Biodegradable silicon nanoneedles for ocular drug delivery

Abstract

Ocular drug delivery remains a grand challenge due to the complex structure of the eye. Here, we introduce a unique platform of ocular drug delivery through the integration of silicon nanoneedles with a tear-soluble contact lens. The silicon nanoneedles can penetrate into the cornea in a minimally invasive manner and then undergo gradual degradation over the course of months, enabling painless and long-term sustained delivery of ocular drugs. The tear-soluble contact lens can fit a variety of corneal sizes and then quickly dissolve in tear fluid within a minute, enabling an initial burst release of anti-inflammatory drugs. We demonstrated the utility of this platform in effectively treating a chronic ocular disease, such as corneal neovascularization, in a rabbit model without showing a notable side effect over current standard therapies. This platform could also be useful in treating other chronic ocular diseases.

Fig. 1.. Platform design and production.

Schematic illustrations (top) and optical images (bottom) for the basic procedures regarding the physical transfer of the as-prepared Si NNs from the Si wafer to a tear-soluble contact lens, including (A) the transfer of Si NNs to a PMMA film, (B) the deposition of a water-soluble film with anti-inflammatory drug, (C) the hot pressing of the resulting structure into a lens-shaped mold, and (D) the loading of therapeutic drugs to the surface of Si NNs.

Fig. 2.. Working principle and control strategy.

(A) Time-lapse schematic illustrations of the biphasic drug delivery process. (B) Time-lapse confocal fluorescence microscopy images for the biphasic release of IgG 488 (green) and 647 (red) from the tear-soluble contact lens and Si NNs, respectively. (C) Time-lapse photographs of the enucleated rabbit eye with the tear-soluble contact lens while being dissolved. (D) Time-lapse cross-sectional confocal fluorescence microscopy images of the enucleated rabbit eye with Si NNs embedded into the cornea.

Fig. 3.. Drug loading mechanism and controls.

(A) Representative confocal fluorescence microscopy image of the covalently loaded IgG 647 (red) and physically loaded IgG 488 (green) on the surface of Si NNs and in the tear-soluble contact lens, respectively. (B) Colored SEM image of a Si NN with the schematic illustration of the drug loading mechanisms. (C) Drug dosage loaded on Si NNs as a function of surface porosity with the fixed length of 60 μm. All data are represented as means ± SD, with n = 3 for each group. (D) Drug dosage loaded on Si NNs as a function of length with the fixed surface porosity of 30%. All data are represented as means ± SD, with n = 3 for each group. (E) Total drug amount when diluted in a 5% (v/v) solution of ethanol diluent (blue) and standard PBS diluent at the pH of 7.4 (red) as compared to a nondiluted solution (black). All data are represented as means ± SD, with n = 3 for each group. (F) Representative results of SDS-PAGE revealing the molecular weight of Bev diluted in ethanol diluent (four lanes on the right) as compared to that of a nondiluted solution (second lane from the left).

Fig. 4.. Dissolution kinetics and drug release kinetics.

(A) Measurement results of the bending stiffness (red lines) and dissolution time (blue lines) of the tear-soluble contact lens when immersed in 5 ml of the simulated tear fluid at 37°C as a function of the thickness ranging from 4 to 80 μm with molecular weights (MW) of 31,000 (triangular symbols) and 61,000 (circular symbols). All data are represented as means ± SD, with n = 5 for each group. (B) Dissolution of Si NNs in a 1.4% (w/v) agarose gel containing 1 ml of the simulated tear fluid at 37°C for 2 months with varied surface porosity ranging from 0 to 60% and with the presence of a 3-nm-thick pinhole-free Al₂O₃ layer. All data are represented as means ± SD, with n = 5 for each group. (C) Cumulative release of IgG 488 and 647 for 120 hours immersed in 1 ml of the simulated tear fluid at 37°C, each of which was physically and covalently loaded in the tear-soluble contact lens (blue line) and on the surface of Si NNs (i.e., porosity = 30%) with (red line) and without (purple line) the presence of the Al₂O₃ passivation layer. All data are represented as means ± SD, with n = 3 for each group. (D) Results of ELISA to quantify the bioactivity of Bev at 12 and 120 hours of release from Si NNs after storage in a refrigerator at 4°C for 1 day (red bars) and 3 days (blue bars), as compared to a new vial of fresh Bev solution as a control (black bars). All data are represented as means ± SD, with n = 3 for each group.

Fig. 5.. In vivo evaluation in a rabbit CNV model.

(A) Time-lapse color, red-free, segmented, and overlay images of CNV on the rabbit eye at day 0 (i.e., pre-therapy) and days 1, 3, 7, 14, and 28 (i.e., on-therapy) using 10-μm-long (left) and 60-μm-long (right) Si NNs. (B) Results of VD analysis to quantify the dynamic change of CNV from days 0 to 28. All data are represented as means ± SD, with n = 3 for each group. (C) Time-lapse cross-sectional OCT images of the rabbit eye under therapy using the 60-μm-long Si NNs at day 0 (i.e., right before and after the lens fitting) and days 1, 7, 14, and 28 (i.e., on-therapy).

Fig. 6.. Biocompatibility and biosafety.

(A) In vitro cell viability assay of HCEpiCs that were seeded with (red bars) and without (black bars) the 60-μm-long Si NNs for 3 days. All data are represented as means ± SD, with n = 5 for each group. (B) Cross-sectional histological view of the rabbit cornea that was stained with both hematoxylin and eosin at day 28 on-therapy using the 10-μm-long (top) and 60-μm-long (bottom) Si NNs with (left) and without (right) the presence of Bev. (C) Measurement results of the corneal epithelium thicknesses. All data are represented as means ± SD, with n = 3 for each group. (D) Representative IHC results of the rabbit limbus that was stained with a p63 cell marker at day 28 on-therapy using the 10-μm-long (top) and 60-μm-long (bottom) Si NNs with (left) and without (right) the presence of Bev. (E) Semiquantification of the p63 cell marker. (F) Quantification of endothelial density. All data are represented as means ± SD, with n = 3 for each group.