Biodegradation-affected fatigue behavior of extrusion-based additively manufactured porous iron-manganese scaffolds

Additively manufactured (AM) biodegradable porous iron-manganese (FeMn) alloys have recently been developed as promising bone-substituting biomaterials. However, their corrosion fatigue behavior has not yet been studied. Here, we present the first study on the corrosion fatigue behavior of an extrusion-based AM porous Fe35Mn alloy under cyclic loading in air and in the revised simulated body fluid (r-SBF), including the fatigue crack morphology and distribution in the porous structure. We hypothesized that the fatigue behavior of the architected AM Fe35Mn alloy would be strongly affected by the simultaneous biodegradation process. We defined the endurance limit as the maximum stress at which the scaffolds could undergo 3 million loading cycles without failure. The endurance limit of the scaffolds was determined to be 90 % of their yield strength in air, but only 60 % in r-SBF. No notable crack formation in the specimens tested in air was observed even after loading up to 90 % of their yield strength. As for the specimens tested in r-SBF, however, cracks formed in the specimens subjected to loads exceeding 60 % of their yield strength appeared to initiate on the periphery and propagate toward the internal struts. Altogether, the results show that the extrusion-based AM porous Fe35Mn alloy is capable of tolerating up to 60 % of its yield strength for up to 3 million cycles, which corresponds to 1.5 years of use of load-bearing implants subjected to repetitive gait cycles. The fatigue performance of the alloy thus further enhances its potential for trabecular bone substitution subjected to cyclic compressive loading. STATEMENT OF SIGNIFICANCE: Fatigue behavior of extrusion-based AM porous Fe35Mn alloy scaffolds in air and revised simulated body fluid was studied. The Fe35Mn alloy scaffolds endured 90 % of their yield strength for up to 3 × 106 loading cycles in air. Moreover, the scaffolds tolerated 3 × 106 loading cycles at 60 % of their yield strength in revised simulated body fluid. The Fe35Mn alloy scaffolds exhibited a capacity of withstanding 1.5-year physiological loading when used as bone implants.

Bone implant substitutes from synthetic polymer and reduced graphene oxide: Current perspective

In the present work, bone implant materials (BIM) were produced, in sheet form which comprises epoxy resin (synthetic polymer) (ER), calcium carbonate (CaCO3), and reduced graphene oxide (R-GO), by open mold method, for the possibility uses in bone tissue engineering. The developed BIM was analyzed for its physico-chemical, mechanical, bioactivity test, antimicrobial study, and biocompatibility. The BIM had excellent mechanical properties such as tensile strength (194.44 + 0.21 MPa), flexural strength (278.76 + 0.41 MPa), and water absorption (02.61 + 0.24%). A pore size distribution study using the HR-SEM has proved the 180 and 255 μm average pore was observed in the BIM structure. The Bioactivity test of BIM was examined after being immersed in a simulated body fluids (SBF) solution. The result of BIM formed an excellent deposition of bone tube apatite crystals. High-resolution scanning electron microscopy (HR-SEM) morphology of the bone tube apatite crystals revealed the diameter size in the range from 100 ± 159 to 210 ± 188 nm. BIM has excellent antimicrobial characteristics against E. coli (8.75 + 0.06 mm) and S. aureus (9.82 + 0.08 mm). The biocompatibility of the study MTT (3-(4, 5-dimethyl) thiazol-2-yl-2, 5-dimethyl tetrazolium bromide) assay using the MG-63 (human osteoblast cell line) has proven to be the 78% viable cell presence in BIM. After receiving the necessary approval, the scaffold with the required strength and biocompatibility could be tested as a bone implant material in large animals.

Natural medicine delivery from 3D printed bone substitutes

Unmet medical needs in treating critical-size bone defects have led to the development of numerous innovative bone tissue engineering implants. Although additive manufacturing allows flexible patient-specific treatments by modifying topological properties with various materials, the development of ideal bone implants that aid new tissue regeneration and reduce post-implantation bone disorders has been limited. Natural biomolecules are gaining the attention of the health industry due to their excellent safety profiles, providing equivalent or superior performances when compared to more expensive growth factors and synthetic drugs. Supplementing additive manufacturing with natural biomolecules enables the design of novel multifunctional bone implants that provide controlled biochemical delivery for bone tissue engineering applications. Controlled release of naturally derived biomolecules from a three-dimensional (3D) printed implant may improve implant-host tissue integration, new bone formation, bone healing, and blood vessel growth. The present review introduces us to the current progress and limitations of 3D printed bone implants with drug delivery capabilities, followed by an in-depth discussion on cutting-edge technologies for incorporating natural medicinal compounds embedded within the 3D printed scaffolds or on implant surfaces, highlighting their applications in several pre- and post-implantation bone-related disorders.

Polyimide biocomposites coated with tantalum pentoxide for stimulation of cell compatibility and enhancement of biointegration for orthopedic implant

Orthopedic implants are an important tool in the treatment of musculoskeletal conditions and helped many patients to improve their quality of life. Various inorganic-organic biocomposites have been broadly investigated particularly in the area of load-bearing orthopedic/dental applications. Polyimide (PI) is a promising organic material and shows excellent mechanical properties, biocompatibility, bio-stability, and its elastic modulus is similar to human bone but it lacks bioactivity, which is very important for cell adhesion and ultimately for bone regeneration. In this research, tantalum pentoxide (Ta2O5) coating was prepared on the surface of PI by polydopamine (PDA) bonding. The results showed that Ta2O5 was evenly coated on the surface of PI, and with the concentration of Ta2O5 in the PDA suspension increased, the content of Ta2O5 particles on the surface of PI increased significantly. In addition, the Ta2O5 coating significantly increased the roughness and hydrophilicity of the PI matrix. Cell experiments showed that PI surface coating Ta2O5 could promote the proliferation, adhesion, and osteogenic differentiation of bone marrow-derived stromal cells (BMSCs). The results demonstrated that fabricating Ta2O5 coating on the surface of PI through PDA bonding could improve the biocompatibility as well as bioactivity of PI, and increase the application potential of PI in the field of bone repair materials.

Macrophage polarization in bone implant repair: A review

Macrophages (MΦ) are highly adaptable and functionally polarized cells that play a crucial role in various physiological and pathological processes. Typically, MΦ differentiate into two distinct subsets: the proinflammatory (M1) and anti-inflammatory (M2) phenotypes. Due to their potent immunomodulatory and anti-inflammatory properties, MΦ have garnered significant attention in recent decades. In the context of bone implant repair, the immunomodulatory function of MΦ is of paramount importance. Depending on their polarization phenotype, MΦ can exert varying effects on osteogenesis, angiogenesis, and the inflammatory response around the implant. This paper provides an overview of the immunomodulatory and inflammatory effects of MΦ polarization in the repair of bone implants.

A Novel Silver-based Metal-Organic Framework Incorporated into Nanofibrous Chitosan Coatings for Bone Tissue Implants

In this work, new multilayer nanocomposite coatings comprised of chitosan (CS) nanofibers functionalized using an innovative silver base metal-organic framework (SOF) were developed. The SOFs were produced via a facile process using green and environmental-friendly materials. The CS-SOF nanocomposites were coated on hierarchical oxide (HO) layer fabricated on titanium surfaces by an innovative two-step etching process. X-ray diffraction revealed fruitful production of the SOF NPs and their stable crystalline structure within the nanocomposite coatings. Energy-dispersive x-ray spectroscopy approved uniform SOFs distribution in the CS-SOF nanocomposites. Atomic force microscopy indicated more than 700% increased nanoscale roughness for treated surfaces compared to the bare sample. In vitro MTT assay revealed proper cell viabilities on the samples, however, high SOFs concentration led to less biocompatibility. All coatings indicated positive cell proliferation rates up to 45% after 72 h. Antibacterial studies showed significant inhibition zones against Escherichia coli and Staphylococcus aureus bacteria with 100-200% effective antibacterial activities. Electron microscopy showed excellent cell attachments on the CS-SOF nanocomposites with expanded morphologies and long filopodia. The prepared coatings exhibited high apatite formation capability and bone bioactivity.

The biological responses of osteoblasts on titanium: Effect of oxygen level and surface roughness

BACKGROUND/PURPOSE

Due to the general application of in vitro test, cell culture is generally selected to evaluate the cytocompatibility of devices and materials. The choice of test condition should depend on the probable site and clinical application. The oxygen content of human body could be estimated around 5%∼12%, and the oxygen level of healing bone fracture range from 0.8%∼3.8%%. However, materials for bone implant are traditionally evaluated under laboratory normoxia condition (21% O₂) in vitro. The aim was to study the effect of oxygen level on osteoblast upon high stiffness titanium with different roughness.

METHODS

After sandblasted and acid-etched (SLA) process, we create titanium surfaces with four different roughness. The differentiation and proliferation of MC3T3-E1 osteoblast cultured on SLA-treated specimens were evaluated in designed chamber with oxygen level of 1%, 5%, 10%, 21%.

RESULTS

By scanning electron microscopy, all samples had sub-micro pit inside the micro-holes upon SLA-treated Ti disk surface. The decrease of oxygen level from 21% to 5% promoted osteoblast growth of SLA-treated specimens, but 1% O₂ delayed cell proliferation. The surface roughness of specimens influenced osteoblast cell differentiation. The differentiation and proliferation ability of the cells upon SLA-treated specimens is proportional to oxygen level.

CONCLUSION

Our results demonstrated that 5% O₂ will easily discriminate osteoblasts responses on different SLA-treated specimens. These results suggest that hypoxia (5% O₂) environment is better model for biological evaluation of bone-related materials.

Vascularized fibular grafts for the treatment of long bone defects: pros and cons. A systematic review and meta-analysis

PURPOSE

To quantify union rate, complication rate, reintervention rate, as well as functional outcome after vascularized fibular bone grafts (VFGs) for the treatment of long-bone defects.

METHODS

A comprehensive search was performed in the PubMed, Web of Science, and Cochrane databases up to August 18, 2020. Randomized controlled trials, comparative studies, and case series describing the various techniques available involving VFGs for the reconstruction of segmental long-bone defects were included. A meta-analysis was performed on union results, complications, and reinterventions. Assessment of risk of bias and quality of evidence was performed with the Downs and Black's "Checklist for Measuring Quality".

RESULTS

After full-text assessment, 110 articles on 2226 patients were included. Among the retrieved studies, 4 were classified as poor, 83 as fair, and 23 as good. Overall, good functional results were documented and a union rate of 80.1% (CI 74.1-86.2%) was found, with a 39.4% (CI 34.4-44.4%) complication rate, the most common being fractures, non-unions and delayed unions, infections, and thrombosis. Donor site morbidity represented 10.7% of the total complications. A 24.6% reintervention rate was documented (CI 21.0-28.1%), and 2.8% of the patients underwent amputation.

CONCLUSIONS

This systematic review and meta-analysis documented good long-term outcomes both in the upper and lower limb. However, VFG is a complex and demanding technique; this complexity means an average high number of complications, especially fractures, non-unions, and vascular problems. Both potential and limitations of VFG should be considered when choosing the most suitable approach for the treatment of long-bone defects.

Nanotopographical cues for regulation of macrophages and osteoclasts: emerging opportunities for osseointegration

Nanotopographical cues of bone implant surface has direct influences on various cell types during the establishment of osseointegration, a prerequisite of implant bear-loading. Given the important roles of monocyte/macrophage lineage cells in bone regeneration and remodeling, the regulation of nanotopographies on macrophages and osteoclasts has arisen considerable attentions recently. However, compared to osteoblastic cells, how nanotopographies regulate macrophages and osteoclasts has not been properly summarized. In this review, the roles and interactions of macrophages, osteoclasts and osteoblasts at different stages of bone healing is firstly presented. Then, the diversity and preparation methods of nanotopographies are summarized. Special attentions are paid to the regulation characterizations of nanotopographies on macrophages polarization and osteoclast differentiation, as well as the focal adhesion-cytoskeleton mediated mechanism. Finally, an outlook is indicated of coordinating nanotopographies, macrophages and osteoclasts to achieve better osseointegration. These comprehensive discussions may not only help to guide the optimization of bone implant surface nanostructures, but also provide an enlightenment to the osteoimmune response to external implant.

Strength enhancement and modulus modulation in auxetic meta-biomaterials produced by selective laser melting

Meta-biomaterials are applied to orthopedic implants to avoid stress shielding effects; however, there is no reason for the yield strength to be comparable to that of human bone. In this study, a composite unit cell was designed by combining the positive Poisson's ratio (PPR) and negative Poisson's ratio (NPR) unit cells, inspired by the second-phase strengthening theory. The purpose was to increase the strength while maintaining the elastic modulus. All structures were successfully fabricated from Ti-6Al-4V via selective laser melting. The relative density is between 0.08 and 0.24, which falls within the optimal range for bone growth. Mechanical tests indicated that the center of the inclined rod fractured in a stepwise fracture mode, which was consistent with the predictions of the Johnson-Cook model. The elastic modulus ranged from 0.652 ± 0.016 to 5.172 ± 0.021 GPa, and the yield strength varied from 10.62 ± 0.112 to 87.158 ± 2.215 MPa. An improved Gibson-Ashby law was proposed to facilitate the design of gradient structures. When the re-entrant angle was 40°, a hybrid body-centered cubic NPR structure was formed, resulting in a significant improvement in the mechanical properties. Importantly, the yield strength of the proposed composite structures increased by 43.23%, and the compression strength increased by 44.70% under the same elastic modulus. The strengthening mechanism has been proven to apply to other bending-dominated structures. Overall, this imparts unprecedented mechanical performance to auxetic meta-biomaterials and provides insights into improving the reported porous structures. STATEMENT OF SIGNIFICANCE: : Auxetic meta-biomaterials exhibit auxetic properties that can improve the contact between the bone-implant interface and reduce the risk of aseptic failure. To avoid the stress shielding effect, the elastic modulus has traditionally been decreased by increasing the porosity. However, the strength is simultaneously reduced. Therefore, a composite unit cell was proposed to increase strength rather than modulus by combining the positive and negative Poisson's ratio unit cells, inspired by the second-phase strengthening theory. We observed a 43.23% increase in the yield strength of the composite structure without increasing the elastic modulus. This strengthening mechanism has been proven to apply to other bending-dominated structures. Our approach provides insights into improving other bending-dominated structures and broadening their applications for bone implantation.

Effect of Mo and space holder content on microstructure, mechanical and corrosion properties in Ti6AlxMo based alloy for bone implant

The porous alloys of Ti6Al(3-15)Mo were developed to replace the fractured bone; the alloy consists of 6 wt% of Al which was taken as α the phase stabilizer and (3-15) wt% Mo with an increment of 3 wt% was taken as β phase stabilizer. The porosity of these fabricated porous alloys was controlled by adjusting volume% of the ammonium bicarbonate (SH). These porous samples were characterized in terms of their microstructure, compressive strength, elastic modulus, energy absorption, ion release and corrosion rate in simulated body fluid (SBF) and these properties are compared with the existing alloys and human bone. The fabricated porous samples were characterized, and the obtained results were analysed as a function of Mo concentration and the volume% of space holder content. Three phases were found in the microstructure: α, α₂ and β phase of titanium. Increase in Mo content from 3 to 15 wt% has increased the volume fraction of β phase from 7.45% to 64.09% and Kirkendall pores also are observed to be increased with increase in Mo content. α and α₂ phase was differentiated by the TEM and phase map of EBSD images. The plateau stress, elastic modulus and energy absorption are observed to be decreased, and the densification strain is observed to be increased with the addition of Mo and SH content. The released ion concentration and corrosion rate are far below the tolerance limits of Ti, Al and Mo elements, in the static immersion test conducted in SBF solution.

3D printing of PEEK and its composite to increase biointerfaces as a biomedical material- A review

Poly ether-ether-ketone (PEEK) is a polymer with better lignin biocompatibility than other polymers. It is good for biomedical engineering applications. This research summarises the outcomes of an evaluation conducted on PEEK material composites, such as cellular calcium hydroxyapatite (CHAp) for medical applications. Prospects of PEEK for medical implant are highlighted. Critical analysis and review on 3D printing of PEEK, CHAp and their biological macromolecular behaviours are presented. An electronic search was carried out on Scupos database, Google search and peer-reviewed papers published in the last ten years. Because of the extraordinary strength and biological behaviours of PEEK and its composite of CHAp, 3D-printed PEEK has several biomedical applications, and its biological macromolecular behaviour leads to health sustainability. This work highlights its biological macromolecular behaviours as a bone implant material and the optimum 3D printing process for PEEK and CHAp for medical applications. The current problems with printing PEEK and CHAp are investigated along with their possible uses. Possible solutions to improve the 3D printability of PEEK and CHAp are explained based on scientific mechanisms. This detailed report stands to benefit both scientific community and medical industry to enhance 3D printing concepts for PEEK and CHAp.

Simultaneous engineering of nanofillers and patterned surface macropores of graphene/hydroxyapatite/polyetheretherketone ternary composites for potential bone implants

Incorporating bioactive nanofillers and creating porous surfaces are two common strategies used to improve the tissue integration of polyetheretherketone (PEEK) material. However, few studies have reported the combined use of both strategies to modify PEEK. Herein, for the first time, dual nanoparticles of graphene oxide (GO) and hydroxyapatite (HAp) were incorporated into PEEK matrix to obtain ternary composites that were laser machined to create macropores with diameters ranging from 200 μm to 600 μm on the surfaces. The surface morphology and chemistry, mechanical properties, and cellular responses of the composites were investigated. The results show that micropatterned pores with a depth of 50 μm were created on the surfaces of the composites, which do not significantly affect the mechanical properties of the resultant composites. More importantly, the incorporation of GO and HAp significantly improves the cell adhesion and proliferation on the surface of PEEK. Compared to the smooth surface composite, the composites with macroporous surface exhibit markedly enhanced cell viability. The combined use of nanofillers and surface macropores may be a promising way of improving tissue integration of PEEK for bone implants.

Multi-material additive manufacturing technologies for Ti-, Mg-, and Fe-based biomaterials for bone substitution

The growing interest in multi-functional metallic biomaterials for bone substitutes challenges the current additive manufacturing (AM, =3D printing) technologies. It is foreseeable that advances in multi-material AM for metallic biomaterials will not only allow for complex geometrical designs, but also improve their multi-functionalities by tuning the types or compositions of the underlying base materials, thereby presenting unprecedented opportunities for advanced orthopedic treatments. AM technologies are yet to be extensively explored for the fabrication of multi-functional metallic biomaterials, especially for bone substitutes. The aim of this review is to present the viable options of the state-of-the-art multi-material AM for Ti-, Mg-, and Fe-based biomaterials to be used as bone substitutes. The review starts with a brief review of bone tissue engineering, the design requirements, and fabrication technologies for metallic biomaterials to highlight the advantages of using AM over conventional fabrication methods. Five AM technologies suitable for metal 3D printing are compared against the requirements for multi-material AM. Of these AM technologies, extrusion-based multi-material AM is shown to have the greatest potential to meet the requirements for the fabrication of multi-functional metallic biomaterials. Finally, recent progress in the fabrication of Ti-, Mg-, and Fe-based biomaterials including the utilization of multi-material AM technologies is reviewed so as to identify the knowledge gaps and propose the directions of further research for the development of multi-material AM technologies that are applicable for the fabrication of multi-functional metallic biomaterials. STATEMENT OF SIGNIFICANCE: Addressing a critical bone defect requires the assistance of multi-functional porous metallic bone substitutes. As one of the most advanced fabrication technology in bone tissue engineering, additive manufacturing is challenged for its viability in multi-material fabrication of metallic biomaterials. This article reviews how the current metal additive manufacturing technologies have been and can be used for multi-material fabrication of Ti-, Mg-, and Fe-based bone substitutes. Progress on the Ti-, Mg-, and Fe-based biomaterials, including the utilization of multi-material additive manufacturing, are discussed to direct future research for advancing the multi-functional additively manufactured metallic bone biomaterials.

A comparative study on compressive deformation and corrosion behaviour of heat treated Ti4wt%Al foam of different porosity made of milled and unmilled powders

Ti4wt%Al alloy foams of various porosities were prepared using milled and unmilled powders through space holder technique. Crystallographic and morphological change in milled powder compared to the unmilled one were also examined. Space holder content was varied to get foams of different porosities. After sintering, foams were thermally oxidized through heat treatment and characterised in terms of their pore size, pore morphology, pore interconnectivity, phase formation and compressive deformation behaviour. It was observed that plastic collapse stress, elastic modulus, plateau stress and energy absorption capacity are strong function of porosity and these are higher for the foam made of milled powder (M_f) than those of the foam made of unmilled one (U_f). Corrosion behaviour of these foams were examined. Open circuit potential, Tafel plot and electrochemical impedance spectroscopy confirm that M_f has higher corrosion resistance than U_f for the same porosity level. Also, with increasing porosity, corrosion resistance of the foam samples reduces.

Correlation Between Conditional Approval and Customized Bone Implant Devices

This report aims to summarize key concerns regarding customized devices and conditional approval during the premarket evaluation of bone implants, and to explore the correlation between them. Based on the experience of approval of the first domestic custom-designed bone implant, we consider the process of gaining conditional approval for urgently-needed medical devices and medical devices for rare diseases, as well as the guidance available for clinical investigation. We also streamlined the scientifically administrative concept of this unique device, from the design and development of premarket technical evaluation to continuous post-market study. The present study found that those two aspects have certain connections, but they are not directly correlated to each other. In contrast to the USA, Canada, Australia and the EU, where regulations and guidelines have been established for the use of customized devices, in this regard, China is still it its infancy. Thus, there is considerable potential for China to develop and perfect the policies relating to customized devices and to develop relevant strategies to ensure their efficacy with the aid of conditional approval. Appropriate scientific conditional approval for mass production of individualized anatomy-matching bone implants could become a valuable approach for precision medicine.

NiTi-Nb micro-trusses fabricated via extrusion-based 3D-printing of powders and transient-liquid-phase sintering

We present a novel additive manufacturing method for NiTi-Nb micro-trusses combining (i) extrusion-based 3D-printing of liquid inks containing NiTi and Nb powders, solvents, and a polymer binder into micro-trusses with 0/90° ABAB layers of parallel, ∼600 µm struts spaced 1 mm apart and (ii) subsequent heat-treatment to remove the binder and solvents, and then bond the NiTi powders using liquid phase sintering via the formation of a transient NiTi-Nb eutectic phase. We investigate the effects of Nb concentration (0, 1.5, 3.1, 6.7 at.% Nb) on the porosity, microstructure, and phase transformations of the printed NiTi-Nb micro-trusses. Micro-trusses with the highest Nb content exhibit long channels (from 3D-printing) and struts with smaller interconnected porosity (from partial sintering), resulting in overall porosities of ∼75% and low compressive stiffnesses of 1-1.6 GPa, similar to those of trabecular bone and in agreement with analytical and finite element modeling predictions. Diffusion of Nb into the NiTi particles from the bond regions results in a Ni-rich composition as the Nb replaces Ti atoms, leading to decreased martensite/austenite transformation temperatures. Adult human mesenchymal stem cells seeded on these micro-trusses showed excellent viability, proliferation, and extracellular matrix deposition over 14 days in culture.

STATEMENT OF SIGNIFICANCE

Near-equiatomic NiTi micro-trusses are attractive for biomedical applications such as stents, actuators, and bone implants because of their combination of biocompatibility, low compressive stiffness, high surface area, and shape-memory or superelasticity. Extrusion-based 3D-printing of NiTi powder-based inks into micro-trusses is feasible, but the subsequent sintering of the powders into dense struts is unachievable due to low diffusivity, large particle size, and low packing density of the NiTi powders. We present a solution, whereby Nb powders are added to the NiTi inks, thus forming during sintering a eutectic NiTi-Nb liquid phase which bonds the solid NiTi powders and improves densification of the struts. This study investigates the microstructure, porosity, phase transformation behavior, compressive stiffness, and cytocompatibility of these printed NiTi-Nb micro-trusses.

Polydopamine-assisted chlorhexidine immobilization on medical grade stainless steel 316L: Apatite formation and in vitro osteoblastic evaluation

Immobilization of chlorhexidine (CHX) on stainless steel 316L (SS316L), assisted by a polydopamine film as an intermediate layer is projected as an approach in combating infection while aiding bone regeneration for coating development on orthopedic and dental implants. This study aimed to investigate the ability of CHX coating to promote apatite layer, osteoblast cells viability, adhesion, osteogenic differentiation and mineralization. Stainless steel 316L disks were pre-treated, grafted with a polydopamine film and immobilized with different concentrations of CHX (10-30mM). The apatite layer formation was determined through an in vitro simulated body fluid (SBF) test by ATR-FTIR and SEM-EDX analyses. The osteoblastic evaluations including cells viability, cells adhesion, osteogenic differentiation and mineralization were assessed with human fetal osteoblast cells through MTT assay, morphology evaluation under FESEM, ALP enzyme activity and Alizarin Red S assay. The apatite layer was successfully formed on the CHX coated disks, demonstrating potential excellent bioactivity property. The CHX coatings were biocompatible with the osteoblast cells at low CHX concentration (<20mM) with good adhesion on the metal surfaces. The increment of ALP activity and calcium deposition testified that the CHX coated disks able to support osteoblastic maturation and mineralization. These capabilities give a promising value to the CHX coating to be implied in bone regeneration area.

AgNPs-decorated 3D printed PEEK implant for infection control and bone repair

Polyetheretherketone (PEEK) is an ideal substitute material for bone tissue engineering, which can avoid the stress shielding phenomenon due to its similar mechanical properties to natural human bone. Complex bone defect and postoperative infection are still two enormous challenges in orthopedic clinics. It's well-known that additive manufacturing possesses the merits of high-precision and rapid prototyping, thus it easily meets the needs of mold processing. In the present study, we developed a novel Ag-decorated 3D printed PEEK via catecholamine chemistry. SEM image showed that silver nanoparticles (AgNPs) were evenly anchored on the surface. The following antibacterial tests, including bacterial inhibition ring, bacterial dynamics curves and antibiofilm test, indicated that the Ag-decorated 3D PEEK scaffolds displayed significant antibacterial effect towards Gram-negative and Gram-positive bacteria. Then MG-63 cells were seeded on samples for cell proliferation and ALP activity tests. The results demonstrated the scaffold modified with AgNPs could support cell proliferation, and enhanced higher alkaline phosphatase activity compared with pure PEEK scaffold. Expectedly, this dual functional 3D material holds great potential application in clinical bone tissue repair.

Simple additive manufacturing of an osteoconductive ceramic using suspension melt extrusion

OBJECTIVE

Craniofacial bone trauma is a leading reason for surgery at most hospitals. Large pieces of destroyed or resected bone are often replaced with non-resorbable and stock implants, and these are associated with a variety of problems. This paper explores the use of a novel fatty acid/calcium phosphate suspension melt for simple additive manufacturing of ceramic tricalcium phosphate implants.

METHODS

A wide variety of non-aqueous liquids were tested to determine the formulation of a storable 3D printable tricalcium phosphate suspension ink, and only fatty acid-based inks were found to work. A heated stearic acid-tricalcium phosphate suspension melt was then 3D printed, carbonized and sintered, yielding implants with controllable macroporosities. Their microstructure, compressive strength and chemical purity were analyzed with electron microscopy, mechanical testing and Raman spectroscopy, respectively. Mesenchymal stem cell culture was used to assess their osteoconductivity as defined by collagen deposition, alkaline phosphatase secretion and de-novo mineralization.

RESULTS

After a rapid sintering process, the implants retained their pre-sintering shape with open pores. They possessed clinically relevant mechanical strength and were chemically pure. They supported adhesion of mesenchymal stem cells, and these were able to deposit collagen onto the implants, secrete alkaline phosphatase and further mineralize the ceramic.

SIGNIFICANCE

The tricalcium phosphate/fatty acid ink described here and its 3D printing may be sufficiently simple and effective to enable rapid, on-demand and in-hospital fabrication of individualized ceramic implants that allow clinicians to use them for treatment of bone trauma.

Porous biomorphic silicon carbide ceramics coated with hydroxyapatite as prospective materials for bone implants

Porous and cytocompatible silicon carbide (SiC) ceramics derived from wood precursors and coated with bioactive hydroxyapatite (HA) and HA-zirconium dioxide (HA/ZrO2) composite are materials with promising application in engineering of bone implants due to their excellent mechanical and structural properties. Biomorphic SiC ceramics have been synthesized from wood (Hornbeam, Sapele, Tilia and Pear) using a forced impregnation method. The SiC ceramics have been coated with bioactive HA and HA/ZrO2 using effective gas detonation deposition approach (GDD). The surface morphology and cytotoxicity of SiC ceramics as well as phase composition and crystallinity of deposited coatings were analyzed. It has been shown that the porosity and pore size of SiC ceramics depend on initial wood source. The XRD and FTIR studies revealed the preservation of crystal structure and phase composition of in the HA coating, while addition of ZrO2 to the initial HA powder resulted in significant decomposition of the final HA/ZrO2 coating and formation of other calcium phosphate phases. In turn, NIH 3T3 cells cultured in medium exposed to coated and uncoated SiC ceramics showed high re-cultivation efficiency as well as metabolic activity. The recultivation efficiency of cells was the highest for HA-coated ceramics, whereas HA/ZrO2 coating improved the recultivation efficiency of cells as compared to uncoated SiC ceramics. The GDD method allowed generating homogeneous HA coatings with no change in calcium to phosphorus ratio. In summary, porous and cytocompatible bio-SiC ceramics with bioactive coatings show a great promise in construction of light, robust, inexpensive and patient-specific bone implants for clinical application.

A Method to Represent Heterogeneous Materials for Rapid Prototyping: The Matryoshka Approach

PURPOSE

The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions of human bones.

DESIGN/METHODOLOGY/APPROACH

Nested STL shells, called Matryoshka models, are described, based on their namesake Russian nesting dolls. In this approach, polygonal models, such as STL shells, are "stacked" inside one another to represent different material regions. The Matryoshka model addresses the challenge of representing different densities and different types of bone when reverse engineering from medical images. The Matryoshka model is generated via an iterative process of thresholding the Hounsfield Unit (HU) data using computed tomography (CT), thereby delineating regions of progressively increasing bone density. These nested shells can represent regions starting with the medullary (bone marrow) canal, up through and including the outer surface of the bone.

FINDINGS

The Matryoshka approach introduced can be used to generate accurate models of heterogeneous materials in an automated fashion, avoiding the challenge of hand-creating an assembly model for input to multi-material additive or subtractive manufacturing.

ORIGINALITY/VALUE

This paper presents a new method for describing heterogeneous materials: in this case, the density distribution in a human bone. The authors show how the Matryoshka model can be used to plan harvesting locations for creating custom rapid allograft bone implants from donor bone. An implementation of a proposed harvesting method is demonstrated, followed by a case study using subtractive rapid prototyping to harvest a bone implant from a human tibia surrogate.

Topographic scale-range synergy at the functional bone/implant interface

We sought to explore the biological mechanisms by which endosseous implant surface topography contributes to bone anchorage. To address this experimentally, we implanted five groups of custom-made commercially pure titanium implants of varying surface topographical complexity in rat femora for 9 days; subjected them to mechanical testing; and then examined the interfacial bone matrix by electron microscopy. The five implant surfaces were prepared by combinations of dual acid etching and grit blasting the titanium substrates and, in some cases, modifying the created surfaces with the deposition of nanocrystals of calcium phosphate, which resulted in 10 samples per group. In parallel, we cultured rat bone marrow cells on surrogate implants constructed from polymer resin coated with the same calcium phosphate nanocrystals, and monitored the deposition of bone sialoprotein by transmission electron immunohisto-micrography. We found that implant samples modified with sub-micron scale crystals were bone-bonding, as described by the interdigitation of a mineralized cement line matrix with the underlying implant surface. The in vitro assay showed that bone sialoprotein could be deposited in the interstices between, and undercuts below, the nanocrystals. In addition, when mineralized, the cement line matrix globules occupied micron-sized pits in the implant surfaces, and in part obliterated them, creating an additional form of anchorage. Our results also showed that collagen, elaborated by the osteogenic cells, wrapped around the coarse-micron features, and became mineralized in the normal course of bone formation. This provided a mechanism by which coarse-micron implant features contributed to a functional interface, which we have previously described, that is capable of resisting the mechanical loading that increases as peri-implant bone matures. Thus, our findings provide mechanistic explanations for the biologically-relevant criteria that can be employed to assess the importance of implant surface topography at different scale-ranges.