Osseointegration of sintered porous-surfaced and plasma spray-coated implants: An animal model study of early postimplantation healing response and mechanical stability

Innate immune regulation in dental implant osseointegration

PURPOSE

Dental implant osseointegration comprises two types of bone formation-contact and distance osteogenesis-which result in bone formation originating from the implant surface or bone edges, respectively. The physicochemical properties of the implant surface regulate initial contact osteogenesis by directly tuning the osteoprogenitor cells in the peri-implant environment. However, whether these implant surface properties can regulate osteoprogenitor cells distant from the implant remains unclear. Innate immune cells, including neutrophils and macrophages, govern bone metabolism, suggesting their involvement in osseointegration and distance osteogenesis. This narrative review discusses the role of innate immunity in osseointegration and the effects of implant surface properties on distant osteogenesis, focusing on innate immune regulation.

STUDY SELECTION

The role of innate immunity in bone formation and the effects of implant surface properties on innate immune function were reviewed based on clinical, animal, and in vitro studies.

RESULTS

Neutrophils and macrophages are responsible for bone formation during osseointegration, via inflammatory mediators. The microroughness and hydrophilic status of titanium implants have the potential to alleviate this inflammatory response of neutrophils, and induce an anti-inflammatory response in macrophages, to tune both contact and distance osteogenesis through the activation of osteoblasts. Thus, the surface micro-roughness and hydrophilicity of implants can regulate the function of distant osteoprogenitor cells through innate immune cells.

CONCLUSIONS

Surface modification of implants aimed at regulating innate immunity may be useful in promoting further osteogenesis and overcoming the limitations encountered in severe situations, such as early loading protocol application.

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.

A macro-micro FE and ANN framework to assess site-specific bone ingrowth around the porous beaded-coated implant: an example with BOX® tibial implant for total ankle replacement

The use of mechanoregulatory schemes based on finite element (FE) analysis for the evaluation of bone ingrowth around porous surfaces is a viable approach but requires significant computational time and effort. The aim of this study is to develop a combined macro-micro FE and artificial neural network (ANN) framework for rapid and accurate prediction of the site-specific bone ingrowth around the porous beaded-coated tibial implant for total ankle replacement (TAR). A macroscale FE model of the implanted tibia was developed based on CT data. Subsequently, a microscale FE model of the implant-bone interface was created for performing bone ingrowth simulations using mechanoregulatory algorithms. An ANN was trained for rapid and accurate prediction of bone ingrowth. The results predicted by ANN are well comparable to FE-predicted results. Predicted site-specific bone ingrowth using ANN around the implant ranges from 43.04 to 98.24%, with a mean bone ingrowth of around 74.24%. Results suggested that the central region exhibited the highest bone ingrowth, which is also well corroborated with the recent explanted study on BOX®. The proposed methodology has the potential to simulate bone ingrowth rapidly and effectively at any given site over any implant surface.

Non-thermal atmospheric pressure plasma treatment increases hydrophilicity and promotes cell growth on titanium alloys in vitro

Most medical implants are made of titanium. When titanium is exposed to air for a long time, hydrocarbons are deposited and the surface becomes hydrophobic. Cell attachment is important for bone ingrowth to occur on the implant surface, and hydrophilicity can enhance this. We examined whether non-thermal atmospheric pressure plasma treatment could increase the hydrophilicity of the titanium surface. Samples coated with four widely used coating types [grit blasting, micro arc oxidation (MAO), titanium plasma spray (TPS), and direct metal fabrication (DMF)] were treated with plasma. Each of the four surface-treated samples was divided into groups with and without plasma treatment. We analysed wettability by surface analysis and evaluation of contact angles, cell proliferation, and adhesion using scanning electron microscopy (SEM), confocal laser scanning microscopy, absorbance tests, and alkaline phosphatase (ALP) activity assay; four different Ti6Al4V surface types were compared. After plasma treatment, the contact angle was reduced on all surfaces, and the carbon content was reduced on all surfaces based on X-ray photoelectron spectroscopy (XPS) surface analysis. Under confocal laser scanning, the cell layer was thicker on the plasma-treated samples, especially in groups TPS and DMF. Cell proliferation was 41.8%, 17.7%, 54.9%, and 83.8% greater for the plasma- than non-plasma-treated grit blasting, MAO, TPS, and DMF samples, respectively. Hydrophilicity increased significantly under plasma treatment, and biological responsivity was also improved.

Irregular porous titanium enhances implant stability and bone ingrowth in an intra-articular ovine model

Two commercially available porous coatings, Gription and Porocoat, were compared for the first time in a challenging intra-articular, weight-bearing, ovine model. Gription has evolved from Porocoat and has higher porosity, coefficient of friction, and microtextured topography, which are expected to enhance bone ingrowth. Cylindrical implants were press-fit into the weight-bearing regions of ovine femoral condyles and bone ingrowth and fixation strength evaluated 4, 8, and 16 weeks postoperatively. Biomechanical push-out tests were performed on lateral femoral condyles (LFCs) to evaluate the strength of the bone-implant interface. Bone ingrowth was assessed in medial femoral condyles (MFCs) as well as implants retrieved from LFCs following biomechanical testing using backscattered electron microscopy and histology. By 16 weeks, Gription-coated implants exhibited higher force (2455 ± 1362 vs. 1002 ± 1466 N; p = 0.046) and stress (12.60 ± 6.99 vs. 5.14 ± 7.53 MPa; p = 0.046) at failure, and trended towards higher stiffness (11,510 ± 7645 vs. 5010 ± 8374 N/mm; p = 0.061) and modulus of elasticity (591 ± 392 vs. 256 ± 431 MPa; p = 0.061). A strong, positive correlation was detected between bone ingrowth in LFC implants and failure force (r = 0.93, p < 10^-13 ). By 16 weeks, bone ingrowth in Gription-coated implants in MFCs was 10.50 ± 6.31% compared to 5.88 ± 2.77% in Porocoat (p = 0.095). Observations of the bone-implant interface, made following push-out testing, showed more bony material consistently adhered to Gription compared to Porocoat at all three time points. Gription provided superior fixation strength and bone ingrowth by 16 weeks.

Rapid Personalised Virtual Planning and On-Demand Surgery for Acute Spinal Trauma Using 3D-Printing, Biomodelling and Patient-Specific Implant Manufacture

Three-dimensional printing is a rapidly growing field, with extensive application to orthopaedics and spinal surgery. Three-dimensional-printed (3DP) patient-specific implants (PSIs) offer multiple potential benefits over generic alternatives, with their use increasingly being described in the spinal literature. This report details a unique, emergency case of a traumatic spinal injury in a 31-year-old male, acquired rurally and treated with a 3DP PSI in a tertiary unit. With increasing design automation and process improvements, rapid, on-demand virtual surgical planning (VSP) and 3DP PSIs may present the future of orthopaedics and trauma care, enabling faster, safer, and more cost-effective patient-specific procedures.

Latest Trends in Surface Modification for Dental Implantology: Innovative Developments and Analytical Applications

An increase in the world population and its life expectancy, as well as the ongoing concern about our physical appearance, have elevated the relevance of dental implantology in recent decades. Engineering strategies to improve the survival rate of dental implants have been widely investigated, focusing on implant material composition, geometry (usually guided to reduce stiffness), and interface surrounding tissues. Although efforts to develop different implant surface modifications are being applied in commercial dental prostheses today, the inclusion of surface coatings has gained special interest, as they can be tailored to efficiently enhance osseointegration, as well as to reduce bacterial-related infection, minimizing peri-implantitis appearance and its associated risks. The use of biomaterials to replace teeth has highlighted the need for the development of reliable analytical methods to assess the therapeutic benefits of implants. This literature review considers the state-of-the-art strategies for surface modification or coating and analytical methodologies for increasing the survival rate for teeth restoration.

Bone Ingrowth Around an Uncemented Femoral Implant Using Mechanoregulatory Algorithm: A Multiscale Finite Element Analysis

The primary fixation and long-term stability of a cementless femoral implant depend on bone ingrowth within the porous coating. Although attempts were made to quantify the peri-implant bone ingrowth using the finite element (FE) analysis and mechanoregulatory principles, the tissue differentiation patterns on a porous-coated hip stem have scarcely been investigated. The objective of this study is to predict the spatial distribution of evolutionary bone ingrowth around an uncemented hip stem, using a three-dimensional (3D) multiscale mechanobiology-based numerical framework. Multiple load cases representing a variety of daily living activities, including walking, stair climbing, sitting down, and standing up from a chair, were used as applied loading conditions. The study accounted for the local variations in host bone material properties and implant-bone relative displacements of the macroscale implanted FE model, in order to predict bone ingrowth in microscale representative volume elements (RVEs) of 12 interfacial regions. In majority RVEs, 20-70% bone tissue (immature and mature) was predicted after 2 months, contributing toward a progressive increase in average Young's modulus (1200-3000 MPa) of the interbead tissue layer. Higher bone ingrowth (mostly greater than 60%) was predicted in the anterolateral regions of the implant, as compared to the posteromedial side (20-50%). New bone tissue was formed deeper inside the interbead spacing, adhering to the implant surface. The study helps to gain an insight into the degree of osseointegration of a porous-coated femoral implant.

Does Low-Magnitude High-Frequency Vibration (LMHFV) Worth for Clinical Trial on Dental Implant? A Systematic Review and Meta-Analysis on Animal Studies

Being as a non-pharmacological medical intervention, low-magnitude high-frequency vibration (LMHFV) has shown a positive effect on bone induction and remodeling for various muscle diseases in animal studies, among which dental implants osteointegration were reported to be improved as well. However, whether LMHFV can be clinically used in dental implant is still unknown. In this study, efficacy, parameters and side effects of LMHFV were analyzed via data before 15th July 2020, collecting from MEDLINE/PubMed, Embase, Ovid and Cochrane Library databases. In the screened 1,742 abstracts and 45 articles, 15 animal studies involving 972 implants were included. SYRCLE's tool was performed to assess the possible risk of bias for each study. The GRADE approach was applied to evaluate the quality of evidence. Random effects meta-analysis detected statistically significant in total BIC (P < 0.0001) and BV/TV (P = 0.001) upon loading LMHFV on implants. To conclude, LMHFV played an active role on BIC and BV/TV data according to the GRADE analysis results (medium and low quality of evidence). This might illustrate LMHFV to be a worthy way in improving osseointegration clinically, especially for osteoporosis.

Systematic Review Registration:https://www.crd.york.ac.uk/PROSPERO, identifier: NCT02612389

Implant resonance and the mechanostat theory: Applications of therapeutic ultrasound for porous metallic scaffolds

The development of treatment strategies for improving secondary stability at the bone-implant interface is a challenge. Porous implants are one solution for improving long-term implant stability, but the osteoconduction process of implants into the bone can be slow. Strain-driven osteogenesis from the mechanostat theory offers insight into pathways for post-operative treatment but mechanisms to deliver strain to the bone-implant interface need refinement. In this work, the use of therapeutic ultrasound is simulated to induce resonance into a porous implant structure. Local strains through the scaffold are measured by varying systemic variables such as damping ratio, applied vibrational force, primary bone-implant stability, and input frequency. At the natural frequency of the system with applied forces of 0.5 N and a damping ratio of 0.5%, roughly half of the nodes in the simulated environment exceed the microstrain threshold of 1000 με required for new bone formation. A high degree of sensitivity was noted upon changing input frequency, with minor sensitivities arising from damping ratio and applied vibrational force. These findings suggest that the application of therapeutic resonance to improve osseointegration of the bone-implant interface may be viable for applications including dental implants or segmental bone defects.

The influence of implant design on the kinetics of osseointegration and bone anchorage homeostasis

Titanium implants have shown considerable success in terms of achieving quick and long-lasting stability in bone through the process of osseointegration. Further work aims to improve implant success rates by modifying implant design on the nano-, micro-, and macro- scales with the goal of achieving higher levels of bone anchorage more quickly. However, the most frequently used methods of analysis do not investigate bone anchorage as a whole but as a series of discrete points, potentially missing relevant insight which could inform the effects of topography on these 3 scale ranges. Herein we utilize an asymptotic curve fitting method to obtain a biologically relevant description of reverse torque data and compare the anchorage of 12 different implant groups. Implant surface topography had a significant effect on the rate and degree of anchorage achieved during the initial bone formation period of osseointegration but was not found to influence the relative change in anchorage during bony remodeling. Threaded implants significantly decreased the time required to reach peak anchorage compared to non-threaded implants and implants with micro-topographically complex surfaces required greater torque to be removed than implants without such features. Nanotopography increased overall anchorage and decreased the time required to reach peak anchorage but to a lesser degree than microtopography or macrogeometry respectively. The curve fitting method utilized in the present study allows for a more integrated analysis of bone anchorage and permits investigation of osseointegration with respect to time, which may lead to a more targeted approach to implant design.

Osseointegration of 3D porous and solid Ti-6Al-4V implants - Narrow gap push-out testing and experimental setup considerations

Porosity in titanium alloy materials improves the bony integration and mechanical properties of implants. In certain areas of application such as vertebral spacers or trabecular bone replacement (e.g. wedge augmentation in prosthetics), surface structures are desirable that promote bone integration and have biomechanical properties that are resistant to intraosseous load transfers and at the same time resemble the stiffness of bone to possible reduce the risk of stress shielding. In the present study, we investigated the biomechanical push-out behavior of an open-porous Ti-6Al-4V material that was produced in a space-holder and sintering method creating a 3-D through-pores trabecular design that corresponds with the inhomogeneity and size relationships of trabecular bone. The short-term and mid-term effects of the material properties on osseointegration in a biomechanical push-out study were compared to those of to a conventional solid Ti-6Al-4V material. In order to raise the measurement accuracy we implemented a strict study protocol. Pairs of cylindrical implants with a porosity of 49% and an average pore diameter of 400 μm and equal sized solid, corundum blasted devices as reference were bilaterally implanted press fit in the lateral femoral condyles of 14 rabbits. After sacrifice at 4 and 12 weeks, a push-out test was performed while the test set-up was designed to ensure conformity of implant axes and direction of applied force. Maximum holding force, Young's modulus, and mode of failure were recorded. Results of maximum push-out force (F-max) revealed a significant material effect (p < 0.05) in favor of porous implants after 4 weeks of osseohealing (6.39 vs. 3.36 N/mm²) as well as after 12 weeks of osseoremodeling (7.58 vs. 4.99 N/mm²). Evaluation of the failure mode resulted in three different types of displacement characteristics, which revealed a different mechanism of osseous anchoring between the two types of implants and substantiate the F-max and Young's modulus results. Conclusively, the porous implant offers surface properties that significantly improve its osseous stability compared to solid material under experimental conditions. In addition, we have optimized our study protocol for biomechanical push-out tests to produce precise and comparable results.

Studies on physiochemical modifications on biologically important hydroxyapatite materials and their characterization for medical applications

Crystalline Hydroxyapatite (Ca10 (PO₄)₆(OH)₂) non linear optical crystal plays a major role in biomedical applications. Crystalline Hydroxyapatite was synthesized using natural human bone sample by thermal methods. This Hydroxyapatite was characterized by Fourier Transform infra-red spectroscopy (FTIR), scanning electron microscope, UV-Vis spectroscopy, X-ray diffraction and conductivity studies. It was found that compared to bovine bone, the changes to the molecular structure associated with the mineral (carbonate) and the organic content (collagen) was good. The sintering methods showed that the synthesized Hydroxyapatite has remarkable heat stability up to 750 °C. The XRD and FTIR results showed a high purity of the synthesized HA powders, in terms of the electronic transitions, in UV-Vis which require a certain amount of energy it is proportional to the wavelength absorbed and absorption coefficient, the optical band energy of the natural human bone is found to be 4.65 eV and the electrical conductivity of the bone material is 9.11 × 10^-6 Ω ^-1 cm^-1. Natural bone Hydroxyapatite gives superior results.

Effect of Autoclaving Time on Corrosion Resistance of Sandblasted Ti G4 in Artificial Saliva

Titanium Grade 4 (Ti G4) is the most commonly used material for dental implants due to its excellent mechanical properties, chemical stability and biocompatibility. A thin, self-passive oxide layer with protective properties to corrosion is formed on its surface. However, the spontaneous TiO₂ layer is chemically unstable. In this work, the impact of autoclaving time on corrosion resistance of Ti G4 in artificial saliva solution with pH = 7.4 at 37 °C was studied. Ti G4 was sandblasted with white Al₂O₃ particles and autoclaved for 30–120 min. SEM, EDS, 2D roughness profiles, confocal laser scanning microscopy, and a Kelvin scanning probe were used for the surface characterization of the Ti G4 under study. In vitro corrosion resistance tests were conducted using open circuit potential, polarization curves, and electrochemical impedance spectroscopy measurements. It was found that Sa parameter, electron work function, and thickness of the oxide layers, determined based on impedance measurements, increased after autoclaving. The capacitive behavior and high corrosion resistance of tested materials were revealed. The improvement in the corrosion resistance after autoclaving was due to the presence of oxide layers with high chemical stability. The optimal Ti G4 surface for dentistry can be obtained by sandblasting with Al₂O₃ with an average grain size of 53 µm, followed by autoclaving for 90 min.

Tissue Integration and Biological Cellular Response of SLM-Manufactured Titanium Scaffolds

Background: SLM (Selective Laser Melting)–manufactured Titanium (Ti) scaffolds have a significant value for bone reconstructions in the oral and maxillofacial surgery field. While their mechanical properties and biocompatibility have been analysed, there is still no adequate information regarding tissue integration. Therefore, the aim of this study is a comprehensive systematic assessment of the essential parameters (porosity, pore dimension, surface treatment, shape) required to provide the long-term performance of Ti SLM medical implants. Materials and methods: A systematic literature search was conducted via electronic databases PubMed, Medline and Cochrane, using a selection of relevant search MeSH terms. The literature review was conducted using the preferred reporting items for systematic reviews and meta-analysis (PRISMA). Results: Within the total of 11 in vitro design studies, 9 in vivo studies, and 4 that had both in vitro and in vivo designs, the results indicated that SLM-generated Ti scaffolds presented no cytotoxicity, their tissue integration being assured by pore dimensions of 400 to 600 µm, high porosity (75–88%), hydroxyapatite or SiO2–TiO2 coating, and bioactive treatment. The shape of the scaffold did not seem to have significant importance. Conclusions: The SLM technique used to fabricate the implants offers exceptional control over the structure of the base. It is anticipated that with this technique, and a better understanding of the physical interaction between the scaffold and bone tissue, porous bases can be tailored to optimize the graft’s integrative and mechanical properties in order to obtain structures able to sustain osseous tissue on Ti.

Optimized Nanointerface Engineering of Micro/Nanostructured Titanium Implants to Enhance Cell-Nanotopography Interactions and Osseointegration

The success of orthopedic implants requires rapid and complete osseointegration which relies on an implant surface with optimal features. To enhance cellular function in response to the implant surface, micro- and nanoscale topography have been suggested as essential. The aim of this study was to identify an optimized Ti nanostructure and to introduce it onto a titanium plasma-sprayed titanium implant (denoted NTPS-Ti) to confer enhanced immunomodulatory properties for optimal osseointegration. To this end, three types of titania nanostructures, namely, nanowires, nanonests, and nanoflakes, were achieved on hydrothermally prepared Ti substrates. The nanowire surface modulated protein conformation and directed integrin binding and specificity in such a way as to augment the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) and induce a desirable osteoimmune response of RAW264.7 macrophages. In a coculture system, BMSCs on the optimized micro/nanosurface exerted enhanced effects on nonactivated or lipopolysaccharide-stimulated macrophages, causing them to adopt a less inflammatory macrophage profile. The enhanced immunomodulatory properties of BMSCs grown on NTPS-Ti depended on a ROCK-medicated cyclooxygenase-2 (COX2) pathway to increase prostaglandin E2 (PGE2) production, as evidenced by decreased production of PGE2 and concurrent inhibition of immunomodulatory properties after treatment with ROCK or COX2 inhibitors. In vivo evaluation showed that the NTPS-Ti implant resulted in enhanced osseointegration compared with the TPS-Ti and Ti implants. The results obtained in our study may provide a prospective approach for enhancing osseointegration and supporting the application of micro/nanostructured Ti implants.

The effect of strontium and silicon substituted hydroxyapatite electrochemical coatings on bone ingrowth and osseointegration of selective laser sintered porous metal implants

Additive manufactured, porous bone implants have the potential to improve osseointegration and reduce failure rates of orthopaedic devices. Substantially porous implants are increasingly used in a number of orthopaedic applications. HA plasma spraying-a line of sight process-cannot coat the inner surfaces of substantially porous structures, whereas electrochemical deposition of calcium phosphate can fully coat the inner surfaces of porous implants for improved bioactivity, but the osseous response of different types of hydroxyapatite (HA) coatings with ionic substitutions has not been evaluated for implants in the same in vivo model. In this study, laser sintered Ti6Al4V implants with pore sizes of Ø 700 μm and Ø 1500 μm were electrochemically coated with HA, silicon-substituted HA (SiHA), and strontium-substituted HA (SrHA), and implanted in ovine femoral condylar defects. Implants were retrieved after 6 weeks and histological and histomorphometric evaluation were compared to electrochemically coated implants with uncoated and HA plasma sprayed controls. The HA, SiHA and SrHA coatings had Ca:P, Ca:(P+Si) and (Ca+Sr):P ratios of 1.53, 1.14 and 1.32 respectively. Electrochemically coated implants significantly promoted bone attachment to the implant surfaces of the inner pores and displayed improved osseointegration compared to uncoated scaffolds for both pore sizes (p<0.001), whereas bone ingrowth was restricted to the surface for HA plasma coated or uncoated implants. Electrochemically coated HA implants achieved the highest osseointegration, followed by SrHA coated implants, and both coatings exhibited significantly more bone growth than plasma sprayed groups (p≤0.01 for all 4 cases). SiHA had significantly more osseointegration when compared against the uncoated control, but no significant difference compared with other coatings. There was no significant difference in ingrowth or osseointegration between pore sizes, and the bone-implant-contact was significantly higher in the electrochemical HA than in SiHA or SrHA. These results suggest that osseointegration is insensitive to pore size, whereas surface modification through the presence of an osteoconductive coating plays an important role in improving osseointegration, which may be critically important for extensively porous implants.

Anterior Lumbar Interbody Fusion Using a Personalized Approach: Is Custom the Future of Implants for Anterior Lumbar Interbody Fusion Surgery?

BACKGROUND

Spine surgery has the potential to benefit from the use of three-dimensional (3D) printing technology (additive manufacturing), particularly in cases of complex anatomic diseases. Custom devices have the potential to reduce operative times, reduce blood loss, provide immediate stability, and improve fusion rates.

CASE DESCRIPTION

A 34-year-old man presented with 3-year history of bilateral L5 radiculopathy caused by bilateral L5 pars defect, L5/S1 degenerative disc disease, and severe foraminal stenosis. Anterior lumbar interbody fusion surgery was determined to be the most efficacious method for distraction of the disc space to increase the foraminal volume and stabilization of the motion segment. Surgical decompression and reconstruction was performed in combination with a 3D printed custom interbody implant. Custom design features included corrective angulation to restore lumbar lordosis, preplanned screw holes in the 3D implant, and device end plate interface geometry designed to shape-match with the patient's end plate anatomy.

CONCLUSIONS

The use of patient-specific implants has reduced operative time significantly, which may offset costs of increased time spent preplanning the procedure. Surgical procedures can be preplanned using 3D models reconstructed from patient computed tomography and/or magnetic resonance imaging scans. Planning can be aided by 3D printed models of patient anatomy, which surgeons can use in training before performing complex procedures. When considering implants and prostheses, the use of 3D printing allows a superior anatomic fit for the patient compared with generic devices, with the potential to improve restoration of nonpathologic anatomy.

The relationship between substrate morphology and biological performances of nano-silver-loaded dopamine coatings on titanium surfaces

Biomedical device-associated infection (BAI) and lack of osseointegration are the main causes of implant failure. Therefore, it is imperative for implants not only to depress microbial activity and biofilm colonization but also to prompt osteoblast functions and osseointegration. As part of the coating development for implants, the interest of in vitro studies on the interaction between implant substrate morphology and the coating's biological performances is growing. In this study, by harnessing the adhesion and reactivity of bioinspired polydopamine, nano-silver was successfully anchored onto micro/nanoporous as well as smooth titanium surfaces to analyse the effect of substrate morphology on biological performances of the coatings. Compared with the smooth surface, a small size of nano-silver and high silver content was found on the micro/nanoporous surface. More mineralization happened on the coating on the micro/nanoporous structure than on the smooth surface, which led to a more rapid decrease of silver release from the micro/nanoporous surface. Antimicrobial tests indicated that both surfaces with resulting coating inhibit microbial colonization on them and growth around them, indicating that the coating eliminates the shortcoming of the porous structure which render the implant extremely susceptible to BAI. Besides, the multiple osteoblast responses of nano-silver-loaded dopamine coatings on both surfaces, i.e. attachment, proliferation and differentiation, have deteriorated, however the mineralized surfaces of these coatings stimulated osteoblast proliferation and differentiation, especially for the micro/nanoporous surface. Therefore, nano-silver-loaded dopamine coatings on micro/nanoporous substratum may not only reduce the risk of infection but also facilitate mineralization during the early post-operative period and then promote osseointegration owing to the good osteoblast-biocompatibility of the mineralized surface. These results clearly highlight the influence of the substrate morphology on the biological performances of implant coating.

L5 En-Bloc Vertebrectomy with Customized Reconstructive Implant: Comparison of Patient-Specific Versus Off-the-Shelf Implant

BACKGROUND

Spine surgery has the potential to benefit from additive manufacturing/3-dimensional printing (3DP) technology with complex anatomical pathologies requiring reconstruction, with the potential to customize surgery to reduce operative times, reduce blood loss, provide immediate stability, and potentially improve fusion rates. We report a unique case of intraoperative trial placement of a custom patient-specific implant (PSI) versus the final implantation of a customizable off-the-shelf (OTS) implant. Data collected for comparison included time to implant, ease of implantation, firmness of press-fit, and fixation options after implantation.

CASE DESCRIPTION

A 64-year-old man presented with low back pain. Computed tomography and magnetic resonance imaging revealed a solitary lesion in the L5 vertebral body, confirmed by positron emission tomography scan. Removal of the L5 vertebral body was performed, and reconstruction was achieved with an expandable cage. The time of implant insertion was minimal with the PSI (90 seconds) versus the OTS (>40 minutes). Immediate press-fit and "firmness" of implantation was clearly superior with the PSI, although this was an intraoperative subjective assessment. Other benefits include integral fixation that is predetermined with the PSI, reduced time and blood loss, and ease of bone grafting with a PSI.

CONCLUSIONS

Use of 3DP has been able to reduce operative time significantly. Surgeons can train before performing complex procedures, which enhances their presurgical planning, with the goal to maximize patient outcomes. When considering implants and prostheses, the use of 3DP allows a superior anatomical fit for the patient, with the potential to improve restoration of anatomy.

Natural and Synthetic Biodegradable Polymers: Different Scaffolds for Cell Expansion and Tissue Formation

The formation of tissue produced by implanted cells is influenced greatly by the scaffold onto which they are seeded. In the long term it is often preferable to use a biodegradable material scaffold so that all the implanted materials will disappear, leaving behind only the generated tissue. Research in this area has identified several natural biodegradable materials. Among them, hydrogels are receiving increasing attention due to their ability to retain a great quantity of water, their good biocompatibility, their low interfacial tension, and the minimal mechanical and frictional irritation that they cause. Biocompatibility is not an intrinsic property of materials; rather it depends on the biological environment and the tolerability that exists with respect to specific polymer-tissue interactions. The most often utilized biodegradable synthetic polymers for 3D scaffolds in tissue engineering are saturated poly-a-hydroxy esters, including poly(lactic acid) (PLA) and poly(glycolic acid) (PGA), as well as poly(lactic-co-lycolide) (PLGA) copolymers. Hard materials provide compressive and torsional strength; hydrogels and other soft composites more effectively promote cell expansion and tissue formation. This review focuses on the future potential for understanding the characteristics of the biomaterials considered evaluated for clinical use in order to repair or to replace a sizable defect by only harvesting a small tissue sample.

Novel Approach in the Use of Plasma Spray: Preparation of Bulk Titanium for Bone Augmentations

Thermal plasma spray is a common, well-established technology used in various application fields. Nevertheless, in our work, this technology was employed in a completely new way; for the preparation of bulk titanium. The aim was to produce titanium with properties similar to human bone to be used for bone augmentations. Titanium rods sprayed on a thin substrate wire exerted a porosity of about 15%, which yielded a significant decrease of Young′s modulus to the bone range and provided rugged topography for enhanced biological fixation. For the first verification of the suitability of the selected approach, tests of the mechanical properties in terms of compression, bending, and impact were carried out, the surface was characterized, and its compatibility with bone cells was studied. While preserving a high enough compressive strength of 628 MPa, the elastic modulus reached 11.6 GPa, thus preventing a stress-shielding effect, a generally known problem of implantable metals. U-2 OS and Saos-2 cells derived from bone osteosarcoma grown on the plasma-sprayed surface showed good viability.

Fortifying the Bone-Implant Interface Part 2: An In Vivo Evaluation of 3D-Printed and TPS-Coated Triangular Implants

BACKGROUND

Minimally invasive surgical fusion of the sacroiliac (SI) joint using machined solid triangular titanium plasma spray (TPS) coated implants has demonstrated positive clinical outcomes in SI joint pain patients. Additive manufactured (AM), i.e. 3D-printed, fenestrated triangular titanium implants with porous surfaces and bioactive agents, such as nanocrystalline hydroxyapatite (HA) or autograft, may further optimize bony fixation and subsequent biomechanical stability.

METHODS

A bilateral ovine distal femoral defect model was used to evaluate the cancellous bone-implant interfaces of TPS-coated and AM implants. Four implant groups (n=6/group/time-point) were included: 1)TPS-coated, 2)AM, 3)AM+HA, and 4)AM+Autograft. The bone-implant interfaces of 6- and 12-week specimens were investigated via radiographic, biomechanical, and histomorphometric methods.

RESULTS

Imaging showed peri-implant bone formation around all implants. Push-out testing demonstrated forces greater than 2500 N, with no significant differences among groups. While TPS implants failed primarily at the bone-implant interface, AM groups failed within bone ~2-3mm away from implant surfaces. All implants exhibited bone ongrowth, with no significant differences among groups. AM implants had significantly more bone ingrowth into their porous surfaces than TPS-coated implants (p<0.0001). Of the three AM groups, AM+Auto implants had the greatest bone ingrowth into the porous surface and through their core (p<0.002).

CONCLUSIONS

Both TPS and AM implants exhibited substantial bone ongrowth and ingrowth, with additional bone through growth into the AM implants' core. Overall, AM implants experienced significantly more bone infiltration compared to TPS implants. While HA-coating did not further enhance results, the addition of autograft fostered greater osteointegration for AM implants.

CLINICAL RELEVANCE

Additive manufactured implants with a porous surface provide a highly interconnected porous surface that has comparatively greater surface area for bony integration. Results suggest this may prove advantageous toward promoting enhanced biomechanical stability compared to TPS-coated implants for SI joint fusion procedures.

The effect of 2 versus 4 implants on implant stability in mandibular overdentures: A randomized controlled trial

STATEMENT OF PROBLEM

Dental research is rich with articles that investigated the influence of host-site variables, some implant-related variables (implant length, diameter, taper, design, location, and surface topography), different loading protocols or surgical procedures, and measurement methodology on dental implant stability. However, the number of implants and its effect on implant stability remain unclear.

PURPOSE

The purpose of this randomized clinical trial was to investigate the influence of implant number on implant stability by comparing 2 versus 4 implants in mandibular implant overdentures.

MATERIAL AND METHODS

The trial included 20 participants with edentulous mandibular ridges. Participants were randomly assigned to 2 equal groups, a 4-implant (experimental) group consisting of 4 implants installed in lateral-canine and premolar regions; and a 2-implant (control) group, consisting of 2 implants in lateral-canine regions. Implant stability was measured using resonance frequency analysis at implant placement and then at 1, 3, 6, 9, and 12 months. The Student t test was used to compare the implant stability quotient (ISQ) values of the anterior implants in the 4-implant and 2-implant groups. One-way ANOVA followed by the post hoc Bonferroni test was used to compare ISQ values among the different follow-up periods within each group (α=.05).

RESULTS

Mean ISQ values for anterior implants in the 4-implant group were slightly higher than those recorded for the 2-implant group at all follow-up periods. However, these differences were not statistically significant (P>.05). Within-group comparison revealed an initial decrease in implant stability for all implants. This decrease was statistically significant for the 2-implant group (P<.001) and for posterior implants in the 4-implant group (P<.001). This was then followed by a gradual increase in ISQ values for all implants in both groups.

CONCLUSIONS

Increasing the number of implants from 2 to 4 in mandibular implant overdentures did not have a significant influence on implant stability.

Role of magnesium oxide and strontium oxide as modifiers in silicate-based bioactive glasses: Effects on thermal behaviour, mechanical properties and in-vitro bioactivity

The composition of a CaO-rich silicate bioglass (BG_Ca-Mix, in mol%: 2.3 Na₂O; 2.3 K₂O; 45.6 CaO; 2.6 P₂O₅; 47.2 SiO₂) was modified by replacing a fixed 10mol% of CaO with MgO or SrO or fifty-fifty MgO-SrO. The thermal behaviour of the modified glasses was accurately evaluated via differential thermal analysis (DTA), heating microscopy and direct sintering tests. The presence of MgO and/or SrO didn't interfere with the thermal stability of the parent glass, since all the new glasses remained completely amorphous after sintering (treatment performed at 753°C for the glass with MgO; at 750°C with SrO; at 759°C with MgO and SrO). The sintered samples achieved good mechanical properties, with a Young's modulus ranging between 57.9±6.7 for the MgO-SrO modified composition and 112.6±8.0GPa for the MgO-modified one. If immersed in a simulated body fluid (SBF), the modified glasses after sintering retained the strong apatite forming ability of the parent glass, in spite of the presence of MgO and/or SrO. Moreover, the sintered glasses, tested with MLO-Y4 osteocytes by means of a multi-parametrical approach, showed a good bioactivity in vitro, since neither the glasses nor their extracts caused any negative effect on cell viability or any inhibition on cell growth. The best results were achieved by the MgO-modified glasses, both BGMIX_Mg and BGMIX_MgSr, which were able to exert a strong stimulating effect on the cell growth, thus confirming the beneficial effect of MgO on the glass bioactivity.

Surface Modifications and Their Effects on Titanium Dental Implants

This review covers several basic methodologies of surface treatment and their effects on titanium (Ti) implants. The importance of each treatment and its effects will be discussed in detail in order to compare their effectiveness in promoting osseointegration. Published literature for the last 18 years was selected with the use of keywords like titanium dental implant, surface roughness, coating, and osseointegration. Significant surface roughness played an important role in providing effective surface for bone implant contact, cell proliferation, and removal torque, despite having good mechanical properties. Overall, published studies indicated that an acid etched surface-modified and a coating application on commercial pure titanium implant was most preferable in producing the good surface roughness. Thus, a combination of a good surface roughness and mechanical properties of titanium could lead to successful dental implants.

Friction coefficient and effective interference at the implant-bone interface

Although the contact pressure increases during implantation of a wedge-shaped implant, friction coefficients tend to be measured under constant contact pressure, as endorsed in standard procedures. Abrasion and plastic deformation of the bone during implantation are rarely reported, although they define the effective interference, by reducing the nominal interference between implant and bone cavity. In this study radial forces were analysed during simulated implantation and explantation of angled porous and polished implant surfaces against trabecular bone specimens, to determine the corresponding friction coefficients. Permanent deformation was also analysed to determine the effective interference after implantation. For the most porous surface tested, the friction coefficient initially increased with increasing normal contact stress during implantation and then decreased at higher contact stresses. For a less porous surface, the friction coefficient increased continually with normal contact stress during implantation but did not reach the peak magnitude measured for the rougher surface. Friction coefficients for the polished surface were independent of normal contact stress and much lower than for the porous surfaces. Friction coefficients were slightly lower for pull-out than for push-in for the porous surfaces but not for the polished surface. The effective interference was as little as 30% of the nominal interference for the porous surfaces. The determined variation in friction coefficient with radial contact force, as well as the loss of interference during implantation will enable a more accurate representation of implant press-fitting for simulations.

Effect of surface roughness on osteogenesis in vitro and osseointegration in vivo of carbon fiber-reinforced polyetheretherketone-nanohydroxyapatite composite

As United States Food and Drug Administration-approved implantable material, carbon fiber-reinforced polyetheretherketone (CFRPEEK) possesses an adjustable elastic modulus similar to cortical bone and is a prime candidate to replace surgical metallic implants. The bioinertness and inferior osteogenic properties of CFRPEEK, however, limit its clinical application as orthopedic/dental implants. In this study, CFRPEEK–nanohydroxyapatite ternary composites (PEEK/n-HA/CF) with variable surface roughness have been successfully fabricated. The effect of surface roughness on their in vitro cellular responses of osteoblast-like MG-63 cells (attachment, proliferation, apoptosis, and differentiation) and in vivo osseointegration is evaluated. The results show that the hydrophilicity and the amount of Ca ions on the surface are significantly improved as the surface roughness of composite increases. In cell culture tests, the results reveal that the cell proliferation rate and the extent of osteogenic differentiation of cells are a function of the size of surface roughness. The composite with moderate surface roughness significantly increases cell attachment/proliferation and promotes the production of alkaline phosphatase (ALP) activity and calcium nodule formation compared with the other groups. More importantly, the PEEK/n-HA/CF implant with appropriate surface roughness exhibits remarkably enhanced bioactivity and osseointegration in vivo in the animal experiment. These findings will provide critical guidance for the design of CFRPEEK-based implants with optimal roughness to regulate cellular behaviors, and to enhance biocompability and osseointegration. Meanwhile, the PEEK/n-HA/CF ternary composite with optimal surface roughness might hold great potential as bioactive biomaterial for bone grafting and tissue engineering applications.

The effect of surface morphology on the primary fixation strength of uncemented femoral knee prosthesis: a cadaveric study

We investigated the effect of surface morphology on the mechanical performance of uncemented femoral knee prosthesis. Eighteen implants were implanted on nine paired femurs and then pushed-off (left legs: a novel surface morphology; right legs: Porocoat as baseline). Bone mineral density (BMD) and anteroposterior dimension were not significantly different between groups. The insertion force was not significantly different, however, the loosening force was significantly higher in the novel group (P=0.007). BMD had a direct relationship with the insertion and loosening force (P<0.001). The effect of surface morphology on implant alignment was very small. We conclude that the surface properties create a higher frictional resistance, thereby providing a better inherent stability of implants featuring the novel surface morphology.

Evaluation of osseous integration of PVD-silver-coated hip prostheses in a canine model

Infection associated with biomaterials used for orthopedic prostheses remains a serious complication in orthopedics, especially tumor surgery. Silver-coating of orthopedic (mega)prostheses proved its efficiency in reducing infections but has been limited to surface areas exposed to soft tissues due to concerns of silver inhibiting osseous integration of cementless stems. To close this gap in the bactericidal capacity of silver-coated orthopedic prostheses extension of the silver-coating on surface areas intended for osseous integration seems to be inevitable. Our study reports about a PVD- (physical-vapor-deposition-) silver-coated cementless stem in a canine model for the first time and showed osseous integration of a silver-coated titanium surface in vivo. Radiological, histological, and biomechanical analysis revealed a stable osseous integration of four of nine stems implanted. Silver trace elemental concentrations in serum did not exceed 1.82 parts per billion (ppb) and can be considered as nontoxic. Changes in liver and kidney functions associated with the silver-coating could be excluded by blood chemistry analysis. This was in accordance with very limited metal displacement from coated surfaces observed by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) 12 months after implantation. In conclusion our results represent a step towards complete bactericidal silver-coating of orthopedic prostheses.

Osseointegration: hierarchical designing encompassing the macrometer, micrometer, and nanometer length scales

OBJECTIVE

Osseointegration has been a proven concept in implant dentistry and orthopedics for decades. Substantial efforts for engineering implants for reduced treatment time frames have focused on micrometer and most recently on nanometer length scale alterations with negligible attention devoted to the effect of both macrometer design alterations and surgical instrumentation on osseointegration. This manuscript revisits osseointegration addressing the individual and combined role of alterations on the macrometer, micrometer, and nanometer length scales on the basis of cell culture, preclinical in vivo studies, and clinical evidence.

METHODS

A critical appraisal of the literature was performed regarding the impact of dental implant designing on osseointegration. Results from studies with different methodological approaches and the commonly observed inconsistencies are discussed.

RESULTS

It is a consensus that implant surface topographical and chemical alterations can hasten osseointegration. However, the tailored combination between multiple length scale design parameters that provides maximal host response is yet to be determined.

SIGNIFICANCE

In spite of the overabundant literature on osseointegration, a proportional inconsistency in findings hitherto encountered warrants a call for appropriate multivariable study designing to ensure that adequate data collection will enable osseointegration maximization and/or optimization, which will possibly lead to the engineering of endosteal implant designs that can be immediately placed/loaded regardless of patient dependent conditions.

Microwave-assisted fabrication of titanium implants with controlled surface topography for rapid bone healing

Morphological surface modifications have been reported to enhance the performance of biomedical implants. However, current methods of introducing graded porosity involves postprocessing techniques that lead to formation of microcracks, delamination, loss of fatigue strength, and, overall, poor mechanical properties. To address these issues, we developed a microwave sintering procedure whereby pure titanium powder can be readily densified into implants with graded porosity in a single step. Using this approach, surface topography of implants can be closely controlled to have a distinctive combination of surface area, pore size, and surface roughness. In this study, the effect of various surface topographies on in vitro response of neonatal rat calvarial osteoblast in terms of attachment and proliferation is studied. Certain graded surfaces nearly double the chance of cell viability in early stages (∼one month) and are therefore expected to improve the rate of healing. On the other hand, while the osteoblast morphology significantly differs in each sample at different periods, there is no straightforward correlation between early proliferation and quantitative surface parameters such as average roughness or surface area. This indicates that the nature of cell-surface interactions likely depends on other factors, including spatial parameters.

Implant osseointegration and the role of microroughness and nanostructures: lessons for spine implants

The use of spinal implants for spine fusion has been steadily increasing to avoid the risks of complications and donor site morbidity involved when using autologous bone. A variety of fusion cages are clinically available, with different shapes and chemical compositions. However, detailed information about their surface properties and the effects of such properties on osteogenesis is lacking in the literature. Here we evaluate the role of surface properties for spinal implant applications, covering some of the key biological processes that occur around an implant and focusing on the role of surface properties, specifically the surface structure, on osseointegration, drawing examples from other implantology fields when required. Our findings revealed that surface properties such as microroughness and nanostructures can directly affect early cell behavior and long-term osseointegration. Microroughness has been well established in the literature to have a beneficial effect on osseointegration of implants. In the case of the role of nanostructures, the number of reports is increasing and most studies reveal a positive effect from the nanostructures alone and a synergistic effect when combined with microrough surfaces. Long-term clinical results are nevertheless necessary to establish the full implications of surface nanomodifications.

In vivo monitoring of implant osseointegration in a rabbit model using acoustic sound analysis

Implant osseointegration can currently only be assessed reliably post mortem. A novel method that relies on the principle of acoustic sound analysis was developed to enable examination of the longitudinal progress of osseointegration. The method is based on a magnetic sphere inside a hollow cylinder of the implant. By excitation using an external magnetic field, collision of the sphere inside the implant produces a sound signal. Custom-made titanium implants equipped thusly were inserted in each lateral femoral epicondyle of 20 New Zealand White Rabbits. Two groups were investigated: Uncoated, machined surface versus antiadhesive surface; and calcium phosphate-coated surface versus antiadhesive surface. The sound analysis was performed postoperatively and weekly. After 4 weeks, the animals were euthanized, and the axial pull-out strengths of the implants were determined. A significant increase in the central frequency was observed for the loose implants (mean pull-out strength 21.1 ± 16.9 N), up to 6.4 kHz over 4 weeks. In comparison, the central frequency of the osseointegrated implants (105.2 ± 25.3 N) dropped to its initial value. The presented method shows potential for monitoring the osseointegration of different implant surfaces and could considerably reduce the number of animals needed for experiments.

Mechanical and in vitro investigation of a porous PEEK foam for medical device implants

PURPOSE

Implantable-grade polyetheretherketone (PEEK-OPTIMA®) is a high-performance thermoplastic that has been used in implant devices such as spinal-fusion cages since its introduction in 1999. Here, a new porous PEEK version was investigated.

METHODS

Porous PEEK was fabricated using industrial scale relevant methods of compounding with porogen filler, extrusion, and subsequent extraction with water at supercritical temperatures and pressures. Mechanical properties were assessed according to ISO standards. Marrow stromal cells were cultured on porous PEEK samples and in vitro cytocompatibility was assessed by total DNA, alkaline phosphatase activity, osteopontin, calcium, and cell morphology to indicate stages of proliferation, differentiation, and mineralization. Compressive strength was assessed statically on 21 day cell cultures and media-soaked samples and dynamically within a medical device application specific context for interbody fusion cages (ASTM F2077).

RESULTS

Manufacturing resulted in a biomaterial with ~50% porosity and a mean pore size of 100 microns. The porous PEEK was found to have: tensile strength (14.5MPa), strain at break (3.5%), impact strength (3.6 kJ/m2), flexural strength (21.6MPa), and flexural modulus (0.8GPa). Production of extracellular mineralized matrix occurred very early in the culture period, indicating a preferred surface for differentiation. SEM images revealed polygonal cell morphology supporting a differentiated osteoblastic-like phenotype. EDS analysis detected levels of carbon, phosphorus, and calcium coinciding with assay results for the proliferation and differentiation stages.

CONCLUSION

Previous observations of cytocompatibility and calcification on the PEEK biomaterial could be carried through to this new porous form of the PEEK biomaterial. This helps porous PEEK to potentially offer more design options for implant devices requiring reduced modulus and/or increased tissue ingrowth aspects at the surface.

The minimum 10-year results of a second-generation cementless acetabular shell with a polished inner surface

The purpose of this prospective study was to evaluate the minimum 10-year outcomes and survivorship of the Reflection shell with a polished inner surface and an improved locking mechanism. Three hundred sixty-three total hip replacements with a mean follow-up of 11.6 years (range, 10.0-15.1) were evaluated. The mean Harris Hip and WOMAC scores at last follow-up were 87 and 77, respectively. Four cups were revised: 2 for infection and 2 for aseptic loosening. Thirteen cases underwent liner exchange for wear. Radiographic review of remaining cups identified 8.8% with identifiable peri-acetabular osteolysis and no cases of loosening. The overall 10- and 15-year Kaplan-Meier survivorship was 94% and 90% for the total hip arthroplasty system while the survivorship of the shell remained 99.4% at 15 years.

Midterm results of 506 solid trispiked reflection cementless acetabular components for primary total hip arthroplasty

The purpose of this prospective study was to evaluate the outcomes and survivorship of a trispiked, sintered bead-coated titanium shell with a polished inner surface, no screw holes, and an improved locking mechanism. A total of 506 total hip arthroplasties with a minimum 5-year follow-up were available for review at a mean of 7 years (range, 5-11 years). Three sockets (0.6%) were revised for reasons other than aseptic loosening, and 14 (2.8%) polyethylene liners were exchanged. There was no difference in revision rate between non-cross-linked and highly cross-linked liners (P = .4). There were no cases of radiographic loosening. Retroacetabular osteolysis was identified in 2%. The overall 5-year and 10-year Kaplan-Meier survivorship was 97.5% and 97.4%, respectively, whereas survivorship of the shell was 99.8%.

The effect of primary stability on load transfer and bone remodelling within the uncemented resurfaced femur

One of the major causes of aseptic loosening in an uncemented implant is the lack of any attachment between the implant and the bone. The implant’s stability depends on a combination of primary stability (mechanical stability) and secondary stability (biological stability). The primary stability may affect the implant–bone interface condition and thus influence the load transfer and mechanical stimuli for bone remodelling in the resurfaced femur. This paper reports the results of a study into the affect of primary stability on load transfer and bone adaptation for an uncemented resurfaced femur. Three-dimensional finite element models were used to simulate the intact and resurfaced femurs and the bone remodelling. As a first step towards assessing the immediate post-operative condition, a debonded interfacial contact condition with varying levels of the friction coefficient (0.4, 0.5, and 0.6) was simulated at the implant–bone interface. Then, using a threshold value of micromotion of 50 µm, the implant–bone interfacial condition was varied along the implant–bone boundary to mechanically represent non-osseointegrated or osseointegrated regions of the interface. The considered applied loading conditions included normal walking and stair climbing. Resurfacing leads to strain shielding in the femoral head (20–75 per cent strain reductions). In immediate post-operative conditions, there was no occurrence of elevated strains in the cancellous bone around the proximal femoral neck–component junction resulting in a lower risk of neck fracture. Predominantly, the micromotions were observed to remain below 50 µm at the implant–bone interface, which represents 97–99 per cent of the interfacial surface area. The predicted micromotions at the implant–bone interface strongly suggest the likelihood of bone ingrowth onto the coated surface of the implant, thereby enhancing implant fixation. For the osseointegrated implant–bone interface, the effect of strain shielding was observed in a considerably greater bone volume in the femoral head as compared to the initial debonded interfacial condition. A 50–80 per cent periprosthetic bone density reduction was predicted as compared to the value of the intact femur, indicating bone resorption within the superior resurfaced head. Although primary fixation of the resurfacing component may be achieved, the presence of high strain shielding and peri-prosthetic bone resorption are a major concern.

Evaluation of bone ingrowth into porous titanium implant: histomorphometric analysis in rabbits

A porous material for bone ingrowth with adequate pore structure and appropriate mechanical properties has long been sought as the ideal bone-implant interface. This study aimed to assess in vivo the influence of three types of porous titanium implant on the new bone ingrowth. The implants were produced by means of a powder metallurgy technique with different porosities and pore sizes: Group 1 = 30 % and 180 µm; Group 2 = 30% and 300 µm; and Group 3 = 40% and 180 µm;. Six rabbits received one implant of each type in the right and left tibiae and were sacrificed 8 weeks after surgery for histological and histomorphometric analyses. Histological analysis confirmed new bone in contact with the implant, formed in direction of pores. Histomorphometric evaluation demonstrated that the new bone formation was statistically significantly lower in the group G1 than in group G3, (P = 0.023). Based on these results, increased porosity and pore size were concluded to have a positive effect on the amount of bone ingrowth.

Stem Cells Grown in Osteogenic Medium on PLGA, PLGA/HA, and Titanium Scaffolds for Surgical Applications

Pluripotent adipose tissue-derived stem cells (hASCs) can differentiate into various mesodermal cell types such as osteoblasts, chondroblasts, and myoblasts. We isolated hASCs from subcutaneous adipose tissue during orthopaedic surgery and induced the osteogenic differentiation for 28 days on three different synthetic scaffolds such as polylactide-co-glycolide (PLGA), polylactide-co-glycolide/hydroxyapatite (PLGA/HA), and trabecular titanium scaffolds (Ti6Al4V). Pore size can influence certain criteria such as cell attachment, infiltration, and vascularization. The aim of this study was to investigate the performance of PLGA and PLGA/HA scaffolds with a higher porosity, ranging between 75% and 84%, with respect to Ti scaffolds but with smaller pore size, seeded with hASCs to develop a model that could be used in the treatment of bone defects and fractures. Osteogenesis was assessed by ELISA quantitation of extracellular matrix protein expression, von Kossa staining, X-ray microanalysis, and scanning electron microscopy. The higher amount of protein matrix on the Ti scaffold with respect to PLGA and PLGA/HA leads to the conclusion that not only the type of material but the structure significantly affects cell proliferation.

Cancellous bone osseointegration is enhanced by in vivo loading

Biophysical stimuli may be an effective therapy to counteract age-related changes in bone structure that affect the primary stability of implants used in joint replacement or fracture fixation. The influence of controlled mechanical loading on osseointegration was investigated using an in vivo device implanted in the distal lateral femur of 12 male rabbits. Compressive loads (1 MPa, 1 Hz, 50 cycles/day, 4 weeks) were applied to a porous titanium foam implant and the underlying cancellous bone. The contralateral limbs served as nonloaded controls. Backscattered electron imaging indicated that the amount of bone ingrowth was significantly greater in the loaded limb than in the nonloaded control limb, whereas the amount of underlying cancellous periprosthetic bone was similar. No significant difference in the mineral apposition rate of the bone ingrowth or periprosthetic bone was measured in the loaded compared to the control limb. Histological analysis demonstrated newly formed woven bone in direct apposition to the implant coating, with a lack of fibrous tissue at the implant-periprosthetic bone interface in both loaded and nonloaded implants. The lack of fibrous tissue demonstrates that mechanical stimulation using this model significantly enhanced cancellous bone ingrowth without the detrimental effects of micromotion. These results suggest that biophysical therapy should be further investigated to augment current treatments to enhance long-term fixation of orthopedic devices. Additionally, this novel in vivo loading model can be used to further investigate the influence of biophysical stimulation on other tissue engineering approaches requiring bone ingrowth into both metallic and nonmetallic cell-seeded scaffolds.

In vitro biocompatibility of titanium alloy discs made using direct metal fabrication

Custom orthopedic implants may be generated using free-form fabrication methods (FFF) such as electron beam melting (EBM). EBM FFF may be used to make solid metal implants whose surface is often polished using CNC machining and porous scaffolds that are usually left unpolished. We assessed the in vitro biocompatibility of EBM titanium-6 aluminum-4 vanadium (Ti6Al4V) structures by comparing the cellular response to solid polished, solid unpolished, and porous EBM discs to the cellular response to discs made of commercially produced Ti6Al4V. The discs were seeded with 20,000 human adipose-derived adult stem cells (hASCs) and assessed for cell viability, proliferation, and release of the proinflammatory cytokines interleukin-6 (IL-6) and interleukin-8 (IL-8). Cell viability was assessed with Live/Dead staining 8 days after seeding. Cell proliferation was assessed using alamarBlue assays at days 0, 1, 2, 3, and 7. The hASCs were alive on all discs after 8 days. Cellular proliferation on porous EBM discs was increased at days 2, 3, and 7 compared to discs made of commercial Ti6Al4V. Cellular proliferation on porous EBM discs was also increased compared to solid polished and unpolished EBM discs. IL-6 and IL-8 releases at day 7 were lower for porous EBM discs than for other discs. Solid polished, unpolished, and porous EBM Ti6Al4V discs exhibited an acceptable biocompatibility profile compared to solid Ti6Al4V discs from a commercial source. EBM FFF may be considered as an option for the fabrication of custom orthopedic implants.

In vivo performance of selective electron beam-melted Ti-6Al-4V structures

Highly porous titanium structures are widely used for maxillofacial and orthopedic surgery because of their excellent mechanical properties similar to those of human bone and their facilitation of bone ingrowth. In contrast to common methods, the generation of porous titaniumproducts by selective electron beam melting (SEBM), an additive manufacturing technology, overcomes difficulties concerning the extreme chemical affinity of liquid titanium to atmospheric gases which consequently leads to strongly reduced ductility of the metal. The purpose of this study was to assess the suitability of a smooth compact and a porous Ti-6Al-4V structure directly produced by the SEBM process as scaffolds for bone formation. SEBM-processed titanium implants were placed into defects in the frontal skull of 15 domestic pigs. To evaluate the direct contact between bone and implant surfaces and to assess the ingrowth of osseous tissue into the porous structure, microradiographs and histomorphometric analyses were performed 14, 30, and 60 days after surgery. Bone ingrowth increased significantly during the period of this study. After 14 days the most outer regions of the implants were already filled with newly formed bone tissue (around 14%). After 30 days the bone volume inside the implants reached almost 30% and after 60 days abundant bone formation inside the implants attained 46%. During the study only scarce bone-implant contact was found around all implants, which did not exceed 9% around compact specimens and 6% around porous specimens after 60 days. This work demonstrates that highly porous titanium implants with excellent interconnectivity manufactured using the SEBM method are suitable scaffolds for bone ingrowth. This technique is a good candidate for orthopedic and maxillofacial applications.