The storage conditions of disposable biopsy needles significantly affect needle rigidity. The core mechanism involves the interaction between material properties, environmental stresses, and residuals from the sterilization process. As a key indicator for evaluating biopsy needle quality, needle rigidity is directly related to stability during puncture and sampling accuracy. Improper storage conditions can lead to creep deformation, elastic modulus degradation, or surface microstructural damage, leading to the risk of bending and fracture during clinical use.
Temperature fluctuations are the primary environmental factor affecting needle rigidity. Disposable biopsy needles are often manufactured from 304 stainless steel or medical-grade polymers, which are extremely sensitive to temperature changes. High temperatures accelerate metal lattice diffusion, resulting in a decrease in yield strength, while low temperatures can cause polymer embrittlement, reducing bending resistance. For example, long-term exposure to temperatures above 40°C can cause a decrease in the elastic modulus of stainless steel needles, while polycarbonate handles can significantly weaken their impact toughness when stored below -20°C. This material degradation is directly reflected in needle rigidity testing results, manifesting as a decrease in the bending stiffness coefficient or a shift in the yield point.
The impact of humidity on needle rigidity primarily manifests itself through corrosion and hydrogen embrittlement. High humidity accelerates electrochemical corrosion of stainless steel needles, forming an oxide layer that weakens the substrate. Furthermore, moisture adsorption can trigger hydrolysis of polymer materials, leading to molecular chain breakage. More critically, a humid environment promotes the hydrolysis of ethylene oxide sterilization residues, releasing acidic substances that corrode the metal surface. This corrosion not only reduces needle rigidity but can also form microcracks at the needle tip, becoming the initial source of fracture.
Light exposure has a long-term cumulative effect on the rigidity of polymer components. Ultraviolet radiation triggers photooxidation in polypropylene protective tubes, reducing the degree of molecular crosslinking and making the material brittle. ABS plastic handles can develop silver streaking on the surface under prolonged light exposure. This microscopic damage can gradually extend into the material, causing a decrease in rigidity. Therefore, disposable biopsy needles are typically packaged in light-proof materials to prevent photodegradation.
The impact of storage pressure on needle rigidity is often overlooked. Improper stacking can cause localized stress concentrations, potentially leading to permanent bending and deformation of the needle. Especially for thin-diameter biopsy needles, when stacked vertically, the compressive stress on the lower needle tubes may exceed their yield strength, causing irreversible plastic deformation. This deformation can directly alter the needle's geometric dimensions, leading to deviations in the puncture trajectory during use.
Biological contamination has the potential to affect needle rigidity. Microbial metabolites in the storage environment may form a biofilm that adheres to the needle surface. This biofilm not only increases surface roughness but also corrodes the metal substrate through the secretion of acidic substances. For polymer components, microbial enzymatic degradation can disrupt the molecular structure, resulting in a decrease in rigidity. Therefore, the storage environment of disposable biopsy needles requires strict control of microbiological indicators.
To ensure the rigidity of disposable biopsy needles, storage conditions must meet multiple technical requirements: the temperature should be controlled between -20°C and 40°C, the humidity should not exceed 60% RH, they should be stored away from light, and the stacking pressure should be less than 50% of the needle's yield strength.
