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SBE Special Supplement: Disposables

Single-use/disposable technology (SU/DT) has emerged over the past decade as a cost-effective and fl exible basis for biopharmaceutical manufacturing (1,2). It

has moved beyond the limited applications of culture bags, liquid storage bags, and sampling devices, and now includes more unit-operation-based capabilities, such as cartridge fi l-tration, depth fi ltration, ultrafi ltration, and chromatography. Biopharmaceutical manufacturing typically involves a limited number of similar unit operations and processes — the primary differences among processes being the number, size and sequence of the unit operations. However, the facil-ities are large, complex and capital-intensive, with multiple interacting systems and operational preferences, so making comparisons between SU/DT and traditional systems is dif-fi cult and subjective. Such an evaluation, therefore, needs to take a whole-facility approach. Toward that end, this article considers a model process carried out in a small-scale biotechnology manufacturing facility designed to maximize SU/DT, and compares that to a facility designed around traditional reusable technology. For each unit operation, an acceptable commercially available SU/DT option that has adequate capacity and is suffi ciently well-developed to support commercial manufacturing is deter-mined. The utility requirements and capital equipment costs associated with a SU/DT-based facility are then estimated and compared with those of a traditional manufacturing plant. The results of the analysis suggest that, for a facility designed around a 1,000-L production-scale bioreactor, most unit operations can be based on SU/DT, which largely eliminates the need for clean-in-place (CIP) systems. This

is accompanied by a signifi cant reduction in the facility’s water consumption and waste generation. The primary reduction in capital costs is associated with process liquid-hold applications, such as intermediate product hold, media hold, and buffer hold steps.

The model process The process manufactures a recombinant conjugated vaccine product and consists of four 1,000-L production bioreactors, a harvest suite, a purifi cation suite, and a down-stream chemistry suite, as depicted in Figures 1 and 2. In the harvest suite, the clarifi cation operations employ microfi l-tration with a fi nal cartridge fi ltration step. The purifi cation suite employs two chromatography steps, two ultrafi ltration steps, an inactivation step, and a bulk fi ll step. The down-stream chemistry suite employs an activation step, a reaction step, a dilution step, two ultrafi ltration steps, and a fi nal bulk fi ll step. The facility is supported by a media preparation area and a buffer preparation area (Figure 3, p. 32), as well as various auxiliaries. To allow comparison to other types of biotechnology manufacturing, the process employs equip-ment similar to that in a monoclonal antibody (mAb) facility designed with two purifi cation trains. The model process uses 1,000-L production bioreactors, as this appears to be the current upper limit on commer-cially available disposable stirred bioreactors. Microfi ltra-tion is used for clarifi cation because the 1,000-L bioreactor volume borders on being too small for centrifugation and too large for depth fi ltration, and microfi ltration can be addressed by SU/DT whereas centrifugation cannot.

Disposable vs. Traditional Equipment —

A Facility-Wide ViewThis analysis shows how to quantify the

capital and operating differences between

single-use and reusable equipment for a

model biopharmaceutical process.

Craig Sandstrom

Fluor

CEP July 2009 www.aiche.org/cep 31

MMM

MM

MM

MM

MM

MM

MM

MMMM

MM

MM

MM

Inoculum PreparationLaboratories

(2 total)

Wave Bioreactor 2/10Wave Bioreactor 20/50

Seed Bioreactor Train(1 per production

bioreactor)

Wave Bioreactor 200

Production Bioreactors

4 @ 1,000 LEach supported by:

200-L BPC (Nutrient Feed #1)100-L BPC (Nutrient Feed #2)

16.6-L SS Can (Anti-foam)100-L SS Can (Bicarbonate)

Cell Culture Suite

Microfiltration Skid

150-L Retentate Vessel20 m2

Harvest Hold1,500 L

Harvest Suite

Purification Suite

Chromatography #1

Bed: 60 cm dia. x 30 cm deep

85 L VolumeEluate Vessel: 250 L

Ultrafiltration #1UF Skid

250-L Retentate Vessel20 m2, 30 kD MWCO

Inactivation/Splitting200 L

Chromatography #2

Bed: 60 cm dia. x 30 cm deep 25 L Volume

Eluate Vessel: 120 L

Intermediate Bulk FillCartridge Filter

1 round x 30-in. Element

16.6-L Bags

Ultrafiltration #2UF Skid

100-L Retentate Vessel10 m2, 30 kD MWCODownstream

Chemistry Suite

16.6-L Bags

Activation

100 L

Ultrafiltration #3UF Skid

50-L Retentate Vessel6 m2, 30 kD MWCO

Reaction

100 L

UltrafiltrationUF Skid

50-L Retentate Vessel6 m2, 30 kD MWCO

Final Bulk FillCartridge Filter

50-L Final Bulk-Fill Vessel1 round x 10-in. ElementDilution

100 L

DownstreamChemistry

Suite

PurificationSuite

CellCultureSuite

HarvestSuite

Media Preparation

and HoldBuffer Preparation and Hold

Figure 2. Multiple steps are carried out in each suite of the

model process.

Figure 1. The model biopharmaceutical manufacturing process consists of cell-culture, harvest, purifi cation, and downstream-chemistry suites.

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SBE Special Supplement: Disposables

Technology evaluation In developing the model process, the unit operations were evaluated to determine whether SU/DT options exist. These were further evaluated to determine if the technol-ogy could be considered state-of-the-art or if it was still in a developmental stage. Manufacturing organizations are gen-erally risk-averse and prefer state-of-the-art technologies over fi rst-of-a-kind technologies that are technically feasible but unproven. Table 1 summarizes the unit operations and their traditional and potential SU/DT design options. Table 2 identifi es SU/DT state-of-the-art for various steps. SU/DT is now widely considered state-of-the-art for applications involving the bioreactor train (volumes up to 500 L), cartridge fi ltration (sizes up to single 30-in. ele-ments), depth fi ltration (size depends on element type, limited to single-element confi gurations), and process hold (disposable bags with volumes up to 1,000 L for portable confi gurations or 2,500 L for fi xed confi gurations). Pre-packed chromatography columns, microfi ltration and ultrafi ltration systems are being developed rapidly, but are still considered to be in a developmental stage. In addition, several hybrid systems combine both reusable and dispos-able components — for instance, the emerging cassette-style depth fi lters that have a disposable fi lter element and a reusable base, and septum-style samplers that employ disposable sample bags attached to a reusable vessel. Bioreactors. The most prevalent SU/DT option for bio-reactors has been a culture bag placed on a rocker platform, which is commercially available from several manufactur-ers. More recently, SU/DT options for stirred bioreactors have emerged. These offer the potential to achieve larger volumes, with units in the 1,000-L size range available. In general, culture-bag reactors employ an electri-

cal heating system, while the stirred-bag systems have a jacketed holding vessel supplied with tempered glycol. The glycol can be heated and cooled using traditional utilities or (more commonly) a self-contained electrical heating and cooling system. Various aseptic connection devices and methods are available to add culture medium and inoculum, and to remove the fi nished culture broth, without the need for clean steam. These SU/DT bioreactors still require clean gases, such as air, carbon dioxide and oxygen. These gases can be provided either by local gas cylinders or a central building-wide system. It is essential that whatever design is selected, the sys-tem must be thoroughly evaluated at scale in a pilot facility before it is designed into a production facility. Ultrafi ltration/microfi ltration. SU/DT is being devel-

Media and Buffer Preparation and Hold

MM

Media Preparation

1 @ 1,000 L1 @ 200 L

Small Scale

Media Hold

Seed Laboratory2 L

16.6 L50 L

Seed Bioreactors200 L

Purification Buffer Hold

MMM

Downstream Chemistry Buffer Hold

M MMMM

Chromatography #15 @ 500L

1 @ 1,000 L

Ultrafiltration #11 @ 1,000 L1 @ 500 L2 @ 200 L

Inactivation1 @ 20 L

Chromatography #26 @ 500 L

Ultrafiltration #21 @ 500 L1 @ 200 L2 @ 100 L

Activation2 @ 20 L

Ultrafiltration #31 @ 500 L1 @ 200 L2 @ 100 L

Reaction2 @ 20 L

Dilution1 @ 1,000L

Ultrafiltration #41 @ 500 L1 @ 200 L2 @ 100 L

Final Bulk Fill2 @ 20 L

Buffer Preparation

1 @ 2,000 L1 @ 1,000 L1 @ 500 L1 @ 200 L

Small Scale

Harvest Buffer Hold

Microfiltration1 @ 1,000 L2 @ 200 L

Figure 3. The cell-culture media and various buffers are made in numerous vessels.

CEP July 2009 www.aiche.org/cep 33

oped, and is commercially available, for ultrafi ltration and microfi ltration. These systems employ a combination of liquid storage bags, disposable fl ow paths with a disposable membrane and membrane holder, and a peristaltic pump for circulation. An advantage of these systems is that they can be designed to be virtually self-cleaning, which can avoid the need for CIP capabilities. Essentially, the reusable vessel and piping are cleaned and sanitized using the same buf-fers as are used for cleaning and sanitizing the membranes. The commercially avail-able systems tend to be very small, and currently are more appropriate for laboratory and small-scale pilot plant opera-tions than for manufacturing. Consequently, these do not appear ready yet for commer-cial manufacturing. Liquid storage. SU/DT is widely used for liquid storage applications, both for inter-mediate product and media and buffers. Many different manufacturers provide systems with volumes up to 2,500 L. Important design issues are safety and containment, and the need for portability, agitation and temperature control. Volumes of 1,000 L or less may be considered portable, while larger volumes need to be used in place. Portability offers fl exibility to accommodate process changes, mini-mizes the fl oor-space requirements immediately adjacent to the supporting process unit operations, and minimizes the length of interconnecting piping or disposable tubing. Disposable bag systems that are agitated and have temperature control are commercially available. Various agitation methods are available, and all provide gentle agitation suffi cient to blend liquids and promote moderate heat transfer for temperature control. The disadvantages of providing agitation within the disposable bag system are the added cost and complexity, so this should be avoided if possible. Similarly, temperature control can be achieved, but

Table 1. Biopharmaceutical manufacturing unit operations can employ traditional reusable equipment or single-use/disposable technology.

Functional Area Unit Operation Traditional Design SU/DT Option

Cell Culture Suite Inoculum Flasks Glass Flasks Plastic Flasks

Seed Bioreactors Type 316L Stainless Steel Bioreactors

Disposable Bag with Reusable Skid

Production Bioreactors

Type 316L Stainless Steel Bioreactors

Disposable Bag with Reusable Skid

Harvest Suite Intermediate Product Hold

Type 316L Stainless Steel Vessel

Disposable Bag with Reusable Support Container

Filtration Disposable Element in Reusable Housing

Disposable Element and Housing

Media and Buffer Preparation

Solution Preparation

Type 316L Stainless Steel Vessel

Disposable Bag with Reusable Skid

Filtration Disposable Element in Reusable Housing

Disposable Element and Housing

Media and Buffer Hold

Solution Hold Type 316L Stainless Steel Vessel

Disposable Bag with Reusable Support Container

Purifi cation Intermediate Product Hold

Type 316L Stainless Steel Vessel

Disposable Bag with Reusable Support Container

Viral Filtration Disposable Element in Reusable Housing

Disposable Element and Housing

Ultrafi ltration Type 316L Stainless Steel Vessel, Pump, Piping and Membrane Holder

Disposable Bag, Tubing and Membranes

Chromatography Reusable Skid and Column

Single-Use Columns and Disposable Flow Path

Final Bulk Product Hold

Product Hold Type 316L Stainless Steel Vessel

Disposable Bag (Maybe Cryobags)

Table 2. Some state-of-the-art SU/DT systems are suitable for manufacturing.

Unit Operation Current Maximum Size

Ready for GMP Manufacturing?

Solution Preparation 2,500-L Bags Yes

Solution Hold 2,500-L Bags Yes

Seed Bioreactors 500 L Yes

Production Bioreac-tors

1,000 L Yes

Depth Filtration Single Elements Yes

Cartridge Filtration 30-in. Elements Yes

Viral Filtration 30-in. Elements Yes

Microfi ltration 2.0 m2 No

Ultrafi ltration 2.0 m2 No

Chromatography N/A No

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SBE Special Supplement: Disposables

adds signifi cantly to the system cost and complexity. A long period of time is required to cool a 500-L bag from ambient to below 10°C if it is merely placed in a cold room. Conse-quently, some type of jacketing on the bag holding device will be required. Volume/weight measurement capabilities are normally desired. This can be accomplished by placing the bag and holder on a fl oor scale or load cells, or by employing a disposable pressure sensor. One of the most signifi cant limitations of disposable bags is the size of the associated disposable tubing. The largest tubing currently available is typically a nominal 1-in.dia., which restricts the maximum fl owrate to approxi-mately 30–35 L/min. Thus, a 2,500-L bag will require in excess of an hour to fi ll or empty. Chromatography systems. SU/DT is being developed, and is commercially available, for chromatography systems, which consist of two components — the chromatography column and the liquid-handling skid. Pre-packed, disposable chromatography columns are becoming commercially available. These eliminate the need to pack the column as well as the column-packing skid and supporting system. Additionally, chromatography resin is

typically supplied in an alcohol/water mixture that is diffi cult to handle due to fl ammability and waste disposal issues. SU/DT is being developed for chromatography liquid-handling systems, which employ a combination of dispos-able cartridge fi lters, disposable fl ow paths, and sensors. These systems vary widely in complexity. The simplest consists of only disposable tubing used in conjunction with a peristaltic pump. Manufacturing requirements add complexity, such as fl ow, pressure, pH, optical density and conductivity monitoring, various column performance tests, and the ability to use buffer concentrates, provide fi ltration, and remove air bubbles. One of the primary advantages of SU/DT is the elimi-nation of the CIP requirement. Chromatography liquid- handling systems are cleaned and sanitized with the same buffers used to clean and sanitize the chromatography column. Consequently, a reusable system appears to be superior to a disposable system. Cartridge fi lters. SU/DT is now widely available for cartridge fi ltration, with all major fi lter element vendors offering disposable capsules available for both liquid and gas applications. The current upper size limit appears to be a 30-in. fi lter element, which is suffi cient for most applica-tions. The real limit on their use is how they are connected to other systems. Bulk product storage. SU/DT is commercially avail-able for fi nal bulk-product storage in cold, frozen (–20°C) and potentially cryogenic temperatures. These provide a very signifi cant cost advantage over reusable containers. Typically, manufacturers want a fairly large inventory of the fi nal bulk product, which requires a large number of containers. Reusable containers present a logistical chal-lenge in that they need to be cleaned, assembled, sterilized, used, and ultimately returned to the manufacturing facility. The primary limit is the system capacity, which is typi-cally less than 20 L per bag.

Process utility comparison The utility requirements necessary to support a facil-ity designed around traditional reusable systems and those for an SU/DT-based plant are summarized in Table 3. Both designs employ the same utilities, so the selection of SU/DT does not eliminate any utility systems. SU/DT does, however, signifi cantly reduce the plant’s water requirements. Biopharmaceutical facilities consume large quantities of high-purity water for both process and cleaning operations, and this water usage ultimately results in large quantities of process waste. Elimination of the CIP requirements reduces the reverse osmosis (RO) and water-for-injection (WFI) generation requirements by one-third

Table 3. SU/DT does not eliminate any utility systems, but does reduce water usage.

Traditional Disposable Reduction

Clean Utilities

Reverse Osmosis Water (ROW)

9,500 L/h 6,500 L/h 32%

Water for Injection (WFI)

2,400 L/h 1,800 L/h 25%

Clean Steam (CS)

1,000 L/h 750 lb/hr 25%

Plant Utilities

100-psig Plant Steam (PS100)

12,000 lb/h 7,500 lb/h 38%

HVAC Hot Water (HHW)

12,000 MBtu/h 12,000 MBtu/h 0%

HVAC Chilled Water (CHW)

1,600 ton 1,600 ton 0%

Process Chilled Glycol (PCG)

300 ton 280 ton 7%

Cooling Tower Water (TW)

8,000 gal/min 8,000 gal/min 0%

Compressed Air

1,500 scfm 1,200 scfm 20%

CEP July 2009 www.aiche.org/cep 35

and one-quarter, respectively. This has a carry-over effect of reducing the capacity requirements for the process waste neutralization system and the plant utility requirements necessary to generate the high-purity water. The reduction in water consumption and waste generation can affect a facility’s feasibility. Biopharmaceutical facilities include signifi cant clean room space, which has large heating, ventilation and air conditioning (HVAC) requirements. For a typical plant, approximately half the plant steam and compressed air is used to support the HVAC systems. For this comparison, the facility size and air classifi cations are assumed to be the same for the traditional reusable design and the SU/DT-based design. Consequently, SU/DT only reduces the plant steam and compressed air generation capacity requirements by approximately 38% and 20%, respectively. The HVAC chilled water and cooling tower water generation require-ments of the two options are the same.

Capital cost comparison Cost estimates for manufacturing facilities can be very detailed and subject to considerable variation with regard to the owner’s standards for air classifi cations, room fi nishes, and many other factors. To avoid these issues, this study focuses on the capital equipment costs, which are summa-rized in Table 4. Capital equipment costs can also vary sig-nifi cantly based on component selection, automation level, and other factors. These capital equipment costs are budget-ary estimates (±30%) based on mid-priced equipment. Overall, capital equipment costs are approximately 17% lower for a facility designed to maximize the use of SU/DT

compared to a traditional facility. The main cost savings are associated with the elimination of process hold vessels and supporting CIP systems. Interestingly, the costs associated with the reusable components of some SU/DT systems were equivalent to or exceeded those for traditional systems. This was particularly true for the bioreactors and the buffer preparation and media preparation systems. SU/DT holds promise for eliminating support systems, which provides much larger cost savings than incrementally reducing support system capacities. The lower cost of the SU/DT facility’s process support system is primarily due to the elimination of CIP systems. The facility still requires a biowaste inactivation system, a process waste neutraliza-tion system, and a central wash system. While these support systems are small for the SU/DT facility, their lower costs are not proportional to their smaller capacity.

Closing thoughts Single-use/disposable technology offers cost-effective and fl exible manufacturing alternatives for the biophar-maceutical industry. This cost and fl exibility advantage is most pronounced for clinical trial, initial product launch, and small commercial-scale manufacturing facilities, which tend to operate at lower throughput rates and utilize smaller-scale and less-automated operations. The lower water requirements of SU/DT can mean the difference between a feasible and an infeasible project at sites with water supply and/or wastewater generation constraints. Expansions at sites that face utility capacity constraints can also benefi t from SU/DT. The industry trend toward a larger number of smaller-volume products is expected to present additional oppor-tunities for new facilities that rely heavily on SU/DT. The state-of-the-art continues to develop and expand potential applications.

Literature Cited

1. Langer, E. S., and J. Ranck, “The ROI Case: Economic Justi-fi cation for Disposables in Biopharmaceutical Manufacturing,” BioProcess International Supplement, pp. 46–50 (Oct. 2005).

2. Sandstrom, C., and B. Schmidt, “Facility-Design Consider-ations for the Use of Disposable Bags,” BioProcess International Supplement, pp. 56–60 (Oct. 2005).

CRAIG SANDSTROM is a Fluor Technical Fellow specializing in biopharma-ceutical process development and facility design. He has more than 17 years of biotech manufacturing experience, with particular cell culture expertise including bioreactor and purifi cation system design and optimization. He has closely followed the development of single-use/disposable systems and has been widely published on the subject. He holds a PhD in chemical engineering.

Table 4. Capital costs are lower for most areas of the SU/DT facility.

Traditional Disposable Reduction

Total $ 23,050,432 $ 19,229,437 17%

Cell Culture $ 6,462,200 $ 6,189,000 4%

Media Prep and Hold

$ 361,000 $ 308,500 15%

Purifi cation $ 4,300,000 $ 2,954,000 31%

Buffer Prep and Hold

$ 1,948,200 $ 939,100 52%

Process

Support

$ 4,084,000 $ 3,234,000 21%

Clean Utilities $ 2,530,600 $ 2,201,622 13%

Plant Utilities $ 2,166,432 $ 2,079,775 4%

Warehouse $ 448,000 $ 573,440 –28%

Laboratories $ 750,000 $ 750,000 0%

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