Exhibit 99.1 Repligen to Acquire FlexBiosys Inc. April 12, 2023 1

Safe Harbor / Non-GAAP Financial Measures This presentation contains forward-looking statements within the meaning of the federal securities laws. Statements in this presentation which are not strictly historical statements including, without limitation, express or implied statements or guidance regarding Repligen’s estimated financial results, future financial performance and other statements identified by words like “estimated,” “anticipated,” guidance, or “goal,” and similar expressions are forward-looking statements. These statements are subject to risks and uncertainties which may cause our plans to change or actual results to differ materially from those anticipated. In particular, unforeseen events outside of our control may adversely impact future results. Additional information concerning these factors is discussed in our reports filed with the Securities and Exchange Commission including recent Form 8-Ks, our most recent Annual Report on Form 10K and our most recent Quarterly Reports on Form 10Q, all of which are available on our website. The forward-looking statements in this presentation reflect management’s current views and may become obsolete as a result of new information, future events or otherwise. We may not update such forward looking statements to reflect a change of events or circumstances that occur after the date hereof, except as required by law. The industry and market data contained in this presentation are based on management’s own estimates, independent publications, government publications, reports by market research firms or other published independent sources, and, in each case, are believed by management to be reasonable estimates. Although we believe these sources are reliable, we have not independently verified the information. This presentation discloses certain financial measures not prepared in accordance with generally accepted accounting principles, or GAAP. Repligen strongly encourages investors to review our consolidated financial statements and publicly filed reports in their entirety and cautions investors that the non-GAAP measures used herein may differ from similar measures used by other companies, even when similar terms are used to identify such measures. 2

Strategic acquisition accelerates Fluid Management growth Strengthens Fluid Management capabilities Expands our Total Addressable Market Meets our acquisition criteria o Accelerates entry into single-use o Entry into single-use bag market o Single-use, scalable product line bag market with bioprocessing and access to other adjacencies o Leverages Repligen commercial capabilities in 2D and 3D bags and o Supports assembly business growth and operations capabilities complex tubing assemblies at newly established centers in o Expected to be accretive to o Builds on our Fluid Management Hopkinton, MA and Waterford, Repligen adjusted earnings per portfolio and addresses a gap; adds Ireland share in 2024 bags to our offering of assemblies, o Increases opportunities to provide components and durables more complete fluid management o Adds a state-of-the-art 22,000 solutions to our customers square manufacturing facility and associated equipment Further expands Repligen portfolio with single-use bag manufacturing capabilities 3

FlexBiosys meets Repligen’s acquisition criteria Complements and expands our Provides operational and Strong revenue growth Fluid Management portfolio commercial leverage potential o Expands single-use Fluid Management o Complement distributor network with o COVID-19 related demand was offerings go direct strategy across regions catalyst for expansion of capacity and manufacturing capabilities o In-house bag manufacturing and o Immediate opportunity to leverage integration into Repligen assemblies Repligen’s global commercial team o $5M-$6M base business revenue (vs. limited commercial footprint) contribution expected in 2023 (9 mo.) o Further enables vertical integration and supply chain control o Product synergies across fluid o Business expected to grow at 25% management annually starting in 2024 o Expect acquisition to be accretive to adjusted EPS in 2024 4

FlexBiosys company profile Founded 2009 Products and capabilities Customer benefits of single-use o Single-use liners o Minimize risk of cross contamination Headquarters Branchburg, NJ o 2D single-use bags o Reduce cleaning costs Employees ~30 o 3D single-use bags o Shorten process turnaround time Leadership Gayle Tarry, CEO, o Custom assemblies Stan Tarry, CTO (Founder) Facilities Revenue overview Customer Primarily U.S. biopharma o 22,000 sq. ft. o $7M base (non-COVID) revenue FY22 Base with some C&GT o 3 clean rooms (ISO Class 7) o $6-$8M base revenue FY23e o Gusseted tubing machinery o 25% revenue growth FY24 Flextreme™ 2D media bags Bottle assemblies with overmolded caps; 6 mL FlexTainer™ 3D Process bags; to 20L for up to 2,000L bioreactors 5

Expanding our Fluid Management portfolio Products Capabilities Repligen Competency COMPONENTS o High precision engineering of valves, valve liners and Valve Blocks exoskeletons o Onsite tubing extrusion capabilities Bottles, Tubing, Over-molding o Expert, first-in-class over-molding capabilities o High precision injection molding Clamps, o Engineering & design of components and tooling Connectors o Rapid prototyping (machining and 3D printing) DURABLES o High quality durable plastic carboys and totes Bins, Totes, Tools o Custom designs, competitive lead times ASSEMBLIES o Expertly designed and engineered, high value consumables Assemblies o Dual sourcing in U.S. and Ireland Bags and Film o 2D and 3D formats 6

Thank you! For questions, contact investors@repligen.com 7