Additive manufacturing of biodegradable porous orthopaedic screw

A novel pedicle screw design to maximize screw-bone interface strength using finite element analysis and design of experiment techniques

STUDY DESIGN

Basic study.

PURPOSE

This study aimed to utilize finite element (FE) analysis and design of experiment (DoE) techniques to propose and optimize a novel pedicle screw design and compare its pull-out force with that of a control device.

OVERVIEW OF LITERATURE

Pedicle screw-based fixation is the gold-standard treatment for spine diseases, particularly in fusion procedures. However, pedicle screw loosening and breakage still occur in osteoporotic and non-osteoporotic patients. This research investigates screw design modifications to enhance screw-bone interface strength and reduce the likelihood of loosening.

METHODS

We conceptualized a novel pedicle screw considering vertebral bone morphology and strength differences. A validated FE model was developed and used in conjunction with DoE to determine the screw՚s optimum geometrical parameters. The FE model was validated through simulation and laboratory experiments using the control device. The optimized thread profiles for cortical bone and cancellous bone were determined, with pull-out force as the primary factor for screw design evaluation.

RESULTS

FE analysis results for the control device closely matched experimental results, with less than 5% difference. The chosen unique pitch/depth ratio showed maximum pull-out force for cortical bone, while DoE enabled the optimization of design parameters for cancellous bone. The optimized pedicle screw exhibited a 15% increase in pull-out force compared to the control device.

CONCLUSIONS

The study proposes a novel pedicle screw design with better pull-out strength than the control device. Combining FE analysis with DoE is an effective approach for screw design optimization, reducing the need for extensive prototyping tests. A two-variable analysis suffices for optimizing cortical bone design parameters, while a multi-variable analysis is more effective for optimizing cancellous bone design parameters.

A Systematic Review of the Contribution of Additive Manufacturing toward Orthopedic Applications

Human bone holds an inherent capacity for repairing itself from trauma and damage, but concerning the severity of the defect, the choice of implant placement is a must. Additive manufacturing has become an elite option due to its various specifications such as patient-specific custom development of implants and its easy fabrication rather than the conventional methods used over the years. Additive manufacturing allows customization of the pore size, porosity, various mechanical properties, and complex structure design and formulation. Selective laser melting, powder bed fusion, electron beam melting, and fused deposition modeling are the various AM methods used extensively for implant fabrication. Metals, polymers, biocrystals, composites, and bio-HEA materials are used for implant fabrication for various applications. A wide variety of polymer implants are fabricated using additive manufacturing for nonload-bearing applications, and β-tricalcium phosphate, hydroxyapatite, bioactive glass, etc. are mainly used as ceramic materials in additive manufacturing due to the biological properties that could be imparted by the latter. For decades metals have played a major role in implant fabrication, and additive manufacturing of metals provides an easy approach to implant fabrication with augmented qualities. Various challenges and setbacks faced in the fabrication need postprocessing such as sintering, coating, surface polishing, etc. The emergence of bio-HEA materials, printing of shape memory implants, and five-dimensional printing are the trends of the era in additive manufacturing.

Polydatin accelerates osteoporotic bone repair by inducing the osteogenesis-angiogenesis coupling of bone marrow mesenchymal stem cells via the PI3K/AKT/GSK-3β/β-catenin pathway

BACKGROUND

Polydatin (POL), a natural stilbenoid, has multiple pharmacological activities. However, its effect on osteoporotic bone defect has not yet been examined. This study was designed to explore the unknown role of POL on osteoporotic bone repair.

METHODS

The effect of POL on osteogenesis and angiogenesis were investigated firstly. Then a series of angiogenesis-related assays were carried out to explore the relationship between osteogenesis and angiogenesis of POL, and the underlying mechanism was further explored. Whereafter, ovariectomy-induced osteoporosis rats with bone defect were treated with POL or placebo, the imageological and histological examinations were conducted to assess the effect of POL on osteoporotic bone repair.

RESULTS

The moderate concentrations (1 μM and 10 μM) of POL enhanced osteogenesis of bone marrow mesenchymal stem cells (BMSCs) and elevated the expression of angiogenic-specific markers. Further research found that POL induced human umbilical vein endothelial cells migration and tube formation through the osteogenesis-angiogenesis coupling of BMSCs, and the POL-induced osteogenesis-angiogenesis coupling was reversed after co-cultured with LY294002, Mechanistically, this was conducted via activating PI3K/AKT/GSK-3β/β-catenin pathway. After that, using osteoporotic bone defect rat model, we observed that POL facilitated osteoporotic bone repair through enhancing osteogenesis and CD31hiEMCNhi type H-positive vessels formation via the PI3K/AKT/GSK-3β/β-catenin pathway.

CONCLUSION

The data above indicated that POL could accelerate osteoporotic bone repair by inducing the osteogenesis-angiogenesis coupling of BMSCs via the PI3K/AKT/GSK-3β/β-catenin pathway, which provided new insight and strategy for osteoporotic bone repair.

Efficacy of 3D printed anatomically equivalent thermoplastic polyurethane guide conduits in promoting the regeneration of critical-sized peripheral nerve defects

Three-dimensional (3D) printing is an emerging tool for creating patient-specific tissue constructs analogous to the native tissue microarchitecture. In this study, anatomically equivalent 3D nerve conduits were developed using thermoplastic polyurethane (TPU) by combining reverse engineering and material extrusion (i.e. fused deposition modeling) technique. Printing parameters were optimized to fabricate nerve-equivalent TPU constructs. The TPU constructs printed with different infill densities supported the adhesion, proliferation, and gene expression of neuronal cells. Subcutaneous implantation of the TPU constructs for three months in rats showed neovascularization with negligible local tissue inflammatory reactions and was classified as a non-irritant biomaterial as per ISO 10993-6. To performin vivoefficacy studies, nerve conduits equivalent to rat's sciatic nerve were fabricated and bridged in a 10 mm sciatic nerve transection model. After four months of implantation, the sensorimotor function and histological assessments revealed that the 3D printed TPU conduits promoted the regeneration in critical-sized peripheral nerve defects equivalent to autografts. This study proved that TPU-based 3D printed nerve guidance conduits can be created to replicate the complicated features of natural nerves that can promote the regeneration of peripheral nerve defects and also show the potential to be extended to several other tissues for regenerative medicine applications.

Osthole accelerates osteoporotic fracture healing by inducing the osteogenesis-angiogenesis coupling of BMSCs via the Wnt/β-catenin pathway

Osthole, a natural coumarin derivative, has been shown to have multiple pharmacological activities. However, its effect on osteoporotic fracture has not yet been examined. This research was designed to explore the unknown role and potential mechanism of osthole on osteoporotic fracture healing. We first evaluated the osteogenic and angiogenic abilities of osthole. Then angiogenesis-related assays were conducted to investigate the relationship between osteogenesis and angiogenesis, and further explore its molecular mechanism. After that, we established osteoporotic fracture model in ovariectomy-induced osteoporosis rats and treated the rats with osthole or placebo. Radiography, histomorphometry, histology, and sequential fluorescent labeling were used to evaluate the effect of osthole on osteoporotic fracture healing. In vitro research revealed that osthole promoted osteogenesis and up-regulated the expression of angiogenic-related markers. Further research found that osthole couldn't facilitate the angiogenesis of human umbilical vein endothelial cells in a direct manner, but it possessed the ability to induce the osteogenesis-angiogenesis coupling of bone marrow mesenchymal stem cells (BMSCs). Mechanistically, this was conducted through activating the Wnt/β-catenin pathway. Subsequently, using ovariectomy-induced osteoporosis tibia fracture rat model, we observed that osthole facilitated bone formation and CD31hiEMCNhi type H-positive capillary formation. Sequential fluorescent labeling confirmed that osthole could effectively accelerate bone formation in the fractured region. The data above indicated that osthole could accelerate osteoporotic fracture healing by inducing the osteogenesis-angiogenesis coupling of BMSCs via the Wnt/β-catenin pathway, which implied that osthole may be a potential drug for treating osteoporosis fracture.

An integrated design strategy coupling additive manufacturing and matrix-assisted pulsed laser evaporation (MAPLE) towards the development of a new concept 3D scaffold with improved properties for tissue regeneration

Bioinspired strategies for scaffold design and optimization were improved by the introduction of Additive Manufacturing (AM), thus allowing for replicating and reproducing complex shapes and structures in a reliable manner, adopting different kinds of polymeric and nanocomposite materials properly combined according to the features of the natural host tissues. Benefiting from recent findings in AM, a Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique was employed for obtaining graphene-like material (GL) uniform coatings on 3D scaffolds for tissue repair strategies, towards the development of a new concept 3D scaffold with controlled morphological/architectural and surface features and mechanical and biological properties. The effect of the material-design combination through an integrated technological approach (i.e., MAPLE deposition of GL on 3D AM PCL scaffolds) was assessed through scanning electron microscopy, atomic force microscopy, contact angle measurements, mechanical measurements and biological analyses (cell viability assay and alkaline phosphatase activity) in conjunction with confocal laser scanning microscopy. The differentiation of hMSCs towards the osteoblast phenotype was also investigated analysing the gene expression profile. The obtained findings provided a further insight into the development of improved strategies for the functionalization or combination of GL with other materials and 3D structures in a hybrid fashion for ensuring a tighter adhesion onto the substrates, improving cell fate over time, without negatively altering the mechanical properties and behaviour of the neat constructs. In particular, the results provided interesting information, making 3D AM GL-coated scaffolds potential candidates for bone tissue engineering.

3D printing in pediatric neurosurgery: experimental study of a novel approach using biodegradable materials

PURPOSE

3D printing technologies have become an integral part of modern life, and the most routinely used materials in reconstructive surgery in children are biodegradable materials. The combination of these two technologies opens up new possibilities for the application of innovative methods in neurosurgery and a patient-centered approach in medical care. The aim of the study was to determine whether a physician without specialized programming and printing skills could independently create materials in a clinical setting for the treatment of patients.

METHODS

We conducted a preclinical study on 15 male Balb-C mice. Cylindrical materials made of polylactic acid (PLA) plastic were 3D printed. Sterilization of the obtained material was performed using a cold plasma sterilizer with hydrogen peroxide vapor and its plasma. The sterile material was implanted subcutaneously into the mice for 30 days, followed by histological examination. Using open-source software for modeling and printing, plates and screws made of PLA plastic were manufactured. The produced components were tested in the biomedical laboratory of the institute.

RESULTS

The histological material showed that no inflammatory changes were observed at the implantation site during the entire observation period. The cellular composition is mainly represented by macrophages and fibroblasts. There was a gradual resolution of the material and its replacement by native tissues. Research conducted to assess the effectiveness of material sterilization in a cold plasma sterilizer demonstrated its high bactericidal efficiency.

CONCLUSION

The method we developed for obtaining biodegradable plates and fixation elements on a 3D printer is easy to use and has demonstrated safety in a preclinical study on an animal model.

Icariin accelerates bone regeneration by inducing osteogenesis-angiogenesis coupling in rats with type 1 diabetes mellitus

BACKGROUND

Icariin (ICA), a natural flavonoid compound monomer, has multiple pharmacological activities. However, its effect on bone defect in the context of type 1 diabetes mellitus (T1DM) has not yet been examined.

AIM

To explore the role and potential mechanism of ICA on bone defect in the context of T1DM.

METHODS

The effects of ICA on osteogenesis and angiogenesis were evaluated by alkaline phosphatase staining, alizarin red S staining, quantitative real-time polymerase chain reaction, Western blot, and immunofluorescence. Angiogenesis-related assays were conducted to investigate the relationship between osteogenesis and angiogenesis. A bone defect model was established in T1DM rats. The model rats were then treated with ICA or placebo and micron-scale computed tomography, histomorphometry, histology, and sequential fluorescent labeling were used to evaluate the effect of ICA on bone formation in the defect area.

RESULTS

ICA promoted bone marrow mesenchymal stem cell (BMSC) proliferation and osteogenic differentiation. The ICA treated-BMSCs showed higher expression levels of osteogenesis-related markers (alkaline phosphatase and osteocalcin) and angiogenesis-related markers (vascular endothelial growth factor A and platelet endothelial cell adhesion molecule 1) compared to the untreated group. ICA was also found to induce osteogenesis-angiogenesis coupling of BMSCs. In the bone defect model T1DM rats, ICA facilitated bone formation and CD31hiEMCNhi type H-positive capillary formation. Lastly, ICA effectively accelerated the rate of bone formation in the defect area.

CONCLUSION

ICA was able to accelerate bone regeneration in a T1DM rat model by inducing osteogenesis-angiogenesis coupling of BMSCs.

Do medical devices contribute to sustainability? The role of innovative polymers and device design

Sustainability of a medical device has not yet become a major issue in public discussions compared to other topics with impact to material performance, clinical application, production economy and environmental pollution. Due to their unique properties, polymers (plastics) allow for multiple, flexible applications in medical device technology. Polymers are part of the majority of disposable and single use medical device and contribute with 3% to the worldwide production of plastics. The global medical polymer market size was valued 19.9 billion US-$ in 2022 and its value projection for 2023 is expected to reach 43.03 billion US-$ Here, a wider concept of related sustainability is introduced for medical devices and their polymer components. A close look on medical device specification reveals that additional properties are required to provide sustainability, such as biodegradability, quality by device design (QbD), as well as an inbuild performance service for patients, healthcare professionals and healthcare providers. The increasing global numbers for chronic and non-communicable diseases require a huge demand for single use medical devices. A careful look at polymer specification and its performance properties is needed, including possible chemical modifications and degradation processes during waste disposal. Bioengineers in charge of design and production of medical devices will only be successful when they apply a holistic and interdisciplinary approach to medical device sustainability.

Forged to heal: The role of metallic cellular solids in bone tissue engineering

Metallic cellular solids, made of biocompatible alloys like titanium, stainless steel, or cobalt-chromium, have gained attention for their mechanical strength, reliability, and biocompatibility. These three-dimensional structures provide support and aid tissue regeneration in orthopedic implants, cardiovascular stents, and other tissue engineering cellular solids. The design and material chemistry of metallic cellular solids play crucial roles in their performance: factors such as porosity, pore size, and surface roughness influence nutrient transport, cell attachment, and mechanical stability, while their microstructure imparts strength, durability and flexibility. Various techniques, including additive manufacturing and conventional fabrication methods, are utilized for producing metallic biomedical cellular solids, each offering distinct advantages and drawbacks that must be considered for optimal design and manufacturing. The combination of mechanical properties and biocompatibility makes metallic cellular solids superior to their ceramic and polymeric counterparts in most load bearing applications, in particular under cyclic fatigue conditions, and more in general in application that require long term reliability. Although challenges remain, such as reducing the production times and the associated costs or increasing the array of available materials, metallic cellular solids showed excellent long-term reliability, with high survival rates even in long term follow-ups.

In vitro fatigue behavior and in vivo osseointegration of the auxetic porous bone screw

The incidence of screw loosening, migration, and pullout caused by the insufficient screw-bone fixation stability is relatively high in clinical practice. To solve this issue, the auxetic unit-based porous bone screw (AS) has been put forward in our previous work. Its favorable auxetic effect can improve the primary screw-bone fixation stability after implantation. However, porous structure affected the fatigue behavior and in vivo longevity of bone screw. In this study, in vitro fatigue behaviors and in vivo osseointegration performance of the re-entrant unit-based titanium auxetic bone screw were studied. The tensile-tensile fatigue behaviors of AS and nonauxetic bone screw (NS) with the same porosity (51%) were compared via fatigue experiments, fracture analysis, and numerical simulation. The in vivo osseointegration of AS and NS were compared via animal experiment and biomechanical analysis. Additionally, the effects of in vivo dynamic tensile loading on the osseointegration of AS and NS were investigated and analyzed. The fatigue strength of AS was approximately 43% lower while its osseointegration performance was better than NS. Under in vivo dynamic tensile loading, the osseointegration of AS and NS both improved significantly, with the maximum increase of approximately 15%. Preferrable osseointegration of AS might compensate for the shortage of fatigue resistance, ensuring its long-term stability in vivo. Adequate auxetic effect and long-term stability of the AS was supposed to provide enough screw-bone fixation stability to overcome the shortages of the solid bone screw, developing the success of surgery and showing significant clinical application prospects in orthopedic surgery. STATEMENT OF SIGNIFICANCE: This research investigated the high-cycle fatigue behavior of re-entrant unit-based auxetic bone screw under tensile-tensile cyclic loading and its osseointegration performance, which has not been focused on in existing studies. The fatigue strength of auxetic bone screw was lower while the osseointegration was better than non-auxetic bone screw, especially under in vivo tensile loading. Favorable osseointegration of auxetic bone screw might compensate for the shortage of fatigue resistance, ensuring its long-term stability and longevity in vivo. This suggested that with adequate auxetic effect and long-term stability, the auxetic bone screw had significant application prospects in orthopedic surgery. Findings of this study will provide a theoretical guidance for design optimization and clinical application of the auxetic bone screw.

Medical 3D printing with polyjet technology: effect of material type and printing orientation on printability, surface structure and cytotoxicity

Due to its high printing resolution and ability to print multiple materials simultaneously, inkjet technology has found wide application in medicine. However, the biological safety of 3D-printed objects is not always guaranteed due to residues of uncured resins or support materials and must therefore be verified. The aim of this study was to evaluate the quality of standard assessment methods for determining the quality and properties of polyjet-printed scaffolds in terms of their dimensional accuracy, surface topography, and cytotoxic potential.Standardized 3D-printed samples were produced in two printing orientations (horizontal or vertical). Printing accuracy and surface roughness was assessed by size measurements, VR-5200 3D optical profilometer dimensional analysis, and scanning electron microscopy. Cytotoxicity tests were performed with a representative cell line (L929) in a comparative laboratory study. Individual experiments were performed with primary cells from clinically relevant tissues and with a Toxdent cytotoxicity assay.Dimensional measurements of printed discs indicated high print accuracy and reproducibility. Print accuracy was highest when specimens were printed in horizontal direction. In all cytotoxicity tests, the estimated mean cell viability was well above 70% (p < 0.0001) regardless of material and printing direction, confirming the low cytotoxicity of the final 3D-printed objects.

A Comprehensive Review of the Current Research Status of Biodegradable Zinc Alloys and Composites for Biomedical Applications

Zinc (Zn)-based biodegradable materials show moderate degradation rates in comparison with other biodegradable materials (Fe and Mg). Biocompatibility and non-toxicity also make them a viable option for implant applications. Furthermore, Pure Zn has poor mechanical behavior, with a tensile strength of around 100-150 MPa and an elongation of 0.3-2%, which is far from reaching the strength required as an orthopedic implant material (tensile strength is more than 300 MPa, elongation more than 15%). Alloy and composite fabrication have proven to be excellent ways to improve the mechanical performance of Zn. Therefore, their alloys and composites have emerged as an innovative category of biodegradable materials. This paper summarizes the most important recent research results on the mechanical and biological characteristics of biodegradable Zn-based implants for orthopedic applications and the most commonly added components in Zn alloys and composites.

Advancement in biological and mechanical behavior of 3D printed poly lactic acid bone plates using polydopamine coating: Innovation for healthcare

The metallic biomaterials have been proclaimed to exhibit stress shielding with discharge of toxic ions, leading to polymeric implants attracting interest in 3D Printing domain. In this study, Poly Lactic Acid based 336 bone plates are fabricated using Fused Filament Fabrication with printing parameters being varied. Polydopamine, being biocompatible, is deposited on fabricated bone plates at varying submersion time, shaker speed and coating solutions concentration. The study involves witnessing the effect of printing and coating parameters on biological behavior of bone plates upon preservation in Simulated Body Fluid and Hank's Balanced Salt Solution. The findings propose the close relation of degradation with apatite growth. The highest degradation rate with significant reduction in mechanical characteristics are shown by uncoated bone plates. These bone plates have porous structure at 20% infill density, 0.5 mm layer height, 0.4 mm wall thickness and 100 mm/s print speed which could result in complete degradation with partial healing of bone fracture. The study suggests the preservation of bone plates coated at 120 h' submersion time and 120 RPM shaker speed in 3 mg/ml concentrated solution which showed lower apatite formation. Thus, the coating would slow down degradation of PLA bone plates, resulting in complete healing of bone fracture.

Biomaterials as Implants in the Orthopedic Field for Regenerative Medicine: Metal versus Synthetic Polymers

Patients suffering bone fractures in different parts of the body require implants that will enable similar function to that of the natural bone that they are replacing. Joint diseases (rheumatoid arthritis and osteoarthritis) also require surgical intervention with implants such as hip and knee joint replacement. Biomaterial implants are utilized to fix fractures or replace parts of the body. For the majority of these implant cases, either metal or polymer biomaterials are chosen in order to have a similar functional capacity to the original bone material. The biomaterials that are employed most often for implants of bone fracture are metals such as stainless steel and titanium, and polymers such as polyethene and polyetheretherketone (PEEK). This review compared metallic and synthetic polymer implant biomaterials that can be employed to secure load-bearing bone fractures due to their ability to withstand the mechanical stresses and strains of the body, with a focus on their classification, properties, and application.

Hyaluronic Acid as Bioink and Hydrogel Scaffolds for Tissue Engineering Applications

Bioprinting is an additive manufacturing technique that focuses on developing living tissue constructs using bioinks. Bioink is crucial in determining the stability of printed patterns, which remains a major challenge in bioprinting. Thus, the choices of bioink composition, modifications, and cross-linking methods are being continuously researched to augment the clinical translation of bioprinted constructs. Hyaluronic acid (HA) is a naturally occurring polysaccharide with the repeating unit of N-acetyl-glucosamine and d-glucuronic acid disaccharides. It is present in the extracellular matrix (ECM) of tissues (skin, cartilage, nerve, muscle, etc.) with a wide range of molecular weights. Due to the nature of its chemical structure, HA could be easily subjected to chemical modifications and cross-linking that would enable better printability and stability. These interesting properties have made HA an ideal choice of bioinks for developing tissue constructs for regenerative medicine applications. In this Review, the physicochemical properties, reaction chemistry involved in various cross-linking strategies, and biomedical applications of HA have been elaborately discussed. Further, the features of HA bioinks, emerging strategies in HA bioink preparations, and their applications in 3D bioprinting have been highlighted. Finally, the current challenges and future perspectives in the clinical translation of HA-based bioinks are outlined.

Controllable Production of Natural Silk Nanofibrils for Reinforcing Silk-Based Orthopedic Screws

As a natural high-performance material with a unique hierarchical structure, silk is endowed with superior mechanical properties. However, the current approaches towards producing regenerated silk fibroin (SF) for the preparation of biomedical devices fail to fully exploit the mechanical potential of native silk materials. In this study, using a top-down approach, we exfoliated natural silk fibers into silk nanofibrils (SNFs), through the disintegration of interfibrillar binding forces. The as-prepared SNFs were employed to reinforce the regenerated SF solution to fabricate orthopedic screws with outstanding mechanical properties (compression modulus > 1.1 GPa in a hydrated state). Remarkably, these screws exhibited tunable biodegradation and high cytocompatibility. After 28 days of degradation in protease XIV solution, the weight loss of the screw was ~20% of the original weight. The screws offered a favorable microenvironment to human bone marrow mesenchymal stem cell growth and spread as determined by live/dead staining, F-action staining, and Alamar blue staining. The synergy between native structural components (SNFs) and regenerated SF solutions to form bionanocomposites provides a promising design strategy for the fabrication of biomedical devices with improved performance.

A road map on synthetic strategies and applications of biodegradable polymers

Biodegradable polymers have emerged as fascinating materials due to their non-toxicity, environmentally benign nature and good mechanical strength. The toxic effects of non-biodegradable plastics paved way for the development of sustainable and biodegradable polymers. The engineering of biodegradable polymers employing various strategies like radical ring opening polymerization, enzymatic ring opening polymerization, anionic ring opening polymerization, photo-initiated radical polymerization, chemoenzymatic method, enzymatic polymerization, ring opening polymerization and coordinative ring opening polymerization have been discussed in this review. The application of biodegradable polymeric nanoparticles in the biomedical field and cosmetic industry is considered to be an emerging field of interest. However, this review mainly highlights the applications of selected biodegradable polymers like polylactic acid, poly(ε-caprolactone), polyethylene glycol, polyhydroxyalkanoates, poly(lactide-co-glycolide) and polytrimethyl carbonate in various fields like agriculture, biomedical, biosensing, food packaging, automobiles, wastewater treatment, textile and hygiene, cosmetics and electronic devices.

Functionally graded additive manufacturing for orthopedic applications

Background

Additive Manufacturing due to its benefits in developing parts with complex geometries and shapes, has evolved as an alternate manufacturing process to develop implants with desired properties. The structure of human bones being anisotropic in nature is biologically functionally graded i,e. The structure possesses different properties in different directions. Therefore, various orthopedic implants such as knee, hip and other bone plates, if functionally graded can perform better. In this context, the development of functionally graded (FG) parts for orthopedic application with tailored anisotropic properties has become easier through the use of additive manufacturing (AM).

Objectives

and Rationale: The current paper aims to study the various aspects of additively manufactured FG parts for orthopedic applications. It presents the details of various orthopedic implants such as knee, hip and other bone plates in a structured manner. A systematic literature review is conducted to study the various material and functional aspects of functionally graded parts for orthopedic applications. A section is also dedicated to discuss the mechanical properties of functionally graded parts.

Conclusion

The literature revealed that additive manufacturing can provide lot of opportunities for development of functionally graded orthopedic implants with improved properties and durability. Further, the effect of various FG parameters on the mechanical behavior of these implants needs to be studied in detail. Also, with the advent of various AM technologies, the functional grading can be achieved by various means e.g. density, porosity, microstructure, composition, etc. By varying the AM parameters. However, the current limitations of cost and material biocompatibility prevent the widespread exploitation of AM technologies for various orthopedic applications.

In-vivo pharmacokinetic studies of Dolutegravir loaded spray dried Chitosan nanoparticles as milk admixture for paediatrics infected with HIV

Dolutegravir (DTG) is an antiretroviral drug approved in the year 2013, and being categorized as a BCS-II molecule, it possesses solubility issues. In order to enhance the solubility and improve its bioavailability, DTG-loaded Chitosan nanoparticles (NPs) were synthesized utilizing spray drying technology. The developed nanoformulation was characterized for its physicochemical properties and investigated for the feasibility of its administration through an oral route along with milk/food as an admixture for paediatric antiretroviral therapy. The in vivo oral bioavailability studies were conducted in Balb-C mice, where the animals were treated with the selected formulation of DTG-loaded Chitosan NPs and compared to pure DTG. The NPs exhibited 2.5-fold increase in the C_max (77.54 ± 7.93 μg/mL) when compared to the pure DTG (30.15 ± 8.06 μg/mL). This phenomenon was further reflected by the improved bioavailability of DTG (AUC: 678.3 ± 10.07 μg/h/mL) in the NPs administered to mice when compared to the AUC of animals administered with pure DTG (405.29 ± 7 μg/h/mL). Altogether, the research findings showed that Chitosan-based NPs were ideal carriers for oral administration of DTG along with milk and exhibited great potential to enhance the bioavailability of the drug and treatment adherence for paediatric HIV patients.

Reverse Manufacturing and 3D Inspection of Mechanical Fasteners Fabricated Using Photopolymer Jetting Technology

Polyjet additive manufacturing is gaining attention owing to its ability to manufacture intricate parts with microscopic resolution. This study investigates the spatial precision of mechanical fasteners utilizing the 3D scanning technology followed by reverse engineering to obtain the accuracy of polyjet fabricated components. Numerous M8 bolts, as well as nuts, are additively manufactured to replace metal fasteners in various industrial fields such as aerospace, medical, electronics, automotive, and food packaging. M8 mild steel fastener was 3D scanned using Carl Zeiss COMET L3D2 3D scanner, and precise details of the products were gathered. Three-dimensional scanning captures a large number of surface points, resulting in a more accurate representation of the object. The gathered data were used to fabricate numerous nuts and bolts utilizing the Object 260 Connex 3 printer utilizing Vero thermoplastic polymer resins. The stability of the 3D printed specimens was investigated using Carl Zeiss COMET L3D2 3D scanner. The fabricated M8 fasteners’ dimensional error is investigated in all orientations and every axes, and the respective dimensional variations are shown in detail. The high-quality production of fasteners through photopolymer jetting met all accuracy criteria and fit within the IT 06 transition fit grade.

Liquid Crystal Modified Polylactic Acid Improves Cytocompatibility and M2 Polarization of Macrophages to Promote Osteogenesis

Liquid crystalline phases (LC phases) are widely present in an organism. The well-aligned domain and liquidity of the LC phases are necessary for various biological functions. How to stabilize the floating LC phases and maintain their superior biology is still under study. In addition, it is unclear whether the exogenous LC state can regulate the immune process and improve osteogenesis. In this work, a series of composite films (PLLA/LC) were prepared using cholesteryl oleyl carbonate (COC), cholesteryl pelargonate (CP), and polylactic acid (PLLA) via a controlled facile one-pot approach. The results showed that the thermo-responsive PLLA/LC films exhibited stable LC phases at human body temperature and the cytocompatibility of the composites was improved significantly after modification by the LC. In addition, the M2 polarization of macrophages (RAW264.7) was enhanced in PLLA/LC films, and the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was improved as co-cultured with macrophages. The in vivo bone regeneration of the materials was verified by calvarial repair, in which the amount of new bone in the PLLA-30% LC group was greater than that in the PLLA group. This work revealed that the liquid crystal-modified PLLA could promote osteogenesis through immunomodulation.

Melatonin Accelerates Osteoporotic Bone Defect Repair by Promoting Osteogenesis-Angiogenesis Coupling

Previous studies have revealed that melatonin could play a role in anti-osteoporosis and promoting osteogenesis. However, the effects of melatonin treatment on osteoporotic bone defect and the mechanism underlying the effects of melatonin on angiogenesis are still unclear. Our study was aimed to investigate the potential effects of melatonin on angiogenesis and osteoporotic bone defect. Bone marrow mesenchymal stem cells (BMSCs) were isolated from the femur and tibia of rats. The BMSC osteogenic ability was assessed using alkaline phosphatase (ALP) staining, alizarin red S staining, qRT-PCR, western blot, and immunofluorescence. BMSC-mediated angiogenic potentials were determined using qRT-PCR, western blot, enzyme-linked immunosorbent assay, immunofluorescence, scratch wound assay, transwell migration assay, and tube formation assay. Ovariectomized (OVX) rats with tibia defect were used to establish an osteoporotic bone defect model and then treated with melatonin. The effects of melatonin treatment on osteoporotic bone defect in OVX rats were analyzed using micro-CT, histology, sequential fluorescent labeling, and biomechanical test. Our study showed that melatonin promoted both osteogenesis and angiogenesis in vitro. BMSCs treated with melatonin indicated higher expression levels of osteogenesis-related markers [ALP, osteocalcin (OCN), runt-related transcription factor 2, and osterix] and angiogenesis-related markers [vascular endothelial growth factor (VEGF), angiopoietin-2, and angiopoietin-4] compared to the untreated group. Significantly, melatonin was not able to facilitate human umbilical vein endothelial cell angiogenesis directly, but it possessed the ability to promote BMSC-mediated angiogenesis by upregulating the VEGF levels. In addition, we further found that melatonin treatment increased bone mineralization and formation around the tibia defect in OVX rats compared with the control group. Immunohistochemical staining indicated higher expression levels of osteogenesis-related marker (OCN) and angiogenesis-related markers (VEGF and CD31) in the melatonin-treated OVX rats. Then, it showed that melatonin treatment also increased the bone strength of tibia defect in OVX rats, with increased ultimate load and stiffness, as performed by three-point bending test. In conclusion, our study demonstrated that melatonin could promote BMSC-mediated angiogenesis and promote osteogenesis-angiogenesis coupling. We further found that melatonin could accelerate osteoporotic bone repair by promoting osteogenesis and angiogenesis in OVX rats. These findings may provide evidence for the potential application of melatonin in osteoporotic bone defect.

Interconnected collagen porous scaffolds prepared with sacrificial PLGA sponge templates for cartilage tissue engineering

Interconnected pore structures of scaffolds are important to control the cell functions for cartilage tissue engineering. In this study, collagen scaffolds with interconnected pore structures were prepared using poly(D,L-lactide-co-glycolide) (PLGA) sponges as sacrificial templates. Six types of PLGA sponges of different pore sizes and porosities were prepared by the solvent casting/particulate leaching method and used to regulate the interconnectivity of the collagen scaffolds. The integral and continuous templating structure of PLGA sponges generated well-interconnected pore structures in the collagen scaffolds. Bovine articular chondrocytes cultured in collagen scaffolds showed homogenous distribution, fast proliferation, high expression of cartilaginous genes and high secretion of cartilaginous extracellular matrix. In particular, the collagen scaffold templated by the PLGA sacrificial sponge that was prepared with a high weight ratio of PLGA and large salt particulates showed the most promotive effect on cartilage tissue formation. The interconnected pore structure facilitated cell distribution, cell-cell interaction and cartilage tissue regeneration.

Reverse engineering of an anatomically equivalent nerve conduit

Reconstruction of peripheral nervous tissue remains challenging in critical-sized defects due to the lack of Büngner bands from the proximal to the distal nerve ends. Conventional nerve guides fail to bridge the large-sized defect owing to the formation of a thin fibrin cable. Hence, in the present study, an attempt was made to reverse engineer the intricate epi-, peri- and endo-neurial tissues using Fused Deposition Modeling based 3D printing. Bovine serum albumin protein nanoflowers (NF) exhibiting Viburnum opulus 'Roseum' morphology were ingrained into 3D printed constructs without affecting its secondary structure to enhance the axonal guidance from proximal to distal ends of denuded nerve ends. Scanning electron micrographs confirmed the uniform distribution of protein NF in 3D printed constructs. The PC-12 cells cultured on protein ingrained 3D printed scaffolds demonstrated cytocompatibility, improved cell adhesion and extended neuronal projections with significantly higher intensities of NF-200 and tubulin expressions. Further suture-free fixation designed in the current 3D printed construct aids facile implantation of printed conduits to the transected nerve ends. Hence the protein ingrained 3D printed construct would be a promising substitute to treat longer peripheral nerve defects as its structural equivalence of endo- and perineurial organization along with the ingrained protein NF promote the neuronal extension towards the distal ends by minimizing axonal dispersion.

Bone tissue regeneration: The role of finely tuned pore architecture of bioactive scaffolds before clinical translation

Spatial dimension of pores and interconnection in macroporous scaffolds is of particular importance in facilitating endogenous cell migration and bone tissue ingrowth. However, it is still a challenge to widely tune structure parameters of scaffolds by conventional methods because of inevitable pore geometrical deformation and poor pore interconnectivity. Here, the long-term in vivo biological performances of nonstoichiometric bioceramic scaffolds with different pore dimensions were assessed in critical-size femoral bone defect model. The 6% Mg-substituted wollastonite (CSi-Mg6) powders were prepared via wet-chemical precipitation and the scaffolds elaborately printed by ceramic stereolithography, displaying designed constant pore strut and tailorable pore height (200, 320, 450, 600 μm), were investigated thoroughly in the bone regeneration process. Together with detailed structural stability and mechanical properties were collaboratively outlined. Both μCT and histological analyses indicated that bone tissue ingrowth was retarded in 200 μm scaffolds in the whole stage (2-16 weeks) but the 320 μm scaffolds showed appreciable bone tissue in the center of porous constructs at 6-10 weeks and matured bone tissue were uniformly invaded in the whole pore networks at 16 weeks. Interestingly, the neo-tissue ingrowth was facilitated in the 450 μm and 600 μm scaffolds after 2 weeks and higher extent of bone regeneration and remodeling at the later stage. These new findings provide critical information on how engineered porous architecture impact bone regeneration in vivo. Simultaneously, this study shows important implications for optimizing the porous scaffolds design by advanced additive manufacture technique to match the clinical translation with high performance.

Fabrication of Biomedical Scaffolds Using Biodegradable Polymers

Degradable polymers are used widely in tissue engineering and regenerative medicine. Maturing capabilities in additive manufacturing coupled with advances in orthogonal chemical functionalization methodologies have enabled a rapid evolution of defect-specific form factors and strategies for designing and creating bioactive scaffolds. However, these defect-specific scaffolds, especially when utilizing degradable polymers as the base material, present processing challenges that are distinct and unique from other classes of materials. The goal of this review is to provide a guide for the fabrication of biodegradable polymer-based scaffolds that includes the complete pathway starting from selecting materials, choosing the correct fabrication method, and considering the requirements for tissue specific applications of the scaffold.

Biomechanical design and analysis of auxetic pedicle screw to resist loosening

BACKGROUND

Pedicle screws are widely used in fusion surgery, while screw loosening often occurrs. An auxetic structures based pedicle screw was proposed to improve the bone-screw fixation by radial expansion of the screw body under tensile force to resist pulling out. It was optimized to obtain excellent anti-pullout ability for a particular bone based on the biomechanical interaction between screw and surrounding bone.

METHODS

The screw was designed based on re-entrant unit cells. The mechanical properties of it were adjusted by the wall thickness (t) and re-entrant angle (θ) of the unit cell, and characterized using finite element (FE) method. The designed screws were manufactured using 3D-printing, and Ti6Al4V as the materials. Subsequently, the pullout FE models were established, and verified by pulling the fabricated screws out of Sawbone blocks. The pulling out processes of screws from bone were simulated to explore the optimizing design of the screw.

RESULTS

The mechanical properties of the screw could be adjusted in a wide range. The biomechanical interaction between the screw and bone can affect the anti-pullout performance of the screw. With an identical elastic modulus (E), better auxiticity of the screw, resulted in a better anti-pullout performance; while an appropriate E is the necessary condition for its excellent anti-pullout performance for a particular bone.

CONCLUSION

Appropriate mechanical properties are necessary for the auxetic pedicle screw with excellent screw-bone fixation performance for a particular bone, which can be obtained by rationally designing the wall thickness and re-entrant angle of the unit cells.

Additive manufacturing pertaining to bone: Hopes, reality and future challenges for clinical applications

For the past 20 years, the democratization of additive manufacturing (AM) technologies has made many of us dream of: low cost, waste-free, and on-demand production of functional parts; fully customized tools; designs limited by imagination only, etc. As every patient is unique, the potential of AM for the medical field is thought to be considerable: AM would allow the division of dedicated patient-specific healthcare solutions entirely adapted to the patients' clinical needs. Pertinently, this review offers an extensive overview of bone-related clinical applications of AM and ongoing research trends, from 3D anatomical models for patient and student education to ephemeral structures supporting and promoting bone regeneration. Today, AM has undoubtably improved patient care and should facilitate many more improvements in the near future. However, despite extensive research, AM-based strategies for bone regeneration remain the only bone-related field without compelling clinical proof of concept to date. This may be due to a lack of understanding of the biological mechanisms guiding and promoting bone formation and due to the traditional top-down strategies devised to solve clinical issues. Indeed, the integrated holistic approach recommended for the design of regenerative systems (i.e., fixation systems and scaffolds) has remained at the conceptual state. Challenged by these issues, a slower but incremental research dynamic has occurred for the last few years, and recent progress suggests notable improvement in the years to come, with in view the development of safe, robust and standardized patient-specific clinical solutions for the regeneration of large bone defects.

A 3D Printed Composite Scaffold Loaded with Clodronate to Regenerate Osteoporotic Bone: In Vitro Characterization

Additive manufacturing (AM) is changing our current approach to the clinical treatment of bone diseases, providing new opportunities to fabricate customized, complex 3D structures with bioactive materials. Among several AM techniques, the BioCell Printing is an advanced, integrated system for material manufacture, sterilization, direct cell seeding and growth, which allows for the production of high-resolution micro-architectures. This work proposes the use of the BioCell Printing to fabricate polymer-based scaffolds reinforced with ceramics and loaded with bisphosphonates for the treatment of osteoporotic bone fractures. In particular, biodegradable poly(ε-caprolactone) was blended with hydroxyapatite particles and clodronate, a bisphosphonate with known efficacy against several bone diseases. The scaffolds' morphology was investigated by means of Scanning Electron Microscopy (SEM) and micro-Computed Tomography (micro-CT) while Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) revealed the scaffolds' elemental composition. A thermal characterization of the composites was accomplished by Thermogravimetric analyses (TGA). The mechanical performance of printed scaffolds was investigated under static compression and compared against that of native human bone. The designed 3D scaffolds promoted the attachment and proliferation of human MSCs. In addition, the presence of clodronate supported cell differentiation, as demonstrated by the normalized alkaline phosphatase activity. The obtained results show that the BioCell Printing can easily be employed to generate 3D constructs with pre-defined internal/external shapes capable of acting as a temporary physical template for regeneration of cancellous bone tissues.

Current standards and ethical landscape of engineered tissues-3D bioprinting perspective

Tissue engineering is an evolving multi-disciplinary field with cutting-edge technologies and innovative scientific perceptions that promise functional regeneration of damaged tissues/organs. Tissue engineered medical products (TEMPs) are biomaterial-cell products or a cell-drug combination which is injected, implanted or topically applied in the course of a therapeutic or diagnostic procedure. Current tissue engineering strategies aim at 3D printing/bioprinting that uses cells and polymers to construct living tissues/organs in a layer-by-layer fashion with high 3D precision. However, unlike conventional drugs or therapeutics, TEMPs and 3D bioprinted tissues are novel therapeutics and need different regulatory protocols for clinical trials and commercialization processes. Therefore, it is essential to understand the complexity of raw materials, cellular components, and manufacturing procedures to establish standards that can help to translate these products from bench to bedside. These complexities are reflected in the regulations and standards that are globally in practice to prevent any compromise or undue risks to patients. This review comprehensively describes the current legislations, standards for TEMPs with a special emphasis on 3D bioprinted tissues. Based on these overviews, challenges in the clinical translation of TEMPs & 3D bioprinted tissues/organs along with their ethical concerns and future perspectives are discussed.

Mechanical properties and osteoblast proliferation of complex porous dental implants filled with magnesium alloy based on 3D printing

In this paper, a complex porous dental implant with biodegradable magnesium alloy was designed based on selective laser melting (SLM). Finite element analysis (FEA) was used to simulate the stress distribution of dental implant and alveolar bone in two models of preliminary and later stages of implant. The stress concentration area of dental implants was found not in the porous structure, and the weak part of mechanical properties accords with the work requirements. The porous structure of dental implants can promote the function of cancellous bone in the process of conducting the stress of the dental implant, thus improving the bearing capacity of dental implants. In vitro fatigue experiments were carried out on the experimental samples produced by 3D printing. Through the cell contrast experiment, it was proved that the decomposed Mg²⁺ could reach the titanium surface smoothly through the porous structure and complete the proliferation of osteoblasts.