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Choosing the right disposable components for your application.
Single-use systems have risen in popularity for numerous reasons, one being disposability that eliminates cleaning requirements and risk of cross contamination. Disposable hose barb and sanitary flange connectors are crucial to both the assembly of individual process systems and to ensuring a controlled fluid path communication between process systems. Many features of disposable connectors, which have been long proven in critical medical equipment design, are now being integrated into a broad spectrum of biopharmaceutical applications.
Process designers in the biopharmaceutical industry are constantly being challenged to come up with user-friendly, cost-effective systems and components that comply with the industry's strict regulations (and potential concerns). A significant amount of time in this design process is put toward the selection of sanitary fittings, clamps, and tubing connectors for the transfer and management of media, buffers, intermediates, APIs, bulk drug products, and final formulations.
Choosing the right disposable components, however, can be a challenge. Plastic connectors offer more options for material selection, user interface, and customized design than metal connectors. Users often rely on system integrators to recommend connector fittings, but a basic understanding of the options available with plastic connectors will help system designers, integrators, and end-users specify the most optimized features to achieve peak performance in the equipment design.
Connectors may be considered in several categories:
Choosing the most ideal connector first requires a careful assessment of the application and its connection and disconnection requirements. The following must be considered:
Once the application is defined, the following are prime factors to be considered:
The requirements of the application will then determine what materials would be best suited for the connectors.
Plastic Connector Material Options
For hose barb and sanitary flange fittings, in most cases, polypropylene connectors provide sufficient physical, chemical, and functional properties suitable for single-use systems. In systems intended to be gamma irradiated, the polypropylene must be formulated as "gamma stable" using appropriate antioxidants to preclude premature degradation after irradiation. For unique applications, additional parameters to consider would include chemical compatibility with the process fluid formulation, extractables, mechanical properties such as toughness, ductility, impact strength, and physical properties such as transparency and lubricity.
Connectors should be manufactured from virgin resins, with accompanying certification of lot traceability. Resins that are either free of animal derivatives or certified to FDA and European Medicines Agency (EMA) BSA/TSK risk per US 21 CFR part 189.5 and EMA 410/01 rev 3, respectively, and meet standards such as ISO 10993 and USP <87> Biological Reactivity, in vitro (MEM Elution Cytotoxicity), and USP <88> Biological Reactivity, in vivo for Class VI plastics are particularly important in biopharmaceutical applications.
A broad spectrum of plastic resins can be selected to produce connectors, each with different characteristics to match the needs of system designers. The lack of need for sterilization in particular can make this choice easier, as steam or ionizing radiation exposure generally rules out a number of materials. These plastic resins are commonly employed in producing connectors used for biopharmaceutical applications:
Connectors are designed to accommodate tubing of varying hardness (durometer), from soft and flexible like PVC, silicone, and thermoplastic elastomer (e.g., C-flex or Advantaflex brands), to semi-rigid types like polypropylene, polyethylene, polyurethane, and ethylene vinyl acetate (EVA).
To facilitate these varying styles of tubing and their respective application needs, different connector types are used, including sanitary fittings, bag ports, tri-clamps, check valves, and barbed luer, quick connect, and tube-to-tube fittings. These basic connector styles can cover a wide range of liquid and air applications in manufacturing:
Many of the latest quick-connect designs focus on the user interface and are equipped with intuitively simple latch mechanisms to make for easy handling in pharmaceutical management applications while mitigating costly leakage.
Sterile (aseptic) connectors/disconnectors
Multiple design options offer the user or system designer a choice of options to make tubing connections outside of a hooded environment. Major benefits of these connectors are to provide sterile connection and disconnection options in uncontrolled environments. Sterile connectors are available in genderless and gendered designed. The gendered designs can provide an additional indication of intended process flow direction.
Barbs. Plastic barb-style connectors provide designers with a capability to accommodate the widest possible range of tubing properties and application conditions, including a multitude of configurations such as tees, "y"s, elbows, and manifolds. A number of barb designs are available—each with unique characteristics to tailor connection performance to specific needs—for handling assembly forces, tensile resistance, and blow-off resistance without the need for clamps.
Barbs derive their holding capability by expanding tubing above its nominal ID, creating some amount of interference for a secure seal and good mechanical retention. The tube expansion can vary dramatically, from lower profile, easier connections to much more aggressive interferences, depending on the pressure and tensile pull requirements.
The selection of the barb style is important to the connector's tube-holding capability. The cylindrical surface behind the barb should allow the tubing to relax against the fitting. In choosing a barb style, it should be ensured that the barb is designed with a sharp peak, allowing it to "bite" into the tubing for optimal retention.
Some tubing or hose connectors may use a multibarb, which can make for an inferior tube connection and seal. Multibarbs cannot create a sharp bite on the tube, inhibiting retention, and do not allow the tube a chance to relax behind the barb, also resulting in poor tensile pull strength.
Multibarbs are also relegated to a manufacturing process that leaves a parting line on the sealing surface, creating a potential leak path. This is an inherent design flaw, yet all multibarb connector designs, including metal connectors, display this liability. An optimally designed and properly injection molded connector will incorporate a singular barb with no parting line, a sharp bite, and a clean sealing surface.
The latest generation of plastic connector technology affords designers and manufacturers wide latitude of flexibility to design and set-up applications that custom fit to their specific needs. Some connector manufacturers provide comprehensive design centers to help single-use system designers and assemblers to achieve the highest level of performance from their connectors. With good consultation up front on the user's application requirements, the pitfalls of inappropriate connection technologies can be avoided and optimal system designs can be executed.
ACKNOWLEDGMENT The author wishes to acknowledge Ken Davis of Value Plastics for his contribution to this column.
Jerold Martin is senior vice-president of Global Scientific Affairs at Pall Life Sciences, email@example.com