|Year : 2018 | Volume
| Issue : 3 | Page : 209-215
The magic of three-dimensional printing in ophthalmology
John Davis Akkara1, Anju Kuriakose2
1 Department of Ophthalmology, Little Flower Hospital and Research Centre, Angamaly; Department of Glaucoma, Westend Eye Hospital, Cochin, Kerala, India
2 Department of Ophthalmology, Jubilee Mission Medical College, Thrissur, Kerala, India
|Date of Web Publication||17-Dec-2018|
John Davis Akkara
Westend Eye Hospital, Kacheripady, Cochin - 682 018, Kerala
Source of Support: None, Conflict of Interest: None
The technology of three-dimensional (3D) printing has evolved over the past few years with cumulative improvements in the resolution, accuracy, cost-effectiveness, and speed of this highly customizable manufacturing process. Ophthalmologists have designed multiple 3D printed smartphone based fundus cameras with some of the designs available as open-source for all to download and 3D-print. Now, the technology has been used for anything from eyewear and medical devices to printing of live cells and tissues like an artificial cornea. It also has uses in education and surgical planning. The author had the opportunity to work with a 3D printer and make some of these models. The future is bright for innovations in this field as we are only beginning to understand the capabilities of this technology.
Keywords: Artificial cornea, bioprinting, canabrava ring, smartphone fundus camera, three-dimensional printing
|How to cite this article:|
Akkara JD, Kuriakose A. The magic of three-dimensional printing in ophthalmology. Kerala J Ophthalmol 2018;30:209-15
| Introduction|| |
Three-dimensional (3D) printing is a technology which allows virtual 3D objects designed using computer aided design (CAD) software to be manufactured into the real world using a “printer” of sorts. The 3D file, once designed in any CAD software, has to be converted into a Stereolithography (.STL) file. This.STL file is again made ready for the 3D printer using a slicer software into G-Code (.gcode file) and then transferred to the 3D printer using a USB pen drive, by LAN or even wirelessly. The most common type of 3D printer [Figure 1] contains a “printer head” which moves in 2 axes (plus 1 axis by movement of print base), melts a raw material from a spool and deposits it onto the base in a precisely controlled manner. This is done layer by layer for every two dimensional slice of the object model, until the entire 3D structure is completed. This process takes between 20 min and 20 h or more depending on the size, complexity, and resolution of the object being “3D printed.” This is called fused deposition modeling and the common raw materials used are poly lactic acid (PLA), Polyvinyl alcohol and acrylonitrile butadiene styrene (ABS) of which PLA is most biocompatible and ABS is most toxic. More advanced 3D printing technologies like photopolymerization use a liquid raw material and ultra violet curing for faster printing. The author used Google SketchUp Make and Solidworks for the 3D models, Ultimaker Cura software for slicing and Ultimaker 3 for 3D printing. There are also free online software like TinkerCAD which can be used for basic designing for 3D printing.
|Figure 1: Ultimaker 3 - three-dimensional printer showing poly lactic acid filament (green arrow), dual extrusion print head (red arrow), heated build plate (blue arrow), pen drive containing G-code files (yellow arrow), control dial (black arrow) and three-dimensional printed parts of oDocs fundus camera (white circle)|
Click here to view
If you have access to a 3D printer and want to immediately get started with 3D printing, you can download free readymade 3D models from Thingiverse, YouMagine, MyMiniFactory, PinShape or search the internet for STL files using STL Finder. In addition, you will need a slicer software compatible with your 3D printer like Cura (for Ultimaker) or MakerWare (for MakerBot). 3D printers are now not very expensive and start at Rs 20,000 for the lower resolution models.
| Ophthalmic Surgical Instruments and Devices|| |
George et al. noted the feasibility and advantages of 3D printing surgical instruments like faster design to production time and surgeon-specific modifications. Several ophthalmic surgical instruments were prototyped using 3D printing including customized vitreoretinal forceps by Dr. David Chow, blepharoplasty instruments by Kotlus, modified muscle hook by Dr. Donny Suh. Canabrava et al. first designed his pupil expansion device Canabrava's Ring using 3D printing and now it is mass manufactured using polymethyl methacrylate (PMMA). Navajas and Ten Hove. also used 3D printing to make a prototype transconjunctival vitrectomy trocar which they tested in pig eyes. Ruzza et al. designed and validated a 3D printed smart storage glide for preserving and delivering posterior lenticules for descemet stripping automated endothelial keratoplasty. Bhattacharjee also used 3D printing to design a storage case for his B-HEX ring.
Being a 3D printable material which is also biocompatible, PLA has good potential for both 3D printed surgical instruments and drug delivery systems.
| Smartphone-Based Fundus Cameras|| |
There have been several smartphone based fundus cameras including a few which have been 3D printed. The author downloaded, 3D printed, assembled and used two of these models. One of those, named oDocs Fundus [Figure 2], has been open sourced and available for free download along with instructions, on Instructables and Thingiverse. Another one designed by an innovative Egyptian Ophthalmologist– Dr. Ahmed Ateya, was also 3d printed [Figure 3]. Bleicher A reports that Kavya Kopparapu designed yet another 3D printed adapter and also made an artificial intelligence software named Eyeagnosis to diagnose Diabetic Retinopathy from the fundus photos thus obtained. Open indirect ophthalmoscope also known as OWL, designed by the LVPEI Centre for Innovation is partially 3D printed with electronics and lenses added inside. The Portable Eye Examination Kit Retina Imager by Andrew Bastawrous was also 3D printed in the early models.
|Figure 2: Two models of three-dimensional printed fundus adapter for smartphone and a commercial adapter – HopeScope. Dr Ahmed Ateya's adapter (red arrow), oDocs fundus camera fully assembled (blue arrow) and and HopeScope smartphone fundus adapter (green arrow) with 3D-printed insert to fix 28D lens|
Click here to view
|Figure 3: Combined slitlamp and fundus adapter designed by Dr. Ahmed Ateya (photo credits: Dr. Ahmed Ateya)|
Click here to view
| Smartphone Based Slitlamp Imaging|| |
There are several universal smartphone slitlamp adapters available, but Dr. Ahmed Ateya designed a 3D printed universal smartphone microscope adapter [Figure 4] and Dr. Hong designed one for iPhone. Boente et al. took a different approach and used a 3D scanner to measure selected smartphones to design customized, 3D printed smartphone slitlamp adapters. Yet another approach is to do away with the slitlamp entirely and use a small 3D printed imaging adapter such as the visoClip by Dr. Sheng Chiong Hong from oDocs Eye Care.
|Figure 4: Dr. Ahmed Ateya's three-dimensional printed smartphone microscope adapter (red arrow) fixing a smartphone to the observer tube of a Lumera 700 Operating microscope to record surgical videos. Same can be done with slit lamp biomicroscope (photo credits: Dr. Ahmed Ateya)|
Click here to view
| Spectacles and Lenses|| |
Several companies have started to offer customized 3D printed eyeglasses to fit your face shape and your style. You can even design and make your own 3D printed spectacles using the instructions at GlassesUSA or Instructables [Figure 5]. Some companies such as Luxexcel also 3D print lenses for spectacles and a study found that their wavefront error was comparable to regular glass lenses. In addition, advances in 3D printing technology has allowed 3D printing of millimeter-size customized aspheric imaging lenses with sub 7-nm surface roughness, to obtain clear images in an optical pathway.
|Figure 5: Basic model of three-dimensional printed eyeglasses made of poly lactic acid using Ultimaker 3 with files downloaded from thingiverse|
Click here to view
| Devices for Patients|| |
Moon et al. showed that 3D printed personalized moisture chamber spectacles provided a better fitting and higher performance in maintaining periocular humidity than commercially available uniformed moisture chamber spectacles.
Dr. Sivagami from Aravind Eye Hospital, Madurai with the help of AuroLab, designed and 3D printed an eyedrop helper guide for patients [Figure 6].
|Figure 6: Three-dimensional printed Eyedrop Helper designed by Dr. Sivagami (photo credits: Dr. Sivagami and Dr. Annamalai)|
Click here to view
| Modifications to Gadgets and Devices|| |
Smartphone fundus cameras such as DIYretcam and HopeScope use a conventional 20D lens of 50 mm diameter. This can be modified to use a 28D lens of smaller diameter, using a very simple 3D printed holder [Figure 7]. Parts of the Periscreener and its much more advanced version C3 Field Analyzer have been 3D printed. Low cost, 3D printed, customized eyelid crutches were designed and used by Sun et al. as an alternative for traditional custom made eyelid crutches in a patient with bilateral blepharoptosis.
|Figure 7: Three-dimensional printed adapter (red arrow) to help fit the smaller 28D lens in place of regular sized 20D lens in smartphone fundus cameras like HopeScope|
Click here to view
| Teaching Tools for Ophthalmologists and Optometrists|| |
Xie et al. designed and constructed a model eye based on Navarro's model eye using 3D printing with a PMMA aspherical cornea and verified that it simulated the optical parameters of the human eye. This can be used for fundus viewing research and teaching. Adams et al. created 3D printed copies of cadaveric orbital dissections that showed a range of anatomical features suitable for education and training of ophthalmology and optometry trainees. These have several advantages over plastinated specimens including rapid reproduction and avoidance of cultural and ethical issues. Bannon et al. used a CT scan and open source software to create a volume rendering of a pterygopalatine fossa which was then printed using a 3D printer. They proposed that this anatomically accurate model would be useful for ophthalmology, ENT, radiology, and neurosurgery residents. The also suggest that this simpler technique of using a CT scan to make a 3D printable model can be used for making other anatomically correct models. Zhao et al. used 3D printed hemispherical models to simulate various morphologies of anterior corneal surface to teach rigid gas-permeable contact lens fitting. Scawn et al. described the process of using a high resolution 1 mm axial CT scan to create a 3D rendering using Osirix Software, (Pixmeo, Geneva). Then, they refined the 3D model using Mimic Innovation Suite, (Materialise, Brussels) before wrapping using MeshLab software before finally preparing for 3D printing using slicing software which was MakerWare for the MakerBot printer in their case. This model would be useful for teaching and planning orbital surgeries.
Several things in the wetlab can easily be 3D printed. The manikin head for practicing eye surgeries can be modeled and printed, as also model eyeballs and artificial anterior chamber. Some companies such as Bioniko offer 3D printed models of eyeballs for capsulorhexis, phacoemulsification surgery, anterior vitrectomy, iris suturing, pupil expansion devices, manual small incision cataract surgery, corneal suturing, scleral buckling, internal limiting membrane peeling, suprachoroidal MIGS, canaloplasty, strabismus surgery, pterygium with autograft, and other ocular surgery training models. Joag et al. assessed the rhexis training model of Bioniko and found it useful for practicing Capsulorhexis. Cabot et al. evaluated the corneal suturing model of Bioniko and noted marked improvements in corneal suturing skills for trainees practicing on it compared to those who did not.
Famery et al. described the use of a 3D printed iris in an artificial anterior chamber (which can potentially be 3D printed easily) to teach and practice Descemet Membrane Endothelial Keratoplasty in a wet lab.
| Surgical Planning|| |
Dorbandt et al. used CT scans to make 3D prints of the heads of three dogs with orbital and peri-orbital masses and found it useful for surgical planning. Mourits et al. used 3D imaging and 3D printing in a case of microphthalmos with large orbital cyst to delineate the cyst from adjacent bony structures. This helped in planning a customized surgical approach and to design and build a custom orbital floor implant. Furdová et al. used 3D printed models of eye with intraocular tumors to plan stereotactic radiosurgery in 139 choroidal melanomas and 11 ciliary body melanomas. Homolka et al. designed a head phantom to measure radiation eye dosimetry in radiotherapy.
Mourits et al. in 2018 used 3D scan of the face and orbit contour to design and 3D print a PMMA conformer for postenucleation sockets. Kang et al. used a 3D printer to make templates to mold orbital implants, thus using conventional 3D printers as opposed to more expensive biocompatible printers. They used these two part templates to press and mold the conventional biocompatible porous polyethylene with embedded titanium (SYNPOR® Implant Titanium Reinforced Fan Plates; DePuy Synthes, Inc., WestChester, PA) and trim the protruding edges to get the exact 3D structure for the biocompatible material. They reported good results with 11 consecutive orbital wall reconstructions using this technique. Callahan et al. also used similar techniques to make stencil and mold to shape the Molded Medpor Titan (Stryker, Kalamazoo, MI) and titanium mesh implantes that were used in 5 orbital reconstructions. Fan et al. compared 29 orbital reconstruction surgeries that used 3D printed mold to 27 cases using conventional techniques and noted that 3D printing helped to predict precise fracture zone, personalized surgery, allowed true-to-original reconstruction, reduced surgery time and improved accuracy and safety of surgery.
Ruiters et al. reported their use of a customized ocular prosthesis designed using a 3D printed mold of an anophthalmic socket.
| Three-Dimensional Printing Optical Coherence Tomography|| |
Maloca et al. used 3D scans from an SSOCT device (DRI OCT Triton; Topcon, Tokyo, Japan) to 3D print choroidal vessels and OCT Angiography scan from a Zeiss Cirrus HD-OCT Model 5000 with ANGIOPLEX (Review software 126.96.36.1991; Carl Zeiss Meditec, Jena, Germany) to print retinal vessels at the macula in large sizes for study and demonstration purposes. Choi et al. used JPEG images from a spectral domain OCT (Heidelberg Engineering, Heidelberg, Germany) to 3D print an enlarged model of Epiretinal Membrane. They used free and open source software (ImageJ, Blender and MeshLab).
| Toys for Blind|| |
Fittle is an innovative braille puzzle toy for the blind, made using 3D printing. It consists of well-recognized flattened shapes such as key, fish, boat, pig, rocket and so on split into several parts which interconnect to form the whole shape. Each part has one letter of the name of the shape embossed in braille to help guide the puzzle and to teach braille [Figure 8]. These are available as open source 3D printing files on the internet. The second generation of Fittle uses more complex, 3D puzzles like a bear and giraffe.
| Bioprinting|| |
Biazar et al. discussed the current state of 3D bio-printing of tissues and organs which may soon develop to a usable product to solve transplant organ shortage and transplant rejection. Sorkio et al. made 3D cornea-mimicking tissues using human stem cells and laser-assisted bioprinting.
Isaacson et al. used 3D bioprinting to make corneal stroma from a collagen-based bio-ink containing encapsulated corneal keratocytes. They demonstrated high viability of the keratocytes both a day 1 and day 7 post bioprinting thus establishing feasibility of 3D printed corneal transplants.
| Conclusion|| |
3D printing is quickly finding multiple uses in various aspects of ophthalmology and this is just the tip of the iceberg of many more potential uses of this technology. As the technology improves and evolves, it is very likely that customized 3D printed devices, surgical instruments, surgical plans, teaching tools, spectacles, and corneas all would become commonplace along with other uses we have not yet fathomed.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
The authors would like to acknowledge the support of Dr R Venkatesh, Chief Medical Officer of Aravind Eye Hospital, Pondicherry and the Aravind Eye Care System for providing the 3D printer used.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Tinkercad Create 3D Digital Designs with Online CAD. Tinkercad. Available from: http://www.tinkercad.com
[Last accessed on 2018 Oct 25].
YouMagine – YouMagine – Where Makers Collaborate on 3D Designs. YouMagine. Available from: https://www.youmagine.com
. [Last accessed on 2018 Oct 25].
Search Free 3d Models for 3d Printing and 3d Design – STLFinder. Available from: https://www.stlfinder.com/
. [Last accessed on 2018 Oct 25].
Makerbricks I3C 3D Printer (Black): 220v: Amazon.in: Industrial & Scientific. Available from: https://www.amzn.to/2JfvBtF
. [Last accessed on 2018 Oct 25].
George M, Aroom KR, Hawes HG, Gill BS, Love J. 3D printed surgical instruments: The design and fabrication process. World J Surg 2017;41:314-9.
Canabrava S, Diniz-Filho A, Schor P, Fagundes DF, Lopes A, Batista WD. Production of an intraocular device using 3D printing: An innovative technology for ophthalmology. Arq Bras Oftalmol 2015;78:393-4.
Navajas EV, Ten Hove M. Three-dimensional printing of a transconjunctival vitrectomy trocar-cannula system. Ophthalmologica 2017;237:119-22.
Ruzza A, Parekh M, Ferrari S, Salvalaio G, Nahum Y, Bovone C, et al.
Preloaded donor corneal lenticules in a new validated 3D printed smart storage glide for descemet stripping automated endothelial keratoplasty. Br J Ophthalmol 2015;99:1388-95.
Bhattacharjee S. Pupil-expansion ring implantation through a 0.9 mm incision. J Cataract Refract Surg 2014;40:1061-7.
Bhattacharjee S. B-HEX pupil expander: Pupil expansion redefined. Indian J Ophthalmol 2017;65:1407-10.
] [Full text]
Tyler B, Gullotti D, Mangraviti A, Utsuki T, Brem H. Polylactic acid (PLA) controlled delivery carriers for biomedical applications. Adv Drug Deliv Rev 2016;107:163-75.
Hsiao WK, Lorber B, Reitsamer H, Khinast J. 3D printing of oral drugs: A new reality or hype? Expert Opin Drug Deliv 2018;15:1-4.
Raju B, Raju NS, Akkara JD, Pathengay A. Do it yourself smartphone fundus camera-DIYretCAM. Indian J Ophthalmol 2016;64:663-7.
] [Full text]
Myung D, Jais A, He L, Ms M, Blumenkranz MS, et al
. 3D Printed smartphone indirect lens adapter for rapid, high quality retinal imaging smartphone ophthalmoscope. J Mob Technol Med 2014;3:9-15.
Livingstone I, Bastawrous A, Giardini ME, Jordan S. Peek: Portable eye examination kit. The smartphone ophthalmoscope. Invest Ophthalmol Vis Sci 2014;55:1612.
Outgeek Cell Phone Adapter Photography Adapter Mount Microscope Adapter: Amazon in: Sports, Fitness & Outdoors. Available from: https://www.amzn.to/2PqRax1
. [Last accessed on 2018 Oct 26].
Boente C, Tu E, Sayegh R. Slitlamp-mounted smartphone adapters using reverse engineering with 3D scanning and 3D printing. Invest Ophthalmol Vis Sci 2015;56:4103.
Gawedzinski J, Pawlowski ME, Tkaczyk TS. Quantitative evaluation of performance of 3D printed lenses. Opt Eng 2017;56. pii: 084110.
Chen X, Liu W, Dong B, Lee J, Ware HOT, Zhang HF, et al.
High-speed 3D printing of millimeter-size customized aspheric imaging lenses with sub 7 nm surface roughness. Adv Mater 2018;30:e1705683.
Moon CH, Kim JY, Kim MJ, Tchah H, Lim BG, Chung JK. Effect of three-dimensional printed personalized moisture chamber spectacles on the periocular humidity. J Ophthalmol 2016;2016:5039181.
Sun MG, Rojdamrongratana D, Rosenblatt MI, Aakalu VK, Yu CQ. 3D printing for low cost, rapid prototyping of eyelid crutches. Orbit 2018;1-5. doi: 10.1080/01676830.2018.1445760.
Xie P, Hu Z, Zhang X, Li X, Gao Z, Yuan D, et al.
Application of 3-dimensional printing technology to construct an eye model for fundus viewing study. PLoS One 2014;9:e109373.
Adams JW, Paxton L, Dawes K, Burlak K, Quayle M, McMenamin PG.3D printed reproductions of orbital dissections: A novel mode of visualising anatomy for trainees in ophthalmology or optometry. Br J Ophthalmol 2015;99:1162-7.
Bannon R, Parihar S, Skarparis Y, Varsou O, Cezayirli E. 3D printing the pterygopalatine fossa: A negative space model of a complex structure. Surg Radiol Anat 2018;40:185-91.
Zhao F, Wang J, Wang L, Chen L. An approach for simulating the fitting of rigid gas-permeable contact lenses using 3D printing technology. Cont Lens Anterior Eye 2018. pii: S1367-0484(18)30051-1.
Zhao F, Zhao G, Weijie F, Chen L. Application of 3D printing technology in RGPCL simulation fitting. Med Hypotheses 2018;113:74-6.
Scawn RL, Foster A, Lee BW, Kikkawa DO, Korn BS. Customised 3D printing: An innovative training tool for the next generation of orbital surgeons. Orbit 2015;34:216-9.
Bioniko Website for 3D Printed Eye Surgery Simulators. Available from: http://www.bioniko.com/
. [Last accessed on 2018 Oct 26].
Joag MG, Wong J, Murillo JC, Sayed-Ahmed IO, Nanji A, Shalabi NM, et al
. The Bioniko ophthalmic surgery model: An innovative approach for teaching capsulorhexis. Invest Ophthalmol Vis Sci 2014;55:1295.
Cabot F, Chhadva P, Joag M, Aguilar MC, Durkee HA, Arrieta E, et al.
Assessment of corneal suturing performance using the bioniko ophthalmic surgery models in inexperienced vs. experienced ophthalmic surgeons. Invest Ophthalmol Vis Sci 2015;56:1555.
Famery N, Abdelmassih Y, El-Khoury S, Guindolet D, Cochereau I, Gabison EE. Artificial chamber and 3D printed iris: a new wet lab model for teaching Descemet's membrane endothelial keratoplasty. Acta Ophthalmol 2018. doi: 10.1111/aos.13852.
Dorbandt DM, Joslyn SK, Hamor RE. Three-dimensional printing of orbital and peri-orbital masses in three dogs and its potential applications in veterinary ophthalmology. Vet Ophthalmol 2017;20:58-64.
Mourits DL, Wolff J, Forouzanfar T, Ridwan-Pramana A, Moll AC, de Graaf P, et al.
3D orbital reconstruction in a patient with microphthalmos and a large orbital cyst – A case report. Ophthalmic Genet 2016;37:233-7.
Furdová A, Sramka M, Thurzo A, Furdová A. Early experiences of planning stereotactic radiosurgery using 3D printed models of eyes with uveal melanomas. Clin Ophthalmol 2017;11:267-71.
Homolka P, Figl M, Wartak A, Glanzer M, Dünkelmeyer M, Hojreh A, et al.
Design of a head phantom produced on a 3D rapid prototyping printer and comparison with a RANDO and 3M lucite head phantom in eye dosimetry applications. Phys Med Biol 2017;62:3158-74.
Mourits DL, Remmers JS, Tan SH, Moll AC, Hartong DT. An individualized 3-dimensional designed and printed conformer after dermis fat grafting for complex sockets. Ophthalmic Plast Reconstr Surg 2018;34:390-2.
Kang S, Kwon J, Ahn CJ, Esmaeli B, Kim GB, Kim N, et al
. Generation of customized orbital implant templates using 3-dimensional printing for orbital wall reconstruction. Eye (Lond) 2018. doi: 10.1038/s41433-018-0193-1.
Callahan AB, Campbell AA, Petris C, Kazim M. Low-cost 3D printing orbital implant templates in secondary orbital reconstructions. Ophthalmic Plast Reconstr Surg 2017;33:376-80.
Fan B, Chen H, Sun YJ, Wang BF, Che L, Liu SY, et al.
Clinical effects of 3-D printing-assisted personalized reconstructive surgery for blowout orbital fractures. Graefes Arch Clin Exp Ophthalmol 2017;255:2051-7.
Ruiters S, Sun Y, de Jong S, Politis C, Mombaerts I. Computer-aided design and three-dimensional printing in the manufacturing of an ocular prosthesis. Br J Ophthalmol 2016;100:879-81.
Maloca PM, Tufail A, Hasler PW, Rothenbuehler S, Egan C, Ramos de Carvalho JE, et al
. 3D printing of the choroidal vessels and tumours based on optical coherence tomography. Acta Ophthalmol 2017. doi: 10.1111/aos.13637.
Maloca PM, Spaide RF, Rothenbuehler S, Scholl HPN, Heeren T, Ramos de Carvalho JE, et al
. Enhanced resolution and speckle-free three-dimensional printing of macular optical coherence tomography angiography. Acta Ophthalmol 2017. doi: 10.1111/aos.13567.
Choi SW, Kwon HJ, Song WK. Three-dimensional printing using open source software and JPEG images from optical coherence tomography of an epiretinal membrane patient. Acta Ophthalmol 2018;96:e399-e402.
Jain T, Christy B, Das AV, Bhaumik D, Satgunam P. Fittle: A novel braille toy. Optom Vis Sci 2018;95:902-7.
Biazar E, Najafi SM, Heidari KS, Yazdankhah M, Rafiei A, Biazar D.3D bio-printing technology for body tissues and organs regeneration. J Med Eng Technol 2018;42:187-202.
Sorkio A, Koch L, Koivusalo L, Deiwick A, Miettinen S, Chichkov B, et al.
Human stem cell based corneal tissue mimicking structures using laser-assisted 3D bioprinting and functional bioinks. Biomaterials 2018;171:57-71.
Isaacson A, Swioklo S, Connon CJ. 3D bioprinting of a corneal stroma equivalent. Exp Eye Res 2018;173:188-93.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]