If you don't remember your password, you can reset it by entering your email address and clicking the Reset Password button. You will then receive an email that contains a secure link for resetting your password
If the address matches a valid account an email will be sent to __email__ with instructions for resetting your password
The use of 3D printing in Orthopedics is set to transform the way surgeries are planned and executed. The development of X rays and later the CT scan and MRI enabled surgeons to understand the anatomy and condition better and helped plan surgeries on images obtained. 3DGraphy a term used for 3D printed orthopedic patient models and Jigs has gone a step further by providing surgeons with a physical copy of the patient's affected part that can not only be seen but also felt and moved around spatially. Similarly 3D printed Jigs are patient specific devices that are used to ensure optimal screw trajectory and implant placement with minimal exposure. While the use of 3D printed models and Jigs have now become routine, a similar revolution is happening in the field of designing and printing patient specific implants. Metal printing along with enhanced capability to print other biocompatible materials like PEEK and PLA is likely to improve the current implant manufacturing process. On the horizon is another interesting development related to this field – 3D Bio printing. Printing human tissues and organs is considered the final frontier and impressive strides have been made in printing bone graft substitutes and cartilage like material. This paper is an overview of all the current developments and the road ahead in this invigorating field.
3D printing was originally called “rapid prototyping”. It was primarily meant to create prototypes of industrial designs in a quick and inexpensive manner. The technology used was radically different from conventional methods, which were primarily casting or machining. The method used was additive manufacturing or layered manufacturing in which the material passed through an extruder, and its layers were deposited on top of each other in a pre designated manner and fused to form the final product. This three-dimensional product creation was computer control driven and hence very accurate. Currently there are various technologies available for additive manufacturing and these are collectively referred to as 3D printing in popular vernacular language.
In 1984 Charles Hull, the co founder of 3D systems, set the foundation for this industry, when he filed a patent for stereolithography fabrication system.
In this system of manufacturing the layers were added by curing the photopolymers with ultraviolet light lasers. Charles Hull invented STL (Stereolithography) file format, introduced the concept of digital slicing and infill strategies and defined this particular printing process as a “system for generating three-dimensional objects by creating a cross sectional pattern of the object to be formed”. It was in the year 1988 that the technology most commonly used in 3D printing today – Fused Deposition Modeling (FDM) involving special extrusion of plastic material, was developed by Scott Crump and commercialized by Stratasys.
U.S. Patent 5,121,329, June 9, 1989, "Apparatus and Method for Creating Three-Dimensional Objects" (A system and a method for building three-dimensional objects in a layer-by-layer manner via fused deposition modeling).
The patent for this technology expired in the year 2009, and led to an exponential growth in the field with numerous low cost machines being available to end user.
1.1 Various types of 3D printing technologies used for biomedical applications
There are three key types of rapid prototyping technologies used for biomedical applications: Extrusion (Nozzle), Laser, and Printer based (Fig. 1). Of these Nozzle based FDM, laser based SLA and SLS are more commonly used and are described below. Inkjet printing is multi coloured and used for educational and teaching purposes.
In the FDM the product is manufactured by extrusion of tiny beads or streams of material that immediately harden post extrusion to form solid layers (Fig. 2). A filament of material usually thermoplastic or metal wire is fed into the extrusion nozzle head that heats up this filament and extrudes it out turning the process off and on depending on the design giving it the desired shape.
The technology works by converting a special type of plastic typically a liquid photopolymer into a solid three-dimensional object in a layered fashion. The photopolymer is turned into semisolid with heat and it then hardens on contact. The whole process uses ultra violet laser triangulated on to surface using X and Y Scanning mirrors (Fig. 3).
This type of printer can be used to print plastic, metals and ceramic. In this the laser draws the shape of the desired object fusing it together with upcoming layer when a second set of the powder in desired shape is laid down by the laser (Fig. 4). It can be used to create extremely accurate representation as the accuracy is limited only by the laser and the fineness of the raw material powder.
Of these for preparation of 3D Models and Jigs – ABS, Nylon and PLA is used. ABS is the most common, it's tough and non-toxic but it has high melting point and can have unpleasant fumes while printing. PLA is easy to print and is biodegradable however its strength degrades over time and the print has a rough texture. Nylon is tough and inexpensive, but has high temperature requirements. As for metal printing, various approved materials like 316 L, Ti4ALV 6 and Co – Cr alloys are used for printing. Bio plotters can print a variety of biocompatible materials ranging from natural to synthetic products common being Alginate, Chitosan, Collagen and PLA.
For the biomedical use, 3D printing has 4 important uses – First and most common is the development of anatomically bio similar model based on imaging of the patient. These 3DGraphy models help understand the anatomy and the condition better and surgeons can use it to simulate the intended intervention for a better execution. This is also called as 3DGraphy.
The next in chain is developing patient specific tools or Jigs that help in executing surgery with more accuracy and in many cases with minimal invasive techniques. Implant printing has picked up over last one decade with reduction in cost of metal printers. Similarly 3D Bio printing is still in infancy although impressive strides have been made in the field of cartilage and bone graft substitute printing (Fig. 5).
Fig. 53D printing Biosphere – Various Applications of 3D printing in Medicine.
3D printed anatomical models added a new dimension to the imaging evaluation of a patient's condition. A new term called as 3DGraphy is often used to refer to these anatomical models and they offer a distinct advantage over available radiographic techniques such as X-rays and CT Scans. While the conventional radiographic modalities allowed the clinicians to find the anatomical anomalies and pathology, software based reconstructions added more information by extrapolating these into a 3rd spatial dimension. With advent of 3DGraphy, clinicians could not only see but also feel and spatially manipulate them. These 3DGraphy models allowed them to simulate the surgical intervention and plan inventory. Most papers on the subject reported a favorable outcome in terms of reduction in surgical time, improved operative accuracy and a better inventory management.
The first challenge with the printing of these 3DGraphy model was the conversion of medical data files into 3D printable formats. With standardization of protocols like one described by the author – MRCP: Medical rapid Prototyping Computer Tomography Protocol, the process became more smooth lined and accessible.
The availability of many free and paid software ensured that even surgeons with working knowledge of computers can now create a 3D printable file from their own desktop. The commonest softwares used are Osirix (free and paid versions available); Slicer (free version) and MIMICS (paid version by Materialise Inc). Typical Flowchart of the process is as follows:
Depending on the area of interest, the type of material is chosen. For most Orthopedic simulations, ABS is preferred. The surgeons can ream, pass screws and pre-contour the plates and implants. It also gives residents and fellows to practice difficult cases (Fig. 6, Fig. 7). The same model can be sterilized and kept on the operating table with simulation drawn for immediate intra operative referencing (Fig. 8). All this ensures an improved surgical outcome with improved fracture reduction accuracy and correct implant positioning apart from reducing the overall surgical time.
Fig. 63DGraphy Model of an acetabulum with fracture of posterior wall and posterior column.
Patient specific cutting blocks had been already popularized by some Knee replacement manufacturing companies. While most companies have some form of this particular instrumentation system in their armamentarium, Visionaire by Smith Nephew and Signature by Biomet are the most popular. The cutting blocks for tibia and femur are 3D printed in Nylon and the input is either MRI and CT that are processed using the proprietary software developed by Materialise Company.
The use of patient specific jigs in complex trauma started a bit late but is now gaining rapid popularity. It has borrowed heavily from dental applications where these are used to print trajectory guides for dental implantation. Once again the leader in providing the back end service was Materialise, with time however multiple companies like Blue sky are increasingly adopting this technology. Other inexpensive but technologically demanding way is to create negative mold using slicer and/or blender software.
These patient specific jigs allow surgeons to perform surgery with small incision and in many cases in a percutaneous fashion. The jigs are made in ABS and can be customized as per the intended implant usage. Of the most versatile uses, the one involving use of these jigs to fix anterior column of acetabulum through a posterior mini open approach and Jigs for high tibial osteotomy have become very popular.
Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) are the most common metal 3D printing technologies. Both of these use a laser to scan and then selectively fuse/melt the metal powder particles that bind to each other in a layered fashion. The raw materials for both come as powder or in a granular form. The major difference between the two technologies is their ability to print different materials based on the individual technologies. While SLM can print only a single metal, SMLS allows printing various alloys as well as the powder with variable melting points can also fuse at molecular level in this particular technology. The layer height for metal 3D printing varies between 20 and 50 μm and depends on the raw material properties like flow ability, particle size, shape and distribution. The modern metal patterns have an amazing accuracy of less than 0.1 mm making them ideal for high precision press fit orthopedic scenarios (Fig. 9). One of the key highlights here is the extremely small degree of wastage of raw material typically less than 5%.
Metals suitable for printing: Both SLM And DMLS can print a variety of metal and their alloys including Stainless steel, Aluminum and its alloys, Titanium and alloy, Cobalt Chrome and Nickel alloy -Inconel. Even precious metals like Gold, Silver, Platinum and Palladium can be printed; their use being limited to Jewelry designing and manufacturing. The cost of the raw material metal powder depends on the alloy and as a benchmark for 316 L medical grade steel is between 300 and 400 USD per Kg.
4.2 Post processing
In order to improve mechanical properties, Osseo integration and tribology, various post processing techniques may be adopted. These include removal of the loose powder and support structures, thermal annealing, surface blasting, CNC machining, micro machining and polishing. One or more of the above can be adopted depending on the nature of requirement, for e g: A wedge to fill in the acetabular defect may have rough surface finish with an Osseo-integrative blast coating and on the other hand a bearing surface may require thermal annealing and polishing to reduce the wear.
5. Bio-printing
5.1 Basics
3D printing gives a unique versatility by enabling combination of various cells, growth factor and supporting material in sophisticated ways in a desired spatial orientation to create a biological tissue. The bio printing materials are now available in several biocompatible and bio-enabler forms and are typically called as bio inks. There is tremendous interest and explosion in popularity of research involving this in the field of regenerative medicine. In orthopedics two tissues are readily amenable to 3D printing - the cartilages and the bone.
Cartilage disorders today form one of the biggest burdens of treating orthopedic surgeons. For large cartilage defect – autologous chondrocyte implantation: a 2-stage procedure is considered gold standard. The success however depends on the quality and quantity of the patient's autologous cells. Given the fact that the cartilage is immune-privileged and that the heterologous cells can be used in grafting, human derived induced pluripotent cell lines (iPSC) are increasingly being investigated for their potential use in cartilage 3D printing. For support material Nano fibrillated Cellulose (NFC) compositions with either Alginate (A) or hyaluronic acid (HA) hydrogels are being tested. NFC has shown to provide necessary structural and mechanical support conducive for physiological mimetic environment.
Bone Printing: Complex trauma, non-unions, tumors and congenital anomalies often result in situation where there is need of extraneous source of bone other than autologous bone grafts. The materials that are commonly used include Hydroxy apatite and Tri Calcium Phosphate (TCP). The use with growth factors like Bone morphogenic protein (BMP) has enhanced their properties.
Hree-dimensional bio-printed scaffold sleeves with mesenchymal stem cells for enhancement of tendon-to-bone healing in anterior cruciate ligament reconstruction using soft-tissue tendon graft.
3D printing is set to revolutionize many aspects of the way orthopedics is currently practiced. While the very basic printing of anatomical models also known as 3DGraphy has nearly become mainstream, use of patient specific jigs are being increasingly used for complex situations. With falling prices of metal printing, patient specific implants are likely to be norm for revision surgeries and critical bone defects. Tissue printing like the cartilage and bone printing are at the moment in realm of research and further developments will be keenly watched not only in orthopedics but by the entire regenerative medicine field.
References
U.S. Patent 4,575,330 ("Apparatus for production of three-dimensional objects by stereolithography").
U.S. Patent 5,121,329, June 9, 1989, "Apparatus and Method for Creating Three-Dimensional Objects" (A system and a method for building three-dimensional objects in a layer-by-layer manner via fused deposition modeling).
Hree-dimensional bio-printed scaffold sleeves with mesenchymal stem cells for enhancement of tendon-to-bone healing in anterior cruciate ligament reconstruction using soft-tissue tendon graft.
Owing to a Publisher error Declaration of Competing Interest statements were not included in the published versions of the following articles, that appeared in previous issues of Journal of Clinical Orthopaedics and Trauma.
Owing to a Publisher error Declaration of Competing Interest statements were not included in the published versions of the following articles, that appeared in previous issues of Journal of Clinical Orthopaedics and Trauma.
30302-3&id=gr1.jpg){kind=link}
30302-3&id=gr2.jpg){kind=link}
30302-3&id=gr3.jpg){kind=link}
30302-3&id=gr4.jpg){kind=link}
30302-3&id=gr5.jpg){kind=link}
30302-3&id=fx1.jpg){kind=link}
30302-3&id=fx2.jpg){kind=link}
30302-3&id=gr6.jpg){kind=link}
30302-3&id=gr7.jpg){kind=link}
30302-3&id=gr8.jpg){kind=link}
30302-3&id=gr9.jpg){kind=link}