## 1 Introduction  
Pectus excavatum is one of the most well-known chest wall deformities, in which the entire chest including the costal cartilage and sternum is depressed due to the overgrowth of the costal cartilage. The exact cause of PE has not been accurately identified, and it affects about one in every 300 children worldwide. For these patients, the PE operation is strongly recommended since the major organs in the chest such as the heart and lungs can be subjected to pressure, and problems such as the degradation of cardiopulmonary function, growth, and physical activities are likely to be caused by PE [1; 2]. Furthermore, the PE operation is also required to solve potential problems related to cosmetic and mental aspects, such as the avoidance of interpersonal relationships. The PE operations include the Ravitch procedure, sternal turnover operation, Silastic molding method, and Nuss procedure. The Ravitch procedure and the sternal turnover operation, which are called open surgery, require a resection of all deformed costal cartilage. They can correct the chest wall effectively, but it has disadvantages such as a large operation range, a long operating time, and a less cosmetic effect. The Silastic molding method is a minimally invasive surgery that is used for cosmetic effect, but this method cannot solve the problems of physical function. [3; 4]. On the other hand, the Nuss procedure, one of the minimally invasive surgeries, was introduced in 1998 by [PERSON], a thoracic surgeon. In this method, a metal bar called a Nuss bar is inserted through the ribs and placed below the sternum to lift the depressed chest. It is widely popular worldwide owing to a small surgical wound, a low risk of infection, and a better cosmetic advantage [5; 6]. Hence, the Nuss procedure was selected in the present study. There are several types of PE, for example, symmetrical, asymmetrical, eccentric, and unbalanced types. Accordingly, the proper type of the Nuss bar should be fabricated prior to operation in order to correct the PE accurately and effectively [7]. However, most Nuss bars are manufactured in a straight shape and provided as such to surgeons. For this reason, the surgeons must manually bend the Nuss bar based on their intuition. However, it is extremely difficult to make a patient-specific shape of the Nuss bar during operation. In addition, the Nuss bar can be damaged due to the repeated bending process, and the adjacent tissues can be damaged if the Nuss bar has a sharp angle. In order to overcome the above obstacle, [PERSON] et al. [8] adopted the three-dimensional (3D) printing method to fabricate a patient-specific Nuss bar. In their research, the polylactic acid-based 3D printed Nuss bar was developed and implemented into 10 PE patients. They called this novel operation the 3 DPMAN (3D Printed Model-Assisted Nuss) procedure, and the initial results of the 3 DPMAN procedure was feasible, easy, convenient, and satisfactory. There are many advantages in fabricating the Nuss bar using polymer 3D printing such as the low fabrication cost, the short fabrication time, and others. However, the polymer Nuss bar has severe shortcomings. The Nuss bars are usually made of titanium alloys or stainless steel since they can maintain high stiffness and strength until they are removed from the body. Accordingly, the chest wall, including the Nuss bar, may be free from sudden failure or fracture due to unexpected excessive external forces. On the other hand, the polymer Nuss bars, such as polylactic acids, have low strength and stiffness compared to titanium alloys or stainless steel. Therefore, the mechanical evaluation of material/structural safety should be sufficiently carried out prior to clinical applications. If the Nuss bar is made using metal 3D printing, the procedure is costly and time-consuming. In other words, the metal powder (titanium alloy powder) is quite expensive, and the 3D printing takes a great amount of time.