Shape analysis of post-extraction needle holes in porcine skin

Hypodermic needle injections are widely used in clinical practice, yet the detailed morphology of skin punctures remains insufficiently characterized. This study aimed to investigate how needle size, insertion depth, sample storage time, and insertion angle influence the dimensions and shape of puncture wounds. Using porcine skin as a human tissue analog, over 200 needle insertions were conducted, and punctures were quantitatively analyzed through optical profilometry. Results demonstrated that puncture dimensions were consistently smaller than the needle's nominal size, indicating the significant influence of the skin's viscoelastic properties. Deeper insertions resulted in more extensive tissue disruption, while refrigerated tissues exhibited increased deformation compared to fresh ones. Additionally, rotating the needle around its axis altered the puncture geometry, reflecting the orientation of collagen fibers beneath the skin. The article also includes images of hypodermic needle skin holes at various stages of insertion, providing visual insight into puncture formation. These findings, together with the proposed theory on puncture formation in the skin caused by hypodermic needles, offer a basis for the development of more optimized injection techniques, with potential to support creation of reference wound-shape patterns.