## 1 Introduction  
Ultrasound guiding has become the standard method for regionally delivering anaesthesia due to its ability to provide the real-time visualization of anatomical structures and the needle trajectory [1]. However, ultrasound has its limitations, particularly in accurately detecting the needle tip, especially in tissues with complex echogenicity, such as nerves [2]. This can make it challenging to achieve precise needle placement and avoid nerve damage during regional anaesthesia interventions. In order purportedly to achieve satisfactory anaesthesia delivery and prevent nerve damage, it is recommended that a local anaestheticis injected distantly from the epineurium [3]. However, this approach fails to account for the myriad of circumneural collagen fibres and fat cells [4] that reduce local anaesthetic delivery to the axons, according to Fick's law of diffusion [5]. Fat-filled circumneural fascial tissue is only visible via histology [4] or experimental 40 MHz microultrasound [6]. Accordingly, different authors [2,5,6] have recommended that the nerve is touched gently [6] so that the aperture of the block needle partially covers the epineurium and the injectate takes the path of least resistance away from the stiff epineurium to the elastic circumneural fat compartments [7]. Although high intraneural pressures [8] and ischemia are acknowledged causes of nerve damage, excessive forces may also cause harm. [PERSON] et al. demonstrated that forceful needle-nerve contact is associated with intraneural haematoma [9]. Furthermore, we recently postulated that forceful nerve damage activates the piezo ion channels, the release of intracellular calcium, and the inhibition of the natural repair mechanism of the nerves [10]. Therefore, understanding the mechanics of needle-tissue interaction is helpful in practical surgical simulation, pre-operation planning, delivering therapeutic drugs, and using robot-assisted mechanical methods [11]. The pressure that generates first in a syringe-tubing needle system at the beginning of fluid injection is called a bolus. This includes the pressure inside the needle, tubing and syringe at the start of the injection. Multiple variables influence the opening injection pressure, including the injection rate, needle size, tubing length and solution viscosity [12]. Meanwhile, the pressure applied when injecting a fluid continuously into tissues with a needle is known as the continuous or inline pressure. It is affected by tissue resistance, the needle type and the injection rate [13]. A puncture force is produced when the tissue surface is penetrated, and its magnitude and duration decrease with an increasing insertion velocity. Larger-diameter needles require higher forces due to increased friction and cutting forces. Increasing the insertion velocity can reduce the puncture force by increasing the energy release rate [14]. Therefore, when monitoring a needle inserted into soft tissues, the interaction forces increase at the tip of the needle and are the same along the shaft of the needle. The needle tip force is generated due to the cutting of tissues, and the force from the needle shaft results from friction between the tissue and needle [15]. [PERSON] et al. studied needle rotation upon insertion. They argue that it might decrease the frictional force, while improving accuracy. However, needle rotations have been found to increase tissue damage because of the drilling nature of insertion [11]. In contrast, highly forceful needle insertion can lead to tissue deformation, increased resistance and potential nerve injuries [16]. A study examined the use of needles by investigating the insertion of a thin bevel-tipped needle, but a thin bevel led to more force and cutting of the tissue [17]. A recent study used Fiber Bragg Gratings (FBGs) to monitor the real-time force during needle insertion. The FBGs were also incorporated into needles for epidural anaesthesia administration and loss-of-resistance detection. OCT imaging was used to visualise the tissue layers.