3D Systems VisiJet RBK-ENT-D55 Multi-Material Composites (VisiJet CR-BK + VisiJet CE-NT) is configured as a multi-material build option for MJP platforms. The material assignment joins a rigid black domain, VisiJet CR-BK, with a natural elastomeric domain, VisiJet CE-NT, to produce a monolithic anatomical model with spatially differentiated Shore hardness. The name RBK-ENT-D55 indicates rigid-black/elastomer-natural ENT anatomy with a nominal composite Shore D 55 target. Published data for this exact configuration is limited; therefore all critical mechanical properties must be verified on test coupons printed in the same build orientation and with the same support wax protocol as the final part.

The deposition method is multi-jet printing rather than vat photopolymerization or powder-bed fusion. A printhead array deposits UV-curable acrylic droplets of CR-BK and CE-NT in the same layer, followed by flattening and UV irradiation. The result is a voxel-level composite in which the local phase ratio determines stiffness. Unlike filled resin systems, the composite does not rely on dispersed particulate fillers; it derives its mechanical contrast from the relative proportion of rigid and elastomeric photopolymer voxels. This creates a continuous transition between osseous and mucosal mechanical domains, but it also means that local properties are sensitive to jet health, UV dose uniformity, and layer thickness. For surgical rehearsal applications, the composite is typically assigned to temporal bone models, nasal septal models, and sinus access trainers where a rigid black structural analogue and a natural compliant analogue must remain in one build.

Processing Constraints and Voxel-Grade Thermal Profiles

Multi-material MJP builds require active control of ink viscosity, jetting waveform, and UV irradiance. The juxtaposition of CR-BK and CE-NT introduces differential polymerization shrinkage: rigid domains acquire modulus rapidly during cure, while elastomeric domains continue to relax after the build. The interface plane should be oriented so that shear stress during part removal and support wax melting does not act directly on a thin compositional transition. Printhead nozzle health is a dominant variable in production-scale systems. A single misfiring nozzle in the CE-NT channel can cause local drift toward the CR-BK phase, producing a hard streak across a soft-tissue analogue. Daily drop mass checks, wire voltage calibration, and nozzle purge cycles reduce this failure mode. UV lamp uniformity should be measured periodically because non-uniform irradiation changes the local degree of cure and therefore the Shore hardness of CE-NT. In an MJP cavity build, the layer thickness is material-profile dependent; switching from a single-phase CR-BK profile to the RBK-ENT-D55 composite profile can alter wax adhesion and cleanability.

The wax support material used in MJP is removed by thermal melting. CE-NT is more thermally compliant than CR-BK, so support removal ovens must be profiled to avoid hot spots. The wax removal cycle should be selected to exceed the wax melting point without exceeding the recommended cleaning temperature for the composite. Internal ENT cavities such as the ethmoid infundibulum, frontal recess, and sphenoid ostium require drainage design; a closed cavity can trap molten wax and leave residue. After support removal, the model should be inspected with an otoscope or borescope. Residual wax and residual solvent are different defects: wax is hydrophobic and may be removed by mineral oil; uncured acrylic residue is polar and may be removed by isopropyl alcohol. This diagnostic distinction should not replace the manufacturer’s cleaning protocol.

Storage of uncured cartridges before use influences jetting stability. Acrylic photoinitiator settling can occur, so cartridges should be brought to a controlled ambient condition and gently mixed according to the supplier instruction. Typical handling for this class of photopolymer uses a dark storage environment between 18–28°C and avoids condensation at relative humidity above 60%. Condensation can alter surface tension and cause irregular droplet formation. Open cartridges should be used within the manufacturer’s specified shelf life; aging resin may increase viscosity and produce jet dropout at the elastomer channel. Production logs should record cartridge lot numbers, printhead serial number, UV lamp age, support wax lot, and oven cycle trace because these variables are necessary to interpret batch-to-batch hardness variation.

Where Does RBK-ENT-D55 Diverge From Single-Phase VisiJet Materials?

The primary difference is monolithic multi-material continuity. VisiJet CR-BK alone provides a rigid black model for bone-only anatomy, while VisiJet CE-NT alone provides a natural elastomeric model for soft-tissue-only anatomy. RBK-ENT-D55 permits both material responses in one build without adhesive bonding, pinning, or silicone overmolding. This eliminates assembly seams and reduces labor, but it also creates a composite whose macroscopic properties are not equal to either component. Maximum rigidity, flexural modulus, and impact resistance of CR-BK are reduced in transition zones; maximum elongation, tear resistance, and surface compliance of CE-NT are not fully realized where rigid voxels are concentrated. A D55 composite is therefore not a substitute for high-shore rigid models when absolute stiffness is required, nor a substitute for very soft elastomer models when extreme deformation is required. It is an intermediate anatomical simulation material.

Compared to MJP single-phase materials, the RBK-ENT-D55 composite consumes a more complex slicing profile and requires more rigorous process control at the material boundary. Compared to PolyJet multi-material systems, which use a removable photopolymer support, the MJP wax support approach enables drainage of deep cavities if correctly vented, but introduces a thermal cleaning step that can soften CE-NT if uncontrolled. Compared to single-material fused filament fabrication or stereolithography anatomical models, RBK-ENT-D55 provides spatially differentiated stiffness without printing separate bone and soft-tissue components. This reduces surface contour interruption and preserves small anatomical features that are frequently lost during assembly.

Solvent compatibility for multi-material ENT models is governed by the CE-NT phase and the CR-BK interface. Ketone, ester, and chlorinated solvents can cause crazing, plasticization, or surface tack in acrylic photopolymers. Prolonged immersion in isopropyl alcohol should be avoided because it can extract unreacted monomer from the elastomer domain and leave a tacky surface. Aqueous rinsing in deionized water with controlled temperature and time is preferred after support removal. If the model is used with cadaveric tissue preservation fluids, lubricants, or silicone sprays, those fluids must be screened against the CE-NT phase, because soft acrylic networks can swell in low-polarity oils. The CR-BK phase is less sensitive to hydrocarbon exposure, but interfacial solvent ingress can still reduce bond strength. Operators should not apply aromatic hydrocarbons, aggressive alkaline cleaners, or high-pressure steam without explicit validation from 3D Systems.

When Support Wax Retention Masquerades as a Material Defect

Incomplete wax removal is frequently misinterpreted as delamination or incomplete cure in the D55 composite. The lower thermal conductivity of the elastomeric phase can shield wax in blind cavities. A model printed without a vent hole near a low point will retain molten wax during the cleaning cycle; the wax cools to a waxy deposit that is mistaken for polymer blooming. The build should include drainage ports at the lowest cavity point or an auxiliary vent in a non-functional surface. After cleaning, internal channels should be inspected. Wax residue can be differentiated from CE-NT surface bloom by a mineral oil wipe test, because mineral oil removes wax without dissolving cured elastomer. A polar solvent such as isopropanol removes acrylic monomer residues but can contribute to surface tack if overused. This diagnostic procedure does not replace a validated cleaning cycle for medical simulation models.

Design rules for the composite should respect the anisotropic nature of MJP layering. Z-direction tensile strength is generally lower than in-plane strength in layered photopolymer parts, and the differential compliance of CR-BK and CE-NT can accentuate edge curls at thin transitions. Abrupt transitions between stiff and soft phases should be replaced with a graded transition zone sized for the anatomy and validated by durometer or micro-CT. Thin soft-tissue flaps in CE-NT are prone to tearing during support removal if they are isolated and unsupported; sacrificial ribs or thickening outside the region of interest improve survival. Hollow structures should be vented to prevent trapped wax and to reduce hydrostatic loading during cleaning. Sharp corners and knife-edge geometries should be avoided at the rigid phase, because CR-BK is brittle in thin sections. The final part should rest in a dark, low-humidity environment for at least 24 h before final dimensional verification, because acrylic post-cure relaxation can shift dimensions in multi-material parts.

Qualification of RBK-ENT-D55 for anatomical evaluation or surgical rehearsal should be structured around a standards matrix. The methods listed below are applicable test approaches; listing does not imply that the material is certified under any particular medical device pathway.

Dimensional tolerance and feature fidelity are not solely determined by the material. The D55 composite inherits the geometric resolution of the MJP print mode and the quality of the segmentation. For middle ear structures below the minimum feature resolution, manual segmentation and verification by micro-CT or optical metrology are necessary. The D55 composite cannot recover anatomy that is absent from the source DICOM. Thresholding errors in CT segmentation will produce a rigid CR-BK region where thin bone is present or a compliant CE-NT region where mucosal thickening is misclassified. DICOM slice thickness should be recorded and used to determine the smallest confidently reconstructable feature. Clinical use of the model for surgical assessment should be preceded by local validation with reference phantoms.

Rheological details of the two component resins are not published as part of the RBK-ENT-D55 data package. However, jetting stability in MJP depends on viscosity at jetting temperature, typically adjusted through the printhead heater setpoint. The natural CE-NT phase may require a different printhead temperature than the rigid CR-BK phase. Multi-material printing systems either maintain separate reservoirs with defined thermal setpoints or use a compromise temperature that can narrow the process window. Operators should not assume that the RBK-ENT-D55 profile uses the same jetting temperature as the single-material modes. Applying an incorrect profile can cause stringing, missing droplets, or interfacial cure mismatch. The material profile lock in 3D Sprint is a control that prevents off-spec conditions.

Surface finish in the D55 composite is not uniform. The rigid CR-BK phase can be sanded and polished; the CE-NT phase resists polishing due to its elastomeric recovery. Layer lines may remain in the soft-tissue regions. Surface roughness requirements for endoscopic navigation may require coating or manual smoothing. Any coating used must be assessed for solvent interaction with CE-NT. When high-speed rotary instruments are used for otologic drilling simulation, burr speed and irrigation should be evaluated because CE-NT is thermoplastically soft under frictional heating and may smear or clog the burr. This does not indicate a material defect but a processing boundary in surgical rehearsal use.

Material handling and disposal should follow the safety data sheet and local regulations. The uncured resin is subject to REACH and RoHS declarations from the material supplier; no final medical device cleaning, biocompatibility, or patient-contact claim is made by these declarations. For hospital workflows, the final printed model should be assessed under the facility’s infection control and quality management procedures. If the model is intended for patient or tissue contact, the facility should perform the applicable risk assessment and biological evaluation rather than relying solely on the material supplier’s regulatory statements.

Production-scale manufacturing logs should include printer serial number, printhead calibration date, cartridge lot numbers for both CR-BK and CE-NT, support material lot, cleaning cycle temperature, and Shore D values from a fixed test coupon at 24 h post-print. Batch-to-batch drift can appear as a shift in average hardness of several Shore D points before any visual change; published data for this specific configuration is limited, and the range is not a vendor specification. Operators should use Shewhart control charts for Shore D and dimensional drift. If the CE-NT phase shows surface haze after cleaning, reduce ultrasonic agitation or solvent exposure and inspect the cleaning bath for dissolved wax loading. If the CR-BK phase shows brittleness in thin-walled regions, verify UV lamp energy and printhead drop mass; do not attribute the failure to material formulation alone. These production observations are applicable to MJP anatomical model workflows and are not a substitute for the 3D Systems material safety data sheet, user guide, or validated cleaning protocol.