Self-Disarming Suture Needle Biomedical Engineering Capstone Design 400, University of Wisconsin-Madison 14 December 2001 Team SWAGE: Briar Duffy, Angela Heppner, Elizabeth Nee, and Jeffrey Phillips Client: Dr. Victor Haughton, Department of Radiology, University of Wisconsin-Madison Hospital Advisor: Mitch Tyler, Department of Biomedical Engineering, University of Wisconsin-Madison2Abstract Accidental sticks from suture needles are an unpublicized but common problem for anyone involved in suturing. Designing a suture needle that has activated and deactivated states could significantly decrease transmission of diseases, such as Hepatitis C or HIV-1, as a result of accidental sticks with a contaminated needle. A safe suture needle does not exist in the market today. The JABE 200, a hollow sheath with two cutaways that expose a fluid filled balloon connected to a sharp metal tip, is only armed when the needle holder clamps down on the balloon, forcing the metal tip to protrude from the sheath. When the holder is unclamped, this “safer” suture needle would be unable to puncture the user’s skin because the sharp metal tip is retracted into the sheath. Future work includes making smaller scale prototypes and testing the mechanism on various types of tissues. Problem Statement In order to prevent accidental needle “sticks” from a suturing device to a surgeon or staff member, a disarming or retracting sterilized suture needle must be developed that allows a reversible action when passing into and through the underlying subcutaneous tissue, dermis, epidermis, or other organ tissues in the body. The device must encompass all features of sharpness, stiffness, maneuverability, and size/shape variance as a conventional needle with the added safety of needle retraction. The goal is to permanently eliminate the risk of needle puncture and infection to the operator during procedures. Background Information Given our lack of prior knowledge, the broad nature, and the time constraints of the project, the research was divided into four main components: the properties and composition of skin, suturing technique, the process of needle fabrication, and the demand for a safer suture. Further information on these topics is contained in Appendices 1-5. Properties and Composition of Skin The skin is mainly composed of the epidermis, the basement membrane and the dermis layers (Figure A1.1). The epidermis, or outermost layer, consists mostly of keratin and functions to prevent water loss from the body, and penetration by mechanical, chemical, or enzymatic3agents into the body. The next layer of skin, the basement membrane, is composed of a specialized form of collagen. Collagen is a triple helical polypeptide that forms three-dimensional waves in the skin, and especially in the dermis, or deepest layer of skin. Although skin samples vary in strength depending on location within the body and direction in which the sample was cut, the multidirectional bundles of collagen increase the shear strength of all samples of skin. With the exception of young developing tissues in the early stages of wound healing, the skin’s cellular components add little to its strength. Skin’s tensile strength is primarily due to collagen, and its strength increases with age (Table A1.1). The chemical properties, specifically the degree of cross-linkage between collagen fibers, contribute greatly to strength. A higher amount of cross-links leads to greater strength. These properties of skin are important with regards to suturing. The collagen fibers can be pushed aside by a small tapered needle, but needles larger than a few millimeters will rupture them during penetration. A needle with a cutting edge that is at a right angle to the plane of the skin’s surface is the most effective type of penetrating attack. Although it can be lifted into folds, the natural tension of skin limits the suturer’s ability to stretch skin to compensate for tissue loss, leading to potential problems in closing the wound. Suturing Technique Due to the wide variety of open wounds, a large assortment of suturing materials, as well as various needle sizes, shapes, and cutting profiles, are available on the market (Appendix 2). The best needles are sharp, rigid, corrosion resistant, able to easily penetrate tissue, and are able to maintain sterility. A cutting needle would typically be used on the skin, while a tapered point needle would be used on softer tissue. Despite the variety of supplies on the market, the general procedure for closing a wound is the same. After choosing the correct suture material and needle, the operator uses a needle holder to grasp the needle about ¼ to ½ of the needle length away from the swage, or eye of the needle. Forceps should always be used to grasp the needle to prevent accidental needle sticks. The resulting suture should allow touching wound edges that are slightly raised from the surface of the skin to allow for the natural flattening of a scar. For simple superficial wounds, a normal interrupted suture stitch is sufficient, but deeper wounds may require stitches with more support, such as mattress stitches. Deeper wounds have a tissue edge separation force than superficial wounds; the deeper penetration gathers more of the tissue and the “double stitch” of the mattress stitch provides more holding force. After passing through the4skin, the needle is grasped with a needle holder or with the fingers while the physician ties the knots to secure the wound (Appendix 2). Process of Needle Fabrication The need for sterility, corrosion resistance, and stiffness in a suture needle have traditionally led to the use of surgical grade stainless steel (Appendix 3) as the preferred material. Its properties allow it to be stiff and sharp in small diameters while still resisting bending. However, specialized equipment is necessary to precisely manipulate steel into the small sized needles. The size, shape, tip profile, and desired use of the needle can vary a great deal (Appendix 4). These differences determine the specific manufacturing steps that are necessary, but most needles require the following steps: extruding a wire of the desired diameter, cutting the wire to the appropriate lengths, grinding off the end to achieve the chosen tip profile, drilling and clamping a hollow cavity to hold the suture material, and forming the head according