The in-vitro production of embryos (IVP) has been a revolution in the field of reproductive medicine, animal breeding and conservation biology. In vitro cultured embryos are less viable, have altered gene expression and have impaired implantation capacity when compared to embryos born in vivo, although they have become a common method [1,2]. This is mainly attributed to the increased and persistent generation of ROS in the presence of supraphysiological oxygen tension, exposure to ambient light and/or exposure to non-filtered visible range radiation of inverted microscopes, as well as the absence of antioxidant protection in chemically defined culture media.

The early cleavage embryo relies on antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) for redox homeostasis. These reserves are rapidly exhausted during the onset of embryonic genome activation, and the morula and blastocyst are particularly vulnerable to oxidative damage [2]. Excessive ROS leads to lipid peroxidation in membranes (MDA), base oxidation (8-OHdG), mitochondrial damage and ultimately to mitochondria-dependent apoptosis through the activation of caspase [3]. Microscopically, the changes are characterized by cytoplasmic vacuolation, blebbing of the trophectoderm, disorganisation of the inner cell mass (ICM), shrinkage of the blastocoel and pyknotic nuclei.

The classical antioxidant supplementation with ascorbate, alpha-tocopherol, N-acetyl-cysteine or beta-mercaptoethanol has shown inconsistent results, with poor half-life in culture media, and with variable cellular uptake and poor therapeutic indices [1,3]. The answer is nanotechnology: Nanoscale antioxidants have a high surface to volume ratio, tunable release characteristics, better cellular uptake and enzyme mimicking (nanozyme) properties that are not seen with classical molecular antioxidants.

Selenium nanoparticles (SeNPs) are especially attractive due to the fact that selenium is a structural component of GPx and thioredoxin reductase [4]. SeNPs can also liberate bioavailable Se which triggers de-novo synthesis and activity of these selenoenzymes, and the particulate form has been shown to be a direct scavenger of peroxyl and superoxide radicals, with higher antioxidant activity and therapeutic-toxic ratio than inorganic selenite and organic selenomethionine [5,6]. Despite their potential to be cytotoxic at high concentrations [7], when synthesized by green methods using plant polyphenols, flavonoids and terpenoids, silver nanoparticles (AgNPs) are known to have ROS-scavenging and Nrf2-activating properties at low concentrations [8,9]. These phytochemicals not only cap the emerging nanoparticles, but also possess intrinsic antioxidant activity. G-AgNPs are therefore not only colloidally stable, but also have a surface chemistry that is biologically compatible.

Despite independent study of each nanoparticle in reproductive biology, head-to-head comparisons—particularly with detailed histological analyses of cultured embryos—are sparse [10]. We postulated that co-supplementation of SeNPs and G-AgNPs in embryo culture media would be more effective in reducing oxidative stress than either nanoparticle individually, thereby increasing blastocyst formation and maintaining normal histoarchitecture. Specific objectives were to: (i) synthesize and characterize SeNPs and G-AgNPs; (ii) establish non-cytotoxic supplementation levels; (iii) measure developmental endpoints in four experimental groups; (iv) quantify oxidative-stress biomarkers in embryo lysates; and (v) quantify blastocyst histology, apoptotic indices, and immunohistochemical markers.

SeNPs exhibited a hydrodynamic diameter of 48 ± 8 nm, PDI of 0.21, zeta potential of -28.4 ± 2.1 mV, quasi-spherical TEM core size of 40-60 nm, and UV-Vis absorption maximum at 395 nm. G-AgNPs showed a hydrodynamic size of 22 ± 4 nm, zeta potential of -32.6 ± 2.4 mV, UV-Vis peak at 430 nm, and FTIR plant-capping bands at 3400 cm-1 (hydroxyl), 1640 cm-1 (carbonyl), and 1050 cm-1 (C-O-C) (Figure 2).

Developmental progression improved significantly with nanoparticle supplementation (Table 2, Figure 3). Blastocyst formation rates at 96 h were 38.5 ± 3.8% in Control, 55.8 ± 3.3% in SeNPs, 51.2 ± 3.5% in G-AgNPs, and 64.7 ± 2.9% in the combined SeNPs + G-AgNPs group (p < 0.001 vs Control). Hatched blastocyst rates doubled in the combined group (34.5 ± 3.1% vs. 16.9 ± 2.7%, p < 0.001), with 45.9 ± 3.2% achieving good-quality grade (Gardner >= 3BB).

Embryo lysate oxidative stress profiling (Table 3, Figure 4) demonstrated a 56% reduction in MDA in the combined group (2.14 ± 0.18 nmol/mg protein vs. 4.82 ± 0.31 in Control, p < 0.001). Concurrently, SOD (11.30 ± 0.61 U/mg), CAT (20.9 ± 1.3 U/mg), GPx (7.62 ± 0.38 nmol/min/mg), GSH (2.64 ± 0.16 µmol/mg), and GSH/GSSG ratio (8.4 ± 0.6) were maximally elevated in the combined group (p < 0.001).

Histological H&E analysis (Figure 5) revealed poorly compacted ICM, irregular blastocoel, cytoplasmic vacuolation, and pyknotic nuclei in controls, which normalized to a tight ICM and cohesive single-layered trophectoderm in the combined group. Composite injury score (Table 4) declined from 8.6 ± 1.1 in controls to 2.3 ± 0.5 in the combined group, correlating strongly and positively with MDA levels (r = 0.82 / Pearson r = 0.98, p < 0.001; Figure 6C). Apoptotic assessment (Table 5, Figure 6A-B) showed marked suppression of TUNEL-positive nuclei (3.9 ± 1.0 vs. 13.2 ± 1.8 in Control, p < 0.001) and cleaved caspase-3 IHC score (0.7 ± 0.25 vs. 3.2 ± 0.4, p < 0.001), alongside higher total blastocyst cell counts (86 ± 7 vs. 52 ± 6) and ICM/TE ratio (0.34 ± 0.03 vs. 0.27 ± 0.03).

Co-supplementation of SeNPs and G-AgNPs in embryo culture media restores redox homeostasis, enhances developmental competence, and preserves blastocyst histoarchitecture through distinct, synergistic antioxidant mechanisms (Figure 7) [1-3].

SeNPs act primarily via an enzymatic axis: intracellular release of bioavailable selenium augments GPx and thioredoxin reductase cofactor pools and elevates the GSH/GSSG ratio [4-6,17]. Phyto-capped G-AgNPs act at the cell-surface interface, transferring electrons directly to incoming ROS while priming cytoprotection via low-level Nrf2 activation (upregulating HO-1, NQO1, and SOD2) [7-9]. In co-delivery, this dual-compartment action produces broad, persistent cytoprotection.

Histological changes closely mirrored biochemical redox improvements. The strong positive correlation between MDA and composite injury scores (r = 0.82) establishes lipid peroxidation as a proximal driver of embryonic cytopathology [10]. Reduction in cytoplasmic vacuolation reflects mitochondrial membrane preservation. Enhanced PAS reactivity indicates preserved glycolytic metabolism, while a 26% increase in blastocyst cell count and optimal ICM/TE ratio (0.34) support enhanced implantation and post-transfer developmental potential [11,12].

Supplementation concentrations (5 µg/mL SeNPs and 2 µg/mL G-AgNPs) remained strictly within the non-cytotoxic therapeutic window established by MTT assays [15,19]. Findings align with single-nanoparticle IVP studies in bovine and porcine models [8-10,18], with the dual regimen demonstrating clear synergistic superiority. Limitations include the murine model scope and lack of post-transfer gestation tracking.

SeNPs and G-AgNPs, especially when combined, greatly reduce oxidative stress, enhance developmental competence, and maintain a normal histoarchitectural profile of murine blastocysts. These histological improvements, confirmed by apoptotic and immunohistochemical indices, confirm biochemical redox restoration and emphasize the complementary mechanisms of both nanoparticles, offering a valid foundation for dual-nanoparticle antioxidant strategies in assisted reproduction.