Poster CC4 - Monkey Business: Development of a 3D-Printed Mini Speculum for Marmoset Embryo Transfer

Friday, October 25, 2024

3:30 PM – 4:30 PM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Azmina Karukappadath, MSE (she/her/hers)

Medical and Engineering Student
Johns Hopkins University
Baltimore , Maryland, United States

Co-Author(s)

JB

Joshua Brennan, MPH (he/him/his)

Research Analyst
Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
Baltimore, Maryland, United States
Gabriella A. Wong (she/her/hers)

Graduate Student
Johns Hopkins University
Baltimore, Maryland, United States
Cole R. Pritchard, BFA (he/him/his)

Design Studio Assistant Manager
Johns Hopkins School of Biomedical Engineering, United States
JP

James Pickel

Research Associate
Johns Hopkins, United States
TB

Thomas Benassi

Design Studio Manager
Johns Hopkins Biomedical Engineering, United States
BS

Bhuchitra Singh, MD, MPH, MS, MBA

Director of Clinical Research
Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
Baltimore, Maryland, United States
RH

Rebecca A. Holton, Ph.D.

Postdoctoral Research Fellow
Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA, United States
Nia Bryan (she/her/hers)

Sr. Lab Coordinator
Johns Hopkins University
Baltimore, Maryland, United States
Xiaoqin Wang, PhD

Professor of Biomedical Engineering, Neuroscience, and Otolaryngology
Johns Hopkins Biomedical Engineering, United States

Primary Investigator(s)

JS

James Segars, MD (he/him/his)

Professor
Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
Baltimore, Maryland, United States

Introduction: A speculum is a medical device used to examine body orifices; it is often used by gynecologists to visualize the vagina. For humans undergoing embryo transfers through assisted reproductive technology, a speculum is used to open the vaginal vault to access the cervix. No such instrument exists for use in marmosets, so researchers often use other implements such as disposable otoscope tips, rely on ultrasound guidance to blindly insert, or use specialized hysteroscopic equipment to place the embryos; these approaches are limited and have variable success. Callithrix jacchus, the common marmoset, is a New World primate that is frequently used as a non-human primate model for human disease. This species works well as an experimental model because they are small, easy to handle, and have a robust reproductive capacity. Experimental model marmosets are generally bred through oocyte extraction, artificial insemination, and implantation of viable embryos into surrogates. Successful embryonal implantation poses a significant bottleneck for marmoset breeding. Surgical embryo implantation demonstrates higher success rates than current nonsurgical approaches but requires three ovarian cycles between transfer attempts and can cause reproductive tract adhesions. Nonsurgical approaches are limited by the inability to visualize and easily traverse the cervix to place the embryos in the lumen of the uterus. This project's objective was to develop a mini speculum to increase the success rate and ease of nonsurgical marmoset embryo transfer.

Materials and

Methods: The speculum was designed through an iterative process with feedback from experts in marmoset anatomy, veterinarians, biomedical engineers, and physicians with expertise in embryo transfer. The mini speculum was designed using OnShape, a browser-based Computer Aided Design (CAD) software, and sliced using GrabCAD. Speculum prototypes were printed using the Stratasys J35 Pro 3D Printer, which sequentially UV-cures ultra-thin layers of VeroUltra polymer resin to achieve the high resolution required for the mini speculum. Water-soluble WSS150 support material was dissolved by placing the speculums in a water bath. Finally, speculums were sterilized using an AN74i EO Gas Sterilizer (Andersen Sterilizers, Inc.)

In the operating room, the female marmoset is administered general anesthesia and positioned in dorsal lithotomy. The mini speculum is inserted into the vaginal canal and opened by pressing the speculum handles together. A colposcope is used to visualize the cervix through the speculum. The embryos, suspended in Quinn's Advantage Cleavage Medium (CooperSurgical) are loaded into a 28-gauge custom MicroFil catheter (World Precision Instruments). Forceps are used to stabilize the cervix while guiding the catheter through. Once inside the uterine lumen, the embryos are transferred from the catheter. Finally, the catheter and speculum are carefully removed.

Results, Conclusions, and Discussions: The mini speculum’s final design has two parts, top and bottom, that are connected via pin and barrel hinges. This allows the speculum nose to open when the handles are pressed together. The handles are broad and thick to support the force needed to open the vaginal vault. The final prototype has a maximum viewing diameter of 12mm and a nose length of 11mm.

The mini speculum also features a coned viewing port which allows for illumination of the vaginal vault and the ability to advance implements laterally for simultaneous visualization and instrumentation of the cervix. The oblong shape of the top’s viewing port also enables greater illumination and view.

The mini speculum’s nose is tapered and rounded to facilitate insertion into and dilation of the marmoset vagina with minimal trauma to the animal. The tapered nose also helps guide the catheter towards the cervical os during insertion.

Several iterations of the mini speculum were designed, printed, and tested to arrive at the final prototype. The original design resembled a human speculum and did not feature the coned viewing port, which was introduced when cervical instrumentation through an early prototype blocked the surgeon’s view of the vagina. The length of the mini speculum was optimized to open the posterior vagina while reducing the radial force upon the introitus. Reinforcement was added to the speculum hinges to support the force needed to open the vaginal vault. Finally, the speculum nose’s degree of taper was optimized to provide lateral support to the vaginal wall while facilitating insertion of the speculum and catheter tip.

Future improvements could include metal manufacturing for improved strength and durability. Metal construction would allow for inclusion of a ratcheting handle to keep the speculum open against resisting force without requiring constant pressure to be applied to the handles. A future study may be designed to assess the usability and efficacy of the mini speculum.

In conclusion, a 3D mini speculum was developed for embryo transfers in marmosets, an animal frequently used to model human disease and treatment, with the goal to support efficient, humane, and collaborative biomedical research.

Acknowledgements (Optional): Our sincere thanks to the Johns Hopkins Center for Bioengineering Innovation and Design for their support and use of the Design Studio!
NIH grant 1U01DA056556-01 to JS, JP, JB, BS, RH, NB, XW