A new innovative injector which can deliver medications to difficult locations of the body has been tested in animal models
Needles are the most important tool in medicine as they are indispensable in delivering countless medications inside our body. The syringes and hollow needles of today have been used since decades for extracting fluids and blood from our body and are important for many invasive delicate medical procedures like dialysis. Trying to target specific tissues by using a conventional needle of a syringe is a challenging task and is limited by skill and levels of precision of the medical personnel as this process is mostly guided by their own sense of pressure and touch since every patient’s tissue feels different. Though injuries or infections have rarely been reported but sometimes a flu shot can cause extreme pain and muscle damage. No new design has been incorporated into standard needles especially in regards to their accuracy.
Traditional needles are difficult and risky to administer medication to delicate regions of our body example the space at back of our eye. The suprachoroidal space (SCS) located between sclera and choroid in the back of the eye is a very difficult location to target using a conventional needle mainly because the needle has to be very precise and it must stop after it has transitioned through the sclera – whose thickness is less than 1 mm – to avoid any damage to retina. This region is considered important for delivery of many medications. Any lapse could cause a serious infection or even blindness. Other challenging areas are peritoneal space in abdomen and tissue between skin and muscles and epidural space around the spinal cord where epidural anesthesia is given during vaginal delivery.
A new pressure-sensitive needle
In a study published in Nature Biomedical Engineering researchers from Brigham and Women’s Hospital, USA have designed a novel intelligent and highly precise injection for targeting tissues – called the I2T2 (intelligent-injector for tissue-targeting). They aimed to improve tissue-targeting while keeping the design neat, simple and practical. The I2T2 device was created using standard hypodermic needle and other parts of commercially sold syringes and functionally I2T2 consists of slight modifications to the traditional syringe-needle system. It is a sliding needle which can penetrate outer layer of tissue, then it can automatically stop at the interface of two tissue layers and release the syringe content into target area as the user pushes the syringe plunger.
The I2T2 consists of a pushing plunger, a needle plunger, a mechanical stop, fluid and a movable needle. The needle is mounted on the needle-plunger which is a sliding support that allows precise movement along the axis of the syringe barrel. First, the needle tip is inserted into the tissue at shallow depth, but just sufficiently to avoid any flow of fluid through the needle. This stage is called ‘pre-insertion’. The syringe barrel prevents unwarranted penetration and needle plunger mechanical lock prevents undesired backward motion of the needle. During the second stage called ‘tissue penetration’, internal fluid gets pressurized by pushing the plunger. The driving forces which act on the needle (that enable forward motion of the needle) overcome the opposing forces (that oppose needle motion) and advance the needle deeper inside the tissue while the syringe barrel stays immobile. These forces play a critical role in controlling the needle’s motion and also its automatic stopping. When the needle tip enters the desired target space, fluid starts to exit so as to reduce the internal pressure which will then lower the driving force below than opposing force and this will subsequently stop the needle at the cavity interface. During this third stage called ‘targeted delivery’ the syringe fluid gets delivered into the cavity having lower resistance as the user pushes the plunger in a single continuous motion. The needle’s position is now affixed at the tissue-cavity interface. Since every biological tissue in our body has a different density, an integrated sensor in this intelligent injector senses loss-of-resistance as it moves through softer tissue or a cavity and then automatically stops its motion when the needle tip penetrates tissue offering lower resistance.
The I2T2 was tested in extracted tissue samples and three animal models including sheep to evaluate its delivery accuracy into suprachoroidal, epidural and peritoneal spaces. The injection automatically detects any changes in resistance so as to safely and accurately deliver medication in preclinical tests. The injector decides instantly allowing for improved tissue targeting and minimal overshoot into any unwanted location past the target tissue which could cause injury. The study is to be extended to human preclinical testing and then to trials in the next 2-3 years to evaluate injector’s utility and safety.
I2T2 preserves equivalent simplicity and cost-effectiveness of standard syringe-needles. The main advantage of I2T2 injector is that it displays higher level of precision and it does not rely on skills of the operating personnel as the injector can sense loss of resistance when it encounters a softer tissue or a cavity and then it stops advancing the needle and starts delivering its cargo of therapeutic agent into the target space. The syringe’s plunger device is a simple mechanical system and does not require additional electronics. The I2T2 injector technology is a new platform to achieve better tissue targeting in different and difficult locations in the body. The needle is simple and easy to manufacture with low costs. No additional technique or training was required to operate it. Such a versatile, sensitive, cost-effective and user-friendly technology could be promising for multiple clinical applications.
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Source(s)
Chitnis GD et al. 2019. A resistance-sensing mechanical injector for the precise delivery of liquids to target tissue. Nature Biomedical Engineering. https://doi.org/10.1038/s41551-019-0350-2
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