Deformation and fatigue of tough 3D printed elastomer scaffolds processed by fused deposition modeling and continuous liquid interface production

3D Printing Materials and Technologies for Orthopaedic Applications

SUMMARY

3D printing technologies have evolved tremendously over the last decade for uses in orthopaedic surgical applications, including being used to manufacture implants for spine, upper extremity, foot and ankle, oncologic, and traumatic reconstructions. Materials used for 3D-printed orthopaedic devices include metals, degradable and nondegradable polymers, and ceramic composites. There are 2 primary advantages for use of 3D printing technologies for orthopaedics: first, the ability to create complex porous lattices that allow for osseointegration and improved implant stability and second, the enablement of complex geometric designs allowing for patient-specific devices based on preoperative imaging. Given continually evolving technology, and the relatively early stage of the materials and 3D printers themselves, the possibilities for continued innovation in orthopaedics are great.

Future trends of additive manufacturing in medical applications: An overview

Additive Manufacturing (AM) has recently demonstrated significant medical progress. Due to advancements in materials and methodologies, various processes have been developed to cater to the medical sector's requirements, including bioprinting and 4D, 5D, and 6D printing. However, only a few studies have captured these emerging trends and their medical applications. Therefore, this overview presents an analysis of the advancements and achievements obtained in AM for the medical industry, focusing on the principal trends identified in the annual report of AM3DP.

Mechanics of 3D-Printed Polymer Lattices with Varied Design and Processing Strategies

Emerging polymer 3D-printing technologies are enabling the design and fabrication of mechanically efficient lattice structures with intricate microscale structures. During fabrication, manufacturing inconsistencies can affect mechanical efficiency, thereby driving a need to investigate how design and processing strategies influence outcomes. Here, mechanical testing is conducted for 3D-printed lattice structures while altering topology, relative density, and exposure time per layer using digital light processing (DLP). Experiments compared a Cube topology with 800 µm beams and Body-Centered Cube (BCC) topologies with 500 or 800 µm beams, all designed with 40% relative density. Cube lattices had the lowest mean measured relative density of ~42%, while the 500 µm BCC lattice had the highest relative density of ~55%. Elastic modulus, yield strength, and ultimate strength had a positive correlation with measured relative density when considering measurement distributions for thirty samples of each design. BCC lattices designed with 50%, 40%, and 30% relative densities were then fabricated with exposure-per-layer times of 1500 and 1750 ms. Increasing exposure time per layer resulted in higher scaling of mechanical properties to relative density compared to design alteration strategies. These results reveal how design and fabrication strategies affect mechanical performance of lattices suitable for diverse engineering applications.

Polymer 3D Printing Review: Materials, Process, and Design Strategies for Medical Applications

Polymer 3D printing is an emerging technology with recent research translating towards increased use in industry, particularly in medical fields. Polymer printing is advantageous because it enables printing low-cost functional parts with diverse properties and capabilities. Here, we provide a review of recent research advances for polymer 3D printing by investigating research related to materials, processes, and design strategies for medical applications. Research in materials has led to the development of polymers with advantageous characteristics for mechanics and biocompatibility, with tuning of mechanical properties achieved by altering printing process parameters. Suitable polymer printing processes include extrusion, resin, and powder 3D printing, which enable directed material deposition for the design of advantageous and customized architectures. Design strategies, such as hierarchical distribution of materials, enable balancing of conflicting properties, such as mechanical and biological needs for tissue scaffolds. Further medical applications reviewed include safety equipment, dental implants, and drug delivery systems, with findings suggesting a need for improved design methods to navigate the complex decision space enabled by 3D printing. Further research across these areas will lead to continued improvement of 3D-printed design performance that is essential for advancing frontiers across engineering and medicine.

Tailoring nitric oxide release with additive manufacturing to create antimicrobial surfaces

The current use of implantable and indwelling medical is limited due to potential microbial colonization leading to severe ailments. The aim of this work is to develop bioactive polymers that can be customized based on patient needs and help prevent bacterial infection. Potential benefits of additive manufacturing technology are integrated with the antimicrobial properties of nitric oxide (NO) to develop NO-releasing biocompatible polymer interfaces for addressing bacterial infections. Using filament-based additive manufacturing and polycarbonateurethane-silicone (PCU-Sil) a range of films possessing unique porosities (Disk-60, Disk-40, solid, capped) were fabricated. The films were impregnated with S-nitroso-N-acetyl-penicillamine (SNAP) using a solvent-swelling process. The Disk-60 porous films had the greatest amount of SNAP (19.59 wt%) as measured by UV-vis spectroscopy. Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed an even distribution of SNAP throughout the polymer. The films exhibited structure-based tunable NO-release at physiological levels ranging from 7-14 days for solid and porous films, as measured by chemiluminescence. The antibacterial efficacy of the films was studied against Staphylococcus aureus using 24 h in vitro bacterial adhesion assay. The results demonstrated a >99% reduction of viable bacteria on the surface of all the NO-releasing films compared to unmodified PCU-Sil controls. The combination of 3D-printing technology with NO-releasing properties represents a promising technique to develop customized medical devices (such as 3D-scaffolds, catheters, etc.) with distinct NO-release levels that can provide antimicrobial properties and enhanced biocompatibility.

Printability and Shape Fidelity of Bioinks in 3D Bioprinting

Three-dimensional bioprinting uses additive manufacturing techniques for the automated fabrication of hierarchically organized living constructs. The building blocks are often hydrogel-based bioinks, which need to be printed into structures with high shape fidelity to the intended computer-aided design. For optimal cell performance, relatively soft and printable inks are preferred, although these undergo significant deformation during the printing process, which may impair shape fidelity. While the concept of good or poor printability seems rather intuitive, its quantitative definition lacks consensus and depends on multiple rheological and chemical parameters of the ink. This review discusses qualitative and quantitative methodologies to evaluate printability of bioinks for extrusion- and lithography-based bioprinting. The physicochemical parameters influencing shape fidelity are discussed, together with their importance in establishing new models, predictive tools and printing methods that are deemed instrumental for the design of next-generation bioinks, and for reproducible comparison of their structural performance.

3D printing of high-strength, porous, elastomeric structures to promote tissue integration of implants

Despite advances in biomaterials research, there is no ideal device for replacing weight-bearing soft tissues like menisci or intervertebral discs due to poor integration with tissues and mechanical property mismatch. Designing an implant with a soft and porous tissue-contacting structure using a material conducive to cell attachment and growth could potentially address these limitations. Polycarbonate urethane (PCU) is a soft and tough biocompatible material that can be 3D printed into porous structures with controlled pore sizes. Porous biomaterials of appropriate chemistries can support cell proliferation and tissue ingrowth, but their optimal design parameters remain unclear. To investigate this, porous PCU structures were 3D-printed in a crosshatch pattern with a range of in-plane pore sizes (0 to 800 μm) forming fully interconnected porous networks. Printed porous structures had ultimate tensile strengths ranging from 1.9 to 11.6 MPa, strains to failure ranging from 300 to 486%, Young's moduli ranging from 0.85 to 12.42 MPa, and porosity ranging from 13 to 71%. These porous networks can be loaded with hydrogels, such as collagen gels, to provide additional biological support for cells. Bare PCU structures and collagen-hydrogel-filled porous PCU support robust NIH/3T3 fibroblast cell line proliferation over 14 days for all pore sizes. Results highlight PCU's potential in the development of tissue-integrating medical implants.

Controlling release from 3D printed medical devices using CLIP and drug-loaded liquid resins

Mass customization along with the ability to generate designs using medical imaging data makes 3D printing an attractive method for the fabrication of patient-tailored drug and medical devices. Herein we describe the application of Continuous Liquid Interface Production (CLIP) as a method to fabricate biocompatible and drug-loaded devices with controlled release properties, using liquid resins containing active pharmaceutical ingredients (API). In this work, we characterize how the release kinetics of a model small molecule, rhodamine B-base (RhB), are affected by device geometry, network crosslink density, and the polymer composition of polycaprolactone- and poly (ethylene glycol)-based networks. To demonstrate the applicability of using API-loaded liquid resins with CLIP, the UV stability was evaluated for a panel of clinically-relevant small molecule drugs. Finally, select formulations were tested for biocompatibility, degradation and encapsulation of docetaxel (DTXL) and dexamethasone-acetate (DexAc). Formulations were shown to be biocompatible over the course of 175 days of in vitro degradation and the clinically-relevant drugs could be encapsulated and released in a controlled fashion. This study reveals the potential of the CLIP manufacturing platform to serve as a method for the fabrication of patient-specific medical and drug-delivery devices for personalized medicine.