Filling of High-Concentration Monoclonal Antibody Formulations into Pre-Filled Syringes: Filling...

10.5731/pdajpst.2014.00973Access the most recent version at doi: 153-16368, 2014 PDA J Pharm Sci and Tech

Wendy Shieu, Sarah A. Torhan, Edwin Chan, et al. Investigation and OptimizationFormulations into Pre-Filled Syringes: Filling Parameter Filling of High-Concentration Monoclonal Antibody

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RESEARCH

Filling of High-Concentration Monoclonal AntibodyFormulations into Pre-Filled Syringes: Filling ParameterInvestigation and OptimizationWENDY SHIEU, SARAH A. TORHAN, EDWIN CHAN, AARON HUBBARD, BENSON GIKANGA,OLIVER B. STAUCH, and YUH-FUN MAA*

Pharmaceutical Processing and Technology Development, Genentech, a member of the Roche Group,South San Francisco, CA ©PDA, Inc. 2014

ABSTRACT: Syringe filling, especially the filling of high-concentration/viscosity monoclonal antibody formulations, is acomplex process that has not been widely published in literature. This study sought to increase the body of knowledge for syringefilling by analyzing and optimizing the filling process from the perspective of a fluid’s physical properties (e.g., viscosity,concentration, surface tension). A bench-top filling unit, comprising a peristaltic pump unit and a filling nozzle integrated witha linear actuator, was utilized; glass nozzles were employed to visualize liquid flow inside the nozzle with a high-speed camera.The desired outcome of process optimization was to establish a clean filling cycle (e.g., absence of splashes, bubbles, and foamingduring filling and absence of dripping from the fill nozzle post-fill) and minimize the risk of nozzle clogging during nozzle idletime due to formulation drying at or near the nozzle tip. The key process variables were determined to be nozzle size, airflowaround the nozzle tip, pump suck-back (SB)/reversing, fluid viscosity, and protein concentration, while pump velocity,acceleration, and fluid/nozzle interphase properties were determined to be relatively weak parameters. The SB parameter playedan especially critical role in nozzle clogging. This study shows that an appropriate combination of optimal SB setting, nozzle size,and airflow conditions could effectively extend nozzle idle time in a large-scale filling facility and environment.

KEYWORDS: Prefilled syringe, High-concentration monoclonal antibody, Peristaltic pump, Suck-back, Formulationdrying.

LAY ABSTRACT: Syringe filling can be considered a well-established manufacturing process and has been imple-mented by numerous contract manufacturing organizations and biopharmaceutical companies. However, its technicaldetails and associated critical process parameters are rarely published. The information on high-concentration/viscosity formulation filling is particularly lacking. The purpose of this study is three-fold: (1) to reveal design detailsof a bench-top syringe filling unit; (2) to identify and optimize critical process parameters; (3) to apply the learningto practical filling operation. The outcomes of this study will benefit scientists and engineers who develop pre-filledsyringe products by providing a better understanding of HC formulation filling principles and challenges.

Introduction

Over the past decade, pre-filled syringes (PFSs) havebecome widely used in pharmaceutical industries andare now one of the primary containers of choice forparenteral drug delivery, especially for subcutaneous

and intramuscular administration (1). It is particularlytrue for high-dose monoclonal antibody (mAb) prod-ucts, which often require several milligrams of proteinper kilogram body weight. The subcutaneous route ofadministration is preferred because it enables homeadministration for patients with chronic conditions,but generally restricts injection volume and time.Thus, a high-concentration (HC) mAb formulation(e.g., �100 mg/mL) is often required (2, 3).

The challenge of a HC mAb formulation in the PFSproduct is well known—its high fluid viscosity maymake syringes less desirable to use (e.g., high injec-tion force) and formulation stability is more difficult

*Corresponding Author: Genentech, a member of theRoche Group, 1 DNA Way South San Francisco, CA94080. Telephone: 650-225-3499; Fax: 650-742-1504;email: [email protected]

doi: 10.5731/pdajpst.2014.00973

153Vol. 68, No. 2, March–April 2014

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to maintain (3–9). The impact of HC and high-viscos-ity formulations on processing and manufacturing,however, is not as well documented, despite the factthat manufacturing a PFS product is a complex processthat includes liquid formulation preparation (thawing,compounding, sterile filtration, etc.), component as-sembly (syringe, stopper, needle, and needle shield),syringe filling, stopper placement, labeling, and pack-aging (4, 5). Syringe filling is a complicated, butmature, operation; highly automated filling facilitieshave been established for many years to fill syringeswhile meeting strict fill weight specifications at aproduction rate of �10,000 units/h. Yet, for engineersand scientists who are interested in learning or devel-oping a PFS filling process, publications or disclosuresdetailing the syringe filling operation are scarce. Par-ticularly lacking is published information regardingfilling HC mAb formulations.

This study aimed to increase the body of knowledgeon HC mAb formulation syringe filling by providinginsight into filling process optimization.

When filling syringes using a pump mechanism, thereare two sets of filling parameters: filling nozzle move-ment and liquid flow generated by the pump. Themotion of the nozzle and the flow of the liquid must bealigned to deliver a clean filling profile, where thenozzle retracts and maintains a constant distance fromthe liquid level, thereby having no contact with thefluid/liquid (too close) or causing undesired splashing/foaming/bubbles (too far apart). In addition, liquiddripping at the end of the fill should be minimized toenhance fill weight (volume) accuracy and reduce therisk of wet stoppers. When developing the PFS fillingprocess, process engineers often use a fixed nozzlemovement profile and adjust the pump parameters tocomplete the fill cycle. This is particularly true whenthe nozzle motion is driven by a mechanical cam withpre-set nozzle movement parameters controlled by asingle variable—the main drive speed. Thus, thisstudy focused only on investigating the parameters ofthe peristaltic pump, which is considered a standardpumping mechanism for biopharmaceutical formula-tions because of its mild stress and closed-systemfeature compared with the piston pump (10, 11).

Modern peristaltic pumps control and deliver liquidthrough three variables: acceleration, velocity, and re-versing (also called suck-back [SB] or back-suction).Acceleration and velocity determine the rate of the liquidfilled into the syringe, while SB offers a particular func-

tion—withdrawing the liquid to minimize dripping at theend of each fill. Sporadic dripping may reduce fill weightaccuracy. This study also delineated another function ofSB, unique to HC protein formulations, in decreasing theprobability of nozzle clogging due to formulation dryingat the tip of the nozzle during filling interruptions (or idletime). The impact of SB in relation to several processvariables on formulation drying was investigated in orderto prolong filling interruption times for fluids of variedviscosity, including a model protein and a mAb formu-lation. The prolonged interruption time derived from thisstudy may provide increased processing flexibility andmay facilitate risk mitigation at filling sites.

Materials and Methods

All experiments in this study used a bovine serumalbumin (BSA, at 370 mg/mL) or a mAb (mAb A at180 mg/mL). These two molecules were formulatedinto the same composition containing 0.04% Tween20. Some experiments also used distilled water con-taining 0.04% Tween 20 for comparison. These for-mulations were filled into either 25 mL PETG bottlesand/or 1.0 mL long, 27G 1⁄2 inch staked needle syringesusing a bench-top filling system. All equipment andmaterials used in these studies are listed in Table I.

Bench-Top Filling System

The bench-top filling unit was assembled and tested byVolo Technologies, Inc. (Roseville, CA). This unit(Figure 1) integrates a Flexicon peristaltic pump systemwith a linear actuator to control nozzle movement. Thepump system consists of a peristaltic pump and control-ler, while the robotic system is composed of a ROBOCylinder® linear actuator and a Volo-integrated control-ler.

Peristaltic Pump Control and Tubing Arrange-ment: The liquid formulation was delivered using aFlexicon PD12 peristaltic pump (“a” in Figure 1) whoseparameters (velocity, acceleration, SB) were controlledby a Flexicon MC12 control unit (“b” in Figure 1). Twopieces of Sani-Tech® platinum-cured 1.6 mm siliconetubing ran through the pump and were Y-connected to3.2 mm silicone tubing before and after the pump unit(see Figure 1). This tubing arrangement was maintainedthroughout the whole study.

Robotic Movement Control: The linear actuator(“c” in Figure 1) provides the diving action for thefilling nozzle. The nozzle moves up and down per

154 PDA Journal of Pharmaceutical Science and Technology




the commands from a Volo controller (“d” in Figure1), which combines the function of a programmablelogic controller and a human–machine interface(HMI). The Volo controller is interfaced with theFlexicon controller to send signals to start and stop

pumping the liquid. To enable diverse nozzle move-ment patterns (dive-in position, fill position, retrac-tion rate, acceleration/deceleration, etc.), variousset points need to be inputted to the Volo HMI andFlexicon unit.

Filling Operation and Experiments

The whole bench-top filling unit was placed inside ahorizontal laminar airflow (LAF) hood at room tem-perature (20 –23 °C) with airflow at a rate of 0.7 m/sfrom the back panel of the hood in parallel to thebench and a relative humidity of 40 –50%. The rate ofthe airflow was not adjustable, but the flow could beturned off.

Nozzle Movement Profile (Cycle): The nozzle move-ment profile was pre-set and fixed (Figure 2) in allexperiments. During operation, the nozzle dives 44mm (measured from the back of the flange) into thesyringe (52 mm in total length) and begins deliveringthe liquid. At the same time, the nozzle retracts withan acceleration of 150 mm/s2 and a constant velocityof 70 mm/s.

Table IEquipment and Materials Used in the Study

Equipment Model/ Supplier/Location

Stainless steel nozzles (1.5, 2.0, and 2.5 mm ID;90 mm long)

INOVA (OPTIMA Pharma GmbH, Germany)

Glass nozzles (1.8 and 2.4 mm ID; 90 mm long) Pegasus Industrial Specialties Inc. (Cambridge, Ontario)

Pump controller module (micro linear actuator) Watson-Marlow (Ringsted, Denmark)/Flexicon

ROBO Cylinder linear actuator IAI America (Torrence, CA)

PETG bottle Thermo Fisher Scientific Inc/Nalgene Nunc InternationalCorporation (Waltham, MA)

Peristaltic pump and controllerHigh-speed cameraCone and plate rheometerContact angle meter

Watson-Marlow (Ringsted, Denmark)/FlexiconHindsight GigE, 20/20 Hindsight, Monitoring TechnologyCorp., (Fairfax, VA)Physica MCR 501with CP20-0.5 measuring cone, AntonPaar GmbH (Austria)Model OCA15, FDS Corp. (Garden City, NY)

Materials Supplier/ModelSyringes (1.0 mL long 27G 1⁄2 inch staked

needle)Becton Dickinson (Swedesboro, NJ)/Hypak Type 1 glass

syringes

Platinum-cured silicone tubing (1.6 mm and 3.2mm ID)

Saint-Gobain Performance Plastics (Taunton, MA)/Sani-Tech

Y-connectors and fittings Value Plastics (Fort Collins, CO)

Formulation buffer Genentech, Inc. (South San Francisco, CA)

Bovine serum albumin (BSA) powder SeraCare Life Sciences (Milford, MA)

Figure 1

Bench-top filling system consisting of (a) Flexiconperistaltic pump, (b) pump controller, (c) linearactuator, and (d) Volo controller.





Peristaltic Pump Parameter Setting: The fill rate ofthe liquid was aligned with the nozzle motion byadjusting acceleration and velocity of the peristalticpump, as monitored through a high-speed camera.Afterwards, the SB setting, from 0 to 10, of the pumpwas selected and optimized to minimize liquid drip-ping at the end of each fill cycle, again with the visualaid of a high-speed camera.

Interruption (or Drying) Studies: At the end of thefill, the filling process was interrupted (idled) for apre-determined duration. After interruption, the fillwas resumed and the fill characteristics were moni-tored using a high-speed camera.

Suck-Back (SB) Experiments Using Glass Nozzles:Glass nozzles of different sizes (inner diameters, IDs)were used to visualize (via a high-speed camera) SBaction and the flow of the liquid formulation at the tipof the glass nozzle. The SB volume, V, in response toSB settings, ranging from 0 to 10, can be calculatedusing eq 1 where H is the measured height of the airpocket and d is the nozzle diameter:

V[mL] � H[cm] � � � (d[cm]/2)2 (1)

Fluid (Formulation) Characterizations

Viscosity Measurement: The viscosity of a fluid wasmeasured using a cone and plate rheometer. Each

sample of 70 – 80 �L was loaded onto the lower mea-suring plate and allowed to come to thermal equilib-rium at 20 °C. A solvent trap was used to prevent fluidevaporation during the measurement. The sample dy-namic viscosity was measured every 10 s for 2 minusing a cone with a 19.98 mm diameter and 0.509degree angle at a shear rate of 1000/s.

Contact Angle Measurement: Static contact angle ofa fluid on glass and stainless steel surfaces was deter-mined using a contact angle meter employing an op-tical contact angle method called sessile drop. Thesubstrates were cleaned with 2% clean-in-place (CIP)cleaning detergent followed by three rinses with waterfor injection (WFI). For static contact angle measure-ment, a photo snapshot is taken once a drop of the fluid(5 �L) is dispensed from the syringe and laid on aclean substrate surface (glass slides or stainless steelcoupons). The angle between the baseline of the dropand the tangent at the drop boundary is measured onboth sides. The complete measurement was obtainedby averaging the two numbers. At least five readingswere recorded for each sample.

Results and Discussion

Fluid Characterizations

Two important fluid properties, viscosity and contactangle, were measured to determine their impact onfilling characteristics and formulation drying patterns.The results are summarized in Table II for three fluids:water containing 0.04% Tween 20, 18% mAb A (buff-ered), and 370 mg/mL BSA (buffered). These fluidscovered a broad range of viscosity, 1 to 25 cP (at 20°C). Contact angles of a fluid on a substrate representthe interactions of the fluid and the substrate surface;low contact angles suggest hydrophilic interactions,while high contact angles demonstrate hydrophobicbehaviors of the interface. Two substrate materials,glass and stainless steel, were used to represent thenozzle materials used in this study. As summarized inTable II, the glass surface is more hydrophilic than thestainless steel surface for all three fluids; the 370mg/mL BSA solution is the most hydrophobic on bothglass and stainless steel surfaces. The impact of vis-cosity and hydrophilicity versus hydrophobicity onfluid flow behaviors inside and at the tip of the nozzle,as well as fluid drying properties, was assessed and isdiscussed later.

Figure 2

Graphic representation of a fixed-nozzle movementcycle used in the study.





Control of Peristaltic Pump Parameters for FillingCharacteristic Optimization

Initially, all experiments were performed with stain-less steel nozzles. With a fixed nozzle movementprofile (Figure 2), pump parameters (i.e., velocity,acceleration, and SB) were visually observed througha high-speed camera to optimize filling characteristics,which included maintaining a constant distance be-tween the fluid level and the nozzle tip and minimizingsplashing, foaming, and dripping. Pump velocity andacceleration are expected to dominate the rate of liquidflow, thereby affecting the relative position of the fluidand the nozzle. Splashing and foaming may occur whenthe distance between the fluid level and the nozzle tip istoo far. Splashing at the end of the filling cycle is aparticular concern because it may result in wetting thestopper after stopper placement. A wet stopper is acritical product defect and will result in filled syringerejection. SB does not affect solution flow rate, but itexerts a reversing action at the end of each fill cycle tomodulate fluid dripping. Dripping should be prevented orminimized because undesired dripping may decrease fillweight accuracy. Additionally, dripping while the nozzleis moving out of the syringe barrel may cause splashingand/or leave fluid drop(s) on the barrel, potentially lead-ing to wet stoppers.

Optimal pump parameters that minimized issues suchas splashing, foaming, and dripping for the three fluidsevaluated in this study are listed in Table II. It waspossible to maintain a pump velocity of 200 rpm forall three fluids, but pump acceleration had to be in-creased with increasing fluid viscosity (4, 50, and 125

for water, 18% mAb A, and 370 mg/mL BSA, respec-tively) to align with nozzle motion. The reason thatpump acceleration had to be increased in relation toincreased fluid viscosity could be described by theHagen-Poiseuille equation (eq 2):

Q � �R4�P/8 �L (2)

For a fluid flowing through a pipe—in this case, thefilling nozzle—the volumetric flow rate is the functionof pressure drop (�P), fluid viscosity (�), tube radius(R), and pipe length (L). For a given pipe/tubing (fixedR and L) and a nozzle motion profile at a fixed Q,filling a fluid of higher viscosity must be counteredwith an increasing pressure drop, which could beachieved with a higher acceleration by the pump (i.e.,�PA � ma, where m is the mass of the fluid, a isacceleration, and A is the surface area where thepressure is applied).

SB setting (0 to10) also had to be increased withincreasing fluid viscosity to minimize dripping, but itcould be decreased using a larger nozzle. These ob-servations may again be explained by the Hagen-Poiseuille equation (eq 2). A greater suction force (inthe direction opposite to the liquid fill) is required topull a more viscous fluid; thus, a higher SB setting isrequired for more viscous fluids. However, the re-quired suction force for a larger nozzle is lower; thus,a lower SB setting can be exerted to reduce the fluid’sdripping tendency.

The function of SB turned out to be more complex andwas found to affect another key filling process perfor-

Table IISummary of Fluid Characterizations and Peristaltic Pump Parameters with Optimal Filling Profile (NoDripping) of Liquid Formulations from Stainless Steel Nozzles of Different Sizes

Characterization/ParameterWater

(with 0.04% Tween 20)mAb A

(180 mg/mL)BSA

(370 mg/mL)

Viscosity at 20 °C (cP) 1 9 25

Contact angle on stainless steel surface (°) 53.6 � 1.0 75.2 � 1.8 86.1 � 1.8

Contact angle on glass surface (°) 32.6 � 1.5 25.4 � 1.1 40.3 � 2.4

Pump velocity (rpm) 200 200 200

Pump acceleration (no unit) 4 50 125

SB setting

1.5 mm stainless steel nozzle 1 5 10







mance indicator—formulation drying at the fill nozzletip during a fill interruption.

Observation and Effect of Formulation Drying

During filling operations, many different type of is-sues (e.g., misalignments and/or malfunctions of therobotic actions, particles) may trigger filling operationinterruptions. During these interruptions, the nozzlesremain idle for uncertain durations. Nozzle clogginghas been observed at the end of a fill interruption dueto the drying of the fluid at or close to the tip of thenozzle, resulting in complete or partial nozzle block-age after the fill was resumed. This drying-inducednozzle blockage is unique to HC and high-viscosityformulations containing high-molecular-weight spe-cies (polymer, proteins, mAbs, etc.) Water evapora-tion from such a fluid rapidly establishes a viscousfilm at the drying front that can easily become elastic,thicken, or solidify.

To fully understand the effect of SB setting and per-formance, a series of experiments was performed inglass nozzles and visualized via a high-speed camera.These experiments were designed to evaluate the ef-fect of interruption time on formulation drying as afunction of SB settings, nozzle size (1.8 mm and 2.4mm ID), and airflow rate (0 and 0.7 m/s). As summa-rized in Table III, nozzle clogging took place, and inmany cases it occurred within 15 min of idle time. Allexperiments were performed under ambient conditions

(20 –23 °C and 40 –50% relative humidity) in a LAFhood, where air was either turned off (without airflow)or on (with an airflow rate of 0.7 m/s). Without air-flow, it took almost twice the time for the mAb Aformulation to clog the nozzle than it did under thehigh-airflow rate, suggesting that airflow near the noz-zle tip is an important parameter affecting formulationdrying. It is important to note, however, that the highrate of parallel airflow experienced by the filling noz-zle in the LAF may represent a worst-case environ-ment compared with an airflow-controlled manufac-turing fill line.

Table III also shows that it took longer for the largernozzle (2.4 mm) to clog compared with the smallerone (1.8 mm). Although the rate of water evaporationper unit cross-section area should be the same regard-less of nozzle size, the observation of the dried resid-ual begins along the inner surface near the nozzle tipto form a dried ring, which grew toward the center ofthe nozzle (Figure 3a). The formation of an inner ring

Table IIISummary of Drying Times for the mAb AFormulation Due to Interruption of Filling fromGlass Nozzles as a Function of Suck-Back (SB)Settings

SB Setting

Drying Time (min)

1.8 mm GlassNozzle

2.4 mm GlassNozzle

0.7 m/sAirflow

0.7 m/sAirflow

0 m/sAirflow

0 10 15 20

1 10 15 30

2 30–40 90 �120*

3 10 15 30

4 10 15 45

*No drying was observed before the end of theexperiment.

Figure 3

Photographic images of (a) dried residual ringforming at the inner nozzle tip and growing towardthe center of the nozzle, (b) thinning flow pattern of370 mg/mL BSA formulation after 30 min idle time,(c) graphic representation of dried ring forming fora small vs large nozzle.





was further verified by the narrowing of the liquid flowstream (Figure 3b) after the 370 mg/mL BSA formu-lation was idled for 30 min. The observation of driedresidual formation along the inner perimeter of thenozzle tip can be related to the observation of forma-tion of coffee stains from dried liquid drops, which isattributed to capillary flow (12). There is a prerequisitefor this phenomenon to occur—the pinning of theliquid–substrate contact line. As the edge (contactline) of the coffee drop is pinned (fixed), water evap-orating from the edge must be replenished by liquidfrom the interior via capillary flow. In the case ofliquid SB inside a filling nozzle, the edge of the fluidmeniscus is pinned to the nozzle inner surface wherewater evaporation will easily leave a dried ring. Theliquid from the interior will flow to the edge to re-plenish water. As this process continues, the dried ringwill keep growing toward the center of the nozzle toleave a smaller opening or eventually clog the nozzle.The rate of dried ring growth is comparable betweenthe small and large nozzles and has a more significantimpact on the smaller nozzle, which will clog fasterthan the large nozzle (Figure 3c).

SB setting was observed to play an important role onthe rate of formulation drying; an interruption timecould be substantially extended by optimizing SB set-ting (i.e., a setting of 2 for the mAb A formulation, inboth nozzle sizes). The effect of SB setting on formu-lation drying can be explained by visual observationsof the physical behavior of the formulation in glassnozzles. When the mAb A formulation was suckedinto a 2.4 mm glass nozzle, it displayed a uniquepattern to each SB setting (0 to 4) as shown in Figure4a. A liquid drop hung at the tip of the nozzle at a SBsetting 0 (without SB). At SB setting 1, the liquid dropwas withdrawn into the nozzle to show a slight con-cave meniscus surface at the very tip of the nozzle.The fluid receded farther into the nozzle as the SBsetting was increased to 2, 3, and 4. However, begin-ning at SB setting 3, an air pocket (“ap” in Figure 4b)was observed to be enclosed by a liquid plug (“lp” inFigure 4b) at the nozzle tip. The size of the air pocketand the liquid plug grew larger when the SB settingwas increased to 4. When testing out interruptiontimes at different SB settings for mAb A formulationin glass nozzles, SB setting 2 was observed to have thelongest interruption time with no nozzle clogging (Ta-ble III). Using the glass nozzles, it was possible tovisually observe that there was neither a drop hangingfrom the nozzle nor a liquid plug at the inner tip of the

nozzle at SB setting 2, which was unlike the physicalbehavior observed with the other SB settings.

From these visual observations, a hypothesis can bemade that correlates SB setting to nozzle clogging.Water can evaporate quickly from the liquid drophanging outside the nozzle tip, and the evaporationrate can be slowed down if the fluid is pulled into thenozzle because of reduced airflow and humidity con-centration gradient. Intuitively, the farther the fluidretreats, the slower the drying rate. However, likedraining a liquid from a container surface, quick fluidflow/removal is normally not complete and can leave athin film along the nozzle’s inner surface. Later, thisfluid film can migrate down to accumulate at thenozzle tip to form a liquid plug which, like the liquiddrop at the nozzle tip, can dry quickly and clog thenozzle. Thus, SB setting is a critical parameter thataffects formulation drying/nozzle clogging, and itneeds to be optimized to minimize liquid dripping or

Figure 4

Photographic images of mAb A formulation suckedback into a 2.4 mm glass nozzle (a) corresponding tosuck-back (SB) settings 0–4 under the pump settingof velocity at 200 rpm and acceleration at 50; (b) atypical SB pattern showing an air pocket (“ap”) anda liquid plug (“lp”) at the tip of the nozzle.





the formation of a liquid plug at the nozzle tip in orderto effectively extend the interruption times, particu-larly in filling a HC or high-viscosity fluid.

The SB setting is likely related to the degree of pumprotation and is dependent on the type of the peristalticpump used. However, despite its importance, the con-trol of SB and the relationship between SB setting andvolume are rarely specified in pump manufacturers’user manuals, and vendors hesitate to provide anyinformation. To generate such data, glass nozzles canserve as a valuable tool, allowing visual observationsand direct measurement to quantify and assess SBperformance.

Control of SB Performance

Having determined that SB setting is a critical param-eter affecting formulation drying, additional experi-ments were performed to assess the effect of other fillparameters on SB.

Effect of Viscosity and Nozzle Size: SB was visual-ized as shown in Figure 5, which portrays a linearrelationship between the height of both the air pocketand liquid plug and the SB setting for two differentnozzle sizes. This linearity held true in both the 1.8mm and 2.4 mm nozzles. The SB volume can becalculated using the measured SB height (eq 1). Thethree solutions listed in Table II were used to assessthe effect of viscosity on SB volume. As summarizedin Figure 6, viscosity has an obvious impact on SBvolume. At the same SB setting, a fluid with higherviscosity is more difficult to be drawn into the nozzle

because a higher pressure must be exerted on thetubing to draw more viscous formulations through thepump. Nozzle size appears to play a less significantrole, at least for less viscous fluids, such as water andmAb A formulation (10 cP). However, a nozzlesize– dependent difference was observed for the moreviscous BSA solution (25 cP), which could not besucked into the 1.8 mm nozzle until the SB settingreached 4.

Effect of Pump Parameters—Velocity and Acceler-ation: The two pump parameters, velocity and accel-eration, were evaluated separately to assess their im-pact on SB volume of the mAb A formulation. In thefirst experiment, pump velocity was set to 200 rpm andpump acceleration was varied in the range of 25 and100, represented by the solid lines in Figure 7a. SBvolumes were not substantially affected by the level of

Figure 5

Suck-back (SB) patterns for (a) 1.8 mm and (b) 2.4 mm glass nozzles in relation to SB settings of 0 –10.

Figure 6

Suck-back (SB) volume vs SB setting for 370mg/mL BSA, mAb A, and water in 1.8 mm and 2.4mm nozzles.





pump acceleration. In the second experiment, pumpacceleration was fixed at 50 and pump velocity wasvaried in the range of 100 and 300 rpm, represented bythe dotted lines in Figure 7a. Pump velocity did notaffect SB volume significantly either, suggesting thatpump velocity did not play a significant role in the SBfunction of the peristaltic pump.

In the third experiment pump velocity was evaluatedagainst air pocket (bubble) formation in the 1.8 mmnozzle at a fixed SB setting of 3 and a pump acceler-ation of 75. The results are shown in Figure 7b, wherethe SB volume fluctuated in a narrow range between

0.05 and 0.08 mL for pump velocity ranging between25 and 400 rpm. Beyond 100 rpm, the bubble volumestayed in an even narrower range of 0.07– 0.08 mL.Because the pump parameters are typically set at�100 rpm, pump velocity was again demonstrated notto be an important variable for bubble volume. Simi-larly, a fourth experiment was conducted with the 1.8mm glass nozzle at a fixed SB setting of 3 and a pumpvelocity of 200 rpm. The results are presented inFigure 7c, where the SB volume varied between 0.05and 0.11 mL for acceleration in the range of 25–200.Bubble volume increased faster initially (at accelera-tion of 25–125) but basically fluctuated in a smallrange (0.09 – 0.11 mL) for acceleration of 125–200.Given that pump acceleration is typically set between25 and 125 for high-viscosity formulations (using the1.6 mm silicone tubing), pump acceleration may havea slightly more significant impact on the SB behaviorthan pump velocity during syringe filling. Overall,pump velocity and acceleration were shown to berelatively weak in affecting SB behavior.

Formulation Drying in Metal Nozzles

Glass nozzles rendered valuable visual information forthe understanding of critical pump parameters. How-ever, glass and stainless steel have different surfaceproperties, and it can be argued that observations madewith glass nozzles are not relevant to stainless steelnozzles. Thus, an experiment was designed to evaluatewhether observations in the glass nozzle can be ap-plied to stainless steel nozzles. Earlier we pointed outthat the 370 mg/mL BSA formulation is the mosthydrophobic on both glass and stainless steel surfaces,but we also showed a big contact angle differencebetween the two: 40.3 � 2.4° on glass and 86.1 � 1.8°on stainless steel. Thus, this fluid was tested on bothglass and stainless steel nozzles of different sizes (seeTable IV).

The optimal SB setting (i.e., positive SB withoutforming a liquid plug or liquid drop) in glass nozzles(1.8 and 2.4 mm) were determined to be 4 and 2,respectively. Applying these optimal SB settings, the370 mg/mL BSA solution still dried much quicker inthe 1.8 mm nozzle than in the 2.4 mm nozzle (20 –30min vs �60 min). For stainless steel nozzles of threedifferent sizes (1.5, 2.0, and 2.5 mm), the formulationdrying (nozzle clogging) results again demonstratedthe same trend. At a comparable nozzle size (2.4 mmglass nozzle and 2.5 mm stainless steel nozzle), theoptimal SB setting and the duration of drying times

Figure 7

Suck-back (SB) volume vs SB setting for 370mg/mL BSA (a) with varying pump velocity (V,dashed lines) and acceleration (A, solid lines) set-tings; (b) illustration of SB volume at SB setting 3and acceleration at 75; (c) illustration of SB volumeat SB setting 3 and velocity at 200 rpm.





were identical. For the 2.0 mm stainless steel nozzle,the SB had to be increased to 4 to significantly extendthe drying time to �60 min, while the 1.8 mm glassnozzle had an optimal SB setting at 3 and 20 –30 mindrying time. Because the nozzle sizes are not identicalfor the stainless steel and glass nozzles, it is difficult topredict if different substrate surfaces play a significantrole. For the smallest stainless steel nozzle (1.5 mm),it was very difficult to draw the fluid into the nozzle.The SB setting was set to the maximum (10), and the370 mg/mL BSA formulation still dried very quickly(approximately 5 min) due to the formation of a liquidplug. Overall, despite the difference in surface prop-erties, the glass nozzle can still serve as valuable toolfor predicting the optimal conditions for filling sy-ringes from standard stainless steel nozzles.

Conclusions

This study identified key parameters that influence thedrying rate of HC protein formulations and extend theinterruption time to slow down the rate of nozzleclogging. The use of glass nozzles in a bench-topsyringe filling unit offers an effective tool that enablesthe understanding and optimization of the function andperformance of different fill parameters. Increasingthe nozzle size and decreasing the water evaporationrate under appropriate environmental conditions canalso effectively alleviate the tendency of nozzles toclog. More importantly, the role of the SB setting inslowing down nozzle blockage due to HC formulationdrying was clearly demonstrated. A small range ofoptimal SB settings must be identified during fillingprocess development. SB performance was also af-fected by fluid viscosity, particularly for fluids of �10cP. The effect of the substrate on SB appeared to beweak, and so observations made with glass nozzlescould be applied to standard stainless steel nozzles.

Acknowledgments

We thank the support from Jacek Guzowski and AaronHubbard of Genentech and Ben Jones of Volo Technol-ogies, Inc. for bench-top filling unit installation andqualification. We are also indebted to Dr. MahmoudAmeri for his assistance in contact angle measurement.

Conflict of Interest Declaration

The authors declare that they have no competinginterests.

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Table IVSummary of Drying Studies for 370 mg/mL BSA Formulation Sucked Back into Glass Nozzles or StainlessSteel Nozzles of Different Sizes

Study Finding

Stainless Steel Nozzle Glass Nozzle

1.5 mm 2.0 mm 2.5 mm 1.8 mm 2.4 mm

Optimal SB setting 10 3 2 4 2

Drying time for nozzle clogging (min) 5 �60* 90 20–30 �60*

Contact angle (°) 86.1 � 1.8 40.3 � 2.4

*Drying experiment and nozzle observation did not exceed 60 min.



http://www.ondrugdelivery.com/publications/prefilled_syringes_2008.pdf;





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Filling of High-Concentration Monoclonal Antibody Formulations into Pre-Filled Syringes: Filling...

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