Osteoanabolic Implant Materials for Orthopedic Treatment

Functionalized TiCu/TiCuN coating promotes osteoporotic fracture healing by upregulating the Wnt/β-catenin pathway

Osteoporosis results in decreased bone mass and insufficient osteogenic function. Existing titanium alloy implants have insufficient osteoinductivity and delayed/incomplete fracture union can occur when used to treat osteoporotic fractures. Copper ions have good osteogenic activity, but their dose-dependent cytotoxicity limits their clinical use for bone implants. In this study, titanium alloy implants functionalized with a TiCu/TiCuN coating by arc ion plating achieved a controlled release of copper ions in vitro for 28 days. The coated alloy was co-cultured with bone marrow mesenchymal stem cells and showed excellent biocompatibility and osteoinductivity in vitro. A further exploration of the underlying mechanism by quantitative real-time polymerase chain reaction and western blotting revealed that the enhancement effects are related to the upregulation of genes and proteins (such as axin2, β-catenin, GSK-3β, p-GSK-3β, LEF1 and TCF1/TCF7) involved in the Wnt/β-catenin pathway. In vivo experiments showed that the TiCu/TiCuN coating significantly promoted osteoporotic fracture healing in a rat femur fracture model, and has good in vivo biocompatibility based on various staining results. Our study confirmed that TiCu/TiCuN-coated Ti promotes osteoporotic fracture healing associated with the Wnt pathway. Because the coating effectively accelerates the healing of osteoporotic fractures and improves bone quality, it has significant clinical application prospects.

Strontium-doping promotes bone bonding of titanium implants in osteoporotic microenvironment

Osteoporosis is a major challenge to oral implants, and this study focused on improving the osseointegration ability of titanium (Ti) implants in osteoporosis environment via surface modification, including doping of strontium ion and preparation of nanoscale surface feature. Our previous studies have shown that strontium (Sr) ions can enhance osteogenic activity. Therefore, we aimed to comprehensively evaluate the effect of hydrothermal treatment of Sr-doped titanium implant coating on bone-binding properties in the microenvironment of osteoporosis in this study. We fabricated Sr-doped nanocoating (AHT-Sr) onto the surface of titanium implants via hydrothermal reaction. The rough Sr-doping had good biological functions and could apparently promote osteogenic differentiation of osteoporotic bone marrow mesenchymal stem cells (OVX-BMSCs). Most importantly, AHT-Sr significantly promoted bone integration in the osteoporosis environment. This study provides an effective approach to implant surface modification for better osseointegration in an osteoporotic environment.

Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices

This review summarizes recent research on the design of polymer material systems based on biomimetic concepts and reports on the medical devices that implement these systems. Biomolecules such as proteins, nucleic acids, and phospholipids, present in living organisms, play important roles in biological activities. These molecules are characterized by heterogenic nature with hydrophilicity and hydrophobicity, and a balance of positive and negative charges, which provide unique reaction fields, interfaces, and functionality. Incorporating these molecules into artificial systems is expected to advance material science considerably. This approach to material design is exceptionally practical for medical devices that are in contact with living organisms. Here, it is focused on zwitterionic polymers with intramolecularly balanced charges and introduce examples of their applications in medical devices. Their unique properties make these polymers potential surface modification materials to enhance the performance and safety of conventional medical devices. This review discusses these devices; moreover, new surface technologies have been summarized for developing human-friendly medical devices using zwitterionic polymers in the cardiovascular, cerebrovascular, orthopedic, and ophthalmology fields.

Gallium-Strontium Phosphate Conversion Coatings for Promoting Infection Prevention and Biocompatibility of Magnesium for Orthopedic Applications

Device-associated infections remain a clinical challenge. The common strategies to prevent bacterial infection are either toxic to healthy mammalian cells and tissue or involve high doses of antibiotics that can prompt long-term negative consequences. An antibiotic-free coating strategy to suppress bacterial growth is presented herein, which concurrently promotes bone cell growth and moderates the dissolution kinetics of resorbable magnesium (Mg) biomaterials. Pure Mg as a model biodegradable material was coated with gallium-doped strontium-phosphate through a chemical conversion process. Gallium was distributed in a gradual manner throughout the strontium-phosphate coating, with a compact structure and a gallium-rich surface. It was demonstrated that the coating protected the underlying Mg parts from significant degradation in minimal essential media at physiological conditions over 9 days. In terms of bacteria culture, the liberated gallium ions from the coatings upon Mg specimens, even though in minute quantities, inhibited the growth of Gram-positiveStaphylococcus aureus, Gram-negative Escherichia coli, andPseudomonas aeruginosa ─ key pathogens causing infection and early failure of the surgical implantations in orthopedics and trauma. More importantly, the gallium dopants displayed minimal interferences with the strontium-phosphate-based coating which boosted osteoblasts and undermined osteoclasts in in vitro co-cultures. This work provides a new strategy to prevent bacterial infection and control the degradation behavior of Mg-based orthopedic implants, while preserving osteogenic features of the devices.

Addressing the Needs of the Rapidly Aging Society through the Development of Multifunctional Bioactive Coatings for Orthopedic Applications

The unprecedented aging of the world's population will boost the need for orthopedic implants and expose their current limitations to a greater extent due to the medical complexity of elderly patients and longer indwelling times of the implanted materials. Biocompatible metals with multifunctional bioactive coatings promise to provide the means for the controlled and tailorable release of different medications for patient-specific treatment while prolonging the material's lifespan and thus improving the surgical outcome. The objective of this work is to provide a review of several groups of biocompatible materials that might be utilized as constituents for the development of multifunctional bioactive coatings on metal materials with a focus on antimicrobial, pain-relieving, and anticoagulant properties. Moreover, the review presents a summary of medications used in clinical settings, the disadvantages of the commercially available products, and insight into the latest development strategies. For a more successful translation of such research into clinical practice, extensive knowledge of the chemical interactions between the components and a detailed understanding of the properties and mechanisms of biological matter are required. Moreover, the cost-efficiency of the surface treatment should be considered in the development process.

Bioactive coatings with anti-osteoclast therapeutic agents for bone implants: Enhanced compliance and prolonged implant life

The use of therapeutic agents that inhibit bone resorption is crucial to prolong implant life, delay revision surgery, and reduce the burden on the healthcare system. These therapeutic agents include bisphosphonates, various nucleic acids, statins, proteins, and protein complexes. Their use in systemic treatment has several drawbacks, such as side effects and insufficient efficacy in terms of concentration, which can be eliminated by local treatment. This review focuses on the incorporation of osteoclast inhibitors (antiresorptive agents) into bioactive coatings for bone implants. The ability of bioactive coatings as systems for local delivery of antiresorptive agents to achieve optimal loading of the bioactive coating and its release is described in detail. Various parameters such as the suitable concentrations, release times, and the effects of the antiresorptive agents on nearby cells or bone tissue are discussed. However, further research is needed to support the optimization of the implant, as this will enable subsequent personalized design of the coating in terms of the design and selection of the coating material, the choice of an antiresorptive agent and its amount in the coating. In addition, therapeutic agents that have not yet been incorporated into bioactive coatings but appear promising are also mentioned. From this work, it can be concluded that therapeutic agents contribute to the biocompatibility of the bioactive coating by enhancing its beneficial properties.

Laser polished fused deposition poly-lactic acid objects for personalized orthopaedic application

Patient-specific surgical guides are increasingly demanded. Material Extrusion (ME) is a popular 3D printing technique to fabricate personalized surgical guides. However, the ME process usually generates deleterious surface topography which is not suitable for orthopaedic emergencies. We designed and optimized parametric combinations of a laser polishing approach as post process to improve the surface quality of ME-made poly-lactic acid (PLA) objects. In this study, we investigated the contribution of processing variables to the mechanical properties and the biocompatibilities in vitro of the ME-made PLA objects. Conventional surface grinding was conducted as comparison. The results demonstrate that the ME-made PLA samples exhibit good mechanical properties and favourable biocompatibility after being post processed using laser polishing. The post laser polishing, as a powerful tool in manufacture of ME-made PLA objects, will open a new approach with a great promise in its applications in personalized and timely management of medical emergencies.

Design and development of metallic biomaterials with biological and mechanical biocompatibility

In the present article, the recent trends in the research and development of metallic biomaterials are discussed with focus on the results obtained by the author's group. The design of biocompatible metallic biomaterials possessing excellent biological and mechanical properties, including titanium alloys with low Young's modulus, is reviewed with focus on Young's modulus, fatigue strength, and peculiar behavior. The evaluation of biological compatibility including cell viability and living tissue compatibility using animal models and surface modifications using bioactive ceramic and blood-compatible polymers are summarized. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 944-954, 2019.

Modification of titanium surface via Ag-, Sr- and Si-containing micro-arc calcium phosphate coating

The current research is devoted to the study of the modification of the titanium implants by the micro-arc oxidation with bioactive calcium phosphate coatings containing Ag or Sr and Si elements. The coatings' microstructure, phase composition, morphology, physicochemical and biological properties were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Ag-containing and Sr-Si-incorporated coatings were formed in alkaline and acid electrolytes, respectively. The formation of the coatings occurred at different ranges of the applied voltages, which led to the significant difference in the coatings properties. The trace elements Ag, Sr and Si participated intensively in the plasma-chemical reactions of the micro-arc coatings formation. Ag-containing coatings demonstrated strong antibacterial effect against Staphylococcus aureus AТСС 6538-P. MTT in vitro test with 3T3-L1 fibroblasts showed no cytotoxicity appearance on Sr-Si-incorporated coatings.

Improving in vitro and in vivo antibacterial functionality of Mg alloys through micro-alloying with Sr and Ga

Despite of technical advancements in design and development of new biomaterials, device-related infections continue to occur and can be life-threatening. Differing from existing research work pertaining to introducing antibacterial function upon device surface, this study attempts to address such germ-infection issues through controlled release of antibacterial species from bulk gallium (Ga) and strontium (Sr) containing magnesium (Mg) alloys. To validate such a conceptual framework, Mg alloys containing micro-level concentrations of Ga and/or Sr (0.1 wt%) are employed as model materials, along with commercially pure Mg and titanium (Ti) as control groups. Biodegradation progress of such metal specimens is examined through pH and mass loss measurements, and inductively coupled plasma - atomic emission spectrometry (ICP-AES) as a function of immersion time in Trypticase Soy Broth (TSB) solution under physiological conditions. In vitro biocompatibility and antibacterial performance are characterised through MTT proliferation assay with human mesenchymal stem cells (hMSCs) and the spread plate method with three representative bacterial strains, i.e. S. aureus (ATCC 43300), E. coli (ATCC 25922), and S. epidermidis (ATCC 35984). Animal tests are performed through implanting target metal rods into femurs of Sprague Dawley rats, accompanied with injection of S. aureus to build a model of osteomyelitis. Results demonstrate that such lean additions of Ga and/or Sr reduce the degradation kinetics of Mg matrix, and the release of Ga³⁺ ions plays a crucial role in disabling the viability of all selected bacterial strains. The histological tests confirm that the growth of fibrous tissue has been accelerated in the vicinity of Mg-based implants, in comparison to that of blank and c.p. Ti controls. It is also striking that the smallest number density of S. aureus bacteria on the surface of the retrieved Ga-containing Mg rod implants. Such a proof-of-concept study provides a new and feasible strategy to address the notorious device-infection issues associated with biomedical implants for bone fracture management.

A water-soluble, upconverting Sr2Yb0.3Gd0.7F7:Er3+/Tm3+@PSIoAm bio-probe for in vivo trimodality imaging

Multi-modality in vivo bioimaging has great renown for offering more comprehensive information in medical diagnosis and research. Incorporating different bioimaging capabilities into one biocompatible nanoprobe requires an elegant structural design. Considering optical and magnetic properties, X-ray absorption ability, and clinical safety, we prepared a water-soluble and upconverting PSIoAm-modified Sr2Yb0.3Gd0.7F7:Er3+/Tm3+ bio-probe that not only had high photostability and excellent cell membrane permeability, but could also distinguish the four types of cancer cells and normal cells tested within the scope of our study. What's more, it could realize the in vivo trimodality imaging of upconversion fluorescence, X-ray computed tomography and magnetic resonance. The histological analysis of visceral sections further demonstrated that the multifunctional bio-probe was highly safe, which could be applied to clinical diagnosis.

A specific HeLa cell-labelled and lysosome-targeted upconversion fluorescent probe: PEG-modified Sr2YbF7:Tm3+

In this study, water-soluble PEG-modified Sr₂YbF₇:Tm³⁺ was prepared conveniently by a one-pot solvothermal method, where the molar ratio of Sr²⁺ to Yb³⁺ was controlled between 3 : 2 and 1 : 1. The optimum red-light emission at 677-699 nm was modulated via 0.7% Tm³⁺ doped under irradiation at 980 nm. Interestingly, biological experimental results showed that the PEG-modified Sr₂YbF₇:Tm³⁺ with low toxicity, excellent cell membrane permeability and high photostability can not only distinguish HeLa cells from mouse embryonic fibroblasts but also target the subcellular organelle lysosome in HeLa cells; therefore it can be anticipated that the as-prepared material would be a potential tool for cancer diagnosis.

Functionalization of Ti-40Nb implant material with strontium by reactive sputtering

BACKGROUND

Surface functionalization of orthopedic implants with pharmaceutically active agents is a modern approach to enhance osseointegration in systemically altered bone. A local release of strontium, a verified bone building therapeutic agent, at the fracture site would diminish side effects, which could occur otherwise by oral administration. Strontium surface functionalization of specially designed titanium-niobium (Ti-40Nb) implant alloy would provide an advanced implant system that is mechanically adapted to altered bone with the ability to stimulate bone formation.

METHODS

Strontium-containing coatings were prepared by reactive sputtering of strontium chloride (SrCl2) in a self-constructed capacitively coupled radio frequency (RF) plasma reactor. Film morphology, structure and composition were investigated by scanning electron microscopy (SEM), time of flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy (HR-TEM) was used for the investigation of thickness and growth direction of the product layer. TEM lamellae were prepared using the focused ion beam (FIB) technique. Bioactivity of the surface coatings was tested by cultivation of primary human osteoblasts and subsequent analysis of cell morphology, viability, proliferation and differentiation. The results are correlated with the amount of strontium that is released from the coating in biomedical buffer solution, quantified by inductively coupled plasma mass spectrometry (ICP-MS).

RESULTS

Dense coatings, consisting of SrOxCly, of more than 100 nm thickness and columnar structure, were prepared. TEM images of cross sections clearly show an incoherent but well-structured interface between coating and substrate without any cracks. Sr2+ is released from the SrOxCly coating into physiological solution as proven by ICP-MS analysis. Cell culture studies showed excellent biocompatibility of the functionalized alloy.

CONCLUSIONS

Ti-40Nb alloy, a potential orthopedic implant material for osteoporosis patients, could be successfully plasma coated with a dense SrOxCly film. The material performed well in in vitro tests. Nevertheless, the Sr2+ release must be optimized in future work to meet the requirements of an effective drug delivery system.

Engineering of Micro- to Nanostructured 3D-Printed Drug-Releasing Titanium Implants for Enhanced Osseointegration and Localized Delivery of Anticancer Drugs

Primary and secondary bone cancers are major causes of pathological bone fractures which are usually treated through implant fixation and chemotherapy. However, both approaches face many limitations. On one hand, implants may suffer from poor osseointegration, and their rejection results in repeated surgery, patient's suffering, and extensive expenses. On the other hand, there are severe systemic adverse effects of toxic chemotherapeutics which are administrated systemically. In this paper, in order to address these two problems, we present a new type of localized drug-releasing titanium implants with enhanced implants' biointegration and drug release capabilities that could provide a high concentration of anticancer drugs locally to treat bone cancers. The implants are fabricated by 3D printing of Ti alloy followed by an anodization process featuring unique micro- (particles) and nanosurface (tubular arrays) topography. We successfully demonstrate their enhanced bone osseointegration and drug loading capabilities using two types of anticancer drugs, doxorubicin (DOX) and apoptosis-inducing ligand (Apo2L/TRAIL). In vitro study showed strong anticancer efficacy against cancer cells (MDA-MB-231-TXSA), confirming that these drug-releasing implants can be used for localized chemotherapy for treatment of primary and secondary bone cancers together with fracture support.

Strontium release from Sr2+-loaded bone cements and dispersion in healthy and osteoporotic rat bone

Drug functionalization of biomaterials is a modern and popular approach in biomaterials research. Amongst others this concept is used for the functionalization of bone implants to locally stimulate the bone healing process. For example strontium ions (Sr²⁺) are administered in osteoporosis therapy to stimulate bone growth and have recently been integrated into bone cements. Based on results of different analytical experiments we developed a two-phase model for the transport of therapeutically active Sr²⁺-ions in bone in combination with Korsmeyer-Peppas kinetics for the Sr²⁺ release from bone cement. Data of cement dissolution experiments into water in combination with inductively coupled plasma mass spectrometry (ICP-MS) analysis account for dissolution kinetics following Noyes-Whitney rule. For dissolution in α-MEM cell culture media the process is kinetically hindered and can be described by Korsmeyer-Peppas kinetics. Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to determine the Sr²⁺ diffusion coefficient in healthy and osteoporotic trabecular rat bone. Therefore, bone sections were dipped in aqueous Sr²⁺-solution by one side and the Sr²⁺-profile was measured by classical SIMS depth profiling. The Sr²⁺ mobility can be described by a simple diffusion model and we obtained diffusion coefficients of (2.28±2.97)⋅10^-12cm²/s for healthy and of (1.55±0.93)⋅10^-10cm²/s for osteoporotic bone. This finding can be explained by a different bone nanostructure, which was observed by focused ion beam scanning electron microscopy (FIB-SEM) and transmission electron microscopy (TEM). Finally, the time and spatially resolved drug transport was calculated by finite element method for the femur of healthy and osteoporotic rats. The obtained results were compared to mass images that were obtained from sections of in vivo experiments by ToF-SIMS. The simulated data fits quite well to experimental results. The successfully applied model for the description of drug dispersion can help to reduce the number of animal experiments in the future.

A closer look at the in vitro electrochemical characterisation of titanium alloys for biomedical applications using in-situ methods

Titanium (Ti) and its alloys are widely used in several biomedical applications, particularly as permanent orthopaedic implants. Electrochemical testing provides a means to perform accelerated corrosion testing, however whilst results from polarisation testing for Ti and its alloys to date have been generally useful, they are also rather limited on the basis of several reasons. One reason is that the polarisation curves for Ti and its alloys in simulated body fluids all appear rather similar, and they do not present a classical 'breakdown' or pitting potential, making discrimination between alloys difficult. Of practical relevance however, are two key issues; (1) how do Ti alloys respond to a breakdown event? (i.e. do they readily 'repassivate'?), and, (2) what is that actual rate of Ti ion loss from exposure to physiological conditions? The answers to these questions are probed herein. Several Ti alloys of either unique composition or different fabrication method were studied, including commercially pure Ti (cp-Ti), Ti-6Al-4V, Ti-29Nb-13Ta-4.5Zr (TNTZ), selective laser melted Ti-6Al-4V, direct laser deposited cp-Ti, Ti-35Nb-15Zr, and Ti-25Nb-8Zr. Results reveal that both fabrication method and alloying influence 'repassivation' behaviour. Furthermore, atomic emission spectroelectrochemistry as applied to cp-Ti indicated actual dissolution currents of ∼2-3μA/cm^-2 (i.e. ∼9μm/yr) in the range of the corrosion potential, also revealing such dissolution is persistent, even with cathodic polarisation, and definitively revealing that the presence of hydrogen peroxide and albumin activate anodic dissolution of Ti.

STATEMENT OF SIGNIFICANCE

We believe the paper makes a significant and important contribution to the field of permanent implant biomaterials. Whilst we concede that the paper does not include any in vivo work, the timeliness of the work, and the completely new nature of the findings, we believe carries the impact required for Acta Biomaterialia. Key highlights include:All of the above combine to produce a manuscript that we believe has wide appeal, and can be used as both a port of reference to those working with Ti biomaterials, and also those wishing to apply useful characterisation techniques to their own work (with two very novel methods demonstrated herein, along with the unique information they provide).

Sub-10 nm Sr2LuF7:Yb/Er@Sr2GdF7@SrF2 Up-Conversion Nanocrystals for Up-Conversion Luminescence-Magnetic Resonance-Computed Tomography Trimodal Bioimaging

Herein, sub-10 nm core-shell nanocrystals (NCs), which select Sr₂LuF₇:Yb/Er as core, Sr₂GdF₇ as middle shell, and SrF₂ as an outermost shell, were synthesized by a seed-mediated growth process. The NCs possess good crystallinity, morphology, and up-conversion luminescent properties. After modification by polyethylenimine branched (PEI), in vitro cell up-conversion imaging with low autofluorescence was realized. Due to the presence of Gd³⁺ ions, in vivo magnetic resonance (MR) imaging was also achieved with these designed NCs. More significantly, these special core-shell NCs exhibited high contrast in in vivo X-ray computed tomography (CT) imaging because of their good X-ray absorption ability. These results indicate that the core-shell up-conversion NCs can serve as promising contrast agents for up-conversion luminescence-MR-CT trimodal bioimaging.