Editorial pubs.acs.org/journal/abseba
Editorial: Special Issue on 3D Printing of Biomaterials to get started experimentally. We are often asked “which is the best type of 3D printing?” to which we respond by noting that the “best” technology depends entirely on the desired material and specific research question or application. Biomaterials fabrication by 3D printing adds important new design constraints to an already complicated manufacturing process, and we note that specific biomaterials are only compatible with a selection of 3D printing approaches. For example, titanium scaffolds can be produced by electron beam melting of powder in a high vacuum, but not by melt extrusion in air due to oxidation. In contrast, soft, hydrated hydrogels require delicate handling, and sometimes even call for design of custom 3D printing systems, to preserve the material integrity.2−4 By first identifying the application of interest and then selecting a particular biomaterial or scaffold architecture, the best methodologies for fabrication will quickly become apparent. Further, the translational potential of 3D printed biomaterials is supported by two important developments. First, there are now numerous examples where 3D printed materials have been successfully implanted into patients, both in humans5 and in the veterinary field,6,7 which exemplifies the significant progress that is being made in the field. Second, because 3D printing makes use of automation equipment, the technology inherently affords reproducibility, reliability, and robustness to biomaterial studies, critical characteristics that will facilitate high-throughput screening of fabricated constructs as well as aid in clearance by government oversight bodies such as the U.S. Food & Drug Administration (FDA) and the European Medicines Agency (EMA). With this special issue, we sought to highlight the advances being made in the field of 3D printing, with a particular emphasis on biomaterials. Toward this, we begin with five review articles that cover various aspects of 3D printing from advances in bioprinted materials to new technologies in manufacturing processes, as well as examples of important applications of 3D printed structures such as to vascularize structures and to fabricate tissue constructs to study disease. The next set of papers includes important technological advances in 3D printing, including new printable biomaterials and new processes to produce 3D printed structures. Finally, we have solicited several examples where 3D printing has been used toward specific applications, including in bone and cartilage repair and as placenta models toward the investigation of disease. The results of these studies include diverse 3D printed structures that function at scales from the cellular to tissue levels (Figure 2). We believe that this special issue covers the breadth of this field and highlights advances as we move toward the future.
he field of three-dimensional (3D) printing has evolved tremendously in the past few decades, with low-cost printers now available for home use, and custom machines being developed for large and high-throughput direct manufacturing applications. How did we get here? 3D printing was originally developed to allow rapid prototyping of plastic parts that would later be mass-produced by injection molding. In his 1984 US patent, Charles Hull described a “desirability for further improvement in more rapid, reliable, economical and automatic means which would facilitate quickly moving from a design stage to the prototype stage and to production”.1 Intriguingly, the historic application of 3D printing to fabricate and screen prototypes perfectly encapsulates the current needs of scientists and engineers toward the production of biomaterial scaffolds. Biomaterials researchers have never had more materials at their disposal, with significant advances in metals, ceramics, polymers, and composites over the past decades. 3D printing affords the ability to construct these materials in any desired shape and size, either with porosity or as solid materials, and with increasingly high resolution as fabrication processes are improved. There are a plethora of technologies that can be used for the printing of biomaterials, from extrusion-based printing to laser-based approaches (Figure 1). Moreover, the growing
T
Figure 1. 3D printing methods commonly adapted for biomaterials fabrication. Extrusion printing and inkjet printing rely on liquid intermediates or precursors which can solidify quickly after ejection. Selective laser sintering provides localized heating to melt or fuse powder granules. Stereolithography relies on photoinduced polymerization of a liquid resin in the specific regions exposed to light. (Artwork by Jacob Albritton and Jordan Miller).
commoditization of 3D printing equipment and the concomitant rise in its accessibility is now providing ripe opportunities for scientists and engineers to harness this unique manufacturing approach to answer fundamental questions in biology. To a new biomaterials researcher, with access to a burgeoning array of natural and synthetic biomaterials combined with the plethora of 3D printing approaches being developed or refined, it can seem daunting just to decide how © 2016 American Chemical Society
Special Issue: 3D Bioprinting Received: September 20, 2016 Published: October 10, 2016 1658
DOI: 10.1021/acsbiomaterials.6b00566 ACS Biomater. Sci. Eng. 2016, 2, 1658−1661
ACS Biomaterials Science & Engineering
Editorial
Figure 2. Diverse 3D printed structures. A range of 3D printing techniques were used to produce 3D printed structures that exhibit topography to influence cell behavior, that place cells within 3D hydrogels, that introduce controlled porosity and channels, and that replicate tissue structures. These advances are made with a wealth of biomaterial components and are advancing applications such as drug screening and tissue repair. (Artwork from various articles included within this Special Issue. Left to right: Hinton et al.,18 Rhee et al.,21 Warner et al.,16 Kuo et al.23 (top), Hung et al.22 (bottom), Bhattacharjee et al.19).
■
■
REVIEWS ON 3D PRINTING
TECHNOLOGICAL ADVANCES IN 3D PRINTING There are numerous technological advances being made in the biomaterial component of 3D printing, either with new materials and composites to be printed or in new printing processes that are expanding printing resolution or our ability to control material structure. Several classes of materials are more widely printed, including hydrogels (e.g., alginates) or polyesters (e.g., polylactic acid). In a first study, Narayanan et al.13 report on the combination of these materials to incorporate advantages of both material systems, including the benefits of a hydrated hydrogel and the incorporation of nanofibers based on polylactic acid. Proof-of-concept of the printing of the biomaterial formulation was illustrated with adipose-derived stem cells and knee meniscus structures, and the nanofibers increased cell proliferation. Such a composite approach may be useful for numerous applications in tissue repair. Expanding on the use of hydrogel inks in 3D printing, Ouyang et al.14 report on the development of shear-thinning hydrogels from hyaluronic acid and their use in extrusion-based printing. The study highlights the ability to harness the shearthinning properties for improved hydrogel extrusion and then a secondary photo-cross-linking to stabilize the hydrogel structure. Printed structures with great resolution and stability were only possible through the combination of both of these properties. Woodfield and co-workers15 then report on the development of a ruthenium and sodium persulfate initiation system that cures hydrogels in the presence of visible light. This approach was compatible for the curing of gelatin-based inks and supported the printing of viable cells. Importantly, the initiation system overcame oxygen inhibition to produce constructs from photo-cross-linkable hydrogels with high shape fidelity. As another example of photo-cross-linkable materials, Chen and co-workers16 present their work on the printing of structures with fractal patterns using photopolymerizable inks and maskless stereolithography. Printed structures were then modified to promote cell adhesion and the topography influenced the organization of cells. The extrusion-based printing of biomaterial inks relies on a balance of material viscosity and then stabilization upon extrusion to form constructs, which can be conducted with light, solvent evaporation, or temperature. Mikos and colleagues17 evaluate the processing of poly(propylene fumarate) (PPF) into 3D scaffolds with extrusion techniques,
The field of 3D printing is moving forward at a rapid pace. We begin the issue with a review by Jose et al.8 that covers the evolution of the field and advances that are being made in both bioinks that are useful in 3D printing and in new techniques for additive manufacturing. This review positions the field for the new advances described in the original review articles included in this issue and also provides commentary on where the field is heading. The next review by Guvendiren et al.9 provides a comprehensive summary on the various biomaterial inks that are being developed for 3D printing applications, ranging from polymers to ceramics. The goal for these inks is to control properties such as mechanics, degradation, and bioactivity. The field is moving to design better materials with good control over such properties, as well as compatibility with evolving 3D printing processes. The applications of 3D printing in biomedicine are only expanding with the technology; however, tissue repair and regeneration has been a major focus, whether for therapeutic application or toward disease models for in vitro study. The review by Malheiro et al.10 highlights the range of techniques that have now been developed to fabricate 3D constructs with vascular structures, including molding and cell patterning, as well as advances in bioprinting. Such approaches are needed to fabricate larger clinically relevant constructs for tissue repair to overcome issues with the diffusion of nutrients to cells, as well as in mechanistic studies of biological processes such as angiogenesis. Next, Zhang et al.11 provide a review on work that has been done to use bioprinting to replicate the complexity of the cancer microenvironment, such as spatially positioning various cell types and modulating the local extracellular matrix. Such structures are useful to study cancer biology and toward the screening of drug candidates and are likely to have a great impact on how the field approaches the consideration of new therapies. Another review by Jang et al.12 summarizes work toward the generation of 3D tissue models for use in drug testing and understanding disease mechanisms. Importantly, 3D printing allows the creation of complex structures where cells, biomolecules, and materials can be controlled with great precision. 1659
DOI: 10.1021/acsbiomaterials.6b00566 ACS Biomater. Sci. Eng. 2016, 2, 1658−1661
ACS Biomaterials Science & Engineering
Editorial
and co-workers,24 outlines the process of advancing patient specific implants with consideration of progression through the FDA approval process. This is illustrated with patient specific imaging information and the laser sintering of PCL to form scaffolds for both pediatric airway and bone formation applications. Ultimately, these examples only highlight the large amount of work that is being done in the 3D printing of biomaterials, advancing the field since the first observations by Hull, more than three decades ago. As new biomaterial formulations are synthesized and new technologies are advanced, the applications of 3D printing from therapeutics to drug screening will only expand and add to the impact that 3D printing is making in the area of biomedicine. This progress also depends on the broadening accessibility of hardware so that even more laboratories will be able to explore 3D printing technologies.
through modifications of important properties such as polymer concentration, printing pressure, printing speed, and fiber spacing. PPF materials are important in the tissue engineering field, because of properties of degradability and cell compatibility, and this study increases the understanding of how processing inputs affect important outputs, including pore size and fiber diameter. Beyond extrusion of materials onto a surface and then building of structures layer-by-layer, numerous techniques are being developed where materials can be printed in 3D. Such techniques are expanding our ability to spatially position materials and cells toward more complex printed structures. Feinberg and his lab18 present their work on the use of a freeform reversible embedding technique to print polydimethylsiloxane (PDMS), using a support of Carbopol gel to stabilize the PDMS during printing and curing. This approach led to the printing of various complex structures in 3D space, such as filaments and tubes, and opens up numerous opportunities to expand the use of PDMS in applications such as microfluidics and as cell culture substrates. Angelini and co-workers19 report on their approach to print within 3D materials comprising packed microgels that fluidize with stress and solidify when stress is removed. Such a material system supports the deformation and then healing of printed cells and materials. Here, they report on the use of this approach to print multicellular structures in 3D and then investigate cellular processes over time. To further evaluate this technology, LeBlanc et al.20 report on how fluid instabilities influence the ability to produce high-resolution structures with this printing process, particularly at high speeds. This study evaluates how material viscosity can control these instabilities. Thus, this is an example where a more fundamental understanding of the material rheological properties will aid in our advancement of processing techniques.
Jordan S. Miller Department of Bioengineering, Rice University
Jason A. Burdick
■
Department of Bioengineering, University of Pennsylvania
AUTHOR INFORMATION
Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
■
REFERENCES
(1) Hull, C. W. Apparatus for production of three-dimensional objects by stereolithography. Patent US 4 575 330, 1986. (2) Hinton, T. J.; Jallerat, Q.; Palchesko, R. N.; Park, J. H.; Grodzicki, M. S.; Shue, H.-J.; Ramadan, M. H.; Hudson, A. R.; Feinberg, A. W. Three-dimensional Printing of Complex Biological Structures by Freeform Reversible Embedding of Suspended Hydrogels. Science Adv. 2015, 1 (9), e1500758. (3) Bhattacharjee, T.; Zehnder, S. M.; Rowe, K. G.; Jain, S.; Nixon, R. M.; Sawyer, W. G.; Angelini, T. E. Writing in Granular Gel Medium. Science Adv. 2015, 1 (8), e1500655. (4) Highley, C. B.; Rodell, C. B.; Burdick, J. A. Direct 3D Printing of Shear-thinning Hydrogels into Self-Healing Hydrogels. Adv. Mater. 2015, 27 (34), 5075−9. (5) Zopf, D. A.; Hollister, S. J.; Nelson, M. E.; Ohye, R. G.; Green, G. E. Bioresorbable Airway Splint Created with a Three-dimensional Printer. N. Engl. J. Med. 2013, 368 (21), 2043−5. (6) Sooppan, R.; Paulsen, S. J.; Han, J.; Ta, A. H.; Dinh, P.; Gaffey, A. C.; Venkataraman, C.; Trubelja, A.; Hung, G.; Miller, J. S.; Atluri, P. In Vivo Anastomosis and Perfusion of a Three-dimensionally-printed Construct Containing Microchannel Networks. Tissue Eng., Part C 2016, 22 (1), 1−7. (7) Zhang, B.; Montgomery, M.; Chamberlain, M. D.; Ogawa, S.; Korolj, A.; Pahnke, A.; Wells, L. A.; Masse, S.; Kim, J.; Reis, L.; Momen, A.; Nunes, S. S.; Wheeler, A. R.; Nanthakumar, K.; Keller, G.; Sefton, M. V.; Radisic, M. Biodegradable Scaffold with Built-in Vasculature for Organ-on-a-chip Engineering and Direct Surgical Anastomosis. Nat. Mater. 2016, 15, 669−78. (8) Jose, R. R.; Rodriguez, M. J.; Dixon, T. A.; Omenetto, F.; Kaplan, D. L. Evolution of Bioinks and Additive Manufacturing Technologies for 3D Bioprinting. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/ acsbiomaterials.6b00088. (9) Guvendiren, M.; Molde, J.; Soares, R. M. D.; Kohn, J. Designing Biomaterials for 3D Printing. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00121. (10) Malheiro, A.; Wieringa, P.; Mota, C.; Baker, M.; Moroni, L. Patterning Vasculature: The Role of Biofabrication to Achieve an Integrated Multicellular Ecosystem. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00269.
■
APPLICATIONS OF 3D PRINTING With these types of technological advances being made, 3D printing can now be used for a wide range of applications from tissue repair to disease models. The specific tissue types that have been pursued are endless. As an example in musculoskeletal repair, Bonassar and co-workers21 investigated the printing of collagen-based constructs for the encapsulation of fibrochondrocytes toward the repair of soft tissues. The technique was further developed for the production of heterogeneous constructs with spatially varied mechanical properties and explored specifically for cartilage applications. Adding to this study, Grayson and co-workers22 report on their approach to 3D print decellularized bone matrix particles with polycaprolactone for the repair of bone tissue. In this application, properties such as mechanics and osteoconductivity are important, and the goal was to introduce needed signals through the combination of natural and synthetic biomaterial components. It was determined through numerous in vitro and in vivo studies that this design is promising for bone regeneration. As an example toward the fabrication of constructs to study disease, Kuo et al.23 used bioprinting to construct a placenta model. This was used to investigate cellular interactions toward understanding preeclampsia, which involves impaired trophoblastic invasion. Also, the influence of growth factors (i.e., epidermal growth factor) was investigated. The work represents an example of where 3D printing is used to fabricate constructs to probe disease environments. The last report, by Hollister 1660
DOI: 10.1021/acsbiomaterials.6b00566 ACS Biomater. Sci. Eng. 2016, 2, 1658−1661
ACS Biomaterials Science & Engineering
Editorial
(11) Zhang, Y. S.; Duchamp, M.; Oklu, R.; Ellisen, L. W.; Langer, R.; Khademhosseini, A. Bioprinting the Cancer Microenvironment. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00246. (12) Jang, J.; Yi, H.-G.; Cho, D.-W. 3D Printed Tissue Models. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00129. (13) Narayanan, L. K.; Huebner, P.; Fisher, M. B.; Spang, J. T.; Starly, B.; Shirwaiker, R. A. 3D-Bioprinting of Polylactic Acid Nanofiber-Alginate Hydrogel Bioink Containing Human AdiposeDerived Stem Cells. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/ acsbiomaterials.6b00196. (14) Ouyang, L.; Highley, C. B.; Rodell, C. B.; Sun, W.; Burdick, J. A. 3D Printing of Shear-Thinning Hyaluronic Acid Hydrogels with Secondary Cross-Linking. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00158. (15) Lim, K. S.; Schon, B. S.; Mekhileri, N. V.; Brown, G. C. J.; Chia, C. M.; Prabakar, S.; Hooper, G. J.; Woodfield, T. B. F. New VisibleLight Photoinitiating System for Improved Print Fidelity in GelatinBased Bionks. ACS Biomater. Sci. Eng. 2016, in press. (16) Warner, J.; Soman, P.; Zhu, W.; Tom, M.; Chen, S. Design and 3D Printing of Hydrogel Scaffolds with Fractal Geometries. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00140. (17) Trachtenberg, J. E.; Placone, J. K.; Smith, B. T.; Piard, C. M.; Santoro, M.; Scott, D. W.; Fisher, J. P.; Mikos, A. G. Extrusion-Based 3D Printing of Poly(propylene fumarate) in a Full-Factorial Design. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00026. (18) Hinton, T. J.; Hudson, A.; Pusch, K.; Lee, A.; Feinberg, A. W. 3D Printing PDMS Elastomer in a Hydrophilic Support Bath via Freeform Reversible Embedding. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00170. (19) Bhattacharjee, T.; Gil, C. J.; Marshall, S. L.; Uruena, J. M.; O’Bryan, C. S.; Carstens, M.; Keselowsky, B.; Palmer, G. D.; Ghivizzani, S.; Gibbs, C. P.; Sawyer, W. G.; Angelini, T. E. Liquidlike Solids Support Cells in 3D. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00218. (20) LeBlanc, K. J.; Niemi, S. R.; Bennett, A. I.; Harris, K. L.; Schulze, K. D.; Sawyer, W. G.; Taylor, C.; Angelini, T. E. Stability of High Speed 3D Printing in Liquid-Like Solids. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00184. (21) Rhee, S.; Puetzer, J. L.; Mason, B. N.; Reinhart-King, C. A.; Bonassar, L. J. 3D Bioprinting of Spatially Heterogeneous Collagen Constructs for Cartilage Tissue Engineering. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00288. (22) Hung, B. P.; Naved, B. A.; Nyberg, E. L.; Dias, M.; Holmes, C. A.; Elisseeff, J. H.; Dorafshar, A. H.; Grayson, W. L. ThreeDimensional Printing of Bone Extracellular Matrix for Craniofacial Regeneration. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/ acsbiomaterials.6b00101. (23) Kuo, C.-Y.; Eranki, A.; Placone, J. K.; Rhodes, K. R.; ArandaEspinoza, H.; Fernandes, R.; Fisher, J. P.; Kim, P. C. W. Development of a 3D PriLnted, Bioengineered Placenta Model to Evaluate the Role of Trophoblast Migration in Preeclampsia. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00031. (24) Hollister, S. J.; Flanagan, C. L.; Morrison, R. J.; Patel, J. J.; Wheeler, M. B.; Edwards, S. P.; Green, G. E. Integrating Image-Based Design and 3D Biomaterial Printing to Create Patient Specific Devices within a Design Control Framework for Clinical Translation. ACS Biomater. Sci. Eng. 2016, DOI: 10.1021/acsbiomaterials.6b00332.
1661
DOI: 10.1021/acsbiomaterials.6b00566 ACS Biomater. Sci. Eng. 2016, 2, 1658−1661
