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PRINTED PARTS WORTH UNDER 10 DOLLARS FROZE FROG SPERM AS WELL AS A PROGRAMMABLE FREEZER COSTING 15,000 DOLLARS OR MORE

A 3D-printed cooling kit with under 10 dollars of material froze frog sperm as well as a programmable freezer, and pharmacy gelatin capsules worked in place of specialist straws.

by Thaiza Rodrigues de Freitas, Danilo P Streit Jr, and colleagues

FULL CAD BOM FIRMWARE DOCS

ScienceOpen-hardware

Built with3D printing

difficulty
●●●●○
time
a weekend-plus
license
CC BY-SA 4.0 (design files); paper CC BY 4.0
repo
repo FINISHED0 stars

WHAT YOU’LL NEED

1
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COMPAREE VERDICT

This is open science hardware for conservation labs, not a weekend maker project. What the paper contributes is a way to use ordinary gelatin capsules in place of French plastic straws, which are tied to livestock-industry suppliers and hard to get in some regions. The capsules are held in two printed pieces: a filling rack at about 0.84 dollars and a modular holder at about 0.18 dollars per set of five modules. In a separate test the printed CryoKit cooling platform, prior work by the same lab network, reached minus 80 C faster than a computer-controlled freezer (4.0 minutes against 6.6), and post-thaw viability was similar: 54 percent against 50 percent, tested on Xenopus laevis sperm in straws. Capsules then performed comparably to straws on cooling and post-thaw quality. The trade-off is honest: the CryoKit takes up to 15 straws per run where a commercial freezer batches hundreds, so this is for low-throughput work or institutions that cannot afford the commercial route. The single thing most likely to go wrong is not reading the methods section carefully before you start: the dry-thawing step is what stops the gelatin capsule dissolving. If you are a conservation biologist working with amphibians and you already have access to liquid nitrogen, this is a practical alternative. If you are printing this to see if it works on something else, you are on your own: the paper validates it only for Xenopus laevis sperm.

GOOD TO KNOW

  • —Design files for the filling rack and modular capsule holder v3.1 are on the NIH 3D Print Exchange (entry 3DPX-021806) under CC BY-SA 4.0.
  • —The paper describes the dry-thawing method and gives all cryopreservation protocols in the methods section.
  • —There is no bill of materials: you need gelatin capsules, liquid nitrogen, a dewar, and standard lab equipment not listed.
  • —The CryoKit positional cooling platform itself is prior work (reference 14 in the paper); this paper adds the capsule system.
  • —The paper is CC BY 4.0; the printable design files on NIH 3D are CC BY-SA 4.0, so remixes must be shared under the same licence.
  • —This is a lab protocol, not a consumer product: you are handling liquid nitrogen and working with biological samples.

Parts to buy

5 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

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Can I build this?

PrintCapsule filling rack and modular capsule holder v3.1, STL files on NIH 3D Print Exchange. Standard FFF printer, material cost under 10 dollars for the platform.
BuyGelatin capsules, liquid nitrogen, dewar, pipettes, cryoprotectant reagents. The paper does not list suppliers or part numbers.
Tools3D printer, liquid nitrogen handling equipment, standard lab pipettes and measuring tools. Lab safety training for cryogenic liquids.
SkillsLab protocol experience and liquid nitrogen handling. You need to follow the methods section exactly, including the dry-thawing step, and work safely with cryogenic liquids. Not a beginner project.
TimeA weekend to print and assemble the parts, then protocol development time that depends on your species and experience. The paper does not give a start-to-finish timeline.
Cost$ for the printed parts. Liquid nitrogen, dewar, and lab consumables dominate the real cost but are not priced in the paper.
SafetyLiquid nitrogen burns skin on contact and displaces oxygen in confined spaces. Wear face shield, cryogenic gloves, and work in a ventilated area. If you do not have lab safety training for cryogens, do not attempt this.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

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Gallery

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Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the full paper (Methods section has the complete protocol. The dry-thawing step is critical and easy to miss.)
  2. 2.Download the STL files(The filling rack and modular holder files are on the NIH 3D Print Exchange (entry 3DPX-021806); the original CryoKit files are on NIH 3D too.)
  3. 3.Print the filling rack and holder(Standard FFF settings. The paper does not specify infill or orientation.)
  4. 4.Source the capsules and build the CryoKit cooling platform(Size 3 or size 0 gelatin capsules are sold by pharmacies and online retailers. The CryoKit platform files are on NIH 3D (entry 21194/2) and its build is described in Hu et al., 2017.)

KNOWN ISSUES

  • The paper validates this for Xenopus laevis sperm only. Other amphibian species will need protocol development, and the paper does not guide you through that.
  • There is no bill of materials. You need gelatin capsules, liquid nitrogen, a dewar, pipettes, and cryoprotectant reagents, none of which are specified by supplier or part number.
  • The dry-thawing method is what stops the gelatin capsule dissolving. If you skip it or get the timing wrong, the capsule will fail.
  • The cooling platform itself (CryoKit V2.4.7, with Styrofoam floats and nested Styrofoam boxes) is described in the earlier Hu et al. 2017 work, not in this paper. Read that build first, and log your own cooling curve before trusting it with real samples.
  • Throughput is 15 straws per run. If you need to freeze hundreds of samples, a commercial freezer is still the practical choice.
  • Liquid nitrogen safety is not optional. If you have never handled cryogenic liquids in a lab, this project is not where you learn.

Can I use this for other species?

The paper only validates it for Xenopus laevis. You would need to develop the protocol for your species, and the paper does not guide you through that.

What is the actual total cost?

Under 10 dollars for the printed parts. Liquid nitrogen, dewar rental or purchase, pipettes, and reagents are not priced in the paper but dominate the real cost.

Do I need a lab to do this?

Yes. You need liquid nitrogen handling equipment, a dewar, pipettes, and safety training. This is not a home project.

Where do I get the capsules?

Ordinary gelatin capsules from a pharmacy or online retailer, no specialist supplier needed. The filling rack holds up to 30 size 3 capsules, or size 0 capsules with the upper piece removed, and the final V3.1 holder is a set of snap-fit modules with caps that stack for storage.

How does the cooling rate work without electronics?

Height above the liquid nitrogen surface sets the cooling rate. You hold the samples at a fixed position in the vapor phase, and the temperature gradient does the rest.

Can I batch hundreds of samples like a commercial freezer?

No. The CryoKit takes up to 15 straws per run. If you need high throughput, a programmable freezer is still the practical choice.

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Discussion1

FROM THE COMPAREE TEAM

In the paper the CryoKit matched a computer-controlled freezer on post-thaw viability, 54 percent against 50, but it holds only 15 samples per run where commercial freezers handle hundreds. If you ran a small conservation programme, would that throughput limit be a deal-breaker?

CompareeTEAM29d agoedited

Practical notes from our verification: the paper is open access under CC BY 4.0, and the 3D design files for the capsule filling rack and modular holder are on the NIH 3D Print Exchange (entry 3DPX-021806) under CC BY-SA 4.0. The CryoKit cooling platform itself is earlier work (Hu et al., 2017); what this study adds is the gelatin capsule system: the filling rack, the modular holder v3.1 and a thawing method for the capsules. Size 3 gelatin capsules (and size 0 with the alternative base) are widely available from pharmacies and online. The protocol is validated for Xenopus laevis only, so with another amphibian species you are developing the protocol yourself. There is no GitHub repository; the paper and the design files are the whole package. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

Thaiza Rodrigues de Freitas, Danilo P Streit Jr, and colleagues

Rodrigues de Freitas and Streit lead the AQUAM Research Group at the Federal University of Rio Grande do Sul in Brazil, working on aquatic germplasm and reproductive biotechnology. This project was done in collaboration with the Aquatic Germplasm and Genetic Resources Center at the Louisiana State University Agricultural Center. The CryoKit platform itself is prior work; this paper contributes the gelatin capsule system and the dry-thawing method.

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