Q&A: Bottom Spray (Wurster) Coating: Understanding the Challenges, Processing & Scale-Up Considerations

Tim Smith, Vector Corporation

Q: Process Airflow measurement indicated by the machine, are those shown as standard cfm, std m3/hr etc?
A: Each manufacturer of equipment would specify the units. F-V provides units based on the customer’s requirements. And do we need to correct for inlet temperature in order to get the actual volume? Yes, if the temperature is different than the reference standard temperature selected for the air flow station. If yes, how to convert? The first step is to know the volumetric air flow at the flow meter under flow conditions (temperature, pressure, and density of the air). An on-line calculator can assist with this, such as can be found at www.dwyer-inst.com/flowcalc/. Note that the initial calculation can be done with dry or moist air. In all processes the air has some moisture. In addition, air flow stations manufacturers may use a correction factor for their flow meters. Once the air flow is known at the flow conditions, the actual volumetric flow at the inlet to the fluid bed can be found utilizing the ideal gas law (reference slide 29 of the presentation).

Q: How does different type of filter affect scale-up? Can you give a more descriptive or specific example? 
A: A switch from bag to cartridge filters, or vice versa, can change the height of the fluid bed above the Wurster partition and therefore change the rate of drying before the product returns in the down bed. In addition, the differences in media may allow for differences in the size of particles being retained. 

Q: What in-process controls are available to monitor coating in real time? 
A: There are particle size analyzers that can be placed on systems to measure average film thickness (provided the beginning spherical core size is known); R&D studies have used NIR to measure coatings as well; however, models must be built for each product to apply it for controlling a given process. Some of the coating manufacturers have “computer tools” to calculate how much coating is required to provide a given thickness, but these tools are proprietary; one needs to contact the coating manufacturer for assistance.

Q: Can you clarify what is the particle/air velocity ratio? e.g. particle number /velocity? particle size/velocity? 
A: If I said “ratio” that was a mistake on my part. Ideally, you want the particle velocity through the spray zone to be the same in both the small and large systems. The particle velocity can be assumed to the same as the air velocity exiting the top of the Wurster partition.

Q: Can tablets be coated in a Wurster process? 
A: Yes; however, the tablets must be robust enough to withstand the vigorous movement that occurs. My personal recommendation would be to use a pan coater for coating tablets since it generally has a more gentle tablet movement as compared to a Wurster process.

Q: How aqueous coating be used for moisture sensitive actives? 
A: Since drying is occurring as fast as the coating is being applied to the product, the small amount of moisture and time it is in contact with the active may not be detrimental; however, that will be product dependent. 

Q: What is lowest RH% that can be achieved inside coater without causing spray-drying? 
A: While RH% of the incoming air has a bearing on how fast drying can occur, other factors are equally or more important with regards to spray drying of droplets; such as air temperature, air flow, percent moisture of solution being sprayed, and droplet size.

Q: Does Spray gun Nozzle size matter? 
A: Yes, as it will have a governing factor on droplet size. In lab scale equipment mostly 1.0 mm size is used whereas large scale equipment has 1.5 mm. A good rule to use as a starting point is to use 1000 times the atomization air flow as the solution flow. Increase this ratio if smaller droplets are desired.

Q: Please explain advantages of bottom spray and why not go for top spray standard fbd for spraying particles and tablets. 
A: Bottom spray is co-current with the product flow and therefore leads to more uniform coating application.

Q: Is it necessary to start spraying at a lower spray rate and then ramp up to target to avoid overwetting? 
A: While not required to commence spraying at a slower rate, it is a good place to start developing a process. Once you know how the process/product responds with no agglomeration, solution application can be started at faster rates.

Q: Can you please again elaborate the required evaporation rate for spray rate? 
A: In order to prevent over-wetting, the evaporation rate must equal the moisture addition rate. The moisture addition rate can be determined by multiplying the spray rate by the percent solvent in the solution/suspension. 

Q: How is the relationship between coating weight gain at small scale and larger scale provide similar drug release? 
A: Provided the same size cores are used at both scales, final moisture content is the same at both scales, and the coating has the same characteristics, the release should be similar.

Q: Is there a similar system to coat particles smaller than 1 micron? 
A: Not that I am aware of.

Q: Can you comment on how to evaluate substrate strength and its possible impact on coating film quality and consistency, especially for ER products? 
A: Friability testing is one way; another way is to put uncoated product in the machine and operate it under expected processing conditions to see how it withstands the vigorous product movement encountered during Wurster processing. If the product attrits, and the small particles are not allowed to leave the processing chamber, these particles can become entrapped in the coating layer and/or on the surface of the coating. This, in turn, will cause a faster release of the active.

Q: You mention the maximum relative size of the sprayed droplets of 1:10 to the size of the coated particle, while this is the maximum, where would you estimate the optimum? 
A: As small as possible without resulting in spray drying of the droplet.

Q: Is there any relationship between particle size and spray gun pressure or solution volume? 
A: If particle size is what is meant, I am not aware of any correlation. However, if droplet size is what is of concern, then yes, there is a relationship between atomization air velocity (volume or velocity is the result of pressure), solution velocity (related to flow), spray gun orifice, and solution viscosity, etc. The best way to determine the correlation is to conduct spray droplet tests for a given solution using a laser diffraction device to measure the droplet size. 

Q: Should the relative humidity of inlet air be under control?
A: Yes, for consistent control of a process; however, if the humidity can not be controlled, one must be able to adjust inlet air temperatures or spray rates to control the process. Note, I did not include process air volume as it really is fixed for a given Wurster process to provide proper product flow. 

Q: Can particles 10 to 100 microns be coated using Wurster coating? 
A: Yes, provided the particles have a narrow particle size distribution. If the distribution is too wide, the particles can agglomerate at a higher percentage. 

Q: How to avoid the doublets/ triplets cause due to static charge during process?
A: One way is to increase the “moisture” in the system. This can be done in a couple of ways:
1) by spraying as soon as the product begins moving or spraying faster (but this may not be sustainable for the duration of the process) and
2) by increasing the humidity level of the incoming process air (this usually means that a slower spray rate will be required to sustain the process).

Q: How can we get the mass flow rate of process air and atomization air? 
A: If you know the volumetric flow and the density of the air (function of humidity and temperature) you can calculate the mass flow rate … where mass flow = volumetric flow (volume/time) x density (mass/volume). 

David Preston
David Preston


David Preston has had 38 years of healthcare experience with publicky Traded and Private companies in the fields of Phammaceuticals, Animal Health and Biotechnology as a Board Member. The last 30 years of his xperience has been in China, Taiwan and Hong Kong building successful igh growth businesses. David Has been Chaiman and CEO for Greater China for Sanofi and Boehringer – Ingelheim as well as the Janssen Corporation since 1991 in China. During this time he build high Growth ousinesses in China through diversified strategies in Innovative Pharmaceuticals. branded Generics. Biotechnology. and Animal Healthcare.

Key highlights in this period indluded building of the first Westem Multinational Biotechnoloqy C.M.O. facility as well as obtaining the first Test CM.OJ MAHI license. Establishment of a number of High tech Vaccine Plants, and R and D facilities in in the field of Animal Health. Signing and development of numerous JV’s as well as Wholly owned Subsidiaries. Mergers and Acquisitions across Phamaceutical’s. Animal Health. and Biotechnology industries

David’s achievement’s in the Healthcare industry and it Growth and development in China is widely recognized By the Chinese Govemnment and the City of Shanghai In 2013 he was awarded the Silver Magnolia ollowed in 2015 the Gold Magnolia award. This was then followed by being awarded in 2017 the Honorary Citizen of Shanghai by 40th People’s Municipal Congress of Shanghai. David Holds a Business Science Degree

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Filippo de Vecchi

Director, Advent Partner

Filippo de Vecchi joined Advent in February 2000. He started in the Advent São Paulo office, then moved to Milan in 2002, in 2012 set up the Advent office in Shanghai and in 2016 set up the Hong Kong office. Before joining Advent, he was a senior consultant with Value Partners, in São Paulo and Milan, focusing on strategy and organization in the automotive, energy, cable and media sectors. He began his career at Wasserstein Perella & Co., working as an analyst in the Mergers and Acquisitions department in London and New York. Filippo holds an undergraduate degree cum laude in Economics, with a major in Business Administration, from the LUISS University and an MBA from Columbia Business School, where he currently serves as a member of the Board of Overseers.

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Andrew Li
Andrew Li

Director, Advent Partner

Andrew Li joined Advent in 2012. He previously worked at Warburg Pincus, HSBC PE, Solera Capital and Credit Suisse where he focused on the retail and consumer, healthcare, industrial, and energy sectors. Andrew has worked in finance and private equity throughout the U.S. and China since 1999. Andrew holds a BA from Middlebury College and an MBA from Harvard Business School.    

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Michael Miltenberger
Michael Miltenberger

Director, Advent Partner

Michael Miltenberger  joined Advent in 2011 as an associate on the healthcare team. Following business school, he rejoined Advent’s Boston office, focusing on healthcare investments. Prior to Advent, Michael was a consultant at McKinsey & Company in their Washington DC office, serving a range of healthcare and private equity clients. Michael earned a BA, cum laude, from Harvard College and an MBA from Harvard Business School, graduating with High Distinction as a Baker Scholar and a Harvey Fellow.

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Masood Tayebi
Masood Tayebi, PhD

Director, Operating Partner

Dr. Masood Tayebi is the Founder of BioDuro. He currently serves as CEO of a nationwide real estate portfolio and is a Partner and Chief Executive Officer of the Bridgewest Group. Prior to BioDuro, Dr. Tayebi was Co-Founder and Chairman of Wireless Facilities, Inc. (NASDAQ: WFI), a global leader in telecommunications outsourcing.

  • Co-Founder of Wireless Facilities, Inc.

  • Co-Founder of BioAtla, LLC

  • Recipient of the Ernst and Young 2000 Entrepreneur of the Year award in San Diego

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Kewen Jin
Kewen Jin, PhD

Director, Operating Partner

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Amit patel
Amit Patel

Director, Operating Partner

Amit Patel has twenty years of healthcare industry experience with publicly-traded, private equity-backed, and start-up companies in the capacity of executive, board member, advisor, and investor.  He is currently Executive Chairman of Azurity Pharmaceuticals (a NovaQuest Capital Management portfolio company) and a board member at BioDuro (Advent International portfolio company), Tergus Pharma (Great Point Partners portfolio company) and Calyptus Pharma.  Recently, Amit was SVP & President of Dosage Form Solutions at Capsugel, a KKR portfolio company (purchased from Pfizer in 2011 and sold to Lonza in 2017).   

Prior to Capsugel, he worked at Dr. Reddy’s Laboratories, Inc. as EVP & Head of North America, and SVP & Head of Global Corporate Development & Strategic Planning. Earlier, Amit was VP of Corporate Development at CTIS, Inc., and Co-founder & CEO of MedOnTime, Inc. (acquired by CTIS).  He started his career as a strategy consultant with Marakon Associates. Amit holds an M.B.A. degree from Harvard Business School, a B.S. degree in Economics from the Wharton School of Business, University of Pennsylvania, and a B.A.S. degree in Systems Engineering from the Moore School of Engineering, University of Pennsylvania.

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Haijun Dong
Haijun Dong

Chief Executive Officer

Dr. Haijun Dong currently serves as global CEO of BioDuro-Sundia. He previously was CEO for over 5 years at PharmaBlock Sciences Inc., a public company listed in the Shenzhen Stock Exchange (300725.SZ). The positions he held prior to PharmaBlock includes, among others, Senior Scientist at Boehringer Ingelheim Pharmaceuticals in Ridgefield, Connecticut; Senior Principal Scientist at Roche in Nutley, New Jersey; Head of DMPK and Drug Safety at Roche China R&D Company in Shanghai; Chief Operating Officer of Eli Lilly China R&D Center in Shanghai.

Dr. Dong received his PhD in organic chemistry from the University of Washington in Seattle, Washington, and MBA from China Europe International Business School in Shanghai. 

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Teo Nee Chuan
Teo Nee Chuan

Chief Financial Officer

Teo Nee Chuan joined us in May 2021 as chief financial officer. Prior to joining us, he was chief financial officer of Huazhu Group from November 2015 to May 2021, and was the chief financial officer for Rnomac International Limited, from November 2011 to August 2015. Mr. Teo worked in DDB Greater China Group, was appointed as the chief financial officer in September 2009, and was additionally appointed as the director of operations in January 2011. He previously served in Focus Media Group and was appointed as the financial deputy director in June 2007. Prior to that, from September 1994 to May 2007, Mr. Teo worked at Ernst & Young and Ernst & Young Business Services Ltd. in various positions in Kuala Lumpur and Toronto, including as a senior manager in the Transaction Advisory Services. Mr. Teo has been an independent director of 111, Inc. (a company listed on the NASDAQ, ticker symbol: YI) since September 2018. Mr. Teo received his Bachelor of Science in Accounting and Financial Analysis degree from The University of Warwick in the United Kingdom in July 1994. He is a Chartered Certified Accountant in the United Kingdom, who has obtained his qualification in July 1998 from The Association of Chartered Certified Accountants, and is a Certified Public Accountant in the United States and Hong Kong, who has obtained his qualification from American Institute of Certified Public Accountants in May 2002 and Hong Kong Society of Accountants in October 2003, respectively.

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TJ Deng, PhD

President, Discovery

Dr TJ Deng joined BioDuro in the initial stages of the company and helped BioDuro grow to an industry leading discovery services organization. He established and managed several scientific departments, including DMPK, before transitioning to a leader of the business and operations functions. Prior to joining BioDuro, Dr. Deng spent six years at PPD, in positions with increasing responsibilities from scientist to scientific manager.




  • Developed the extractable/leachable capabilities at PPD
  • 18 years industry experience

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Kent Payne
Kent M. Payne, PhD

Chief Executive Officer

Kent is distinguished as a business operator and leader in areas of sales, commercial manufacturing and product development. He has extensive executive experience in M&A as well as successfully running, start up, growth and turn around businesses. This includes both Fortune 500 and Private Equity environments. He combines strong business leadership, successful P&L track record, and technical background to strategically lead and grow enterprise value across Biotechnology and Pharmaceutical market segments. He has successfully led the geographic expansion of businesses into Europe, Asia, and South America in addition to the United States.  He currently serves as CEO for BioDuro-Sundia, LLC (an Advent International company). He also currently serves as a board member for Goodwin Biotechnologies (a Signet Healthcare company). 

Prior Roles

  • President, Global CMC Solutions BioDuro-Sundia, a global
  • CEO Socorro Pharmaceuticals, LLC, a generic pharmaceutical
  • President Americas, Qualicaps Inc.(a Mitsubishi Chemical Holdings subsidiary)
  • Principal Consultant and Partner at CoreFactor LLC, providing executive strategic, licensing and operational advisory services to clients.
  • Vice President/General Manager Catalent Pharma Solutions, Inc. (a Blackstone Group company formed in 2007, formerly part of Cardinal Health)
  • Progressive leadership responsibility at: Novartis, Monsanto and G.D. Searle.  

Prior Brand Position

  • Board Advisor Vitruvias Therapeutics
  • Board Member Qualicaps, Inc. (a wholly owned subsidiary of
    Mitsubishi Chemical Holdings)
  • Board member Technophar, Inc. (a wholly owned subsidiary of
    Mitsubishi Chemical Holdings)
  • Board Advisor, Corporate Strategy Office, Life Science Institute
    Inc. (a wholly owned subsidiary of Mitsubishi Chemical Holdings)
  • Non-executive Chair and Board Member PDS Biotechnology·        (PDSB: NASDAQ)

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John Phillips
John Phillips

Vice President, Business Development (US & EU)

Coming soon…



  • Coming soon…

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Roy Xu
Roy Xu

Chief Strategy Officer

Roy has over 25 years of healthcare industry experience.  He started his career as an orthopedic surgeon.  Roy joined Eli Lilly as a sales rep in 1997.  Since then he has had various roles in market research, business intelligence, BU head, strategy, regional general management, business development etc., both at Eli Lilly and Boehringer Ingelheim (BI).  Roy also spent more than two years in Germany where he was BI’s Director of Corporate Business and Enabling Strategy.

Roy obtained a bachelor’s degree in Clinical Medicine at Zhejiang Traditional Chinese Medicine University, and an MBA from Zhejiang University.



  • 25 years of healthcare industry experience including Eli Lily and Boehringer Ingelheim. 
  • Former Director of Corporate Business & Enabling Strategy at oehringer Ingelheim in Germany.

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San Diego

San Diego - BioDuro-Sundia

Our San Diego site is our corporate headquarters. The facility is home to BioDuro-Sundia’s drug product development technologies and has 9 GMP clean rooms. Development and manufacturing operations are conducted for projects up to Phase III clinical trials.

Size: 44,000 sq. ft.
Featured capabilites: Tableting, Coating, Hot Melt Extrusion, Spray Dried Dispersion

11011 Torreyana Rd.
San Diego
CA 92121
United States

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BioDuro Beijing

Operating since 2006, our Beijing site is home to BioDuro-Sundia’s first wet chemistry operations. With 300 regular fume hoods and 18 scale-up chemistry hoods the Beijing facility houses most of BioDuro’s chemistry operations, while also hosting labs for biology and monoclonal antibody discovery.

Size: 100,000 sq. ft. 
Featured capabilities: Radioactivity Lab, Monoclonal Antibody Discovery, Medicinal Chemistry

No. 29 Life Science Park Road
Changping District Beijing,
P.R. China

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BioDuro- Shanghai Facility

Established in 2012, BioDuro-Sundia’s Shanghai facility has been growing with its departments. The cutting edge facility contains labs for ADME, bioanalysis, in vitro assays and translational research. The site includes a 18,000 sq. ft vivarium and 20,000 sq. ft of office space.

Size: 92,000 sq. ft.
Featured capabilities: Scale-up Chemistry, Discovery Biology, DMPK, In Vivo Pharmacology

No. 233 North Fu Te Road
Waigaoqiao Free Trade Zone
Shanghai, 200131
P.R. China

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Cathy Yen
Cathy Yen

Director, Operating Partner

Cathy joined the Board of Directors of BioDuro-Sundia in 2020, with the Advent-led acquisition of Sundia and creation of BioDuro-Sundia. Prior to that, she was Chairman of the Board at Sundia Meditech Group, where she was the key architect of Sundia’s strategic vision and growth. Under her leadership, Sundia solidified its position as one of the leading pre-clinical CROs in China.

Prior to Sundia, Cathy had a distinguished career as a seasoned venture capitalist, having led numerous investments in high-growth companies in Asia. Cathy served as a Partner of AsiaVest Partners, TCW/YFY Ltd., a global venture capital firm, for over a decade, Vice President at Global Financial Services, Vice President at Crimson Ventures/Chinatrust Bank and Senior Manager at Fortune Capital. She brings over 20 years of experience in corporate finance, accounting, strategic planning and private equity investments. 

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Wuxi - BioDuro

Established in 2019, BioDuro-Sundia’s fully integrated discovery facility located at the heart of Jiangsu Wuxi Life Science & Technology Industrial Park with plans of growing staff to 1000+ scientists.

Size: 300,000 sq. ft.
Featured capabilities:
Discovery Chemistry & Biologics, Biology, DMPK, Pharmacology, CMC Services

no.1699,Huishan avenue
Huishan Economic 
Development Zone,Wuxi
P.R. China

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Hebei - Sundia

Established in 2011, this pilot plant this handles mg to kg scale up.

Size: 45,208 sq. ft.

Featured capabilities: SFFS Chemistry: mg to kg scale up
(150 hood)

238 Changjiang Road
Hebei province
P.R. China

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