New depowdering-friendly designs for three-dimensional printing of calcium phosphate bone substitutes

Binder Jetting 3D Printing of Binary Cement-Siliceous Sand Mixture

Three-dimensional printing allows accurate geometries to be obtained across a wide range of applications and it is now also moving into the architecture and construction industry. In the present work, a unique binary mix composed of ordinary Portland cement (OPC) and quick-setting cement (QSC) was combined with silica sand aggregate in different proportions for a customized binder jetting 3D printing (BJ3DP) process. Specimens were printed using the blended dry powders and deionized water to determine the impact of the processing variables on the properties of the realized specimens. The results show that the properties are influenced by the binary mix proportions and the layer thickness. The investigation found significant improvement in mechanical performance on increasing the proportion of OPC and optimal conditions were identified with proportions of 35 wt% OPC and 5 wt% QSC. Notable enhancements were also observed as the layer thickness was reduced.

Functioning tailor-made 3D-printed vascular graft for hemodialysis

BACKGROUND

The two ends of arteriovenous graft (AVG) are anastomosed to the upper limb vessels by surgery for hemodialysis therapy. However, the size of upper limb vessels varies to a large extent among different individuals.

METHODS

According to the shape and size of neck vessels quantified from the preoperative computed tomography angiographic scan, the ethylene-vinyl acetate (EVA)-based AVG was produced in H-shape by the three-dimensional (3D) printer and then sterilized. This study investigated the function of this novel 3D-printed AVG in vitro and in vivo.

RESULTS

This 3D-printed AVG can be implanted in the rabbit's common carotid artery and common jugular vein with ease and functions in vivo. The surgical procedure was quick, and no suture was required. The blood loss was minimal, and no hematoma was noted at least 1 week after the surgery. The blood flow velocity within the implanted AVG was 14.9 ± 3.7 cm/s. Additionally, the in vitro characterization experiments demonstrated that this EVA-based biomaterial is biocompatible and possesses a superior recovery property than ePTFE after hemodialysis needle cannulation.

CONCLUSIONS

Through the 3D printing technology, the EVA-based AVG can be tailor-made to fit the specific vessel size. This kind of 3D-printed AVG is functioning in vivo, and our results realize personalized vascular implants. Further large-animal studies are warranted to examine the long-term patency.

Customized Additive Manufacturing in Bone Scaffolds-The Gateway to Precise Bone Defect Treatment

In the advancing landscape of technology and novel material development, additive manufacturing (AM) is steadily making strides within the biomedical sector. Moving away from traditional, one-size-fits-all implant solutions, the advent of AM technology allows for patient-specific scaffolds that could improve integration and enhance wound healing. These scaffolds, meticulously designed with a myriad of geometries, mechanical properties, and biological responses, are made possible through the vast selection of materials and fabrication methods at our disposal. Recognizing the importance of precision in the treatment of bone defects, which display variability from macroscopic to microscopic scales in each case, a tailored treatment strategy is required. A patient-specific AM bone scaffold perfectly addresses this necessity. This review elucidates the pivotal role that customized AM bone scaffolds play in bone defect treatment, while offering comprehensive guidelines for their customization. This includes aspects such as bone defect imaging, material selection, topography design, and fabrication methodology. Additionally, we propose a cooperative model involving the patient, clinician, and engineer, thereby underscoring the interdisciplinary approach necessary for the effective design and clinical application of these customized AM bone scaffolds. This collaboration promises to usher in a new era of bioactive medical materials, responsive to individualized needs and capable of pushing boundaries in personalized medicine beyond those set by traditional medical materials.

The Application and Challenge of Binder Jet 3D Printing Technology in Pharmaceutical Manufacturing

Three-dimensional (3D) printing is an additive manufacturing technique that creates objects under computer control. Owing to the rapid advancement of science and technology, 3D printing technology has been widely utilized in processing and manufacturing but rarely used in the pharmaceutical field. The first commercial form of Spritam® immediate-release tablet was approved by FDA in 2015, which promoted the advancement of 3D printing technology in pharmaceutical development. Three-dimensional printing technology is able to meet individual treatment demands with customized size, shape, and release rate, which overcomes the difficulties of traditional pharmaceutical technology. This paper intends to discuss the critical process parameters of binder jet 3D printing technology, list its application in pharmaceutical manufacturing in recent years, summarize the still-open questions, and demonstrate its great potential in the pharmaceutical industry.

Porous biomaterials for tissue engineering: a review

The field of biomaterials has grown rapidly over the past decades. Within this field, porous biomaterials have played a remarkable role in: (i) enabling the manufacture of complex three-dimensional structures; (ii) recreating mechanical properties close to those of the host tissues; (iii) facilitating interconnected structures for the transport of macromolecules and cells; and (iv) behaving as biocompatible inserts, tailored to either interact or not with the host body. This review outlines a brief history of the development of biomaterials, before discussing current materials proposed for use as porous biomaterials and exploring the state-of-the-art in their manufacture. The wide clinical applications of these materials are extensively discussed, drawing on specific examples of how the porous features of such biomaterials impact their behaviours, as well as the advantages and challenges faced, for each class of the materials.

Discussion on the possibility of multi-layer intelligent technologies to achieve the best recover of musculoskeletal injuries: Smart materials, variable structures, and intelligent therapeutic planning

Although intelligent technologies has facilitated the development of precise orthopaedic, simple internal fixation, ligament reconstruction or arthroplasty can only relieve pain of patients in short-term. To achieve the best recover of musculoskeletal injuries, three bottlenecks must be broken through, which includes scientific path planning, bioactive implants and personalized surgical channels building. As scientific surgical path can be planned and built by through AI technology, 4D printing technology can make more bioactive implants be manufactured, and variable structures can establish personalized channels precisely, it is possible to achieve satisfied and effective musculoskeletal injury recovery with the progress of multi-layer intelligent technologies (MLIT).

Urchin-like Hydroxyapatite/Graphene Hollow Microspheres as pH-Responsive Bone Drug Carriers

Hydroxyapatite (HA) is the main inorganic component of human bones and teeth. It has good biocompatibility and bioactivity, which promotes its good application prospects in the field of bone drug carriers. In this study, tetraethylenepentamine-graphene (rGO-TEPA)/CaCO₃:HA composite microspheres were prepared via microwave hydrothermal synthesis using rGO-TEPA/CaCO₃ solid microspheres as intermediates. Furthermore, the incompletely transformed CaCO₃ was removed by soaking in a citric acid buffer to obtain rGO-TEPA/HA hollow composite microspheres. The two types of as-prepared composite microspheres exhibited sea urchin-like structures, large BET surface areas, and good dispersibility. Mouse preosteoblast cells (MC3T3-E1) were used for in vitro cytotoxicity experiments. The in vitro cell viability test showed that the two composite drug carriers exhibited noncytotoxicity. Moreover, the doxorubicin (DOX) loading and releasing investigations revealed that the two types of prepared carriers had mild storage-release behaviors and good pH responsiveness. Hence, these rGO-TEPA/HA hollow microspheres have promising applications as bone drug carriers.

3D-Printed Objects for Multipurpose Applications

3D printing is a popular nonconventional manufacturing technique used to print 3D objects by using conventional and nonconventional materials. The application and uses of 3D printing are rapidly increasing in each dimension of the engineering and medical sectors. This article overviews the multipurpose applications of 3D printing based on current research. In the beginning, various popular methods including fused deposition method, stereolithography 3D printing method, powder bed fusion method, digital light processing method, and metal transfer dynamic method used in 3D printing are discussed. Popular materials utilized randomly in printing techniques such as hydrogel, ABS, steel, silver, and epoxy are overviewed. Engineering applications under the current development of the printing technique which include electrode, 4D printing technique, twisting object, photosensitive polymer, and engines are focused. Printing of medical equipment including artificial tissues, scaffolds, bioprinted model, prostheses, surgical instruments, COVID-19, skull, and heart is of major focus. Characterization techniques of the printed 3D products are mentioned. In addition, potential challenges and future prospects are evaluated based on the current scenario. This review article will work as a masterpiece for the researchers interested to work in this field.

Effects of surface area and topography on 3D printed tricalcium phosphate scaffolds for bone grafting applications

Additive manufacturing (AM), or 3D printing, of bioceramic scaffolds promises personalized treatment options for patients with site-specific designability for repair and reconstruction of bone defects. Although the theory for creating these complex geometries has already been made possible through AM's advancement, such shapes' manufacturability is difficult due to printing with ceramics' inherent complexities. Ceramics have the added challenge of being highly brittle, poor handleability of green (pre-sintered) parts, making complex shape high strength parts challenging to manufacture. This has led to a significant literature gap regarding the feasibility of creating bioceramic scaffolds with unique architectures that can be used in site-specific, individualized patient treatment. This work aims to successfully create complex topographical surfaces of cylindrical bone-like scaffolds to understand the correlation of increasing the scaffold surface area on mechanical properties and in vitro osteoblast cell proliferation. An increase in osteoblast cell proliferation and facilitation in cellular attachment can ultimately lead to improved bone healing. This work explores the printing parameters within an Innovent+® ExOne binder jet 3D printer to produce scaffold designs from synthesized tricalcium phosphate powder. Mechanical testing reveals the designed structures enhance scaffold compressive strength by 30% compared to control dense cylindrical scaffolds. Osteoblast cell proliferation is also increased due to changes in surface topography with a nearly 2-fold increase. Our work incorporates macro-level topographical changes to increase surface area, which is another avenue that could be combined with other scaffold features such as porosity. Results show bulk surface topography modifications via 3D printing can increase surface area to support enhanced biological response without compromising mechanical properties. This discovery may enable a future generation of porous scaffolds with external structures for further progress towards proper defect-specific synthetic bone grafts.

3D printing technology as innovative solutions for biomedical applications

3D printing was once predicted to be the third industrial revolution. Today, the use of 3D printing is found across almost all industries. This article discusses the latest 3D printing applications in the biomedical industry.

Three-Dimensional Extrusion Printing of Porous Scaffolds Using Storable Ceramic Inks

In this study, we describe the additive manufacturing of porous three-dimensionally (3D) printed ceramic scaffolds prepared with hydroxyapatite (HA), β-tricalcium phosphate (β-TCP), or the combination of both with an extrusion-based process. The scaffolds were printed using a novel ceramic-based ink with reproducible printability and storability properties. After sintering at 1200°C, the scaffolds were characterized in terms of structure, mechanical properties, and dissolution in aqueous medium. Microcomputed tomography and scanning electron microscopy analyses revealed that the structure of the scaffolds, and more specifically, pore size, porosity, and isotropic dimensions were not significantly affected by the sintering process, resulting in scaffolds that closely replicate the original dimensions of the 3D model design. The mechanical properties of the sintered scaffolds were in the range of human trabecular bone for all compositions. All ceramic bioinks showed consistent printability over a span of 14 days, demonstrating the short-term storability of the formulations. Finally, the mass loss did not vary among the evaluated compositions over a period of 28 days except in the case of β-TCP scaffolds, in which the structural integrity was significantly affected after 28 days of incubation in phosphate-buffered saline. In conclusion, this study demonstrates the development of storable ceramic inks for the 3D printing of scaffolds of HA, β-TCP, and mixtures thereof with high fidelity and low shrinkage following sintering that could potentially be used for bone tissue engineering in load-bearing applications.

3D Printing of Bioceramics for Bone Tissue Engineering

Bioceramics have frequent use in functional restoration of hard tissues to improve human well-being. Additive manufacturing (AM) also known as 3D printing is an innovative material processing technique extensively applied to produce bioceramic parts or scaffolds in a layered perspicacious manner. Moreover, the applications of additive manufacturing in bioceramics have the capability to reliably fabricate the commercialized scaffolds tailored for practical clinical applications, and the potential to survive in the new era of effective hard tissue fabrication. The similarity of the materials with human bone histomorphometry makes them conducive to use in hard tissue engineering scheme. The key objective of this manuscript is to explore the applications of bioceramics-based AM in bone tissue engineering. Furthermore, the article comprehensively and categorically summarizes some novel bioceramics based AM techniques for the restoration of bones. At prior stages of this article, different ceramics processing AM techniques have been categorized, subsequently, processing of frequently used materials for bone implants and complexities associated with these materials have been elaborated. At the end, some novel applications of bioceramics in orthopedic implants and some future directions are also highlighted to explore it further. This review article will help the new researchers to understand the basic mechanism and current challenges in neophyte techniques and the applications of bioceramics in the orthopedic prosthesis.

Reconsidering Osteoconduction in the Era of Additive Manufacturing

Bone regeneration procedures in clinics and bone tissue engineering stand on three pillars: osteoconduction, osteoinduction, and stem cells. In the last two decades, the focus in this field has been on osteoinduction, which is realized by the use of bone morphogenetic proteins and the application of mesenchymal stem cells to treat bone defects. However, osteoconduction was reduced to a surface phenomenon because the supposedly ideal pore size of osteoconductive scaffolds was identified in the 1990s as 0.3-0.5 mm in diameter, forcing bone formation to occur predominantly on the surface. Meanwhile, additive manufacturing has evolved as a new tool to realize designed microarchitectures in bone substitutes, thereby enabling us to study osteoconduction as a true three-dimensional phenomenon. Moreover, by additive manufacturing, wide-open porous scaffolds can be produced in which bone formation occurs distant to the surface at a superior bony defect-bridging rate enabled by highly osteoconductive pores 1.2 mm in diameter. This review provides a historical overview and an updated definition of osteoconduction and related terms. In addition, it shows how additive manufacturing can be instrumental in studying and optimizing osteoconduction of bone substitutes, and provides novel optimized features and boundaries of osteoconductive microarchitectures. Impact Statement This review updates the definition of osteoconduction and draws clear lines to discriminate between osteoconduction, osseointegration, and osteoinduction. Moreover, additively manufactured libraries of scaffolds revealed that: osteoconduction is more a three-dimensional than a surface phenomenon; microarchitecture dictates defect bridging, which is the measure for osteoconduction; pore diameter or the diagonal of lattice microarchitectures of osteoconductive bone substitutes should be ∼1.2 mm.

A comprehensive review of biodegradable synthetic polymer-ceramic composites and their manufacture for biomedical applications

The application of various materials in biomedical procedures has recently experienced rapid growth. One area that is currently receiving significant attention from the scientific community is the treatment of a number of different types of bone-related diseases and disorders by using biodegradable polymer-ceramic composites. Biomaterials, the most common materials used to repair or replace damaged parts of the human body, can be categorized into three major groups: metals, ceramics, and polymers. Composites can be manufactured by combining two or more materials to achieve enhanced biocompatibility and biomechanical properties for specific applications. Biomaterials must display suitable properties for their applications, about strength, durability, and biological influence. Metals and their alloys such as titanium, stainless steel, and cobalt-based alloys have been widely investigated for implant-device applications because of their excellent mechanical properties. However, these materials may also manifest biological issues such as toxicity, poor tissue adhesion and stress shielding effect due to their high elastic modulus. To mitigate these issues, hydroxyapatite (HA) coatings have been used on metals because their chemical composition is similar to that of bone and teeth. Recently, a wide range of synthetic polymers such as poly (l-lactic acid) and poly (l-lactide-co-glycolide) have been studied for different biomedical applications, owing to their promising biocompatibility and biodegradability. This article gives an overview of synthetic polymer-ceramic composites with a particular emphasis on calcium phosphate group and their potential applications in tissue engineering. It is hoped that synthetic polymer-ceramic composites such as PLLA/HA and PCL/HA will provide advantages such as eliminating the stress shielding effect and the consequent need for revision surgery.

Current state of fabrication technologies and materials for bone tissue engineering

A range of traditional and free-form fabrication technologies have been investigated and, in numerous occasions, commercialized for use in the field of regenerative tissue engineering (TE). The demand for technologies capable of treating bone defects inherently difficult to repair has been on the rise. This quest, accompanied by the advent of functionally tailored, biocompatible, and biodegradable materials, has garnered an enormous research interest in bone TE. As a result, different materials and fabrication methods have been investigated towards this end, leading to a deeper understanding of the geometrical, mechanical and biological requirements associated with bone scaffolds. As our understanding of the scaffold requirements expands, so do the capability requirements of the fabrication processes. The goal of this review is to provide a broad examination of existing scaffold fabrication processes and highlight future trends in their development. To appreciate the clinical requirements of bone scaffolds, a brief review of the biological process by which bone regenerates itself is presented first. This is followed by a summary and comparisons of commonly used implant techniques to highlight the advantages of TE-based approaches over traditional grafting methods. A detailed discussion on the clinical and mechanical requirements of bone scaffolds then follows. The remainder of the manuscript is dedicated to current scaffold fabrication methods, their unique capabilities and perceived shortcomings. The range of biomaterials employed in each fabrication method is summarized. Selected traditional and non-traditional fabrication methods are discussed with a highlight on their future potential from the authors' perspective. This study is motivated by the rapidly growing demand for effective scaffold fabrication processes capable of economically producing constructs with intricate and precisely controlled internal and external architectures. STATEMENT OF SIGNIFICANCE: The manuscript summarizes the current state of fabrication technologies and materials used for creating scaffolds in bone tissue engineering applications. A comprehensive analysis of different fabrication methods (traditional and free-form) were summarized in this review paper, with emphasis on recent developments in the field. The fabrication techniques suitable for creating scaffolds for tissue engineering was particularly targeted and their use in bone tissue engineering were articulated. Along with the fabrication techniques, we emphasized the choice of materials in these processes. Considering the limitations of each process, we highlighted the materials and the material properties critical in that particular process and provided a brief rational for the choice of the materials. The functional performance for bone tissue engineering are summarized for different fabrication processes and the choice of biomaterials. Finally, we provide a perspective on the future of the field, highlighting the knowledge gaps and promising avenues in pursuit of effective scaffolds for bone tissue engineering. This extensive review of the field will provide research community with a reference source for current approaches to scaffold preparation. We hope to encourage the researchers to generate next generation biomaterials to be used in these fabrication processes. By providing both advantages and disadvantage of each fabrication method in detail, new fabrication techniques might be devised that will overcome the limitations of the current approaches. These studies should facilitate the efforts of researchers interested in generating ideal scaffolds, and should have applications beyond the repair of bone tissue.

Lattice Microarchitecture for Bone Tissue Engineering from Calcium Phosphate Compared to Titanium

Additive manufacturing of bone tissue engineering scaffolds will become a key element for personalized bone tissue engineering in the near future. Several additive manufacturing processes are based on extrusion where the deposition of the filament will result in a three-dimensional lattice structure. Recently, we studied diverse lattice structures for bone tissue engineering realized by laser sintering of titanium. In this work, we used lithography-based ceramic manufacturing of lattice structures to produce scaffolds from tricalcium phosphates (TCP) and compared them in vivo to congruent titanium scaffolds manufactured with the identical computer-aided design data to look for material-based differences in bony healing. The results show that, during a 4-week period in a noncritical-size defect in a rabbit calvarium, both scaffolds with the identical microarchitecture performed equally well in terms of bony regeneration and bony bridging of the defect. A significant increase in both parameters could only be achieved when the TCP-based scaffolds were doped with bone morphogenetic protein-2. In a critical-size defect in the calvarial bone of rabbits, however, the titanium scaffold performed significantly better than the TCP-based scaffold, most likely due to its higher mechanical stability. We conclude that titanium and TCP-based scaffolds of the same microarchitecture perform equally well in terms of bone regeneration, provided the microarchitecture meets the mechanical demand at the site of implantation.

Identification of Magnesium Oxychloride Cement Biomaterial Heterogeneity using Raman Chemical Mapping and NIR Hyperspectral Chemical Imaging

The present study investigated spatial heterogeneity in magnesium oxychloride cements within a model of a mould using hyperspectral chemical imaging (HCI). The ability to inspect cements within a mould allows for the assessment of material formation in real time in addition to factors affecting ultimate material formation. Both macro scale NIR HCI and micro scale pixel-wise Raman chemical mapping were employed to characterise the same specimens. NIR imaging is rapid, however spectra are often convoluted through the overlapping of overtone peaks, which can make interpretation difficult. Raman spectra are more easily interpretable, however Raman imaging can suffer from slower acquisition times, particularly when the signal to noise ratio is relatively poor and the spatial resolution is high. To overcome the limitations of both, Raman/NIR data fusion techniques were explored and implemented. Spectra collected using both modalities were co-registered and intra and inter-modality peak correlations were investigated while k-means cluster patterns were compared. In addition, partial least squares regression models, built using NIR spectra, predicted chemical-identifying Raman peaks with an R2 of up to >0.98. As macro scale imaging presented greater data collection speeds, chemical prediction maps were built using NIR HCIs.

3D printing of ceramic-based scaffolds for bone tissue engineering: an overview

Currently, one of the most promising strategies in bone tissue engineering focuses on the development of biomimetic scaffolds. Ceramic-based scaffolds with favorable osteogenic ability and mechanical properties are promising candidates for bone repair. Three-dimensional (3D) printing is an additive manufacturing technique, which allows the fabrication of patient-specific scaffolds with high structural complexity and design flexibility, and gains growing attention. This review aims to highlight advances in 3D printing of ceramic-based scaffolds for bone tissue engineering. Technical limitations and practical challenges are emphasized and design considerations are also discussed.

Calcium phosphate cements for bone engineering and their biological properties

Calcium phosphate cements (CPCs) are frequently used to repair bone defects. Since their discovery in the 1980s, extensive research has been conducted to improve their properties, and emerging evidence supports their increased application in bone tissue engineering. Much effort has been made to enhance the biological performance of CPCs, including their biocompatibility, osteoconductivity, osteoinductivity, biodegradability, bioactivity, and interactions with cells. This review article focuses on the major recent developments in CPCs, including 3D printing, injectability, stem cell delivery, growth factor and drug delivery, and pre-vascularization of CPC scaffolds via co-culture and tri-culture techniques to enhance angiogenesis and osteogenesis.

Different post-processing conditions for 3D bioprinted α-tricalcium phosphate scaffolds

The development of 3D printing hardware, software and materials has enabled the production of bone substitute scaffolds for tissue engineering. Calcium phosphates cements, such as those based on α-tricalcium phosphate (α-TCP), have recognized properties of osteoinductivity, osteoconductivity and resorbability and can be used to 3D print scaffolds to support and induce tissue formation and be replaced by natural bone. At present, however, the mechanical properties found for 3D printed bone scaffolds are only satisfactory for non-load bearing applications. This study varied the post-processing conditions of the 3D powder printing process of α-TCP cement scaffolds by either immersing the parts into binder, Ringer's solution or phosphoric acid, or by sintering in temperatures ranging from 800 to 1500 °C. The porosity, composition (phase changes), morphology, shrinkage and compressive strength were evaluated. The mechanical strength of the post-processed 3D printed scaffolds increased compared to the green parts and was in the range of the trabecular bone. Although the mechanical properties achieved are still low, the high porosity presented by the scaffolds can potentially result in greater bone ingrowth. The phases present in the scaffolds after the post-processing treatments were calcium-deficient hydroxyapatite, brushite, monetite, and unreacted α-TCP. Due to their chemical composition, the 3D printed scaffolds are expected to be resorbable, osteoinductive, and osteoconductive.

Angiogenic and osteogenic regeneration in rats via calcium phosphate scaffold and endothelial cell co-culture with human bone marrow mesenchymal stem cells (MSCs), human umbilical cord MSCs, human induced pluripotent stem cell-derived MSCs and human embryonic stem cell-derived MSCs

Angiogenesis is a limiting factor in regenerating large bone defects. The objective of this study was to investigate angiogenic and osteogenic effects of co-culture on calcium phosphate cement (CPC) scaffold using human umbilical vein endothelial cells (hUVECs) and mesenchymal stem cells (MSCs) from different origins for the first time. hUVECs were co-cultured with four types of cell: human umbilical cord MSCs (hUCMSCs), human bone marrow MSCs (hBMSCs) and MSCs from induced pluripotent stem cells (hiPSC-MSCs) and embryonic stem cells (hESC-MSCs). Constructs were implanted in 8 mm cranial defects of rats for 12 weeks. CPC without cells served as control 1. CPC with hBMSCs served as control 2. Microcapillary-like structures were successfully formed on CPC in vitro in all four co-cultured groups. Microcapillary lengths increased with time (p < 0.05). Osteogenic and angiogenic gene expressions were highly elevated and mineralization by co-cultured cells increased with time (p < 0.05). New bone amount and blood vessel density of co-cultured groups were much greater than controls (p < 0.05) in an animal study. hUVECs co-cultured with hUCMSCs, hiPSC-MSCs and hESC-MSCs achieved new bone and vessel density similar to hUVECs co-cultured with hBMSCs (p > 0.1). Therefore, hUCMSCs, hiPSC-MSCs and hESC-MSCs could serve as alternative cell sources to hBMSCs, which require an invasive procedure to harvest. In conclusion, this study showed for the first time that co-cultures of hUVECs with hUCMSCs, hiPSC-MSCs, hESC-MSCs and hBMSCs delivered via CPC scaffold achieved excellent osteogenic and angiogenic capabilities in vivo. The novel co-culture constructs are promising for bone reconstruction with improved angiogenesis for craniofacial/orthopaedic applications. Copyright © 2017 John Wiley & Sons, Ltd.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

Bioactive calcium phosphate-based glasses and ceramics and their biomedical applications: A review

An overview of the formation of calcium phosphate under in vitro environment on the surface of a range of bioactive materials (e.g. from silicate, borate, and phosphate glasses, glass-ceramics, bioceramics to metals) based on recent literature is presented in this review. The mechanism of bone-like calcium phosphate (i.e. hydroxyapatite) formation and the test protocols that are either already in use or currently being investigated for the evaluation of the bioactivity of biomaterials are discussed. This review also highlights the effect of chemical composition and surface charge of materials, types of medium (e.g. simulated body fluid, phosphate-buffered saline and cell culture medium) and test parameters on their bioactivity performance. Finally, a brief summary of the biomedical applications of these newly formed calcium phosphate (either in the form of amorphous or apatite) is presented.

Dimensional evaluation of patient-specific 3D printing using calcium phosphate cement for craniofacial bone reconstruction

The 3D printing process is highlighted nowadays as a possibility to generate individual parts with complex geometries. Moreover, the development of 3D printing hardware, software and parameters permits the manufacture of parts that can be not only used as prototypes, but are also made from materials that are suitable for implantation. In this way, this study investigates the process involved in the production of patient-specific craniofacial implants using calcium phosphate cement, and its dimensional accuracy. The implants were previously generated in a computer-aided design environment based on the patient's tomographic data. The fabrication of the implants was carried out in a commercial 3D powder printing system using alfa-tricalcium phosphate powder and an aqueous solution of Na₂HPO₄ as a binder. The fit of the 3D printed implants was measured by three-dimensional laser scanning and by checking the right adjustment to the patient's anatomical biomodel. The printed parts presented a good degree of fitting and accuracy.

Designing Biomaterials for 3D Printing

Three-dimensional (3D) printing is becoming an increasingly common technique to fabricate scaffolds and devices for tissue engineering applications. This is due to the potential of 3D printing to provide patient-specific designs, high structural complexity, rapid on-demand fabrication at a low-cost. One of the major bottlenecks that limits the widespread acceptance of 3D printing in biomanufacturing is the lack of diversity in "biomaterial inks". Printability of a biomaterial is determined by the printing technique. Although a wide range of biomaterial inks including polymers, ceramics, hydrogels and composites have been developed, the field is still struggling with processing of these materials into self-supporting devices with tunable mechanics, degradation, and bioactivity. This review aims to highlight the past and recent advances in biomaterial ink development and design considerations moving forward. A brief overview of 3D printing technologies focusing on ink design parameters is also included.

Shape Optimization for Additive Manufacturing of Removable Partial Dentures--A New Paradigm for Prosthetic CAD/CAM

With ever-growing aging population and demand for denture treatments, pressure-induced mucosa lesion and residual ridge resorption remain main sources of clinical complications. Conventional denture design and fabrication are challenged for its labor and experience intensity, urgently necessitating an automatic procedure. This study aims to develop a fully automatic procedure enabling shape optimization and additive manufacturing of removable partial dentures (RPD), to maximize the uniformity of contact pressure distribution on the mucosa, thereby reducing associated clinical complications. A 3D heterogeneous finite element (FE) model was constructed from CT scan, and the critical tissue of mucosa was modeled as a hyperelastic material from in vivo clinical data. A contact shape optimization algorithm was developed based on the bi-directional evolutionary structural optimization (BESO) technique. Both initial and optimized dentures were prototyped by 3D printing technology and evaluated with in vitro tests. Through the optimization, the peak contact pressure was reduced by 70%, and the uniformity was improved by 63%. In vitro tests verified the effectiveness of this procedure, and the hydrostatic pressure induced in the mucosa is well below clinical pressure-pain thresholds (PPT), potentially lessening risk of residual ridge resorption. This proposed computational optimization and additive fabrication procedure provides a novel method for fast denture design and adjustment at low cost, with quantitative guidelines and computer aided design and manufacturing (CAD/CAM) for a specific patient. The integration of digitalized modeling, computational optimization, and free-form fabrication enables more efficient clinical adaptation. The customized optimal denture design is expected to minimize pain/discomfort and potentially reduce long-term residual ridge resorption.

Recent developments and directions in printed nanomaterials

In this review, we survey several recent developments in printing of nanomaterials for contacts, transistors, sensors of various kinds, light-emitting diodes, solar cells, memory devices, and bone and organ implants. The commonly used nanomaterials are classified according to whether they are conductive, semiconducting/insulating or biological in nature. While many printing processes are covered, special attention is paid to inkjet printing and roll-to-roll printing in light of their complexity and popularity. In conclusion, we present our view of the future development of this field.

Effect of layer thickness and printing orientation on mechanical properties and dimensional accuracy of 3D printed porous samples for bone tissue engineering

Powder-based inkjet 3D printing method is one of the most attractive solid free form techniques. It involves a sequential layering process through which 3D porous scaffolds can be directly produced from computer-generated models. 3D printed products' quality are controlled by the optimal build parameters. In this study, Calcium Sulfate based powders were used for porous scaffolds fabrication. The printed scaffolds of 0.8 mm pore size, with different layer thickness and printing orientation, were subjected to the depowdering step. The effects of four layer thicknesses and printing orientations, (parallel to X, Y and Z), on the physical and mechanical properties of printed scaffolds were investigated. It was observed that the compressive strength, toughness and Young's modulus of samples with 0.1125 and 0.125 mm layer thickness were more than others. Furthermore, the results of SEM and μCT analyses showed that samples with 0.1125 mm layer thickness printed in X direction have more dimensional accuracy and significantly close to CAD software based designs with predefined pore size, porosity and pore interconnectivity.