Single-layer Film Bags vs. Multi-layer Film Bags Biopharmaceutical Manufacturing

Since the early 1970s, single-use, disposable plastic technology for the manufacturing of biopharmaceutical products according to the U.S. Food and Drug Administration’s (FDA) current Good Manufacturing Practices (cGMPs), has been steadily replacing traditional production facilities that relied on relatively inflexible, hard-piped equipment, including large stainless-steel bioreactors and tanks to hold product intermediates and buffers.[1][2]

In the early development of single-use, disposable, plastic technology Contract Manufacturing Organizations (CMOs) with a relative lack of legacy production systems were early adopters of plastic technology, primarily as a capital expenditure (CAPEX) cost-saving measure. Historically, it cost U.S. $ 500M – U.S. $1B to build and outfit a new stainless-steel facility.

Replacing traditional equipment with plastics technology allowed for a quick change and easy set-up. This improved productivity and reduced equipment expenses.

Early adoption
First introduced in a clinical environment for media storage and transportation of blood and intravenous liquids such as saline solution, plastic technologies were adopted into the manufacturing environment in the late 1970s, about the time when multilayer food packaging films were being introduced to the market. This evolved to include three-dimensional process containers and filter assemblies.

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In the late 1990s and early 2000s, a paradigm shift driven by several bioprocessing companies, saw bioreactors converting to plastics as the fluid contact layer. With end-to-end plastic manufacturing in full swing, it was now possible to move from small-scale manufacturing of clinical-trial materials to full-scale cGMP commercial production.

In this article we take takes a closer look at plastic storage bags for bioprocessing applications, the challenges associated with them, and technology developments to address these challenges. We specifically focus on materials that enable a shift from multi-layer to single-layer storage solutions.

Why switching to plastics?
Speed and flexibility are critical to succeed in the bioprocessing market. The first to patent a process for a particular drug product reaps the most benefit. Plastics provide the required speed to evaluate many more possibilities and get to the successful one quicker.

Additionally, plastics technology enables small-batch, single-use packaging solutions for customized drugs, which serve a smaller patient population than blockbuster drugs. These solutions lower energy and water consumption while simultaneously improving facility utilization and creating a smaller carbon footprint, reducing the risk of contamination, as well as analytical and quality-control costs.[3]

Today, single-use and disposable plastics have been adopted across the upstream manufacturing process, downstream purification and fill-finish of entire classes of biologic drugs. The adoption is especially growing in the development and manufacturing of biologics and complex drugs like Antibody-drug Conjugates (ADCs), highly potent biopharmaceutical drugs designed as a targeted therapy in the treatment of cancer. These targeted agents are highly hazardous materials, often with occupational exposure limits (OEL) below 100ng/M³/8Hr workday.

One of the main drivers for disposable, single-use technology in the manufacturing of biopharmaceutical products, includes the cost of energy and the reduction of risk. For example, traditional stainless steel manufacturing systems use substantially more energy for sterilization and cleaning, while less for the production of biopharmaceutical materials. However, the primary reason to consider disposable and single-use technology is not only reducing energy cost but also the elimination of cleaning, cleaning validation, and cross-contamination risk. In addition, less steal requires lower capital investment and may speed-up time to market.

Sterilization
The development of gamma-irradiation stable plastic technology is probably one of the most important evolutions seen in the industry, greatly advancing the application of single-use technology. Gamma irradiation, a common means of sterilization, kills bacteria at a molecular level by breaking down bacterial DNA and inhibiting bacterial cell division.

Having been gamma-irradiated at levels between 25k and 50k gray (Gy), the need for subsequent sterilization of most single-use materials and products is eliminated. [4]

Challenges
Plastic bags that store, transport, and protect valuable biopharmaceutical agents are designed with two distinct functions in mind: contact with biopharmaceutical fluids and functionality. As such, these bags need to meet a series of unique and different specifications.

Today, these distinct criteria and characteristics are generally met through composite, multilayer, plastic, or polymer film constructs with a different and specific outer layer or shell to protect against environmental impacts and guarantee durability. Additionally, there is a contact layer on the inside of plastic vessels to keep the biopharmaceutical fluids safe. The various layers composing the multilayer construct are tied together with adhesives to unite incompatible materials harmoniously in single, homologous constructs. [5]

There has been an increased concern about bag contamination from extractables and leachables (E/L) arising from the binding material used to adhere to the various layers of the film materials used to manufacture them.

This contamination can impact cell growth and affect product yield, quality, or stability, leading to significant quality concerns. Recent studies show this may be due to an increase in the transition of products produced using plastic technology moving into later-stage clinical development. [6]

The way ahead: New and improved materials
Historically, these complex, multilayer constructs were designed for the storage and transportation of liquid materials and critical buffers and media. Now that materials are primarily transported in dry powder form, the concern has lessened, again allowing manufacturers to search for alternative materials for making plastic products. Therefore, homogenous, single-layer polymers without adhesives, and unitary molded, solid, and structurally self-supporting plastics, may enable major design innovations. [7]

Multilayer vs. single-layer
The chemical and physical properties of the polymeric materials used to manufacture the bag layers are influenced by the molecular structure, polymerization process, stabilization, and processing additives, as well as manufacturing factors such as extrusion conditions. Also, the physicochemical properties of these materials are affected by factors such as heat, light, oxygen, and sterilization (i.e. irradiation) conditions.

Plastic materials are generally made from multilayer films and may include variants of PE such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ultra low-density polyethylene (ULDPE), ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVOH), polyamide (PA), or polyethylene terephthalate (PET). [8]

Each layer in these multilayer films contributes to the overall film properties, while resin selection is based on predetermined criteria, such as barrier properties or transparency requirements.

Because not all plastics are compatible, the different polymer layers in a multilayer film structure may express limited interlayer adhesion. This is why the aforementioned “tie-layer” is used to provide adhesion between adjacent film layers, helping these different polymer layers adhere. [9]

Alleviating concerns
To address ongoing contamination concerns, both manufacturers of plastic technologies and end-users in the biopharmaceutical industry are looking for new and improved plastics to use in their products. At the same time, purity-improvement measures for plastic technologies are being driven by the stringent technical and regulatory demands for high purity in biopharmaceuticals, the sensitivity of cell cultures to trace impurities, and the clinical impact of particulates on patient safety.

One such improvement includes the use of homogeneous films that eliminate the lamination and adhesives of a multilayer film.

Multilayer, polymer-based, plastic products may become brittle and fragile under cold temperatures. Because they are made of varying materials that will react differently to thermo-expansion, they may incur delamination and cold cracks (micro fraction across all layers.

However, in single-layer fluoropolymer plastics, thermo-expansion is better and will not cause microfractures across different layers that could potentially harm bag integrity, as often seen in multilayer plastic constructs. Overall, the increased strength and durability help to avoid costly assembly failure at downstream fill-finish operations. [10]

Without the additional polymeric layers in multilayer film bags, storage vessels or bags made from fluoropolymer plastics offer lower permeation to control gas diffusion rates, ensuring that gas content (O₂ and CO₂) inside the vessel or bag remains within an acceptable range.

Unlike multilayered films, single-layered films ensure against a material failure of plastic bags due to delamination, offering higher purity, greater compatibility, and increased safety for critical and high-value process materials and final biopharmaceutical agents.

Quality of plastic
Today, there are only a few known materials that meet the distinct and different criteria to allow them to be used for manufacturing plastic materials for (bio-) pharmaceutical production as a single-layer plastic film.

Fluoropolymer plastics are a special class of fluorocarbon-based polymers with multiple carbon-fluorine bonds characterized by high resistance to solvents, strong acids, and bases. They are well suited to meet the requirements for challenging applications in which durability, inertness, purity, and cleanliness are important.

It’s important to note that not all fluoropolymers on the market are the same. Many are not gamma stable. While greatly benefitting biopharmaceutical production by reducing batch rejection, gamma irradiation may also significantly breakdown certain plastics and trigger the release of E/L from these traditional multilayers, polymer-based materials. This limits acceptance in bioprocessing. [11]

For example, polyvinylidene difluoride is a copolymer formulation often used to provide the bags with flexibility but using it can lead to additional E/L. Polytetrafluoroethylene and fluorinated ethylene propylene are not gamma stable beyond 5 kGy, limiting use in bioprocessing as well.

There is only one fluoropolymer film out on the market known to have the ultimate purity and be gamma stable to address the market’s concerns with E/L. It also serves a wide temperature range. This material promises to be a game-changer for the industry, displacing the legacy products that are limiting consistency in bioprocessing production.

When used for manufacturing plastic products, such as vessels or bags, this novel fluoropolymer material, engineered and manufactured to be used in extreme environmental conditions, allows for increased efficacy in frozen applications, such as storage and shipment of stem-cell materials and critical buffers and media.

Using these novel fluoropolymer plastics reduces the risk of breakage while at the same time provides an increased level of security and flexibility. As the plastics don’t contain curing agents, antioxidants, plasticizers, or adhesives, potential contaminants are reduced, improving overall universal material compatibility. When used in the development of plastic vessels or bags, these characteristics reduce the risk of material and assembly failures.

In addition, high-grade fluoropolymer films (the material used in the development of plastic tools and equipment) are the only available plastics with a broad operating temperature range from 260°C (500°F) down to –240°C (–400°F).

In fact, in comparative freeze-thaw cycles and frozen drop tests, one type of plastic 2D bag made from this high-grade, single-layered, fluoropolymer plastic and manufactured in an ISO Class 5 cleanroom, was proven most reliable under cryogenic temperature conditions, down to a temperature of –85°C (–121°F) or lower without negatively affecting the film.

Bags made from this ultrapure, advanced fluoropolymer film technology are free of adhesives, binders, curing agents, photo-stabilizers, lubricants, acid scavengers, pigments, antioxidants, and plasticizers commonly used to meld multiple film layers together for added protection. This limits the potential impact on high-value (bio-) pharmaceutical compounds.

Lastly, products made from single-layer fluoropolymer plastics offer universal material compatibility, a much-desired characteristic of these products.

Conclusion
As the market grows and the adoption of plastic technology expands, the materials used to design, develop, and manufacture these products are expected to greatly improve.

In particular, novel fluoropolymer plastics help to reduce costs, meet batch-size requirements, and protect and maintain the purity of bioprocess materials.

Additionally, the integrity of the bag is improved to withstand a variety of temperatures, handling, and transportation. Bags made from single-layer fluoropolymer plastics equaled or surpassed the integrity of multilayer polyethylene bags. This helps meet the ever-changing and more stringent requirements of drug developers, (bio-) pharmaceutical manufacturers, and regulators.

References
[1] Shukla AA, Gottschalk U. Plastic disposable technologies for biopharmaceutical manufacturing. Trends Biotechnol. 2013;31(3):147–154. doi:10.1016/j.tibtech.2012.10.004.
[2] U.S. Department of Health and Human Services, Food and Drug Administration, Center for Biologics Evaluation and Research. Guidance for Industry: Current Good Tissue Practice (CGTP) and Additional Requirements for Manufacturers of Human Cells, Tissues, and Cellular and Tissue-Based Products (HCT/Ps). December 2011.
[3] W. Whitford, M. Petrich, SUStainability — Concerning Single-Use Systems and the Environment, Bioprocess International, eBook, June 2018 http://www.bioprocessintl.com/manufacturing/single-use/sustainability-concerning-single-use-systems-and-the-environment/
[4] Lopes AG, Brown A. Practical Guide to Single-use Technology: Design and Implementation. Akron, OH: Smithers Rapra; 2016.
[5] BioPlan Associates, Inc. Top 15 Trends in Biopharmaceutical Manufacturing: a summary of global findings from the 12th Annual Report and Survey of Biopharmaceutical Manufacturing Capacity and Production. September 2015.
[6] Twelfth Annual Report and Survey of Biopharmaceutical Manufacturing Capacity and Production. Rockville, MD: BioPlan Associates, Inc.; April 2015:294.
[7] Jurkiewicz E, Husemann U, Greller G, et al. Verification of a new biocompatible plastic film formulation with optimized additive content for multiple bioprocess applications. Biotechnol Prog. 2014;30(5):1171–1176. doi:10.1002/btpr.1934.
[8] Sinclair A, Monge M. Quantitative economic evaluation of single-use disposables in bioprocessing. Pharmaceutical Engineering. 2016;22(3):20–34.
[9] Hammond M, Nunn H, Rogers G, et al. Identification of a leachable compound detrimental to cell growth in single-use bioprocess containers. PDA J Pharm Sci Technol. 2013;67(2):123–134. doi:10.5731/pdajpst.2013.00905.
[10] Johnson MW. Understanding particulates in single-use bags. BioProcess Int. 2014;22–28.
[11] Jurkiewicz E, Husemann U, Greller G, et al. Verification of a new biocompatible single-use film formulation with optimized additive content for multiple bioprocess applications. Biotechnol Prog. 2014;30(5):1171–1176. doi:10.1002/btpr.1934.