Current bio-imaging devices are able to display and reconstruct three-dimensional (3D) anatomical details, and diagnostics are becoming increasingly vital to the quality of patient treatment planning and clinical treatment [12]. It is important to know that radiographic images obtained by techniques, such as computed tomography (CT) and magnetic resonance imaging, can be converted to 3D files and produce a 3D solid model with a 3D printer [3]. Radiographic images and image processing tools are being used for the segmentation and reconstruction of tissue images in 3D to determine bone and muscle characteristics [4]. However, the results are not satisfactory when the focus is on the stress and strain distributions near boundaries [5]. Generally, the finite-element method is used to compensate the defects [6].

Today, radiographic images are being used to study biomechanical systems with several aims, namely, to describe and simulate the mechanical behavior of certain anatomical systems, to analyze pathological bone conditions, to study tissues structure and tissues properties, and to create a solid model using a 3D printer to support surgical planning and reduce experimental costs [7].

The rapid prototyping process known as 3D printing is expanding rapidly in clinical application; it provides novel possibilities and potentials for modeling, simulation and analysis of the human body [8]. There have already been attempts to use this novel technology in various fields of clinical applications. For example, in the fields of orthopedics and oral and maxillofacial surgery, it has been used in designing implant prosthetics and tissues. Moreover, it can be used in planning surgeries, to investigate possibilities, and improve accuracy before surgery [9]. Especially in the dental field, 3D printing is actively used to design implants and crowns. In addition, 3D printing can be used in a special way to facilitate facial reconstruction [10].

The use of 3D-printed solid models has many benefits in clinical fields, including determining whether a specific surgical procedure is too risky to perform for an individual patient, implant prosthetics designing, and medical research (too costly for in vivo experiments), thus improve surgical accuracy. It can also be useful for educational programs, such as medical student education and training to aid understanding of complex anatomical structures [1112].

Various 3D printing methods have been developed to build 3D structural models, such as stereolithography, fused-deposition modeling, selective-laser sintering, selective-laser melting, electronic-beam melting, and laminated-object manufacturing [13]. The 3D printer (ProJet 3510 HD; 3D Systems Inc., Rock Hill, SC, USA) is owned by the National Cancer Center using the stereolithography printing method. This method is the oldest and has a wide range of application. The whole process consists of the sequential printing of layers, which is similar to the functioning of the traditional inkjet printer. However, the printer differs from the conventional printer in that it produces 3D solid objects layer-by-layer [14]. The 3D printer first follows the instructions of computer-aided design (CAD) to build the foundation of an object, while the printer-head moves along the X, Y-planes and along the Z-plane to build the object's vertical layers [15]. It can build almost any shape defined in a CAD file and can use various types of materials and forms, such as plastics, rubber, gypsum, metals powders, liquids and solid which can be selected depending on the object's intended use [1617].

In this study, we used special image processing tools for image segmentation and 3D reconstruction to generate meshes necessary for production of solid objects with a 3D printer from CT images of the human tibia's trabecular and cortical bones (Figure 1).

These days, research regarding the use of image processing tools and segmentation techniques to analyze bone structures to produce a solid model with a 3D printer is rapidly becoming increasingly important. The aim of this work was to use a 3D solid model to predict the mechanical loads of human bone fracture risk for bone disease conditions using biomechanical engineering parameters. The 3D printing technique has potential for use in a variety of clinical applications, such as analyzing human anatomical structure, implant design, medical research, as well as surgical planning and training. However, 3D printing is not used often in clinical practice yet because of its limitations.

The limited choice of materials is an issue in the clinical field. It is imperfect represented by using polymers, rubber, gypsum, and metal for human body tissues. To build an object, two kinds of materials are required for both the support and part materials. A support material is needed to build the object which uses the part material. However, the materials are expensive to build objects for only research purposes so, user should be sure to check the file before produce a 3D solid model. The software is difficult to use by people who are not experts; it is difficult to learn, and it takes time to become an expert user. Furthermore, the process of creating a 3D file has not been fully automated before 3D printing, and they the software is still expensive. Even expensive software does not include a fully automated program from start to end to obtain a 3D file. The limitations are producing a small version of large structure or dividing the whole model into smaller parts which can be combined after printing. Normally, a 3D printer only prints models of certain sizes with certain levels of complexity, and it usually takes a long time to obtain a solid model, depending on its size. Commonly, 3D printers use polymer or a polymer mix with rubber for the material, and these are not strong enough to build joint implant prosthetics or dental implants. They could break or crack because they are too weak.

The potential and benefits of 3D printing have already has been demonstrated in several studies in various fields. Clinical research has conducted on the development of artificial organs, prosthetics, and tissues using a 3D printer. Models can be produced by 3D printing that are suitable to use for the education of medical student, surgical planning, and to help patients understand surgical procedures. The additional cost of 3D printing might be compensated by reducing operating time and achieving higher success rates for surgical procedure. However, it is still has not been approved to use 3D printers to produce clinical support devices, and applications of artificial medical tissues are limited and still in an early stage of research. Furthermore, 3D printers can only print model of certain sizes and certain levels of complexity. Also, the use of part and support materials depends on a model's size and the structures which lie within time and cost spent as 3D solid object. The clinical application of 3D printing is technically in an early stage. In the near future, it will have enormous potential for expanded utilization and the development of new applications in the fields of individual patient care as well as academic and research activities.

The study here is different in terms of aims and impacts on medical applications. However, it is common in the methodological approach that is use of 3D printer based on medical image processing techniques with the goal of improving clinical processes.