Low elastic modulus contributes to the osteointegration of titanium alloy plug

Corrosion and Biological Behaviors of Biomedical Ti-24Nb-4Zr-8Sn Alloy under an Oxidative Stress Microenvironment

Biomaterials can induce an inflammatory response in surrounding tissues after implantation, generating and releasing reactive oxygen species (ROS), such as hydrogen peroxide (H2O2). The excessive accumulation of ROS may create a microenvironment with high levels of oxidative stress (OS), which subsequently accelerates the degradation of the passive film on the surface of titanium (Ti) alloys and affects their biological activity. The immunomodulatory role of macrophages in biomaterial osteogenesis under OS is unknown. This study aimed to explore the corrosion behavior and bone formation of Ti implants under an OS microenvironment. In this study, the corrosion resistance and osteoinduction capabilities in normal and OS conditions of the Ti-24Nb-4Zr-8Sn (wt %, Ti2448) were assessed. Electrochemical impedance spectroscopy analysis indicated that the Ti2448 alloy exhibited superior corrosion resistance on exposure to excessive ROS compared to the Ti-6Al-4V (TC4) alloy. This can be attributed to the formation of the TiO2 and Nb2O5 passive films, which mitigated the adverse effects of OS. In vitro MC3T3-E1 cell experiments revealed that the Ti2448 alloy exhibited good biocompatibility in the OS microenvironment, whereas the osteogenic differentiation level was comparable to that of the TC4 alloy. The Ti2448 alloy significantly alleviates intercellular ROS levels, inducing a higher proportion of M2 phenotypes (52.7%) under OS. Ti2448 alloy significantly promoted the expression of the anti-inflammatory cytokine, interleukin 10 (IL-10), and osteoblast-related cytokines, bone morphogenetic protein 2 (BMP-2), which relatively increased by 26.9 and 31.4%, respectively, compared to TC4 alloy. The Ti2448 alloy provides a favorable osteoimmune environment and significantly promotes the proliferation and differentiation of osteoblasts in vitro compared to the TC4 alloy. Ultimately, the Ti2448 alloy demonstrated excellent corrosion resistance and immunomodulatory properties in an OS microenvironment, providing valuable insights into potential clinical applications as implants to repair bone tissue defects.

Heat Treatment's Vital Role: Elevating Orthodontic Mini-Implants for Superior Performance and Longevity-Pilot Study

Orthodontic mini-implants are devices used for anchorage in various orthodontic treatments. We conducted a pilot study which aimed to observe preliminary trends regarding the impact of heat treatment on the elastic modulus of Ti6Al4V alloy and stainless steel 316L mini-implants. The initial phase involved testing the impact of heat treatment on the mechanical properties of Ti6Al4V alloy and stainless steel 316L mini-implants.

MATERIAL AND METHODS

Ten self-drilling mini-implants sourced from two distinct manufacturers (Jeil Medical Corporation® and Leone®) with dimensions of 2.0 mm diameter and 10 mm length were tested. They were separated into two material groups: Ti6Al4V and 316L. Using the CETRUMT-2 microtribometer equipment, indentation testing was conducted employing a diamond-tipped Rockwell penetrator at a constant force of 4.5 N.

RESULTS

Slight differences were observed in the elastic modulus of the Ti6Al4V alloy (103.99 GPa) and stainless steel 316L (203.20 GPa) compared to natural bone. The higher elastic moduli of these materials indicate that they are stiffer, which could potentially lead to stress-shielding phenomena and bone resorption. Heat treatment resulted in significant changes in mechanical properties, including elastic modulus reductions of approximately 26.14% for Ti6Al4V and 24.82% for 316L, impacting their performance in orthodontic applications.

CONCLUSION

Understanding the effects of heat treatment on these alloys is crucial for optimizing their biomechanical compatibility and longevity in orthodontic treatment. To fully evaluate the effects of heat treatment on mini-implants and to refine their design and efficacy in clinical practice, further research is needed.

Fabricated High-Strength, Low-Elastic Modulus Biomedical Ti-24Nb-4Zr-8Sn Alloy via Powder Metallurgy

With the huge demands of an aging society, it is urgent to develop a new generation of non-toxic titanium alloy to match the modulus of human bone. Here, we prepared bulk Ti2448 alloys by powder metallurgy technology, and focused on the influence of the sintering process on the porosity, phase composition, and mechanical properties of the initial sintered samples. Furthermore, we performed solution treatment on the samples under different sintering parameters to further adjust the microstructure and phase composition, so as to achieve strength enhancement and reduction of Young's modulus. Solution treatment can effectively inhibit the continuous α phase precipitated along the grain boundaries of the β matrix, which is beneficial to the fracture resistance. Therefore, the water-quenched sample exhibits good mechanical properties due to the absence of acicular α-phase. Samples sintered at 1400 °C and subsequently water quenched have excellent comprehensive mechanical properties, which benefit from high porosity and the smaller feature size of microstructure. To be specific, the compressive yield stress is 1100 MPa, the strain at fracture is 17.5%, and the Young's modulus is 44 GPa, which are more applicable to orthopedic implants. Finally, the relatively mature sintering and solution treatment process parameters were screened out for reference in actual production.

Self-Powered Respiratory Monitoring Strategy Based on Adaptive Dual-Network Thermogalvanic Hydrogels

As a low-grade sustainable heat source, the breath waste heat exhaled by human bodies is always ignored, although producing a greater temperature than ambient. Converting this heat into electric energy for use as power sources or detecting signals is extremely important in cutting-edge wearable medicine. This heat-to-electricity conversion is possible with thermogalvanic hydrogels. However, challenges remain in their antifreezing and antidrying properties, significantly restricting the durability of thermogalvanic gels in practical applications. Herein, a dual-network poly(vinyl alcohol)/gelatin (PVA/GEL) gel thermogalvanic device with Fe(CN)₆^3-/4- as a redox pair is developed, with an outstanding low-temperature durability and antidrying capacity. These features result from the use of a binary H₂O/GL (glycerin) solvent to limit hydrogen bonding between water molecules. The prepared thermogalvanic gel patch is capable of easily converting physiological data into understandable electrical impulses using the temperature difference between the ambient environment and the heat produced by human breathing, realizing a simple self-powered respiratory monitoring strategy for the first time. Even below zero temperature, the gel patch-based mask can operate normally, implying it fits into low-temperature environments. This study sheds fresh light on the development of active wearable medical electronics that are powered by demic low-level heat.

Martens Hardness of CAD/CAM Resin-Based Composites

(1) Background: The properties of CAD/CAM resin-based composites differ due to differences in their composition. Instrumented indentation testing can help to analyze these differences with respect to hardness, as well as energy-converting capabilities due to viscoelastic behavior. (2) Methods: Eleven materials were investigated using instrumented indentation testing. Indentation depth (hr), Martens hardness (HM), indentation hardness (HIT), indentation modulus (EIT), the elastic part of indentation work (ηIT), and indentation creep (CIT) were investigated, and statistical analysis was performed using one-way ANOVA, Bonferroni post-hoc test, and Pearson correlation (α = 0.05). (3) Results: All of the investigated parameters revealed differences between the analyzed materials. Besides the differences in hardness-associated parameters (hr, HM, and HIT), instrumented indentation testing demonstrated differences in energy-converting properties. The subsequent one-way ANOVA revealed significant differences (p < 0.001). A significant (p < 0.01, Pearson correlation >0.576) correlation between the materials and HM, HIT, or EIT was identified. (4) Conclusions: Due to the differences found in the energy-converting properties of the investigated materials, certain CAD/CAM resin-based composites could show superior stress-breaking capabilities than others. The consequential reduction in stress build-up may prove to beneficial, especially for implant-retained restorations or patients suffering from parafunctions.

Three-Dimensionally Printed Ti2448 With Low Stiffness Enhanced Angiogenesis and Osteogenesis by Regulating Macrophage Polarization via Piezo1/YAP Signaling Axis

Previous studies have found that the novel low-elastic-modulus Ti2448 alloy can significantly reduce stress shielding and contribute to better bone repair than the conventional Ti6Al4V alloy. In this study, the promotion of osteogenesis and angiogenesis by three-dimensionally printed Ti2448 were also observed in vivo. However, these were not significant in a series of in vitro tests. The stiffness of materials has been reported to greatly affect the response of macrophages, and the immunological regulation mediated by macrophages directly determines the fate of bone implants. Therefore, we designed more experiments to explore the role of three-dimensionally printed Ti2448 in macrophage activation and related osteogenesis and angiogenesis. As expected, we found a significant increase in the number of M2 macrophages around Ti2448 implants, as well as better osteogenesis and angiogenesis in vivo. In vitro studies also showed that macrophages pre-treated with Ti2448 alloy significantly promoted angiogenesis and osteogenic differentiation through increased PDGF-BB and BMP-2 secretion, and the polarization of M2 macrophages was enhanced. We deduced that Ti2448 promotes angiogenesis and osteogenesis through Piezo1/YAP signaling axis-mediated macrophage polarization and related cytokine secretion. This research might provide insight into the biological properties of Ti2448 and provide a powerful theoretical supplement for the future application of three-dimensionally printed Ti2448 implants in orthopaedic surgery.

Ultrasound-Based Quantification of Cartilage Damage After In Vivo Articulation With Metal Implants

OBJECTIVE

This study aims to evaluate the applicability of the ultrasound roughness index (URI) for quantitative assessment of cartilage quality ex vivo (post-mortem), after 6 months of in vivo articulation with a Focal Knee Resurfacing Implant (FKRI).

DESIGN

Goats received a metal FKRI (n = 8) or sham surgery (n = 8) in the medial femoral condyles. After 6 months animals were sacrificed, tibial plateaus were stained with Indian ink, and macroscopic scoring of the plateaus was performed based on the ink staining. The URI was calculated from high-frequency ultrasound images at several sections, covering both areas that articulated with the implant and non-articulating areas. Cartilage quality at the most damaged medial location was evaluated with a Modified Mankin Score (MMS).

RESULTS

The URI was significantly higher in the FKRI-articulating than in the sham plateaus at medial articulating sections, but not at sections that were not in direct contact with the implant, for example, under the meniscus. The mean macroscopic score and MMS were significantly higher in the FKRI-articulating group than in the sham group (P=0.035, P<0.001, respectively). Correlation coefficients between URI and macroscopic score were significant in medial areas that articulated with the implant. A significant correlation between URI and MMS was found at the most damaged medial location (ρ=0.72,P=0.0024).

CONCLUSIONS

This study demonstrates the potential of URI to evaluate cartilage roughness and altered surface morphology after in vivo articulation with a metal FKRI, rendering it a promising future tool for quantitative follow-up assessment of cartilage quality.

Wearable Electronics Based on the Gel Thermogalvanic Electrolyte for Self-Powered Human Health Monitoring

There is always a temperature difference of more than 10 degrees between the human body, as a sustainable heat source, and the ambient temperature. Converting body heat into electricity that in turn is used to drive personal medical electronics is of significance in smart wearable medicine. To avoid the frangibility and complex preparation of traditional thermoelectric materials, we fabricated a gel electrolyte-based thermogalvanic generator with Fe³⁺/Fe²⁺ as a redox pair, which presents not only moderate thermoelectric performance but also excellent flexibility. With a micropore-widespread polyvinylidene fluoride diaphragm implanted in the gel, a thermal barrier was created between the two halves, effectively improving the Seebeck coefficient by reducing its thermal conductivity. Considering the superior temperature response of the gel, a self-powered body temperature monitoring system was established by conformally affixing it to the forehead. Meanwhile, the gel patch with a high specific heat capacity can effectively cool down fever patients. This work may offer a new train of thought for exploiting self-powered wearable medical electronics by scavenging low-grade body heat.

Mechanical aspects of dental implants and osseointegration: A narrative review

With the need of rapid healing and long-term stability of dental implants, the existing Ti-based implant materials do not meet completely the current expectation of patients. Low elastic modulus Ti-alloys have shown superior biocompatibility and can achieve comparable or even faster bone formation in vivo at the interface of bone and the implant. Porous structured Ti alloys have shown to allow rapid bone ingrowth through their open structure and to achieve anchorage with bone tissue by increasing the bone-implant interface area. In addition to the mechanical properties of implant materials, the design of the implant body can be used to optimize load transfer and affect the ultimate results of osseointegration. The aim of this narrative review is to define the mechanical properties of dental implants, summarize the relationship between implant stability and osseointegration, discuss the effect of metallic implant mechanical properties (e.g. stiffness and porosity) on the bone response based on existing in vitro and in vivo information, and analyze load transfer through mechanical properties of the implant body. This narrative review concluded that although several studies have presented the advantages of low elastic modulus or high porosity alloys and their effect on osseointegration, further in vivo studies, especially long-term observational studies are needed to justify these novel materials as a replacement for current Ti-based implant materials.

Influence of the Elastic Modulus on the Osseointegration of Dental Implants

The load transfer from metallic prosthesis to tissue plays an important role in the success of a designed device. From a mechanical behavior point of view, the load transfer will be favored when the elastic modulus between the metallic implant and the bone tissue are similar. Titanium and Ti-6Al-4V are the most commonly used metals and alloys in the field of dental implants, although they present high elastic moduli and hence trigger bone resorption. We propose the use of low-modulus β-type titanium alloys that can improve the growth of new bone surrounding the implant. We designed dental implants with identical morphology and micro-roughness composed of: Ti-15Zr, Ti-19.1Nb-8.8Zr, Ti-41.2Nb-6.1Zr, and Ti-25Hf-25Ta. The commercially pure Ti cp and Ti-6Al-4V were used as control samples. The alloys were initially mechanically characterized with a tensile test using a universal testing machine. The results showed the lowest elastic modulus for the Ti-25Hf-25Ta alloy. We implanted a total of six implants in the mandible (3) and maxilla (3) for each titanium alloy in six minipigs and evaluated their bone index contact (i.e., the percentage of new bone in contact with the metal—BIC%) after 3 and 6 weeks of implantation. The results showed higher BIC% for the dental implants with lowest elastic modulus, showing the importance of decreasing the elastic modulus of alloys for the successful osseointegration of dental implants.

Large Animal Models for Osteochondral Regeneration

Namely, in the last two decades, large animal models - small ruminants (sheep and goats), pigs, dogs and horses - have been used to study the physiopathology and to develop new therapeutic procedures to treat human clinical osteoarthritis. For that purpose, cartilage and/or osteochondral defects are generally performed in the stifle joint of selected large animal models at the condylar and trochlear femoral areas where spontaneous regeneration should be excluded. Experimental animal care and protection legislation and guideline documents of the US Food and Drug Administration, the American Society for Testing and Materials and the International Cartilage Repair Society should be followed, and also the specificities of the animal species used for these studies must be taken into account, such as the cartilage thickness of the selected defect localization, the defined cartilage critical size defect and the joint anatomy in view of the post-operative techniques to be performed to evaluate the chondral/osteochondral repair. In particular, in the articular cartilage regeneration and repair studies with animal models, the subchondral bone plate should always be taken into consideration. Pilot studies for chondral and osteochondral bone tissue engineering could apply short observational periods for evaluation of the cartilage regeneration up to 12 weeks post-operatively, but generally a 6- to 12-month follow-up period is used for these types of studies.