A mechanical model for adjustable passive stiffness in rabbit detrusor

Area of Science:

• Physiology
• Biomechanical Engineering
• Smooth Muscle Physiology

Background:

• Detrusor smooth muscle (DSM) exhibits strain softening, a decrease in stiffness after stretching, distinct from viscoelasticity.
• This phenomenon is linked to cross-link dynamics, being irreversible in passive muscle but reversible upon activation.

Purpose of the Study:

• To investigate the history-dependent adjustable passive stiffness of rabbit detrusor smooth muscle.
• To provide empirical data and propose a mechanical model explaining strain softening reversibility.

Main Methods:

• Experimental analysis of passive isometric force relaxation in rabbit DSM over extended periods.
• Application of quick-release protocols to assess force redevelopment and relaxation dynamics.
• Development of a mechanical model incorporating a novel cross-linking element into a hybrid Kelvin/Voigt viscoelastic framework.

Main Results:

• Passive isometric force relaxation in DSM includes a slow component lasting hours.
• Previously strain-softened DSM maintains less steady-state passive force.
• Quick-release protocols reveal a biphasic response: force redevelopment followed by relaxation.

Conclusions:

• Detrusor smooth muscle possesses adjustable passive stiffness influenced by strain and activation history.
• A proposed mechanical model, including a novel cross-linking element, can explain these observed phenomena.
• Understanding these properties is crucial for bladder function and dysfunction research.