Quantifying Local Strain Field and Deformation in Active Contraction of Bladder Using a Pretrained Transformer Model:...

Area of Science:

• Biomechanics
• Biomedical Engineering
• Computational Biology

Background:

• Accurate quantification of local strain fields during bladder contraction is crucial for understanding micturition biomechanics in health and disease.
• Conventional digital image correlation (DIC) requires artificial speckling, potentially altering tissue properties.

Purpose of the Study:

• To introduce and validate a speckle-free framework for quantifying local strain fields in bladder tissue.
• To enable more physiologically relevant biomechanical measurements without artificial markers.

Main Methods:

• Utilized a state-of-the-art, zero-shot transformer model (CoTracker3) for strain field quantification.
• Employed a custom-designed, portable isotonic biaxial apparatus integrated with multiphoton microscopy (MPM).
• Tracked natural bladder lumen textures without artificial speckling.

Main Results:

• Achieved high accuracy with a tracking Root Mean Square Error (RMSE) of less than 1.5 pixels and low strain errors.
• Successfully captured heterogeneous deformation patterns, including complex folding and buckling, which are often missed by conventional DIC.
• Demonstrated statistically significant anisotropy in rat bladder contractions (p<0.01), with greater longitudinal than circumferential contraction.
• Confirmed heterogeneous morphological changes, such as fold formation, using MPM.

Conclusions:

• The speckle-free framework using CoTracker3 provides accurate and physiologically relevant measurements of bladder tissue biomechanics.
• This non-invasive approach eliminates speckle-induced artifacts, offering broader applicability for biological and engineered material testing.
• The findings highlight significant anisotropic behavior in bladder contraction, advancing our understanding of micturition.