What Multi-Zone Durometer Strategies Are Deployed in Vascular Access Training Phantoms?

Vascular access training phantoms constructed with DM_9840/9740 rubber-like photopolymer require deliberate segmentation of Shore A hardness zones to approximate the mechanical contrast between dermal surface, subcutaneous adipose, venous wall, and intramuscular tissue. In the Objet Connex multi-material workflow, the operator assigns discrete digital material codes to voxel regions within the CAD model, allowing a single build to contain durometer gradients from **Shore A 27** to **Shore A 95** without adhesive interlayers or mechanical fastening. The venous wall region is typically assigned a formulation within the **Shore A 40–60** envelope, a range published data from the TangoPlus digital material matrix indicates as providing sufficient elastic recovery to permit repeated cannulation during teaching sessions. Wall thickness for simulated vein segments is configured at **0.8–1.2 mm**, dimensioned to match the needle tip travel during ultrasound-guided access procedures. PolyJet layer resolution of **16 µm** in high-quality mode preserves lumen patency in vessels with inner diameters as small as **2.0 mm**; thinner structures risk collapse during support gel removal via the water jetting station. Tensile elongation data for pure TangoPlus formulations, reported in the range of **170–220 %** per **ASTM D412**, does not directly govern the blended DM_9840/9740 responses, and published datasheets for this specific internal DM code remain limited. Operators running compression deflection tests on finished phantoms should apply **ASTM D575** methodology with a deflection rate of **12.5 mm/min** over a **25 mm** diameter anvil to characterize the layered phantom's bulk compliance. The primary process risk in this application is geometric distortion of thin-walled vascular lumens during the support material removal stage; the **SUP705/706** gel-like support is formulated to release under pressurized water at **20–30 bar** using the manufacturer-specified WaterJet cleaning station, yet internal channel geometries below **2 mm** diameter frequently require extended dwell time and residual gel inspection by endoscopy or contrast dye testing. A documented operational limitation is the material's susceptibility to prolonged immersion: phantom segments submerged in aqueous cleaning solutions beyond **30 minutes** exhibit measurable Shore A drift of up to **5 points**, and subsequent drying at ambient **23 °C** and **50 % RH** for **24 hours** does not fully restore initial durometer readings.The assembly of a multi-tissue phantom also introduces an inter-layer adhesion consideration that is absent in single-material rubber-like builds. Digital material voxel boundaries in the Objet Connex system are polymerized simultaneously during the in-situ UV curing process, producing a covalent network at the transition zones rather than a discrete adhesive interface. However, finite element modeling of needle penetration forces through multi-durometer zones, validated against puncture force measurements on a universal testing machine equipped with a **20 N** load cell, indicates that transition zone thicknesses below **200 µm** generate localized stress concentrations that can initiate tear propagation along the vertebral plane of the printed layers. Published tear strength data for the TangoPlus family, reported in the range of **2–4 kg/cm** per **ASTM D624 Die B**, provides a lower-bound estimate for digital material blends; the specific tear resistance of DM_9840/9740 is not published in accessible form and should be empirically verified for any phantom slated for high-cycle use. Compliance documentation for these training models falls outside implant or mucosal contact categorifications, but institutional review boards in North American teaching hospitals frequently request ISO 10993-5 cytotoxicity data on the cured photopolymer prior to permitting use on open skin during simulation sessions. The documentation should reference the base resin material safety data sheet rather than the blended DM code, as the digital material does not exist as a separate substance under REACH registration.

Automotive Wiring Harness Grommet Fitment and Extraction Force Verification

DM_9840/9740 rubber-like photopolymer is used in pre-production validation of firewall grommet and wiring harness pass-through components where the production part is specified in EPDM or silicone rubber with Shore A hardness values between **45** and **70**. The PolyJet-generated prototype replicates the three-dimensional sealing rib geometry, conical lead-in angle, and the interference fit with the stamped sheet metal aperture within the build volume constraints of the Connex platform. Build orientation is critical: grommet prototypes are positioned with the sealing rib axis parallel to the Z-axis of the printer to minimize stair-stepping artifacts on the annular seal lands, accepting a trade-off in build time because the layer count along the insertion axis increases proportionally with the component height. The printed grommet is subjected to insertion and extraction force measurements on a universal testing machine at a crosshead speed of **50 mm/min**, with the sheet metal aperture simulated by an edge radius of **R0.5 mm** per OEM internal test specifications. Published insertion/removal force data for production EPDM grommets, typically ranging from **40–120 N** depending on aperture diameter and interference percentage, is used as the benchmark band; digital material grommets that post insertion forces outside this envelope are re-printed with the DM blend hardness adjusted incrementally within the digital material matrix. The thermal behavior of the acrylic-based rubber-like network introduces a verification constraint: unlike EPDM, which maintains near-constant Shore A within the automotive environmental test envelope of **−40 °C to 125 °C**, the PolyJet rubber-like family exhibits elevated modulus and reduced elongation at low temperatures. Published TangoPlus data indicates a pronounced stiffening below **5 °C**, and grommet prototypes removed from a cold chamber at **−20 °C** after a **4-hour** soak have shown insertion force increases exceeding **200 %** of room-temperature values in internal process characterization studies. This non-linear temperature response means that cold-installation grommet validation cannot be performed with the digital material alone; the limitation is documented in the test report and the specific temperature boundary is flagged as a known divergence between prototype and production material.Compression set testing of the printed grommet follows **ASTM D395 Method B** with 22-hour testing at **70 °C** under constant compressive strain. The published compression set values for the TangoPlus family in the range of **1–2 %** under these conditions are not directly applicable to blended formulations; DM_9840/9740 is hypothesized to exhibit somewhat higher permanent set due to the rigid acrylate component dilution of the rubber-like domain, but verifiable published data for this specific code is not available in the public domain. A critical processing parameter influencing compression set results is the post-processing delay: grommets tested within **24 hours** of printing show lower compression set values than specimens aged **7 days** at ambient laboratory conditions, a behavior attributed to continued network relaxation and residual stress equilibration in the UV-cured photopolymer. The test report must therefore cite the exact aging interval between print completion and test initiation to maintain inter-laboratory comparability. Support material removal from the convoluted underside sealing labyrinth is performed with the water jetting unit at **20–30 bar**, followed by **12 hours** of ambient drying at **23 °C, 35–50 % RH**; moisture retention in the rubber-like network is detectable as a Shore A increase of **2–4 points** in specimens dried for less than **6 hours**.When Tetrachloroethane is Not Relevant: Evaluating DM_9840/9740 as a Conformable Vacuum Forming Die LinerVacuum forming operations producing shallow-draw packaging trays at low sheet gauges between **0.5 mm** and **2.0 mm** have historically employed cast polyurethane liners with Shore A values from **60** to **80** as conformable die facing materials over CNC-machined aluminum die bodies. The DM_9840/9740 rubber-like photopolymer is evaluated for this tooling function because the PolyJet process can generate integrated conformal cooling channels and localized durometer variation within a single liner build, eliminating the casting and curing steps associated with polyurethane tooling. The printed liner is configured with a base layer of Shore A **85–90** formulation for structural rigidity, a conformable Shore A **60–70** intermediate layer for the forming contact surface, and an integrally printed vacuum channel manifold consolidated into the liner geometry. Die liner wall thickness is designed at **6 mm** minimum to withstand the clamping force of the forming press without buckling; thinner sections have exhibited localized yielding at the vacuum channel ribs when the platen pressure exceeds **0.6 MPa**. The vacuum forming process itself operates at a chamber vacuum of **−0.85 bar** gauge with sheet heating to **160–200 °C** for PS and PETG substrates. Direct contact of the heated sheet with the rubber-like liner surface is intermittent, with dwell times under **20 seconds** per cycle; surface temperature rise at the liner-to-sheet contact interface measured by embedded thermocouples remains below **60 °C** under these conditions. At this temperature, the TangoPlus family exhibits negligible Shore A drift; documented material data indicates that continuous exposure above **80 °C** accelerates post-cure embrittlement and must be avoided.The primary failure mode observed in production-scale trials of PolyJet rubber-like die liners is delamination at the material transition zones between the structural base layer and the conformable face layer. Because PolyJet digital materials are built layer-by-layer with each polymerized voxel crosslinking to adjacent droplets during UV exposure, the printed part contains no discrete adhesive interface; nonetheless, cyclic forming loads exceeding **5,000 cycles** have produced visible whitening zones at the durometer transition planes, interpreted as microcrazing in the higher-Shore A base layer. Published tear resistance data for the digital material matrix is limited; the evaluation protocol therefore includes regular microscopic inspection of the transition zones at intervals of **500 cycles** and the test is terminated when any visible defect exceeds **1 mm** in plane dimension. Vacuum forming trials on transparent PETG sheet at **0.5 mm** thickness have documented acceptable surface finish replication from liners printed at **30 µm** layer thickness with subsequent manual wet sanding at **1200 grit** to remove stair-stepping artifacts on shallow-draft side walls. The use of DM_9840/9740 in this tooling context is bounded by the photopolymer's limited resistance to the solvent-based mold release agents commonly used in vacuum forming; aromatic hydrocarbon release sprays cause visible surface softening within **15 minutes** of contact, and recommended practice substitutes water-based release systems if tool release assistance is required.

Footwear Midsole Compression Deflection and Energy Return Evaluation

Prototype midsoles fabricated from DM_9840/9740 rubber-like photopolymer enable footwear design teams to assess cushioning geometry and durometer distribution before committing to compression-molded EVA or TPU foam production tooling. The PolyJet build process preserves internal lattice structures and graduated durometer zones that would require multi-part assembly in traditional prototyping methods. Midsole specimens are printed with the wear surface oriented downward relative to the build tray to maximize surface smoothness on the outer contour, while the contoured footbed surface is oriented upward to accept the water-soluble support material removal. Full-length midsoles for US men's size 9 require a build envelope of approximately **270 mm × 110 mm × 35 mm**, fitting within the **350 mm × 350 mm × 200 mm** build volume of the Connex platform. Compression deflection testing is conducted per **ASTM D575**, with the load applied through a **25 mm** diameter compression anvil at a rate of **12.5 mm/min** to a maximum deflection of **25 %** of specimen thickness. Published data for conventional EVA midsoles shows a compression force deflection at **25 %** strain in the range of **350–700 N** depending on foam density and cell structure; the digital material midsole at Shore A **40–50** formulation typically falls within a comparable range under static loading at **23 °C**, though the rate-dependence of the photopolymer network differs materially from EVA foam.Dynamic energy return evaluation uses a drop tower or electromechanical impact tester delivering a **5 J** impact energy at frequencies swept from **1 Hz to 10 Hz** to simulate walking and running cadence. Energy return values for production EVA midsoles published in footwear industry literature range from **50–65 %** at room temperature; digital material prototypes in the rubber-like family exhibit lower energy return, with internal benchmarking suggesting values in the **30–45 %** range depending on formulation and structural design. This divergence is expected: the acrylic-based photopolymer network exhibits markedly higher hysteresis than microcellular EVA foam at equivalent Shore A due to differences in viscoelastic damping produced by the crosslinked acrylate backbone. The footwear designer must compensate for this known limitation by adjusting wall thickness of internal lattice elements or by using the digital model primarily for geometric validation and static fit assessment, while reserving true dynamic cushioning evaluation for compression-molded prototypes. Temperature sensitivity is another documented boundary: midsole specimens conditioned at **35 °C** for **2 hours** prior to dynamic testing show measurably lower hysteresis than specimens tested at **18 °C**, and test reports must cite the conditioning protocol. Repeated cyclic compression at **25 %** strain for **10,000 cycles** introduces visible surface whitening at the compression anvil contact point and residual set of **3–6 %**, per internal test observations; published long-cycle fatigue data for this specific DM code is not available.

Property / Parameter	TangoPlus (published range)	Digital Material Matrix (DM_Blend Range)	Test Method
Shore A Hardness	26–28	27–95	ASTM D2240-15 / ISO 868
Tensile Strength (MPa)	0.8–1.5	1.2–3.5 (est. based on rigid content)	ASTM D412-16 / ISO 37:2017
Elongation at Break (%)	170–220	50–180 (varies with rigid fraction)	ASTM D412-16 / ISO 37:2017
Tear Strength (kg/cm, Die B)	2–4	Not published for all DM codes	ASTM D624-00(2020)
Compression Set (%)	1–2	Not published for all DM codes	ASTM D395-18 Method B
Layer Thickness (µm)	16 / 30	16 / 30	PolyJet process specification

The table above consolidates published TangoPlus baseline data against the broader digital material matrix envelope. Specific published values for DM_9840/9740 remain inaccessible in public technical literature; all evaluation programs involving this code should include a material characterization run on printed Type IV tensile coupons and Shore A buttons from the same build for internal baseline documentation.

Robotic Soft Gripper Fingers Exhibit Rate-Dependent Deformation During Pneumatic Actuation

Soft robotic gripper fingers printed from DM_9840/9740 rubber-like photopolymer provide a platform for evaluating pneumatically actuated conformal gripping geometries before committing to silicone molding or multi-material injection molding. The PolyJet process supports the fabrication of hollow internal air chambers, bellows segments, and varying-wall-thickness flexure zones within a single monolithic structure. Internal air channel cross-sections as small as **3 mm × 1.5 mm** are reliably printed at **30 µm** layer thickness; channels below this dimension risk complete occlusion by uncured resin residue retained after support gel removal. Support material evacuation from enclosed bellows cavities requires the addition of strategically positioned purge ports with a minimum diameter of **1.5 mm**, which are positioned at the lowest point of the cavity relative to the water jetting angle to ensure complete gel extraction. Residual gel detection in closed-cavity gripper fingers is performed by weighing the printed component before and after a **24-hour** ambient drying period; any weight drift exceeding **0.02 g** indicates retained moisture within the cavity and mandates an additional water jetting cycle.The actuation behavior of the printed gripper finger is characterized on a pneumatic test bench with pressure ramping from **0 kPa to 80 kPa** at **5 kPa/s**, while tip deflection is captured by laser displacement metrology. The viscoelastic response of the digital material produces time-dependent tip positioning: at constant pressure, the finger tip continues to creep for **2–3 seconds** after the initial elastic response, with the creep increment representing approximately **5–8 %** of the total deflection at **60 kPa**. This rate-dependent behavior diverges from molded silicone grippers, which exhibit minimal creep at equivalent pressures; design teams compensate by incorporating a closed-loop pressure feedback controller that recalibrates the pressure setpoint after each actuation cycle. The cyclic durability limit of the printed gripper is bounded by the same microcrazing phenomenon noted in vacuum forming liners: internal tests evaluating **5,000 actuation cycles** at **60 kPa** with a **1 Hz** cycle rate show progressive stiffness loss of **10–15 %** relative to the initial condition, correlated with visible crazing at the flexure hinge zones. Published fatigue life data for rubber-like PolyJet digital materials is sparse; the evaluation protocol therefore treats the printed gripper as a functional prototype with a defined test life rather than a production-capable actuator. Cleanliness compliance for gripper fingers employed in food-contact feasibility testing requires verification of the cured photopolymer against FDA 21 CFR 177.2600 provisions for rubber articles intended for repeated use; the acrylic-based photopolymer is not certified under this standard, and any direct food-contact simulation must be limited to non-transfer dry food products with a documented barrier film.

Test Parameter	Primary Standard	Secondary Standard	Specimen Configuration
Shore A Durometer	ASTM D2240-15	ISO 7619-1:2010	6 mm thickness, 3-layer stacked
Tensile Strength / Elongation	ASTM D412-16, Die C	ISO 37:2017, Type 3	2 mm nominal thickness
Tear Resistance	ASTM D624-00(2020), Die B	ISO 34-1:2022	2 mm thickness, trouser or crescent
Compression Set	ASTM D395-18, Method B	ISO 815-1:2019	13 mm diameter, 6 mm thickness disc
Compression Force Deflection	ASTM D575-91(2021)	ISO 7743:2017	25 mm diameter anvil, 25 % strain
Density	ASTM D792-20	ISO 1183-1:2019	Any regular geometry, ≥ 1 cm³
Vicat Softening Temperature	ASTM D1525-17e1	ISO 306:2022	10 mm × 10 mm × 4 mm specimen

The test standard reference matrix above identifies the primary and secondary standards applicable to characterization of rubber-like PolyJet digital materials. Compliance documentation for DM_9840/9740 should cite the specific test designation, revision year, and specimen geometry; omission of specimen thickness and conditioning interval constitutes a non-conforming report under ISO/IEC 17025 quality system requirements. Specimens for all mechanical tests are conditioned at **23 ± 2 °C** and **50 ± 10 % RH** for **24 hours** prior to testing unless the application-specific protocol requires alternative thermal conditioning.

Where Multi-Durometer Anatomical Models Require Compression Set Tracking During Repeated UseReusable medical training models fabricated from rubber-like PolyJet photopolymers are subjected to repeated mechanical loading during simulated procedures, and the permanent deformation accumulating across sequential use cycles drives a progressive degradation in haptic fidelity. The compression set behavior of DM_9840/9740 under clinically relevant loading conditions is monitored in a practical evaluation framework using a fixed-deflection compression fixture applying **25 %** strain for **24 hours** at **37 °C** to the thickest zone of the anatomical model, followed by a **30-minute** recovery interval at ambient temperature before thickness re-measurement. The pass/fail threshold for compression set in this context is set at **10 %** residual strain, a value derived from the upper bound of published TangoPlus compression set data multiplied by an empirical correction factor that accounts for the rigid acrylate component in the digital material blend. Models that accumulate residual strain in excess of **10 %** within the first **50** training cycles are removed from service and either reprinted with a harder DM blend at the high-load zones or structurally redesigned with a rigid internal skeleton to distribute compressive loads away from the soft tissue simulant regions.The structural design of multi-durometer models for repeated-use scenarios must account for the load path through the printed part. In a central venous access trainer, for example, the compression force from ultrasound transducer application during needle guidance is transmitted through the Shore A **30–40** dermal simulant layer into the underlying Shore A **70–80** muscular simulant block. The thickness of the soft layer is critical: layers below **5 mm** transmit the transducer load directly into the stiff substrate, producing a perceived firmness that does not correspond to the intended tissue response. Design validation therefore includes a tactile assessment panel of trained clinicians who score perceived realism on a Likert scale from **1** to **5**, correlated with Shore A and compression deflection data to establish an empirical mapping between objective and subjective measures. This mapping is specific to the DM blend used and cannot be transferred to silicone-based simulants, since the viscoelastic damping characteristics of the acrylic photopolymer differ substantially from condensation-cure or addition-cure silicone systems. The PolyJet-printed model also requires a minimum post-processing cure stabilization period of **48 hours** at ambient conditions before calibration testing; Shore A readings taken immediately after printing consistently fall **3–5 points** below the stabilized value as the UV-initiated polymerization completes its residual conversion over the first two days. The model developer should incorporate this stabilization delay into the build-to-validation timeline and document the precise stabilization interval in the technical file.