a method of creating a printed specimen using a fiber-reinforced viscoelastic ink formulated in accordance with exemplary embodiments.
[0011] FIGS. 5A, 5B and 5C show geometric designs of printed specimens constructed in accordance with exemplary embodiments.
[0012] FIG. 6A and 6B show results of in-plane compression testing of specimens printed using fiber-reinforced viscoelastic inks.
[0013] FIG. 7 shows a side elevation view of a manual injector for extruding fiber-reinforced viscoelastic inks formulated in accordance with exemplary embodiments.DETAILED DESCRIPTION
[0014] The present disclosure is directed to fiber-reinforced viscoelastic inks well suited for use in direct ink writing (“DIW’") manufacturing processes, together with methods for creating the fiber-reinforced viscoelastic inks, and methods to create specimens using the novel fiber-reinforced viscoelastic inks. The fiber-reinforced viscoelastic inks formulated in accordanceFILED MARCH 10, 2026 P2974PC01 (2025-041)with embodiments covered by the present disclosure are referred to herein as “FRVI” and the formulations for these inks are referred to as “FRVI formulations.” In some embodiments, the FRVI formulations include a matrix material, a reinforcing filler, a first rheology modifier, and a second rheology modifier. The matrix material serves as a material binder that holds the constituents of the mixture. The reinforcing filler includes structures that act to strengthen the printed specimen, reduce fabrication-induced defects, improve print accuracy, and improve mechanical performance of the printed specimen. The first and second rheology modifiers impart reversible shear-thinning and viscoelastic properties and endow tunable thixotropic behavior to the FRVI. The FRVI exhibits unique shear-thinning properties, allowing the FRVI to reversibly transition between liquid-like and solid-like states upon the application, or removal, of external stress, shear, or a combination thereof. This unique property makes the FRVI an excellent feed material for use in DIW.
[0015] In some non-limiting embodiments, the matrix material includes an epoxy. The epoxy can be a two-part epoxy including a first-part epoxy resin and a second-part epoxy hardener. In some embodiments, the FRVI includes between about 53 wt.% and about 82 wt.% of epoxy. As discussed below, the resin and hardener are combined in a strategic sequence with the reinforcing filler and rheological modifiers. In some embodiments, the first rheology modifier is a powdered rheological modifier, such as fumed silica. In some embodiments, the FRVI formulations include between about 2.2 wt.% and about 6.5 wt.% of fumed silica. In some embodiments, the reinforcing filler includes carbon fiber filler material. Suitable carbon fiber filler material includes cylindrical carbon fiber. The FRVI can include about 10 wt.% to about 40 wt.% of carbon fiber filler material. In some embodiments, the second rheological modifier is a liquid-based rheological modifier. Suitable rheological modifiers include silicone additives or platinum-catalyzed silicone additives. In some embodiments, the FRVI formulations include about 2 wt.% of the second, liquid-based rheology modifier.
[0016] In other embodiments, the present disclosure is directed to methods for creating the FRVI. The methods begin with the step of mixing an epoxy resin with fumed silica to increase the viscosity of the epoxy resin. Next, carbon fiber filler material is added to further increase the viscosity of the resulting fiber-reinforced epoxy. The process of adding the carbon fiber filler material can be accomplished using an iterative process that repeats until the desired carbon fiber filler material weight concentration has been reached. Once the desired carbon fiber filler material concentration has been reached, an epoxy hardener is added to react with the modified epoxy resin. A liquid-based rheology modifier, such as a silicone-based liquid additive, can then be introduced to control the final viscosity of the FRVI. In someFILED MARCH 10, 2026 P2974PC01 (2025-041)embodiments there is an additional defoaming and degassing step to remove entrapped voids once the FRVI is formed.
[0017] In other embodiments, the present disclosure covers a method for creating a fabricated specimen using the FRVI that includes the steps of providing a quantify of FRVI, loading the FRVI into a dispenser, degassing and defoaming the FRVI, and mounting the dispenser into a direct ink writing printer system. The method includes the steps of activating the direct ink writing printer system, which in turn applies a pressure to the FRVI. Once a threshold pressure is applied to the FRVI, the FRVI transitions to a liquid-like state and the FRVI is extruded and deposited. Once the FRVI has been extruded into a predetermined architecture, it is pre-cured and post-cured to produce the fabricated specimen.
[0018] Before further describing various embodiments of the compositions and methods of the present disclosure in more detail by way of exemplary description, examples, and results, it is to be understood that the embodiments of the present disclosure are not limited in application to the details of compositions and methods as set forth in the following description. The embodiments of the composition and methods of the present disclosure are capable of being practiced or carried out in various ways not explicitly described herein. As such, the language used herein is intended to be given the broadest possible scope and meaning; and the embodiments are meant to be exemplary', not exhaustive. Also, it is to be understood that the phraseology and terminology’ employed herein is for the purpose of description and should not be regarded as limiting unless otherwise indicated as so. Moreover, in the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the disclosure. Hoyvever, it yvill be apparent to a person having ordinary' skill in the art that the embodiments of the present disclosure may be practiced without these specific details. In other instances, features which are well known to persons of ordinary skill in the art have not been described in detail to avoid unnecessary complication of the description. While the apparatus and methods of the present disclosure have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the apparatus, compositions and / or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the inventive concepts as described herein. All such similar substitutes and modifications apparent to those having ordinary' skill in the art are deemed to be within the spirit and scope of the inventive concepts as disclosed herein.
[0019] All patents, published patent applications, and non-patent publications referenced or mentioned in any portion of the present specification are indicative of the level of skill of thoseFILED MARCH 10, 2026 P2974PC01 (2025-041)skilled in the art to which the present disclosure pertains, and are hereby expressly incorporated by reference in their entirety to the same extent as if the contents of each individual patent or publication was specifically and individually incorporated herein.
[0020] Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those having ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.
[0021] As utilized in accordance with the methods and compositions of the present disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings:
[0022] The use of the word “a” or "an" when used in conjunction with the term "‘comprising” in the claims and / or the specification may mean ‘‘one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or when the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” The use of the term “at least one” will be understood to include one as well as any quantity more than one, including but not limited to, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 100, or any integer inclusive therein. The term “at least one” may extend up to 100 or 1000 or more, depending on the term to which it is attached; in addition, the quantities of 100 / 1000 are not to be considered limiting, as higher limits may also produce satisfactory results. In addition, the use of the term “at least one of X, Y and Z” will be understood to include X alone, Y alone, and Z alone, as well as any combination of X, Y and Z.
[0023] As used in this specification and claims, the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.
[0024] The term “or combinations thereof’ as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof’ is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AAB, BBC, AAABCCCC, CBBAAA, CABABB,FILED MARCH 10, 2026 P2974PC01 (2025-041)and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.
[0025] Throughout this application, the terms '‘about’’ or “approximately” are used to indicate that a value includes the inherent variation of error for the apparatus or the methods or the variation that exists among the objects, or study subjects. As used herein the qualifiers “about” or “approximately” are intended to include not only the exact value, amount, degree, orientation, or other qualified characteristic or value, but are intended to include some slight variations due to measuring error, manufacturing tolerances, stress exerted on various parts or components, observer error, wear and tear, and combinations thereof, for example. The terms “about” or “approximately”, where used herein when referring to a measurable value such as an amount, percentage, temporal duration, and the like, is meant to encompass, for example, variations of ± 20% or ± 10%, or ± 5%, or ± 1%, or ± 0.1% from the specified value, as such variations are appropriate to perform the disclosed methods and as understood by persons having ordinary skill in the art. As used herein, the term “substantially” means that the subsequently described event or circumstance completely occurs or that the subsequently described event or circumstance occurs to a great extent or degree. For example, the term “substantially” means that the subsequently described event or circumstance occurs at least 90% of the time, or at least 95% of the time, or at least 98% of the time.
[0026] As used herein any reference to "one embodiment" or "an embodiment" means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.
[0027] As used herein, all numerical values or ranges include fractions of the values and integers within such ranges and fractions of the integers within such ranges unless the context clearly indicates otherwise. Thus, to illustrate, reference to a numerical range, such as 1-10 includes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, as well as 1.1, 1.2, 1.3, 1.4, 1.5, etc., and so forth. Reference to a range of 1-50 therefore includes 1, 2, 3, 4, 5, 6. 7, 8, 9. 10. 11. 12. 13, 14, 15, 16, 17, 18, 19, 20, etc., up to and including 50, as well as 1.1, 1.2, 1.3, 1.4, 1.5, etc., 2.1, 2.2, 2.3, 2.4, 2.5, etc., and so forth. Reference to a series of ranges includes ranges which combine the values of the boundaries of different ranges within the series. Thus, to illustrate reference to a series of ranges, for example, a range of 1-1,000 includes, for example, 1-10, 10-20, 20-30, 30-40, 40-50. 50-60, 60-75, 75-100, 100-150, 150-200, 200-250, 250-300, 300-400, 400-500, 500-750, 750-1,000, and includes ranges of 1-20, 10-50, 50-100, 100-500, and 500-1,000. The range 100FILED MARCH 10, 2026 P2974PC01 (2025-041)units to 2000 units therefore refers to and includes all values or ranges of values of the units, and fractions of the values of the units and integers within said range, including for example, but not limited to 100 units to 1000 units, 100 units to 500 units, 200 units to 1000 units, 300 units to 1500 units, 400 units to 2000 units, 500 units to 2000 units, 500 units to 1000 units, 250 units to 1750 units, 250 units to 1200 units, 750 units to 2000 units, 150 units to 1500 units, 100 units to 1250 units, and 800 units to 1200 units. Any two values within the range of about 100 units to about 2000 units therefore can be used to set the lower and upper boundaries of a range in accordance with the embodiments of the present disclosure.
[0028] As used herein any reference to "we" as a pronoun herein refers generally to laboratory personnel or other contributors who assisted in the laboratory' procedures and data collection and is not intended to represent an inventorship role by said laboratory personnel or other contributors in any subject matter disclosed herein.
[0029] Returning now' to the various embodiments disclosed herein, several non-limiting examples w ill be described and discussed. As previously noted, prior art DIW ink formulations struggle to meet the rheological properties required for the extrusion of the ink during DIW processes, while also meeting the mechanical properties of the finished printed specimens. In many cases, prior art DIW inks formulated for improved dispensing during the printing process produce parts with insufficient structural strength and rigidity. To overcome these deficiencies in the prior art. the FRVI formulated in accordance with exemplary’ embodiments includes an increased fiber concentration to improve printed specimen properties, and carefully formulated rheological modifiers required to permit accurate application through the DIW printing process. The FRVI formulations disclosed herein make possible the production of printed specimens that have superior and customizable mechanical attributes and print qualities.
[0030] In the past, efforts to improve the mechanical properties of parts printed with DIW techniques have focused on the addition of continuous or discontinuous fibers. However, the prior art suffers from insufficient fiber concentration, typically reaching a maximum fiber weight content of approximately 22 wt.%. The low' fiber concentration tends to increase the number of fabrication induced defects (e.g.. shrinkage and warping), leading to reduced print accuracy and impaired mechanical performance of printed parts. To overcome these deficiencies, the FRVI formulated in accordance with exemplary' embodiments includes fiber concentrations up to about 40 wt.%. The FRVI formulations disclosed herein produce specimens with high print accuracy, improved mechanical performance, and tailored architecture. Additionally, the disclosed FRVI formulations require reduced extrusion pressure (e g., about 6 psi to about 10 psi) to create printed specimens.FILED MARCH 10, 2026 P2974PC01 (2025-041)
[0031] In various embodiments, the FRVI includes a matrix material, a reinforcing filler, a first rheology modifier, and a second rheology modifier. The matrix material serves as a material binder that holds the constituents added to the mixture. In an embodiment, the matrix material is an epoxy. The epoxy may be a two-part epoxy in which the first part is an epoxy resin and the second party7is a hardener. Suitable two-part epoxies are sold under the PRO-SET® brand. The reinforcing filler strengthen specimens printed during the DIW process. In some embodiments, the reinforcing filler includes carbon fiber filler materials. Suitable carbon fiber filler materials are available from Teijin Carbon America. The carbon fiber filler materials may be cylindrical, with a length up to about ten times greater than the diameter of the carbon fiber filler materials. In some embodiments, the carbon fiber filler materials have a length of 71.14 pm ± 11.66 pm. In some embodiments, the reinforcing filler includes carbon nanotubes and graphene, which may be used alone or in combination with other carbon fiber filler materials.
[0032] The first and second rheology modifiers serve to impart shear-thinning, viscoelastic properties, and thixotropic behavior. As used herein, shear-thinning refers to a material's reduction in viscosity with increasing shear rate, and thixotropic behavior refers to a timedependent response of a material’s ability to become less viscous when agitated (e.g., stirred, subjected to stress, subjected to shear, etc.) and to return to its original viscosity when no longer agitated. In an embodiment, the first rheology7modifier is fumed silica. Suitable fumed silica is available under the AEROSIL® brand. In some embodiments, the first rheological modifier includes a blend of fumed silica and / or nano-clay. The use of fumed silica allows for regulation of FRVI viscosity, enhances interfacial adhesion between the carbon fiber filler material and the epoxy, and imparts shear thinning, viscoelastic, and thixotropic behavior. In exemplary embodiments, the second rheology modifier includes liquid-based, thixotropic additives. In exemplary embodiments, the second rheological modifier is a silicone-based liquid additive or a platinum-catalyzed silicone liquid additive. The second liquid-based rheological modifier is used to fine-tune the rheological properties of the designed FRVI and to enable the incorporation of higher weight concentrations of reinforcement filler materials.
[0033] Different embodiments of the FRVI incorporate varying concentrations of epoxy, reinforcing filler, and the first and second rheology7modifiers. In some embodiments, the FRVI incorporates epoxy concentrations ranging from about 53 wt.% to about 82 wt.%; carbon fiber filler material concentrations ranging from about 10 wt.% to about 40 wt.%; fumed silica concentrations ranging from about 2.2 wt.% to about 6.5 wt.%. and second rheological modifier concentrations of about 2 wt.%. These fumed silica concentrations were selected to balanceFILED MARCH 10, 2026 P2974PC01 (2025-041)between enhancing the matrix viscosity to stabilize fiber dispersion and allowing higher fiber content to be incorporated while preserving the desired rheological properties of the FRVI. Several non-limiting FRVI formulations (Inks 1-4) are presented in Table 1 below.TABLE 1Carbon fiber Fumed Silica Liquid-based Rheology Modifier Epoxy (wt.%) (wt.%) (wt.%) (wt.%)Ink-1 81.5 - 82.5 10 5.5 - 6.5 2Ink-2 72.5 - 73.5 20 4.5 - 5.5 2Ink-3 63.6 - 63.8 30 4.2 - 4.4 2Ink-4 55 - 55.8 40 2.2 - 3.0 2
[0034] The combination of matrix material, reinforcing material, solid state (powder) first rheology modifier, and liquid state second rheology modifier creates a three-dimensional (3D) network of the constituents within the matrix of the FRVI that responds to external stress, shear, or a combination thereof with reversible shear-thinning and viscoelastic behavior. Therefore, when external stress, shear, or a combination thereof is applied to the mixture, the 3D network temporarily breaks down, reducing the viscosity of the FRVI; the FRVI transitions to a liquidlike state, thus allowing extrusion of the FRVI. However, once the external stress, shear, or a combination thereof is removed, the 3D network within the FRVI reforms, restoring the FRVI’s initial viscosity, and the FRVI reverts to a solid-like state. This reversible shear-thinning behavior allows for DIW of freestanding structures because when an external stress, shear, or a combination thereof is applied, the FRVI transitions to a liquid-like state and the FRVI can be easily extruded and deposited accurately on a surface. Once the external stress, shear, or combination thereof is removed, the FRVI promptly reverts back to a solid-like state and can withstand the self-weight and gravitational forces experienced during layer-by-layer deposition without deformation. When the FRVI reverts back to its solid-like state, it maintains the same geometry in which it was extruded. Managing the rheological properties of the FRVI is helpful for achieving precise control of the DIW printing process, thereby allowing printed specimens to accurately reflect design architectures and geometries.
[0035] Turning to FIG. 1, shown therein is a depiction of the viscosity of the FRVI ink formulations presented in Table 1 with increasing shear rate. The FRVI formulations exhibit significant shear-thinning behavior, with viscosity7decreasing by anywhere from about two and about three orders of magnitude as the shear rate applied to the FRVI increases from about 0.01 s’1to about 30 s’1. The increase in shear rate can be caused by the application of external stress, shear, or a combination thereof (e g., applying pressure to the FRVI while it is contained withinFILED MARCH 10, 2026 P2974PC01 (2025-041)a dispenser). At a shear rate of about 0.01 s'1the FRVI formulations exhibit a viscosity ranging between about 1.000 Pa s to about 11.000 Pa s. As the shear rate increases to about 30 s'1the viscosity of the FRVI formulations decreases to a range between about 5 Pa s to about 30 Pa s.
[0036] As shown in FIG. 1, the initial viscosity is directly proportional to the concentration of fumed silica in each of the FRVI formulations listed in Table 1. As the fumed silica content is reduced, the initial viscosity of the FRVI formulations also decreases. It will be noted that the changes in viscosity as shear rate is applied to the FRVI is reversible. As shear rate decreases, the viscosity of the FRVI formulations will increase to initial, pre-shear values. Lower viscosity levels of the FRVI allows for the use of smaller extrusion orifices during DIW deposition, which makes possible the high-resolution deposition of the FRVI.
[0037] The FRVI formulations are highly correlated with analytical expectations and models based on the Herschel-Bulkley fluid model provided below, as shown in FIG. 1. The rheological parameters of the FRVI for specific FRVI formulations are presented in Table 2. The numbered FRVI inks in Table 2 correspond to the FRVI formulations provided in Table 1.where, rj = viscosity (Pa s),T0= shear yield stress (Pa),y = shear rate (s'1),K = consistency index (Pa s); andn = flow index.TABLE 2Inks K n ioPa s PaInk 1 10.24 0.98 144.49Ink 2 32.04 0.93 78.16Ink 3 5.11 0.95 12.93Ink 4 30.21 0.59 18.86
[0038] The FRVI exhibits viscoelastic properties in its storage modulus (G ) and loss modulus (G"), as depicted in FIG. 2. FIG. 2 presents the storage modulus and loss modulus for the FRVI formulations of Table 1. For example, the curve of Il-G' correlates with the FRVI formulation of Ink-1 in Table 1 and is depicted by a solid black line. The curve of Il-G" correlates with the FRVI formulation of Ink-1 in Table I and is depicted by a dotted black line. The FRVI exhibitsFILED MARCH 10, 2026 P2974PC01 (2025-041)elastic behavior (G' is greater than G") when the applied shear stress is less than the FRVI’s shear yield stress (r0). However, once the applied shear stress exceeds the FRVFs shear yield stress (T0), G" becomes greater than G' and the FRVI transitions from a solid-like state to a liquid-like state. Therefore, r0is the stress threshold where the FRVI transitions between liquid-like and solid-like states. During the specimen printing process it is important that the FRVI has an appropriate T0SO that extruded FRVI can withstand its own weight without transitioning to its liquid-like state (e.g., preventing smudging, slumping or sagging of the multi-layered printed geometry under its own weight). It should be noted that as fumed silica concentration increases, the shear yield stress (T0) of the FRVI increases and the storage modulus (G ) of the FRVI increases. This trend can be seen in FRVI formulations for Inks 1 to 3 by comparing Table 1, Table 2, and FIG. 2. Furthermore, substantial increase in carbon fiber filler material weight concentration (i.e. 40 wt.%) as well as slight reduction in silica weight content as seen in Table 1 for Ink 4 can increase the storage modulus (G ) substantially while maintaining similar range of values for the shear yield stress of the FRVI when compared to Inks 1-3. Across the FRVI formulations provided in Table 1, it can be seen in FIG. 2 that the FRVI’s storage modulus (G') ranges from about 1,857 Pa to about 6,326 Pa at the lowest oscillatory shear stress and in Table 2 that the FRVFs shear yield stress (T0) values range from about 12.93 Pa to about 144.49 Pa.
[0039] FIG. 3 depicts a method 100 for creating an exemplary embodiment of the fiber-reinforced viscoelastic ink (FRVI). First, at step 102, the epoxy resin and first rheological modifier (fumed silica) are mixed to enhance the viscosity7and impart desired rheological properties to the epoxy by creating a primary reversible 3D silica network within the epoxy resin. The silica-infused epoxy resin can be prepared by blending the epoxy resin and fumed silica together using a planetary mixer (e g., a mixer that mixes its contents along two axes) at a minimum of about 2000 rpm for at least about two minutes. The mixing time does not have to be completed in one continuous step: for example, mixing may occur for about one minute, then allowing the epoxy resin and fumed silica mixture to rest for a predetermined time, and then mixing for about one minute. The use of a planetary mixer encourages the elimination of entrapped voids while maintaining a sufficient shear to encourage good mixing and / or dispersion of the fumed silica.
[0040] Next, at step 104. a quantity of carbon fiber filler material is added to the silica-infused epoxy resin. The carbon fiber filler material creates a secondary 3D network within the silica-infused epoxy resin upon mixing and dispersion. At step 106, the carbon fiber filler materialFILED MARCH 10, 2026 P2974PC01 (2025-041)and silica-infused epoxy resin are mixed to produce a fiber-reinforced, silica-infused epoxy resin. Mixing of the silica-infused epoxy resin and carbon fiber filler material can occur within a planetary mixer at a minimum of about 2000 rpm for at least about one minute. At step 108, a determination is made about whether the desired concentration of carbon fiber filler material has been reached. This determination may be made manually by observation or direct measurement. If the desired carbon fiber filler material concentration has not been reached, the method 100 cycles back to step 104 and a subsequent quantity of carbon fiber filler material is added to reach the desired weight concentration of carbon fiber filler material in the silica-infused epoxy resin. In some cases, if the concentration of carbon fiber filler material is high at step 108, the fiber-reinforced epoxy can be diluted with an additional volume of silica-infused epoxy resin.
[0041] If the desired concentration of carbon fiber filler material has been added to the fiber-reinforced epoxy at step 108, the method progresses to step 110, where a volume of epoxy hardener is added to the fiber-reinforced, silica-infused epoxy resin. At step 112, the fiber-reinforced, silica-infused epoxy resin and epoxy hardener are mixed together to produce a fiber-reinforced, silica-infused epoxy. Suitable mixing can be provided with a planetary mixer at a minimum of about 2000 rpm for at least about two minutes. The mixing time does not have to be completed in one continuous step. For example, mixing may occur for about one minute, allowing the fiber-reinforced, silica-infused epoxy resin and epoxy hardener mixture to rest for a predetermined time, and then mixing for about one minute.
[0042] At step 114, the liquid-based rheology modifier is added to the fiber-reinforced, silica-infused epoxy. At step 116, the liquid-based rheology modifier is mixed with the fiber-reinforced, silica-infused epoxy to produce the fiber-reinforced viscoelastic ink (FRVI). The liquid-based rheology modifier and the fiber-reinforced, silica-infused epoxy can be mixed with a planetary mixer. Suitable mixing can be completed at about 2000 rpm for about one minute. In exemplary embodiments, steps 114 and 116 can be carried out promptly after step 112, without waiting for an exothermic reaction to complete. Lastly, in some embodiments, the FRVI can be defoamed and degassed at step 118.
[0043] In another embodiment, steps 110 and 112 may be completed after steps 114 and 116. Once the epoxy hardener is added and mixed in steps 110 and 112, a chemical reaction is initiated that begins a polymerization process, thereby setting the pot life of the mixture. The pot life of the mixture is carried over to the FRVI produced at the completion of step 118. During the pot life of the FRVI, the FRVI maintains its reversible shear-thinning behavior.FILED MARCH 10, 2026 P2974PC01 (2025-041)Therefore, the steps 110 and 112 should be conducted when the FRVI can be used for DIW during its pot life. In an embodiment, the pot life of the FRVI is about two hours.
[0044] Turning to FIG. 4, shown therein is a method 200 for creating a printed specimen using the FRVI as disclosed herein. At step 202, a quantity of FRVI is provided using the method 100. Next, at step 204, the FRVI created using method 100 is loaded into a dispenser. The dispenser includes an orifice through which the FRVI may be extruded and a mechanism by which external pressure can be applied to the contained FRVI (e.g., a syringe with a plunger). Then, in step 206, the FRVI is degassed and defoamed.
[0045] Next, in step 208, the dispenser is mounted into a direct ink writing (DIW) printer. The DIW printer includes an extrusion head, a control unit, a build platform, a 3D motion mechanism, a pneumatic hose, a pneumatic valve, and a pressure regulator. Suitable DIW printers are available from the Direct Ink Writing by SY GNIS company under the F-NIS brand.
[0046] Then, in step 210, the DIW printer is activated. On activation, the DIW printer applies an external stress, shear, or combination thereof to the FRVI. In an embodiment, the external stress, shear, or combination thereof is achieved by exerting a pneumatic pressure in the FRVI dispenser. The applied pressure is a static / fixed pressure value that does not change with time. Pressure is applied via the pneumatic hose and regulated via pneumatic valve. The pressure regulator prevents the applied pneumatic pressure from exceeding a predetermined level, e.g., about 10 pounds per square inch (psi). The applied pressure allows the DIW printer to modulate the state of the FRVI between solid-like and liquid-hke. Once sufficient pressure is applied to the FRVI, the FRVI transitions to a low viscosity, liquid-like state, thereby allowing the FRVI to flow from the dispenser with liquid-like behavior. The FRVI disclosed herein is formulated so that when pressure is removed, the FRVI returns to a solid-like state and will not be extruded from the dispenser.
[0047] In some embodiments, the applied extrusion pressure ranges from about 0 psi to about 10 psi, and more particularly about 6 psi to about 10 psi. This is an important distinction over prior art DIW systems, where the extrusion pressures applied by the DIW system are greater than about 20 psi and often reach about 200 psi. Many of the embodiments of the FRVI formulations disclosed herein permit the use of low-pressure DIW systems that apply extrusion pressures of between about 6 psi and about 10 psi. For the FRVI formulations disclosed herein, this pressure range provides the desired w all dimensions, print resolution, and quality of the printed architecture.
[0048] At step 212 the FRVI is extruded from the nozzle of the DIW printer. The novel FRVI created by method 100 can be formulated for extrusion through nozzles of various sizes andFILED MARCH 10, 2026 P2974PC01 (2025-041)geometries. The nozzle can have various cross-sectional geometries (e.g., circular cross section, elliptic cross section, etc.), and within a given geometry can vary in size (e.g.. for a circular cross section may have a diameter of 0.41 mm or 0.58 mm). Larger nozzles produce thicker walls, more wall-to-wall interaction, and reduced geometric precision during deposition; however, smaller nozzles may become clogged with ink containing high concentration of reinforcing filler. Additionally, larger nozzles deposit an increased amount of FRVI, while smaller nozzles deposit a decreased amount of FRVI.
[0049] The FRVI is extruded onto the build platform or directly onto a previous deposition of FRVI during a multilayer build. Once the FRVI is extruded, the extrusion pressure and resulting shear stress are no longer applied to the FRVI, allowing the FRVI to transition back to a solid-like state, capable of supporting multiple subsequent layers of FRVI without deforming. Once the FRVI is fully extruded to form the desired architecture, the extruded FRVI is pre-cured at room temperature for about eight hours in step 214. After the extruded FRVI is pre-cured, the extruded FRVI will be post cured for eight hours at about 82 °C in step 216. The pre-curing and post-curing steps create strong bonds between adjacent printed layers, as well as strong bonds between edges of the geometries of the specimen. In some embodiments, about 70% of the carbon fibers within the extruded FRVI are aligned along the print path by ±5°.
[0050] In other embodiments, the FRVI is deposited using a manual injector 300, as depicted in FIG. 7. The FRVI is placed in a dispenser 302 and loaded into the manual injector 300 and manually extruded onto a deposition surface 304. Suitable manual injectors 300 include a plunger 306 and piston 308 that is manually' advanced through a cylinder 310 by a ratchet mechanism 312. The dispenser 302 may include a pressure regulator that prevents pressure applied to the FRVI from exceeding a predetermined amount (e.g., 10 psi). Various FRVI formulations may include different predetermined pressure limits (e.g., ranging from about 6 psi to about 10 psi). This enables in-situ extrusion and deposition of the FRVI.EXPERIMENTAL
[0051] Four test FRVIs (II, 12, 13, 14) were prepared according to the formulations described in Table 1 using the preparation method 100. Test parts were produced in a variety of geometries, including those depicted in FIG. 5. The test parts were produced with the printing method 200 using each of the four test FRVIs. Table 3 describes the properties and dimensions of the test parts. Within Table 3, the test parts are identified with a nomenclature of “la-P-Iy” wherein a represents the type of FRVI used to create the test part (e.g., a = 1 indicates that Ink-1 according to the formulation of Table 1 was used); 3 indicates the geometry of the test part, with P = H representing a hexagonal cell geometry, = T representing a triangular cellFILED MARCH 10, 2026 P2974PC01 (2025-041)geometry, and = S representing a square cell geometry; and y indicates the infill concentration of the geometries (e.g., y = 30 indicates an infill concentration of about 30% while y = 50 indicates an infill concentration of about 50%). Within Table 3, W indicates the width of the test part; H represents the height of the test part; T represents overall thickness of the test part; s, h, and 1 represent the size of the cell within the test part; ti and t2 represent cell wall thickness for inclined walls and vertical walls, respectively; ph represents core density, wherein ph is calculated as ph= based on nominal mass, width, height, and thickness of the test part; prrepresents relative density; psrepresents density of the base material and was measured using a gas pycnometer (AccuPyc II 1340); and 0 represents the cell wall angle.TABLE 3mm mm mm mm mm deg mm mm mm g g / cc g / cc I1-H-I30 21.7 3.8 21.3 3.5 2.2 60 0.92 1.84 3.59 0.92 0.53 1.10 0.48 I1-H-I40 20.4 4.0 23.8 2.8 1.4 60 1.18 1.91 2.19 1.37 0.71 1.10 0.65 11-H-I50 19.0 3.7 24.8 2.3 0.9 60 1.05 1.78 1.43 1.38 0.78 1.10 0.71 12-H-I30 21.1 3.4 21.6 3.5 2.2 60 1.03 1.88 3.40 0.97 0.62 1.05 0.59 I2-H-I40 20.3 3.6 23.8 2.8 1.4 60 1.03 1.78 2.20 1.21 0.70 1.05 0.67 12-H-I50 19.1 3.6 25.1 2.3 0.9 60 1.00 1.75 1.49 1.37 0.79 1.05 0.75 13-H-I30 21.9 3.4 21.8 3.5 2.2 60 1.13 2.08 3.39 1.00 0.61 0.89 0.69 I3-H-I40 20.1 3.6 24.0 2.8 1.4 60 1.13 2.00 2.12 1.16 0.66 0.89 0.74 13-H-I50 19.4 3.6 25.3 2.3 0.9 60 1.11 1.83 1.46 1.30 0.74 0.89 0.83 14-H-I30 21.2 4.6 22.2 3.5 2.2 60 1.39 2.51 2.99 1.32 0.62 0.92 0.67 I4-H-I40 19.9 4.4 24.1 2.8 1.4 60 1.28 2.23 1.89 1.44 0.69 0.92 0.75 I4-H-I50 19.3 4.3 25.3 2.3 0.9 60 1.12 1.86 1.38 1.47 0.71 0.92 0.77 I1-T-I30 21.4 3.6 20.2 — 10.2 60 0.87 — 7.72 0.48 0.31 1.10 0.28 I1-T-I40 18.7 3.6 21.4 — 6.9 60 0.77 — 4.98 0.56 0.39 1.10 0.35 11-T-I50 18.1 3.6 23.3 — 5.5 60 0.75 — 3.83 0.66 0.44 1.10 0.40 12-T-I30 20.9 3.1 20.5 — 10.2 60 1.20 — 7.53 0.46 0.34 1.05 0.33 I2-T-I40 18.2 3.3 21.9 — 6.9 60 1.05 — 4.88 0.59 0.45 1.05 0.42 12-T-I50 17.9 3.4 23.4 — 5.5 60 0.82 — 3.92 0.61 0.43 1.05 0.41 13-T-I30 20.8 3.4 20.6 — 10.2 60 1.13 — 7.45 0.46 0.31 0.89 0.35 I3-T-I40 18.3 3.4 21.8 — 6.9 60 1.11 — 4.78 0.58 0.42 0.89 0.47 13-T-I50 17.5 3.5 23.8 — 5.5 60 1.06 — 3.66 0.74 0.50 0.89 0.57 14-T-I30 20.8 4.0 21.1 — 10.2 60 1.31 — 6.95 0.64 0.37 0.92 0.40 I4-T-I40 17.9 4.1 22.3 — 6.9 60 1.33 — 4.29 0.80 0.49 0.92 0.53 I4-T-I50 17.4 4.0 24.1 — 5.5 60 1.16 — 3.37 0.88 0.52 0.92 0.57 I1-S-I30 21.3 3.6 24.4 5.3 5.3 90 1.09 1.97 4.97 0.95 0.50 1.10 0.45 I1-S-I40 22.6 3.8 27.0 4.0 4.0 90 1.23 1.93 3.67 1.35 0.58 1.10 0.53 11-S-I50 19.2 3.6 21.9 3.2 3.2 90 1.16 1.83 2.94 0.97 0.64 1.10 0.58 12-S-I30 21.2 3.5 24.4 5.3 5.3 90 1.18 1.98 4.96 0.91 0.51 1.05 0.48FILED MARCH 10, 2026 P2974PC01 (2025-041)T pct„ t W T H H L 9 h tz S m p Phpsp artrmm mm mm mm mm deg mm mm mm g g / cc g / cc I2-S-I40 22.8 3.4 26.9 4.0 4.0 90 1.00 1.78 3.82 1.12 0.55 1.05 0.52 12-S-I50 19.5 3.4 22.2 3.2 3.2 90 1.13 1.86 2.94 0.97 0.65 1.05 0.62 13-S-I30 21.2 3.4 24.3 5.3 5.3 90 1.05 1.85 5.15 0.75 0.43 0.89 0.49 I3-S-I40 22.6 3.6 27.0 4.0 4.0 90 1.14 1.90 3.74 1.13 0.51 0.89 0.57 13-S-I50 19.3 3.6 22.1 3.2 3.2 90 1.05 1.76 3.11 0.84 0.55 0.89 0.62 14-S-I30 20.6 4.3 24.9 5.3 5.3 90 1.63 2.59 4.41 1.10 0.50 0.92 0.54 I4-S-I40 22.2 4.4 27.7 4.0 4.0 90 1.85 2.65 3.01 1.66 0.62 0.92 0.67 I4-S-I50 18.8 4.5 22.8 3.2 3.2 90 1.60 2.51 2.50 1.33 0.69 0.92 0.75
[0052] The test parts of Table 3 underwent in-plane compression tests to determine the mechanical properties of the test parts. Compression tests were conducted on the test parts with a hexagonal infill — the results of which are presented in FIG. 6, wherein compression was applied to a double walled member of the test part. FIG. 6A depicts the in-plane compressive stress results, and FIG. 6B presents the same in-plane compressive stress results over a low strain regime. Results of the in-plane compression tests indicate that increasing carbon fiber content in the FRVI significantly enhances the stiffness and strength of in-plane compression-tested honeycomb core test parts (e.g., I4-T-I50. 14-H-I50, and I4-S-I50 test parts demonstrate respective stiffness improvements of 70%, 13%, and 81%. and strength gains of 49%, 36%, and 84% over 11 -T-I50, 11-H-I50, and I1-S-I50 test parts, respectively).
[0053] Table 4 presents a summary of tensile test results. Tensile testing was accomplished following ASTM D638 Type-V standards using the FRVIs with the compositions of Table 1. Optical microscopy analysis confirmed homogenous fiber distribution and strong fiber-matrix bonding.TABLE 4Stfffoess Tensile Strength Density Test Part Name (s) (Ps) (GPa) (MPa) (g / cc) 11-L 1.08 ± 0.15 62.75 ± 1.55 1.1 12-L 1.66 ± 0.12 73.57 ± 5.07 1.05 13-L 2.00 ± 0.19 76.92 ± 2.80 0.89 14-L 3.08 ± 0.17 85.94 ± 3.73 0.92
[0054] Test parts with hexagonal cell patterns also underwent surface roughness analysis, the results of which are show n in Table 5. As shown in Table 5, values for surface roughness onFILED MARCH 10, 2026 P2974PC01 (2025-041)the test parts were low, and in some cases approaching a surface roughness of 13-30 pm. In comparison, surface roughness for polylactide composites (“PLA?’) can range from -453.6 pm to 446.8 pm (with a specific PLA having an average surface roughness of 32 ± 5.2 pm), while typical carbon fiber-reinforced composites have been measured with a surface roughness ranging from 236.8 pm to 552.8 pm (with a specific continuous fiber reinforced composite having an average surface roughness of 19 ± 2.6 pm post application roller press after fabncation). The reduced roughness of the test parts produced with the test FRVIs is attributed to the consistent rheological properties of the inks, the semi-elliptical cross-section of the DIW-printed filaments, and the absence of print path overlap. Moreover, the inks designed in this study exhibit the desired rheo-viscoelastic properties, demonstrating strong shear-thinning behavior and high storage modulus. These consistent and comparable properties enable smooth extrusion, uniform layer stacking, and geometry preservation while minimizing surface defects such as surface irregularities and warping.TABLE 5Surface roughness SaHoneycomb structures(pm)11-H-I30 / 40 / 50 20.3712 -H -130 / 40 / 50 13.5613-H-I30 / 40 / 50 30.9714-H -130 / 40 / 50 22.96
[0055] It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Claims
FILED MARCH 10, 2026 P2974PC01 (2025-041) What is claimed is:
1. A fiber-reinforced viscoelastic ink for use in direct ink writing, the fiber-reinforced viscoelastic ink comprising:a matrix material;a reinforcing filler, wherein the reinforcing filler comprises about 10 wt.% to about 40 wt.% of carbon fiber filler material;a first rheology modifier; anda second rheology modifier.
2. The fiber-reinforced viscoelastic ink of claim 1, wherein the matrix material comprises an epoxy.
3. The fiber-reinforced viscoelastic ink of claim 2, wherein the epoxy comprises: a first-part epoxy resin; anda second-part epoxy hardener.
4. The fiber-reinforced viscoelastic ink of claim 3, wherein the first rheology modifier comprises fumed silica.
5. The fiber-reinforced viscoelastic ink of claim 4, wherein the fiber-reinforced viscoelastic ink comprises about 55 wt.% to about 82.5 wt.% of epoxy.
6. The fiber-reinforced viscoelastic ink of claim 5, wherein the fiber-reinforced viscoelastic ink comprises about 2.2 wt.% to about 6.5 wt.% of fumed silica.
7. The fiber-reinforced viscoelastic ink of claim 6, wherein a majority of the carbon fiber filler material comprises carbon fiber cylinders having a length-to-diameter ratio of about 10:1.FILED MARCH 10, 2026 P2974PC01 (2025-041) 8. The fiber-reinforced viscoelastic ink of claim 4, wherein the second rheology modifier comprises a liquid based rheological modifier selected from the group consisting of silicone-based additives, platinum-catalyzed silicone-based additives, and combinations thereof.
9. The fiber-reinforced viscoelastic ink of claim 8, wherein the fiber-reinforced viscoelastic ink comprises about 2 wt.% of the liquid-based rheology modifier.
10. The fiber-reinforced viscoelastic ink of claim 9, wherein the fiber-reinforced viscoelastic ink comprisesabout 55 wt.% to about 82.5 wt.% of epoxy; andabout 2.2 wt.% to about 6.5 wt.% of fumed silica.
11. A method for creating a fiber-reinforced viscoelastic ink for direct ink writing, the method comprising:mixing a predetermined amount of epoxy resin and a predetermined amount of fumed silica in a first mixing process to produce a silica-infused epoxy resin; mixing a predetermined amount of carbon fiber filler material with the silica-infused epoxy resin to produce a fiber-reinforced, silica-infused epoxy resin; mixing a predetermined amount of epoxy hardener with the fiber-reinforced, silica- infused epoxy resin to produce a fiber-reinforced, silica-infused epoxy; mixing a predetermined amount of a liquid silicone-based rheology modifier with the fiber-reinforced, silica-infused epoxy fiber-reinforced epoxy to form the fiber- reinforced viscoelastic ink.
12. The method of claim 11, further comprising the step of defoaming and degassing the fiber-reinforced viscoelastic ink.FILED MARCH 10, 2026 P2974PC01 (2025-041) 13. The method of claim 11, wherein the step of mixing the predetermined amount of carbon fiber filler material further comprises:adding an incremental amount of carbon fiber filler material to the silica-infused epoxy resin;mixing the incremental amount of carbon fiber filler material into the silica-infused epoxy resin; andrepeating the steps of adding the incremental amount of carbon fiber filler material and mixing the incremental amount of carbon fiber filler material until a desired concentration of carbon fiber filler material within the fiber-reinforced, silica- infused epoxy resin is reached.
14. The method of claim 13, wherein each of the mixing processes comprise placing a mixing container in a planetary' centrifugal system to rotate contents inside the mixing container about an axis of the mixing container and a central axis of the planetary centrifugal system.
15. A method for creating a printed specimen using a fiber-reinforced viscoelastic ink, wherein the method comprises:providing a quantity of the fiber-reinforced viscoelastic ink;loading the fiber-reinforced viscoelastic ink into a dispenser;degassing and defoaming the fiber-reinforced viscoelastic ink;mounting the dispenser into a direct ink writing printer system, wherein the direct ink writing printer system comprises an extrusion head, a three-dimension motion mechanism, a pressure regulator, and a build platform;activating the direct ink writing printer system, wherein the pressure regulator of the direct ink writing printer system applies a predetermined pressure to the fiber-FILED MARCH 10, 2026 P2974PC01 (2025-041) reinforced viscoelastic ink to cause an extrusion of the fiber-reinforced viscoelastic ink through the extrusion head;extruding the fiber-reinforced viscoelastic ink through the extrusion head onto the build platform at a predetermined extrusion rate to deposit an extruded fiber- reinforced viscoelastic ink onto the build platform;pre-curing the extruded fiber-reinforced viscoelastic ink at room temperature for a predetermined pre-curing time; andpost-curing the extruded fiber-reinforced viscoelastic ink for a predetermined postcuring time at a predetermined temperature.
16. The method of claim 15, wherein the step of providing the quantity of fiber-reinforced viscoelastic ink comprises:mixing a predetermined amount of epoxy resin and a predetermined amount of fumed silica to produce a silica-infused epoxy resin;mixing a predetermined amount of carbon fiber filler material with the silica-infused epoxy resin to form a fiber-reinforced, silica-infused epoxy resin; mixing the fiber-reinforced, silica-infused epoxy resins with a predetermined amount of epoxy hardener to produce a fiber-reinforced, silica-infused epoxy; and mixing the fiber-reinforced, silica-infused epoxy and a predetermined amount of liquid silicone-based rheology7modifier to produce the fiber-reinforced viscoelastic ink.
17. The method of claim 16, wherein the step of extruding the fiber-reinforced viscoelastic ink through the extrusion head comprises the step of the extrusion head following a predetermined path controlled by the three-dimension motion mechanism, wherein the predetermined path comprises multi-stroke print paths comprising print- and non-print paths,FILED MARCH 10, 2026 P2974PC01 (2025-041) wherein the fiber-reinforced viscoelastic ink is selectively deposited along the print-paths by modifying the pressure applied to the fiber-reinforced viscoelastic ink.
18. The method of Claim 16. wherein the predetermined pressure is between about 6 psi and about 10 psi;the predetermined extrusion rate is about 10 mm / min;the predetermined pre-curing time is about eight hours;the predetermined post-curing time is about eight hours: andthe predetermined temperature is about 82 °C.