Low-Cost Resin 3-D Printing for Rapid Prototyping of Microdevices: Opportunities for Supporting Aquatic Germplasm Repositories

Exploring pathways toward open-hardware ecosystems to safeguard genetic resources for biomedical research communities using aquatic model species

Development of reliable germplasm repositories is critical for preservation of genetic resources of aquatic species, which are widely utilized to support biomedical innovation by providing a foundational source for naturally occurring variation and development of new variants through genetic manipulations. A significant barrier in repository development is the lack of cryopreservation capability and reproducibility across the research community, posing great risks of losing advances developed from billions of dollars of research investment. The emergence of open scientific hardware has fueled a new movement across biomedical research communities. With the increasing accessibility of consumer-level fabrication technologies, such as three-dimensional printers, open hardware devices can be custom designed, and design files distributed to community members for enhancing rigor, reproducibility, and standardization. The overall goal of this review is to explore pathways to create open-hardware ecosystems among the communities using aquatic model resources for biomedical research. To gain feedback and insights from community members, an interactive workshop focusing on open-hardware applications in germplasm repository development was held at the 2022 Aquatic Models for Human Disease Conference, Woods Hole, Massachusetts. This work integrates conceptual strategies with practical insights derived from workshop interactions using examples of germplasm repository development. These insights can be generalized for establishment of open-hardware ecosystems for a broad biomedical research community. The specific objectives were to: (1) introduce an open-hardware ecosystem concept to support biomedical research; (2) explore pathways toward open-hardware ecosystems through four major areas, and (3) identify opportunities and future directions.

A Modified-Herringbone Micromixer for Assessing Zebrafish Sperm (MAGS)

Sperm motility analysis of aquatic model species is important yet challenging due to the small sample volume, the necessity to activate with water, and the short duration of motility. To achieve standardization of sperm activation, microfluidic mixers have shown improved reproducibility over activation by hand, but challenges remain in optimizing and simplifying the use of these microdevices for greater adoption. The device described herein incorporates a novel micromixer geometry that aligns two sperm inlet streams with modified herringbone structures that split and recombine the sample at a 1:6 dilution with water to achieve rapid and consistent initiation of motility. The polydimethylsiloxane (PDMS) chip can be operated in a positive or negative pressure configuration, allowing a simple micropipettor to draw samples into the chip and rapidly stop the flow. The device was optimized to not only activate zebrafish sperm but also enables practical use with standard computer-assisted sperm analysis (CASA) systems. The micromixer geometry could be modified for other aquatic species with differing cell sizes and adopted for an open hardware approach using 3D resin printing where users could revise, fabricate, and share designs to improve standardization and reproducibility across laboratories and repositories.

Initial assessment of the toxicologic effects of leachates from 3-dimensional (3-D) printed objects on sperm quality in two model fish species

The use of 3-dimensional (3-D) printing is gaining popularity in life sciences and driving innovation in fields including aquatic sperm cryopreservation. Yet, little is known about the effects leachates from these objects may have on biological systems. In this study, we investigated if exposure to leachates from 3-D printed objects fabricated from different photo-curable resins could affect sperm quality in two model fish species, zebrafish (Danio rerio) and goldfish (Carassius auratus). Leachates were collected following contact periods of 10 min and 22 h with objects manufactured using a mask LCD resin printer and three different commercially available resins (i.e., standard, eco-friendly, and impact-resistant). Sperm cells were exposed to the leachates for 18 min, and parameters related to sperm motility, cell count, and membrane integrity were evaluated. All experiments were blinded. Leachate originating from contact with impact-resistant resin for 10 min significantly reduced the cell count of zebrafish sperm, while leachate originating from contact with standard resin for 22 h significantly increased the beat cross frequency of goldfish sperm. The changes were not observed across species and no adverse effects were recorded in percent motility, velocity, amplitude of lateral head movement, or membrane integrity of sperm. Our findings demonstrate that exposure to leachates from certain 3-D printed resins can affect sperm quality, while other resins may support sperm quality evaluation. Further investigations are warranted to assess other parameters, effects, and their biological relevance for a variety of aquatic species.

An automated modular open-technology device to measure and adjust concentration of aquatic sperm samples for cryopreservation

Repositories for aquatic germplasm are essential for safeguarding valuable genetic diversity for species relevant to aquaculture, biomedical research, and conservation. Development of aquatic germplasm repositories is impeded by a lack of standardization within laboratories and across the research community. Protocols for cryopreservation are often developed ad hoc and without close attention to variables, such as cell concentration, that strongly affect the success and reproducibility of cryopreservation. The wide dissemination and use of specialized tools and devices as open hardware can improve processing reliability and save costs. The goal of the present work was to develop and prototype a modular and open-technology approach to help to standardize the cell concentration of germplasm samples prior to cryopreservation. The specific objectives were to: 1) design and fabricate prototypes of the automated concentration measurement and adjustment system (CMAS), incorporating custom peristaltic pumps and optical evaluation modules, and 2) evaluate the performance of the CMAS with biological samples. Linear regression models were obtained for estimation of aquatic sperm concentration >10⁸ cells/mL and for algae concentration > (3 × 10⁵) cells/mL. Algae were diluted with extender medium by an automated process, resulting in a dilution precision of ±12.6% and ±6.7% in two trials, attaining means of 89% and 71% of the target cell concentration. The development of the CMAS as open technology can provide opportunities for community-level standardization in cryopreservation of aquatic germplasm and can invite new users, makers, and developers into the open-technology community. This will increase the reach and capabilities of much-needed aquatic germplasm repositories.

Development of a Single-Piece Sperm Counting Chamber (SSCC) for Aquatic Species

Accurate determination of sperm concentration in aquatic species is important for assisted reproduction and cryopreservation, yet is challenging as current counting methods are costly or not suitable for many species. The goal of this work was to develop a simple (single-piece and single-layer photolithography) sperm counting chamber (SSCC) for aquatic species. Goldfish (Carassius auratus) and zebrafish (Danio rerio) sperm were used for evaluation in the device, which was created with soft lithography. Four designs with different geometries were evaluated for counting accuracy. Open-corner and open-midpoint designs were the most accurate with no significant differences (P > 0.05) for most of the target sperm concentrations (0.5-1.0 × 10⁸ cells/mL). The open-corner design was not significantly different from the Makler^® counting chamber intended for human sperm cells (P = 0.6) but was significantly different from a hemocytometer (P < 0.001) intended for other cell sizes. Material cost of device production was USD 16 per unit, including photolithography supplies, glass slide and coverslip, and polydimethylsiloxane. The cost can be reduced to USD 2 per unit with repeated wafer casts. This device could be further refined for resin 3-D printing and sharing via open-hardware approaches and modified to best suit species specific applications.

A 3-D printed vitrification device integrated with French straws

The goal of this work was to develop prototypes of open-hardware vitrification devices for sperm cryopreservation that can be integrated with existing straw platforms. The open-hardware Vitrification Device for French Straws (VD-FS) is low-cost, customizable, 3-D printable, standardized, and allows long-term sample storage and identification. The feasibility was shown for vitrifying and storing samples with multiple configurations. The results can be improved by design alternation and evaluation of various vitrification solutions. This is the first complete open-hardware vitrification device that can be integrated with existing French-straw storage systems, providing a foundation for future community-level modifications and improvements.

A practical evaluation of machine learning for classification of ultrasound images of ovarian development in channel catfish (Ictalurus punctatus)

Machine learning is a powerful tool to improve efficiency of industrial processes, but it has not yet been well utilized in aquacultural and hatchery applications. The goal of the present study was to evaluate the feasibility of using a broad array of machine learning approaches (testing of > 200 vectorization and model combinations, reporting on 20) to classify ultrasound images spanning annual ovarian development (i.e., from undeveloped to mature) of channel catfish (Ictalurus punctatus). The specific objectives were to: 1) establish dataset preprocessing to standardize image features; 2) develop and train image classification models with deep learning methods; 3) develop and train models with traditional machine learning methods; 4) compare performance of deep learning and traditional methods on two classification problems (2-class and 5-class), and 5) propose insights to deploy models in practical aquaculture applications for research and hatchery use. A total of 931 ultrasound images of catfish ovaries were used to train and evaluate models for a 2-class problem (as a 'yes' or 'no' answer) to support hormone-injection decisions for spawning management in hatcheries, and a 5-class problem for classifying gonadal development stages for research. By using feature extraction, cropping, dimension reduction, and histogram normalization, a preprocessing method was created to standardize images to develop traditional (i.e., vector input), and deep learning convolutional neural network (CNN) (i.e., image input) approaches. Traditional machine learning models with image classification achieved 100% median accuracy on the 2-class problem (with the models RN-50 and RN-152), and 96% median accuracy for the 5-class problem (with VGG-19 image vectorization). The deep learning approach for the 2-class problem had a median accuracy of > 98% for 15models. The 5-class deep learning models produced a steady increase in median accuracy with training net size, achievable through expansion of the dataset. These models can be developed further, but traditional models (using CNN architectures to simply calculate image vectors) outperformed the deep learning approach. These models can be directly applicable to aquaculture in hatcheries and reproductive biology research, in addition to a wide variety of other image-based applications.

An Open-Hardware Insemination Device for Small-Bodied Live-Bearing Fishes to Support Development and Use of Germplasm Repositories

Small-bodied live-bearing fishes attract broad attention because of their importance in biomedical research and critical conservation status in natural habitats. Artificial insemination is an essential process to establish hybrid lines and for the operation of sperm repositories. The existing mouth-pipetting technique for artificial insemination of live-bearing fishes has not been substantially upgraded since the first implementation in the 1950s. The goal of this work was to develop a standardized artificial inseminator device (SAID) to address issues routinely encountered in insemination by mouth-pipetting, including lack of reproducibility among different users, difficulty in training, and large unreportable variation in sample volume and pressure during insemination. Prototypes of the SAID were designed as relatively inexpensive (<USD 80) open hardware based on commercially available and 3-D printed components to enable broad community access. A linear actuator was used to accurately control the position of a piston for fluid transfer with a standard deviation of <0.1 mm over a 4 mm range of travel. The volume of sample transfer was precisely controlled with a linear relationship (r2 > 0.99) between the piston position and volume. Pressure generation from eight mouth-pipetting operators and SAID prototypes were assessed by pressure sensors. The pressure control by SAID was superior to that produced by mouth-pipetting, yielding lower pressures (31−483 Pa) and smaller variations (standard deviation <11 Pa). These pressures were sufficient to deliver 1−5 μL of fluid into female reproductive tracts yet low enough to avoid physical injury to fish. Community-level enhancements of the SAID prototype could enable standardized insemination with minimal training and facilitate the participation of research communities in the use of cryopreserved genetic resources.