## 1 Introduction  
Erythropoietin (EPO) has both extrahematopoietic actions and hematopoietic functions. Among its extrahematopoietic activities, neuroprotection and neurodegeneration have been widely reported both in vitro and in vivo in animal models of central nervous system (CNS) injury [1, 2, 3]. Furthermore, EPO guarantees more readily available applications for patients with CNS injuries than other experimental therapeutics and has been used worldwide for several decades to treat hematologic diseases [4]. However, EPO shows a limited therapeutic window (6-8 h after insult) in small animal models [5, 6, 7, 8]; therefore, quick arrival of EPO at the injured CNS area is required. Additionally, considering the neuroprotective benefits of intravenous EPO injection over the first three days to patients who have suffered a stroke [9], initial EPO administration should certainly be provided as soon as possible in the clinic. However, such administration in real-world situations is very difficult due to various problems, including hospitals being located far away, traffic jams, or time delays in the hospitals. As an alternative, preemptive EPO administration before insult to prevent neuronal injury has been proposed in brain-ischemic rodent models [10], but this kind of intervention is not relevant to healthy human populations due to potential hematologiccomplications such as thrombosis, polycythemia vera, and teratogenicity [11]. Moreover, phylogenetic differences and the heterogeneity of extrahematopoietic/hematopoietic EPO receptors cause limited amounts of administered EPO to reach the injured CNS area and bind EPO receptors in situ [12]. Taking into consideration the aforementioned limitations, neuroprotective trials using EPO have remained a challenge in CNS injury.  
To overcome these obstacles, targeted EPO delivery has been proposed. Indirect methods, such as epicortical implantation and focused ultrasound with microbubbles [7; 13], have been studied since the late 1970s and remain at the experimental level. An alternative direct method suggested by [PERSON] is referred to as the \"magic bullet\" [14]; in this method, superparamagnetic/paramagnetic nanoparticles (MNPs) under magnetic navigation, which have emerged as promising tools in cancer models [15; 16; 17], can be used for targeted EPO delivery. The authors confirmed that fabricated alginate-encapsulated EPO-MNPs, namely, EPO-nanobots (ENBs), could achieve magnetic navigation [18]. However, alginate, which was used as the vehicle to encapsulate EPO and MNPs, is a biodegradable polymer that, similar to other polymers, requires several days to spontaneously break down and release EPO from the ENBs. Therefore, the ENBs remain unbroken even if they are quickly and selectively delivered to the injured CNS area. As a result, the ENBs cannot expose EPO receptors to EPO within the limited therapeutic time window of EPO. Notably, preemptive sonication can promote the breakdown of encapsulating biodegradable polymers and control the release of the contained materials [19]. However, cross-links in biodegradable polymers can reform upon re-exposure to physiologic fluids after sonication-induced breakdown [20; 21]. Therefore, it remains unclear whether the breakdown of ENBs is sufficient to ensure the binding of EPO to EPO receptors and the subsequent neuroprotective cascade. To evaluate the feasibility of ENBs as potential therapeutic tools in CNS injury, the authors conducted an in vitro study on the controllability of EPO release by preconditioning sonication and determined the neuroprotective bioequivalence of ENBs to EPO in an endoplasmic reticulum (ER) stress-induced neuronal cell injury model.