Development and validation of a sperm-freezing device created using 3D printer technology

To develop and evaluate the effectiveness of a 3D-printed prototype to hold semen straws during the freezing process under safe and reproducible conditions.

A prototype capable of holding ten straws in liquid nitrogen vapor (LN2) was 3D printed. A second support that is commonly used was assembled from pieces of expanded polyethylene (EPS), respecting the identical distance between the straws and the LN2 surface. Temperatures were registered with a thermocouple placed inside a straw. Semen samples were frozen in the presence of cryoprotectant using the prototype (n=20) and the EPS support (n=20) in two independent series of measurements. Sperm parameters (motility, vitality, and DNA fragmentation) were measured for fresh and frozen-thawed samples.

The temperature cooling curves measured on the prototype were remarkably reproducible. The prototype material withstood over 300 freezing cycles without damage. The mean motility and vitality of fresh (64.2%, 72.0%) and frozen-thawed (25.7%, 38.8%) samples were significantly different (p<0.001) using either support. Recovery rates of motility, vitality, and sperm DNA fragmentation in frozen-thawed sperm samples were equal regardless of straw position on the prototype or support type used.

The developed device allows a homogeneous, quantifiable, reproducible cooling of the straws in liquid nitrogen vapor. The recovery rates are comparable to those reported in the literature for both tested supports. The designed 3-D printed prototype favors the safe handling of the straws, an explicit way of describing freezing conditions, and a better intra-operator and inter-laboratory reproducibility of the cryopreservation process.