Biodegradation of a Magnesium Alloy Fixation Screw Used in a Guided Bone Regeneration Model in Beagle Dogs.

Nowadays, the most commonly used fixation systems are non-resorbable, but new resorbable magnesium alloy fixation screws have been introduced recently. Therefore, the aim of this study was to compare the magnesium fixation screw and the commonly used non-resorbable titanium screw in an animal model. Four 3-wall defect sites were covered with collagen membranes in the mandible of twenty beagle dogs (two sites on the left and two on the right). Each membrane was fixed with either four magnesium screws or four titanium screws. Post-operative follow-up revealed the expected observations such as transient inflammation and pain. Both groups showed a good healing response, with no differences between groups. Micro-CT analysis showed no significant difference between groups in terms of BV/TV or soft tissue volume. The void volume in the magnesium fixation screw group continued to decrease on average between the different timepoints, but not significantly. Furthermore, a gradual progression of the degradation process of the magnesium screws was observed in the same group. Magnesium screws and titanium screws showed equal performance in tissue regeneration according to GBR principles. An additional advantage of magnesium screws is their resorbable nature, which eliminates the need for a second surgical step to remove the screws.

Characterization of an Acute Rodent Osteomyelitis Infectious Model Using a Tibial Intramedullary Implant Inoculation.

Chronic osteomyelitis in presence of orthopedic implants is a condition observed in the field of biomaterials as it impairs early bone-implant contact, fixation and integration. In this study, a surgical intramedullary tibial insertion was performed using a titanium wire previously inoculated with Staphylococcus aureus in order to develop an osteomyelitis model in a clinically relevant long bone and in absence of any prophylactic treatment. As such, twenty-two male Sprague-Dawley rats received a sterile or inoculated intramedullary biomaterial with either 2 × 106 or 1 × 107 S. aureus colony forming units. Bacterial burden, inflammation, morphological changes, as well as newly formed bone tissues were evaluated for histopathology following a period of either eight or fifteen days of implantation. The implant inoculated in presence of the highest bacterial load was effective to produce significant periprosthetic infection observations in addition to hard and soft tissue inflammation consistent with the development of osteomyelitis. In contrast, neither the sterile nor the low-dose implant inoculation showed inflammation and clinical infection signs, but rather produced an expected bone remodeling and appropriate healing associated with biomaterial implantation. Complete health assessment is presented with histopathological periprosthetic results.

Histopathological Evaluation of Orthopedic Medical Devices: The State-of-the-art in Animal Models, Imaging, and Histomorphometry Techniques.

Orthopedic medical devices are continuously evolving for the latest clinical indications in craniomaxillofacial, spine, trauma, joint arthroplasty, sports medicine, and soft tissue regeneration fields, with a variety of materials from new metallic alloys and ceramics to composite polymers, bioresorbables, or surface-treated implants. There is great need for qualified medical device pathologists to evaluate these next generation biomaterials, with improved biocompatibility and bioactivity for orthopedic applications, and a broad range of knowledge is required to stay abreast of this ever-changing field. Orthopedic implants require specialized imaging and processing techniques to fully evaluate the bone-implant interface, and the pathologist plays an important role in determining the proper combination of histologic processing and staining for quality slide production based on research and development trials and validation. Additionally, histomorphometry is an essential part of the analysis to quantify tissue integration and residual biomaterials. In this article, an overview of orthopedic implants and animal models, as well as pertinent insights for tissue collection, imaging, processing, and slide generation will be provided with a special focus on histopathology and histomorphometry evaluation.

Fracture Healing and Bone Remodeling With Human Standard-Sized Magnesium Versus Polylactide-Co-Glycolide Plate and Screw Systems Using a Mini-Swine Craniomaxillofacial Osteotomy Fixation Model.

PURPOSE: This study compared the degradation profile, safety, and efficacy of bioresorbable magnesium alloy and polylactide-co-glycolide (PLGA) polymer osteosynthesis systems for the treatment of fractures in a load-sharing maxillofacial environment using a new mini-swine fracture fixation model. MATERIALS AND METHODS: Two types of clinically relevant situations were evaluated in 5 Yucatan miniature pigs. Defined porcine midface osteotomies of the supraorbital rim and zygoma were created and fixed with either a coated magnesium (test animals) or PLGA plate and screw osteosynthesis system (control animals). After surgery, the mini-pigs were able to recover for either 1 or 9 months with continuous in vivo post-implantation monitoring. Standardized computed tomography (CT) imaging was taken immediately postoperatively and at termination for all animals. The 9-month cohort also underwent CT at 2, 4, and 6 months after surgery. At necropsy, osteotomy sites and bone-implant units were harvested, and healing was evaluated by micro-CT, histopathology, and histomorphometry. RESULTS: After clinical and radiologic follow-up examination, all fracture sites healed well for both the magnesium and polymer groups regardless of time point. Complete bone union and gradually disappearing osteotomy lines were observed across all implantation sites, with no major consistency change in periprosthetic soft tissue or in soft tissue calcification. Macroscopic and microscopic examination showed no negative influence of gas formation observed with magnesium during the healing process. Histopathologic analysis showed similar fracture healing outcomes for both plating systems with good biocompatibility as evidenced by a minimal or mild tissue reaction. CONCLUSIONS: This study confirms that WE43 magnesium alloy exhibited excellent fracture healing properties before its full degradation without causing any substantial inflammatory reactions in a long-term porcine model. Compared with PLGA implants, magnesium represents a promising new biomaterial with reduced implant sizes and improved mechanical properties to support fracture healing in a load-sharing environment.

Host responses to a strontium releasing high boron glass using a rabbit bilateral femoral defect model.

Borate glasses have shown promising potential as bioactive materials. With recent research demonstrating that glass properties may be modulated by appropriate compositional design. This may provide for indication specific material characteristics and controlled release of therapeutic inorganic ions (i.e., strontium); controlling such release is critical in order to harness the therapeutic potential. Within this sub-chronic pilot study, a rabbit long-bone model was utilized to explore the safety and efficacy of a high borate glass (LB102: 70B2 O3 -20SrO-6Na2 O-4La2 O3 ) particulate (90 - 710 µm) for bone regeneration. Six bilateral full-thickness defects (Ø = 3.5 mm; L = 8 mm) were created in three white New Zealand rabbits. Longitudinal non-decalcified sections of each defect site were produced and stained with Goldner's Trichrome. Histopathological examination revealed that LB102 demonstrated osteoconductive and osseointegrative properties with greater new bone being formed within and surrounding LB102 particles, when compared to the sham control. The inflammatory cell infiltration was observed to be slightly higher in the control when compared to LB102 defect sites, while no significant difference in fibrosis and neovascularization was determined, indicating that healing was occurring in a normal fashion. These data further suggest the possible utility of high borate glasses with appropriate compositional design for medical applications, such as bone augmentation. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1818-1827, 2017.

Enhanced bioactivity and osseointegration of PEEK with accelerated neutral atom beam technology.

Polyetheretherketone (PEEK) is growing in popularity for orthopedic, spinal, and trauma applications but has potential significant limitations in use. PEEK is biocompatible, similar in elasticity to bone, and radiolucent, but is inert and therefore does not integrate well with bone. Current efforts are focusing on increasing the bioactivity of PEEK with surface modifications to improve the bone-implant interface. We used a novel Accelerated Neutral Atom Beam (ANAB) technology to enhance the bioactivity of PEEK. Human osteoblast-like cells seeded on ANAB-treated PEEK result in significantly enhanced proliferation compared with control PEEK. Cells grown on ANAB-treated PEEK increase osteogenic expression of ALPL (1.98-fold, p < 0.002), RUNX2 (3.20-fold, p < 0.002), COL1A (1.94-fold, p < 0.015), IBSP (2.78-fold, p < 0.003), and BMP2 (1.89-fold, p < 0.004). Cells grown on these treated surfaces also lead to an increased mineralization (6.4-fold at 21 days, p < 0.0005). In an ovine study, ANAB-treated PEEK implants resulted in enhanced bone-in-contact by 3.09-fold (p < 0.014), increased push-out strength (control 1959 ± 1445 kPa; ANAB 4068 ± 1197 kPa, p < 0.05), and evidence of bone ingrowth at both the early (4 weeks) and later (12 weeks) time points. Taken together, these data suggest that ANAB treatment of PEEK has the potential to enhance its bioactivity, leading to bone formation and significantly decreasing osseointegration time of orthopedic and spinal implants. ANAB treatment, therefore, may significantly enhance the performance of PEEK medical implants and lead to improved clinical outcomes. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 531-543, 2017.

Efficacy of silicate-substituted calcium phosphate with enhanced strut porosity as a standalone bone graft substitute and autograft extender in an ovine distal femoral critical defect model.

A synthetic bone graft substitute consisting of silicate-substituted calcium phosphate with increased strut porosity (SiCaP EP) was evaluated in an ovine distal femoral critical sized metaphyseal defect as a standalone bone graft, as an autologous iliac crest bone graft (ICBG) extender (SiCaP EP/ICBG), and when mixed with bone marrow aspirate (SiCaP EP/BMA). Defects were evaluated after 4, 8, and 12 weeks with radiography, decalcified paraffin-embedded histopathology, non-decalcified resin-embedded histomorphometry, and mechanical indentation testing. All test groups exhibited excellent biocompatibility and osseous healing as evidenced by an initial mild inflammatory response followed by neovascularization, bone growth, and marrow infiltration throughout all SiCaP EP-treated defects. SiCaP EP/ICBG produced more bone at early time points, while all groups produced similar amounts of bone at later time points. SiCaP EP/ICBG likewise showed more favorable mechanical properties at early time points, but was equivalent to SiCaP EP and SiCaP EP/BMA at later time points. This study demonstrates that SiCaP EP is efficacious as a standalone bone graft substitute, mixed with BMA, and as an autograft extender.

Biocompatibility and strength retention of biodegradable Mg-Ca-Zn alloy bone implants.

The biocompatibility and strength retention of a Mg-Ca-Zn alloy were studied to evaluate its efficacy for osteosynthesis applications. Mg-Ca-Zn alloy and self-reinforced poly l-lactide (SR-PLLA) bone screws were implanted into New Zealand rabbits for radiography analysis, micro computed tomography analysis, histomorphometry, hematology, serum biochemistry, histopathology, and inductively coupled plasma mass spectrometry analysis. Bending and torsion tests were performed on intact specimens to find the initial mechanical strength of these Mg-Ca-Zn alloy bone screws. Strength retention of the Mg-Ca-Zn alloy implants were calculated from in vivo degradation rates and initial mechanical strength. Based on the animal study, Mg-Ca-Zn alloy bone screw showed absence of subcutaneous gas pockets, characteristic surface erosion properties, faster degradation rate than SR-PLLA bone screw, normal reference range of hematology and serum biochemistry, better histopathological response than SR-PLLA bone screw, and stable concentrations of each constituent element in soft tissues surrounding the implants. The initial strength and strength retention of Mg-Ca-Zn alloy were compared with those of various biomaterials. The initial strength of Mg-Ca-Zn alloy was higher than those of biostable and biodegradable polymers. The strength retention of Mg-Ca-Zn alloy bone screws was similar to those of biodegradable polymer. Therefore, this Mg-Ca-Zn alloy represents an excellent biodegradable biomaterial candidate for osteosynthesis applications.

Load-bearing capacity and biological allowable limit of biodegradable metal based on degradation rate in vivo.

In this study, a newly developed Mg-Ca-Zn alloy for low degradation rate and surface erosion properties was evaluated. The compressive, tensile, and fatigue strength were measured before implantation. The degradation behavior was evaluated by analyzing the microstructure and local hardness of the explanted specimen. Mean and maximum degradation rates were measured using micro CT equipment from 4-, 8-, and 16- week explants, and the alloy was shown to display surface erosion properties. Based on these characteristics, the average and minimum load bearing capacities in tension, compression, and bending modes were calculated. According to the degradation rate and references of recommended dietary intakes (RDI), the Mg-Ca-Zn alloy appears to be safe for human use.

The spinal cord dura mater reaction to nitinol and titanium alloy particles: a 1-year study in rabbits.

This investigation was undertaken to simulate in an animal model the particles released from a porous nitinol interbody fusion device and to evaluate its consequences on the dura mater, spinal cord and nerve roots, lymph nodes (abdominal para-aortic), and organs (kidneys, spleen, pancreas, liver, and lungs). Our objective was to evaluate the compatibility of the nitinol particles with the dura mater in comparison with titanium alloy. In spite of the great use of metallic devices in spine surgery, the proximity of the spinal cord to the devices raised concerns about the effect of the metal debris that might be released onto the neural tissue. Forty-five New Zealand white female rabbits were divided into three groups: nitinol (treated: N = 4 per implantation period), titanium (treated: N = 4 per implantation period), and sham rabbits (control: N = 1 per observation period). The nitinol and titanium alloy particles were implanted in the spinal canal on the dura mater at the lumbar level L2-L3. The rabbits were sacrificed at 1, 4, 12, 26, and 52 weeks. Histologic sections from the regional lymph nodes, organs, from remote and implantation sites, were analyzed for any abnormalities and inflammation. Regardless of the implantation time, both nitinol and titanium particles remained at the implantation site and clung to the spinal cord lining soft tissue of the dura mater. The inflammation was limited to the epidural space around the particles and then reduced from acute to mild chronic during the follow-up. The dura mater, sub-dural space, nerve roots, and the spinal cord were free of reaction. No particles or abnormalities were found either in the lymph nodes or in the organs. In contact with the dura, the nitinol elicits an inflammatory response similar to that of titanium. The tolerance of nitinol by a sensitive tissue such as the dura mater during the span of 1 year of implantation demonstrated the safety of nitinol and its potential use as an intervertebral fusion device.

Morphological characterization and in vitro biocompatibility of a porous nickel-titanium alloy.

Disks consisting of macroporous nickel-titanium alloy (NiTi, Nitinol, Actipore) are used as implants in clinical surgery, e.g. for fixation of spinal dysfunctions. The morphological properties were studied by scanning electron microscopy (SEM) and by synchrotron radiation-based microtomography (SRmuCT). The composition was studied by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and energy-dispersive X-ray spectroscopy (EDX). The mechanical properties were studied with temperature-dependent dynamical mechanical analysis (DMA). Studies on the biocompatibility were performed by co-incubation of porous NiTi samples with isolated peripheral blood leukocyte fractions (polymorphonuclear neutrophil granulocytes, PMN; peripheral blood mononuclear leukocytes, PBMC) in comparison with control cultures without NiTi samples. The cell adherence to the NiTi surface was analyzed by fluorescence microscopy and scanning electron microscopy. The activation of adherent leukocytes was analyzed by measurement of the released cytokines using enzyme-linked immunosorbent assay (ELISA). The cytokine response of PMN (analyzed by the release of IL-1ra and IL-8) was not significantly different between cell cultures with or without NiTi. There was a significant increase in the release of IL-1ra (p<0.001), IL-6 (p<0.05), and IL-8 (p<0.05) from PBMC in the presence of NiTi samples. In contrast, the release of TNF-alpha by PBMC was not significantly elevated in the presence of NiTi. IL-2 was released from PBMC only in the range of the lower detection limit in all cell cultures. The material, clearly macroporous with an interconnecting porosity, consists of NiTi (martensite; monoclinic, and austenite; cubic) with small impurities of NiTi2 and possibly NiC(x). The material is not superelastic upon manual compression and shows a good biocompatibility.

Porous titanium-nickel for intervertebral fusion in a sheep model: part 1. Histomorphometric and radiological analysis.

Porous titanium-nickel (PTN) implants represent an alternative to traditional intervertebral fusion cages. Indeed, PTN materials possess interconnecting pores with cell capillarity properties that may promote bone ingrowth and intervertebral fusion without the need for bone grafting. In this study, a PTN intervertebral fusion device was compared to a conventional TiAlV cage packed with autologous bone in a sheep model. The two devices were implanted at two noncontiguous intervertebral lumbar sites for 3, 6, and 12 months. PTN osseointegration showed a time-dependent trend increasing from 21.4% to 37.6% (3-12 months), whereas TiAlV cages remained at the same level of bone ingrowth (22.7%-25.4%; 3-12 months). Furthermore, PTN bone apposition (10.9%-24.2%; 3-12 months) was significantly higher than that of TiAlV implants (1.1%-5.1%; 3-12 months; p < 0.001, ANOVA). Radiological fusion scores increased with postsurgery time regardless of material type, but were consistently superior for PTN (12.5-18.5; 3-12 months) than for TiAlV cages (2.0-15.0; 3-12 months; p < 0.001, ANOVA). Implant materials were not significantly different according to the radiological interbody index based on preoperative disc height: Interbody index began at 132.6% (PTN) and 123.5% (TiAlV) immediately after surgery, then declined to 80.8% (PTN) and 91.0% (TiAlV) after 12 months. Nevertheless, ungrafted PTN constituted an excellent substrate for osteogenic cell integration and represents a new osteoconductive biomaterial with improved fusion characteristics in comparison to conventional TiAlV cages.

A new porous titanium-nickel alloy: Part 1. Cytotoxicity and genotoxicity evaluation.

Porous titanium-nickel (PTN) alloys represent new biomaterials for long-term implantation. Their porosity properties might confer them the capacity to trigger fluid capillarity, tissue ingrowth, as well as good tissue-implant apposition and fixation. Before PTN materials are used as long-term implants, their biocompatibility level must be assessed. In this study, porous titanium-nickel was therefore extracted in a saline semi-physiological solution and materials were evaluated for potential cytotoxicity and genotoxicity reactions. The cytocompatibility elution test was performed in order to determine PTN toxic potential at the in vitro cellular level: no reactivity was detected in cell layers exposed to PTN extracts or the negative controls. In parallel, the genocompatibility of porous titanium-nickel was evaluated using three different assays in order to assess potential damage at the DNA level: the test for chemical induction of chromosome aberrations, the Salmonella typhimurium and Escherichia coli reverse mutation assay, and the mouse micronucleus test. No significant increase in the number of chromosomal aberrations, bacterian revertant colonies, or micronuclei was observed in presence of PTN extracts when compared to negative control exposition. Based on the above results, porous titanium-nickel can be considered completely cytocompatible and genocompatible, and therefore represents a good candidate for long-term implantation.

A new porous titanium-nickel alloy: part 2. Sensitization, irritation and acute systemic toxicity evaluation.

Porous titanium-nickel (PTN) represents a new biomaterial with orthopedic applications as a long-term implant. Because of its nickel content, PTN was tested for its potential to stimulate sensitization, irritation, and systemic toxicity reactions after semi-physiological extraction. In order to do so, an in vivo biocompatibility evaluation was performed following three ISO-standardized methods using accepted animal models for immunity testing: the classical skin sensitization assay (Buehler patch test) in guinea pigs, the rabbit intracutaneous test, and the systemic injection test in mice. The Buehler patch test in guinea pigs revealed no significant change in skin reactions such as erythema or swelling between the induction and the challenge period. In the rabbit intracutaneous irritation test, no irritation or sensitization reactions were observed in saline-extracted PTN samples. Negligible to slight irritation was observed at some of the sites involving PTN samples extracted in cottonseed oil, however the resulting primary irritation index was similar to the one elicited by the blank solution itself. Finally, no toxic symptoms were observed with any of the mice injected with porous titanium-nickel extracts during the acute systemic toxicity test. Based on the above results, porous titanium-nickel is considered to be a non-sensitizing, non-irritant, and non-toxic biomaterial for medical applications.