Micro Friction Stir welding (μFSW) has found its broader application in the area of packaging of MEMS devices, biomedical components, and joining of micro-mechanical assemblies. This study focuses on the effect of process parameters over the joint strength while joining Al6061-T6 and pure copper sheets of 0.3 mm thickness. Also, a coupled Eulerian-Lagrangian (CEL) numerical model has been developed in the finite element suite of ABAQUS ® . The boundary conditions used in the numerical simulation are kept almost similar to the experimental conditions to record thermal results. Moreover, an analytical approach for finding microhardness of welded joints using the Hall-Petch equation is also presented. The process parameters like rotational tool speed and welding traverse speed were found to be dominating in order to get better joint strength. The essential μFSW process parameters combination suggested that 1100rpm rotational speed, 20mm/min. traverse speed and 0.15mm pin depth (tool) result in superior flexural, thermal, and morphological properties of the joint. A good agreement between the experimental and simulation results was found with a maximum of 8% error in the predicted temperature values. The anticipated joint strength and surface characterization of the samples revealed a complex flow and homogeneous mixture at the pin-sheet interaction zone with higher micro-hardness values.

Bioprinting technology has a great potential in the fields of tissue engineering and regenerative medicine. In tissue engineering, for a bioprinted tissue to be successful in supporting regeneration of new tissue, it should morphologically mimic the native tissue in vivo. Therefore, the bioprinted tissue needs to be dimensionally accurate. In extrusion-based bioprinting, 3D printing process parameters and bioink properties affect dimensional accuracy of printed constructs. Currently, little information is available on effects of bioink composition and printing direction on dimensional accuracy of 3D printed constructs using alginate:methylcelluolose based bioink. In this study, strands were printed using four compositions of alginate:methylcellulose bioink and two printing directions. The four compositions of alginate:methylcellulose bioink were 1:1.5, 1:2, 1:2.5 and 1:3, and the two printing directions were vertical and horizontal. The statistical analysis of strand width measurement data revealed that while bioink composition has significant effect, printing direction does not affect the strand width of 3D printed constructs at the significance level of 0.05.

In bioprinting, biomaterials are deposited layer-by-layer to fabricate structures. Bioprinting has many potential applications in drug screening, tissue engineering, and regenerative medicine. Both animal cells and plant cells can be used to synthesize bioinks. Green bioprinting uses bioinks that have been synthesized using plant cells. Constructs fabricated via green bioprinting contain immobilized plant cells, with these cells arranged at desired locations. The constructs provide scaffolds for cell growth. Printing parameters affecting the growth of cells in green bioprinted constructs include print speed, needle diameter, extrusion temperature, and extrusion pressure. This paper reports a study to examine effects of extrusion pressure on cell growth (measured by cell count) in bioprinted constructs, using bioink containing Chlamydomonas reinhardtii algae cells. Three levels of extrusion pressure were used: 3, 5, and 7 bar. Cell counts in the bioprinted constructs were measured on the third and sixth days after bioprinting. It was found that, as extrusion pressure increased, cell count decreased on both the third and sixth days after bioprinting. Furthermore, the difference in cell counts between the third and the sixth days decreased as extrusion pressure increased. These trends suggest that increasing extrusion pressure during green bioprinting negatively affects cell growth. A possible reason for these trends is physical damage to or death of cells in the bioprinted constructs when extrusion pressure became higher.

Linear Friction Welding (LFW) is a uniquely important manufacturing process because it allows welding of dissimilar materials without filler material. In this study, bi-metallic Ti6Al4V-CoCrMo joints were manufactured using LFW process and analyzed the weldability and bonding strength. Ti6Al4V and CoCrMo cylinders were manufactured to a standard size of tensile specimens and cut into two identical pieces. The surfaces to be welded were polished and cleaned before performing welding. The experimental thermal data was recorded with an IR camera. In the thermal stress simulation model, the temperature-dependent thermal properties of Ti-6al-4V were used. The thermal properties of CoCrMo were assumed constant due the fact that CoCrMo does not change phase until it reaches its melting temperature. The heat losses due to radiation was different for each workpiece because both materials had a different emissivity and the heat loss by convection is a function of the surface temperature by natural convection. The left boundary of the Ti-6Al-4V and the right boundary of the Co-Cr-Mo workpiece were constrained at a constant temperature of 45°C. The maximum deformation of the simulation model is well matched with the measured data within 5% error.

Cancer is an ever-prevalent disease accounting for a large portion of medical services. With an aging world population, it is imperative to have non-invasive diagnostics which are efficient and not traumatic to the patient. Biopsy methods such as core needle biopsy (CNB) and fine needle aspiration (FNA), in combination with histopathology or cytology, are some of the most common practices used to garner an accurate diagnosis. The goal of this paper is to explore the feasibility of using 3D printing to fabricate biopsy needles with advanced designs that cannot be otherwise manufactured by traditional methods. In this study, we focus on changing the tip geometry and the addition of an internal feature to the biopsy needle to improve yield amounts. Four needle designs were tested, two with a bevel shaped tip, and two with a five-pronged tip, both with and without the internal feature. Both pronged-tip design and internal features are shown to have significant effect on tissue sampling efficiency. The 3D printed needles create higher insertion force than that of the stainless-steel needles. The quality of biopsied tissue which was confirmed by histopathological analysis. This study demonstrates the feasibility of using 3D printing to fabricate biopsy needles with enhanced tissue sampling efficiency.

Polymeric materials are often used as structural binders for biomedical applications. The mechanical properties of the material strongly depend on the fabrication process. To this end, we illustrate a set of casting methods for the production of samples to be tested via destructive methods. The curing process of the artifact was controlled during fabrication, and the molds were also made of polymeric materials. The fabrication of molds is illustrated where particular emphasis is posed on the manufacturing and testing of silicone molds using off-the-shelf material. Cyanoacrylate (CA), Epoxy resin (EP) and Methacrylate ester monomers (MEMs) artifacts have been fabricated using said molds. Of the aforementioned resins, MEMs are a class of thermosetting biocompatible polymers in which fabrication is especially problematic because of the very narrow temperature window at which the monomers polymerize. This research analyzes the casting process of curable materials highlighting the setbacks of using plastic-based molds. Among the cast based manufacturing techniques, specific focus was given to the case where MEMs is made to polymerize in a silicone mold controlling the temperature of the environment. The thermal properties that the silicone-based molds require for the appropriate curing of the polymer are analyzed. It was found that due to the very high heat capacity of silicone, the regulation of the temperature within the mold is difficult often exciding the boiling point of the casted resin.

The objective of this work is to investigate the hardness and abrasion resistance of a cobalt-chromium-molybdenum (Co-Cr-Mo) alloy fabricated via directed energy deposition (DED) additive manufacturing. Being a bio-compatible alloy, Co-Cr-Mo is commonly used in biomedical implants. Hence, its small-scale tribological behavior needs to be characterized, especially when fabricated via a newer process such as DED; thus the focus at nano scale. For this, a design of experiments was utilized to investigate the relevant process parameter design space for the laser engineered net shaping (LENS) process, with an objective to manufacture structurally-integral samples. Further, the effects of these process parameters were correlated with the resulting material properties at the nanoscale (viz., hardness modulus, and abrasion resistance). Results showed certain samples with competitively-high corresponding properties when compared to traditional made Co-Cr-Mo alloys, but with a large spread in properties, as is typical for such manufacturing processes. Also, microstructural characteristics were in line with traits observed when fabricating via traditional methods. Especially worth noting is the formation of metal carbides at the boundaries of cell-shaped grains; this causes a depletion of carbon at the center of the grain and thin carbides at the boundaries, thus significantly affecting the composite properties of the material. Altogether, this work shows the promise of using LENS to fabricate tailored structurally-integral Co-Cr-Mo alloys.

Ti6Al4V is a highly favorable material in biomedical, aerospace and many other industries. However, rapid tool wear during machining has made Ti6Al4V into a difficult-to-machine material. Electrochemical machining may be a solution to that challenge. Moreover, high chemical affinity and formation of oxide layer over the surface have limited the application electrochemical machining for Ti6Al4V. In this paper, an experimental approach of electrochemical micro turning of Ti6Al4V has been described. The electrolyte was 10% aqueous solution of NaOH and the tool was SS 310. For each and every experiment workpiece rotational speed and machining time were kept constant. Constant DC voltage was applied and the inter-electrode gap between tool and workpiece was kept constant for each experiment. Experiments were performed using two different levels of applied voltage, axial feed rate and inter-electrode gap. Their effects over MRR and surface roughness have been determined. Additionally, the optimum working condition was determined in order to maximize MRR and minimize surface roughness. For each experiment, acceptable material removal and good surface finish have been achieved. The maximum surface roughness (Ra) was found 1.128 μm in experiment 1. The utilization of NaOH solution has resulted in controlled electrolyzing current, controlled material removal and therefore, good surface finish.

It is an unarguably fact is that the current trend in manufacturing is miniaturization of products with extreme surface finish. I addition, the surface finish and dimensional accuracy requirements of products as well components are getting remarkably stringent, especially in the areas of vision, information, biotech, environmental, measurement and medical industries. Moreover, these products need to accommodate increased number of functions. Production of such products and parts of micron level size with very high dimensional accuracy of nano meter level is getting more importance because of a steadily increasing demand for such industrial products. To satisfactorily meet these challenges micro/nanomachining technology must be developed. Such machining is usually performed either using techniques based on energy beams (beam-based micro-machining) or using solid cutting tools (tool-based micro/nanomachining). Some of the limitations of beam-based micro-machining are due to poor control of 3D structures, low aspect ratio of products and also low material removal rate. In addition, special facilities are required to perform these processes and the maximum achievable dimensions are relatively small. However, with the application of tool-based micro/nanomachining technology some of these limitations can be satisfactorily overcome using ultra precision machine tools and solid cutting tools to produce the micro-features with well-controlled shape, features and tolerances. In many cases, compound or hybrid or simultaneous machining process is required for effectively performing micromachining. To meet the challenges, multi-process machines are required and unfortunately such machines are not available. Consequently, the author will present the development of a first-of-its-kind multi-process machine tool and the innovative approaches to develop various compound, hybrid and simultaneous machining processes for the successful implementation of micromachining. Recently, nanomachining of difficult-to-machine materials is also getting more importance with the pervasive demand for fabrication of miniature, thinner and lighter products, intricate micro-shapes and structures on such materials. In addition, the products also require nano meter level surface finish. The author would like to present his contribution especially in the area ductile mode machining of brittle materials. This paper also presents the recent developments in the areas of deeper understanding of the mechanisms and machining technologies to generate nano-finish surface by machining processes. In this paper, the basic understanding of nanomachining mechanism, ‘extrusion-like’ chip formation metal cutting is briefly discussed. With the emergence of hybrid freeform surfaces to increase the optical performance and to provide new functions. To fulfill these objectives, the author and his team have carried out ultra-precision machining using fast tool servo (FTS) and slow slide servo (SSS) mechanisms. Some typical examples of the development of innovative nano machining processes and products have been presented in this paper. Finally, the development of a rotating tool for continuous production of radial Fresnel lenses has been presented.

In-situ monitoring of a Laser Powder-Bed Fusion (LPBF) additive manufacturing process is crucial in enhancing the process efficiency and ensuring the built part integrity. In this work, we present an in-situ monitoring method using an off-axis camera for monitoring layer-wise process anomalies. The in-situ monitoring is performed with a spatial resolution of 512 × 512 pixels, with each pixel representing 250 × 250 μm and a relatively high data acquisition rate of 500 Hz. An experimental study is conducted by using the developed in-situ off-axis method for monitoring the build process for a standard tensile bar. Real-time video data is acquired for each printed layer. Data analytics methods are developed to identify layer-wise anomalies, observe powder bed characteristics, reconstruct 3D part structure, and track the spatter dynamics. A deep neural network architecture is trained using the acquired layer-wise images and tested by images embedded with artificial anomalies. The real-time video data is also used to perform a preliminary spatter analysis along the laser scan path. The developed methodology is aimed to extract as much information as possible from a single set of camera video data. It will provide the AM community with an efficient and capable process monitoring tool for process control and quality assurance while using LPBF to produce high-standard components in industrial (such as, aerospace and biomedical industries) applications.

Applications of hybrid technology are expanding from refurbishment and repair to low quantity, specialty part production, which are staple characteristics in medical implant, energy, and aerospace industry sectors, among others. This expansion has led to the development of the Mazak VC-500A/5X AM HWD, a wire fed laser cladding unit equipped with a standard 5 axis CNC. This unit is capable of building near net geometry of complex medium to large parts within a profitable timeframe, due to its comparatively high rate of deposition to that of a powder fed hybrid system. In this study, deposition and machining capabilities of the VC-500A/5X AM HWD are assessed through the production of three different test geometries by different process plans. Production of these test geometries is supported by an open loop sensor package primarily for monitoring machine health, data collection, and machine operator aid. The viability of extended deposition followed by machining is evaluated against a more cyclical strategy of reoccurring deposition and machining operations. Lastly, common defects in as-built geometries are evaluated and addressed through revisions to original process plans and toolpaths, indicating the need for continued innovation in hybrid manufacturing specific CAM/CAD software, as well as closed loop machine monitoring and quality control.

Three-dimensional (3D) extrusion printing of cellular/acellular structures with biocompatible materials has been widely investigated in recent years. However, the requirement of suitable solidification rate of printable ink materials constrains the utilization of extrusion-based 3D printing technique. In this study, the yield-stress nanoclay suspension-enabled extrusion-based 3D printing system has been investigated and demonstrated to overcome solidification rate constraints during printing. Utilizing the liquid-solid transition property of nanoclay suspension, two fabrication approaches, including nanoclay support bath-enabled printing and nanoclay-enabled direct printing, have been proposed. For the former approach, nanoclay (Laponite EP) has been used as a support bath material to fabricate alginate-based tympanic membrane patches. The constituents of alginate-based ink have been investigated to have the desired mechanical property of alginate-based tympanic membrane patches and facilitate the printing process. For the latter approach, nanoclay (Laponite XLG) has been used as an internal scaffold material to help print poly (ethylene glycol) diacrylate (PEGDA)-based neural chambers, which can be further cross-linked in air. Mechanical stress analysis has been performed to explore the geometric limitation of printable Laponite XLG-PEGDA neural chambers.

3D bioprinting has more and more applications in tissue engineering, in vitro drug testing, and regenerative medicine. The bioink consisting of the biocompatible polymer (as extracellular matrix) and the living cells is the starting material. Because the typical bioprinting process may take several hours, the suspended cells in the bioink sediment with time, which significantly affects the bioink stability as well as the following bioprinting quality and reliability. The cell sedimentation is determined by the integral effects of drag force and buoyancy and gravity. The gravitational force is related to the cells, and the drag force and buoyant force is related to the polymer concentration. This paper is the first paper to quantify the cell sedimentation process of the bioink within 0.5% and 1% (w/v) polymer concentrations respectively. The cell sedimentation phenomenon has been observed using the bioink within 0.5% and 1% (w/v) polymer concentrations. The cell sedimentation velocity has been estimated to be 1.18 μm/s with the polymer concentrations to be 0.5% (w/v) and 0.88 μm/s for the bioink with the polymer concentrations to be 1% (w/v). It is also found that the cell concentration increases significantly at the bottom of the bioink reservoir, resulting in cell aggregates due to cell-cell interaction.

Despite numerous applications of Fused Filament Fabrication (FFF), the poor surface finish, being an inherent defect, is major obstruction against utilization of prototypes for rapid casting applications. The conventional finishing methods are effective, however, the dimensional stability is compromised which is completely unacceptable in case of biomedical implants as minute dimension variations may lead to post-operative complications. The paper explores possibilities to produce chemically finished plastic replicas of hip implant through FFF which can be further used as patterns for investment casting. An advanced post-processing technique i.e. Chemical Vapor Smoothing (CVS) is tested to improve surface characteristics and dimensional accuracy of ABS replicas. The repeatability and consistency of coupled CVS and FFF processes is tested through experimentation and statistical analysis in order to endorse an alternative process for mass production of biomedical implants. The Taguchi L18 DOE was used to perform experiments which measures impact of two input parameters of FFF i.e. orientation angle and density, and four parameters of Chemical Vapor Smoothing i.e. pre-cooling time, smoothing time, smoothing time and number of cycles. The multi response optimization technique was employed to acquire optimum set of parameters yielding best surface finish, dimensional accuracy and surface hardness and hence, the overall desirability of 0.7891 was achieved. The process capability and reliability was tested at optimum settings by manufacturing twenty replicas by measuring surface roughness, hardness and dimensional accuracy at different locations of parts. It was observed that values of Cp for all the response parameters was greater than 1.33 while Cpk was greater than 1. The analysis of histograms and capability indices reveal that the FFF-CVS process carried out at optimized conditions can be defined as “statistically controlled” for fabrication of ABS replicas for biomedical applications.

Formation of biofilm on implant surface is one of the major causes for port-operative infection. Incorporation of antimicrobial silver nanoparticles (AgNPs) on implant surface has been studied as an effective remedy in recent decades. This paper presents a novel AgNPs-titanium composite foil manufactured through covalent attachment of AgNPs for biofilm control. This composite foil was fabricated by a series of chemical reactions including thiol-derivatization and formation of Ag-S covalent bonds. The film structure and properties were characterized through scanning electron microscopy (SEM), Energy dispersive X-ray Spectroscopy (EDS) and surface profiling. The antimicrobial performance was examined against gram positive bacterial strain Staphylococcus aureus . Results indicate that the prepared composite foil effectively reduced bacterial attachment in short term exposure and possess high stability against the release of nanoparticles. This novel antimicrobial composite material has a great potential to be used in the future biomedical instrumentation.

Additive manufacturing (AM) has had an enormous impact in the manufacturing sector. Its role has evolved from printing prototypes to manufacturing functional parts for a variety of applications in the automotive, aerospace, and medical industries. Recently, AM processes have also been applied in the infrastructure construction industry. Applications of AM processes could bring in significant improvements in infrastructure construction, specifically in the areas of productivity and safety. It is desirable to have a review on the current state of emerging AM processes for infrastructure construction as well as existing gaps in this field. This paper reviews AM processes in infrastructure construction. It discusses the process principle, application examples, and gaps for each of the AM processes.

Viscoelastic polymer solutions have been extensively utilized in drop-wise manufacturing (such as inkjet printing) for a variety of biomedical applications. The pinch-off of viscoelastic jets is a key step towards generation of droplets in inkjet printing. This complex process is governed by interplay of four stresses including inertial stress, capillary stress, viscous stress, and elastic stress. Depending on polymer solution properties and process conditions, four types of pinch-off phenomenon were observed during inkjetting of viscoelastic alginate solutions. In this study, material properties of alginate solutions with different concentrations have been characterized, and three dimensionless numbers (Ohnesorge number Oh , Deborah number De and Weber number We ) have been proposed to analyze different pinch-off behaviors. Phase diagram in terms of these three dimensionless numbers has been constructed to classify the regimes for different pinch-off types during inkjetting of viscoelastic alginate solutions. It is found that: 1) At low De and Oh , the viscoelastic effect is small. The capillary stress is mainly balanced by the inertial stress, resulting in front pinching. 2) At medium De and low Oh , the capillary stress is still mainly balanced by the inertial stress, but the elastic effect starts to show its effect by delaying the ligament thinning near the front-pinching location. With the increase of We , the pinch-off type may change from front pinching to hybrid pinching to exit pinching. 3) At low Oh and high De , the viscous and inertial effects are small. The capillary stress is mainly balanced by the elastic stress, resulting in exit pinching. 4) At high Oh and De , the viscoelastic effect is dominant. The capillary stress is mainly balanced by the viscous and elastic stresses. With the increase of We , middle pinching turns to be exit pinching due to the increase of the initial ligament diameter near the forming droplet.

3D printing processes have found several applications in automobile, aerospace, and biomedical industries. Recent development of large-scale 3D printing processes has fueled applications in the construction industry. Materials such as ceramic clay (porcelain) can now be used in additive manufacturing (AM). However, information regarding the effect of process parameters on part quality is limited. There is a need to study the effects of various parameters on the successful printing of samples for the construction industry. This paper presents an experimental study to determine the feasible parameter regions for extrusion-based 3D printing of porcelain using a Delta WASP 2040 Clay printer. The printing parameters studied are extruder height, layer thickness, print speed and air pressure. The effects of these parameters on the surface quality of the printed samples are examined. The identified feasible parameter regions from this study would provide preliminary insights on material extrusion-based 3D printing of porcelain.

Shape Memory Alloys are smart materials that tend to remember and return to its original shape when subjected to deformation. These materials find numerous applications in robotics, automotive and biomedical industries. Micromachining of SMAs is often a considerable challenge using conventional machining processes. Micro-Electrical Discharge Machining is a combination of thermal and electrical processes, which can machine any electrically conductive material at micron scale independent of its hardness. It employs dielectric medium such as hydrocarbon oils, deionized water, and kerosene. Using liquid dielectrics has adverse effects on the machined surface causing cracking, white layer deposition, and irregular surface finish. These limitations can be minimized by using a dry dielectric medium such as air or nitrogen gas. This research involves the experimental study of micromachining of Shape Memory Alloys using dry Micro-Electrical Discharge Machining process. The study considers the effect of critical process parameters including discharge voltage and discharge current on the material removal rate and the tool wear rate. A comparison study is performed between the Micro-Electrical Discharge Machining process with using the liquid as well as air as the dielectric medium. In this study, microcavities are successfully machined on shape memory alloys using dry Micro-Electrical Discharge Machining process. The study found that the dry Micro-Electrical Discharge Machining produces a comparatively better surface finish, has lower tool wear and lesser material removal rate compared to the process using the liquid as the dielectric medium. The results of this research could extend the industrial applications of Micro Electrical Discharge Machining processes.

Smart materials are new generation materials which possess great properties to mend themselves with a change in environment. Smart materials find applications in a wide range of industries including biomedical, aerospace, defense and energy sector and so on. These materials possess unique properties including high hardness, high strength, high melting point and low creep behavior. Manufacturing of these materials is a huge challenge, particularly at the micron scale. Abrasive waterjet micromachining (AWJMM) is a non-traditional material removal process which has the capability of machining extremely hard and brittle materials such as glasses and ceramics. AWJMM process is usually performed with nozzle and workpiece placed in air. However, machining in the air causes spreading of the waterjet resulting in low machining quality. Performing the AWJMM process with a submerged nozzle and workpiece could eliminate this problem and also reduce noise, splash, and airborne debris particles during the machining process. This research investigates Submerged Abrasive Waterjet Machining (SAWJMM) process for micromachining smart ceramic materials. The research involves experimental study on micromachining of smart materials using an in-house fabricated SAWJMM setup. The effect of critical parameters including stand-off distance, abrasive grain size and material properties on the cavity size, kerf angle and MRR during SAWJMM and AWJMM processes are studied. The study found that SAWJMM process is capable of successfully machining smart materials including shape memory alloys and piezoelectric materials at the micron scale. The machined surfaced are free of thermal stresses and did not show any cracking around the edges. The critical process parameter study revealed that stand-off distance and abrasive grit size significantly affect the machining results.