This article provides an overview of currently available metal AM processes for the medical industry; outlines a step-by-step review of the typical workflow for design, manufacturing, evaluation, and implantation of patient-specific AM devices; and examines the existing research trends in medical applications of AM with specific focus on metallic biomedical implants. Finally, challenges and opportunities for future developments in AM pertaining to the medical field are also explored.

Three-dimensional plotting of biomaterials (also known as bioprinting) has been a major milestone for scientists and engineers working in nanobiotechnology, nanoscience, and nanomedicine. It is typically classified into two major categories, depending on the plotting principle, as contact and noncontact techniques. This article focuses on the working principles of contact and noncontact printing methods along with their advantages, disadvantages, applications, and challenges. Contact printing methods include micro-plotter, pen printing, screen printing, nanoimprint printing, flexography printing, and gravure printing. Noncontact printing methods include extrusion printing, droplet printing, laser-based polymerization, and laser-based cell transfer. The wide variety of printable biomaterials, such as DNA, peptides, proteins, lipids, and cells, also are discussed.

This article begins with a description of extrusion-based bioprinting for tissue scaffold fabrication. It also examines various extrusion-based bioprinting processes and related tissue scaffolding strategies, presents the selection criteria of various bioinks with various polymers and their printed scaffolds for applications in tissue engineering and regenerative medicines, and provides future research recommendations to address the shortcomings and issues found in current extrusion-based bioprinting processes.

This article discusses alginate/gelatin-based bioinks in 3D bioprinting applications, providing a summary of the most relevant previous work in the field. It presents advanced compositions to enhance functionality and/or optimize hydrogels for 3D bioprinting. The article discusses advanced printing techniques for alginate/gelatin-based bioinks.

Due to its layer-by-layer process, 3D printing enables the formation of complex geometries using multiple materials. Three-dimensional printing for bone tissue engineering is called bioprinting and refers to the use of material-transfer processes for patterning and assembling biologically relevant materials, molecules, cells, tissues, and biodegradable biomaterials with a prescribed organization to accomplish one or more biological functions. Currently, 3D bioprinting constructs can be classified into two categories: acellular and cellular. This article introduces and discusses these two approaches based on the suitable materials for these constructs and the fabrication processes used to manufacture them. The materials are grouped into polymers, metals, and hydrogels. The article also summarizes the commonly used 3D printing techniques for these materials, as well as cell types used for various applications. Lastly, current challenges in tissue engineering are discussed.

Additive manufacturing (AM), or three-dimensional (3D) printing, is a class of manufacturing processes that create the desired geometries of an object, or an assembly of objects, layer by layer or volumetrically. AM has been used extensively for manufacturing medical devices, due to its versatility to satisfy the specific needs of an intended medical field for the product/device. This article provides a comprehensive review of AM in medical devices by the medical specialty panels of the Food and Drug Administration (FDA) Code of Federal Regulations, Parts 862 to 892, including anesthesiology, ear and nose, general hospital, ophthalmic, plastic surgery, radiology, cardiovascular, orthopedic, dental, neurology, gynecology, obstetrics, physical medicine, urology, toxicology, and pathology. It is classified under these panels, and critical reviews and future outlooks are provided. The application of AM to fabricate medical devices in each panel is reviewed; lastly, a comparison is provided to reveal relevant gaps in each medical field.

Vat polymerization is a form of three-dimensional (3D) printing. Historically, it is the oldest additive manufacturing technique, with the development of stereolithography apparatus (SLA) by Charles Hull in 1986. This article outlines the various forms of vat polymerization techniques used for biomedical applications. Due to the complex nature of this printing process, many key print parameters and material properties need to be considered to ensure a successful print. These influential parameters are addressed throughout the article to inform the reader of the considerations that should be taken when using the vat polymerization technique. The article provides information on vat polymerization printer setup, the photo-cross-linking mechanism, and considerations using vat polymerization. In addition, it outlines and discusses the advancements of vat polymerization in the biomedical industry.

According to International Organization for Standardization (ISO)/ASTM International 52900, additive manufacturing (AM) can be classified into material extrusion, material jetting, vat photo polymerization, binder jetting, sheet lamination, powder-bed fusion (PBF), and directed-energy deposition. This article discusses the processes involved in polymer powder 3D printing using laser fusion/ sintering and fusing agents and energy, as well as the thermally fused PBF. It provides information on polymer powder parameters and modeling, the powder-handling system, powder characterization, the flowability of powder feedstock, and polymer part characteristics. The article describes the types of polymers in PBF, the processes involved in powder recycling, and the prospects of PBF in AM. In addition, the biomedical application of polyether ether ketone (PEEK) is also covered.

Additive manufacturing (AM) technologies print three-dimensional (3D) parts through layer-by-layer deposition based on the digital input provided by a computer-aided design file. This article focuses on the binder jet printing process, common biomaterials used in this AM technique, and the clinical applications relevant to these systems. It reviews the challenges and future directions of binder-jetting-based 3D printing.

Hydroxyapatite (HA) is one of the most popular materials in tissue scaffold engineering due to its similarity to the nature of human bone; it accounts for more than half of the total weight of the latter. Selective laser sintering (SLS) is an additive manufacturing method that is used in producing tissue engineering parts from HA feedstocks. This article provides a brief overview of the process itself, along with a detailed review of HA-based tissue engineering applications using SLS. Discussion on the various polymer composites is presented. A detailed overview of selected publications on HA-based SLS studies is listed, which provides insight regarding technical aspects of processing HA powder feedstocks.

Calcium phosphates react to form more stable salts in aqueous solutions. This phenomenon has been applied to the solidification process for the dental and medical cement calcium phosphate cement, which consists of multiple phases of calcium phosphates and calcium salts; solidification occurs by the formation of hydroxyapatite. Dicalcium phosphate consists of crystal water along with anhydrous and dihydrate salts. This article summarizes research achievements regarding dicalcium phosphate dihydrate (DCPD) production with controlled morphology and reactivity, including effects of an additive and of production conditions on precipitation. It also summarizes achievements made in the hybridization of nano-apatite onto DCPD particles.

Additive manufacturing (AM) techniques include powder-bed fusion (PBF), directed-energy deposition, binder jetting (BJ), extrusion-based desktop, vat photopolymerization, material jetting, and sheet lamination. The development of suitable powders for AM is a challenging task because of critical design parameters including chemical composition, flowability of powders, and melt surface tension. This article explains the fabrication methods of metal and novel alloy powders for medical applications. The development of zirconium alloy powder for laser-PBF is introduced as a case study.

Metallic alloys that are typically used for medical purposes include stainless steels, Ti-6Al-4V, and Co-Cr-Mo. This article discusses the relative merits of each of these alloys. The utilization of stainless steels in the biomedical industry, especially in relation to the additive manufacturing (AM) process, is the main focus of this article. The characteristics of various stainless steels are described subsequently, and the categories that are of relevance to the biomedical industry are identified. The types of stainless steels covered are austenitic, ferritic, martensitic, duplex, and precipitation-hardened stainless steels. The article discusses the potential benefits of AM for biomedical devices. It describes the types of AM processes for stainless steels, namely binder jet, directed-energy deposition, and laser powder-bed fusion. The article reviews the AM of austenitic, martensitic, and PH stainless steels for biomedical applications. In addition, the challenges and obstacles to the clinical use of AM parts are covered.

This article discusses some of the additive manufacturing (AM) based fabrication of alloys and their respective mechanical, electrochemical, and in vivo performance. Firstly, it briefly discusses the three AM techniques that are most commonly used in the fabrication of metallic biomedical-based devices: binder jetting, powder-bed fusion, and directed-energy deposition. The article then characterizes the electrochemical properties of additive-manufactured/processed cobalt-chromium alloys. This is followed by sections providing an evaluation of the biological response to CoCr alloys in terms of the material and 3D printing fabrication. Discussion on the biological response as a function of direct cellular activity on the surface of CoCr alloys in static conditions (in vitro), in dynamic physiological conditions (in vivo), and in computer-simulated conditions (in silico) are further discussed in detail. Finally, the article provides information on the qualification and certification of AM-processed medical devices.

Additive manufacturing, or three-dimensional printing technologies, for biomedical applications is rather different from other engineering components, particularly for biomedical implants that are intended to be used within the human body. This article contains two sections: "Design and Manufacturing Considerations of 3D-Printed, Commercially Pure Titanium and Titanium Alloy-Based Orthopedic Implants" and "Device Testing Considerations Following FDA Guidance" for additive-manufactured medical devices. These are further subdivided into five major focus areas: materials; design, printing, printing characteristics and parameters as well as postprinting validation; removal of the many manufacturing material residues and sterilization; physical, chemical, and mechanical assessments of the final devices; and biological considerations of all the final devices including biocompatibility.

Bioprinting has been advancing in the field of tissue engineering as the process for fabricating scaffolds, making use of additive manufacturing technologies. In situ bioprinting (also termed intraoperative bioprinting) is a promising solution to address the limitations of conventional bioprinting approaches. This article discusses the main approaches and technologies for in situ bioprinting. It provides a brief overview of the bioprinting pipeline, highlighting possible solutions to improve currently used approaches. Additionally, case studies of in situ bioprinting are provided and in situ bioprinting future perspectives are discussed.

The field of bioprinting is a subset of additive manufacturing (AM) that is rapidly expanding to meet the needs of regenerative medicine and tissue engineering. Bioprinting encompasses a broad spectrum of issues, from cell expansion and novel bioink development to cell/stem cell printing, from organoid-based tissue organization to bioprinting of human-scale tissue structures, and from building cell/tissue/organ-on-a-chip to biomanufacturing of multicellular engineered living systems. This article focuses on two challenges regarding bioprinting: bioinks and crosslinking. It describes the methods for characterizing the performance of bioink formulations and the effectiveness of crosslinking strategies. The topics covered include modalities of bioprinting, characteristics of bioink, rheological properties of bioink sols, rheological measurements, mathematical models of bioink rheology, postfabrication polymer network mechanics, mechanical properties of crosslinked bioinks, and printability of bioinks. Finally, specific strategies used for crosslinking bioinks, as well as some emerging strategies to further improve bioinks and their crosslinking, are summarized.

Stereolithographic (STL) additive manufacturing (AM) can be used to fabricate practical components. This article discusses the processes involved in STL-AM of biological scaffolds, providing information on bioscaffold processing, cavity arrangements, and microlattice distributions. Within the last topic, the sub-topic of scaffold modulation is discussed.

The use of 3D bioprinting techniques has contributed to the development of novel cellular patterns and constructs in vitro, ex vivo, and even in vivo. There are three main bioprinting techniques: inkjet printing, extrusion printing (also known as bioextrusion), laser-induced forward transfer (LIFT) printing, which is also known as modified LIFT printing, matrix-assisted pulsed-laser evaporation direct write, and laser-based printing (laser-assisted bioprinting, or biological laser printing). This article provides an overview of the LIFT process, including the LIFT process introduction, different implementations, jetting dynamics, printability phase diagrams, and printing process simulations. Additionally, materials involved during LIFT are introduced in terms of bioink materials and energy-absorbing layer materials. Also, the printing of single cells and 2D and 3D constructs is introduced, showcasing the current state of the art with the ultimate goal for tissue- and organ-printing applications.

Inkjet printing is extremely precise in terms of the ejected microdroplets (picoliter volume), contributing an unparalleled lateral resolution. Additionally, the benefits of high-speed deposition, contactless ink delivery, and the use of a range of ink materials endorse this technique as suitable for high-throughput 3D manufacturing. This article provides an overview of inkjet 3D printing (also referred to as 3D inkjetting). It then highlights the major components and accessories used in commercial and laboratory-based 3D inkjet printers. Next, the article describes the process physics of the transient phenomena involved in both binder-jetting- and direct-inkjetting-based 3D printing. It then discusses the scope and advantages of 3D inkjetting in the manufacturing of metallic, ceramic, and polymer-based biomaterials. The article also discusses several approaches and methodologies to examine the in vitro cytocompatibility and in vivo biocompatibility of both binder-jetted and direct-inkjetted scaffolds for biomedical applications. Finally, it discusses the challenges and troubleshooting methodologies in 3D inkjetting of biomaterials.