Interdisciplinary research that integrates medical science, biotechnology, materials science, mechanical engineering, and manufacturing has seen rapid progress in recent years. Not only fundamental research into biological functions but also the development of clinical approaches to treating patients are being actively carried out by experts in different fields. For example, artificial materials, such as those used in orthopedic surgery and dental implants, are being used more widely in medical treatments. In the area of minimally invasive surgery using X-rays, CT, and MRI, medical devices possessing radiolucent and nonmagnetic properties are playing a major role. Medical auxiliary equipment, such as wheelchairs, prosthetic feet, and other objects used to supplement medical treatment, is also critical. To assure that such advances continue into the future, material development and manufacturing processes should eventually satisfy the requirements of medical and biological applications, which are being debated by experts in different fields.

The applicable materials should have excellent specific strength and rigidity, high biocompatibility, and good formability. The various needs for material characteristics and functions make interdisciplinary research essential. Mechanical engineering and manufacturing technologies should be further developed to solve problems involved in the establishment of basic principles by integrating the knowledge of materials science, medical science, biology, chemistry, and other fields.

This special issue addresses the latest research advances into the biomedical applications of different manufacturing technologies. This covers a wide area, including biotechnologies, biomanufacturing, biodevices, and biomedical technologies. We hope that learning more about these advances will enable the readers to share in the authors’ experience and knowledge of technologies and development.

All papers were refereed through careful peer reviews. We would like express our sincere appreciation to the authors for their submissions and to the reviewers for their invaluable efforts, which have ensured the success of this special issue.

Precision machining of sintered zirconia ceramics is expected for various applications such as dental prostheses or artificial femoral heads. However, machining of zirconia is a major challenge because of its high hardness. We have found that the bending strength and fracture toughness of this material decrease with an increase in temperature. To use this characteristic, we propose a high-speed milling process with a cutting speed of more than 500 m/min because high-cutting speed can generate a large amount of heat during cutting. According to the results of trials, precision machining of the surface was possible with a cutting speed of 670 m/min. Moreover, the amount of flank wear was decreased by the high-speed milling. These results confirmed the possibility of precision cutting of sintered zirconia ceramics.

In recent years, one common cure for losses in joint function caused by osteoarthritis or rheumatoid arthritis is replacement with an artificial joint. For this reason, it is necessary to add osteoconductivity to artificial joint component surfaces that make contact with bone, thereby reducing the period of time necessary to fixate the bone tissue and the artificial joint component. With the intent of efficiently machining the joint shape by electrical discharge machining (EDM) and simultaneously formation of a surface with osteoconductivity, this study discusses the possibility of adding osteoconductivity to a titanium EDMed surface.

Recently, a lot of attention has been paid to a single-cell analysis using microfluidic chips, since each cell is known to have several different characteristics. The microfluidic chip manipulates cells and performs high-speed and high-resolution analysis. In the meanwhile, femtosecond (fs) laser has become a versatile tool for the fabrication of microfluidic chips because the laser can modify internal volume solely at the focal area, resulting in three-dimensional (3D) microfabrication of glass materials. However, little research on surface microfabrication of materials using an fs laser has been conducted. Therefore, in this study, we demonstrate the surface microfabrication of a conventional glass slide using fs laser direct-writing for microfluidic applications. The fs laser modification, with successive wet etching using a diluted hydrofluoric (HF) acid solution, followed by annealing, results in rapid prototyping of microfluidics on a conventional glass slide for fluorescent microscopic cell analysis. Fundamental characteristics of the laser-irradiated regions in each experimental procedure were investigated. In addition, we developed a novel technique combining the fs laser direct-writing and the HF etching for high-speed and high-resolution microfabrication of the glass. After establishing the fs laser surface microfabrication technique, a 3D microfluidic chip was made by bonding the fabricated glass microfluidic chip with a polydimethylsiloxane (PDMS) polymer substrate for clear fluorescent microscopic observation in the microfluidics.

This study aims to verify whether the three-dimensional internal information acquisition system we have developed can be applied successfully to the microstructures of consecutively precision-machined biological samples, and to those of metallic samples. Therefore, this study mainly deals with biological hard tissue samples like bones. In this paper, we first studied the precision-machining characteristics of bones. From this, we determined that, to obtain machined surfaces sufficient for internal observations, we need to determine the maximum uncut chip thickness and the cutting speeds, taking the bone’s anisotropy into consideration. Next, we acquired three-dimensional internal information on consecutively precision-machined bone samples using the three-dimensional internal acquisition system we developed. Subsequently, we visualized the internal structures of these machined samples. Our tiling observations acquired an 18×9×3 mm segment as a 6.2×6.2×10μm resolution image. We obtained a three-dimensionally reconstructed image of complex blood vessel networks inside the bone by making the acquired images binary.

Most spine implant devices are fabricated outside Japan, and therefore do not always fit the bodies of Japanese people. This causes a quality-of-life (QOL) problem in which patients feel the embedded implant devices on their back. The aim of this study was to develop more compact and lower-profile spine implant devices. Three types of devices with different heights and different screw threads were created, and the removal torque (fitting force) of the devices was measured after a static load test and cyclic load test. In addition, the screw thread surface was observed in detail after the tests. The results indicated that the mechanism of the reduction in the fitting force was related to partial contact due to abrasion or plastic deformation of the screw thread surface and decrease in the contact area between the screw threads caused by the increased diameter of the upper opening of the implant device after tightening. Therefore, we concluded that lowering the height of the implant device, securing the number of the screw threads, and securing the contact area of the threads are important in developing a low-profile spine implant.

Apatite formation due to mineralization has important implications in the biological function of hard tissues. The mechanical properties of mineralized tissues such as teeth enamel, dentin, and bone depend strongly on the apatite structure in the tissue. The control of both volume fraction and apatite texture is important in determining the structural characteristics. It is also important to create an apatite layer on the surface of implanted materials to improve biocompatibility between the surface and the tissues. In this study, apatite deposition and formation on Ti plates and bone surfaces were studied by means of electric stimulation conducted in apatite-neutralizing solution. Apatite particles were deposited not only on the Ti plate surfaces but also on the bone, combined with Ti wires wrapped under DC loading. Apatite crystal growth was observed on the samples during electric stimulation.

The purpose of this study is to evaluate interfacial strength of plasma-sprayed HAp coating by using more general adhesives. Plasma-sprayed HAp coating has been applied to bond bones with the surfaces of artificial hip joints. However, HAp coating is subjected to crack or delamination by mechanical loading. Conventional standard codes for measurement of interfacial strength of calcium phosphate coating determine the use of a specific adhesive irrationally. Our group previously proposed pre-immersion treatment process in preparation of interfacial testing specimens in order to obtain valid value of interfacial strength. However, the type of the adhesive was for medical purpose and not general one. To widen applicability of the proposed method, a selection policy of adhesive is indispensable. Metal Lock Y610 (ML adhesive) was selected as one of general adhesives. Interfacial strength tests by using ML adhesive were conducted. The results of interfacial strength test were compatible with the one reported by previous study, which suggest that the selection of general type of adhesive was successful. Raman spectroscopy analyses were also conducted to confirm a suppressed infiltration of ML adhesives.

Fine particle peening (FPP) using hydroxyapatite (HAp) shot particles can form a HAp layer on room-temperature substrates by the transfer and microstructural modification of the shot particles. In this study, FPP with HAp shot particles was applied to form a HAp surface layer and improve the fatigue properties of Ti–6Al–4V extra-low interstitial (ELI) for use in bio-implants. The surface microstructures of the FPP-treated specimens were characterized by micro-Vickers hardness testing, scanning electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. FPP with HAp shot particles successfully formed a HAp layer on the surface of Ti–6Al–4V ELI in a relatively short period by shot particle transfer at room temperature; however, the thickness and elemental composition of the HAp layer were independent of the FPP treatment time. The original HAp crystal structure remained in the surface-modified layer formed on Ti–6Al–4V ELI after FPP. Furthermore, FPP increased the surface hardness and generated compressive residual stresses at the treated surface of Ti–6Al–4V ELI. Four-point bending fatigue tests were performed at stress ratios of 0.1 and 0.5 to examine the effect of FPP with HAp shot particles on the fatigue properties of Ti–6Al–4V ELI. The fatigue life of the FPP-treated specimen was longer than that of the un-peened specimen because of the formation of a work-hardened layer with compressive residual stress. However, no clear improvement in the fatigue limit of Ti–6Al–4V ELI occurred after FPP with HAp shot particles because of subsurface failures from characteristic facets.

A cell culture module capable of cooling stimulus to collect cells efficiently on a metal culture substrate was developed. We evaluated the cell collection ratio and morphology of the collected cells. Following a cooling stimulus (0°C) for 20 min, the number of collected cells was increased by 50% compared to that collected after trypsin treatment without pipetting from the metal culture substrate. Following the cooling stimulus, cells were observed by fluorescence microscopy and scanning electron microscopy; the cell filopodia were shrunken compared to non-cooling-stimulated cells. Furthermore, the combination of collagenase and cooling stimulation resulted in the collection of a comparable number of cells as that obtained using only trypsin. Thus, cell proliferation was improved compared to that following trypsin treatment. Therefore, this method can be applied for culturing cells that are susceptible to trypsin damage.

In this study, the change in the tensile fracture behavior of HAp/PLA composites, interface-controlled using pectin and chitosan, was evaluated for the case of the early-stage hydrolysis. Here, the reaction between the HAp particles and modification polymers was controlled using o-nitrobenzyl alcohol. Tensile tests after immersion in a pseudo biological environment indicated that the interface-control method employed in this study improved the fracture properties of HAp/PLA composites significantly, inducing the large plastic deformation. In addition, the effects of early-stage hydrolysis on fracture behavior and mechanism are discussed from the viewpoint of interfacial structures for the interface-controlled HAp/PLA composites. Observations of fracture morphologies and surfaces suggest that the interface-control employed in this study successfully improved interfacial bonding, enabling the effective usage of the deformability of the PLA matrix. The interface-control method employed in this study also maximized the fracture strain through the combination of improved interfacial bonding and an increase in the ductility of the PLA matrix after a 2-week immersion. Test results also suggest that the cancelation induced by the degradation of chitosan accelerated the degradation of the PLA matrix after a longer immersion.

A bio-chip using cultured cells is developed for an application to drug screening. Carbon nanotubes (CNTs) are a candidate for this electrode material. A transfer-prints is expected to be a CNT-patterning technique applicable to soft material. This present paper is intended to show some basic properties about the transfer-print of CNTs, and also to demonstrate the possibility of the CNTs as a cell scaffold. The present study prepared several types of surface-modified Si substrate with different wettability to investigate the effects of wettability on the transferring ratio of CNTs. Some Si substrates are terminated by OH or H groups, while other substrates are coated with hydrophobic or hydrophilic self-assembled monolayers. The stamps for transfer-print, which have circular dots (50-μm diameter) or a straight ridge (50-μm width) array, are fabricated using poly-dimethyl-siloxane (PDMS). The surfaces of PDMS stamps are inked by single-walled CNTs by a pre-transferring or casting process. The transfer-prints to surface-modified Si surfaces allow the CNTs to be formed in lines of several tens of micrometers, while the coverage of transfer-printed CNTs is also dominated by surface wettability. The coverage of transfer-printed CNTs increases with the water contact angle of the Si surface. It is reasonable that the transfer-print of CNTs is performed by hydrophobic interactions. Meanwhile, two kinds of polymer (polystyrene (PS) and polyethylene terephthalate (PET)) sheets are also utilized as a substrate. The transfer-prints with heating around the softening point of the polymer allow CNTs to be accurately patterned into an array of 50-μm dots. The coverage of CNTs is 94% on the PET substrate. The PS sheet with patterned CNTs is applied to a cell scaffold. PC12 cells are cultured on the PS sheets so that the cells are selectively adhered to the transfer-printed CNTs. The adhered cells are extended with some pseudopods. It is demonstrated that the transfer-printed CNTs are expected to be electrodes of the cell scaffold.

The machining of deformable parts is both an old and new problem. Because the standard procedures for machining operations implicitly assume a rigid workpiece and ideal chip removal, workpiece deformation has been considered a disturbance in machining operations. Due to the increasing need for lightweight and compact products, deformable parts, such as thin-structured parts and soft materials, are now widely utilized. For the effective and accurate production of deformable parts, die-less direct machining of deformable parts is a promising approach because of its applicability to various materials and shapes. This technical trend has increased the attentions given to the machining of deformable parts.

This special issue addresses advanced research done on the machining of deformable parts. This covers investigations into non-metallic parts machining, the estimation of fixed-parts deformation, and deformation analyses for thin-structured parts.

We would like to express our sincere appreciation to the authors and reviewers, whose invaluable efforts have made the publication of this special issue possible. We hope that this special issue will trigger further research on the machining of deformable parts, leading to advances.

Ultra-high molecular weight polyethylene (UHMWPE) is a polyethylene with a molecular weight ranging from one million to seven million. UHMWPE is often used for constructing sliding parts such as artificial knees, hip joints, and gears owing to its self-lubrication, wear resistance, biocompatibility, and light weight structure. High accuracy and smooth surfaces are required for UHMWPE parts. Cutting operations of UHMWPE are particularly suitable for small numbers of products and to realize high shape accuracy. This paper describes some surface properties due to ball end mill operations of inclined surfaces. Some inclined workpieces are fixed by jigs and various cutting conditions are analyzed. Two tool path patterns, namely contour line and raster line (scanning line), are also evaluated for various cutting conditions by surface observations and surface roughness measurement.

Elastomer end-milling is attracting attention for its role in the small-lot production of elastomeric parts. In order to apply end-milling to the production of elastomeric parts, it is important that the workpiece be held stably to avoid deformation. To evaluate the stability of workholding, it is necessary to predict cutting forces in elastomer end-milling. Cutting force prediction for metal workpiece end-milling has been investigated for many years, and many process models for end-milling have been proposed. However, the applicability of these models to elastomer end-milling has not been discussed. In this paper, the characteristics of the cutting force in elastomer end-milling are evaluated experimentally. A standard cutting force model and its parameter identification method are introduced. By using this cutting force model, measured cutting forces are compared against the calculated results. The comparison makes it clear that the standard cutting force model for metal end-milling can be applied to down milling for a rough evaluation.

During cutting of low rigidity workpieces, avoiding elastic deformation due to machining forces is important. In multi-axis cutting of jet engine blades, tool posture is typically determined by trial and error based on the computer-aided machining operator’s experience. In this study, we developed a system of quantitative evaluation of machining error for blade surface finishing process by estimating the cutting force at each cutting point of the blade with different relative tool postures, and analyzing the deformation at each point with a finite element analysis. With the system, we become be able to perform simulations to evaluate tool posture with less shape error, maintaining the machining efficiency.

Recently, the aviation, shipping, and energy industries have been using components that are more thin-walled. Deformations occurring during the cutting of these thin-walled components could lead to dimensional errors. This paper describes a finite element method that requires fewer processes and less processing time than other methods, developed to predict the deformation of workpieces during their cutting. Using this method in conjunction with cutting simulations allows for the analysis of workpiece deformations through the modification of stiffness matrices containing information from cutting simulations, rather than recreating meshes or stiffness matrices. Moreover, part of the processing makes use of an accelerated method of solving simultaneous equations using large scale parallel computations with GPU.

The workholding process in small batch production is one of the least automated processes in machining. In order to ensure appropriate workholding, it is necessary to estimate actual deformation of the workpiece. Recently, near net shape technologies, such as thin-wall casting and additive manufacturing, have become common. Increased requirements for the finish machining of thin-structured parts has increased the need for the appropriateness of workholding to be evaluated. An objective of this study is to investigate an on-machine estimation method that can evaluate the actual deformation of parts with thin-structures. Thin-structured parts are usually held by means of multipoint fixturing or vise fixturing. A hybrid estimation method combining FEM analysis and local strain measurements is adopted to estimate the deformation. The effectiveness of the proposed method is evaluated with example problems. The results indicate the feasibility of the on-machine estimation of the deformation of thin-structured parts.

Weldlines are a type of defect in polymer injection molding and are known to impair the appearance and mechanical strength of the molded product. A previous study involved designing and fabricating an induction heating and cooling mold that incorporates an induction coil, allowing it to rapidly heat up. The study verified that the use of this mold prevents weldlines and improves the surface properties of the molded product. Although it is possible to prevent impairment of the external appearance caused by weldlines or the exposure of glass fibers on the surface when the mold is applied to glass fiber reinforced thermoplastic, the results of the previous study indicated that it did not significantly improve the mechanical strength. Hence, the present study involved designing and fabricating an injection mold capable of melt flow control in addition to induction heating and cooling by incorporating a melt flow control mechanism that employs a movable core pin to control the flow direction in the mold used in the previous study. The mold is used to form samples of short- and long-glass fiber reinforced polypropylene while simultaneously performing heating and cooling and melt flow control to obtain samples with smooth flat surfaces in which the exposure of glass fibers is prevented while exhibiting increased bending strength.