Although needle-based surgeries are considered as minimally invasive surgeries, the damage caused by the needle insertion in soft tissues, namely brain needs to be reduced. Any minor damage, swelling or bleeding in the brain tissue can lead to a long-lasting traumatic brain injury. Our approach to this challenge is to search for a proper solution in nature such as honeybees. In our previous studies, some new bioinspired needles (passive/active) mimicking honeybee stingers have been proposed and tested by conducting needle insertion tests in tissue gel phantoms. The main feature of the bioinspired needles is specially-design barbs on the needle structures. It was discovered that the insertion forces of the bioinspired needles are decreased by as much as 35%, which means that there is a decrease in tissue gel phantom damages. It was also observed that the needle path deflection in the tissue was greatly affected by the reduction in needle bending stiffness and the insertion force. The reduction in the bending stiffness would require lower forces of Nitinol actuators to navigate our smart/active needle inside the tissues. This work specifically aims to investigate the mechanics of the bioinspired needles in bovine brain tissues. The needle insertion tests in real tissues are designed and performed. The insertion mechanics of the bioinspired needles in bovine brain is studied and presented.

Needles are among the most common used instruments in surgery by medical professionals either for diagnosing the disease such as biopsy or for medical intervention such as drug delivery. Generally, needles are assumed to be minimally invasive, however it is desirable to decrease the insertion and pulling out force in order to prevent tissue damages. The hypothesis is that reducing the resistance forces caused by needle-tissue interaction leads to less tissue damage and less pain. Bioinspired needles mimicking insect stingers have been designed to reduce this resistance force and this design could provide to a more sophisticated steering of needle. Although our earlier study on honeybee-mimicking needle has shown the reduction of insertion force by having barbs on the needle body, the pull-out force is a big concern in particular during the extraction of the needle. A special mechanism to control the barbs at the end of the insertion procedure is designed. In this study, we investigated the use of SMA to control the barb functions so that it will reduce the pull-out force of the bioinspired needles. In this work, smart barb design is proposed. Circular barbs are divided to two symmetric parts connected by a ring around the central axis of the needle and the rings are connected to form the base part of its structure. Barbs are designed to have parallel faces with a desired angle through the insertion mechanism and are connected with a SMA wire at their bottom that is connected to the rear and front part of the needle. After insertion, actuating the SMA wires force the barbs to rotate around the rings due to the torque provided by wire shrinkage. As a result, barbs have now the same angle along the movement of needle for pulling out as they have for insertion mechanism.

Biopsy involves removing a piece of tissues for further medical examination. Brain biopsy is generally performed using different techniques, such as open biopsy, stereotactic core biopsy, and needle biopsy. Open biopsy is the most common and the most invasive form of the brain biopsy. During the procedure, a piece of the skull is removed and the brain is exposed. Stereotactic core and needle biopsies are minimally invasive. In these procedures, a hole is usually drilled into the skull and a needle is inserted through the hole to extract the tissue. Brain biopsy has its risks and complications due to the vulnerability of the brain tissue. Although using needle or stereotactic biopsies reduce the risks, brain biopsy may cause swelling or bleeding in the brain, and in some cases, can result in infection, stroke, seizure or even coma. A needle biopsy with conventional needles involves pulling or pushing the cutting stylet inside the needle hollow body (cannula). The manual pulling and pushing procedure induces lateral movement of the needle, which increases the damage in brain tissue. The goal here is to completely remove the needle harmful lateral movement. In this work, design of smart biopsy needles is proposed and demonstrated by incorporating nitinol wires and springs to control the lateral movement of the cutting stylet. The first design comprises of two parts. The first part of the needle is a 360° tissue cutting stylet, and the second part is the cannula. The cutting stylet can slide inside the cannula and a nitinol wire is embedded at the end of the stylet and the end of the cannula. As the electric current is applied on the nitinol wire, it shrinks and pulls the cutting stylet. The second design is almost similar to the first design, but it has a 180° tissue cutting stylet with a similar actuating mechanism. The last design uses a nitinol torsion spring that is attached to the cutting stylet. It cuts tissue samples by activating the nitinol spring to rotate the cutting stylet.

Surgical needles are commonly used by medical professionals to reach target locations inside of the body for disease diagnosis or other medical interventions — such as biopsy, brachytheraphy, thermal ablation, and drug delivery [1, 2]. The effectiveness of these procedures depends on the accuracy with which the needle tips reach the targets, such as tumors or certain organs/tissues. In procedures, such as deep brain stimulation and prostate brachytheraphy, it is impossible to reach the surgical sites via simple needle trajectory because of anatomical constraints. Although needles are considered minimally invasive devices, needle insertion still causes tissue damage of varying degrees so it is desirable to reach multiple targets, or multiple sites on a single target, to obtain multiple high-quality biopsy samples with each insertion [1, 2]. Recently there has been a substantial and growing interest in the medical community to develop innovative surgical needles for percutaneous interventional procedures. The answer to the challenge of developing advanced surgical needles could be found in nature. Insects such as honeybees (Fig. 1), mosquitos, and horse flies have sophisticated sting mechanics and stinger structures, which they use to steer their stingers to a specific target, such as a human, and to release their venom in a certain path in skin [3]. We are studying these mechanisms, evolved in nature over millions of years, as a basis to develop bioinspired needles. Surgical needles are typically consisted of a hollow cylindrical component (cannula) and an inner solid cylindrical component (stylet). Our hypothesis is that a surgical needle (stylet) that mimics insect stinger mechanics and structures can be easily controlled for sophisticated needle steering during surgery and can result in more effective and less invasive percutaneous procedures. The focus of this work is to mimic honeybee stinger such as shown in Fig. 1 to design innovative surgery needles. One of the critical issues in designing surgery needles is the insertion force required to penetrate and to navigate the needle inside the tissue [2]. Larger insertion forces increase tissue damages thus may result in a more painful procedure [2]. Another consideration is the needle trajectory path (needle tip deflection) and the difficulty to control the needle path. The needle deviates from the target and thus it is very difficult to navigate the needle in the tissue. There is a need to design advanced surgery needles that provide smaller insertion force. This can lead to a less invasive procedure, in other words, less tissue damage and pain [3]. The needle trajectory path of these new needle designs must be understood for the needle design optimization. As stated previously, it is hypothesized that a honeybee-inspired needle can be utilized to reduce the insertion force. In this work, the experimental work to understand the mechanics of bioinspired needles is presented. 3D printing of the needles and their insertion tests are performed to investigate the effect of the needle designs on the insertion force and the needle deflection (trajectory path) curves. Understanding these factors should shed some lights on some design parameters to develop innovative surgery needles.