Evaluation Of Stryphnodendron Adstringens Extract As A Chemical Corneal Crosslinking Agent: Biomechanical And Thermal Analyses In Ex Vivo Rabbit Corneas.

To evaluate whether a butanolic extract of Stryphnodendron adstringens (barbatimão), rich in condensed tannins/proanthocyanidins, induces ex vivo corneal stromal changes consistent with collagen crosslinking without UV-A irradiation. We assessed dose–time effects in rabbit corneal buttons using dynamic mechanical analysis (storage modulus E′, loss modulus E″, and tan δ) and corroborated collagen stabilization by differential scanning calorimetry (denaturation temperature, Td) in paired control–treated hemicorneas.

Laboratory of Biochemistry, Translational Medicine and Bioengineering – UNIFESP

Central corneal buttons from New Zealand White rabbit eyes were de-epithelialized and treated ex vivo with a butanolic extract of Stryphnodendron adstringens at 0.5, 1.25, or 2.0 mg/mL for 30–120 minutes (n = 3 per condition; 1.25 mg/mL/75 min in duplicate). Viscoelastic properties were assessed by dynamic mechanical analysis under oscillatory unconfined compression (1 Hz), obtaining storage modulus (E′), loss modulus (E″), and damping factor (tan δ) from the linear viscoelastic region. Collagen thermal stability was evaluated by differential scanning calorimetry using paired control–treated hemicorneas, and the denaturation temperature (Td) was reported. The DSC samples were assessed at 30-60 minutes and 1.25-2 mg/ml.

DMA showed significant differences among groups for E′, E″, and tan δ (all p ≤ 0.0006), with significant effects of concentration, exposure time, and their interaction. Higher extract concentrations were associated with increased E′ and reduced tan δ, indicating stromal stiffening and reduced viscoelastic damping. The strongest and most consistent mechanical response was observed at 1.25–2.0 mg/mL, particularly at 2.0 mg/mL (E′ ~32–33 kPa at 30–120 min vs 7.1 kPa at 0.5 mg/mL/30 min) .DSC demonstrated significant increases in denaturation temperature at 60 minutes for both 1.25 mg/mL (ΔTd = 1.90 °C, p = 0.041) and 2.0 mg/mL (ΔTd = 3.53 °C, p = 0.017), with a pooled 60-min effect of +2.71 °C (p = 0.004).

A butanolic extract of Stryphnodendron adstringens induced dose- and time-dependent biomechanical stiffening and collagen thermal stabilization in ex vivo rabbit corneas, consistent with a CXL-like stromal effect without UV-A irradiation. The most consistent responses were observed at 1.25–2.0 mg/mL, particularly at 2.0 mg/mL within 60–120 minutes of exposure. These findings support further investigation of barbatimão as a potential chemical approach for corneal stromal reinforcement in ophthalmology.