Design of Additively Manufactured Structures for Biomedical Applications: A Review of the Additive Manufacturing Processes Applied to the Biomedical Sector

Biomechanical Comparison of Subsidence Between Patient-Specific and Non-Patient-Specific Lumbar Interbody Fusion Cages

STUDY DESIGN

Biomechanical study.

OBJECTIVES

Several strategies to improve the surface of contact between an interbody device and the endplate have been employed to attenuate the risk of cage subsidence. 3D-printed patient-specific cages have been presented as a promising alternative to help mitigate that risk, but there is a lack of biomechanical evidence supporting their use. We aim to evaluate the biomechanical performance of 3D printed patient-specific lumbar interbody fusion cages in relation to commercial cages in preventing subsidence.

METHODS

A cadaveric model is used to investigate the possible advantage of 3D printed patient-specific cages matching the endplate contour using CT-scan imaging in preventing subsidence in relation to commercially available cages (Medtronic Fuse and Capstone). Peak failure force and stiffness were analyzed outcomes for both comparison groups.

RESULTS

PS cages resulted in significantly higher construct stiffness when compared to both commercial cages tested (>59%). PS cage peak failure force was 64% higher when compared to Fuse cage (P < .001) and 18% higher when compared to Capstone cage (P = .086).

CONCLUSIONS

Patient-specific cages required higher compression forces to produce failure and increased the cage-endplate construct' stiffness, decreasing subsidence risk.

Unlocking the future of precision manufacturing: A comprehensive exploration of 3D printing with fiber-reinforced composites in aerospace, automotive, medical, and consumer industries

Rapid advancements in the field of 3D printing in the last several decades have made it possible to produce complex and unique parts with remarkable precision and accuracy. Investigating the use of 3D printing to create various high-performance materials is a relatively new field that is expanding exponentially worldwide. Automobile, biomedical, construction, aerospace, electronics, and metal and alloy industries are among the most prolific users of 3D printing technology. Modern 3D printing technologies, such as polymer matrices that use fiber-reinforced composites (FRCs) to enhance the mechanical qualities of printed components greatly, have been useful to several industries. High stiffness and tensile strength lightweight components are developed from these materials. Fiber-reinforced composites have a wide range of applications, such as military vehicles, fighter aircraft, underwater structures, shelters, and warfare equipment. Fabricating FRCs using fused deposition modeling (FDM) is also advantageous over other 3D printing methods due to its low cost and ease of operation. The impact of different continuous fiber and matrix polymer selections on FRC performance is covered in this review paper. We will also evaluate the important parameters influencing FRC characteristics and review the most recent equipment and methods for fabricating FRCs. Furthermore, the challenges associated with 3D printing fiber-reinforced composites are covered. The constraints of present technology have also been used to identify future research areas.

Electron Beam Powder Bed Fusion of Ti-48Al-2Cr-2Nb Open Porous Scaffold for Biomedical Applications: Process Parameters, Adhesion, and Proliferation of NIH-3T3 Cells

Titanium aluminide (TiAl)-based intermetallics, especially Ti-48Al-2Cr-2Nb, are a well-established class of materials for producing bulky components using the electron beam powder bed fusion (EB-PBF) process. The biological properties of Ti-48Al-2Cr-2Nb alloy have been rarely investigated, specifically using complex cellular structures. This work investigates the viability and proliferation of NIH-3T3 fibroblasts on Ti-48Al-2Cr-2Nb dodecahedral open scaffolds manufactured by the EB-PBF process. A process parameter optimization is carried out to produce a fully dense part. Then scaffolds are produced and characterized using different techniques, including scanning electron microscopy and X-ray tomography. In vitro viability tests are performed with NIH-3T3 cells after incubation for 1, 4, and 7 days. The results show that Ti-48Al-2Cr-2Nb represents a promising new entry in the biomaterial field.

Evaluation of the contact surface between vertebral endplate and 3D printed patient-specific cage vs commercial cage

Biomechanical study. To evaluate the performance of the contact surface for 3D printed patient-specific cages using CT-scan 3D endplate reconstructions in comparison to the contact surface of commercial cages. Previous strategies to improve the surface of contact between the device and the endplate have been employed to attenuate the risk of cage subsidence. Patient-specific cages have been used to help, but only finite-element studies have evaluated the effectiveness of this approach. There is a possible mismatch between the CT-scan endplate image used to generate the cage and the real bony endplate anatomy that could limit the performance of the cages. A cadaveric model is used to investigate the possible mismatch between 3D printed patient-specific cages and the endplate and compare them to commercially available cages (Medtronic Fuse and Capstone). Contact area and contact stress were used as outcomes. When PS cage was compared to the Capstone cage, the mean contact area obtained was 100 ± 23.6 mm² and 57.5 ± 13.7 mm², respectively (p < 0.001). When compared to the Fuse cage, the mean contact area was 104.8 ± 39.6 mm² and 55.2 ± 35.1 mm², respectively(p < 0.001). Patient-specific cages improve the contact area between the implant and the endplate surface, reducing the contact stress and the risk of implant subsidence during LIF surgeries.

Optimisation of the additive manufacturing parameters of polylactic acid (PLA) cellular structures for biomedical applications

Fused deposition modelling (FDM) is an additive manufacturing technology used to create functional and complex geometries directly from computer-generated models. This technique can be utilised to generate cellular structures with controllable pore size, pore shape, and porosity. Cellular structures are fundamental in orthopaedics scaffolds because of its low elastic modulus, high compressive strength, and adequate cell accommodation spaces. This paper aims at investigating and optimising the FDM additive manufacturing process parameters of polylactic Acid (PLA) for two lattice structures namely Schoen Gyroid and Schwarz Primitive. The effect of additive manufacturing critical process parameters including layer height, flow rate, and print speed on the geometrical accuracy and compressive strength of the specimens were analysed. In addition, other parameters that have minimal effect on the geometrical accuracy of the printed parts were discussed. A Full Factorial Analysis (FFA) using Minitab software was undertaken to identify the perfect combination of printing parameters to provide the most geometrically accurate structure. In this study, samples of the Schoen Gyroid and the Schwarz Primitive lattices and a solid control cylinder were 3D printed using the ideal printing combination to assess the manufacturability, the geometrical accuracy, and the mechanical behaviour of both designs. It was found that the optimised FDM process parameters for the studied cellular structures were a layer height of 0.16 mm, a printing speed of 50 mm/s and a flow rate of 90%. As a result of using these parameters, the solid, Schoen Gyroid and Schwarz Primitive specimens demonstrated elastic moduli values of 951 MPa, 264 MPa, and 221 MPa, respectively. In addition, the Schoen Gyroid and the Schwarz Primitive have reached their stress limits at around 8.68 MPa and 7.06 MPa, respectively. It was noticed that the Schoen Gyroid structure exhibited ∼ 18% higher compressive strength and ∼ 16% higher elastic modulus compared to the Schwarz Primitive structure for the same volume fraction of porosity, overall dimensions, and the manufacturing process parameters. Although both structures revealed mechanical properties that fall within the range of the human trabecular bone, but Schoen Gyroid exhibited improved structural integrity performance that is evident by its post-yield behaviour.

3D printing technique applied in vaginoplasty: A case report

Background

We present the first case report of the treatment of congenital vaginal atresia by 3D-printed patient-specific vaginal scaffold from China.

Case presentation

A 17-year-old female patient was referred to our department for treatment of congenital vaginal atresia and complications arising from previous failed operations. Pelvic examination was conducted to understand the morphological characteristics and severity of stenosis, and based on which we designed our prototypes of vaginal scaffold using software UG NX10.0. We finally obtained our patient-specific mold, which was 50 mm in length, 28 mm in diameter, 2 mm of thickness with a whole weight of 7.6 g, and it was made of polycaprolactone. After removing scar tissues caused by vaginal stenosis, an 8 cm long artificial tunnel was created, and then the polycaprolactone (PCL) vaginal mold was placed and sutured. The patient had no discomfort after surgery and was discharged 3 days after the surgery. Follow-up for 1 year after surgery, through hysteroscopy and colposcopy, it was found that the cervix was smooth, the vaginal wall was covered with stratified squamous epithelium, and the vaginal wall was soft and lubricated, which was close to a normal vagina. The incompletely absorbed mold was taken out one year after the operation. Hysteroscopy and colposcopy were performed one year and two years after the mold was taken out. The vagina was unobstructed and the length was about 12 cm. The appearance of the vaginal wrinkles was normal. The patient's quality of sexual life was good.

Conclusion

Our team tried to treat congenital vaginal atresia by 3D-printed patient-specific vaginal scaffold, which can effectively reduce patient complications and reduce patient pain. Through long-term follow-up, we found that this technique has achieved favorable results and improved the patient's quality of sexual life.

3D printing biocompatible materials with Multi Jet Fusion for bioreactor applications

In the evolving three-dimensional (3D) printing technology, the involvement of different materials in any new 3D printing process necessitates a thorough evaluation of the product's biocompatibility for biomedical application. Here, we examined the ability of Multi Jet Fusion (MJF)-printed PA-12 to support cell proliferation and osteogenesis. Our results show that leachate from MJF-printed PA-12 does not inhibit the growth of L929 fibroblast and MC3T3e1 osteoblast. The substrate supports the attachment and proliferation of both cell types, though not at a level comparable to conventional polystyrene culture plate. Neither plasma treatment, poly-D-lysine, nor collagen coatings narrowed the gap substantially, suggesting the possible influence of other limiting factors. The substrate can also support MC3T3e1 osteogenesis. However, MJF-printed PA-12 exhibits varying ability in supporting the proliferation of different cell types, especially in subsequent passages. While L929's proliferation is comparable from passage-to-passage, MC3T3e1's growth ability is noticeably compromised. Interestingly, our results show that L929 subcultured back to polystyrene plate retains the ability to grow as robustly as those on the conventional plate, suggesting that MJF-printed PA-12 does not permanently impair cell proliferation. In addition, we have shown the successful culture of bacterial Escherichia coli on MJF-printed PA-12. Together, our study demonstrated the potential of MJF-printed PA-12 for biological applications.

Use of Polyesters in Fused Deposition Modeling for Biomedical Applications

In recent years, 3D printing techniques experienced a growing interest in several sectors, including the biomedical one. Their main advantage resides in the possibility to obtain complex and personalized structures in a cost-effective way impossible to achieve with traditional production methods. This is especially true for Fused Deposition Modeling (FDM), one of the most diffused 3D printing methods. The easy customization of the final products' geometry, composition and physico-chemical properties is particularly interesting for the increasingly personalized approach adopted in modern medicine. Thermoplastic polymers are the preferred choice for FDM applications, and a wide selection of biocompatible and biodegradable materials is available to this aim. Moreover, these polymers can also be easily modified before and after printing to better suit the body environment and the mechanical properties of biological tissues. This review focuses on the use of thermoplastic aliphatic polyesters for FDM applications in the biomedical field. In detail, the use of poly(ε-caprolactone), poly(lactic acid), poly(lactic-co-glycolic acid), poly(hydroxyalkanoate)s, thermo-plastic poly(ester urethane)s and their blends has been thoroughly surveyed, with particular attention to their main features, applicability and workability. The state-of-the-art is presented and current challenges in integrating the additive manufacturing technology in the medical practice are discussed. This article is protected by copyright. All rights reserved.

Three-Dimensional Printing of Medical Devices Used Directly to Treat Patients: A Systematic Review

Until recently, three-dimensional (3D) printing/additive manufacturing has not been used extensively to create medical devices intended for actual clinical use, primarily on patient safety and regulatory grounds. However, in recent years there have been advances in materials, printers, and experience, leading to increased clinical use. The aim of this study was to perform a structured systematic review of 3D-printed medical devices used directly in patient treatment. A search of 13 databases was performed to identify studies of 3D-printed medical devices, detailing fabrication technology and materials employed, clinical application, and clinical outcome. One hundred and ten papers describing one hundred and forty medical devices were identified and analyzed. A considerable increase was identified in the use of 3D printing to produce medical devices directly for clinical use in the past 3 years. This is dominated by printing of patient-specific implants and surgical guides for use in orthopedics and orthopedic oncology, but there is a trend of increased use across other clinical specialties. The prevailing material/3D-printing technology used were titanium alloy/electron beam melting for implants, and polyamide/selective laser sintering or polylactic acid/fused deposition modeling for surgical guides and instruments. A detailed analysis across medical applications by technology and materials is provided, as well as a commentary regarding regulatory aspects. In general, there is growing familiarity with, and acceptance of, 3D printing in clinical use.

New Insights into the Application of 3D-Printing Technology in Hernia Repair

Abdominal hernia repair using prosthetic materials is among the surgical interventions most widely performed worldwide. These materials, or meshes, are implanted to close the hernial defect, reinforcing the abdominal muscles and reestablishing mechanical functionality of the wall. Meshes for hernia repair are made of synthetic or biological materials exhibiting multiple shapes and configurations. Despite the myriad of devices currently marketed, the search for the ideal mesh continues as, thus far, no device offers optimal tissue repair and restored mechanical performance while minimizing postoperative complications. Additive manufacturing, or 3D-printing, has great potential for biomedical applications. Over the years, different biomaterials with advanced features have been successfully manufactured via 3D-printing for the repair of hard and soft tissues. This technological improvement is of high clinical relevance and paves the way to produce next-generation devices tailored to suit each individual patient. This review focuses on the state of the art and applications of 3D-printing technology for the manufacture of synthetic meshes. We highlight the latest approaches aimed at developing improved bioactive materials (e.g., optimizing antibacterial performance, drug release, or device opacity for contrast imaging). Challenges, limitations, and future perspectives are discussed, offering a comprehensive scenario for the applicability of 3D-printing in hernia repair.

Three-Dimensional Engineered Peripheral Nerve: Toward a New Era of Patient-Specific Nerve Repair Solutions

Reconstruction of peripheral nerve injuries (PNIs) with substance loss remains challenging because of limited treatment solutions and unsatisfactory patient outcomes. Currently, nerve autografting is the first-line management choice for bridging critical-sized nerve defects. The procedure, however, is often complicated by donor site morbidity and paucity of nerve tissue, raising a quest for better alternatives. The application of other treatment surrogates, such as nerve guides, remains questionable, and it is inefficient in irreducible nerve gaps. More importantly, these strategies lack customization for personalized patient therapy, which is a significant drawback of these nerve repair options. This negatively impacts the fascicle-to-fascicle regeneration process, critical to restoring the physiological axonal pathway of the disrupted nerve. Recently, the use of additive manufacturing (AM) technologies has offered major advancements to the bioengineering solutions for PNI therapy. These techniques aim at reinstating the native nerve fascicle pathway using biomimetic approaches, thereby augmenting end-organ innervation. AM-based approaches, such as three-dimensional (3D) bioprinting, are capable of biofabricating 3D-engineered nerve graft scaffolds in a patient-specific manner with high precision. Moreover, realistic in vitro models of peripheral nerve tissues that represent the physiologically and functionally relevant environment of human organs could also be developed. However, the technology is still nascent and faces major translational hurdles. In this review, we spotlighted the clinical burden of PNIs and most up-to-date treatment to address nerve gaps. Next, a summarized illustration of the nerve ultrastructure that guides research solutions is discussed. This is followed by a contrast of the existing bioengineering strategies used to repair peripheral nerve discontinuities. In addition, we elaborated on the most recent advances in 3D printing and biofabrication applications in peripheral nerve modeling and engineering. Finally, the major challenges that limit the evolution of the field along with their possible solutions are also critically analyzed.

Topological, Mechanical and Biological Properties of Ti6Al4V Scaffolds for Bone Tissue Regeneration Fabricated with Reused Powders via Electron Beam Melting

Cellularized scaffold is emerging as the preferred solution for tissue regeneration and restoration of damaged functionalities. However, the high cost of preclinical studies creates a gap between investigation and the device market for the biomedical industry. In this work, bone-tailored scaffolds based on the Ti6Al4V alloy manufactured by electron beam melting (EBM) technology with reused powder were investigated, aiming to overcome issues connected to the high cost of preclinical studies. Two different elementary unit cell scaffold geometries, namely diamond (DO) and rhombic dodecahedron (RD), were adopted, while surface functionalization was performed by coating scaffolds with single layers of polycaprolactone (PCL) or with mixture of polycaprolactone and 20 wt.% hydroxyapatite (PCL/HA). The mechanical and biological performances of the produced scaffolds were investigated, and the results were compared to software simulation and experimental evidence available in literature. Good mechanical properties and a favorable environment for cell growth were obtained for all combinations of scaffold geometry and surface functionalization. In conclusion, powder recycling provides a viable practice for the biomedical industry to strongly reduce preclinical costs without altering biomechanical performance.

Additive Manufacturing Processes in Medical Applications

Additive manufacturing (AM, 3D printing) is used in many fields and different industries. In the medical and dental field, every patient is unique and, therefore, AM has significant potential in personalized and customized solutions. This review explores what additive manufacturing processes and materials are utilized in medical and dental applications, especially focusing on processes that are less commonly used. The processes are categorized in ISO/ASTM process classes: powder bed fusion, material extrusion, VAT photopolymerization, material jetting, binder jetting, sheet lamination and directed energy deposition combined with classification of medical applications of AM. Based on the findings, it seems that directed energy deposition is utilized rarely only in implants and sheet lamination rarely for medical models or phantoms. Powder bed fusion, material extrusion and VAT photopolymerization are utilized in all categories. Material jetting is not used for implants and biomanufacturing, and binder jetting is not utilized for tools, instruments and parts for medical devices. The most common materials are thermoplastics, photopolymers and metals such as titanium alloys. If standard terminology of AM would be followed, this would allow a more systematic review of the utilization of different AM processes. Current development in binder jetting would allow more possibilities in the future.

Discovery of New Ti-Based Alloys Aimed at Avoiding/Minimizing Formation of α” and ω-Phase Using CALPHAD and Artificial Intelligence

In this work, we studied a Ti-Nb-Zr-Sn system for exploring novel composition and temperatures that will be helpful in maximizing the stability of β phase while minimizing the formation of α” and ω-phase. The Ti-Nb-Zr-Sn system is free of toxic elements. This system was studied under the framework of CALculation of PHAse Diagram (CALPHAD) approach for determining the stability of various phases. These data were analyzed through artificial intelligence (AI) algorithms. Deep learning artificial neural network (DLANN) models were developed for various phases as a function of alloy composition and temperature. Software was written in Python programming language and DLANN models were developed utilizing TensorFlow/Keras libraries. DLANN models were used to predict various phases for new compositions and temperatures and provided a more complete dataset. This dataset was further analyzed through the concept of self-organizing maps (SOM) for determining correlations between phase stability of various phases, chemical composition, and temperature. Through this study, we determined candidate alloy compositions and temperatures that will be helpful in avoiding/minimizing formation of α” and ω-phase in a Ti-Zr-Nb-Sn system. This approach can be utilized in other systems such as ω-free shape memory alloys. DLANN models can even be used on a common Android mobile phone.

Influence of the Surface Roughness of PEEK GRF30 and Ti6Al4V SLM on the Viability of Primary Human Osteoblasts Determined by the MTT Test

The aim of the study was to clearly determine whether selected modern medical materials and three dimensional printing allow for satisfactory viability of human osteoblasts, which is important from the point of view of the subsequent osseointegration process. Moreover, as implants are produced with various topography, the influence of surface roughness on viability of bone cells was evaluated. To conduct the research, primary human osteoblasts (PromoCell) were used. Cells were seeded on samples of glass-reinforced polyetheretherketone (30% of the filling), Ti6Al4V manufactured with the use of selective laser melting technology and forged Ti6Al4V with appropriately prepared variable surface roughness. To assess the viability of the tested cells the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was used. Results showed that all evaluated materials do not exhibit cytotoxic properties. Moreover, on their basis it can be concluded that there is a certain surface topography (designated i.a. as roughness equal to approx. Ra = 0.30 μm), which ensures the highest possible viability of human osteoblasts. On the basis of the received data, it can also be concluded that modern glass-reinforced polyetheretherketone or Ti6Al4V produced by rapid prototyping method allow to manufacture implants that should be effectively used in clinical conditions.

A Metal Powder Bed Fusion Process in Industry: Qualification Considerations

An additive manufacturing process should produce repeatable results as far as the properties of the material and the geometric dimensions that have to be adopted by a company as a production method are concerned. This represents a challenge for such high-volume sectors as the automotive industry, where quality and reliability are extremely important. One way of addressing this challenge is to qualify the process. A common framework has here been identified starting from the analysis of the factors that influence the stability of the result in the main phases of metal powder bed fusion (PBF) processes. A qualification procedure (QP), which offers possible solutions to help reduce risk factors, has been proposed. This procedure is independent of the industrial sectors, of which type of materials and metal PBF processes, and of the manufacturer of the used PBF system.

Stress analysis in a bone fracture fixed with topology-optimised plates

The design of commercially available fixation plates and the materials used for their fabrication lead to the plates being stiffer than bone. Consequently, commercial plates are prone to induce bone stress shielding. In this study, three-dimensional fixation plates are designed using topology optimisation aiming to reduce the risk of bone stress shielding. Fixation plate designs were optimised by minimising the strain energy for three levels of volume reduction (i.e. 25%, 45% and 75%). To evaluate stress shielding, changes in bone stress due to the different fixation plate designs were determined on the fracture plane of an idealised shaft of a long bone under a four-point bending load considering the effect of a patient walking with crutches of a transverse fractured tibia. Topology optimisation is a viable approach to design less stiff plates with adequate mechanical strength considering high volume reductions, which consequently increased the stress transferred to the bone fracture plane minimising bone stress shielding.