Porous titanium fiber mesh with tailored elasticity and its effect on stromal cells

The sensitivity of the stiffness and thickness of a titanium inlay in a cementless PEEK femoral component to the micromotions and bone strain energy density

Polyetheretherketone (PEEK) has been proposed as alternative material for total knee arthroplasty implants due to its low stiffness, which may reduce stress-shielding. In cementless fixation, a proper primary fixation is required for long-term fixation. Previous research showed that the lower stiffness of a cementless PEEK femoral component results in larger micromotions at the implant-bone interface compared to a cobalt-chrome femoral component. A titanium inlay on the PEEK implant surface may improve the primary fixation while maintaining the favourable stiffness properties. Therefore, the effect of thickness and stiffness of a titanium inlay on the primary fixation and stress-shielding was investigated. A finite element model of the femur and femoral component was created with five titanium inlay variants. The micromotions and strain energy density (SED) were quantified as outcome measures. The distal thin - proximal thick variant showed the largest resulting micromotions (51.2 µm). Relative to the all-PEEK femoral component, the addition of a titanium inlay reduced the micromotions with 30 % to 40 % without considerably affecting the stress-shielding capacity (strain energy difference of 6 % to 10 %). Differences in micromotions (43.0-51.2 µm) and SED between the variants were relatively small. In conclusion, the addition of a titanium inlay could lead to a reduction of the micromotions without substantially affecting the SED distribution.

Finite element analysis of a hybrid corrugated hip implant for stability and loading during gait phases

Implants used in total hip replacements (THR) exhibit high failure rates and up to a decade of operational life. These surgical failures could be mainly attributed to the improper positioning, post-surgical stability and loading, of the implants during different phases of the gait. Typically, revised surgeries are suggested within a few years of hip implantation, which requires multiple femoral drilling operations to remove an existing implant, and to install a new implant. The pain and trauma associated with such procedures are also challenging with the existing hip implants. In this work, we designed a novel corrugated hip implant with innovative dimensioning as per ASTM standards, and grooves for directed insertion and removal (using a single femoral drilling and positioning operation). Biocompatible titanium alloy (Ti6Al4V) was chosen as the implant material, and the novel implant was placed into a femur model through a virtual surgery to study its stability and loading during a dynamic gait cycle. A detailed mesh convergence study was conducted to select a computationally accurate finite element (FE) mesh. Tight fit and frictional fit attachment conditions were simulated, and the gait induced displacements and stresses on the implant, cortical and cancellous bone sections were characterized. During walking, the implant encountered the maximum von-Mises stress of 254.97 MPa at the femoral head. The analyses indicated low micro-motions (i.e., approximately 7μm) between the femur and implant, low stresses at the implant and bone within elastic limits, and uniform stress distribution, which unlike existing hip implants, would be indispensable for bone growth and implant stability enhancement, and also for reducing implant wear.

Histological evaluation of titanium fiber mesh-coated implants in a rabbit femoral condyle model

OBJECTIVES

This study was aimed to comparatively evaluate new bone formation into the pores of a flexible titanium fiber mesh (TFM) applied on the surface of implant.

METHODS

Twenty-eight custom made cylindrical titanium implants (4 ×10 mm) with and without a layer of two different types of TFM (fiber diameter of 22 µm and 50 µm, volumetric porosity ~70%) were manufactured and installed bilaterally in the femoral condyles of 14 rabbits. The elastic modulus for these two TFM types was ~20 GPa and ~5 GPa respectively, whereas the solid titanium was ~110 GPa. The implants (Control, TFM-22, TFM-50) were retrieved after 14 weeks of healing and prepared for histological assessment. The percentage of the bone area (BA%), the bone-to-implant contact (BIC%) and amount were determined.

RESULTS

Newly formed bone into mesh porosity was observed for all three types of implants. Histomorphometric analyses revealed significantly higher (~2.5 fold) BA% values for TFM-22 implants (30.9 ± 9.5%) compared to Control implants (12.7 ± 6.0%), whereas BA% for TMF-50 did not significantly differ compared with Control implants. Furthermore, both TFM-22 and TFM-50 implants showed significantly higher BIC% values (64.9 ± 14.0%, ~2.5 fold; 47.1 ± 14.1%, ~2 fold) compared to Control (23.6 ± 17.4%). Finally, TFM-22 implants showed more and thicker trabeculae in the peri-implant region.

SIGNIFICANCE

This in vivo study demonstrated that implants with a flexible coating of TFM improve bone formation within the inter-fiber space and the peri-implant region.

Effect of Exposure Rates with Customized versus Conventional Titanium Mesh on Guided Bone Regeneration: A Systematic Review and Meta-Analysis

Titanium mesh exposure is the main complication of bone regeneration. In this study, a meta-analysis and performed to clarify the effect of customized titanium mesh versus conventional titanium mesh complications and the time of mesh exposure on edentulous alveolar ridge GBR. Databases, including PubMed, EMBASE, Web of Science and Cochrane Central Register Controlled Trials, were searched by two independent reviewers to retrieve articles published from January 2010 to March 2020, regarding the incidence of complications after GBR surgery, with language limited to English articles. A total of 705 articles were found, and 9 articles were quantitatively analyzed. A funnel plot was made for 10 comprehensive datasets. The combined value of the total exposure rate of titanium mesh was 0.44 (44%, 95% CI=0.30~0.58). The results of subgroup analysis showed that the combined value of the customized titanium mesh exposure rate was 0.31 (31%, 95% CI=0.15~0.51), and the combined value of the conventional titanium mesh exposure rate was 0.51 (51%, 95% CI=0.33~0.69). Based on the findings of the present study, the exposure rate of customized titanium mesh is lower than that of conventional titanium mesh. The design of 3D printing customized titanium mesh avoids nerves and blood vessels, which is of great significance to improve the accurate reconstruction of GBR and provides enough space for implantation and reducing the exposure rate. Soft tissue management (i.e., technical sensitivity) is also an important factor to avoid soft tissue fractures.

Porous titanium fiber mesh with tailored elasticity and its effect on stromal cells

Porous titanium fiber mesh (TFM) is considered a suitable scaffold material for bone reconstruction. Also, TFM can be used to cover the surface of bone‐anchored devices, that is, orthopedic or dental implants. The titanium fiber size has an effect of the stiffness as well as porosity of the titanium mesh, which can influence the behavior of bone forming cells. Therefore, the aim of this study was to vary TFM composition, in order to achieve different stiffness, and to assess the effects of such variation on the behavior of bone marrow‐derived stromal cells (BMSCs). With that purpose, nine types of TFM (porosities 60–87%; fiber size 22–50 μm), were examined for their mechanical properties as well as their effect on the proliferation and differentiation of rat bone marrow‐derived stromal cells (rBMSCs) up to 21 days. Dynamic mechanical analysis revealed that the stiffness of TFM were lower than of solid titanium and decreased with larger fiber sizes. The stiffness could effectively be tailored by altering fiber properties, which altered the pore simultaneously. For the 22 and 35 μm size fiber meshes with the highest porosity, the stiffness closely matched the value found in literature for cortical bone. Finally, all tested TFM types supported the growth and differentiation of rBMSCs. We concluded that TFM material has been proven cytocompatible. Further preclinical studies are needed to assess which TFM type is most suitable as clinical use for bone ingrowth and bone regeneration.