Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....

Polymers for 3D Printing and Customized Additive Manufacturing

Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate ...

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Three-dimensional scaffolds for tissue engineering applications : role of porosity and pore size

https://pure.hw.ac.uk/ws/files/10766137/Melchels2010_Biomaterials_31_24_6121.pdf

A review on stereolithography and its applications in biomedical engineering

Additive manufacturing (AM) technology has been researched and developed for more than 20 years. Rather than removing materials, AM processes make three-dimensional parts directly from CAD models by adding materials layer by layer, offering the beneficial ability to build parts with geometric and material complexities that could not be produced by subtractive manufacturing processes. Through intensive research over the past two decades, significant progress has been made in the development and commercialization of new and innovative AM processes, as well as numerous practical applications in aerospace, automotive, biomedical, energy and other fields. This paper reviews the main processes, materials and applications of the current AM technology and presents future research needs for this technology.

Additive manufacturing: technology, applications and research needs

Bone tissue engineering using 3D printing

This article reports a new process chain for custom-made three-dimensional (3D) porous ceramic scaffolds for bone replacement with fully interconnected channel network for the repair of osseous defects from trauma or disease. Rapid prototyping and especially 3D printing is well suited to generate complex-shaped porous ceramic matrices directly from powder materials. Anatomical information obtained from a patient can be used to design the implant for a target defect. In the 3D printing technique, a box filled with ceramic powder is printed with a polymer-based binder solution layer by layer. Powder is bonded in wetted regions. Unglued powder can be removed and a ceramic green body remains. We use a modified hydroxyapatite (HA) powder for the fabrication of 3D printed scaffolds due to the safety of HA as biocompatible implantable material and efficacy for bone regeneration. The printed ceramic green bodies are consolidated at a temperature of 1250 degrees C in a high temperature furnace in ambient air. The polymeric binder is pyrolysed during sintering. The resulting scaffolds can be used in tissue engineering of bone implants using patient-derived cells that are seeded onto the scaffolds. This article describes the process chain, beginning from data preparation to 3D printing tests and finally sintering of the scaffold. Prototypes were successfully manufactured and characterized. It was demonstrated that it is possible to manufacture parts with inner channels with a dimension down to 450 microm and wall structures with a thickness down to 330 microm. The mechanical strength of dense test parts is up to 22 MPa.

Three-dimensional printing of porous ceramic scaffolds for bone tissue engineering

Nowadays, there is a significant need for synthetic bone replacement materials used in bone tissue engineering (BTE). Rapid prototyping and especially 3D printing is a suitable technique to create custom implants based on medical data sets. 3D printing allows to fabricate scaffolds based on Hydroxyapatite with complex internal structures and high resolution. To determine the in vitro behaviour of cells cultivated on the scaffolds, we designed a special test-part. MC3T3-E1 cells were seeded on the scaffolds and cultivated under static and dynamic setups. Histological evaluation was carried out to characterise the cell ingrowth. In summary, the dynamic cultivation method lead to a stronger population compared to the static cultivation method. The cells proliferated deep into the structure forming close contact to Hydroxyapatite granules.

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Hydroxyapatite scaffolds for bone tissue engineering made by 3D printing.

Bone replacement materials used in tissue engineering require a high degree of safety and biological compatibility. For these reasons synthetic bone replacement materials based on calcium-phosphates are being used more widely. To mimic natural bone, rapid prototyping processes and especially 3D printing are favourable. Using 3D printing, complex 3 dimensional structures can be made easily. 



In this study we successfully performed biocompatibility tests with a Hydroxyapatite test structure (HA-S) made by 3D printing. Cytotoxicity tests were carried out according to DIN ISO 10993-5 in static and dynamic cultivation setups. To estimate cell proliferation and analyze morphology, histological evaluation was done. In summary, good cell viability as well as good proliferation behaviour were found. Moreover, these results show that the 3D printing process in combination with the suitable material presented in this study is well suited for fabricating scaffolds for TE in the required accuracy and biological compatibility.



Biokompatibilitat 3D gedruckter keramischer Scaffolds als Knochenersatz



Knochenersatzmaterialien fur das Tissue Engineering (TE) erfordern ein hohes Mas an Sicherheit und biologischer Vertraglichkeit. Aus diesen Grunden nehmen synthetische Knochenersatzmaterialien auf der Basis von Calciumphosphaten einen immer groser werdenden Stellenwert ein. Um der Struktur des naturlichen Knochens so nahe wie moglich zu kommen, bieten sich Verfahren aus dem Rapid Prototyping, insbesondere das 3D Drucken an. Dadurch lassen sich komplexe, dreidimensionale Strukturen fur das TE einfach herstellen. 



In dieser Studie haben wir erfolgreich eine mittels 3D Drucken hergestellte Struktur (HA-S) auf der Basis von Hydroxylapatit auf ihre Biokompatibilitat getestet. Zytotoxizitatsuntersuchungen wurden analog DIN ISO 10993-5 in statischer und dynamischer Kultivierung durchgefuhrt. Zudem wurden histologische Schnitte zur Beurteilung der Zellproliferation und -morphologie durchgefuhrt. Insgesamt konnte eine gute Zellvitalitat und Zellproliferation nachgewiesen werden. Daruber hinaus zeigen die Ergebnisse, dass das hier vorgestellte 3D Druckverfahren mit dem hier verwendeten Material dazu geeignet ist, Strukturen fur das TE in ausreichender Prazision und biologischer Vertraglichkeit herzustellen.

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Biocompatibility of ceramic scaffolds for bone replacement made by 3D printing

Purpose – To describe the development of a novel polyether(meth)acrylate‐based resin material class for stereolithography with alterable material characteristics.Design/methodology/approach – A complete overview of details to composition parameters, the optimization and bandwidth of mechanical and processing parameters is given. Initial biological characterization experiments and future application fields are depicted. Process parameters are studied in a commercial 3D systems Viper stereolithography system, and a new method to determine these parameters is described herein.Findings – Initial biological characterizations show the non‐toxic behavior in a biological environment, caused mainly by the (meth)acrylate‐based core components. These photolithographic resins combine an adjustable low Young's modulus with the advantages of a non‐toxic (meth)acrylate‐based process material. In contrast to the mostly rigid process materials used today in the rapid prototyping industry, these polymeric formulations are ...

https://www.h-brs.de/files/fb05_tobiasch_rpjournalpaper-vol13-issue1-page38-45.pdf

Non‐toxic flexible photopolymers for medical stereolithography technology

For the fabrication of patient individual bone replacement scaffolds using rapid prototyping (RP) technology, materials with properties adapted to the 3D printing process are needed. First of all the granulate properties of the building material have to match certain specifications concerning particle size and morphology. To fulfil these demands in laboratory scale a commercial fluidized bed granulator was modified to match the specific needs. The changes were tested spraying a sample granulate for the fabrication of synthetic bone grafts. This granulate could successfully be processed in the 3D printer.



Biokeramikgranulate fur die Verwendung in einem 3D Drucker: Verfahrenstechnische Aspekte



Fur die Herstellung von synthetischem Knochenersatz mit rapid prototyping Verfahren werden Baumaterialien mit besonderen Eigenschaften benotigt. Insbesondere das keramische Granulat muss bestimmte Anforderung hinsichtlich Partikelform und -grose erfullen. Um diese Anforderung im Labormasstab erfullen zu konnen, wurde eine kommerzielle Granulationsmaschine an die gegebenen Anforderung angepasst und modifiziert. Die Maschinenmodifikation wurde getestet und ein erstes synthetisches Knochenersatzmaterial hergestellt, dass erfolgreich in einem 3D Drucker verarbeitet werden konnte.

Carsten Dr. Tille

Papers

Three-dimensional printing of porous ceramic scaffolds for bone tissue engineering

Hydroxyapatite scaffolds for bone tissue engineering made by 3D printing.

Biocompatibility of ceramic scaffolds for bone replacement made by 3D printing

Non‐toxic flexible photopolymers for medical stereolithography technology

Bioceramic Granulates for use in 3D Printing: Process Engineering Aspects