加速老化系数怎么选才站得住

结论：加速老化是估算手段，结论最终要靠实时老化确认

产品的有效期需要数据支撑，但实时等待三年才能支持三年有效期，对上市时间是不可接受的。加速老化的作用是用高温缩短试验时间，先得到一个估算结论，让产品可以先上市。

但它是估算，不是证明。 加速条件下的老化与实际储存条件下的老化，机理未必完全相同。所以规范的做法是：加速老化支持初始的有效期声称，同时启动实时老化，用实时数据最终确认。

只做加速不做实时，是常见的不完整做法。 短期内看不出问题，但一旦实时数据与加速结论不符，已经在市场上的产品就要处理。

加速的原理与前提

加速老化基于一个假设：温度升高会加快化学反应速率，而老化过程主要是化学反应。 温度每升高一定幅度，反应速率提高一定倍数，这个倍数就是加速系数。

这个假设成立有几个前提：

老化机理不随温度改变。 加速温度下发生的应当是同样的反应，只是更快。如果高温引发了常温下不会发生的反应（比如材料软化、相变、新的降解途径），加速的结论就不适用。

材料在加速温度下不发生物理变化。 温度接近材料的软化点或玻璃化温度时，物理状态改变，老化行为也随之改变。

加速的是老化，不是其他过程。 比如水分迁移、应力松弛，这些过程的温度依赖性与化学老化不同。

所以加速温度的选择不能只考虑「越高越快」，还要确认在该温度下上述前提仍然成立。

系数选择的考虑

「保守性」是实务中的关键取舍。 系数取得大，所需的加速试验时间短，但结论的可靠性下降；系数取得小，试验时间长，但结论更稳。

建议取较保守的系数。 因为加速老化的结论如果偏乐观，实时数据出来后可能推翻，代价很大；偏保守则最多是试验时间长一些。

湿度的处理

加速因素不只有温度，湿度对某些材料的老化影响很大：

吸湿材料。 水分会加速水解类的降解。

包装材料。 湿度影响阻隔性能和密封。

金属件。 湿度影响腐蚀。

电子元件。 湿度影响绝缘和腐蚀。

建议在加速条件中同时考虑温度和湿度，并说明湿度条件的设定依据。只控温不控湿，结果的可解释性会打折扣。

适用与不适用的情形

比较适用： 以化学降解为主要老化机理的材料；有类似材料的加速老化经验可参考；储存条件相对稳定；以及有实时数据可以后续验证。

不太适用或需谨慎： 老化机理复杂或不明确；材料在加速温度下有物理变化；产品含多种材料且老化机理不同；涉及活性成分或生物材料；以及加速温度接近材料的使用温度上限。

「多种材料老化机理不同」在器械产品上很常见。 一个产品可能同时包含塑料、橡胶、金属、粘接剂、包装材料，各自的老化机理和温度敏感性不同。用同一个系数覆盖全部材料，论证上是有缺口的。

可行的做法是：识别老化最敏感的材料或性能，按它确定加速条件；或者对不同材料分别评估。

测什么

加速老化之后要测的性能，应当覆盖与有效期相关的所有方面：

产品性能。 功能、力学性能、尺寸。

包装性能。 密封强度、完整性、阻隔性能。

材料状态。 外观、硬度、可能的降解迹象。

化学变化。 必要时做化学表征对比，看是否产生新的物质。

无菌性（无菌产品）。 无菌屏障是否保持。

取样点的安排。 不只测终点，中间点也要测，这样能看出变化趋势而不只是终点状态。

「中间点」的价值常被低估。 只测起点和终点，如果终点合格就认为没问题；但如果中间某个时点已经出现明显下降而终点恰好还合格，说明产品处在边缘状态，批次差异可能导致不合格。

实时老化的配合

同步启动。 加速老化和实时老化同时开始，不要等加速结果出来再启动实时。

取样点对应。 实时老化的取样点应当覆盖声称的有效期。

条件记录。 实时老化的储存条件要监控并记录。

数据比对。 实时数据出来后与加速结论比对，不符时要分析原因并处理。

结论的更新。 实时数据支持更长有效期时可以延长，不支持时要缩短。

「不符时的处理」应当事先有预案。 如果实时数据显示产品在声称的有效期前就不合格，已在市场上的产品怎么办，这个问题要提前想清楚。

常见的问题

系数无依据。 直接用某个常见数值而不说明为什么适用于本产品。

未做实时老化。 只有加速数据。

加速温度过高。 引发了常温下不会发生的变化。

未考虑湿度。 对湿度敏感的产品。

只测终点。 看不出变化趋势。

样品不是最终状态。 未经灭菌或未按最终包装。

未覆盖包装。 只测产品不测包装，而包装的老化同样影响有效期。

结论怎么表述

有效期结论的表述应当说明依据，建议包含：

声称的有效期。 具体数值。

支持的数据类型。 加速老化、实时老化、或两者。

加速条件与系数。 温度、湿度、时间、所用系数及其依据。

测试项目与结果。 测了什么、结果如何。

实时老化的进展。 已完成到哪个时点、后续计划。

储存条件。 声称的有效期对应什么储存条件。

最后一项容易被忽略。 有效期总是与储存条件绑定的——「常温下三年」与「不限条件三年」是完全不同的声称。标签和说明书中应当标明储存条件。

与产品变更的关系

以下变更可能影响有效期结论：

材料或供应商变更；加工工艺变更；灭菌方式或参数变更；包装材料或结构变更；以及产品结构变更。

变更后应当评估是否需要重新做老化研究。 判断依据是变更是否影响老化行为——换一个牌号的同类材料，添加剂配方可能不同，老化行为也可能不同。

建议把有效期的复核纳入变更评审的固定环节，与生物学评价的复核一起做。

我们的做法

做老化相关验证时，我们会先与委托方确认几件事：产品中老化最敏感的材料是哪个、加速温度是否安全（不引发物理变化）、以及是否需要控制湿度。 这三点确定之后，条件设定才有依据。

测试安排上，我们建议设置中间取样点而不只测终点，因为变化趋势比终点状态更有信息量 ——它能说明产品是稳定的还是处在边缘。

如果你在规划有效期验证，不确定加速条件怎么定，可以把材料信息和包装形式发过来一起讨论，或者直接联系：132 4819 8029。能力范围见服务介绍，送检要求见送检要求，流程见检测流程。

English version

Conclusion. Shelf life claims need data, but waiting three years in real time to support a three-year claim is unacceptable for time to market. Accelerated ageing shortens the test by raising temperature, producing an estimate that lets the product launch. It is an estimate, however, rather than proof: ageing under accelerated conditions may not follow the same mechanism as ageing in storage. The proper approach is therefore to support the initial shelf life claim with accelerated data while starting real-time ageing in parallel and confirming with real-time results. Doing accelerated ageing alone is a common incomplete practice: nothing shows in the short term, but if real-time data later contradict the accelerated conclusion, product already in the market must be dealt with.

Principle and preconditions. Accelerated ageing rests on an assumption: raising temperature increases reaction rates, and ageing is principally chemical reaction. Each increment of temperature multiplies the rate by a factor, and that factor is the acceleration factor. Several preconditions must hold. The ageing mechanism must not change with temperature, meaning the same reactions occur at the accelerated temperature only faster; where high temperature triggers reactions that do not occur at ambient, such as softening, phase change or new degradation pathways, the accelerated conclusion does not apply. The material must undergo no physical change at the accelerated temperature, since approaching a softening point or glass transition changes physical state and with it ageing behaviour. And what is accelerated must be ageing rather than some other process, since moisture migration and stress relaxation have different temperature dependence from chemical ageing. Selecting the accelerated temperature therefore cannot simply favour higher and faster; it must confirm that these preconditions still hold.

Choosing the factor. Material characteristics matter, since temperature sensitivity differs between materials. The accelerated temperature must not approach a phase transition. Storage conditions set the temperature baseline. Conservatism matters, since a smaller factor gives a more conservative conclusion. And supporting data make a factor more defensible. Conservatism is the key trade-off in practice: a large factor shortens the test while reducing reliability, and a small factor lengthens it while making the conclusion more robust. Take the more conservative factor, because an optimistic accelerated conclusion may be overturned by real-time data at considerable cost, while a conservative one costs only test time.

Humidity. Temperature is not the only accelerating factor, and humidity strongly affects ageing in some materials. Hygroscopic materials degrade faster by hydrolysis in the presence of water. Packaging materials change in barrier performance and sealing with humidity. Metals corrode. And electronic components are affected in insulation and corrosion. Consider both temperature and humidity in accelerated conditions and state the basis for the humidity setting; controlling temperature alone weakens the interpretability of the result.

Where it applies and where it does not. It applies reasonably well to materials ageing principally by chemical degradation; where experience with similar materials exists; where storage conditions are stable; and where real-time data will later verify. It applies poorly, or demands caution, where the ageing mechanism is complex or unclear; where materials change physically at the accelerated temperature; where a product contains several materials with different ageing mechanisms; where active or biological materials are involved; and where the accelerated temperature approaches the material's upper use temperature. Multiple materials with different mechanisms is common in devices: one product may combine plastics, rubbers, metals, adhesives and packaging materials, each with its own mechanism and temperature sensitivity, and covering all with one factor leaves a gap in the argument. Workable approaches are identifying the most ageing-sensitive material or property and setting conditions by it, or assessing materials separately.

What to measure. Measurements after accelerated ageing should cover everything bearing on shelf life. Product performance, covering function, mechanical properties and dimensions. Packaging performance, covering seal strength, integrity and barrier. Material condition, covering appearance, hardness and signs of degradation. Chemical change, with comparative characterisation where needed to see whether new substances appear. Sterility for sterile products, confirming the barrier holds. And sampling points, measuring intermediate points as well as the end so that trends appear rather than only the end state. Intermediate points are undervalued: measuring only start and end, an acceptable end result is taken as satisfactory, whereas a marked decline at an intermediate point with the end just passing indicates a product at the margin where batch variation may fail.

Pairing with real-time ageing. Start both together rather than waiting for accelerated results. Set real-time sampling points covering the claimed shelf life. Monitor and record real-time storage conditions. Compare real-time data against the accelerated conclusion and investigate any discrepancy. And update the conclusion, extending shelf life where real-time data support it and shortening it where they do not. Plan in advance for discrepancy: if real-time data show the product failing before the claimed shelf life, what happens to product already in the market must be thought through beforehand.

Common problems. An unjustified factor, adopting a common value without explaining its applicability. No real-time ageing, leaving only accelerated data. An excessive accelerated temperature that triggers changes not occurring at ambient. Humidity ignored for moisture-sensitive products. Only end-point measurement, revealing no trend. Samples not in final condition, unsterilised or not in final packaging. And packaging not covered, since packaging ageing also affects shelf life.

How we handle it. For ageing work we confirm several things with the client first: which material in the product is most ageing-sensitive, whether the accelerated temperature is safe in the sense of not causing physical change, and whether humidity needs controlling. With those settled, the conditions have a basis. On scheduling we suggest intermediate sampling points rather than end-point only, because the trend carries more information than the end state and shows whether the product is stable or marginal.

Send us the material information and packaging format and we will work through the conditions. Phone or WeChat: +86 132 4819 8029.