Liquid silicone rubber (LSR) molding and overmolding for implantable medical devices, such as catheters, seals, and valves, demand rigorous contamination control in ISO Class 7/8 cleanrooms to ensure biocompatibility (ISO 10993), regulatory compliance (FDA, EMA), and high yield. Foreign material (FM), including fibers, metallic particles from equipment wear, and silicone residues, causes device rejections due to visible defects that contrast with the LSR’s translucent nature. Silicone residues include:
- Uncured Liquid Silicone: Tacky, liquid-state silicone from spills or drips, highly adhesive and prone to trapping FM.
- Sticky Undercured Silicone: Partially cured, gummy silicone that adheres firmly to molds and curing ovens, resisting standard wiping.
- Thermally Degraded Silicone: Hardened or sticky residues from overheating in curing ovens, forming brittle or discolored layers that trap FM.
These residues adhere to surfaces, exacerbating FM contamination. The LSR process’s diverse cleaning needs mean a single wiper cannot maximize yield and quality. Nonwoven polycellulose wipers, used for liquid silicone spills, shed massive quantities of fibers (>25 µm), contaminating cleanrooms. In contrast, sealed-edge polyester wipers, used for molds and ovens, are much cleaner but still shed large quantities of fibers (>25 µm) and lack scrubbing power for sticky residues. Foamtec’s MiraWIPE, UltraSORB, and Sahara wipers, widely deployed across LSR molding and overmolding facilities globally, provide a comprehensive solution. MiraWIPE and UltraSORB are primary wipers for general cleaning and spill management. At the same time, Sahara specializes in scrubbing sticky undercured or thermally degraded silicone from curing ovens and molds, ensuring residue-free critical process tooling.
Reject Devices due to polycellulose/polyester wiper FM contamination.
Limitations of Current Wiper Solutions
- Nonwoven Polycellulose Wipers:
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- Strengths: High absorbency (≥500 g/m²) for uncured liquid silicone spills, cost-effective.
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- Weaknesses: Shed large fibers (>25 µm), causing cleanroom-wide FM contamination. Low abrasion resistance increases fiber release, making it unsuitable for mold or oven cleaning.
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- Impact: Fiber FM reduces yield by contaminating devices.
- Sealed-Edge Polyester Wipers:
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- Strengths: Lower linting than polycellulose, sealed edges reduce fiber release.
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- Weaknesses: Shed fibers exceeding 25 µm under abrasion, insufficient scrubbing power for sticky undercured or thermally degraded silicone, and limited absorbency for spills.
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- Impact: Ineffective residue removal increases maintenance time and defect rates.
Foamtec Wiper Solutions
Foamtec’s MiraWIPE, UltraSORB, and Sahara wipers are widely deployed in LSR molding and overmolding facilities, addressing FM challenges with specialized properties for uncured liquid silicone cleanup, general mold and equipment cleaning, and targeted removal of sticky undercured or thermally degraded silicone residues. Their proven performance in high-volume medical device production makes them industry standards for contamination control.
1. MiraWIPE Wipers
- Material: Woven microfiber (continuous-filament polyester/nylon) with ultrasonically sealed edges.
- Key Characteristics:
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- Low Fiber Shedding: Minimal submicron and >0.5 µm particle release (<30–200 µm fibers per IEST-RP-CC004.3), reducing FM compared to polyester wipers.
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- Superior Cleaning Efficiency: The star-shaped microfiber structure effectively dislodges and entraps uncured liquid silicone, metallic particles, and light silicone residues from molds, ovens, and equipment.
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- High Absorbency: >400 g/m² for solvents (e.g., 70% IPA/30% UPW), enabling effective cleaning of sticky residues with minimal streaking.
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- Abrasion Resistance: The durable fabric resists snagging on rough surfaces, maintaining its integrity during heavy-duty wiping
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- Sterility: Gamma-irradiated (SAL 10^-6), ISO Class 3–5, USP <797> compliant for aseptic areas.
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- Biocompatibility: ISO 10993-5/11 compliant, no residues affecting device safety.
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- Chemical Compatibility: Free of amines, sulfur, or chlorides, <0.5 µg/cm² NVR, compatible with LSR curing.
- Applications:
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- General Mold and Oven Cleaning: Removes uncured liquid silicone and light undercured residues from molds and curing oven surfaces, outperforming polyester wipers.
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- Equipment Maintenance: Cleans tooling, automation, and filling machines, reducing FM (e.g., metallic particles).
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- Aseptic Processing: Sterile MiraWIPE cleans isolators and workstations, removing disinfectant residues and FM without shedding.
- Deployment: Widely used in LSR facilities for versatile cleaning of molds, ovens, and equipment, ensuring low FM and high device quality.
- Benefit: Primary wiper for general cleaning, reducing fiber FM, improving yield, and minimizing downtime.
2. UltraSORB Wipers
- Material: Hydrophilic, open-cell polyurethane foam (ester-based, medical-grade).
- Key Characteristics:
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- Ultra-Low Shedding: 100% lint-free, fiber-free, eliminating fiber FM (>25 µm), surpassing polycellulose and polyester.
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- High Absorbency: Sponge-like structure with >600 g/m² capacity for uncured liquid silicone spills, minimizing FM spread.
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- Abrasion Resistance: The durable foam prevents particle generation on rough surfaces, making it ideal for workstation cleaning.
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- Static Dissipative: 10^6–10^9 ohms/square, reducing ESD-related FM attraction and tribocharging of silicone devices
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- Biocompatibility: ISO 10993-5/11 compliant, no residues affecting device safety.
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- Chemical Compatibility: Free of amines, sulfur, or chlorides, <0.5 µg/cm² NVR, compatible with LSR curing.
- Applications:
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- Uncured Liquid Silicone Cleanup: Absorbs tacky LSR spills at workstations or dipping stations, preventing FM entrapment.
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- Device Cleaning: Cleans catheters, balloons, and implants without introducing FM, enhancing biocompatibility.
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- Bioburden Control: Lint-free structure supports USP <797> compliance in aseptic areas.
- Deployment: Extensively adopted in LSR facilities for spill management and device cleaning, replacing polycellulose to eliminate fiber contamination.
- Benefit: Primary wiper for spill cleanup, preventing cleanroom-wide FM spread and boosting yield.
3. Sahara Wipers
- Material: Cross-linked ester-based polyurethane foam.
- Key Characteristics:
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- Scratch-Free Scrubbing Power: Soft, conformable foam delivers aggressive, Scotch-Brite-like scrubbing to dislodge sticky undercured silicone (gummy, partially cured) and thermally degraded silicone (brittle or sticky from overheating) from curing ovens and molds. Unlike Scotch-Brite, Sahara’s non-abrasive structure prevents scratching or particle generation, preserving precision tooling.
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- Targeted Residue Removal: High surface area and mechanical action break down tenacious undercured and thermally degraded silicone, compatible with solvents (IPA, xylene, toluene, n-butyl acetate) to dissolve residues.
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- Ultra-Low Particle Shedding: Fiber-free, ISO Class 5–8 certified, eliminating particle FM compared to abrasive pads.
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- Absorbency: >500 g/m² for solvents, supporting residue removal.
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- Abrasion Resistance: High tear resistance prevents shedding on textured surfaces.
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- Chemical Compatibility: Free of LSR curing inhibitors, ensuring no impact on platinum catalysts.
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- Biocompatibility: ISO 10993 compliant, no residues affecting device safety.
- Applications:
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- Curing Oven Cleaning: Scrubs sticky undercured and thermally degraded silicone from oven surfaces, ensuring residue-free conditions for consistent curing.
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- Mold Cleaning: Dislodges undercured and thermally degraded silicone from LSR injection molds and dip casting tooling, maintaining tolerances and extending mold life.
- Deployment: Broadly implemented in LSR facilities as a specialized scrubbing tool for tenacious silicone residues, complementing MiraWIPE and UltraSORB.
- Benefit: Ensures residue-free tooling, reducing defects and maintenance time without damaging critical surfaces.
Integrated Contamination Control Strategy
The LSR process requires a multi-wiper approach, with Foamtec’s widely deployed wipers addressing all cleaning needs:
- MiraWIPE: Primary wiper for general cleaning of molds, ovens, and equipment, removing uncured liquid silicone and light residues with low fiber shedding.
- UltraSORB: Primary wiper for uncured liquid silicone spill cleanup, eliminating fiber FM and preventing contamination spread.
- Sahara: Specialized scrubbing tool for dislodging sticky undercured and thermally degraded silicone from curing ovens and molds, ensuring residue-free tooling.
Benefits include:
- Higher Yield: Reduced FM (fibers, residues, particles) lowers rejection rates.
- Improved Quality: Residue-free tooling and clean devices ensure biocompatibility (ISO 10993, USP <797>).
- Lower Downtime: Efficient residue removal streamlines maintenance.
- Regulatory Compliance: Lot-traceable wipers with Certificates of Analysis support FDA/EMA audits.
Implementation Notes
- Cleaning Protocols: Use MiraWIPE for general cleaning (linear wiping), UltraSORB for spills (quarter-fold wiping), and Sahara for scrubbing ovens and molds with solvent (gentle, linear motion to avoid over-scrubbing).
- Validation: Test wipers for residue removal (gravimetric analysis) and particle release (LPC, Helmke drum), especially for the Sahara, to assess undercured or thermally degraded silicone.
- Training: Train operators on wiper-specific techniques, emphasizing Sahara’s gentle scrubbing to maintain tooling in pristine condition.
- Supply: Source from Foamtec’s Wilshire Contamination Control Division, ISO 13485-compliant.
Recommended Wiper Profile
- MiraWIPE: Sterile microfiber, ultrasonic sealed edges, ISO Class 3–5, for general cleaning.
- UltraSORB: Hydrophilic polyurethane foam, pre-saturated with 70% IPA/30% UPW, ISO Class 5, for spill cleanup.
- Sahara: Cross-linked polyurethane foam, ISO Class 5–8, for scrubbing undercured/thermally degraded silicone.
- Availability: Foamtec HT5790SM (MiraWIPE), UltraSORB and, Sahara wiper.
Conclusion
The LSR process’s contamination control demands a multi-wiper strategy. Polycellulose and polyester wipers fail due to fiber shedding and poor scrubbing power. Foamtec’s MiraWIPE, UltraSORB, and Sahara wipers, widely deployed in LSR molding and overmolding facilities, address the cleanup of uncured liquid silicone, general cleaning, and the removal of sticky undercured or thermally degraded silicone. MiraWIPE and UltraSORB are primary wipers for versatile cleaning and spill management, while Sahara is a specialized scrubbing tool for tenacious residues in curing ovens and molds. This approach minimizes FM, enhances yield, ensures quality, and supports regulatory compliance, driving efficiency and patient safety.