Japanese Oblate Film as a Novel Method for Seed Handling and Activation in Microgravity

As long-duration space missions extend beyond low Earth orbit to sustained operations on the Moon and eventual exploration of Mars, the feasibility of regular resupply diminishes significantly (Douglas et al., 2020; NASA, 2022). Developing sustainable in-situ food production methods through crop cultivation becomes essential to support crew nutrition and alleviate menu fatigue caused by reliance on repetitive prepackaged meals (Yamashita et al., 2009; Perchonok et al., 2020; Poulet et al., 2022; Douglas et al., 2024).

By enabling astronauts to grow and handle fresh crops, these systems offer much-needed dietary variety and enhance the overall mission experience (Wheeler et al., 2003; Johnson et al., 2021). Seed handling in microgravity presents unique technical and operational difficulties. In microgravity, seeds can become particulate debris, posing risks to both spacecraft systems and crew health. These particulates can interfere with sensitive equipment such as air filtration and ventilation systems and create potential hazards to humans, including eye injuries or accidental inhalation (Lockhart, 2021). NASA has been actively exploring the application of polymer-based seed films to address similar challenges in space agriculture (Padgett, 2018).

Ground tests using these films have demonstrated faster germination rates compared to on-flight growth experiments, highlighting their potential to enhance crop productivity and adaptability for space applications (Lockhart, 2021; Cawley, 2022). These advancements underscore the capability of film-based technologies to overcome barriers associated with space-based food production.

This growing demand for reliable and efficient seed handling solutions highlights the necessity of integrating novel technologies that can mitigate risks associated with particulate debris and ensure successful crop cultivation in the unique constraints of space environments. The need for innovative approaches to seed handling has led to the exploration of Japanese oblate film as a potential solution. Japanese oblate film is a thin, starch-based edible material traditionally used in pharmaceutical applications to encase powdered medicines. Research into edible films, including those made from polysaccharides like potato starch, indicates their biodegradability, environmental friendliness, and safety for consumption. These films serve as effective barriers in food packaging, enhancing both quality and safety (Wang et al., 2024). When exposed to water or moisture, the film rapidly dissolves. This feature was observed to facilitate water transfer to the seeds, initiating their activation. Additionally, the dissolving film helps immobilize the seeds on the surface it contacts, ensuring stability during the initial stages of growth. This water-soluble property allows it to integrate into hydroponic or passive watering systems. These qualities make oblate film particularly attractive for space applications, where minimizing mass, waste, and operational challenges are critical considerations.

The physical and chemical properties of oblate film align well with the challenges of seed handling in microgravity. The immobilization of seeds using oblate film, either through adherence or encapsulation, prevents particulate generation during handling and transfer. This approach also enables astronaut crews to store seeds securely and exercise preferential selection during crop production operations.

Beyond addressing seed handling and activation challenges, oblate film offers additional applications for space agriculture. Current systems, such as the Advanced Plant Habitat (APH) and Veggie hardware aboard the International Space Station (ISS), rely on pre-glued seeds for planting (Massa et al., 2017). While effective, this approach limits the flexibility of on-demand planting and crop selection by crew members. Oblate films provide a modular and adaptable alternative, allowing astronauts to handle and plant seeds dynamically as needed. When producing seed films, seeds may be strategically oriented to optimize growth outcomes, particularly in microgravity environments where orientation plays a critical role under both light and dark conditions. In microgravity, the precise handling of seeds using films allows for controlled orientation, reducing variability and ensuring consistent positioning. Specifically, aligning the seed’s micropyle to direct radicle emergence away from the light vector enhances root development and overall growth efficiency (Bekele & Hudnall, 2015; Wojciechowski et al., 2019; Zhang & Lin, 2024). Additionally, this method could serve as an effective storage and transfer system for seeds.

In this study, Japanese cherry red radish seeds were adhered to oblate film and placed on non-enriched agar media to evaluate the potential of this method in addressing the challenges of seed handling and activation. The agar served as an analog to passive hydroponic systems, providing a stable, moisture-retentive surface for seed germination. Agar-based media are widely utilized in both spaceflight and ground-based plant biology experiments for tissue cultivation and small-scale plant growth studies, as they provide a reliable and well-established method for supporting plant development under controlled conditions (Meyers et al., 2022; Teng et al., 2022). The findings suggest that Japanese oblate film is a promising tool for improving seed handling, activation, and overall crop production in space (Figure 1). By addressing key challenges posed by microgravity, this method has the potential to significantly enhance the efficiency and sustainability of space agriculture, supporting the nutritional and psychological well-being of astronauts on long-duration missions as humanity advances toward deeper exploration of the solar system.

Figure 1.

Examples of successful Japanese cherry red radish microgreen germination at Day After Planting (DAP) 7. (A) Post-experiment specimens grown using the oblate film method, showing successful germination and early development. (B) Close-up of healthy microgreens cultivated using the oblate film method.

Commercially available potato starch oblate film sheets (Matsuko Kiyoshi brand; 10% w/w potato starch, 90% w/w water) measuring 9 cm in diameter and 0.01 mm in thickness were used in this study. Japanese cherry red radish seeds (Akamara Hatsuka seed type, variety number 01151, Provider: Tohoku Seeds) were selected for adhesion to the films due to previous success in spaceflight (Farid John & Abou-Issa, 2021; NASA, 2020; Hasenstein et al., 2023). Prior to adhesion, all radish seeds were surface-sterilized using a 70% v/v ethanol wash. The seeds were immersed and agitated in 70% v/v ethanol, then thoroughly rinsed with sterile distilled water. Following surface-sterilization, the seeds were allowed to off-gas for 24 hours in a sterile biosafety cabinet to ensure complete evaporation of residual ethanol. Each oblate film was adhered with 25 sterilized Japanese cherry red radish seeds. A small amount of 2% w/v (2M) guar gum solution was added to the seeds to achieve adhesion to the film, with the seeds arranged in a 5×5 grid-like formation (Figure 2). Similar methods using guar gum and films have been employed in space biology research to optimize plant growth and hardware compatibility (Kiss et al., 2007).

Figure 2.

Oblate Film Seed Arrangement. (A) Oblate film arranged with 25 seeds in a uniform grid formation, showcasing its lightweight and flexible properties before placement on agar media. (B) Seeds adhered to the oblate film after placement, demonstrating secure adhesion

The films were allowed to dry for 24 hours before integration. Initial testing consisted of 28 seed film sheets and plates and 28 control group plates. During pre-experiment trials, adhesion was achieved by using clear non-toxic craft glue. This method resulted in successful adhesion, immobilization, activation, and germination as well.

An initial set of 54 non-enriched agar plates were prepared, each plate measuring 90 mm in diameter. The agar media used in this study, derived from red algae, was prepared as a 2% w/v solution (2 g of agar powder per 100 mL of water) with a molarity of 2 mM, using Yoneyama Extra Pure Reagent 01793 (Product of Yoneyama Medical Industry Supplies, Osaka, Japan; Lot No. TNL 0571). Of these, 28 plates were designated as controls, while the remaining 28 plates were used for the experimental group. The agar served as an analog to passive hydroponic germination systems, providing a stable, nutrient-free medium that maintains consistent hydration for seed activation and initial growth. Its structure enabled water diffusion similar to passive hydration methods applicable in reduced or microgravity environments.

For the control group, 25 sterilized radish seeds were evenly distributed in a grid formation directly on the surface of each agar plate. In the experimental group, each agar plate was covered with an oblate film embedded with 25 sterilized radish seeds in the same formation. The films were carefully placed on the surface of the agar, ensuring full contact between the seeds and the agar medium. (Figure 3) All plates were closed and placed in a controlled cultivation chamber (ADVANTEC, TVG241AA Incubation Chamber). (Figure 4) The chamber was maintained at a temperature between 25–27°C with 60% relative humidity. Plates were illuminated under LED magenta grow lights with a light spectrum composed of 52% red (620 nm), 35% blue (460 nm), and 13% broad-spectrum white LEDs. The lights were positioned at a distance of 60 cm, providing an intensity of approximately 4725 lux and a Photosynthetically Active Radiation (PAR) of approximately 78.66 µmol m⁻² s⁻¹, set to a 16-hour photoperiod per 24 hours. Germination was determined by the visible emergence of radicle or cotyledon structures from the seeds, marking the initiation of plant growth development. Visible germination percentages were recorded 24 hours after planting and then again 7 days after planting (DAP). Following the initial DAP 7 observation period, an additional 9 oblate films were prepared and embedded with sterilized seeds. These films were stored under ambient conditions, average temperature 24°C, 35% RH, for 30 days to test the preservation efficacy of the films. During the storage period, no germination was observed. After 30 days, the stored films were placed on 9 new plates of non-enriched agar. In parallel, 9 additional control plates were prepared, each with 25 sterilized radish seeds distributed directly on the agar surface. Both groups were then incubated under the same controlled conditions as described above and observed for germination over a 7-day period. A total of 74 plates were prepared and observed, comprising 28 experimental plates with oblate films and 28 control plates in the initial setup, followed by 9 experimental plates with stored films and 9 corresponding control plates. Altogether, 1,850 seeds were planted across the study. Germination rates for both the initial and stored films were analyzed, compared to the control groups, and statistically evaluated using a t-test to assess how the use of oblate films influenced activation and germination rates. All values are reported as mean ± standard error (SE).

Figure 3.

Seed Arrangement and Film Interaction with Agar Media. (A) Seeds arranged in a grid formation directly placed on the surface of the agar media. (B) Oblate film with adhered seeds upon contact with the agar media; the film adheres fully to the agar due to moisture, beginning to dissolve and ensuring the seeds establish direct contact with the moisture for germination.

Figure 4.

(A) Oblate film with seeds positioned on the agar media, shown prior to sealing the plates and placing them in the growth chamber. (B) View of multiple plates arranged within the growth chamber under controlled environmental conditions for the germination study.

This study highlights the significant potential of films, such as Japanese oblate film, as innovative tools for space agriculture, particularly in addressing the challenges of seed handling and activation in microgravity. The oblate film demonstrated its ability to support both seed immobilization and water-mediated activation, features that are critical for maintaining control over seed placement and germination in the absence of gravity. These properties align with NASA’s ongoing research into seed films, which have also shown promise for improving germination rates and offering flexibility in space crop production systems (O’Rourke & Romeyn, 2023; Cawley, 2022; Lockhart, 2021).

The film’s versatility extends to biopriming, wherein it can potentially be infused with growth hormones, fertilizers, and beneficial microbes to enhance seed germination and plant productivity. NASA is conducting ongoing studies to evaluate the effectiveness of similar films inoculated with plant growth-promoting microbes, which have shown potential to enhance biomass yields and improve plant resilience under stress conditions (Padgett, 2018; O’Rourke & Romeyn, 2023). Future research should explore the enrichment of oblate films with such agents to further optimize their efficacy in space environments.

While the results of this study are promising, achieving full flight readiness will require additional testing and validation. Establishing standardized metrics, such as a Crop Readiness and Flight Readiness Index, will be essential for evaluating the performance of oblate film under spaceflight conditions, including germination rates, plant growth metrics, and system integration efficiency. Microbial proliferation testing is also critical to investigate the potential for microbial growth on or within the films and to refine sterilization methods to ensure both astronaut safety and crop viability. Comparisons of various sterilization techniques, such as autoclaving, chemical treatments, and radiation-based methods, will help determine the most effective approach for maintaining seed viability while minimizing contamination risks. Additionally, the variable utility of oblate films, such as encapsulating seeds in seed pockets, can facilitate precise placement, handling, and storage during planting operations, further supporting system integration in space agriculture (Figure 7).

Figure 7.

Seed encapsulated within oblate film, forming a seed pocket for optimized handling and germination. In the background, a mature cherry red radish plant grown from these seed pockets during preliminary testing is displayed, demonstrating the effectiveness of the encapsulation method.

In this study, a non-enriched agar was deliberately chosen as the control to mimic passive hydroponic methods without the influence of external nutrients. While the addition of the oblate film significantly improved germination rates compared to the control, it is acknowledged that the starch content in the film may have contributed to this increase by providing a localized energy source for germinating seeds. This is an important distinction from standard agar-based formulas commonly used in spaceflight experiments, which include salts, vitamins, and sugars optimized for growth. Future studies could explore how the germination rates achieved in this study compare directly to those using enriched agar formulas.

Different crops exhibit varying germination behaviors, growth rates, and environmental tolerances, making it essential to expand testing to include a diverse array of species. Future research would greatly benefit from developing a catalog of crops tested with oblate film technology under similar conditions. Such a catalog could provide valuable insights into the adaptability of this method across multiple plant types and its scalability for diverse mission requirements.