Considerations and Functional Elements of Closed Systems: Isolators and Single Use Systems
Dr. Humberto Vega, President and CEO, HMV Food and Pharma Consulting
Dr. Bassem Gayed, Site Head, MSAT, Legend Biotech
Mr. Frank E. Matos, Director, Sterility Assurance, Sofie Biosciences
Technological advances have enabled the routine use of isolators and single-use systems in manufacturing, especially in aseptic processing, reducing chemical, particulate, and microbiological contamination risks. These closed systems create barriers between operators and products, minimising human-borne contamination while also providing containment that protects personnel from hazardous materials and microorganisms.
Introduction
Advances in technology have demonstrated the feasibility of using isolators and single-use systems (SUS) in routine pharmaceutical manufacturing operations, particularly in aseptic processing. Their implementation has significantly reduced the risk of chemical, particulate, and microbiological contamination.
A fundamental principle of both isolators and single-use systems is to create a physical barrier between the manufacturing process and the surrounding environment. This barrier separates the product and process from direct operator contact and is designed to remain free from contaminants, such as microorganisms. By minimising human intervention, these systems reduce or eliminate contamination risks associated with the human body, including skin particles, hair, and respiratory droplets. In certain applications, they also function as containment systems to protect operators from exposure to hazardous materials during manufacturing activities. Collectively, these applications are often referred to as closed systems. A third category of closed systems—rigid stainless-steel tanks and piping—exists but is outside the scope of this discussion.
Isolators may be classified as open or closed systems and consist of enclosed units designed to perform specific operations under environmental conditions that are controlled independently from the surrounding room (PDA, 2001; Denk, 2022). These units are sealed or supplied with filtered air to prevent ingress of external air and may operate under positive or negative pressure. Prior to use, isolators undergo standardised and validated decontamination procedures (PDA, 2001 & 2025). Materials introduced into the isolator must be decontaminated and are transferred through rapid transfer ports or decontamination systems. Operators interact with the process using attached glove systems or suits, without physically entering the enclosure. Isolators are typically installed in processing rooms classified as Grade C (ISO 8).
Shielded isolators such as Dispensing Hot Cell (DHC) are essential for radio pharmaceutical manufacturers. A DHC isolator creates a Class A (ISO5) environment to aseptically dispense product into syringe or vial doses. DHC units typically have vertical laminar air flow that covers the entire work area. Sanitised materials are introduced into the work area through a pre-chamber. Product dose dispensing into syringes or vials is done using telemanipulators or automatic dispensers. An automatic dose ejection system places the syringe or vial into a shielded container in the external environment for transport. DHC units protect the product from contamination and operators from radiation exposure.
A single-use system (SUS) is a preassembled application commonly composed of polymeric components such as bags, tubing, connectors, and clamps. These systems are sterilised by steam, radiation, or chemical methods and are supplied ready for use in sealed packaging. After a single production cycle, they are discarded. Raw materials, intermediates, and finished products are transferred into and out of SUS assemblies using aseptic connectors, thereby maintaining system integrity. Like isolators, single-use systems are typically operated in Grade C (ISO 8) environments.
In summary, isolators and single-use systems are both considered closed systems. They provide enhanced protection for sterile materials, in-process products, formulated drug products, and components, while also offering operator protection when handling hazardous substances.
Key Considerations for Closed Systems
As previously discussed for isolators and single-use systems (SUS), a closed system establishes a physical barrier between the manufacturing process and the surrounding environment. To ensure this function is achieved and maintained, the system design should incorporate the following elements (PDA, 2001, 2008, & 2025; Agalloco, 2020):
• Designed, installed, and qualified to maintain integrity across the full range of intended operating conditions and throughout its lifecycle:
- Documentation
The documentation associated with the systems should include completed risk assessments, reviewed and approved drawings, a list of materials and constructions with special attention to product contact surfaces, and a complete list of instrumentation required for the operation of the system (as applicable).
- Installation / Operational / Performance Qualification
Qualification protocols and documentation (as applicable for isolators or SUS) shall contain complete system specifications and drawings, complete list of required utilities and process conditions (e.g., minimum air pressure or flow, operating voltage and power requirements, data ports, calibration requirements and results, cleaning and disinfection/sterilization development and validation, integrity/leak testing, results of engineering runs, compatibility data including leachable and extractable studies. Aseptic process simulations are utilised as part of the qualification activities.
• Operated without compromising system integrity, avoiding unintended breaches during use.
- Documentation
Detailed procedures and batch records are utilised for the assembly (e.g., SUS), ensuring no contamination (e.g., particulate) and use of the systems. Validated cleaning, sterilisation/disinfection, and leak testing procedures for proper set-up and operation of the systems.
- Sterilised/disinfection prior to use through a validated procedure (either in place or as a closed system). Single-use systems are typically sterilised off-line after final assembly, and their integrity must be preserved until and throughout use.
- Documentation
The documentation associated with the sterilisation/disinfection of the system includes approved protocols and final reports with all raw data. Additional documents include filter integrity testing as well as container closure integrity validation.
• Materials and components transferred into and out of the system in a manner that maintains aseptic conditions.
- Documentation
Detailed procedures, instructions, and batch records are utilised for the transfer of materials.
- Testing
Environmental monitoring and pre-use/post-sterilisation filter integrity testing to ensure integrity of the sterile boundaries.
• Preventive maintenance and approved procedures are established and implemented to ensure system integrity before and during operation.
- Documentation
Detailed procedures and records involving preventive maintenance are in place, as well as operating procedures to ensure the integrity of the system before and during operation.
• Use of sterilising-grade filters for liquids and gases, where applicable. These filters function as sterile barriers and are integrity tested as part of routine manufacturing operations.
- Documentation
Completed filter validation reports for liquids and gases applications. In the case of isolators, qualification and integrity testing of the HEPA filters shall be included.
- Testing
Pre-use and post-use testing of filters is expected to ensure the sterile boundaries are intact.
• Connection to other closed systems performed in a way that does not compromise the integrity of either system.
- Type of Connection
Typical connections in isolators include rapid transfer ports, steamed connections (piping), tube welding, and aseptic connectors. Meanwhile, typical connections in SUS include tube welding and aseptic connectors.
• System modifications managed through formal change control procedures, with appropriate documentation and assessment of impact on integrity and sterility assurance.
Functional Elements of Closed Systems
The following functional differences can be identified when comparing isolators and single-use systems (SUS) as closed systems (PDA, 2006, 2008 & 2025; Agalloco, 2020; Denk, 2022):
- Application:
A SUS is limited by its designed capacity (e.g., volume) and can be moved within the processing area for subsequent operations or storage. In contrast, activities performed within an isolator are confined to the fixed enclosure of the unit. Additionally, in a SUS, materials and products are in direct contact with the internal surfaces of the system, whereas in an isolator, there is typically no direct contact between the product and the isolator’s structural surfaces.
- Materials of Construction:
SUS components (e.g., bags, tubing, clamps, and filters) are primarily manufactured from polymeric materials such as silicone, polyethylene, polypropylene, polyvinyl chloride, ethylene vinyl acetate, polycarbonate, polysulfone, polyethersulfone, and fluoropolymers.
Isolators, by contrast, are predominantly constructed from stainless steel (304L or 316L) for structural elements, frames, and rapid transfer ports. Viewing panels and certain transfer ports may be made from tempered glass, polycarbonate, or acrylic. Gloves and sleeves are typically composed of elastomers such as neoprene, nitrile, butyl rubber, or ethylene propylene diene monomer (EPDM), while seals and gaskets commonly utilize silicone or fluoropolymers.
- Liquids and Gases:
SUS are primarily designed for the handling and transfer of liquids, whereas isolators rely on sterilised air or inert gases to maintain controlled environmental conditions within the enclosure.
- Sterilising Devices:
Both SUS and isolators may incorporate sterilising-grade filters for liquids and gases associated with raw materials or products. However, isolators additionally employ HEPA filtration systems to sterilise the air or gas supplied to the internal environment.
- Sterilisation of the System:
SUS are generally sterilised off-line by steam, gamma irradiation, or ethylene oxide prior to use. Isolators undergo in-place bio-decontamination, commonly using vaporised hydrogen peroxide or other gaseous disinfectants.
- Environmental Classification:
The internal environment of an isolator is typically maintained at Grade A (ISO 5) conditions and is supported by routine environmental monitoring programs, including viable and nonviable particle monitoring of air and surfaces. This classification does not apply to SUS itself, as they do not create a classified environment.
- Cleaning:
Cleaning requirements apply to isolators, where cleaning may be performed on a batch-by-batch basis or following a defined campaign. SUS, being disposable, does not require cleaning after use.
These distinctions highlight the differing design philosophies and operational controls associated with each type of closed system.
Final Remark
Isolators and single-use systems are both considered closed systems. They provide enhanced protection for sterile materials, in-process products, formulated drug products, and components, while also offering operator protection when handling hazardous substances. The key element of a closed system is the physical barrier they create between the process/product and the surrounding environment, reducing the risk for contamination of the product.
References
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Agalloco, J. 2020. Straight Talk on Closed Aseptic Systems. BioPharm International. May 2020, pages 32-36.
- Denk, R. 2022. How to Maximise Productivity by Using Closed Systems & Disposables: Annex 1 Implementation Between GXP Compliance & Cost Containment. Pharmaceutical Engineering/iSpeak. https://ispe.org/pharmaceutical-engineering/ispeak/how-maximize-productivity-using-closed-systems-disposables-annex?utm_source=chatgpt.com#.
- PDA, 2001. Technical Report 34. Design and Validation of Isolator Systems for the Manufacture and Testing of Health Care Products. PDA Journal of Pharmaceutical Sci. and Tech. Vol. 55, No. 5. Bethesda, MA.
- PDA, 2008. Technical Report 28. Process Simulation Testing for Sterile Bulk Pharmaceutical Chemicals. PDA Journal of Pharmaceutical Sci. and Tech. Vol. 60, Supplement S-2. Bethesda, MA.
- PDA, 2025. Technical Report 22. Process Simulation for Aseptically Filled Products. Revised 2025. Bethesda, MA
Dr. Humberto Vega is the President and CEO of HMV Food and Pharma Consulting, following a series of progressively senior leadership roles within major multinational pharmaceutical companies. He brings more than 37 years of experience across the pharmaceutical and food industries and maintains professional memberships with PDA, IFT, and ISPE.
Dr. Bassem Gayed serves as Site Head of MSAT at Legend Biotech, bringing extensive expertise in cell therapy, advanced manufacturing, and regulatory engagement. He bridges science and operational execution across the product lifecycle to enhance access and efficiency. He earned his B.S. and Ph.D. in Biomedical Engineering from UMDNJ/NJIT.
Mr. Frank E. Matos is the Director of Sterility Assurance at Sofie Biosciences, a manufacturer of radiopharmaceutical products based in Dulles, VA. In this role, he is responsible for overseeing contamination control and microbiology testing programs. He holds a master’s degree in medical microbiology from the University of Oklahoma.
