The Evolution from Fixed to Single-Use Systems - An overview of applications for disposable components and important property considerations. This article is part of a special issue on Single-Use Tech

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The Evolution from Fixed to Single-Use Systems
An overview of applications for disposable components and important property considerations. This article is part of a special issue on Single-Use Technologies.


BioPharm International Supplements
pp. s15-s20

PLASTIC COMPONENTS AND SINGLE-USE SYSTEM RESEARCH

Many questions were raised over initial plastic designs. These issues were exacerbated by the general lack of polymer knowledge after years of metal use.


Table I: Chemical, brand name, and application of common plastics.
The list of candidate plastics for single-use pharmaceutical processing includes those currently used in industry designs (see Table I). One of the strengths of these plastic components is the diversity of properties and designs presented. However, this also represents one of the main challenges as biopharm engineers struggled with how to incorporate a number of material components into a system and industry designed to minimize risk.

Membrane and filtration

The longest running polymer components used in biopharmaceutical applications are filter membranes and cartridges. These components have been used in fixed systems for many years. Membrane filtering applications have primarily used polytetrafluoroethylene (PTFE), polyvinyldene fluoride (PVDF), polypropylene (PP), and polyethersulfone (PES) (2). PVDF has been the resin of choice for over 20 years in protein synthesis and separation for biopharm applications. The large surface to volume ratios required in filter membranes exceeds that of other common components including tubing and containers. Therefore, this fluoropolymer resin has been long vetted and provides biopharmaceutical process engineers with a track record and history of successful performance in industry processes.

Piping

Polymer materials, especially PP and PVDF, have experienced success supplanting stainless steel in some fixed industry piping designs as the materials could be used in various water service criteria, including United States Pharmacopeia (USP) purified water for both plastic resins. Additionally, PVDF piping lends itself to use in ultra high purity water, laboratory reagent grade water Type 1, as well as Semiconductor UHPW ASTM Type 1 service criteria. One advantage of polymer components to stainless steel is the latter's capacity to rust or rouge in high-purity water causing system contamination. Chemical passivation is frequently required to remove free ions from the surface and restore the oxide film that gives stainless steel its corrosion resistance (4).

Tubing and fittings

Tubing is the most highly utilized component within a disposable system because large fluid transfer is required with the single-use system design. Multiple materials have been used ranging from silicone, EVA, TPE compounds, low density PE, PTFE, and PVDF copolymers.

Molded fittings are required to attach or weld to other process componetry including bags and containers. Therefore, welding and processability becomes an important design criteria. The most common industry fitting materials are PE, PP, polycarbonate (PC), silicone, and PVDF.

Bags

Film bags and containers pose possibly the most significant challenge as they are needed in numerous disposables functions starting with reaction vessels and progressing to transfer, storage and media preparation. Long dwell times are the norm, which makes purity concerns paramount despite being only one of a host of factors that affect their maximum utilization. These bags must be strong and tough, possess barrier properties and have the ability to melt bond effectively in multilayer structures. Purity, melt processability and bonding, as well as the contact layers ability to be sterilized while providing a significant barrier or permeation properties is a tall task. Common bag layers include EVA, PE, and PVDF.


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