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

Osseointegration of functionally graded Ti6Al4V porous implants: Histology of the pore network

The additive manufacturing of titanium into porous geometries offers a means to generate low-stiffness endosseous implants with a greater surface area available for osseointegration. In this work, selective laser melting was used to produce gyroid-based scaffolds with a uniform pore size of 300 μm or functionally graded pore size from 600 μm to 300 μm. Initial in vitro assessment with Saos-2 cells showed favourable cell proliferation at pore sizes of 300 and 600 μm. Following implantation into rabbit tibiae, early histological observations at four weeks indicated some residual inflammation alongside neovessel infiltration into the scaffold interior and some early apposition of mineralized bone tissue. At twelve weeks, both scaffolds were filled with a mixture of adipocyte-rich marrow, micro-capillaries, and mineralized bone tissue. X-ray microcomputed tomography showed a higher bone volume fraction (BV/TV) and percentage of bone-implant contact (BIC) in the implants with 300 μm pores than in the functionally graded specimens. In functionally graded specimens, localized BV/TV measurement was observed to be higher in the innermost region containing smaller pores (estimated at 300-400 μm) than in larger pores at the implant exterior. The unit cell topology of the porous implant was also observed to guide the direction of bone ingrowth by conducting along the implant struts. These results suggest that in vivo experimentation is necessary alongside parametric optimization of functionally graded porous implants to predict short-term and long-term bone apposition.

In Vivo Prevention of Implant-Associated Infections Caused by Antibiotic-Resistant Bacteria through Biofunctionalization of Additively Manufactured Porous Titanium

Additively manufactured (AM) porous titanium implants may have an increased risk of implant-associated infection (IAI) due to their huge internal surfaces. However, the same surface, when biofunctionalized, can be used to prevent IAI. Here, we used a rat implant infection model to evaluate the biocompatibility and infection prevention performance of AM porous titanium against bioluminescent methicillin-resistant Staphylococcus aureus (MRSA). The specimens were biofunctionalized with Ag nanoparticles (NPs) using plasma electrolytic oxidation (PEO). Infection was initiated using either intramedullary injection in vivo or with in vitro inoculation of the implant prior to implantation. Nontreated (NT) implants were compared with PEO-treated implants with Ag NPs (PT-Ag), without Ag NPs (PT) and infection without an implant. After 7 days, the bacterial load and bone morphological changes were evaluated. When infection was initiated through in vivo injection, the presence of the implant did not enhance the infection, indicating that this technique may not assess the prevention but rather the treatment of IAIs. Following in vitro inoculation, the bacterial load on the implant and in the peri-implant bony tissue was reduced by over 90% for the PT-Ag implants compared to the PT and NT implants. All infected groups had enhanced osteomyelitis scores compared to the noninfected controls.

Biomechanical analysis of functionally graded porous interbody cage for lumbar spinal fusion

Functionally graded porous (FGP) interbody cage might offer a trade-off between porosity-based reduction of stiffness and mechanical properties. Using finite element models of intact and implanted lumbar functional spinal unit (FSU), the study investigated the quantitative deviations in load transfer and adaptive changes in bone density distributions around FGP interbody cages. The cage had three graded porosities: FGP-A, -B, and -C corresponded to a maximum porosity levels of 48%, 65% and 78%, respectively. Efficacy of the FGP cages were evaluated by comparing the numerically predicted results of solid-Ti and uniformly porous 78% porosity (P78) cage. Variations in stiffness and interface condition affected the strain distribution and bone remodelling around the cages. Peak strains of 0.5-1% were observed in less number of peri-prosthetic bone elements for the FGP cages as compared to the solid-Ti cage. Strains and bone apposition were considerably higher for the bonded implant-bone interface condition than the debonded case. For the FGP-C with bonded interface condition, bone apposition of 11-20% was predicted in the L4 and L5 regions of interest (ROIs); whereas the debonded model exhibited 6-10% increase in bone density. The deviations in bone density change between FGP-C and P78 model were 3-8% for L4 and L5 ROIs. FGP resulted in a reduced average micromotion (∼70-106 μm) as compared to solid-Ti (116 μm), for all physiologic movements. Compared to solid-Ti and uniformly porous cages, the FGP cage seems to be a viable alternative considering the conflicting nature of strength and porosity.

Facts to Consider in Developing Materials That Emulate the Upper Jawbone: A Microarchitecture Study Showing Unique Characteristics at Four Different Sites

The maxilla is generally acknowledged as being more trabecular than the mandible. Allograft currently available for use in the maxillofacial region is harvested from the hip and long bones, irrespective of their local characteristics, and grafted onto the jawbones. Other alternative are autograft or commercially available bone substitutes. Due to their inherent differences, an in-depth understanding of the bone microarchitecture is important to develop the most compatible graft for use at the maxilla. This cross-sectional study aimed to determine the microstructures of bone harvested from different sites of the maxilla, to be used for standard setting. Forty-nine specimens from seven human cadavers were harvested from the zygomatic buttress, anterior maxillary sinus wall, anterior nasal spine and anterior palate. Each bone block, measuring of 10 mm × 5 mm, was harvested using rotary instruments. Bone analysis was performed following micro-computed tomography to obtain trabecular number (Tb.N), trabecular separation (Tb.Sp), trabecular thickness (Tb.Th), and bone volume fraction (BV/TV). There were site-related differences, with BV/TV that ranged between 37.38% and 85.83%. The Tb.N was the lowest at the palate (1.12 (mm−1)) and highest at the anterior maxillary sinus wall (1.41 (mm−1)) region. The palate, however, had the highest trabecular separation value (Tb.Sp) at 0.47 mm. The TB.Th was the lowest at the anterior nasal spine (0.34 mm) but both the zygoma and anterior maxillary sinus regions shared the highest Tb.Th (0.44 mm). Except for having the lowest Th.Sp (0.35 mm), the anterior maxillary sinus wall consistently showed higher values together with the zygomatic buttress in all other parameters. Concurring with current clinical practice of harvesting autograft from the zygomatic buttress and anterior maxillary sinus wall, their bony characteristic serve as the microarchitecture standard to adopt when developing new bone graft materials for use in the maxilla.

Corrosion Resistance of 3D Printed Ti6Al4V Gyroid Lattices with Varying Porosity

Corrosion of medical implants is a possible failure mode via induced local inflammatory effects, systemic deposition and corrosion related mechanical failure. Cyclic potentiodynamic polarisation (CPP) testing was utilized to evaluate the effect of increased porosity (60% and 80%) and decreased wall thickness in gyroid lattice structures on the electrochemical behaviour of LPBF Ti6Al4V structures. The use of CPP allowed for the landmarks of breakdown potential, resting potential and vertex potential to be analysed, as well as facilitating the construction of Tafel plots and qualitative Goldberg analysis. The results indicated that 60% gyroid samples were most susceptible to the onset of pitting corrosion when compared to 80% gyroid and solid samples. This was shown through decreased breakdown and vertex potentials and were found to correlate to increased lattice surface area to void volume ratio. Tafel plots indicated that despite the earlier onset of pitting corrosion, both gyroid test groups displayed lower rates of corrosion per year, indicating a lower severity of corrosion. This study highlighted inherent tradeoffs between lattice optimisation and corrosion behaviour with a potential parabolic link between void volume, surface area and corrosion being identified. This potential link is supported by 60% gyroid samples having the lowest breakdown potentials, but investigation into other porosity ranges is suggested to support the hypothesis. All 3D printed materials studied here showed breakdown potentials higher than ASTM F2129's suggestion of 800 mV for evaluation within the physiological environment, indicating that under static conditions pitting and crevice corrosion should not initiate within the body.

Mesh Ti6Al4V Material Manufactured by Selective Laser Melting (SLM) as a Promising Intervertebral Fusion Cage

Intervertebral cages made of Ti6Al4V alloy show excellent osteoconductivity, but also higher stiffness, compared to commonly used polyether-ether-ketone (PEEK) materials, that may lead to a stress-shielding effect and implant subsidence. In this study, a metallic intervertebral fusion cage, with improved mechanical behavior, was manufactured by the introduction of a three-dimensional (3D) mesh structure to Ti6Al4V material, using an additive manufacturing method. Then, the mechanical and biological properties of the following were compared: (1) PEEK, with a solid structure, (2) 3D-printed Ti6Al4V, with a solid structure, and (3) 3D-printed Ti6Al4V, with a mesh structure. A load-induced subsidence test demonstrated that the 3D-printed mesh Ti6Al4V cage had significantly lower tendency (by 15%) to subside compared to the PEEK implant. Biological assessment of the samples proved that all tested materials were biocompatible. However, both titanium samples (solid and mesh) were characterized by significantly higher bioactivity, osteoconductivity, and mineralization ability, compared to PEEK. Moreover, osteoblasts revealed stronger adhesion to the surface of the Ti6Al4V samples compared to PEEK material. Thus, it was clearly shown that the 3D-printed mesh Ti6Al4V cage possesses all the features for optimal spinal implant, since it carries low risk of implant subsidence and provides good osseointegration at the bone-implant interface.

Fabrication and Characterization of PCL/HA Filament as a 3D Printing Material Using Thermal Extrusion Technology for Bone Tissue Engineering

The most common three-dimensional (3D) printing method is material extrusion, where a pre-made filament is deposited layer-by-layer. In recent years, low-cost polycaprolactone (PCL) material has increasingly been used in 3D printing, exhibiting a sufficiently high quality for consideration in cranio-maxillofacial reconstructions. To increase osteoconductivity, prefabricated filaments for bone repair based on PCL can be supplemented with hydroxyapatite (HA). However, few reports on PCL/HA composite filaments for material extrusion applications have been documented. In this study, solvent-free fabrication for PCL/HA composite filaments (HA 0%, 5%, 10%, 15%, 20%, and 25% weight/weight PCL) was addressed, and parameters for scaffold fabrication in a desktop 3D printer were confirmed. Filaments and scaffold fabrication temperatures rose with increased HA content. The pore size and porosity of the six groups’ scaffolds were similar to each other, and all had highly interconnected structures. Six groups’ scaffolds were evaluated by measuring the compressive strength, elastic modulus, water contact angle, and morphology. A higher amount of HA increased surface roughness and hydrophilicity compared to PCL scaffolds. The increase in HA content improved the compressive strength and elastic modulus. The obtained data provide the basis for the biological evaluation and future clinical applications of PCL/HA material.

How to Prevent Aseptic Loosening in Cementless Arthroplasty: A Review

Aseptic loosening is the main late postoperative complication of cementless total hip arthroplasties (THAs), leading to pain and functional impairment. This article aims to update the orthopedic surgeon on the various methods by which the aseptic loosening rate can be reduced. We performed a systematic review by searching the PubMed database for hip aseptic loosening. We included meta-analysis, randomized controlled trials, reviews, and systematic reviews in the last 10 years, which provided information on techniques that can prevent aseptic loosening in total hip arthroplasty. From a total of 3205 articles identified, 69 articles (2%) met the inclusion criteria, leading to a total of 36 recommendations. A lot of research has been conducted in terms of septic loosening in the last decade. Currently, we have various techniques by which we can reduce the rate of aseptic loosening. Nevertheless, further randomized clinical trials are needed to expand the recommendations for aseptic loosening prevention.

Effect of the Processing Parameters on the Porosity and Mechanical Behavior of Titanium Samples with Bimodal Microstructure Produced via Hot Pressing

Commercially pure (c.p.) titanium grade IV with a bimodal microstructure is a promising material for biomedical implants. The influence of the processing parameters on the physical, microstructural, and mechanical properties was investigated. The bimodal microstructure was achieved from the blends of powder particles with different sizes, while the porous structure was obtained using the space-holder technique (50 vol.% of ammonium bicarbonate). Mechanically milled powders (10 and 20 h) were mixed in 50 wt.% or 75 wt.% with c.p. titanium. Four different mixtures of powders were precompacted via uniaxial cold pressing at 400 MPa. Then, the specimens were sintered at 750 °C via hot pressing in an argon gas atmosphere. The presence of a bimodal microstructure, comprised of small-grain regions separated by coarse-grain ones, was confirmed by optical and scanning electron microscopies. The samples with a bimodal microstructure exhibited an increase in the porosity compared with the commercially available pure Ti. In addition, the hardness was increased while the Young's modulus was decreased in the specimens with 75 wt.% of the milled powders (20 h).

Effects of pore size and porosity on cytocompatibility and osteogenic differentiation of porous titanium

To find out the optimal porosity and pore size of porous titanium (Ti) regarding the cytocompatibility and osteogenic differentiation. Six groups of porous Ti samples with different porosities and pore sizes were fabricated by the powder metallurgy process. The microstructure and compressive mechanical properties were characterized. The cytocompatibility was examined by a series of biological tests as protein absorption with BCA assay kit, cell attachment with laser scanning confocal microscopy and vinculin expression, cell proliferation with CCK-8 assay. Cell differentiation and calcification were detected by qPCR and Alizarin Red S dying respectively. Pores distributed homogeneously throughout the porous Ti samples. The compressive test results showed that Young's modulus ranged from 2.80 ± 0.03 GPa to 5.43 ± 0.34 GPa and the compressive strength increased from 112.4 ± 3.6 MPa to 231.1 ± 9.4 MPa. Porous Ti with high porosity (53.3 ± 1.2%) and small pore size (191.6 ± 3.7 μm) adsorbed more proteins. More MC3T3-E1 cells adhered onto dense Ti samples than onto any other porous ones already after culture and no difference was identified within the porous groups. The porous structure of porous Ti with a porosity of 53.3 ± 1.2% and an average pore size of 191.6 ± 3.7 μm facilitated cell differentiation and calcification. Small pores were not beneficial to the osteo-initiation at the very beginning. Porous Ti with a porosity of 53.3 ± 1.2% and an average pore size of 191.6 ± 3.7 μm fabricated by powder metallurgy process showed the expected mechanical property and improved osseointegration as implants in dental treatment.

The impact of multimodal pore size considered independently from porosity on mechanical performance and osteogenic behaviour of titanium scaffolds

Titanium porous scaffolds comprising multimodal pore ranges (i.e., uni-, bi-, tri-modal and random) were studied to evaluate the effect of pore size on osteoblastogenesis. The scaffolds were manufactured using spaceholder-powder metallurgy, and porosity and pore size were kept independent. Their mechanical and physical properties (i.e., stiffness, strength, total and open porosity) were determined. In a first step, unimodal porous samples were tested with a mouse osteoblastic clonal cell line to ascertain pore size and porosity effects on cellular behaviour. Their proliferation (via cell number and total protein content), differentiation (via ALP enzyme levels) and maturation potency (with gene markers (Runx2, osteocalcin) and cytoplasmatic calcium) were investigated. In a second step informed by the previous results, multimodal scaffolds were shortlisted according to a set of criteria that included stiffness similar to that of cortical or trabecular bone, high strength and high open porosity. Their bioactivity performance was then studied to assess the benefits of mixing different pore ranges. The study concludes that pre-osteoblasts cultivated in unimodal microstructures with a pore range 106-212 μm of 36% total (actual) porosity and 300-500 μm of 55% total (actual) porosity achieved the largest extent of maturation. Bimodal microstructures comprising small (106-212 μm) and large (300-500 μm) pore ranges, distinctively distributed within the volume, and 40% (actual) porosity outperformed others, including multimodal (i.e. three or more pore ranges) and non-porous samples. They displayed a synergistic effect over the unimodal distributions. This should be a consideration in the design of scaffolds for implantation and bioengineering applications.

Superior Osteo-Inductive and Osteo-Conductive Properties of Trabecular Titanium vs. PEEK Scaffolds on Human Mesenchymal Stem Cells: A Proof of Concept for the Use of Fusion Cages

Fusion cages composed of titanium and its alloys are emerging as valuable alternative to standard polyetheretherketone (PEEK) ones routinely used in cervical and lumbar spine surgery. Aim of this study was to evaluate osteo-inductive and osteo-conductive ability of an innovative trabecular titanium (T-Ti) scaffold on human mesenchymal stem cells (hMSCs), in both absence and presence of biochemical osteogenic stimuli. Same abilities were assessed on PEEK and standard 2D plastic surface, the latter meant as gold-standard for in vitro differentiation studies. hMSCs adhered and colonized both T-Ti and PEEK scaffolds. In absence of osteogenic factors, T-Ti triggered osteogenic induction of MSCs, as demonstrated by alkaline phosphatase activity and calcium deposition increments, while PEEK and standard 2D did not. Addition of osteogenic stimuli reinforced osteogenic differentiation of hMSCs cultured on T-Ti in a significantly higher manner with respect to standard 2D plastic culture surfaces, whereas PEEK almost completely abolished the process. T-Ti driven differentiation towards osteoblasts was confirmed by gene and marker expression analyses, even in absence of osteogenic stimuli. These results clearly indicate superior in vitro osteo-inductive and osteo-conductive capacity of T-Ti compared to PEEK, and make ground for further studies supporting the use of T-Ti cages to improve bone fusion.

Current interpretations on the in vivo response of bone to additively manufactured metallic porous scaffolds: A review

Recent advances in the field of metallic additive manufacturing have expanded production capabilities for bone implants to include porous lattice structures. While traditional models of de novo bone formation can be applied to fully dense implant materials, their applicability to the interior of porous materials has not been well-characterized. Unlike other reviews that focus on materials and mechanical properties of lattice structures, this review compiles biological performance from in vivo studies in pre-clinical models only. First, we introduce the most common lattice geometry designs employed in vivo and discuss some of their fabrication advantages and limitations. Then lattice geometry is correlated to quantitative (histomorphometric) and qualitative (histological) assessments of osseointegration. We group studies according to two common implant variables: pore size and percent porosity, and explore the extent of osseointegration using common measures, including bone-implant contact (BIC), bone area (BA), bone volume/total volume (BV/TV) and biomechanical stability, for various animal models and implantation times. Based on this, trends related to in vivo bone formation on the interior of lattice structures are presented. Common challenges with lattice structures are highlighted, including nonuniformity of bone growth through the entirety of the lattice structure due to occlusion effects and avascularity. This review paper identifies a lack of systematic in vivo studies on porous AM implants to target optimum geometric design, including pore shape, size, and percent porosity in controlled animal models and critical-sized defects. Further work focusing on surface modification strategies and systematic geometric studies to homogenize in vivo bone growth through the scaffold interior are recommended to increase implant stability in the early stages of osseointegration.

Selective Voronoi tessellation as a method to design anisotropic and biomimetic implants

The geometry of a metallic scaffold is important for the success of bone implants, where the introduction of porosity can reduce stress shielding effects and allow for bone tissue integration. In this work, porous scaffolds were designed to closely mimic the natural structure of trabecular bone using selective Voronoi tessellation with preferential seeding. A workflow to generate these structures is introduced, where voided regions of seeds in the starting volume create preferential texture during polyhedral expansion, resulting in modified strut orientation in the implant. Anisotropy was digitally characterized by mean-intercept length and star volume distribution measurements to determine similarity to trabecular orientation. This work demonstrates that selective Voronoi tessellation is an effective method to generate biomimetic porous scaffolds with increased anisotropy and tunable strut architecture in three dimensions as a suitable alternative to patient-derived bone geometries.

Reinforcement and Fatigue of a Bioinspired Mineral-Organic Bioresorbable Bone Adhesive

Bioresorbable bone adhesives may provide remarkable clinical solutions in areas ranging from fixation and osseointegration of permanent implants to the direct healing and fusion of bones without permanent fixation hardware. Mechanical properties of bone adhesives are critical for their successful application in vivo. Reinforcement of a tetracalcium phosphate-phosphoserine bone adhesive is investigated using three degradable reinforcement strategies: poly(lactic-co-glycolic) (PLGA) fibers, PLGA sutures, and chitosan lactate. All three approaches lead to higher compressive strengths of the material and better fatigue performance. Reinforcement with PLGA fibers and chitosan lactate results in a 100% probability of survival of samples at 20 MPa maximum compressive stress level, which is almost ten times higher compared to compressive loads observed in the intervertebral discs of the spine in vivo. High adhesive shear strength of 5.1 MPa is achieved for fiber-reinforced bone adhesive by tuning the surface architecture of titanium samples. Finally, biological and biomechanical performance of the fiber-reinforced adhesive is evaluated in a rabbit distal femur osteotomy model, showing the potential of the bone adhesive for clinical use.

Peri-Implant bone response around porous-surface dental implants: A preclinical meta-analysis

Introduction

This meta-analysis of relevant animal studies was conducted to assess whether the use of porous-surface implants improves osseointegration compared to the use of non-porous-surface implants.

Material and methods

An electronic search of PubMed (MEDLINE) resulted in the selection of ten animal studies (out of 865 publications) for characterization and quality assessment. Risk of bias assessment indicated poor reporting for the majority of studies. The results for bone-implant contact (BIC%) and peri-implant bone formation (BF%) were extracted from the eligible studies and used for the meta-analysis. Data for porous-surface implants were compared to those for non-porous-surface implants, which were considered as the controls.

Results

The random-effects meta-analysis showed that the use of porous-surface implants did not significantly increase overall BIC% (mean difference or MD: 3.63%; 95% confidence interval or 95% CI: −1.66 to 8.91; p = 0.18), whereas it significantly increased overall BF% (MD: 5.43%; CI: 2.20 to 8.67; p = 0.001), as compared to the controls.

Conclusion

Porous-surface implants promote osseointegration with increase in BF%. However, their use shows no significant effect on BIC%. Further preclinical and clinical investigations are required to find conclusive evidence on the effect of porous-surface implants.

Bone and Cartilage Interfaces With Orthopedic Implants: A Literature Review

The interface between a surgical implant and tissue consists of a complex and dynamic environment characterized by mechanical and biological interactions between the implant and surrounding tissue. The implantation process leads to injury which needs to heal over time and the rapidity of this process as well as the property of restored tissue impact directly the strength of the interface. Bleeding is the first and most relevant step of the healing process because blood provides growth factors and cellular material necessary for tissue repair. Integration of the implants placed in poorly vascularized tissue such as articular cartilage is, therefore, more challenging than compared with the implants placed in well-vascularized tissues such as bone. Bleeding is followed by the establishment of a provisional matrix that is gradually transformed into the native tissue. The ultimate goal of implantation is to obtain a complete integration between the implant and tissue resulting in long-term stability. The stability of the implant has been defined as primary (mechanical) and secondary (biological integration) stability. Successful integration of an implant within the tissue depends on both stabilities and is vital for short- and long-term surgical outcomes. Advances in research aim to improve implant integration resulting in enhanced implant and tissue interface. Numerous methods have been employed to improve the process of modifying both stability types. This review provides a comprehensive discussion of current knowledge regarding implant-tissue interfaces within bone and cartilage as well as novel approaches to strengthen the implant-tissue interface. Furthermore, it gives an insight into the current state-of-art biomechanical testing of the stability of the implants. Current knowledge reveals that the design of the implants closely mimicking the native structure is more likely to become well integrated. The literature provides however several other techniques such as coating with a bioactive compound that will stimulate the integration and successful outcome for the patient.

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.

3D-printed Patient-specific Spine Implants: A Systematic Review

STUDY DESIGN

Systematic review.

OBJECTIVE

To review the current clinical use of 3-dimensional printed (3DP) patient-specific implants in the spine.

SUMMARY OF BACKGROUND DATA

Additive manufacturing is a transformative manufacturing method now being applied to spinal implants. Recent innovations in technology have allowed the production of medical-grade implants with unprecedented structure and customization, and the complex anatomy of the spine is ideally suited for patient-specific devices. Improvement in implant design through the process of 3DP may lead to improved osseointegration, lower subsidence rates, and faster operative times.

METHODS

A comprehensive search of the literature was conducted using Ovid MEDLINE, EMBASE, Scopus, and other sources that resulted in 1842 unique articles. All manuscripts describing the use of 3DP spinal implants in humans were included. Two independent reviewers (N.W. and N.E.S.) assessed eligibility for inclusion. The following outcomes were collected: pain score, Japanese Orthopedic Association (JOA) score, subsidence, fusion, Cobb angle, vertebral height, and complications. No conflicts of interest existed. No funding was received for this work.

RESULTS

A total of 17 studies met inclusion criteria with a total of 35 patients. Only case series and case reports were identified. Follow-up times ranged from 3 to 36 months. Implant types included vertebral body replacement cages, interbody cages, sacral reconstruction prostheses, iliolumbar rods, and a posterior cervical plate. All studies reported improvement in both clinical and radiographic outcomes. 11 of 35 cases showed subsidence >3 mm, but only 1 case required a revision procedure. No migration, loosening, or pseudarthrosis occurred in any patient on the basis of computed tomography or flexion-extension radiographs.

CONCLUSIONS

Results of the systematic review indicate that 3DP technology is a viable means to fabricate patient-matched spinal implants. The effects on clinical and radiographic outcome measures are still in question, but these devices may produce favorable subsidence and pseudoarthrosis rates. Currently, the technology is ideally suited for complex tumor pathology and atypical bone defects. Future randomized controlled trials and cost analyses are still needed.

LEVEL OF EVIDENCE

IV-systematic review.

Microstructure and Porosity Evolution of the Ti-35Zr Biomedical Alloy Produced by Elemental Powder Metallurgy

In the present study, the structure and porosity of binary Ti-35Zr (wt.%) alloy were investigated, allowing to consider powder metallurgy as a production method for new metallic materials for potential medical applications. The porous Ti-Zr alloys were obtained by milling, cold isostatic pressing and sintering. The pressure during cold isostatic pressing was a changing parameter and was respectively 250, 500, 750 and 1000 MPa. The X-ray diffraction study revealed only the α phase, which corresponds to the Ti-Zr phase diagram. The microstructure of the Ti-35Zr was observed by optical microscopy and scanning electron microscopy. These observations revealed that the volume fraction of the pores decreased from over 20% to about 7% with increasing pressure during the cold isostatic pressing. The microhardness measurements showed changes from 137 HV0.5 to 225 HV0.5.

Orthopaedic osseointegration: Implantology and future directions

Osseointegration (OI) is the direct anchorage of a metal implant into bone, allowing for the connection of an external prosthesis to the skeleton. Osseointegration was first discovered in the 1960s based on the microscopic analysis of titanium implant placed into host bone. New bone was observed to attach directly to the metal surface. Following clinical investigations into dentistry applications, OI was adapted to treat extremity amputations. These bone anchored implants, which penetrate the skin and soft tissues, eliminate many of the challenges of conventional prosthetic sockets, such as poor fit and suspension, skin breakdown, and pain. Osseointegrated implants show promise to improve prosthesis use, pain, and function for amputees. The successful process of transcutaneous metal integration into host bone requires three synergistic systems: the host bone, the metal implant, and the skin-implant interface. All three systems must be optimized for successful incorporation and longevity of the implant. Osseointegration begins during surgical implantation of the metal components through a complex interplay of cellular mechanisms. While implants can vary in design-including the original screw, press fit implants, and compressive osseointegration-they face common challenges to successful integration and maintenance of fixation within the host bone. Overcoming these challenges requires the understanding of the complex interactions between each element of OI. This review outlines (a) the basic components of OI, (b) the science behind both the bone-implant and the skin-implant interfaces, (c) the current challenges of OI, and (d) future opportunities within the field.

Compassionate use of a custom 3D-printed sacral implant for revision of failing sacrectomy: case report

Reconstruction of the spinopelvic continuity after sacral resection for primary sacral tumors remains challenging. Complex anatomical and biomechanical factors of this transition zone may be addressed with the advancement of 3D-printed implants. Here, the authors report on a 67-year-old patient with a sacral chordoma who initially underwent total en bloc sacrectomy followed by standard spinopelvic reconstruction. Pseudarthrosis and instrumentation failure of the lumbosacral junction construct subsequently developed. A custom 3D-printed sacral prosthesis was created using high-resolution CT images. Emergency Food and Drug Administration approval was obtained, and the custom device was implanted as a salvage reconstruction surgery. Made of porous titanium mesh, the custom artificial sacrum was placed in the defect based on the anticipated osteotomic planes and was fixed with a screw-rod system along with a fibular bone strut graft. At the 18-month follow-up, the patient was disease free and walking short distances with assistance. CT revealed excellent bony incorporation into the graft.The use of a custom 3D-printed prosthesis in spinal reconstruction has been rarely reported, and its application in sacral reconstruction and long-term outcome are novel. While the implant was believed to be critical in endowing the region with enough biomechanical stability to promote healing, the procedure was difficult and several key learning points were discovered along the way.

Effects of Surface Topography and Chemistry on Polyether-Ether-Ketone (PEEK) and Titanium Osseointegration

STUDY DESIGN

An in vivo study examining the functional osseointegration of smooth, rough, and porous surface topographies presenting polyether-ether-ketone (PEEK) or titanium surface chemistry.

OBJECTIVE

To investigate the effects of surface topography and surface chemistry on implant osseointegration.

SUMMARY OF BACKGROUND DATA

Interbody fusion devices have been used for decades to facilitate fusion across the disc space, yet debate continues over their optimal surface topography and chemistry. Though both factors influence osseointegration, the relative effects of each are not fully understood.

METHODS

Smooth, rough, and porous implants presenting either a PEEK or titanium surface chemistry were implanted into the proximal tibial metaphyses of 36 skeletally mature male Sprague Dawley rats. At 8 weeks, animals were euthanized and bone-implant interfaces were subjected to micro-computed tomography analysis (n = 12), histology (n = 4), and biomechanical pullout testing (n = 8) to assess functional osseointegration and implant fixation.

RESULTS

Micro-computed tomography analysis demonstrated that bone ingrowth was 38.9 ± 2.8% for porous PEEK and 30.7 ± 3.3% for porous titanium (P = 0.07). No differences in fixation strength were detected between porous PEEK and porous titanium despite titanium surfaces exhibiting an overall increase in bone-implant contact compared with PEEK (P < 0.01). Porous surfaces exhibited increased fixation strength compared with smooth and rough surfaces regardless of surface chemistry (P < 0.05). Across all groups both surface topography and chemistry had a significant overall effect on fixation strength (P < 0.05), but topography accounted for 65.3% of the total variance (ω = 0.65), whereas surface chemistry accounted for 5.9% (ω = 0.06).

CONCLUSIONS

The effect of surface topography (specifically porosity) dominated the effect of surface chemistry in this study and could lead to further improvements in orthopedic device design. The poor osseointegration of existing smooth PEEK implants may be linked more to their smooth surface topography rather than their material composition.

LEVEL OF EVIDENCE

N/A.

The state of the art of osseointegration for limb prosthesis

Osseointegration (OI) is the direct attachment of bone onto a titanium implant. Recently, the term is used to describe "transdermal" implants that allow an external prosthesis to be connected directly to the skeleton. This technology eliminates the challenges of conventional socket-based prostheses, such as skin breakdown and poor fit, which are common in patients with major extremity amputations. Osseointegration patients demonstrate encouraging improvements in quality of life and function. Patients report improvement in prosthetic use, prosthetic mobility, global health, and pain reduction on a variety of clinical assessment tools. Various implants have been developed for osseointegration for amputees. These implants use a variety of fixation strategies and surface augments to allow for successful integration into the host bone. Regardless of design, all OI implants face similar challenges, particularly infections. Other challenges include the inability to determine when integration has occurred and the inability to detect loss of integration. These challenges may be met by incorporating sensing systems into the implants. The percutaneous nature of the metal devices can be leveraged so that internal sensors need not be wireless, and can be interrogated by external monitoring systems, thus providing crucial, real-time information about the state of the implant. The purpose of this review is to (1) review the basic science behind osseointegration, (2) provide an overview of current implants, practice patterns, and clinical outcomes, and (3) preview sensor technologies which may prove useful in future generations of transdermal orthopaedic implants.

Evaluation of Peri-Implant Bone Grafting Around Surface-Porous Dental Implants: An In Vivo Study in a Goat Model

Dental implants with surface-porous designs have been recently developed. Clinically, peri-implant bone grafting is expected to promote early osseointegration and bone ingrowth when applied with surface-porous dental implants in challenging conditions. The aim of this study was to comparatively analyze peri-implant bone healing around solid implants and surface-porous implants with and without peri-implant bone grafting, using biomechanical and histomorphometrical assessment in a goat iliac bone model. A total of 36 implants (4.1 mm wide, 11.5 mm long) divided into three groups, solid titanium implant (STI; n = 12), porous titanium implants (PTI; n = 12) and PTI with peri-implant bone grafting using biphasic calcium phosphate granules (PTI + BCP; n = 12), were placed bilaterally in the iliac crests of six goats. The goats were sacrificed seven weeks post-operatively and then subjected to biomechanical (n = 6 per group) and histomorphometrical (n = 6 per group) assessment. The biomechanical assessment revealed no significant differences between the three types of implants. Although the peri-implant bone-area (PIBA%) measured by histomorphometry (STI: 8.63 ± 3.93%, PTI: 9.89 ± 3.69%, PTI + BCP: 9.28 ± 2.61%) was similar for the three experimental groups, the percentage of new bone growth area (BGA%) inside the porous implant portion was significantly higher (p < 0.05) in the PTI group (10.67 ± 4.61%) compared to the PTI + BCP group (6.50 ± 6.53%). These data demonstrate that peri-implant bone grafting around surface-porous dental implants does not significantly accelerate early osseointegration and bone ingrowth.

Controlled release of BMP-2 from titanium with electrodeposition modification enhancing critical size bone formation

In this study, a porous Ti-alloy based implant with an interconnected channel structure (MAO-CaP-BMP2) is fabricated using a method combining 3D printing, microarc oxidation (MAO) treatment, and co-precipitation of Ca,P layer with BMP-2 technique. The macroporous structure with pore size of 600 μm made by 3D printing not only enhances the ingrowth of cells but also allows the formation of blood vessels inside the implant. As a result, the new bond formation is promoted. In addition, the microporous dioxide layer formed on the implant surface by MAO provides the sites for co-precipitation of Ca,P layer with BMP-2. The microstructure allows the prolonged release of BMP-2. Our results show that a sustained release of BMP-2 over 35 days is achieved for MAO-CaP-BMP2 group longer than Ti without MAO modification group and without Ca,P electrochemical deposition group. The slow release of BMP-2 at the bone/implant interface for a long period of time leads to enhancement of the osseointegration between the implant and surrounding bones. This result indicates that MAO-CaP-BMP2 is a good candidate of growth factor carrier. Successful regeneration of bone requires the concomitant processes of osteogenesis and neovascularization. MAO-CaP-BMP2 modified Ti-alloy implant is both osteoinductive and osteoconductive which can create better osteogenesis and angiogenesis. As a result, it can enhance bone formation.

Osseointegration of titanium scaffolds manufactured by selective laser melting in rabbit femur defect model

The aim of this study was to assess the osseointegration of two series of titanium (Ti) scaffolds with 0.8 and 1 mm cell size obtained by Selective Laser Melting (SLM) technique. One of the series had the Ti surface unmodified, while the other had the Ti surface coated with silicon-substituted nano-hydroxyapatite (nano-HapSi). The scaffolds were implanted in the femur bone defects of 6 White Californian male rabbits: three animals were implanted with 0.8 mm cell size scaffolds and three animals with 1 mm cell size scaffolds, respectively. The bone fragments and scaffolds harvested at 2, 4 and 6 months were histologically analyzed using conventional light microscopy (LM) and scanning electron microscopy (SEM) for the qualitative evaluation of the bone tissue formed in contact with the scaffold. Both LM and SEM images indicated a better osseointegration for nano-HapSi coated Ti scaffolds. LM revealed that the compact bone formed in the proximity of nano-HapSi-coated scaffolds was better organized than spongy bone associated with unmodified scaffolds. Moreover, Ti scaffolds with meshes of 0.8 mm showed higher osseointegration compared with 1 mm. SEM images at 6 months revealed that the bone developed not only in contact with the scaffolds, but also proliferated inside the meshes. Nano-HapSi-coated Ti implants with 0.8 mm meshes were completely covered and filled with new bone. Ti scaffolds osseointegration depended on the mesh size and the surface properties. Due to the biocompatibility and favorable osseointegration in bone defects, nano-HapSi-coated Ti scaffolds could be useful for anatomical reconstructions.

In vitro and in vivo evaluations of mechanical properties, biocompatibility and osteogenic ability of sintered porous titanium alloy implant

A new sintering technique using Ti6Al4V powder suspension was performed to prepare porous Ti6Al4V alloys. The porous alloys could be fabricated with different porosities and pore sizes by controlling the quantity and size of spacer particles added to the Ti6Al4V powder. The characteristics and biological properties of the porous Ti6Al4V with two different porosities were evaluated by mechanical tests, cell tests and implantation. Dense Ti6Al4V was used as the control. Compared with the control group, the porous Ti6Al4V showed good biocompatibility and osteogenic ability, which makes this type of porous alloy a good prospective material for biomedical application. And compared with 50% porosity, the alloy with 75% porosity had the optimal mechanical properties, and suitable pore size and porosity, which allowed more bone ingrowth.

Direct Contact Test for Evaluating Bacterial Growth on Machined and Rough Surface Implants: An In Vitro Study

OBJECTIVE

To use a modified direct contact test (DCT) to evaluate the bacterial growth on 3 commercially available implants.

MATERIALS AND METHODS

Streptococcus salivarius growth was tested on 1 machined surface and 2 commercial rough surface implants. Seven implants from each group were fixed to the cover of a 96-well microtiter plate. Bacterial suspension was placed on each implant, and the plate was incubated at 37°C for 1 hour to allow the suspension fluid to evaporate. Fresh medium was added to 7 corresponding wells in the microtiter plate, and the cover holding the implants was placed on the plate to enable immersion of the implant. Noncontaminated implant samples served as control. Bacterial growth was monitored spectrophotometrically at 650 nm for 24 hours.

RESULTS

There was a significant S. salivarius growth in all groups of test implants compared with the control. There was no significant difference between bacterial growth kinetics on treated and nontreated implant surfaces (P = 0.241).

CONCLUSION

Using the DCT, we found no difference in bacterial growth between machined and rough surface implants.

Current methods of preventing aseptic loosening and improving osseointegration of titanium implants in cementless total hip arthroplasty: a review

Hip osteoarthritis is the most common joint disorder, and is represented by a degenerative process, resulting in pain and functional impairment. If conservative treatment for hip osteoarthritis fails, the only remaining option is hip arthroplasty. Despite good survival of implants, loosening of components is the most common complication. This leads to revision surgeries, which are technically demanding, expensive, and result in a low satisfaction rate. Uncemented hip replacements require proper osseointegration for increased survival. Physical characteristics of implants include biocompatibility, Young’s modulus of elasticity, strength, and corrosion resistance, and each influence fixation of implants. Moreover, implant surface treatments, pore size, pore density, and femoral stem design should be appropriately selected. Patients’ optimization of obesity, osteoporosis, cardiovascular disease, psychotic disorders, and smoking cessation are associated with a higher survival of implants. Surgical factors, such as approach, drilling and rasping, acetabular bone coverage, acetabular cup positioning, and implant size, also affect survival of implants. Avoiding drugs, which may impair osseointegration of implants, and having an appropriate rehabilitation protocol are important. Future directions include anabolic and anti-catabolic bone-acting drugs to enhance osseointegration of implants. Comprehensive knowledge of the factors mentioned above is important for preventing aseptic loosening, with important socioeconomic consequences.

In vivo testing of porous Ti-25Nb alloy serving as a femoral stem prosthesis in a rabbit model

The aim of the present study was to observe the performance of Ti-25Nb alloys with various porosities as femoral stem prostheses in a rabbit model, thus providing basic experimental evidence for the development of porous prostheses. The porous Ti-25Nb alloy prostheses were designed according to the morphology of the medullary cavity. These prostheses were placed into the femoral medullary cavities in 36 New Zealand white rabbits. Postoperative X-ray films, scanning electron microscopy (SEM) of the implant interface, energy-dispersive spectroscopy (EDS) analysis of the implant surface, pulling-out test and general observations were conducted. The specimens showed good biocompatibility; there was no obvious bone absorption in porous Ti-25Nb specimens with different porosities at different time points observed using X-ray films. Under SEM examination, calcium deposits were observed inside the pores and in the interface between bone and prostheses. The EDS analysis demonstrated that calcium deposits were present on the surface of the prostheses at the eight-week point postoperatively. The pulling-out test showed good bonding strength between bone and implant; after pulling out, the surface and inside the pores of the prostheses all presented bone mass. Porous Ti-25Nb alloy implants presents good biocompatibility as well as providing a biological fixation between the bone and implant. A porosity of 70% is more advantageous to the newborn bone ingrowth, combined with achieving a more solid bone-implant interface.

Titanium scaffold osteogenesis in healthy and osteoporotic rats is improved by the use of low-level laser therapy (GaAlAs)

The present study aimed to assess the effects of low-level laser therapy (GaAlAs) on the bone repair process within titanium scaffolds in the femurs of healthy and osteoporotic rats. Fifty-six rats were divided into four groups: group Sh: SHAM animals that received scaffolds; group LSh: SHAM animals that received scaffolds and were subjected to laser therapy; group OV: ovarietomized (OVX) animals that received scaffolds; and group LOV: OVX animals that received scaffolds and were subjected to laser therapy. Thirty days following ovariectomy or sham surgery, scaffolds were implanted in the left femurs of all animals in the study. Immediately after opening the surgical site, the inner part of the surgical cavity was stimulated with low-level laser (GaAlAs). In addition to this procedure, the laser group was also subjected to sessions of low-level laser therapy (LLLT) at 48-h intervals, with the first session performed immediately after surgery. The rats were sacrificed at 2 and 6 weeks, time in which femur fragments were submitted for histological and histomorphometric examination, and skin tissue above the scaffold was submitted to histological analysis. At the end of the study, greater bone formation was observed in the animals submitted to LLLT. At 2 and 6 weeks, statistically significant differences were observed between LSh and Sh groups (p = 0.009 and 0.0001) and LOV and OV (p = 0.0001 and 0.0001), respectively. No statistical difference was observed when assessing the estrogen variable. On the basis of our methodology and results, we conclude that LLLT improves and accelerates bone repair within titanium scaffolds in both ovariectomized and healthy rats, when compared to animals not subjected to radiation.

Post Processing and Biological Evaluation of the Titanium Scaffolds for Bone Tissue Engineering

Nowadays, post-surgical or post-accidental bone loss can be substituted by custom-made scaffolds fabricated by additive manufacturing (AM) methods from metallic powders. However, the partially melted powder particles must be removed in a post-process chemical treatment. The aim of this study was to investigate the effect of the chemical polishing with various acid baths on novel scaffolds' morphology, porosity and mechanical properties. In the first stage, Magics software (Materialise NV, Leuven, Belgium) was used to design a porous scaffolds with pore size equal to (A) 200 µm, (B) 500 µm and (C) 200 + 500 µm, and diamond cell structure. The scaffolds were fabricated from commercially pure titanium powder (CP Ti) using a SLM50 3D printing machine (Realizer GmbH, Borchen, Germany). The selective laser melting (SLM) process was optimized and the laser beam energy density in range of 91-151 J/mm³ was applied to receive 3D structures with fully dense struts. To remove not fully melted titanium particles the scaffolds were chemically polished using various HF and HF-HNO₃ acid solutions. Based on scaffolds mass loss and scanning electron (SEM) observations, baths which provided most uniform surface cleaning were proposed for each porosity. The pore and strut size after chemical treatments was calculated based on the micro-computed tomography (µ-CT) and SEM images. The mechanical tests showed that the treated scaffolds had Young's modulus close to that of compact bone. Additionally, the effect of pore size of chemically polished scaffolds on cell retention, proliferation and differentiation was studied using human mesenchymal stem cells. Small pores yielded higher cell retention within the scaffolds, which then affected their growth. This shows that in vitro cell performance can be controlled to certain extent by varying pore sizes.

Effect of low-level mechanical vibration on osteogenesis and osseointegration of porous titanium implants in the repair of long bone defects

Emerging evidence substantiates the potential of porous titanium alloy (pTi) as an ideal bone-graft substitute because of its excellent biocompatibility and structural properties. However, it remains a major clinical concern for promoting high-efficiency and high-quality osseointegration of pTi, which is beneficial for securing long-term implant stability. Accumulating evidence demonstrates the capacity of low-amplitude whole-body vibration (WBV) in preventing osteopenia, whereas the effects and mechanisms of WBV on osteogenesis and osseointegration of pTi remain unclear. Our present study shows that WBV enhanced cellular attachment and proliferation, and induced well-organized cytoskeleton of primary osteoblasts in pTi. WBV upregulated osteogenesis-associated gene and protein expression in primary osteoblasts, including OCN, Runx2, Wnt3a, Lrp6 and β-catenin. In vivo findings demonstrate that 6-week and 12-week WBV stimulated osseointegration, bone ingrowth and bone formation rate of pTi in rabbit femoral bone defects via μCT, histological and histomorphometric analyses. WBV induced higher ALP, OCN, Runx2, BMP2, Wnt3a, Lrp6 and β-catenin, and lower Sost and RANKL/OPG gene expression in rabbit femora. Our findings demonstrate that WBV promotes osteogenesis and osseointegration of pTi via its anabolic effect and potential anti-catabolic activity, and imply the promising potential of WBV for enhancing the repair efficiency and quality of pTi in osseous defects.

Mechanical properties and in vitro biological response to porous titanium alloys prepared for use in intervertebral implants

The generation of titanium foams is a promising strategy for modifying the mechanical properties of intervertebral reinforcements. Thus, the aim of this study was to compare the in vitro biological response of Ti6Al4V alloys with different pore sizes for use in intervertebral implants in terms of the adhesion, proliferation, and differentiation of pre-osteoblastic cells. We studied the production of Ti6Al4V foams by powder metallurgy and the biological responses to Ti6Al4V foams were assessed in terms of different pore interconnectivities and elastic moduli. The Ti6Al4V foams obtained had similar porosities of approximately 34%, but different pore sizes (66 µm for fine Ti6Al4V and 147 µm for coarse Ti6Al4V) due to the sizes of the microsphere used. The Ti6Al4V foams had a slightly higher Young׳s modulus compared with cancellous bone. The dynamic mechanical properties of the Ti6Al4V foams were slightly low, but these materials can satisfy the requirements for intervertebral prosthesis applications. The cultured cells colonized both sizes of microspheres near the pore spaces, where they occupied almost the entire area of the microspheres when the final cell culture time was reached. No statistical differences in cell proliferation were observed; however, the cells filled the pores on fine Ti6Al4V foams but they only colonized the superficial microspheres, whereas the cells did not fill the pores on coarse Ti6Al4V foams but they were distributed throughout most of the material. In addition, the microspheres with wide pores (coarse Ti6Al4V) stimulated higher osteoblast differentiation, as demonstrated by the Alcaline Phosphatase (ALP) activity. Our in vitro results suggest that foams with wide pore facilitate internal cell colonization and stimulate osteoblast differentiation.

Entangled titanium fibre balls combined with nano strontium hydroxyapatite in repairing bone defects

OBJECTIVE

To investigate the effect of entangled titanium fibre balls (ETFBs) combined with nano strontium hydroxyapatite (nano-Sr-HAP) on the repair of bone defects in vivo.

MATERIALS AND METHODS

Twenty-four 6-month-old, specific pathogen-free, male Sprague-Dawley rats were used. Drill defects were created in bilateral femoral condyles. ETFBs combined with nano-Sr-HAP were selected randomly from 72 samples and implanted into the femoral bone defects of left legs, which served as the experimental group, while ETFBs without nano-Sr-HAP were implanted into right legs for comparison. The bone defects on both sides were X-rayed. The anteroposterior positions and histological procedures and evaluations of each sample were performed at 1, 2, 4 and 8 weeks post-surgery.

RESULTS

Histological results showed that the ETBs allowed new bone to grow within their structure. Additionally, an increase in new bone was seen on the nano-Sr-HAP side compared to the control side. The results of histomorphometric analysis confirmed that the new bone formation on the left side gradually increased with time. There was a statistical increase in new bone at 2, 4 and 8 weeks, and the differences between the two sides were statistically significant at weeks 4 and 8 (p < 0.05 for all comparisons).

CONCLUSION

The results showed that ETFBs possess a unique 3-dimensional interconnective porous structure and have excellent biocompatibility, cell affinity and osteoconductivity, which makes them useful as scaffold materials for repairing bone defects. On the other hand, nano-Sr-HAP improved the bone defect-repairing capacity of the ETFBs, which showed osteoinductive properties.

Trabecular titanium can induce in vitro osteogenic differentiation of human adipose derived stem cells without osteogenic factors

Trabecular Titanium (TT) is an innovative highly porous structure that imitates the morphology of trabecular bone with good mechanical properties. Adipose-derived stem cells are a multipotent cell population that can be used in regenerative medicine, in particular, for bone therapeutic applications. The ability of TT to induce the osteogenic differentiation of human adipose derived stem cells (hASCs) in the absence of osteogenic factors was evaluated using molecular biological, biochemical, and immunohistochemical methods. At 7 and 21 days from differentiation, the hASCs grown on TT scaffolds showed similar expressions of alkaline phosphatase (ALP) and Runx-2 both in the presence and in the absence of osteogenic factors, as well as at transcript and protein levels. hASCs cultured on monolayer in the presence of the medium obtained from the wells where hASCs/scaffold constructs were cultured in the absence of osteogenic factors differentiated towards the osteogenic phenotype: their gene and protein expression of ALP and Runx-2 was similar to that of the same cells cultured in the presence of osteogenic factors, and significantly higher than that of the ones cultured in growth medium.

Long-term biocompatibility and osseointegration of electron beam melted, free-form–fabricated solid and porous titanium alloy: Experimental studies in sheep

The purpose of the present study was to evaluate the long-term osseointegration and biocompatibility of electron beam melted (EBM) free-form–fabricated (FFF titanium grade 5 (Ti6Al4V) implants. Porous and solid machined cylindrical and disk-shaped implants were prepared by EBM and implanted bilaterally in the femur and subcutaneously in the dorsum of the sheep. After 26 weeks, the implants and surrounding tissue were retrieved. The tissue response was examined qualitatively and quantitatively using histology and light microscopic (LM) morphometry. Selected bone implants specimens were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and micro-computed tomography (mCT). The results showed that both porous and solid implants were osseointegrated and high bone–implant contact was observed throughout the porous implant. In the soft tissue, the porous implants showed thinner fibrous encapsulation while no signs of intolerance were observed for either implant type. Taken together, the present experimental results show that FFF Ti6Al4V with and without porous structures demonstrate excellent long-term soft tissue biocompatibility and a high degree of osseointegration. The present findings extend earlier, short-term experimental observations in bone and suggest that EBM, FFF Ti6Al4V implants possess valuable properties in bone and soft tissue applications.

Novel production method of porous surface Ti samples for biomedical application

A porous implant material with adequate pore structure and the appropriate mechanical properties for bone ingrowth has long been sought. This article presents details of the development, characterization and in vivo evaluations of powder metallurgy-processed titanium samples exhibiting a dense core with an integrated porous surface for biomedical applications. A space-holder method was applied to investigate the effects of different percentages and particle sizes of the urea on bone neoformation in 30 rabbits. The samples were previously characterized using scanning electron microscopy and mechanical testing. After 8 and 12 weeks of implantation, bone ingrowth was histologically and histometrically analyzed and push-out testing was performed. This study demonstrated that the association of a dense core integrated with the greatest number of interconnected pores of the smallest size is a promising biomaterial for bone tissue engineering. This sample exhibits appropriate mechanical properties combined with increased bone ingrowth, providing enhanced resistance to displacement.

Long-term biocompatibility and osseointegration of electron beam melted, free-form-fabricated solid and porous titanium alloy: experimental studies in sheep

The purpose of the present study was to evaluate the long-term osseointegration and biocompatibility of electron beam melted (EBM) free-form-fabricated (FFF titanium grade 5 (Ti6Al4V) implants. Porous and solid machined cylindrical and disk-shaped implants were prepared by EBM and implanted bilaterally in the femur and subcutaneously in the dorsum of the sheep. After 26 weeks, the implants and surrounding tissue were retrieved. The tissue response was examined qualitatively and quantitatively using histology and light microscopic (LM) morphometry. Selected bone implants specimens were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and micro-computed tomography (mCT). The results showed that both porous and solid implants were osseointegrated and high bone-implant contact was observed throughout the porous implant. In the soft tissue, the porous implants showed thinner fibrous encapsulation while no signs of intolerance were observed for either implant type. Taken together, the present experimental results show that FFF Ti6Al4V with and without porous structures demonstrate excellent long-term soft tissue biocompatibility and a high degree of osseointegration. The present findings extend earlier, short-term experimental observations in bone and suggest that EBM, FFF Ti6Al4V implants possess valuable properties in bone and soft tissue applications.