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The Importance of Sterile Isolators in Sterility Inspections

2022-05-23

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Marya

Sterility inspection isolators are currently the most common isolators of two materials in the domestic market. One is a "hard cabin" isolator with stainless steel and tempered glass as the main materials; the other is a PVC membrane as the cabin structure.

 1. Development stage ..................................................................................................................................................................... 
As early as the 1980s, isolation technology has been widely used around the world, and as the first laboratory sterility inspection industry to introduce isolation technology in the pharmaceutical industry, it has undergone several generations of changes in the international market:
The first generation: PVC and other soft materials are used as the main structural material, and the air handling system is designed as a turbulent structure; the operating components are mainly gloves/sleeves and half-length clothing, and disinfection methods such as ozone or peracetic acid are used to control microorganisms.
The second generation: With the development of aseptic isolation technology and sterilization technology, the isolator has developed into a stainless steel material as the main structural material, but the structure still retains the turbulent flow design in the cabin. The sterilization method is mainly connected to an external vaporized or sprayed hydrogen peroxide device.
The third generation: In order to strengthen the risk control during the use of the sterile inspection isolator and consider the occupational health of the operators, the isolator is developed with stainless steel as the main material, one-way flow design, integrated online environmental monitoring device, vaporized The hydrogen oxide sterilization system is integrated with the isolator.


 2. Technical requirements ..............................................................................................................................................................
1) The material of the isolator
Sterility inspection isolators are currently the most common isolators of two materials in the domestic market. One is a "hard cabin" isolator with stainless steel and tempered glass as the main materials; the other is a PVC membrane as the cabin structure. "Soft pod" isolator.
Compared with the hard wall isolator, the soft cabin isolator designed and manufactured with PVC as the main material has the following advantages and disadvantages:

No.

project

Hard wall isolator (stainless steel main structure)

Soft wall isolator (PVC main structure)

1

Single machine manufacturing cost

Usually more than 2 times of soft wall isolator

cheap price

2

Operating field of view

The field of view is greatly affected by the ergonomic design

Unobscured

3

Internal airflow during production

One-way flow is generated during production to ensure that the internal cleanliness reaches the set level A (dynamic/static)

Turbulent flow design during production, long self-cleaning time, unable to guarantee internal cleanliness

4

service life

Stainless steel designed hard cabin isolator can ensure stable operation for more than 10 years

In the case of repeated use of the sterilant, the PVC will deteriorate and need to be replaced regularly as a whole

5

Seal Interface Integrity

Fixed connection without breakage of sealed interface

Usually, seals and throat hoop are used for connection, and the sealing interface is prone to damage and leakage.

6

reliability

Strong and reliable physical structure, good sealing, strong ability to maintain aseptic

It is easy to cause damage and leakage, destroying the maintenance of sterile state

7

Sterilization effect

More than 6 log kills on interior spaces and exposed surfaces

The internal space and exposed surface can achieve more than 6 logarithmic killing effect (internal stirring fan needs to be added)

8

Residual time after sterilization

Stainless steel has no obvious adsorption to vaporized hydrogen peroxide, the residual discharge time is short, and the expected residual discharge effect (≤1ppm) can be achieved within the set time.

The PVC plastic material will absorb a large amount of vaporized hydrogen peroxide, and the residual discharge time will be longer.

Note: When using PVC material as the main structure of the soft chamber isolator, the influence of the residual vaporized hydrogen peroxide in the isolator on the sterility inspection process should be considered.
2) Airflow form
Although the regulations do not explicitly require the airflow in the sterility check isolator, the one-way flow isolator can maintain a dynamic class A, further improving the reliability of the sterility check process operation and avoiding the generation of false positives. Compared with the turbulent flow design, the air flow of the one-way flow isolator is evenly distributed, and the sterilization gas is distributed and diffused evenly. In addition, in the process of discharging residue, the residual concentration of vaporized hydrogen peroxide is more uniform and stable than that of the turbulent design isolator, which is convenient for testing and more representative.
When selecting a turbulent isolator, the number of air changes and self-cleaning time of the isolator should be tested. The ventilation effect after sterilization meets the requirements.
Different air inlet and outlet positions, different air volume/ventilation times will affect the internal air flow. Therefore, the turbulent isolator needs to carry out the airflow pattern test to confirm the airflow dead angle. These dead ends of the airflow may not have an impact on the sterilization effect, but create a blind spot for the control of microorganisms during the use of the isolator.
3) Ergonomic design of the isolator
The sterility inspection operation usually takes 4 to 5 hours or more, so a reasonable ergonomic design can effectively reduce the operator's fatigue and convenience in long-term operation.
Manufacturers of sterile inspection isolators should carry out ergonomic design of standard isolators, from the height of the equipment, the position of the glove/sleeve assembly, the height of the operating platform, the size of the operating window, the relative position of the bacteria collector and the glove port, etc. Factors are considered to ensure that it meets the needs of most domestic operators.
Due to the structure of the isolator for sterility inspection, corresponding auxiliary tools should be provided inside the isolator to make up for the relatively limited operating space in the isolator and ensure the convenience of sterility inspection operations.
The ergonomic design of the sterile inspection isolator should meet the following points:
Wearing the glove/sleeve assembly or half-body garment of the sterility check isolator can access or fully utilize the tools in the isolator for sterility check operations;
During the sterility inspection, no excessive stretching of the glove occurs, and the glove should touch the least surface;
During the sterility inspection, the operator will not exert local muscle force for a long time;
During the sterility inspection, the operator's operating field of vision is not blocked, and the key process positions can be observed in a natural state;
For the standard sterile inspection isolator, it can be adapted to a wide range of population operations.
Generally, for customized isolators, the MOCK-UP simulation operation process should be performed.
4) Sterilization with vaporized hydrogen peroxide
Vaporized hydrogen peroxide sterilization is the most commonly used surface sterilization method for isolators. According to PDA TR51, it is mentioned that the key influencing factors in the development and verification process of hydrogen peroxide sterilization cycle are: the temperature of the isolator cabin before sterilization. Humidity, concentration of hydrogen peroxide solution, evaporation efficiency of hydrogen peroxide, total vaporized amount of peroxide vaporized, temperature of other vaporized peroxide entering the chamber to be sterilized, distribution of hydrogen peroxide in the chamber and the amount of hydrogen peroxide in the chamber placement of items. Therefore, at least the amount of peroxide vaporization, the evaporation temperature, the temperature and humidity before sterilization, and the placement of items in the cabin should be controlled. Ensure reproducibility of sterilization effects.


 3. Application requirements ..........................................................................................................................................................
1) Background environment
From a regulatory point of view, the 9206 Guidelines for Validation of Isolation Systems for Sterility Inspections mentioned: "It is recommended not to be lower than the Class D air cleanliness requirements in my country's current GMP,..."
The mainstream foreign regulations, PIC/S, USP, etc., do not require the background environment level of the sterile inspection isolator, but only require the control of the entering personnel.
From the perspective of risk analysis, the higher the background cleanliness, the lower the bioburden on the surface of the items in the background environment during the delivery of the items, and the probability of contamination risks is relatively lower. However, generally, before the isolator items are passed into the isolator, the surface of the items will be wiped and disinfected, and vaporized hydrogen peroxide will be sterilized in the isolator. Validated sterilization processes are capable of reducing logarithms in excess of 6log. Always keep the isolator sealed when testing with the isolator and will not be affected by the background environment.
2) The placement of items
In the selection of isolators, it is very important how to choose an isolator with a volume that matches its own test batch. The user should first clearly enumerate the quantity, packaging, and size of the test substance used in the daily test volume, as well as the quantity, packaging and size of the medium and buffer. And consider the daily work schedule to select the appropriate isolator volume to ensure that the isolator can load the corresponding materials. Place in the isolator according to the proven loading method. Generally, a corresponding frame should be designed and placed for different test product packaging. Materials should not be close together to avoid dead ends of sterilization. The image below shows the isolator cavity after loading. Once verified, the placement and placement of various items should be fixed and written into the SOP.
3) Cleaning of the isolator
Isolators should be cleaned and disinfected before use. It is usually wiped with a lint-free cloth moistened with alcohol or isopropyl alcohol.
The order of cleaning is from high to low, from relatively clean areas to relatively dirty areas, and from dry areas to wet areas. Each time you wipe the cleaning surface with the rag, the wiping paths overlap to a certain extent. Cleaning cannot be done in a circular fashion.
Gloves are cleaned and disinfected in addition to being tested for integrity. You can wipe the surface of the glove with a rag moistened with the disinfectant, from the hand part to the sleeve part. When using the gloves, you can also spray the disinfectant on the palm, and then rub the surface of the finger part of the glove until the disinfectant is used. dry.
The method of cleaning the isolator, the cleaning agent or disinfectant used, and the frequency of cleaning should form a standard procedure.
4) Sterilization with vaporized hydrogen peroxide
In practical applications, sterilization verification should consider the following three aspects:
(1) Sterilization effect and its reproducibility:
Although there are no special requirements for the temperature and humidity of the laboratory, it is generally enough to meet the comfort of the operator. However, it must be ensured that the temperature and humidity conditions in the laboratory are not subject to large fluctuations due to seasonal climatic factors.
(2) Packaging integrity
In addition to considering the risk of false positives, the isolator also evaluates the risk of false negatives in the risk analysis. In addition to considering the influence of the antibacterial components of the product itself, the occurrence of false positives may also arise from improper surface disinfection and sterilization.
Permeation of hydrogen peroxide during surface sterilization increases the risk of undetectable micro-organisms in plastic or other packaging methods with a risk of penetration. Therefore, packaging integrity testing is required for this type of packaging.
(3) Residual hydrogen peroxide
In addition, after the hydrogen peroxide sterilization cycle is over, excessive residual hydrogen peroxide concentration in the isolator cavity may also lead to false negatives and also affect the recovery growth performance of the environmental microbial culture medium. The sterility inspection isolator should be equipped with a low-concentration vaporized hydrogen peroxide concentration sensor or other appropriate detection means to monitor or test the vaporized hydrogen peroxide residual concentration inside the isolator in real time after the residual discharge is completed.
To ensure the health and safety of operators, the residual concentration of hydrogen peroxide in the laboratory space should not be higher than 1 ppm.
5) Isolator Gloves
(1) Glove integrity test
Sterility check isolator gloves should be tested for integrity before use and after sterility checks have been completed. There are two ways to inspect gloves. Visual inspection is the simplest and most effective test method. Generally, properly stretch the most easily damaged part of the glove to check for obvious damage. At the same time, check the gloves for cracks and aging. It is generally checked before and after use, and it can also be checked during the process. Check the integrity of the gloves with a glove leak detector and check the gloves with the pressure holding method. Regular inspections are generally required.
Regardless of the method used to inspect the glove, the results of the test need to be recorded.
(2) Cleaning and disinfection of gloves
Gloves need to be cleaned and properly disinfected prior to aseptic manipulation. Use a dust-free rag dipped in an appropriate amount of disinfectant alcohol, IPA or other required disinfectant to wipe the surface of the glove exposed on the isolator side.
The direction of wiping should be unidirectional from the fingers towards the palm and cuff. After each wipe, turn the rag over to an unused surface before wiping.
If necessary, before operation, wear isolator gloves, spray IPA or alcohol directly on the hands, and then rub the palms, backs of the hands, and the fingers of the crossed hands like washing hands, and rub the parts between the fingers. Users should specify the SOP for cleaning and disinfection of gloves according to their own process characteristics, and operate in strict accordance with the SOP.
Gloves of the isolator should not touch any surface inside the isolator at will. For example, contact with critical sterile surfaces, sterilization risk points such as sealing rings, and objects or surfaces that are prone to wear or damage to the surface of the gloves should be avoided. If necessary, you can wear a layer of sterile gloves after wearing the isolator gloves for some process operations.
The isolator gloves can be sterilized with vaporized hydrogen peroxide along with the interior of the isolator cavity. During the sterilization process, the glove holder is used to spread the glove so that the surface of the glove (the main part of the hand) can be exposed to the sterilizing steam.
6) Environmental testing
Sedimentary bacteria, planktonic bacteria and microorganisms on critical surfaces should be detected in the isolator. Environmental microbiological testing should address the following issues in the SOP:
 Sampling amount of planktonic bacteria, and sampling;
 Sampling location of settled bacteria, exposure time of each petri dish;
 Determine the location of surface microbial sampling, whether to take samples during the test or after the test. Whether sampling with a contact dish or a swab;
 Establish microbial warning limits and action limits, as well as measures to be taken and investigation of causes and results;
 After sampling the surface, what to do with the surface that came into contact with the medium.
 Microbiological control needs to be established for the piping on the isolator, the waste liquid piping, and the piping of the environmental monitoring system.
7) Aseptic Practice in Isolators
Operators inside the isolator must adhere to the most basic aseptic procedures. In the isolator, it is also necessary to pay attention to the following issues according to the characteristics of the isolator:
All movements in the isolator must not be too large or too fast. For example, quickly waving the gloves in the isolator will cause huge fluctuations in the internal pressure of the isolator. The rapid removal of the hand from the isolator glove can cause a momentary negative pressure inside the isolator.
Gloves must not touch any surface unrelated to process operations.
Sterility check isolators must be operated by personnel qualified in microbiology and trained in isolator operation.


 4. Summary ......................................................................................................................................................................................
This article puts forward opinions and explanations from the structural design of the isolator and the operation and use of the isolator. The equipment function and performance of the isolator should be required and regulated based on the requirements of the sterility inspection process, the perspective of risk, and the requirements of regulations. At the same time, the isolator is not just a process equipment, but a process combined with sterility inspection. Therefore, the isolator factor needs to be fully considered when performing sterility inspection process validation.