## 1 Introduction  
Hair loss treatment includes medication and management treatment, electromagnetic field treatment, and hair transplantation. Among them, hair transplantation is adopted when the hair does not increase through other treatments or if the hair is innately deficient [1]. Hair transplantation refers to a surgical technique in which the hair of the posterior scalp, which is not affected by hormones, is extracted, separated into hair follicle (HF) units, and transplanted into a hair-deficient area of the scalp [2; 3; 4]. This minimally-invasive surgery is mainly used to treat hair loss in men. According to the International Society of Hair Restoration Surgery, the global market for hair transplantation has increased by 76% from 2006 to 2014 [5]. The total market size for hair transplantation surgery has increased 28% since 2012, from $1.9 billion USD in 2012 to $2.5 billion USD in 2014. Approximately 397,048 hair transplantation surgeries were performed worldwide in 2014, with 112,409 in the US. Hair transplant surgery is classified into follicular unit transplantation (FUT) [3; 6; 7] and follicular unit extraction (FUE) [8; 9; 10; 11; 12], depending on how HFs are harvested. The FUT is known as the strip procedure, where a patient's hair is transplanted in naturally occurring groups of 1-3 hairs, called follicular units (FUs) [7]. In the strip harvesting for the FUT, a surgeon harvests a strip of skin from an area with good hair growth in the posterior scalp, as shown in Figure 1a. The excised strip has the size of approximately (1-1.5) \(\times\) (15-30) cm. While closing the resulting wound, nurses begin to dissect individual FU grafts, which are small, naturally formed groupings of HFs, from the strip [8]. They carefully remove excess fatty and fibrous tissue while avoiding damage to the follicular cells that will be transplanted. In the FUE, individual FUs, each containing 1-4 hair strands, are extracted under local anesthesia [10]. This micro removal typically uses tiny punches with a diameter between 0.6 and 1.0 mm, as shown in Figure 1b. The surgeon then uses very small micro-blades or fine needles to puncture the extraction sites to receive the grafts and place them in a predetermined density and pattern in the target area [11]. Although the FUE has restrictions on patient candidacy, is considered to be more time consuming, and is dependent on the skill of the surgeon, the FUE has many advantages, including a small donor wound, less pain, and a slender graft without extra surrounding tissue. For safe transplantation of HFs, a manual implanter is used in the both FUE and FUT [12]. An improved procedure for FUE with a motor-driven handpiece, the powered FUE (P-FUE) was introduced in the recent years [13; 14]. Since the P-FUE uses pneumatic pressure to extract the HFs, it eliminates the need for touching the follicles with forceps during harvesting. Recently, the ARTAS robotic system was developed to harvest FUs automatically using imaging technology and robotics [15; 16; 17; 18; 19]. The ARTAS system automated traditional HFs harvesting method by FUE using accuracy image-guided robotic techniques, as shown in Figure 1c. However, it was not widely used owing to the rather high transection rate of FU in actual use. As mentioned previously, various HF extraction methods have been proposed. However, the only tool developed for transplanting HF is the manual implanter [20; 21; 22]. Further, an equipment for HF transplantation is very difficult to develop because HF transplantation comprises more complex operations when compared to HF extraction. The most representative manual implanter is the KNU implanter [21; 23; 24]. There are three different sizes of the KNU implanter: S, M, and L. The S, M, and L types are used for one, two, and three hair units, respectively. Figure 1d shows the loading of the HFs. The procedure involves inserting the HF tissue inside the needle of the manual implanter using forceps, and applying the hair to the needle groove.