Hospitals and medtech manufacturers know the stakes: a single reprocessing failure can cascade from a quality glitch into a patient safety event, a product hold, or a public recall. For years, training and validation programs have emphasized “follow the IFU, verify the cycle, document everything.” Yet a growing body of research shows a subtler, more treacherous threat hiding in plain sight—soil that dries on a device before it is cleaned.
A recent peer-reviewed investigation has quantified what many sterile processing leaders have suspected: allowing clinical soil to dry—even for relatively short windows—changes its chemistry and physics in ways that can defeat otherwise sound cleaning steps. The problem compounds on complex features (hinges, lumens, threaded interfaces, bearings, leaf springs, and tight-tolerance mates), where fluid dynamics are already unfavorable. For medtech manufacturers, device designers, and sterile processing departments (SPDs), these findings sharpen the mandate to rethink pre-cleaning at point of use, feature-level risk assessment, and cleaning validation design.
This article unpacks the mechanisms behind drying-driven cleaning failures, translates the latest evidence into day-to-day practice, and outlines how CMDC Labs partners with clients to build defensible, data-driven device processing validations that hold up in the real world.
Why “Don’t Let It Dry” Is More Than a Slogan
Every device reprocessing talk track includes a version of “keep it moist.” The reason is not merely convenience; it’s chemistry.
Clinical soils—blood, mucin, tissue fragments, lipid/protein mixtures—are multi-component matrices that coagulate, denature, cross-link, and embed into surface microtopographies as they dry. Temperature and humidity accelerate or slow these transitions. As soils pass through semi-dry states (coagulated but not fully dry), they become paradoxically harder to remove than either fresh or fully desiccated residues. On metals, polymers, and coatings, the drying process promotes adhesion and mechanical interlocking; within lumens or joints, capillary forces, meniscus effects, and stagnant zones reduce mechanical shear from flushing.
Two operational consequences follow:
- Same cycle, different outcome. A validated cleaning process that works on “freshly soiled” test articles may underperform on in-use devices that sat for 30–120 minutes before pre-cleaning.
- Feature-specific failures. Even when overall bioburden drops, residual proteins and soils persist in hard-to-reach geometries—precisely where sterilant penetration later is least reliable.
Bottom line: the time-to-pre-clean and micro-design features are as determinative as the detergent, temperature, or brush you choose.
The Evidence: What Recent Studies Reveal
A multi-feature experimental series evaluated cleaning outcomes across 23 representative device features—from open surfaces to occluded assemblies—under two contrasting conditions: (1) soils kept moist until cleaning and (2) soils allowed to dry for defined periods. The results show a consistent pattern:
- Drying markedly increases cleaning challenge, with feature-dependent variability.
- Fluid dynamics (e.g., access for flow, turbulence, and shear) and soil chemistry changes explain why some designs resist cleaning after drying even when others clean acceptably.
- Certain features require manual action (brushing/flushing) regardless of drying time; automated soaking or sonication alone may not compensate for geometry.
- Environmental conditions (temperature and relative humidity) modulate the extent of soil chemical fixation; higher humidity slows “hard-set” formation, preserving solubility.
Complementary work has mapped the time–temperature–humidity envelope where soils transition from removable to recalcitrant, and clinical studies have demonstrated that semi-dried blood within 1–2 hours can become significantly more difficult to remove than fresh contaminants. These findings align with long-standing FDA, multi-society, and infection prevention guidance emphasizing point-of-use pre-cleaning and keeping devices moist when delays are inevitable.
Implication: The “validation soil” and “use conditions” must reflect worst-credible drying intervals and environments—not merely idealized bench conditions.
Where Cleaning Fails First: High-Risk Features by Design
Design teams and SPDs intuitively recognize that some features are magnets for residuals. Evidence-based prioritization helps channel resources:
- Occluded moving parts (ball bearings, leaf springs, telescoping segments): create micro-gaps with stagnant fluid and capillary retention.
- Threaded interfaces and mated surfaces: trap soil in helical grooves and contact patches; frictional locking and compression worsen adhesion as residues dry.
- Long, narrow lumens or abrupt internal transitions: reduce Reynolds number and turbulence; boundary layers insulate soils from shear forces.
- Textured, blasted, or coated surfaces: increase effective surface area and provide micro-asperities for mechanical interlock.
- Sealed or semi-sealed subassemblies: enable diffusion-limited drying, creating sticky, partially dried residues that resist both flushing and sonication.
For each of these, the same cleaning parameters that pass a validation on moist soils may underperform after even modest pre-cleaning delays.
The Drying Trap in Real Workflows
Even well-run ORs and clinics face delays between use and pre-cleaning:
- Transport lags while cases turn over or instruments await pickup.
- Staffing constraints during peak periods.
- Device IFU complexity causes hesitation: “Do we brush here or there? Which lumen adapter?”
- Shared device pools sit exposed on trays where evaporative drying is rapid under warm, low-humidity HVAC conditions.
Notably, soil doesn’t need to be visibly “crusty” to cross the line; the semi-dried coagulation phase is often the worst for removal, and it can occur within the first hour. Meanwhile, biofilm risk escalates with time, especially on residuals within protected geometries, compounding future cycles’ difficulty.
Validations That Miss the Point (and How to Fix Them)
Pitfall 1: Idealized test soils and timelines.
Validations often soil test coupons or simple surrogates and move quickly to cleaning—conditions friendlier than reality.
Solution: Incorporate time-to-pre-clean profiles that mirror the clinical pathway (e.g., 30, 60, 120 minutes), span expected temperature/humidity, and include semi-dry states before cleaning.
Pitfall 2: Geometry under-representation.
Flat coupons don’t capture the hydraulic complexity of a ball-and-socket, a threaded junction, or a 1.2-mm lumen with a 90° elbow.
Solution: Use feature-accurate surrogates and actual devices with the difficult geometries of interest. Map flow access and brush reach realistically.
Pitfall 3: Over-reliance on automation.
Soaking or sonication can help but may not overcome stagnant pockets or meniscus-shielded zones once soils have partially dried.
Solution: Validate manual action requirements (brush type/size, strokes, angles) and flow-assisted flushing with lumen adapters. Define when automation is supplemental, not substitutive.
Pitfall 4: Inadequate endpoints.
Visual clean checks alone miss proteinaceous micro-residues that block sterilant or seed biofilms.
Solution: Add quantitative residual protein assays, ATP, or chromogenic markers with limits aligned to clinical risk and recognized acceptance criteria. Confirm with microbial challenges where appropriate.
Pitfall 5: Poor sampling hygiene for validation.
Protein assays and low-level endpoints are notoriously sensitive to cross-contamination and inconsistent swabbing.
Solution: Standardize swab pressure/area, use validated extraction buffers, run field blanks/positives, and document limit of detection/quantification for each matrix.
Designing for Cleanability (Before You Ever Clean)
Many “hidden” cleaning challenges are design problems wearing process hats. Medtech teams can de-risk cleanability upstream:
- Reduce occlusions: replace hidden springs/ball bearings with cleanable equivalents or expose them with serviceable covers.
- Prefer straight, larger-diameter lumens with gentle radii and access for adapters.
- Avoid non-functional textures where soils anchor; specify finishes that balance function and cleanability.
- Provide cleaning access: ports for flushing, removable segments, or fixtures for holding angles during cleaning.
- Embed pre-cleaning in the user pathway: supply moist-hold accessories (enzymatic gels, dampened wraps), clear point-of-use steps, and labeled lumen adapters to reduce error.
Good design shrinks the gap between bench validation and real-world processing—especially under drying risk.
Sterile Processing Playbook: What to Change Tomorrow
1) Treat time as a critical control parameter.
Measure time from end-of-use to pre-cleaning at the point of use, not just time to central decontam. Trend it on dashboards.
2) Keep it moist—reliably.
Standardize moist-hold: enzymatic sprays/gels that prevent drying without cooking soils; damp towels in sealed trays for transport (per IFU and multi-society guidance).
3) Upgrade point-of-use pre-cleaning.
Minimal brushing/flushing before transport (when permitted) can prevent the worst soil chemistry from locking in.
4) Match tools to features.
Stock brushes by diameter and bristle; use lumen adapters for pressurized flushing; document strokes/flows by device/feature, not one-size-fits-all.
5) Align decontam capacity with case volume.
If delays exceed targets during peak blocks, re-balance pickups or stage additional staff; drying time will fall as a matter of operational design.
6) Validate to the hard cases.
Rebuild validations to include semi-dry soils, realistic environmental conditions, and feature-accurate test articles. Adopt protein/ATP endpoints with risk-based acceptance criteria.
7) Close the loop on rework.
When a load fails inspection or testing, capture the root cause: was it time-to-pre-clean, a feature bottleneck, or method drift? Feed findings back into design and staffing.
For Medtech Manufacturers: Make Cleanability a Label Claim
Your device’s clinical value depends on safe reuse. Consider elevating cleanability:
- Publish feature-specific cleaning instructions with brush diameters, adapters, and minimum strokes/flows based on drying-inclusive validations.
- Provide moist-hold instructions and compatible products.
- Offer validated kits (brushes, adapters, caps) to simplify compliance.
- Share validation summaries with hospitals—especially how your testing accounted for drying intervals and environmental stressors.
Hospitals will increasingly prefer devices with transparent, drying-aware validations because they map to real workflows—and reduce downstream risk.
How CMDC Labs Helps (and Why It Matters Now)
CMDC Labs supports medtech manufacturers, hospitals, and integrated delivery networks with end-to-end device processing validation programs that reflect the science and the reality on the ground.
What we do:
- Risk-informed study design that embeds time-to-pre-clean, temperature/humidity ranges, and semi-dry states into test matrices—so your validation mirrors clinical use.
- Feature-level testing with actual devices and geometry-accurate surrogates (threads, hinges, lumens, mated surfaces) to capture the hydraulics that defeat cleaning after drying.
- Orthogonal endpoints (residual protein assays, ATP, visual grading, and where appropriate, microbial challenges) with LOD/LOQ transparency and real acceptance criteria.
- Method hygiene and controls (field blanks/positives, extraction efficiency checks, repeatability/reproducibility assessments) to ensure data are defensible.
- Actionable interpretation: We translate results into specific IFU refinements (brush specs, stroke counts, flush volumes, soak times), workflow controls (moist-hold SOPs, time targets), and design feedback for engineering.
- Training & implementation: On-site or virtual support to roll out new SOPs, coach staff on feature-matched tools, and set up time-to-pre-clean dashboards that drive sustained improvement.
Why now: Regulators, accreditors, and multisociety groups are tightening expectations around pre-cleaning and drying prevention. Plaintiffs’ attorneys increasingly scrutinize validation realism versus actual use. Drying-aware, geometry-accurate validations are not a “nice to have”—they are your evidence of due diligence.
A 90-Day Plan to De-Risk Drying
Days 1–30: Baseline & triage
- Time-study point-of-use → pre-clean across service lines; identify worst intervals.
- Inventory high-risk devices/features; map which require manual action regardless of drying.
- Standardize moist-hold and transport SOPs; train and audit.
Days 31–60: Validate what matters
- With CMDC Labs, design a drying-inclusive validation on a pilot device set (feature-rich).
- Run multi-endpoint assays (protein/ATP + visual) at 0, 30, 60, 120 minutes, and at ambient and high-temp/low-RH conditions.
- Compare automation-only vs automation + manual hybrids; document thresholds where manual action is non-negotiable.
Days 61–90: Operationalize
- Update IFUs/SOPs with evidence-based brush specs, strokes, flows, and soak/sonication parameters.
- Implement real-time time-to-pre-clean tracking; set alert thresholds.
- Expand validation to additional device families; create a cleanability risk register to guide design procurement and capital planning.
The Payoff: Fewer Surprises, Stronger Safety
By treating drying as a primary risk variable—on par with detergent choice or washer cycle—you raise the floor on cleaning reliability. The benefits are tangible:
- Fewer reworks and wet-pack delays
- Lower residual protein failure rates
- More credible audits and inspections (your validation matches actual use)
- Better collaboration with OR/clinical teams (time-to-pre-clean becomes a shared KPI)
- Design feedback that yields easier-to-clean devices in the next product iteration
Reusable medical devices are here to stay, and so are the pressures to reprocess them faster, safer, and more economically. Drying-aware strategies give you the leverage to do all three.
Conclusion
Sterilization failures rarely start in the sterilizer. They begin at the moment a device leaves the patient and the clock starts ticking. Within minutes, soils pass through a chemical transformation that can flip a passing cleaning cycle into a marginal one—especially on complex features. The latest research doesn’t just confirm this; it quantifies when and where the risks are highest.
The fix is not mysterious, but it is systemic: build drying into validations, design for cleanability, keep devices moist, act on feature-level risks, and measure time-to-pre-clean the way you measure anything that truly matters. With the right data and discipline, you can turn an invisible vulnerability into a controllable variable.
CMDC Labs is ready to help you do exactly that—with evidence, not assumptions.
Sources
- Nature / Scientific Reports: “Left to dry: unseen risks lurking on reusable medical devices” (feature-level cleaning outcomes; drying vs moist conditions; manual action needs). NaturePMC
- Journal of Hospital Infection: Quantitative risk method across 23 device features; soil drying & fluid dynamics as top risks to cleaning efficacy. ScienceDirectJournal of Hospital Infection
- Journal of Hospital Infection: “Influence of drying time on the removal of blood from stainless steel coupons” (semi-dry window hardest to clean). Journal of Hospital Infection
- Infection Control literature: Pre-cleaning and moisture preservation to prevent biofilm formation; point-of-use recommendations. MDPIMacquarie University
- FDA guidance: “Reprocessing Medical Devices in Health Care Settings” (validation soils, worst-case conditions, drying considerations). U.S. Food and Drug Administration
- Environmental/biochemistry context: Effects of time, temperature, and humidity on soil drying and solubility; humidity prevents fixation. PMC
- Multisociety guidance (2025): Keep devices moist between use and treatment; remediation steps if delays occur. Cambridge University Press & Assessment
- AJIC overview: Reprocessing failures linked to transmission; importance of validated cleaning and high-level disinfection/sterilization. AJIC Journal
- Background on endoscope outbreaks and cleanability risk. PMC
