Bone Ingrowth Research Articles

Highly Porous Titanium Cups Frequently Presenting with Radiolucent Lines in Cementless Primary Total Hip Arthroplasty: A Retrospective Cohort Study.

Background/Objectives: A highly porous titanium cup with a three-dimensional metal interface was recently introduced to improve biological fixation and survival. However, radiography has revealed concerns regarding these cups, despite their excellent short- and mid-term clinical outcomes. This study compared the clinical and radiographic results of a highly porous titanium cup with those of a hydroxyapatite-coated porous titanium cup after primary total hip arthroplasty (THA). Methods: Fifty-one primary THAs were investigated. A highly porous titanium cup was used in 17 hips, and a hydroxyapatite-coated porous titanium cup was used in 34 hips. No significant differences in preoperative patient demographic characteristics were observed between the two groups. The 2-year postoperative clinical and radiographic results were compared. Results: Radiolucent lines were observed in 13 (76%) of 17 hips with highly porous titanium cups and in none (0%) of 34 hips with hydroxyapatite-coated porous titanium cups (p < 0.001). In the highly porous titanium cup group, radiolucent lines were observed in five hips (29%) in one zone, two hips (11%) in two zones, and six hips (35%) in three zones. No cup loosening was observed in either group. Conclusions: Radiolucent lines were significantly more frequent in highly porous titanium cups. This study suggests that, compared to the three-dimensional structure of porous titanium, the hydroxyapatite coating of porous titanium had a greater influence on bone ingrowth in the short term. The meaning of these findings in the long-term is unclear yet.

Alendronate as Bioactive Coating on Titanium Surfaces: An Investigation of CaP-Alendronate Interactions.

The surface modification of dental implants plays an important role in establishing a successful interaction of the implant with the surrounding tissue, as the bioactivity and osseointegration properties are strongly dependent on the physicochemical properties of the implant surface. A surface coating with bioactive molecules that stimulate the formation of a mineral calcium phosphate (CaP) layer has a positive effect on the bone bonding process, as biomineralization is crucial for improving the osseointegration process and rapid bone ingrowth. In this work, the spontaneous deposition of calcium phosphate on the titanium surface covered with chemically stable and covalently bound alendronate molecules was investigated using an integrated experimental and theoretical approach. The initial nucleation of CaP was investigated using quantum chemical calculations at the density functional theory (DFT) level. Negative Gibbs free energies show a spontaneous nucleation of CaP on the biomolecule-covered titanium oxide surface. The deposition of calcium and phosphate ions on the alendronate-modified titanium oxide surface is governed by Ca2+-phosphonate (-PO3H) interactions and supported by hydrogen bonding between the phosphate group of CaP and the amino group of the alendronate molecule. The morphological and structural properties of CaP deposit were investigated using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and attenuated total reflectance Fourier transform infrared spectroscopy. This integrated experimental-theoretical study highlights the spontaneous formation of CaP on the alendronate-coated titanium surface, confirming the bioactivity ability of the alendronate coating. The results provide valuable guidance for the promising forthcoming advancements in the development of biomaterials and surface modification of dental implants.

The effect of a barrier membrane on the incorporation of deproteinized bovine bone mineral (DBBM) in experimental defects at the time of early implant placement. A preclinical study

ObjectivesThis study aimed to assess membrane use with a bone substitute graft for guided bone regeneration (GBR) in experimental dehiscence defects.Materials and methodsMaxillary second incisors (I2) in 9 dogs were extracted. Six weeks later, implants were inserted and experimental dehiscence defects (5 × 3 mm) created on the buccal aspect. The defects and surrounding bone were grafted with deproteinized bovine bone mineral. One side (test) was covered with a resorbable collagen membrane whereas the contralateral side (control) was not. After 6 weeks, histomorphometrical analysis was performed to evaluate: (a) first bone-to-implant contact (fBIC), (b) buccal bone thickness at 1 mm increments from implant shoulder, (c) regenerated area (RA), (d) area and percentages of new bone (B), bone substitute (BS) and mineralized tissue (MT).ResultsThe histological appearance was similar between test and control sites. At central and lateral sections, there were no differences between groups for fBIC, buccal bone thickness, RA, BS, B, %B, MT and %MT. At central sections, membrane use favoured more %BS and %MT (p = 0.052). There was significantly more B, %B and MT at lateral compared to central sections.ConclusionsMembrane use tended to retain more bone substitute, but had no effect on new bone ingrowth. Lateral sections showed significantly more bone ingrowth and mineralized tissue compared to central sections, confirming that new bone ingrowth takes place mainly from the lateral walls of the defect.Clinical relevancePreclinical research to clarify the dynamics of bone regeneration in GBR procedures is relevant in clinical practice.

Selective ion doping core-shell bioceramic fiber-derived granules readily tuning biodegradation and initiating osteoporotic bone defect repair

Osteoporotic bone defect repair is one of the challenges in orthopedics because there are no preferable biomaterials to readily initiate new bone regeneration in critical-size pathological bone damage. Our previous studies revealed that core–shell Ca-phosphate/silicate microspheres can tune time-evolving biodegradation, which is beneficial for modulating bone repair. Herein, we expanded this strategy to develop core–shell-type 5 % Sr- and 8 % Zn-doped wollastonite fiber-derived granules with different porosities (0 %, 10 %, 20 %) in the shell layer. Physicochemical analyses indicated that granules with higher porosity in the shell layer exhibited more appreciable Sr and Zn ion release and biodissolution in vitro. Osteoporotic femoral bony defects in rabbits were used to verify the osteogenic efficacy of the core–shell granules. The granules with 10 % porosity could initiate more osteogenesis within 6 weeks, and the new bone tissue could grow into the defect region, while the new bone tissue only migrated into the periphery pores under the other granule conditions. Histological evaluation also revealed appreciable new bone ingrowth in the granules with 10 % porosity, whereas the other implant groups had limited new bone tissue. These findings demonstrate that bone repair initiation can be enhanced by finely designed local porosity in specific components of core–shell bioceramic fiber-tailoring granules to control bioactive ion release and osteo-stimulation in vivo; moreover, such bioceramic fabrication is promising for developing osteo-stimulative implants to resolve clinically challenging bone defect repair.

Correlation between Ca Release and Osteoconduction by 3D-Printed Hydroxyapatite-Based Templates.

The application of hydroxyapatite (HA)-based templates is quite often seen in bone tissue engineering since that HA is an osteoconductive bioceramic material, which mimics the inorganic component of mineralized tissues. However, the reported osteoconductivity varies in vitro and in vivo, and the levels of calcium (Ca) release most favorable to osteoconduction have yet to be determined. In this study, HA-based templates were fabricated by melt-extrusion 3D-printing and characterized in order to determine a possible correlation between Ca release and osteoconduction. The HA-based templates were blended with poly(lactide-co-trimethylene carbonate) (PLATMC) at three different HA ratios: 10, 30, and 50%. The printability and physical properties of the HA templates were compared with those of pristine PLATMC. In vitro, osteoconductivity was assessed using seeded human bone marrow-derived mesenchymal stem cells. A mild rate of Ca release was observed for HA10 templates, which exhibited higher mineralized extracellular matrix (ECM) secretion than PLATMC at 14 and 21 days. In contrast, the high rate of Ca release exhibited by HA30 and HA50 templates was associated with reduced osteoconduction and impeded mineralized ECM secretion in vitro. Similar results were observed in vivo. In the calvarial defect model in rabbit, PLATMC and HA10 templates exhibited the highest amount of new bone formation, with obvious contact osteogenesis on their surfaces. In contrast, HA30 and HA50 exhibited distant osteogenesis and reduced amounts of new bone ingrowth. It is concluded that HA-based templates are osteoconductive only at low rates of Ca release.

TPMS Microarchitectures for Vertical Bone Augmentation and Osteoconduction: An In Vivo Study.

Triply periodic minimal surface microarchitectures (TPMS) were developed by mathematicians and evolved in all kingdoms of living organisms. Renowned for their lightweight yet robust attributes, TPMS structures find application in diverse fields, such as the construction of satellites, aircrafts, and electric vehicles. Moreover, these microarchitectures, despite their intricate geometric patterns, demonstrate potential for application as bone substitutes, despite the inherent gothic style of natural bone microarchitecture. Here, we produced three TPMS microarchitectures, D-diamond, G-gyroid, and P-primitive, by 3D printing from hydroxyapatite. We explored their mechanical characterization and, further, implanted them to study their bone augmentation and osteoconduction potential. In terms of strength, the D-diamond and G-gyroid performed significantly better than the P-primitive. In a calvarial defect model and a calvarial bone augmentation model, where osteoconduction is determined as the extent of bony bridging of the defect and bone augmentation as the maximal vertical bone ingrowth, the G-gyroid performed significantly better than the P-primitive. No significant difference in performance was observed between the G-gyroid and D-diamond. Since, in real life, the treatment of bone deficiencies in patients comprises elements of defect bridging and bone augmentation, ceramic scaffolds with D-diamond and G-gyroid microarchitectures appear as the best choice for a TPMS-based scaffold in bone tissue engineering.

Impacts of permeability and effective diffusivity of porous scaffolds on bone ingrowth: In silico and in vivo analyses

The permeability and the effective diffusivity of a porous scaffold are critical in the bone-ingrowth process. However, design guidelines for porous structures are still lacking due to inadequate understanding of the complex physiological processes involved. In this study, a model integrating the fundamental biological processes of bone regeneration was constructed to investigate the roles of permeability and effective diffusivity in regulating bone deposition in scaffolds. The in silico analysis results were confirmed in vivo by examining bone depositions in three diamond lattice scaffolds manufactured using selective laser melting. The findings show that the scaffolds with better permeability and effective diffusivity had deeper bone ingrowth and greater bone volume. Compared to permeability, effective diffusivity exhibited greater sensitivity to the orientation of porous structures, and bone ingrowth was deeper in the directions with higher effective diffusivity in spite of identical pore size. A 4.8-fold increase in permeability and a 1.6-fold increase in effective diffusivity by changing the porous structure led to a 1.5-fold increase in newly formed bone. The effective diffusivity of the porous scaffold affects the distribution of osteogenic growth factor, which in turn impacts cell migration and bone deposition through chemotaxis effects. Therefore, effective diffusivity may be a more suitable indicator for porous scaffolds because our study shows changes in this parameter determine changes in bone distribution and bone volume.

Analysis of mechanical characteristics and permeability of TPMS and Voronoi porous structure for bone scaffold

Bionic porous structure has been widely used in the field of bone implantation, because it can imitate the topological structure of bone, reduce the elastic modulus of metal bone implantation, and meet the mechanical properties and material transmission characteristics after implantation. This paper mainly studies the effects of different bionic porous structures on the mechanical and material transport properties of bone scaffolds. Firstly, under the same porosity condition, 12 groups of bionic porous structures with different shapes were designed, including G, P, D, I-type three period minimal surface (TPMS) and Voronoi porous structures with different irregularities. Then uses ABAQUS to carry out mechanical finite element simulation on different bionic porous structures, and uses Ti-6Al-4V alloy as forming material, uses laser powder bed fusion technology (LPBF) to prepare the scaffold, then carries out compression experiments. At the same time, COMSOL software is used to simulate the flow characteristics, analyze the permeability characteristics, and verified through cell experiment in vivo. The results show that the mechanical and permeability are different with vary scaffolds. In terms of topology, the morphological characteristics of TPMS are similar to trabecular bone, its compressive strength is relatively strong. Voronoi scaffold has lower elastic modulus, which can provide sufficient mechanical support while reducing stress shielding. In addition, the permeability of TPMS scaffold is better than Voronoi scaffold, which is helpful to promote cell proliferation and bone ingrowth. These bionic porous structures have their own advantages. Therefore, when designing porous structures for bone implantation, it is necessary to select the appropriate porous structure according to different bone implantation requirements. The research will help promote the clinical application of porous structures in the field of bone implantation, and provide theoretical support for the exploration of bone implantation structure design.

Finite element analysis of patient-specific additive-manufactured implants.

Introduction: Bone tumors, characterized by diverse locations and shapes, often necessitate surgical excision followed by custom implant placement to facilitate targeted bone reconstruction. Leveraging additive manufacturing, patient-specific implants can be precisely tailored with complex geometries and desired stiffness, enhancing their suitability for bone ingrowth. Methods: In this work, a finite element model is employed to assess patient-specific lattice implants in femur bones. Our model is validated using experimental data obtained from an animal study (n = 9). Results: The results demonstrate the accuracy of the proposed finite element model in predicting the implant mechanical behavior. The model was used to investigate the influence of reducing the elastic modulus of a solid Ti6Al4V implant by tenfold, revealing that such a reduction had no significant impact on bone behavior under maximum compression and torsion loading. This finding suggests a potential avenue for reducing the endoprosthesis modulus without compromising bone integrity. Discussion: Our research suggests that employing fully lattice implants not only facilitates bone ingrowth but also has the potential to reduce overall implant stiffness. This reduction is crucial in preventing significant bone remodeling associated with stress shielding, a challenge often associated with the high stiffness of fully solid implants. The study highlights the mechanical benefits of utilizing lattice structures in implant design for enhanced patient outcomes.

A Preclinical Trial Protocol Using an Ovine Model to Assess Scaffold Implant Biomaterials for Repair of Critical-Sized Mandibular Defects.

The present work describes a preclinical trial (in silico, in vivo and in vitro) protocol to assess the biomechanical performance and osteogenic capability of 3D-printed polymeric scaffolds implants used to repair partial defects in a sheep mandible. The protocol spans multiple steps of the medical device development pipeline, including initial concept design of the scaffold implant, digital twin in silico finite element modeling, manufacturing of the device prototype, in vivo device implantation, and in vitro laboratory mechanical testing. First, a patient-specific one-body scaffold implant used for reconstructing a critical-sized defect along the lower border of the sheep mandible ramus was designed using on computed-tomographic (CT) imagery and computer-aided design software. Next, the biomechanical performance of the implant was predicted numerically by simulating physiological load conditions in a digital twin in silico finite element model of the sheep mandible. This allowed for possible redesigning of the implant prior to commencing in vivo experimentation. Then, two types of polymeric biomaterials were used to manufacture the mandibular scaffold implants: poly ether ether ketone (PEEK) and poly ether ketone (PEK) printed with fused deposition modeling (FDM) and selective laser sintering (SLS), respectively. Then, after being implanted for 13 weeks in vivo, the implant and surrounding bone tissue was harvested and microCT scanned to visualize and quantify neo-tissue formation in the porous space of the scaffold. Finally, the implant and local bone tissue was assessed by in vitro laboratory mechanical testing to quantify the osteointegration. The protocol consists of six component procedures: (i) scaffold design and finite element analysis to predict its biomechanical response, (ii) scaffold fabrication with FDM and SLS 3D printing, (iii) surface treatment of the scaffold with plasma immersion ion implantation (PIII) techniques, (iv) ovine mandibular implantation, (v) postoperative sheep recovery, euthanasia, and harvesting of the scaffold and surrounding host bone, microCT scanning, and (vi) in vitro laboratory mechanical tests of the harvested scaffolds. The results of microCT imagery and 3-point mechanical bend testing demonstrate that PIII-SLS-PEK is a promising biomaterial for the manufacturing of scaffold implants to enhance the bone-scaffold contact and bone ingrowth in porous scaffold implants. MicroCT images of the harvested implant and surrounding bone tissue showed encouraging new bone growth at the scaffold-bone interface and inside the porous network of the lattice structure of the SLS-PEK scaffolds.

A numerical investigation for the development of functionally graded Ti/HA tibial implant for total ankle replacement: Influence of material gradation law and volume fraction index.

Stress shielding is one of the major concerns for total ankle replacement implants nowadays, because it is responsible for implant-induced bone resorption. The bone resorption contributes to the aseptic loosening and failure of ankle implants in later stages. To reduce the stress shielding, improvements can be made in the implant material by decreasing the elastic mismatch between the implant and the tibia bone. This study proposes a new functionally graded material (FGM) based tibial implant for minimizing the problem of stress shielding. Three-dimensional finite element (FE) models of the intact tibia and the implanted tibiae were created to study the influence of material gradation law and volume fraction index on stress shielding and implant-bone micromotion. Different implant materials were considered that is, cobalt-chromium, titanium (Ti), and FGM with Ti at the bottom and hydroxyapatite (HA) at the top. The FE models of FGM implants were generated by using different volume fractions and the rule of mixtures. The rule of mixtures was used to calculate the FGM properties based on the local volume fraction. The volume fraction was defined by using exponential, power, and sigmoid laws. For the power and sigmoid law varying volume fraction indices (0.1, 0.2, 0.5, 1, 2, and 5) were considered. The geometry resembling STAR® ankle system tibial implant was considered for the present study. The results indicate that FGMs lower stress shielding but also marginally increase implant-bone micromotion; however, the values were within the acceptable limit for bone ingrowth. It is observed that the material gradation law and volume fraction index influence the performance of FGM tibial implants. The tibial implant composed of FGM using power law with a volume fraction index of 0.1 was the preferred option because it showed the least stress shielding.

Assessment of bone ingrowth around beaded coated tibial implant for total ankle replacement using mechanoregulatory algorithm

The long-term performance of porous coated tibial implants for total ankle replacement (TAR) primarily depends on the extent of bone ingrowth at the bone-implant interface. Although attempts were made for primary fixation for immediate post-operative stability, no investigation was conducted on secondary fixation. The aim of this study is to assess bone ingrowth around the porous beaded coated tibial implant for TAR using a mechanoregulatory algorithm. A realistic macroscale finite element (FE) model of the implanted tibia was developed based on computer tomography (CT) data to assess implant-bone micromotions and coupled with microscale FE models of the implant-bone interface to predict bone ingrowth around tibial implant for TAR. The macroscale FE model was subjected to three near physiological loading conditions to evaluate the site-specific implant-bone micromotion, which were then incorporated into the corresponding microscale model to mimic the near physiological loading conditions. Results of the study demonstrated that the implant experienced tangential micromotion ranged from 0 to 71 μm with a mean of 3.871 μm. Tissue differentiation results revealed that bone ingrowth across the implant ranged from 44 to 96 %, with a mean of around 70 %. The average Young's modulus of the inter-bead tissue layer varied from 1444 to 4180 MPa around the different regions of the implant. The analysis postulates that when peak micromotion touches 30 μm around different regions of the implant, it leads to pronounced fibrous tissues on the implant surface. The highest amount of bone ingrowth was observed in the central regions, and poor bone ingrowth was seen in the anterior parts of the implant, which indicate improper osseointegration around this region. This macro-micro mechanical FE framework can be extended to improve the implant design to enhance the bone ingrowth and in future to develop porous lattice-structured implants to predict and enhance osseointegration around the implant.

Novel nano-thin amorphous Ta-coating on 3D-printed porous TC4 implant: Microstructure and enhanced biological effects

Bone defects caused by tumors, trauma, or other bone diseases are common in clinical practice. Titanium alloy (TC4) and tantalum (Ta) are the primary metallic materials for bone repair. However, TC4 frequently suffers from poor osseointegration and implant loosening, while the high cost of Ta limits its widespread use for reconstructing large bone defects. To address this issue, this research employs magnetron sputtering (MSP) to deposit a nano-thin amorphous Ta-coating on the 3D-printed TC4 implant. SEM examinations of compressed samples show robust interfacial bonding without shedding, while the presence of Ta within the porous structure indicates high coverage. High-resolution TEM analysis first reveals a distinct multilayer amorphous zone consisting of surface TaOx, Ta-coating, and hybrid TaOx and TiOx, along with an impact-refinement nanocrystalline TC4 zone. Insufficient energy leads to the formation of amorphous layers. Meanwhile, interfacial bonding is strengthened through the solid solution of oxygen and interfacial densification of amorphous-crystalline bonding and impact compression. Biological evaluations demonstrate that the Ta-coating exhibits superior cell proliferation and bone ingrowth effects compared to TC4 and pure Ta implants, primarily attributed to the amorphous oxide composition on the surface. This study offers novel, cost-efficient, and excellent biological performance materials for bone defect implants.

Hip joint center lateralization minimally affects the biomechanics of patient-specific flanged acetabular components: A computational model.

Patient-specific flanged acetabular components are utilized to treat failed total hip arthroplasties with large acetabular defects. Previous clinical studies from our institution showed that these implants tend to lateralize the acetabular center of rotation. However, the clinical impact of lateralization on implant survivorship is debated. Our goal was to develop a finite element model to quantify how lateralization of the native hip center affects periprosthetic strain and implant-bone micromotion distributions in a static level gait loading condition. To build the model, we computationally created a superomedial acetabular defect in a computed tomography 3D reconstruction of a native pelvis and designed a flanged acetabular implant to address this simulated bone defect. We modeled two implants, one with ~1 cm and a second with ~2 cm of hip center lateralization. We applied the maximum hip contact force and corresponding abductor force observed during level gait. The resulting strains were compared to bone fatigue strength (0.3% strain) and the micromotions were compared to the threshold for bone ingrowth (20 µm). Overall, the model demonstrated that the additional lateralization only slightly increased the area of bone at risk of failure and decreased the areas compatible with bone ingrowth. This computational study of patient-specific acetabular implants establishes the utility of our modeling approach. Further refinement will yield a model that can explore a multitude of variables and could be used to develop a biomechanically-based acetabular bone loss classification system to guide the development of patient-specific implants in the treatment of large acetabular bone defects.

NOVEL APPROACH: PERCUTANEOUS INJECTION OF BONE-SUBSTITUTE (CERAMENT-GTM) TO AID BONY HEALING IN STIFF NONUNITED COMPLEX OPEN TIBIAL FRACTURES

IntroductionTreatment of non-union in open tibial fractures Gustilo-Anderson(GA)-3A/3B fractures remains a challenging problem. Most of these can be dealt using treatment methods that requires excision of the non-union followed by bone grafting, masquelet technique, or acute shortening. Circular fixators with closed distraction or bone transport also remains a useful option. However, sometimes due to patient specific factors these cannot be used. Recently antibiotic loaded bone substitutes have been increasingly used for repairing infected non-unions. They provide local antibiotic delivery, fill dead space, and act as a bone conductive implant, which is resorted at the end of a few months. We aimed to assess the outcome of percutaneous injection of bone substitute while treating non-union of complex open tibial fractures.Materials &amp; MethodsThree cases of clinical and radiological stiff tibial non-union requiring further intervention were identified from our major trauma open fracture database. Two GA-3B cases, treated with a circular frame developed fracture-related-infection(FRI) manifesting as local cellulitis, loosened infected wires/pins with raised blood-markers, and one case of GA-3A treated with an intramedullary nail. At the time of removal of metalwork/frame, informed consent was obtained and Cerament-GTM(bone-substitute with gentamicin) was percutaneously injected through a small cortical window using a bone biopsy(Jamshedi needle). All patients were allowed to weight bear as tolerated in a well-fitting air-cast boot and using crutches. They were followed up at 6 weekly intervals with clinical assessment of their symptoms and radiographs. Fracture union was assessed using serial radiographs with healing defined as filling of fracture gap, bridging callus and clinical assessment including return to full painless weight bearing.ResultsFollow-up at 6 months showed all fractures had healed with no defect or gaps with evidence of new trabecular bone and significant resorption of Cerament-GTM at final follow-up. There was no evidence of residual infection with restoration of normal limb function. Fractures with no internal fixation showed a mild deformity that had developed during the course of the healing, presumed due to mild collapse in the absence of fixation. These were less than 10 degrees in sagittal and coronal planes and were clinically felt to be insignificant by the patients.ConclusionsCerament-G's unique combination of high dose antibiotics and hydroxy apatite matrix provided by calcium sulphate might help provide an osteoconductive environment to allow these stiff non-unions to heal. The matrix appears to provide a scaffold-like structure that allows new bone in-growth with local release of antibiotics helping reduce deep-seated infections. The final deformation at fracture site underlines the need for fixation- and it is very unlikely that this technique will work in mobile nonunions. Whilst similar fractures may heal without the use of bone substitute injections, the speed of healing in presence of significant fracture gap suggests the use of these bone substitutes did help in our cases. Further studies with a larger cohort, including RCTs, to evaluate the effectiveness of this technique compared to other methods are needed.

A 3D printed ultra-short dental implant based on lattice structures and ZIRCONIA/Ca2SiO4 combination

Additive Manufacturing (AM) enables the generation of complex geometries and controlled internal cavities that are so interesting for the biomedical industry due to the benefits they provide in terms of osseointegration and bone growth. These technologies enable the manufacturing of the so-called lattice structures that are cells with different geometries and internal pores joint together for the formation of scaffold-type structures. In this context, the present paper analyses the feasibility of using diamond-type lattice structures and topology optimisation for the re-design of a dental implant. Concretely, a new ultra-short implant design is proposed in this work. For the manufacturing of the implant, digital light processing additive manufacturing technique technology is considered. The implant was made out of Nano-zirconia and Nano-Calcium Silicate as an alternative material to the more common Ti6Al4V. This material combination was selected due to the properties of the calcium-silicate that enhance bone ingrowth. The influence of different material combination ratios and lattice pore sizes were analysed by means of FEM simulation. For those simulations, a bio-material bone-nanozirconia model was considered that represents the final status after the bone is integrated in the implant. Results shows that the mechanical properties of the biocompatible composite employed were suitable for dental implant applications in dentistry. Based on the obtained results it was seen that those designs with 400 μm and 500 μm pore sizes showed best performance and led to the required factor of safety.

Fixation strength of conformal additively manufactured Ti6Al4V implants in large animal model

Additive manufacturing (AM) enables patient-specific lattice-based implants with porosity engineered to encourage bone ingrowth and to mimic bone’s mechanical stiffness. The strength of the bone-implant interface can be measured through a destructive ‘push-out’ testing. The aim of this study is to explore the effect of implant-bone stiffness ratio (γ) on the push-out force using numerical simulation and a small experimental study. Numerical simulations of an implant-bone interface during a push-out test showed a fundamental change of failure mode for γ ranging from 0.1 to 10. For the geometry considered, the largest push-out forces were predicted for γ ≈ 0.7, essentially doubling the push-out force compared to a solid titanium implant. The experimental and simulation results also demonstrated that using an intermediate stiffness metal implant lattice geometry, γ ≈ 1.35, does not significantly improve the peak force of the push-out test compared to the solid implant. For the experimental study, critical-sized defects were simulated via robotic bone resection in the right lateral distal femur of a group of ~ 2.5-year-old healthy sheep, and then solid or lattice-based Ti6Al4V implants inserted. The femurs were harvested 6 months after implantation. Nine of the implanted femurs (six solid and three lattice-based) were used for fixation testing. The experimental study showed no significant difference in push-out force between a solid and moderately stiff lattice metal implant as indicated by the numerical simulation.

Highly biologically functional magnesium silicate-coated 3D printed round pore-shaped titanium scaffold alters exosomal miRNA expression to promote osteogenic differentiation for bone defect repair

Bone defects are a serious condition that has a significant impact on the function and quality of life of the patient. In severe bone defects, restoring the structure and function of bone tissue is a complex task, and titanium (Ti) implants designed with superior performance can be an alternative. In this study, in order to develop a Ti implant that effectively promotes osseointegration and new bone ingrowth, 3D printing-based magnesium silicate (MgSiO3)-coated round pore-shaped Ti scaffold (S-R/MgSi) was fabricated by standardizing pore size and porosity and designing different pore shapes and selecting the optimal pore shape (round) as well as subsequent hydrothermal synthesis to finally form MgSiO3 coating. The experimental results of Ti scaffolds with different pore shapes showed that S-R is optimal for promoting osteogenic differentiation. After S-R was coated with MgSiO3, S-R/MgSi enhanced the adhesion, proliferation, migration, and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), as well as regulated angiogenesis. In vivo studies, S-R/MgSi significantly promoted new bone ingrowth and was effective in repairing bone defects. Following the mechanism exploration, it was found that exosomes secreted by BMSCs co-cultured with S-R/MgSi (Exo_S-R/MgSi) were more able to promote the osteogenic differentiation of BMSCs. In conclusion, this study not only successfully prepared a new type of Ti implant with superior ability to promote new bone ingrowth, but also provided a new explanation for the mechanism of scaffold surface chemistry affecting osteogenesis from the viewpoint of scaffold surface coating affecting the amount and function of cellular exosome secretion.

From clinic to lab: Advances in porous titanium-based orthopedic implant research

Solid titanium alloys are extensively employed in orthopedic applications due to their reliable mechanical strength, but the stress shielding phenomenon caused by its high elastic modulus and the disadvantage of lack of bone integration may lead to clinical complications. The design of porous structure is a feasible approach to reduce the elastic modulus and promote bone and vascular ingrowth. This paper reviewed the application and current challenges of solid titanium implants in orthopedics. To address the drawbacks and explore porous titanium implants that can effectively integrate with bone tissue while possessing sufficient mechanical strength, this review discussed the latest preclinical research from the perspectives of structural design, surface modification, and material composition. The porous structure parameters that affect bone ingrowth and mechanical strength in implants, including porosity, pore size, cellular structure, and gradient structure, were presented. Based on the current research progress, various surface modification techniques aimed at enhancing the performance of porous titanium implants were overviewed. Moreover, a range of titanium alloys including nickel-titanium alloy, β-titanium alloy, high-entropy alloy, and composite alloys are investigated for their prospective applications in orthopedics. Overall, this review provided valuable insights into the current state of research and highlighted the potential of porous titanium alloys in improving clinical outcomes in orthopedics.

Cyclic flexural fatigue of porous Ti6Al4V constructs for use in mandibular reconstruction

Porous Ti6Al4V constructs have been developed to replace mandibular bone, however the flexural fatigue properties of these constructs must first be assessed. In this study, porous constructs were built by selective laser melting (SLM) and subjected to cyclic flexural loading using a three-point bending setup and a servo-hydraulic Instron machine. Maximum flexural stress was plotted against the number of cycles. Also, numerical models were developed to predict the fatigue strength of porous constructs. These models were validated using experimental test data and extended to account for bone ingrowth. Scanning electron microscopy was used to study the internal and surface structures of dynamically loaded constructs. We found that numerical models of the SLM-built constructs accurately predicted flexural fatigue strength within ≈10 % deviation. Numerical fatigue models and experimental tests demonstrated that fatigue strength of constructs were ≈30 % of their flexural yield strengths. Numerical models with bone ingrowth revealed that fatigue strength was doubled when compared to models without bone ingrowth. This may have been due to a damping effect of bone, resulting in reduction of fatigue failure. Overall, our study demonstrates the effectiveness of using numerical modeling in estimating the fatigue strength of SLM-built constructs intended for mandibular implant designs.