Zenflow has closed an oversubscribed $52 million Series D round led by Cook Medical, which simultaneously became the exclusive U.S. distributor of the company’s Spring System, a reversible implant for benign prostatic hyperplasia (BPH). The announcement, made 5 October 2026, pairs new capital with Cook’s national urology sales network less than a year after Spring’s FDA premarket approval.
Delivered by scope, not scalpel
Zenflow’s Spring System is a small nitinol (nickel-titanium) implant placed inside the prostatic urethra to hold the channel open against an enlarged prostate. It is delivered through the Zenflow Spring Scope, a single-use flexible cystoscope that won its own FDA 510(k) clearance on 30 September 2025, in an office visit that needs no general anesthesia and leaves no incision. FDA’s approval covers men with a prostatic urethral length of 25–45mm and prostate volume of 25–80cc, and the device comes in multiple sizes to match.
What distinguishes Spring from most of the minimally invasive BPH field is reversibility: the implant is designed to be removed rather than left permanently in place or used to ablate tissue. That single property shapes the edge section below and the comparison table later in this piece.
Three things Spring is betting on
No general anesthesia
Placement happens in a urology office through the Spring Scope, with no incision and, per the company, typically no post-procedure catheter — a lower bar to clear than a hospital-based surgical alternative.
Reversible by design
Spring can be removed, unlike tissue-ablating options such as Rezum or tissue-resecting surgery such as TURP. FDA’s approval and the company’s own materials both describe the implant this way.
A second bet from the same investor
Cook Medical didn’t just write a check: it led the Series C that funded the PMA submission in 2024, then returned to lead the Series D and take on exclusive U.S. distribution — a commercial commitment beyond typical venture participation.
Spring's pivotal data, in four figures
Clinical figures from Zenflow's BREEZE pivotal trial data, presented at the American Urological Association annual meeting; financing figures from the 5 October 2026 announcement.
Cook doubles down on Spring
According to the 5 October 2026 announcement, the $52 million Series D was oversubscribed and included new investor ClavystBio alongside returning backers Invus Opportunities, F-Prime and Medtech Venture Partners, plus venture debt from HSBC Bank USA and Trinity Capital. Cook Medical’s role goes beyond capital: under the agreement, Cook becomes Spring’s exclusive distributor to urologists and health systems nationwide, drawing on relationships the company has built over decades in urology.
“Cook Medical’s deep relationships within urology and proven commercialization capabilities make them the ideal partner to help bring the benefits of the Zenflow Spring to patients across the country.” Shreya Mehta, CEO, Zenflow — 5 October 2026 announcement
Cook had already backed Zenflow once: it led the company’s $24 million Series C in November 2024, which funded the PMA submission behind Spring’s eventual approval. Returning to lead the Series D and add exclusive distribution rights is a larger bet than a typical follow-on round, and it ties Zenflow’s commercial reach directly to one of urology’s more established device distributors rather than a sales team Zenflow would have had to build itself.
BPH's office-based shift
Spring enters a BPH device market that has been steadily moving procedures out of the operating room and into the urology office. iData Research’s MedCore franchise puts the global BPH treatment device market above $1.0 billion in 2024, growing to more than $1.4 billion by 2031 — a market already anchored by two other office-based options, UroLift and Rezum, that proved patients and payers would accept a same-day alternative to surgery.
BPH devices, sized toward 2031
$1.0B → $1.4B+
Global BPH treatment device market, 2024 to 2031, as forecast by iData Research's MedCore franchise.
Sources: iData Research, MedCore — BPH Treatment Device Market Report
Regulatory News outlook
We expect reversible, office-based implants like Spring to take a growing share of this market as urologists and payers favor options that avoid general anesthesia and preserve the option to remove the device, particularly as Cook’s distribution network carries Spring into community urology practices Zenflow could not reach alone.
How we got here: iData Research's $1.0 billion 2024 base compounded at its own 5.1% guided CAGR reaches roughly $1.4 billion by 2031; we assign no specific share of that total to Spring, since the company has not disclosed procedure volume.
Spring against the rest of the BPH shelf
| Product | Mechanism | Setting | Reversible | U.S. regulatory basis |
|---|---|---|---|---|
| Zenflow Spring | Nitinol implant props open the prostatic urethra | In-office, no general anesthesia | Yes, designed to be removable | FDA PMA P250007, Dec 2025 |
| UroLift (Teleflex) | Permanent implants retract prostate lobes | Office-based, local anesthesia | Not used as a reversible option | FDA De Novo, 2013 |
| Rezum (Boston Scientific) | Convective water-vapor thermal ablation | Office-based, no general anesthesia | No, tissue is ablated | FDA cleared, 2015 |
| TURP | Surgical electrocautery resection | Hospital, general or spinal anesthesia | No, tissue is removed | Longstanding surgical procedure |
From each company's labelling, FDA records and published clinical literature; not a head-to-head trial.
From Stanford Biodesign to a second Cook round
Spring's path to a distribution deal
- 2014
Zenflow founded
A spinout of Stanford's Byers Center for Biodesign Innovation Fellowship, built around an office-based alternative to surgical BPH treatment.
- February 2018
$31.4 million Series A
Early venture financing to advance the Spring implant through clinical testing.
- November 2024
$24 million Series C
Cook Medical participates for the first time; proceeds fund the PMA submission.
- 30 September 2025
Spring Scope cleared
FDA 510(k) clearance for the single-use flexible cystoscope used to deliver the implant.
- 11 December 2025
Spring System approved
FDA premarket approval, PMA P250007, for the implant and delivery system.
- 5 October 2026
$52M Series D and Cook distribution deal
Cook Medical leads the oversubscribed round and becomes Spring's exclusive U.S. distributor.
- Ahead
Distribution scale-up
Spring's reach into community urology practices depends on how quickly Cook's existing sales network adds the device.
What the distribution deal has to prove
A financing round is not, by itself, proof that an office-based implant will change how BPH gets treated. What makes this one notable is the identity of the lead: Cook Medical is a private, century-old device company with an existing urology sales force, and putting it in charge of Spring’s U.S. distribution is a different bet than raising capital to build a Zenflow sales team from scratch. If the exclusive arrangement works as intended, Spring’s reach should expand faster than a single company’s commercial build-out typically allows — and faster than its direct office-based competitors scaled in their own early years.
- Distribution start: Cook Medical becomes the exclusive U.S. distributor of the Spring System immediately, per the 5 October 2026 announcement.
- Clinical basis: FDA's approval rests on the BREEZE pivotal trial — a 60% one-year responder rate versus 33% on sham, and 37% mean IPSS improvement.
- Financing: $52 million Series D, oversubscribed, plus venture debt from HSBC Bank USA and Trinity Capital.
- Unresolved: Neither company has published a procedure-volume target or a timeline for when Spring reaches the scale UroLift and Rezum did in their first years on the market.
What the announcement does not say is also worth noting: no sales or revenue figures accompanied the financing, and Zenflow has not disclosed how many Spring procedures have been performed since the device's December 2025 approval. Regulatory News will update this page if that data becomes public.
Sources & further reading
- Zenflow, “Zenflow Secures $52M Series D Financing and Announces Exclusive U.S. Distribution Partnership with Cook Medical,” press release, 5 October 2026. globenewswire.com
- Cook Medical, newsroom announcement on the Zenflow distribution partnership, 5 October 2026. cookmedical.com
- Amanda Pedersen, “Cook Medical Leads $52M Financing for Zenflow,” MD+DI, October 2026. mddionline.com
- MedTech Dive, “Zenflow raises $52M, inks distribution deal with Cook Medical,” October 2026. medtechdive.com
- MassDevice, “Zenflow nets $52M, Cook Medical deal for in-office enlarged prostate implant,” October 2026. massdevice.com
- U.S. FDA, Premarket Approval (PMA) database record P250007, decision 11 December 2025. accessdata.fda.gov
- BioSpace, “Zenflow Presents the BREEZE Pivotal Clinical Trial at the American Urological Association Annual Meeting.” biospace.com
- Stanford Byers Center for Biodesign, Zenflow technology profile. med.stanford.edu
Regulatory News reports on public regulatory documents. It is not legal advice, and the primary sources above govern. If we have made an error, we will say so in public: see corrections.
Frequently asked questions
What is the Zenflow Spring System?
A nitinol (nickel-titanium) implant placed inside the prostatic urethra to relieve obstruction from an enlarged prostate. It is delivered in an office setting through the Zenflow Spring Scope, a single-use flexible cystoscope, without general anesthesia or incisions.
Is the Spring implant permanent?
No. Unlike tissue-ablating or tissue-removing BPH therapies, Spring is designed to be removable, which the company and FDA's approval both describe as reversible.
Why did Cook Medical invest in Zenflow twice?
Cook participated in Zenflow's $24 million Series C in November 2024, which funded the PMA submission. It returned to lead the $52 million Series D in October 2026 and simultaneously became Spring's exclusive U.S. distributor — a deeper commercial commitment than the earlier investment alone.
What did the BREEZE trial show?
In the sham-controlled pivotal trial behind Spring's FDA approval, 60% of patients met the responder criteria at one year compared with 33% on sham, and mean IPSS symptom scores improved 37%, exceeding the trial's pre-specified 30% threshold for clinical success.
