Wess O. et al., 2025: The interaction of shock waves with biological tissue - momentum transfer, the key for tissue stimulation and fragmentation.
Othmar Wess 1, Juergen Mayer
1Department Applied Research, Storz Medical AG, Taegerwilen, Thurgau, Switzerland.
Abstract
Background: Shock waves in medicine have gained enormous importance and have spread since 1980, and the first kidney stone was successfully fragmented in a patient in Munich. Meanwhile, the spectrum of medical applications of shock waves ranges from powerful fragmentation of kidney stones to diverse indications such as wound healing, chronic pelvic pain, spasticity, erectile dysfunction, and others, to neuro-stimulation in the context of Alzheimer's disease. A comprehensive working mechanism for this diverse field of medical indications is still missing.
Objective: Investigation of the physical basis of the working mechanism of shock waves in medical applications.
Methods: We developed a model based on the mechanical forces generated by the momentum transfer at the acoustic interfaces of different layers of biological tissue. The generated forces are strong enough to crash brittle material and provide an adequate mechanical stimulus to activate mechano-transduction and mechano-sensory-transduction with nerve stimulation, thereby affecting the neural memory function of the central nervous system.
Results: The key to generating appropriate forces in the millisecond range is the mechanism of momentum transfer at the interfaces between tissue layers with different acoustic impedances. According to Newton's laws of motion, a change in momentum (momentum transfer) generates force F = d P /d t . The inherent shear forces can stretch biological membranes to release biomolecules such as vascular endothelial growth factor and nitric oxide. A most favorable feature of this mechanism is the selective effect on soft tissue interfaces and small tissue inhomogeneities to generate small forces in the range of few (≤10) Newton to stimulate tissue and nerve cells, while the same shock wave can generate forces ≥200 Newton and more on hard tissue interfaces such as bones or stones.
Conclusion: The mechanism of momentum transfer is the basis for mechano-transduction and mechano-sensory transduction. It offers the opportunity to stimulate peripheral nerves and modify the motor reflex patterns of "pathologic" reflexes by hyper stimulation. The new technique of transcranial pulse stimulation may be based on direct stimulation and reactivation of neurons in the brain. Momentum transfer is the basic physical mechanism and the initiator for successive biological processes in medical shock wave therapy.
Int J Surg. 2025 Apr 1;111(4):2810-2818. doi: 10.1097/JS9.0000000000002261. PMID: 40009555; PMCID: PMC12175785
Comments 1
Objective:
The article discusses the interactions of shock waves with biological tissues, focusing on their ability to transfer momentum, which is crucial for both tissue stimulation and stone fragmentation. Shock waves, first used in the 1980s for breaking kidney stones, have evolved to stimulate various tissues, including skin, muscles, and bones, without causing significant damage. This adaptability has led to diverse applications in fields such as urology, orthopaedics, cardiology, neurology, and pain management.
Methods:
The study emphasizes that the effectiveness of shock waves depends not just on their energy levels but also on tissue types. A key focus is the role of momentum transfer—a feature rarely addressed in literature—highlighting how shock waves induce mechanical forces that can catalyze biological responses. The authors propose that appropriate force generation occurs through the interaction of shock waves with different tissues, based on their physical characteristics, such as density and acoustic impedance.
Results:
The article details how shock waves generate mechanical forces by reflecting off tissue interfaces, which are translated into therapeutic effects. It outlines that mechano-transduction—a process where mechanical forces affect cell membranes and trigger biological responses—plays a fundamental role in the healing mechanisms stimulated by shock waves. These forces lead to the release of various biochemical substances that promote healing, vasodilation, and metabolic activity.
Discussion
The article discusses the following issues inetensively:
1. Physical Properties of Shock Waves:
Shock waves are characterized by parameters such as high peak pressure, steep pressure rise, and momentum. The theory suggests that effective shock wave applications rely on understanding momentum rather than just energy levels.
2. Tissue Interaction:
When shock waves encounter different tissues, they undergo reflection and transmission, which produces mechanical forces that can stimulate biological responses. Momentum transfer at tissue interfaces is essential for generating these forces. Here, it is evident, that other theories for stone disintegration like quasi-static squeezing (Eisenmenger), dynamic squeezing (Cleveland) or even cavitation cannot explain the phenomen of shock-wave induced mechano-transduction.
3. Mechanotransduction:
The article emphasizes mechanotransduction as a primary mechanism through which shock waves affect living tissues. Mechanical forces exerted by shock waves facilitate the opening of ion channels in cell membranes, leading to the release of biochemical substances that promote healing processes.
4. Therapeutic Applications:
The findings underline the dual capability of shock waves to effectively fragment hard tissues while gently stimulating soft tissues, which supports their wide-ranging medical applications.
Conclusion
The study presents new insights into the physical mechanisms of shock wave therapy, aiming to enhance the understanding of their therapeutic applications and efficiency in medical treatments.
Jens Rassweiler