Abstract
BackgroundDuring traditional acupuncture therapy, soft tissues attach to and wind around the acupuncture needle. To study this phenomenon in a controlled and quantitative setting, we performed acupuncture needling in vitro.MethodsAcupuncture was simulated in vitro in three-dimensional, type I collagen gels prepared at 1.5 mg/ml, 2.0 mg/ml, and 2.5 mg/ml collagen, and either crosslinked with formalin or left untreated. Acupuncture needles were inserted into the gels and rotated via a computer-controlled motor at 0.3 rev/sec for up to 10 revolutions while capturing the evolution of birefringence under cross-polarization.ResultsSimulated acupuncture produced circumferential alignment of collagen fibers close to the needle that evolved into radial alignment as the distance from the needle increased, which generally matched observations from published tissue explant studies. All gels failed prior to 10 revolutions, and the location of failure was near the transition between circumferential and radial alignment. Crosslinked collagen failed at a significantly lower number of revolutions than untreated collagen, whereas collagen concentration had no effect on gel failure. The strength of the alignment field increased with increasing collagen concentration and decreased with crosslinking. Separate studies were performed in which the gel thickness and depth of needle insertion were varied. As gel thickness increased, gels failed at fewer needle revolutions. For the same depth of insertion, alignment was greater in thinner gels. Alignment increased as the depth of insertion increased.ConclusionThese results indicate that the mechanostructural properties of soft connective tissues may affect their response to acupuncture therapy. The in vitro model provides a platform to study mechanotransduction during acupuncture in a highly controlled and quantitative setting.
Highlights
During traditional acupuncture therapy, soft tissues attach to and wind around the acupuncture needle
Crosslinking the collagen significantly decreased the ability of the collagen gels to withstand needle rotation without tearing (*, 2-way ANOVA, P < 0.001), whereas changing the collagen concentration had no effect (P = 0.274)
We imaged a simple, in vitro, acellular collagen gel system using polarized light microscopy during acupuncture needle rotation and measured the degree of winding in terms of fiber alignment to identify relationships between collagen concentration, crosslinking, and winding, as well as the failure of the gels. We found that both collagen concentration and crosslinking influenced the response to controlled acupuncture needle rotation
Summary
Soft tissues attach to and wind around the acupuncture needle. Fine needles are inserted into the skin at specific points on the body and manipulated manually, typically by needle rotation. During this process, it is important to achieve the characteristic of "de qi", a physical sensation experienced by the patient, and a biomechanical phenomenon experienced by the acupuncture therapist that is known as needle grasp. Recent studies by Langevin et al suggest that needle grasp results when collagen fibers of the loose, subcutaneous connective tissue couple to and wind around the rotating needle [2,3,4]. Acupuncture needle manipulation in connective tissue explants induces cytoskeletal remodeling by fibroblasts [5,6], the predominant cell type in loose connective tissue, supporting the hypothesis that tissue deformation due to needle manipulation mechanically stimulates fibroblasts, resulting in mechanotransduction effects that may contribute to therapeutic benefits [2,3]
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