We conducted an online survey, Public Survey on Brain Organoid Research in Japanese, on 8 December 2022. Participants were recruited through Lancers, Inc., a Japanese crowdsourcing service, and we obtained 326 valid responses from a total of 353 participants). ⁴ Participants received 500 Japanese yen as compensation for their participation. ⁵ The main demographic characteristics of the participants are summarized in Table 1. The median completion time for the entire questionnaire was approximately 19.7 min (SD = 13.9). ⁶ For details on recruitment and further demographic information, see the Supplementary Material.

Most participants (n = 297, 91%) were unaware of HBOs prior to this study. A smaller proportion of participants had some prior knowledge of HBOs, with 7% (n = 24) reporting that they had heard of them and 2% (n = 5) indicating that they were familiar enough to explain them to some extent. Collectively, those who had prior knowledge of HBOs accounted for less than 10% of the participants.

Regarding willingness to donate cells for HBO research, 12% of participants indicated that they would be willing to donate. The majority of participants (64%) stated that their willingness would depend on the specific details of the study, while 78 participants (24%) reported that they would not be willing to donate (Figure 1). As previously noted, it can be reasonably inferred that participants considered project-specific consent when responding to this question.

Regarding research purposes for which cells could be donated, basic research was selected by 42% of the participants. Disease exploration was chosen by 61% of the participants, Treatment development by 68%, and drug discovery by 65%. Medical applications for themselves were selected by 70% of the participants, and medical applications for family was chosen by 67% of the participants. Finally, nothing received 34 selections (10%) (Figure 2).

Logically, all 78 respondents who previously indicated not willing to donate should have selected nothing in this question. However, only 34 participants did so. This discrepancy may suggest that individuals who were initially reluctant to donate cells when asked in a general context reconsidered their stance when the purpose of donation was specified.

Overall, 15% of the participants indicated that they would be willing to donate their cells to institutions adopting broad consent. 37% of the participants responded with it depends. Notably, 36% of participants selected not willing to donate. Don’t know was selected by 13% of participants (Figure 3).

To better understand the conditions under which broad consent would be supported, we examined the reasons provided by participants who selected it depends. Among the 121 respondents who chose this option, 64 participants (53%) provided an explanation for their choice. After one of the authors coded the responses, we identified the following eight categories of reasons (with overlapping responses):

• Explanation: Participants wanted to be informed about the nature and purpose of the research (n = 19, 30%).

Additionally, to investigate potential reasons for the not willing to donate responses, we analyzed the reasons given for this selection using the same approach. Among the 116 participants who chose this option, 74 (64%) provided an explanation. This analysis revealed seven categories of reasons (with overlapping responses):

• Explanation: Participants wanted to be informed about the nature and purpose of the research (n = 34, 53%).

We conducted a survey on the attitudes of Japanese citizens toward cell donation for HBO research to determine whether this research involves a controversial use of biological materials by examining participants’ views on project-specific and broad consent.

First, when asked about their willingness to donate cells for HBO research under project-specific consent, 64% of participants selected it depends, while only 12% expressed full willingness to donate. Regarding research purposes, there was a clear difference in participant attitudes toward basic research (42%) compared to medical applications (65%–70%). In other words, even when provided with sufficient information about a specific study in advance, at least 24% of participants remained unwilling to donate cells for HBO research, and depending on the circumstances, especially when the purpose is basic research, the reluctance rate rises even further. This trend aligns with findings from previous studies. MacDuffie et al. (2023) reported that interviewees often stated that their willingness to consent to HBO research was contingent on the study having a medical purpose. ⁷ Furthermore, Haselager et al. (2020) identified strong altruistic motivations for cell donation in HBO research. Given that, our findings suggest that participants may not fully understand the intrinsic connection between basic research and medical applications which help people more directly. ⁸ This highlights the need for scientific communication strategies emphasizing the essential relationship between basic research and medical applications (Akatsuka et al., 2023).

Most importantly for our study, 36% of participants disagreed with broad consent when informed about the possibility of HBO research, representing a substantial proportion ⁹ . The analysis of free-response descriptions suggests that a key factor in this opposition is the lack of autonomous decision-making based on sufficient research information. This aligns with previous studies, where participants emphasized the need for clear explanations and autonomy in cell donation for HBO research (Haselager et al., 2020; Bollinger et al., 2021; Ravn et al., 2023). ¹⁰ Beyond the need for explanation and autonomy, our results indicate that participants also prioritized the trustworthiness of researchers, concerns about unethical misuse, and the perceived benefits and risks associated with participation in HBO research. While all these factors have been identified in prior studies (Haselager et al., 2020; Bollinger et al., 2021; MacDuffie et al., 2023; Ravn et al., 2023), our data further highlights that their significance is substantial enough to drive 36% of participants to refuse broad consent.

Similarly, a comparable proportion of participants (37%) stated that their acceptance of broad consent would depend on specific circumstances. The key considerations for this group mostly mirrored those outlined above, including the explanation of the research, research objectives (with basic research receiving less support), trust in researchers, ethical concerns, and perceived risks and benefits. Depending on how these elements are addressed in HBO research, some among the 37% may ultimately reject broad consent.

Summarily, at least 36% of our participants do not support broad consent when donated cells may be used for HBO research, and this percentage could increase further depending on the situation. Although our survey is not perfectly representative and has some limitations (see below), the results may suggest that HBO research in Japan would involve the controversial use of donated cells.

The notably negative attitudes toward broad consent in the context of HBO research align with findings from deliberative workshops on organoid research reported by Ravn et al. (2023), where only seven out of 51 participants supported broad consent without restrictions. However, these findings contrast sharply with those from interviews conducted by MacDuffie et al. (2023), where all 67 interviewees supported broad consent if the HBO research served medical purposes. Several factors may explain this contrast. In MacDuffie et al. (2023), interviewees appeared to develop a deep understanding of the practical value of broad consent during the interviews. Additionally, unlike our study, all interviewees had prior experience with cell donation for HBO research or had acted as legal guardians for individuals who had donated. This prior exposure may have naturally predisposed them to view the possibility of their donated cells being widely used in other HBO studies more favorably. Furthermore, if regional and cultural differences between the participants (Japanese vs predominantly US citizens) play a significant role, this would suggest that the optimal approach to cell donation for HBO research varies across regions. Since the donation process should respect individuals' moral views, and moral perspectives are shaped in part by cultural factors, the ideal consent model would reflect its cultural contexts.

To further examine the possible implications of our survey, let us put aside the limitations of our survey tentatively and assume that HBO research in Japan does involve the controversial use of donated cells. How should biobanks, research institutions, and scientists respond to this situation? One option is to maintain the status quo. In our results, only 15% of respondents supported broad consent, and even when including those who selected it depends, the overall support reached just 52%. However, this is not entirely unexpected. Numerous social surveys conducted in various countries have assessed public preferences for consent models in biobanks, revealing considerable variation in support for broad consent. Master et al. (2012) reported that support rates across different countries range approximately 35%–80%. Similarly, a recent survey conducted in Japan found that only 23.9% of respondents preferred broad consent (Oikawa et al., 2023). ¹¹ Despite its relatively low support in some populations, broad consent continues to be widely adopted and is often considered ethically justifiable. Therefore, it could be argued that opposition to HBO research does not introduce fundamentally new ethical concerns beyond those already associated with broad consent in biobanking.

However, while maintaining broad consent may be a practical approach, it is not necessarily the most ethical option when we know that controversial use is involved. In fact, some scholars have proposed alternative models for cell donation in HBO research. For instance, Boers and Bredenoord (2018) advocate for a “consent for governance” model in organoid research, where donors provide consent for the governance of research including privacy protection, benefit sharing, and ethical oversight rather than consenting to specific studies. Under this model, donated cells are only used in research that adheres to the agreed-upon governance conditions. However, our findings may raise concerns about the applicability of this model to HBO research. While consent for governance could mitigate concerns related to trust, benefit sharing, and potential misuse, it would not fully address the objections of individuals who oppose broad consent due to their desire for study-specific explanations, and their preference for restricting the purpose of the related HBO research. In other words, the consent for governance model does not sufficiently respect the autonomy of individual donors in detail (Lewis and Holm, 2022).

Therefore, if our results are considered sufficiently representative, they suggest that one of the most ethically appropriate method for HBO research in Japan appears to be project-specific consent at least for now, which remains the most obvious way to respect donors' moral views (Greely, 2020; Kataoka et al., 2024a). Of course, project-specific consent increases the burden on researchers in obtaining materials. So, if broad consent is to be maintained, it should, at minimum, be accompanied by a general explanation of the potential use of donated cells in HBO creation (Boers and Bredenoord, 2018). It should be noted here that our data focuses only on specific consent and broad consent, and thus does not address other alternatives that may be ethically desirable (see below). However, regardless of the chosen consent model, ensuring donor autonomy requires that individuals receive adequate explanations about HBO research. This need is particularly urgent given that our findings on public awareness indicate that HBOs are almost entirely unknown to the general public in Japan in the current situation. These claims of ours are broadly consistent with the consensus recently presented by interdisciplinary researchers regarding the provision of cells for brain organoid research: they recommend that, when acquiring new material for HBO research, sufficient explanation about HBOs be provided in the consent form, and that any consent preferences observed be tracked and respected (Cohn et al., 2025). We believe that it is difficult to adhere to these recommendations in broad consent.

We emphasize that the at-least-for-now clause is crucial in our recommendation of specific-consent above. Our results identified various potential reasons against broad consent under the possibility of HBO research. First, there would be individuals who refused broad consent or selected it depends due to vague negative feelings or ethical concerns about HBO research in itself. However, at least some of these public concerns could be scientifically unfounded, such as the misconception that an HBO might inherit the donor’s memories or personality (Evans, 2024; Kataoka et al., 2025a). Indeed, among researchers in the field, the prevailing view is that HBO research does not introduce novel ethical concerns that fundamentally differ from those associated with other forms of stem cell research, at least under current and near-future conditions (Hyun et al., 2022). Therefore, science communication can play a critical role in alleviating misconceptions and reducing unnecessary ethical concerns surrounding HBO research. Insights from recent studies examining the psychological factors underlying moral judgements about HBOs may be valuable in shaping public discourse (Evans, 2024; Ota et al., 2024; Villanueva et al., 2025). Moreover, the reasons not being directly related to HBO research are also important. To further enhance public understanding, it is important to address concerns about institutional trustworthiness, research objectives, and potential risks to donors. In addition, both types of reasons for opposition could be amplified by media reports which have often exaggerated ethical concerns surrounding HBO research (Hostiuc et al., 2022; Presley et al., 2022; Kataoka et al., 2023). Mitigating such sensationalism may help influence public attitudes toward HBO research in the future.

That said, it is also crucial to emphasize that even unfounded concerns must be respected in the context of cell donation. Donor autonomy implies that donated cells should not be used in research that donors perceive as morally unacceptable. Even if the relevant research is deemed ethically permissible by an ethics committee, for example, the moral values of donors must still be acknowledged and respected. This is particularly important given that public perceptions of HBOs are not entirely “materialistic” in nature unlike the views of most scientists and bioethicists (Evans, 2024).

Our claim that HBO research in Japan involves the controversial use of donated cells is, as we have suggested, only tentative due to several limitations. First, while our question emphasized the possibility of cells being used in HBO research, it could not clearly distinguish between those who oppose broad consent because of this very possibility and those who oppose it for more general reasons: among the 36% who oppose broad consent, both groups may be included. Future studies with designs that compare groups that have been exposed to the possibility of HBO research with those that have not will be needed to accurately identify the effects of the possibility of HBO research to the support for broad consent.

Second, since we explicitly stated that we would not actually ask for cell donations after the survey, the participants answered the questions in a completely hypothetical manner. This may have prevented us from eliciting participants' genuine attitudes, and they may behave differently if given the actual opportunity. ¹² To address this problem, future survey can incorporate the deception that cell donation opportunities will be provided.

Further, the representativeness of the participants poses certain challenges. The age distribution is skewed toward individuals in their 40s compared to the overall Japanese population, and educational background is biased toward university graduates. Conducting surveys that specifically target younger and older generations would provide a more precise understanding of the distribution of moral views. Additionally, our study was unable to comprehensively explore the depth of each participant’s attitude, highlighting the need for qualitative research to supplement our findings. For instance, as previously noted, some responses about supported research purposes were difficult to interpret logically, suggesting the necessity of a more detailed investigation into which research purposes are deemed acceptable.

Another set of limitations concerns the implications of our results for desirable methods. Mainly due to space limitations, our questionnaire did not examine all candidates for appropriate consent models in full depth. ¹³ Therefore, our claim that specific consent is desirable is tentative. For example, in our questionnaire, the explanation of specific consent had to be concise, not fully reflecting its several important elements (such as the need to re-obtain consent for future use). Although people’s attitude of emphasizing the need for detailed explanations has been consistently observed in various surveys, the exact percentages in our results may not be entirely representative.

Even those who did not agree to specific or broad consent might have supported other models. In fact, since our questions primarily focused on the initial consent process, we were unable to directly assess participants’ attitudes toward models emphasizing ongoing engagement in research, whose importance is now strongly emphasized for HBO research (Cohn et al., 2025). One of the most important models we could not handle was dynamic consent: donors can monitor the use of their samples and manage their consent preferences via digital devices (Teare et al., 2021). Although this model needs further consideration in terms of effectiveness and costs, it could help donors avoid involvement in research with controversial use of their donated material. Indeed, previous studies indicate that some individuals expect interim reports on HBO studies to which they have contributed, and prefer greater control over how their donated cells are utilized throughout the research process (Haselager et al., 2020; MacDuffie et al., 2023; Ravn et al., 2023). Future research will need to directly compare various consent methods in the context of HBO research.

The survey reported in this paper, alongside Sawai et al. (2025), represents one of the quantitative studies investigating public attitudes toward HBO research (Evans, 2024; Ota et al., 2024; Villanueva et al., 2025), and the first to specifically examine perspectives on cell donation and consent. Our findings indicate that when participants were informed about the potential creation of HBOs, a substantial proportion of them declined broad consent. Although there are some limitations, this empirical evidence may suggest that HBO research is likely to involve the controversial use of donated cells, at least within the current Japanese context. Therefore, broad consent may not be the most appropriate model for obtaining consent in this research. Preferable alternative would be project-specific consent, while broad consent with general information about HBOs or more dynamic models would be acceptable as well.

While ethical frameworks and regulatory guidelines for biomedical research should ideally aim for universality and international coherence, a culturally sensitive approach is particularly necessary for cell donation, where individual moral beliefs play a central role. Thus, rather than generalizing our findings on cell donation for HBOs beyond the Japanese context, it is crucial to conduct similar social surveys in diverse populations and integrate their results into region-specific consent practices.

Finally, HBO research is not the only domain in which the use of donated biological materials may be ethically contentious. For instance, it may be desirable to inform potential donors that their cells might be used in human-animal chimera research, an area that has raised ethical and societal concerns (Johnston et al., 2022). Public perceptions of what constitutes controversial uses of the donated material are shaped not only by the scientific nature of the research itself but also by citizens' moral frameworks, which in turn are influenced by their knowledge and cultural backgrounds. This underscores the importance of systematically assessing public attitudes through social surveys (Grady et al., 2015) and implementing science communication strategies that can clarify misconceptions and, if appropriate, help shape public understanding.