## 2 Discussion  
### Effectiveness of Magnetic Nanoparticles in Enhanced Delivery of HCECs  
The effectiveness of MNPs in enhancing the delivery of HCECs has been investigated through various experimental approaches, aiming to optimise targeted cell transplantation while preserving cell morphology and function (Table 2). An essential focus across these studies was to demonstrate that the use of MNPs enhances cell delivery efficiency beyond gravitational forces alone, while ensuring procedural safety. [PERSON] et al. explored the impact of 50 nm diameter MNPs on the delivery of cadaveric donor HCECs, revealing a significant 2.4-fold increase in cell density compared to conventional gravity-driven methods [80]. This enhancement was found to correlate logarithmically with the strength of the magnetic field and the initial concentration of nanoparticles within the cells, indicating a dose-dependent relationship for enhancing cell delivery efficiency with MNPs. Additionally, treatment with higher concentrations of nanoparticles also resulted in higher velocity of cells. Nevertheless, there was no notable change in the number of cells whose path was affected by the electromagnet at the volume of 10 uL nanoparticles or higher. This indicates a saturation effect where the magnetic guidance system's efficacy plateaued despite higher nanoparticle concentrations, suggesting an optimal concentration range for effective cell delivery under magnetic guidance. When conducting histological analysis, [PERSON] et al. discovered that, at the target location, the magnetic HCECs formed tight junctions, arranging themselves into a functional monolayer, thus replicating a significant function of endogenous HCECs in vivo [80]. Therefore, these data indicate the potential effectiveness of cultured HCECs in replacing deficient or repopulating damaged corneal endothelium. [PERSON] et al. observed similar histological findings when utilising MNPs to guide injected HCECs in rabbit models with corneal endothelial dysfunction [81]. They reported preserved corneal morphology, maintenance of cellular tight junction protein expression including ZO-1 and neural cell adhesion marker (NCAM), and functional integration into a monolayer in the innermost corneal layer. Therefore, following transplantation in vivo, donor cells exhibited markers indicative of the essential functions of HCECs. Regarding the restoration of corneal clarity and function, the research conducted by [PERSON] et al. evidenced improved post-operative corneal clarity and reduced thickness relative to control groups administered with balanced salt solution plus (BSS+) [81]. Optical coherence tomography (OCT) imaging confirmed thinner corneal profiles and highlighted distinct endothelial layers in eyes treated with magnetic HCECs, indicative of successful  
Figure 2: Magnetic nanoparticle-guided delivery of corneal endothelial cells for ocular regeneration. Depiction of the general method for targeted delivery of corneal endothelial cells using magnetic nanoparticles. Corneal endothelial cells are combined with magnetic nanoparticles and injected into the anterior chamber of the eye. An external magnet is utilised to localise the cell–nanoparticle complex precisely to the central area of damaged endothelial cells. This approach aims to enhance the efficiency and efficacy of cell therapy for corneal regeneration, offering precise targeting for the treatment of corneal dysfunction. transplantation and integration into the host tissue. All eight eyes treated with BSS+ had corneal thickness measurements that exceeded the upper limit of the pachymeter's range (>1500 \(\upmu\)m), whilst six of the twelve eyes injected with magnetic HCECs had measurable corneal thickness values that were below the pachymeter's range limit (<1500 \(\upmu\)m). Transplanted magnetic HCECs were successfully delivered to the posterior corneal surface, with no migration of cells to the iris or trabecular meshwork and no acute fluctuations in IOP.