Anti-infective and osteointegration properties of silicon nitride, poly(ether ether ketone), and titanium implants

Customized Therapeutic Surface Coatings for Dental Implants

Dental implants are frequently used to support fixed or removable dental prostheses to replace missing teeth. The clinical success of titanium dental implants is owed to the exceptional biocompatibility and osseointegration with the bone. Therefore, the enhanced therapeutic effectiveness of dental implants had always been preferred. Several concepts for implant coating and local drug delivery had been developed during the last decades. A drug is generally released by diffusion-controlled, solvent-controlled, and chemical controlled methods. Although a range of surface modifications and coatings (antimicrobial, bioactive, therapeutic drugs) have been explored for dental implants, it is still a long way from designing sophisticated therapeutic implant surfaces to achieve the specific needs of dental patients. The present article reviews various interdisciplinary aspects of surface coatings on dental implants from the perspectives of biomaterials, coatings, drug release, and related therapeutic effects. Additionally, the various types of implant coatings, localized drug release from coatings, and how released agents influence the bone–implant surface interface characteristics are discussed. This paper also highlights several strategies for local drug delivery and their limitations in dental implant coatings as some of these concepts are yet to be applied in clinical settings due to the specific requirements of individual patients.

Si-Fe-C-N Coatings for Biomedical Applications: A Combinatorial Approach

Ceramic coatings may prolong the lifetime of joint implants. Certain ions and wear debris may however lead to negative biological effects. SiN-based materials may substantially reduce these effects, but still need optimization for the application. In this study, a combinatorial deposition method enabled an efficient evaluation of a range of Si-Fe-C-N coating compositions on the same sample. The results revealed compositional gradients of Si (26.0-33.9 at.%), Fe (9.6-20.9 at.%), C (8.2-13.9 at.%) and N (39.7-47.2 at.%), and low oxygen contaminations (0.3-0.6 at.%). The mechanical properties varied with a hardness (H) ranging between 13.7-17.3 GPa and an indentation modulus (M) between 190-212 GPa. Both H and M correlated with the Si (H and M increased as Si increased) and Fe (H and M decreased as Fe increased) content. A slightly columnar morphology was observed in cross-sections, as well as a surface roughness in the nm range. A cell study revealed adhering pre-osteogenic MC3T3 cells, with a morphology similar to that of cells seeded on a tissue culture plastic control. The investigated coatings could be considered for further investigation due to the ability to tune their mechanical properties while maintaining a smooth surface, together with their promising in vitro cell response.

Surface Functionalization of Polyethylene by Silicon Nitride Laser Cladding

Functional coatings are commonly applied to biomaterials in order to improve their properties. In this work, polyethylene was coated with a silicon nitride (Si3N4) powder using a pulsed laser source in a nitrogen gas atmosphere. Several analytical techniques were used to characterize the functionalized surface of the polymer, including Raman spectroscopy, laser microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Antibacterial properties were tested in vitro against Staphylococcus epidermidis. The Si3N4 coating sensibly reduced the amount of living bacteria when compared to the uncoated polymer. Osteoconductivity was also tested in vitro using SaOS-2 osteosarcoma cells. The presence of Si3N4 coating resulted in an increased amount of hydroxyapatite. Coating of polyethylene with silicon nitride may lead to improved performance of indwelling orthopaedic or less invasive medical devices.

Scientific, Clinical, Regulatory, and Economic Aspects of Choosing Bone Graft/Biological Options in Spine Surgery

Spinal arthrodesis is a major element of the spinal surgeon's practice. To attain successful fusion rates, attention must be paid to spinal segment immobilization and proper selection of bone graft. Autogenous bone graft (ie, ICBG), the "gold standard," with or without graft extenders and enhancers provides the foundation for most spinal fusions. ABG is the only graft option containing all 3 factors of new bone growth: osteoconductivity, osteoinductivity, and osteogenicity. While many bone graft alternatives function well as bone graft extenders, only growth factors proteins (ie, rhBMP-2 or OP-2) function as bone graft enhancers and substitutes. The search for optimal hybrid interbody cages, bone graft substitutes, autogenous or allogenic stem cells, and nanostructure scaffolds for release of growth factors continues.

Design of dental implants at materials level: An overview

Due to the excellent restoration of masticatory function, satisfaction on aesthetics and other superiorities, dental implants represent an effective method to resolve tooth losing and damaging. Current dental implant systems still have problems waiting to be addressed, and problems are centralized on the materials of implant bodies. This review aims to summarize major developments in the field of dental implant materials, starting with an overview on structures, procedures of dental implants and challenges of implant materials. Next, implant materials are examined in three categories, that is, metals, ceramics, and polymers, their mechanical properties, biocompatibility, and bioactivity are summarized. And as an important aspect, strategies of surface modification are also reviewed, along with some finite element analysis to guiding the research direction of implant materials. Finally, the conclusive remarks are outlined to provide an outlook on the future research directions and prospects of dental implants.

Clinical outcomes for lumbar fusion using silicon nitride versus other biomaterials

BACKGROUND

In lumbar fusion surgery, intervertebral spacer cages made of silicon nitride (Si3N4) ceramic are an available option among other biomaterials. While the surface chemistry of Si3N4 is known to favor bone fusion, large-scale clinical studies attesting to its efficacy are lacking. This multicenter retrospective study compared lumbar fusion outcomes for Si3N4 cages to previously reported data for other cage materials.

METHODS

Pre-operative patient demographics, comorbidities, changes in visual analog scale (ΔVAS) pain scores, complications, adverse events, and secondary surgical interventions (SSI) were compiled from the records of 450 patients who underwent Si3N4 lumbar spinal fusion at four separate U.S. surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches identified studies reporting similar outcomes for other biomaterials. A total of 1,025 patients from 26 cohorts reported in 14 publications met inclusion criteria for this control group.

RESULTS

Overall, the mean last-follow-up for all patients was 341±293 days (11.4±9.8 months), with the longest follow-up being 6.4 years. Patients with Si3N4 implants were similar in gender and age distribution to the control group but had higher BMI values (30.9±6.1 vs. 25.8±4.1, P<0.01) and lower tobacco use (15.8% vs. 30.0%, P<0.01). Both the Si3N4 and control groups showed significant improvements in VAS pain scores from preoperative to last follow-up. For the Si3N4 group, ΔVAS was 36.8±35.4 points compared to 37.6±22.5 points (P=0.63) for the metadata group. Complications and reoperations for the Si3N4 and the control groups were similar (i.e., 9.8% and 3.1% versus 12.4% and 2.9%, P=0.16 and P=0.84, respectively).

CONCLUSIONS

Lumbar fusion with Si3N4 spacers compared favorably with the improvements reported with other commonly used biomaterial cages.

Dense, Strong, and Precise Silicon Nitride-Based Ceramic Parts by Lithography-Based Ceramic Manufacturing

Due to the high level of light absorption and light scattering of dark colored powders connected with the high refractive indices of ceramic particles, the majority of ceramics studied via stereolithography (SLA) have been light in color, including ceramics such as alumina, zirconia and tricalcium phosphate. This article focuses on a lithography-based ceramic manufacturing (LCM) method for β-SiAlON ceramics that are derived from silicon nitride and have excellent material properties for high temperature applications. This study demonstrates the general feasibility of manufacturing of silicon nitride-based ceramic parts by LCM for the first time and combines the advantages of SLA, such as the achievable complexity and low surface roughness (Ra = 0.50 µm), with the typical properties of conventionally manufactured silicon nitride-based ceramics, such as high relative density (99.8%), biaxial strength (σf = 764 MPa), and hardness (HV10 = 1500).

Clinical outcomes for anterior cervical discectomy and fusion with silicon nitride spine cages: a multicenter study

BACKGROUND

Intervertebral spacers made of silicon nitride (Si3N4) are currently used in cervical and thoracolumbar fusion. While basic science data demonstrate several advantages of Si3N4 over other biomaterials, large-scale clinical results on its safety and efficacy are lacking. This multicenter retrospective study examined outcomes for anterior cervical discectomy and fusion (ACDF) using Si3N4 cages. Results were compared to compiled metadata for other ACDF materials.

METHODS

Pre-operative patient demographics, comorbidities, changes in visual analog scale (VAS) pain scores, complications, adverse events, and secondary surgical interventions were collected from the medical records of 860 patients who underwent Si3N4 ACDF at four surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches were performed for ACDF using other cage or spacer materials. Nine studies with 13 cohorts and 736 patients met the inclusion criteria for this control group.

RESULTS

Overall, the mean last-follow-up for all patients was 319±325 days (10.6±10.8 months), with the longest follow-up being 6.5 years. In comparison to the metadata, patients from the Si3N4 groups were older (57.9±12.2 vs. 56.8±11.1 y, P=0.06) and had higher BMI values (30.0±6.3 vs. 28.1±6.5, P<0.01), but gender and smoking were not different. The Si3N4 patients reported significant improvements in VAS pain scores at last follow-up (i.e., pre-op of 71.0±22.1 vs. follow-up of 36.4±31.5, P<0.01). Although both preoperative and last-follow-up pain scores were higher for Si3N4 patients than the control, the overall change in scores (ΔVAS) was similar. From pre-op to last-follow up, ΔVAS values were 35.4±34.3 for patients receiving the Si3N4 implants versus 34.4±27.3 for patients from the meta-analysis (P=0.56). The complication and reoperation rate for the Si3N4 and the metadata were also comparable (i.e., 7.39% and 0.31% versus 9.79% and 0%, P=0.17 and 0.25, respectively).

CONCLUSIONS

ACDF outcomes using Si3N4 implants matched the clinical efficacy of other cage biomaterials.

3D-additive deposition of an antibacterial and osteogenic silicon nitride coating on orthopaedic titanium substrate

A 3D-additive manufacturing approach produced a dense Si₃N₄ ceramic coating on a biomedical grade commercially pure titanium (cp-Ti) substrate by an automatic laser-sintering procedure. Si₃N₄ coatings could be prepared with thicknesses from the single to the tens of microns. A coating thickness, t = 15 ± 5 μm, was selected for this study, based on projections of homogeneity and scratching resistance. The Si₃N₄ coating met the 20 N threshold required for biomaterial applications, according to the standard scratch testing (ASTM C1624-05). The Si₃N₄ coating imparted both the antibacterial and osteogenic properties of bulk Si₃N₄ to the cp-Ti substrate. Both properties were comparable to those previously described for bulk Si₃N₄ biomedical implants. The newly developed Si₃N₄-coating was applied to commercially available Ti-alloy acetabular shells for total hip arthroplasty. A "glowing" test based on luciferase gene transformation was applied to visualize the colonization of gram-negative Escherichia coli on Si₃N₄-coated and uncoated Ti-alloy acetabular shells. The results showed that the coating technology conferred resistance to Staphylococcus epidermidis and Escherichia coli adhesion onto the bulk acetabular sockets.

Enhanced bioactivity of Si3N4 through trench-patterning and back-filling with Bioglass®

Using a simple and innovative sandblasting process, disks of monolithic biomedical silicon nitride (β-Si₃N₄) were texturized with a matrix of regular, discrete square trenches with a total depth in the range of hundreds of microns. The process consisted of sandblasting Si₃N₄ substrates through a stainless-steel wire-mesh (150 or 200 μm) using abrasive silicon carbide powders (α-SiC, ∼40 μm) under 1,034 kPa (150 psi) of gas pressure. The depth of the porosities could be controlled varying both the treatment time and the distance from the surface. Part of the samples were then filled with 45S5 Bioglass® powders to improve the osteointegration and stimulate the production of bone tissue. Due to the increased macroscopic and microscopic roughness, biological testing using human osteosarcoma cells (SaOS-2) showed improved cell proliferation and greater production of both mineral (hydroxyapatite) and organic (collagen) phases on the patterned surfaces compared to untreated β-Si₃N₄ or to the biomedical titanium control samples. Both of these effects were further enhanced when the porosities were filled with Bioglass®.

The Effect of Coating Density on Functional Properties of SiNx Coated Implants

Ceramic coatings may be applied onto metallic components of joint replacements for improved wear and corrosion resistance as well as enhanced biocompatibility, especially for metal-sensitive patients. Silicon nitride (SiNx) coatings have recently been developed for this purpose. To achieve a high coating density, necessary to secure a long-term performance, is however challenging, especially for sputter deposited SiNx coatings, since these coatings are insulating. This study investigates the time-dependent performance of sputter-deposited SiNx based coatings for joint applications. SiNx coatings with a thickness in the range of 4.3-6.0 µm were deposited by reactive high power impulse magnetron sputtering onto flat discs as well as hip heads made of CoCrMo. SiNx compositional analysis by X-ray photoelectron spectroscopy showed N/Si ratios between 0.8 and 1.0. Immersion of the flat disks in fetal bovine serum solution over time as well as short-term wear tests against ultra-high molecular weight polyethylene (UHMWPE) discs showed that a high coating density is required to inhibit tribocorrosion. Coatings that performed best in terms of chemical stability were deposited using a higher target power and process heating.

Off-Stoichiometric Reactions at the Cell-Substrate Biomolecular Interface of Biomaterials: In Situ and Ex Situ Monitoring of Cell Proliferation, Differentiation, and Bone Tissue Formation

The availability of osteoinductive biomaterials has encouraged new therapies in bone regeneration and has potentially triggered paradigmatic shifts in the development of new implants in orthopedics and dentistry. Among several available synthetic biomaterials, bioceramics have gained attention for their ability to induce mesenchymal cell differentiation and successive bone formation when implanted in the human body. However, there is currently a lack of understanding regarding the fundamental biochemical mechanisms by which these materials can induce bone formation. Phenomenological studies of retrievals have clarified the final effect of bone formation, but have left the chemical interactions at the cell-material interface uncharted. Accordingly, the knowledge of the intrinsic material properties relevant for osteoblastogenesis and osteoinduction remains incomplete. Here, we systematically monitored in vitro the chemistry of mesenchymal cell metabolism and the ionic exchanges during osteoblastogenesis on selected substrates through conventional biological assays as well as via in situ and ex situ spectroscopic techniques. Accordingly, the chemical behavior of different bioceramic substrates during their interactions with mesenchymal cells could be unfolded and compared with that of biomedical titanium alloy. Our goal was to clarify the cascade of chemical equations behind the biological processes that govern osteoblastogenic effects on different biomaterial substrates.

The role of nitrogen off-stoichiometry in the osteogenic behavior of silicon nitride bioceramics

The surface chemistry of silicon nitride plays an important role in stimulating osteoblasts to proliferate and produce bone tissue with improved efficiency. This property, which is advantageous in spinal fusion surgery has a chemical origin and is a direct consequence of the cleavage of covalent SN bonds in an aqueous environment. Building upon a wealth of published research on the stimulation of osteoblastic activity by silicon, the aim of this paper is to explore the role of nitrogen and, more specifically, the N/Si atomic ratio on the osteogenic response of Si₃N₄. The surface stoichiometry of Si₃N₄ was gradually altered toward a silicon-rich composition by systematically treating the Si₃N₄ surface with a high-power pulsed laser in an Ar gas atmosphere (i.e., operated at different pulse times, spot sizes, and voltages). Different analytical probes were used to characterize the surface including X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and energy dispersive X-ray spectroscopy (EDS). Osteoconductivity was tested in vitro using SaOS-2 osteosarcoma cells, and samples with different surface stoichiometry were compared for their osteogenic response. These experiments clearly indicated a fundamental role for nitrogen off-stoichiometry in osteogenesis, and showed that both cell proliferation and growth of bone tissue diminished with decreasing nitrogen content.

Silicon Nitride: A Bioceramic with a Gift

In the closing decades of the 20th century, silicon nitride (Si₃N₄) was extensively developed for high-temperature gas turbine applications. Technologists attempted to take advantage of its superior thermal and mechanical properties to improve engine reliability and fuel economy. Yet, this promise was never realized in spite of the worldwide research, which was conducted at that time. Notwithstanding this disappointment, its use in medical applications in the early 21st century has been an unexpected gift. While retaining all of its engineered mechanical properties, it is now recognized for its peculiar surface chemistry. When immersed in an aqueous environment, the slow elution of silicon and nitrogen from its surface enhances healing of soft and osseous tissue, inhibits bacterial proliferation, and eradicates viruses. These benefits permit it to be used in a wide array of different disciplines inside and outside of the human body including orthopedics, dentistry, virology, agronomy, and environmental remediation. Given the global public health threat posed by mutating viruses and bacteria, silicon nitride offers a valid and straightforward alternative approach to fighting these pathogens. However, there is a conundrum behind these recent discoveries: How can this unique bioceramic be both friendly to mammalian cells while concurrently lysing invasive pathogens? This unparalleled characteristic can be explained by the pH-dependent kinetics of two ammonia species-NH₄⁺ and NH₃-both of which are leached from the wet Si₃N₄ surface.

Biocompatibility of common implantable sensor materials in a tumor xenograft model

Real-time monitoring of tumor microenvironment parameters using an implanted biosensor could provide valuable information on the dynamic nature of a tumor's biology and its response to treatment. However, following implantation biosensors may lose functionality due to biofouling caused by the foreign body response (FBR). This study developed a novel tumor xenograft model to evaluate the potential of six biomaterials (silicon dioxide, silicon nitride, Parylene-C, Nafion, biocompatible EPOTEK epoxy resin, and platinum) to trigger a FBR when implanted into a solid tumor. Biomaterials were chosen based on their use in the construction of a novel biosensor, designed to measure spatial and temporal changes in intra-tumoral O2 , and pH. None of the biomaterials had any detrimental effect on tumor growth or body weight of the murine host. Immunohistochemistry showed no significant changes in tumor necrosis, hypoxic cell number, proliferation, apoptosis, immune cell infiltration, or collagen deposition. The absence of biofouling supports the use of these materials in biosensors; future investigations in preclinical cancer models are required, with a view to eventual applications in humans. To our knowledge this is the first documented investigation of the effects of modern biomaterials, used in the production of implantable sensors, on tumor tissue after implantation. © 2018 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc. J Biomed Mater Res Part B, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1620-1633, 2019.

Bone Morphogenetic Protein 2-Conjugated Silica Particles Enhanced Early Osteogenic Differentiation of Adipose Stem Cells on the Polycaprolactone Scaffold

Background

Silica particles (SPs) induce cell proliferation and osteogenic differentiation. We reported that SPs in the scaffold induced early stage osteogenic differentiation.

Methods

A polycaprolactone (PCL) scaffold was fabricated with a 10 wt% SPs. The surface of PCL scaffold was coated with a 10 µg/mL collagen solution. Next, the scaffold was conjugated with 2 μM SPs, 2 μg/mL bone morphogenetic protein 2 (BMP2), or 2 μM BMP2-conjugated SPs (BCSPs). Green fluorescent protein-coupled BMP2 was applied to fabricate the scaffold. The fluorescence intensity was analyzed by confocal microscopy. The mRNA levels of the early osteogenic differentiation marker, alkaline phosphatase (ALP), were analyzed by real-time quantitative polymerase chain reaction. Levels of BMP2, RUNX2, ERK1/2, and AKT were assessed by western blotting.

Results

ALP mRNA levels were significantly higher in the BCSP-conjugated scaffold than in the other scaffolds. In the early stage of osteogenic differentiation, the protein levels of BMP2, RUNX2, ERK1/2, and AKT in cells were significantly higher in the BCSP-conjugated scaffold than in other scaffolds. Thus, the BCSP composite scaffold induced rapid osteogenic differentiation.

Conclusion

These results suggest that BCSP composite can be used to promote early stage osteogenic differentiation and show promise as a material for use in scaffolds for bone regeneration.

Highly Effective Bone Fusion Induced by the Interbody Cage Made of Calcium Silicate/Polyetheretherketone in a Goat Model

Interbody fusion surgery is often used to settle matters such as degenerative disc disease or disc herniation in clinical orthopedics. Considering the deficiencies of the current treatment methods, we developed an interbody fusion cage made of calcium silicate (CS)/polyetheretherketone (PEEK) and hoped that the bioactive cage could exhibit great fusion ability and maintain stable mechanical function. In the goat model of cervical interbody fusion, the CS/PEEK cage showed stronger interbody fusion at 12 and 26 weeks compared with pure PEEK cage based on the X-ray analysis. The micro-CT scanning and analysis indicated that the CS/PEEK cage induced more new bone ingrowth than the PEEK cage and led to nearly complete interbody fusion at 26 weeks. Moreover, the CS/PEEK group showed excellent mechanical stability and stiffness as evaluated by the spine kinematic assay at the time points. The histological assessment showed the rapid osseointegration and mineralized bone formation around the CS/PEEK cage. This study confirmed that the bioactive CS/PEEK cage is capable of inducing highly effective bone fusion and has high potential to be used in the clinics of spine surgery.

Silicon nitride enhances osteoprogenitor cell growth and differentiation via increased surface energy and formation of amide and nanocrystalline HA for craniofacial reconstruction

The bioactive silicon nitride (Si₃N₄) has been FDA cleared for use as spinal intervertebral arthrodesis devices. Because its surface properties promote bone ongrowth and ingrowth, it also has the potential to benefit craniofacial reconstruction. Thus, the aim of this work was to determine whether the surface properties of Si₃N₄ could enhance the osteoblast cell growth, differentiation and nucleation of hydroxyapatite (HA) crystals compared to conventional implant materials such as titanium (Ti) and polyether ether ketone (PEEK). X-ray absorbance near-edge structure analysis (XANES) indicated the presence of Si-Si, Si-O and Si-N bonding. Surface wettability studies confirmed that Si₃N₄ exhibits the lowest contact angle and highest surface energy. Cell culture studies showed that osteoblast growth was enhanced on Si₃N₄ after 1 day and up to 7 days. Si₃N₄ surface induced highest surface coverage and thickness of nanocrystalline HA (211) and (203) in cell-free in vitro studies after 7 days of culture. Raman spectroscopy analysis confirmed the presence of surface functional groups consisting of phosphate and carbonate species. Interestingly, Si₃N₄ surface showed amide and hydroxyproline groups, the precursors to collagen, which were not observed on Ti and PEEK surfaces. Furthermore, Si₃N₄ surface indicated high expression of RUNX2, enhanced cell differentiation and dense collagenous ECM after 30 days of the in vitro study. The present study concluded that Si₃N₄ surface enhances osteoprogenitor cell adhesion, growth, RUNX2 expression and ECM formation via the coupled effects of higher surface energy and the presence of amide and nanocrystalline HA functional groups.

Microporous Coatings of PEKK/SN Composites Integration with PEKK Exhibiting Antibacterial and Osteogenic Activity, and Promotion of Osseointegration for Bone Substitutes

To improve the antibacterial and osteogenic activities of poly(etherketoneketone) (PEKK), concentrated sulfuric acid (H₂SO₄) suspension with silicon nitride (SN) microparticle was utilized to modify PEKK surface. Through sulfonation reaction, microporous coatings of PEKK/SN composites were created on PEKK surface, which were integrated with PEKK substrate. The results showed that the content of SN in the microporous coatings increased with the increase of SN content in H₂SO₄ suspension (PKS without SN, PKSC5 and PKSC10 with 5 and 10 wt % SN content in H₂SO₄) and that the surface roughness and hydrophilicity of microporous coatings on PEKK were significantly improved with the SN content increasing. In addition, the microporous coating of PKSC10 with high SN content exhibited excellent antibacterial activity due to the synergistic action of the presence of amino (-NH₂) and sulfonic acid (-SO₃H) groups as well as the improvement of protein absorption. Moreover, the microporous coating of PKSC10 obviously stimulated adhesion, proliferation, and osteogenic differentiation of rat bone mesenchymal stem cells. Furthermore, histological and push-out load evaluation indicated that the microporous coating of PKSC10 significantly promoted osteogenesis and osseointegration in vivo. The results suggested that the microporous coating of PKSC10 with high SN content display good biocompatibility, antibacterial and osteogenic activities, and osseointegration ability, which would have great potential for bone substitutes.

3-dimensional printing for anterior cervical surgery: a review

Age-related degenerative changes and non-spondylotic pathologies of the cervical spine such as trauma and tumor can lead to compression of neurological structures and result in substantial alteration of the structural anatomy. The end-goal of surgical intervention is to decompress the neural structures which can be achieved via an anterior or a posterior approach, and stabilization of segments to restore stability and alignment. Three-dimensional printing (3DP or Additive Manufacturing) has been applied to the field of medicine, in particular orthopedics and neurosurgery. Coupled with advances of medical imaging such as computed tomography (CT) scans and magnetic resonance imaging (MRI), accurate 3D models of patient anatomy can be produced, and patient-specific implants (PSIs) for complex anatomical reconstruction have all been applied with positive outcomes. 3D printed implants have been applied in particular to the cervical spine predominantly due to the complex and relatively small osteological anatomy and the proximity of important neurovascular structures to the surgical sites. The purpose of this review is to evaluate the current application of 3DP for cervical spinal implants. This includes a review on the available literature on 3D printed PSIs and current available 3D printed "off-the-shelf" (OTS) implants (3D-OTS). Suitable materials for 3DP of spinal implants and the future prospect of cervical implants will be discussed. The review will be concluded with a suggested guide for carrying future studies to evaluate the efficacy and safety of 3DP for cervical spinal implants.

Infection burden and immunological responses are equivalent for polymeric and metallic implant materials in vitro and in a murine model of fracture-related infection

The development of an infection is a major complication for some patients with implanted biomaterials. Whether the material or surface composition of the used biomaterial influences infection has not been directly compared for key biomaterials currently in use in human patients. We conducted a thorough in vitro and in vivo investigation using titanium (Ti) and polyether-ether-ketone (PEEK) as both commercially available and as modified equivalents (surface polished Ti, and oxygen plasma treated PEEK). Complement activation and cytokine secretion of cell of the immune system was assessed in vitro for all materials in the absence and presence of bacterial stimulants. In a follow-up in vivo study, we monitored bacterial infection associated with clinically available and standard Ti and PEEK inoculated with Staphylococcus aureus. Complement activation was affected by material choice in the absence of bacterial stimulation, although the material based differences were largely lost upon bacterial stimulation. In the in vivo study, the bacterial burden, histological response and cytokine secretion suggests that there is no significant difference between both PEEK and Ti. In conclusion, the underlying material has a certain impact in the absence of bacterial stimulation, however, in the presence of bacterial stimulation, bacteria seem to dictate the responses in a manner that overshadows the influence of material surface properties. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1095-1106, 2019.

Endowing polyetheretherketone with synergistic bactericidal effects and improved osteogenic ability

Biomedical associated infections (BAI) are difficult to treat and may even lead to amputation and death, especially after the emergence of drug-resistant bacteria. The aim of this study was to harness the potential synergistic effects of multiple bactericidal agents to endow polyetheretherketone (PEEK) with the ability of achieving full eradication of planktonic and adherent bacteria while maintaining acceptable biocompatibility. In this work, a mussel inspired, silver nanoparticles (AgNPs) incorporated silk fibroin (SF)/gentamicin sulfate (GS) coating was constructed upon porous PEEK surface. The obtained coating greatly enhanced the bactericidal efficiency to Gram-positive bacteria and Gram-negative bacteria. The number of bacteria survived in the culture medium after treated with this coating was 10⁶ fold lower than that survived after treated with PEEK sample, while the number of viable bacteria adhered to this coating was 10⁵ lower than that adhered to PEEK sample. Furthermore, release of Ag⁺ and GS increased with decreasing pH, indicating great potential of this coating to be a "smart" bacteria-triggered self-defensive coating. Meanwhile, this functional coating shows favorable cytocompatibility and osteogenic ability. The mechanism behind this dual function is also partially revealed. Expectedly, this "smart" dual function coating can give a promise for PEEK to become a solution to increasingly deteriorated BAI.

STATEMENT OF SIGNIFICANCE

In this study, a mussel inspired, silver nanoparticles (AgNPs) incorporated silk fibroin (SF)/gentamicin sulfate (GS) coating was constructed upon porous polyetheretherketone (PEEK) surface. This design was aimed to provide a solution to the increasingly deteriorated biomedical associated infections (BAI). Actually, this design endowed PEEK with dual function: bacteria-triggered synergistic bactericidal effect and improved osteogenic ability. The combination of silver and GS exhibited synergistic bacteria killing effect on both Gram-positive and Gram-negative bacteria, which showed 10⁶ times higher in releasing-killing and 10⁵ times higher in anti-adhesion than that of untreated PEEK. Furthermore, release of bactericidal agents increased with decreasing pH, indicating great potential of this coating to be a bacteria-triggered self-defensive coating. More interestingly, this study revealed the mechanism of synergistic effect between silver and GS.

Anterior Lumbar Interbody Fusion Using Reaction Bonded Silicon Nitride Implants: Long-Term Case Series of the First Synthetic Anterior Lumbar Interbody Fusion Spacer Implanted in Humans

BACKGROUND

In this study, a historical case series is reported of reaction bonded silicon nitride (Si₃N₄) implants for anterior lumbar interbody fusion (ALIF) for a patient population of 30 and surgery levels L3/4, L4/5, and/or L5/S1. Before the study, the only work on Si₃N₄ as a biomedical material was associated preliminary work, which involved animal trials using a rabbit model. The objective was to undertake the first use of Si₃N₄ as a biomedical material for humans, as an implant for ALIF.

METHODS

The Si₃N₄ implants were prepared by die-pressing silicon powder and reaction bonding in 95 N₂/5 H₂ at ∼1400°C for ∼50 hours. The surgeries involved a retroperitoneal approach for L3/4 and L4/5 levels and a transperitoneal approach for L5/S1 level. The patient follow-up involved assessment of radiologic fusion up to 30 years and clinical outcomes to 10 years.

RESULTS

The reaction bonded Si₃N₄ implants were found to be biologically safe and to show high fusion rates with minimal subsidence, no abnormal reaction, and no other complications. The primary outcome measure, visual analog scale back pain, improved from a preoperative mean of 8.4 (range, 6-10) to a mean of 3.7 (range, 0-9) at 5 years and a mean of 4.9 (range, 0-9) at 10 years. The Oswestry Disability Index improved from a preoperative mean of 48 (range, 26-84) to a mean of 35 (range, 4-76) at 10 years.

CONCLUSIONS

This study confirms that Si₃N₄ is biologically safe in the long-term, with capacity for excellent radiologic osseointegration.

Comparison of polyetheretherketone versus silicon nitride intervertebral spinal spacers in a caprine model

Polyetheretherketone (PEEK) is commonly used as a spinal spacer for intervertebral fusion surgery. Unfortunately, PEEK is bioinert and does not effectively osseointegrate into living bone. In contrast, comparable spacers made of silicon nitride (Si₃ N₄ ) possess a surface nanostructure and chemistry that encourage appositional bone healing. This observational study was designed to compare the outcomes of these two biomaterials when implanted as spacers in an adult caprine model. Lumbar interbody fusion surgeries were performed at two adjacent levels in eight adult goats using implants of PEEK and Si₃ N₄ . At six-months after surgery, the operative and adjacent spinal segments were extracted and measured for bone fusion, bone volume, bone-implant contact (BIC) and soft-tissue implant contact (SIC) ratios, and biodynamic stability. The null hypothesis was that no differences in these parameters would be apparent between the two groups. Fusion was observed in seven of eight implants in each group with greater bone formation in the Si₃ N₄ group (52.6%) versus PEEK (27.9%; p = 0.2). There were no significant differences in BIC ratios between PEEK and Si₃ N₄ , and the biodynamic stability of the two groups was also comparable. The results suggest that Si₃ N₄ spacers are not inferior to PEEK and they may be more effective in promoting arthrodesis. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 00B: 000-000, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 688-699, 2019.

Biological Impact of Silicon Nitride for Orthopaedic Applications: Role of Particle Size, Surface Composition and Donor Variation

The adverse biological impact of orthopaedic wear debris currently limits the long-term safety of human joint replacement devices. We investigated the role of particle size, surface composition and donor variation in influencing the biological impact of silicon nitride as a bioceramic for orthopaedic applications. Silicon nitride particles were compared to the other commonly used orthopaedic biomaterials (e.g. cobalt-chromium and Ti-6Al-4V alloys). A novel biological evaluation platform was developed to simultaneously evaluate cytotoxicity, inflammatory cytokine release, oxidative stress, and genotoxicity potential of particles using peripheral blood mononuclear cells (PBMNCs) from individual human donors. Irrespective of the particle size, silicon nitride did not cause any adverse responses whereas cobalt-chromium wear particles caused donor-dependent cytotoxicity, TNF-α cytokine release, oxidative stress, and DNA damage in PBMNCs after 24 h. Despite being similar in size and morphology, silicon dioxide nanoparticles caused the release of significantly higher levels of TNF-α compared to silicon nitride nanoparticles, suggesting that surface composition influences the inflammatory response in PBMNCs. Ti-6Al-4V wear particles also released significantly elevated levels of TNF-α cytokine in one of the donors. This study demonstrated that silicon nitride is an attractive orthopaedic biomaterial due to its minimal biological impact on human PBMNCs.

A single center retrospective clinical evaluation of anterior cervical discectomy and fusion comparing allograft spacers to silicon nitride cages

BACKGROUND

Iliac crest autograft or allograft spacers have been traditionally utilized in anterior cervical discectomy and fusion (ACDF) to provide vertebral stabilization and enhanced osteogenesis. However, abiotic cages have largely replaced these allogenic sources due to host-site morbidities and disease transmission risks, respectively. Although devices made of polyetheretherketone (PEEK) or titanium-alloys (Ti) have gained wide popularity, they lack osteoinductive or conductive capabilities. In contrast, silicon nitride (Si3N4) is a relatively new implant material that also provides structural stability and yet purportedly offers osteopromotive and antimicrobial behavior. This study compared radiographic outcomes at ≥12 months of follow-up for osseous integration, fusion rate, time to fusion, and subsidence in ACDF patients with differing intervertebral spacers.

METHODS

Fifty-eight ACDF patients (108 segments) implanted with Si3N4 cages were compared to thirty-four similar ACDF patients (61 segments) implanted with fibular allograft spacers. Lateral radiographs (normal, flexion, and extension) were obtained at 3, 6, 12, and 24 months to assess osseous integration, the presence of bridging bone, the absence of peri-implant radiolucencies, subsidence, and fusion using both interspinous distance (ISD) and Cobb angle methods.

RESULTS

In patients with ≥12 months of follow-up, fusion for the allograft spacers and Si3N4 cages was 86.84% and 96.83%, respectively (ISD method, P=0.10), and 67.65% and 84.13%, respectively (Cobb angle method P=0.07), while osseointegration was 76.32% and 93.65%, respectively (P=0.02). The time to fusion significantly favored the Si3N4 cages (4.08 vs. 8.64 months (ISD method, P=0.01), and 6.76 vs. 11.74 months (Cobb angle method, P=0.04). The assessed time for full osseointegration was 7.83 and 19.24 months for Si3N4 and allograft, respectively (P=0.00). Average subsidence at 1-year follow-up was 0.51 and 2.71 mm for the Si3N4 and allograft cohorts, respectively (P=0.00).

CONCLUSIONS

In comparison to fibular allograft spacers, Si3N4 cages showed earlier osseointegration and fusion, higher fusion rates, and less subsidence.

Treatment of lumbar discitis using silicon nitride spinal spacers: A case series and literature review

INTRODUCTION

Septic infection of a lumbar intervertebral disc is a serious disorder which is often difficult to diagnose and appropriately treat because of the rarity of the disease, the varied presentation of symptoms, and the frequency of low-back pain within the overall population. Its etiology can be pyogenic, granulomatous, fungal, or parasitic; its incidence is rising due to increased patient susceptibility and improved diagnostic tools. Conservative treatments involve antibiotics, physical therapy, and/or immobilization. More aggressive management requires discectomy, debridement, and spinal fusion in combination with local and systemic antibiotic administration.

PRESENTATION OF CASES

Presented here are two case studies of lumbar pyogenic discitis associated with Escherichia coli and Candida albicans infections. Both required single-level anterior discectomy followed by spinal fusion using an antimicrobial silicon nitride (Si3N4) spacer for stabilization without instrumentation. Localized antibiotics were used for only one of the patients. Follow-up CT and MRI scans showed that the infections had been resolved with no recurrence of symptoms.

DISCUSSION

Si3N4 is a relatively new spinal spacer material. It was utilized in these two cases because it reportedly provides a local environment which promotes rapid arthrodesis while resisting bacterial adhesion and biofilm formation. It is also highly compatible with X-ray, MRI, and CT imaging modalities. These properties were particularly attractive for these two cases given the patients' histories, presentation of symptoms, and the decision to forego instrumentation.

CONCLUSION

The use of Si3N4 as an antimicrobial spacer may lead to improved outcomes for patients with pyogenic discitis of the lumbar spine.

In vitroantibacterial activity of oxide and non-oxide bioceramics for arthroplastic devices: II. Fourier transform infrared spectroscopy

The metabolic response of Gram-positiveStaphylococcus epidermidisbacteria to bioceramic substrates was probed by Fourier transform infrared spectroscopy.

New alternate bearing surfaces in total hip arthroplasty: A review of the current literature

As indications for total hip arthroplasty (THA) have expanded, the incidence of THA has increased among younger patients, who live longer and tend to place more strain on implants via higher activity levels. This demographical shift accentuates the importance of advancing innovation to ensure implant longevity for younger and more active patients. Future innovation, as it pertains to THA components, is likely to focus on modifying implant designs and tribology in conjunction with identification and application of newer biomaterials. By reviewing the literature for development status of various materials and novel design advancements in THA component outside of the standard highly cross-linked polyethylene, this investigation provided an update on the current and future status of design initiatives as they pertain to THA. Though the highlighted alternative bearing surfaces have shown promising in vitro and limited, yet encouraging clinical data, they lack larger and longer-term clinical trial results. Further research and innovation is warranted to identify the optimal bearing surface to most effectively accommodate for the trend of younger and more active patients undergoing THA. Implant longevity is crucial if the clinical success of THA is to be maintained.

Bacteria antibiotic resistance: New challenges and opportunities for implant-associated orthopedic infections

There has been a dramatic increase in the emergence of antibiotic-resistant bacterial strains, which has made antibiotic choices for infection control increasingly limited and more expensive. In the U.S. alone, antibiotic-resistant bacteria cause at least 2 million infections and 23,000 deaths a year resulting in a $55-70 billion per year economic impact. Antibiotics are critical to the success of surgical procedures including orthopedic prosthetic surgeries, and antibiotic resistance is occurring in nearly all bacteria that infect people, including the most common bacteria that cause orthopedic infections, such as Staphylococcus aureus (S. aureus). Most clinical cases of orthopedic surgeries have shown that patients infected with antibiotic-resistant bacteria, such as methicillin-resistant S. aureus (MRSA), are associated with increased morbidity and mortality. This paper reviews the severity of antibiotic resistance at the global scale, the consequences of antibiotic resistance, and the pathways bacteria used to develop antibiotic resistance. It highlights the opportunities and challenges in limiting antibiotic resistance through approaches like the development of novel, non-drug approaches to reduce bacteria functions related to orthopedic implant-associated infections. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:22-32, 2018.

In vitroantibacterial activity of oxide and non-oxide bioceramics for arthroplastic devices: I.In situtime-lapse Raman spectroscopy

Raman spectroscopy proved why the antibacterial response of non-oxide Si₃N₄bioceramic is superior to those of alumina-based oxide bioceramics.

Human osteoblasts grow transitional Si/N apatite in quickly osteointegrated Si3N4 cervical insert

Silicon nitride (Si₃N₄) ceramics possesses surface chemistry that accelerates bone repair, as previously established by in vitro experiments using both osteosarcoma and mesenchymal cells. The release of silicic acid and nitrogen compounds from the surface Si₃N₄ enhanced in vitro cellular activity. The results of this study demonstrate for the first time that the osseointegration behavior previously observed is operative with a peculiar chemistry within the human milieu. Si and N elements stimulated progenitor cell differentiation and osteoblastic activity, which ultimately resulted in accelerated bone ingrowth. At the molecular scale, insight into the effect of silicon and nitrogen ions released from the Si₃N₄ surface was obtained through combined histomorphometric analyses, Raman, Fourier-transform-infrared, and X-ray photoelectron spectroscopies. Identical analyses conducted on a polyetheretherketone (PEEK) spinal explant showed no chemical changes and a lower propensity for osteogenic activity. Silicon and nitrogen are key elements in stimulating cells to generate bony apatite with crystallographic imperfections, leading to enhanced bioactivity of Si₃N₄ biomedical devices.

STATEMENT OF SIGNIFICANCE

This research studies osseointegration processes comparing results from explanted PEEK and Si₃N₄ spinal spacers. Data show that the formation of hydroxyapatite on silicon nitride bio-ceramic surfaces happens with a peculiar mechanism inside the human body. Silicon and nitrogen were incorporated inside the bony tissue structure allowing the developing of off-stoichiometric bony apatite and stimulating progenitor cell differentiation/osteoblastic activity. Silicon and nitrogen ions released from the Si₃N₄ surface were detected through combined histologic analyses, Raman microspectroscopy, Fourier-transform-infrared, and X-ray photoelectron spectroscopies.

Novel Osteobiologics and Biomaterials in the Treatment of Spinal Disorders

Spinal osteobiologics have evolved substantially in this century after the development of many product categories such as growth factors, allograft, and stem cells. The indications for the use of novel biologics within spine surgery are rapidly expanding as the mechanism of each is elucidated. While the knowledge base of bone morphogenetic protein increases with each subsequent year, the application of new nanotechnology and cell-based strategies are being reported. This review will discuss the most recent data in novel osteobiologics, and where we could use future study.

Surface topography of silicon nitride affects antimicrobial and osseointegrative properties of tibial implants in a murine model

While silicon nitride (Si₃ N₄ ) is an antimicrobial and osseointegrative orthopaedic biomaterial, the contribution of surface topography to these properties is unknown. Using a methicillin-resistant strain of Staphylococcus aureus (MRSA), this study evaluated Si₃ N₄ implants in vitro utilizing scanning electron microscopy (SEM) with colony forming unit (CFU) assays, and later in an established in vivo murine tibia model of implant-associated osteomyelitis. In vitro, the "as-fired" Si₃ N₄ implants displayed significant reductions in adherent bacteria versus machined Si₃ N₄ (2.6 × 10⁴ vs. 8.7 × 10⁴ CFU, respectively; p < 0.0002). Moreover, SEM imaging demonstrated that MRSA cannot directly adhere to native as-fired Si₃ N₄ . Subsequently, a cross-sectional study was completed in which sterile or MRSA contaminated as-fired and machined Si₃ N₄ implants were inserted into the tibiae of 8-week old female Balb/c mice, and harvested on day 1, 3, 5, 7, 10, or 14 post-operatively for SEM. The findings demonstrated that the antimicrobial activity of the as-fired implants resulted from macrophage clearance of the bacteria during biofilm formation on day 1, followed by osseointegration through the apparent recruitment of mesenchymal stem cells on days 3-5, which differentiated into osteoblasts on days 7-14. In contrast, the antimicrobial behavior of the machined Si₃ N₄ was due to repulsion of the bacteria, a phenomenon that also limited osteogenesis, as host cells were also unable to adhere to the machined surface. Taken together, these results suggest that the in vivo biological behavior of Si₃ N₄ orthopaedic implants is driven by critical features of their surface nanotopography. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3413-3421, 2017.

Effects of Nano-Hydroxyapatite/Polyetheretherketone-Coated, Sandblasted, Large-Grit, and Acid-Etched Implants on Inflammatory Cytokines and Osseointegration in a Peri-Implantitis Model in Beagle Dogs

Background

This study explored the effects of nano-hydroxyapatite/polyetheretherketone (n-HA/PEEK)-coated sandblasted, large-grit, and acid-etched (SLA) implants on inflammatory cytokines and osseointegration in peri-implantitis model beagle dogs.

Material/Methods

Peri-implantitis models were established. Eight beagle dogs were randomly and evenly assigned into SLA tied, SLA + n-HA/PEEK tied, SLA untied, or SLA + n-HA/PEEK untied groups. A special periodontal probe was used to detect the plaque index (PLI), probing depth (PD), and modified Sulcus Bleeding Index (mSBI). Gingival crevicular fluid was collected and an ELISA kit was utilized to detect IL-1, IL-6, and IL-17 levels. The colony-forming units were counted and the maximum shear strength of implants was tested using the axial pullout test. HE staining was used to detect the inflammation of peri-implant bone tissues. Osseointegration was observed through toluidine blue staining. Bone-to-implant contact (BIC) was obtained through histological observation and the mineral apposition rate (MAR) was calculated after immune fluorescent double staining.

Results

The SLA tied group demonstrated higher levels of PLI, PD, mSBI, IL-1, IL-6, and IL-17 and a higher degree of inflammation than the SLA + n-HA/PEEK tied group. The tied groups also displayed similar results over the untied groups at the same time point. The maximum shear strength, BIC, and MAR in the SLA tied group were significantly lower than in the SLA + n-HA/PEEK tied group.

Conclusions

Our findings demonstrate that SLA + n-HA/PEEK implants can promote osseointegration and relieve the inflammation response of peri-implantitis in beagle dogs.

Antibacterial properties of PEKK for orthopedic applications

Orthopedic implant infections have been steadily increasing while, at the same time, antibiotics developed to kill such bacteria have proven less and less effective with every passing day. It is clear that new approaches that do not rely on the use of antibiotics are needed to decrease medical device infections. Inspired by cicada wing surface topographical features, nanostructured surfaces represent a new approach for imposing antibacterial properties to biomaterials without using drugs. Moreover, new chemistries with altered surface energetics may decrease bacterial attachment and growth. In this study, a nanostructured surface was fabricated on poly-ether-ketone-ketone (PEKK), a new orthopedic implant chemistry, comprised of nanopillars with random interpillar spacing. Specifically, after 5 days, when compared to the orthopedic industry standard poly-ether-ether-ketone (PEEK), more than 37% less Staphylococcus epidermidis were found on the PEKK surface. Pseudomonas aeruginosa attachment and growth also decreased 28% after one day of culture, with around a 50% decrease after 5 days of culture when compared to PEEK. Such decreases in bacteria function were achieved without using antibiotics. In this manner, this study demonstrated for the first time, the promise that nanostructured PEKK has for numerous anti-infection orthopedic implant applications.

Pathogenic Mechanisms and Host Interactions in Staphylococcus epidermidis Device-Related Infection

Staphylococcus epidermidis is a permanent member of the normal human microbiota, commonly found on skin and mucous membranes. By adhering to tissue surface moieties of the host via specific adhesins, S. epidermidis is capable of establishing a lifelong commensal relationship with humans that begins early in life. In its role as a commensal organism, S. epidermidis is thought to provide benefits to human host, including out-competing more virulent pathogens. However, largely due to its capacity to form biofilm on implanted foreign bodies, S. epidermidis has emerged as an important opportunistic pathogen in patients receiving medical devices. S. epidermidis causes approximately 20% of all orthopedic device-related infections (ODRIs), increasing up to 50% in late-developing infections. Despite this prevalence, it remains underrepresented in the scientific literature, in particular lagging behind the study of the S. aureus. This review aims to provide an overview of the interactions of S. epidermidis with the human host, both as a commensal and as a pathogen. The mechanisms retained by S. epidermidis that enable colonization of human skin as well as invasive infection, will be described, with a particular focus upon biofilm formation. The host immune responses to these infections are also described, including how S. epidermidis seems to trigger low levels of pro-inflammatory cytokines and high levels of interleukin-10, which may contribute to the sub-acute and persistent nature often associated with these infections. The adaptive immune response to S. epidermidis remains poorly described, and represents an area which may provide significant new discoveries in the coming years.

Biotransformation of Silver Released from Nanoparticle Coated Titanium Implants Revealed in Regenerating Bone

Antimicrobial silver nanoparticle coatings have attracted interest for reducing prosthetic joint infection. However, few studies report in vivo investigations of the biotransformation of silver nanoparticles within the regenerating tissue and its impact on bone formation. We present a longitudinal investigation of the osseointegration of silver nanoparticle-coated additive manufactured titanium implants in rat tibial defects. Correlative imaging at different time points using nanoscale secondary ion mass spectrometry, transmission electron microscopy (TEM), histomorphometry, and 3D X-ray microcomputed tomography provided quantitative insight from the nano- to macroscales. The quality and quantity of newly formed bone is comparable between the uncoated and silver coated implants. The newly formed bone demonstrates a trabecular morphology with bone being located at the implant surface, and at a distance, at two weeks. Nanoscale elemental mapping of the bone-implant interface showed that silver was present primarily in the osseous tissue and colocalized with sulfur. TEM revealed silver sulfide nanoparticles in the newly regenerated bone, presenting strong evidence that the previously in vitro observed biotransformation of silver to silver sulfide occurs in vivo.

Silicon Nitride (Si3N4) Implants: The Future of Dental Implantology?

For decades titanium has been the preferred material for dental implant fabrication, with mechanical and biological performance resulting in high clinical success rates. These have been further enhanced by incremental development of surface modifications aimed at improving speed and degree of osseointegration and resulting in enhanced clinical treatment options and outcomes. However, increasing demand for metal-free dental restorations has also led to the development of ceramic-based dental implants, such as zirconia. In orthopedics, alternative biomaterials, such as polyetheretherketone or silicon nitride, have been used for implant applications. The latter is potentially of particular interest for oral use as it has been shown to have antibacterial properties. In this article we aim to shed light on this particular biomaterial as a future promising candidate for dental implantology applications, addressing basic specifications required for any dental implant material. In view of available preclinical data, silicon nitride seems to have the essential characteristics to be a candidate for dental implants material. This novel ceramic has a surface with potentially antimicrobial properties, and if this is confirmed in future research, it could be of great interest for oral use.

Development of a SiYAlON glaze for improved osteoconductivity of implantable medical devices

The application of bioactive coatings onto orthopaedic appliances is commonly performed to compensate for the otherwise bioinert nature of medical devices and to improve their osseointegration. Calcium phosphates, hydroxyapatite (HAp), and bioglasses are commercially available for this purpose. Until recently, few other inorganic compounds have been identified with similar biofunctionality. However, silicon nitride (Si₃ N₄ ) has emerged as a new orthopaedic material whose unique surface chemistry also enhances osteoconductivity. Recent research has confirmed that its minority intergranular phase, consisting of silicon yttrium aluminum oxynitride (SiYAlON), is principally responsible for this improvement. As a result, it was hypothesized that SiYAlON itself might serve as an effective osteoconductive coating or glaze for medical devices. To test this hypothesis, a process inspired by traditional ceramic whiteware glazing was developed. A slurry containing ingredients similar to the intergranular SiYAlON composition was applied to a Si₃ N₄ surface, which was then subjected to a heat treatment to form a glaze. Various analytical tools were employed to assess its chemistry and morphology. It was found that the glaze was comprised predominately of Y₅ Si₃ O₁₂ N, a compound commonly referred to as N-apatite, which is isostructural to native HAp. Subsequent exposure of the glazed surface to acellular simulated body fluid led to increased deposition of biomimetic HAp-like crystals, while exposure to Saos-2 osteosarcoma cells in vitro resulted in greater HAp deposition relative to control samples. The observation that SiYAlON exhibits enhanced osteoconductivity portends its potential as a therapeutic aid in bone and tissue repair. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1084-1096, 2018.

Bioactive silicon nitride: A new therapeutic material for osteoarthropathy

While the reciprocity between bioceramics and living cells is complex, it is principally governed by the implant's surface chemistry. Consequently, a deeper understanding of the chemical interactions of bioceramics with living tissue could ultimately lead to new therapeutic strategies. However, the physical and chemical principles that govern these interactions remain unclear. The intricacies of this biological synergy are explored within this paper by examining the peculiar surface chemistry of a relatively new bioceramic, silicon nitride (Si3N4). Building upon prior research, this paper aims at obtaining new insights into the biological interactions between Si3N4 and living cells, as a consequence of the off-stoichiometric chemical nature of its surface at the nanometer scale. We show here yet unveiled details of surface chemistry and, based on these new data, formulate a model on how, ultimately, Si3N4 influences cellular signal transduction functions and differentiation mechanisms. In other words, we interpret its reciprocity with living cells in chemical terms. These new findings suggest that Si3N4 might provide unique new medicinal therapies and effective remedies for various bone or joint maladies and diseases.

Bacteriostatic behavior of surface modulated silicon nitride in comparison to polyetheretherketone and titanium

Perioperative and latent infections are leading causes of revision surgery for orthopaedic devices resulting in significant increased patient care, comorbidities, and attendant costs. Identifying biomaterial surfaces that inherently resist biofilm adhesion and bacterial expression is an important emerging strategy in addressing implant-related infections. This in vitro study was designed to compare biofilm formation on three biomaterials commonly employed in spinal fusion surgery-silicon nitride (Si₃ N₄ ), polyetheretherketone (PEEK), and a titanium alloy (Ti6Al4V-ELI) -using one gram-positive and one gram-negative bacterial species. Disc samples from various surface treated Si₃ N₄ , PEEK, and Ti6Al4V were inoculated with 10⁵ CFU/mm² Staphylococcus epidermidis (ATCC®14990™) or Escherichia coli (ATCC^® 25922™) and cultured in PBS, 7% glucose, and 10% human plasma for 24 and 48 h, followed by retrieval and rinsing. Vortexed solutions were diluted, plated, and incubated at 37 °C for 24 to 48 h. Colony forming units (CFU/mm² ) were determined using applicable dilution factors and surface areas. A two-tailed, heteroscedastic Student's t-test (95% confidence) was used to determine statistical significance. The various Si₃ N₄ samples showed the most favorable bacterial resistance for both bacilli tested. The mechanisms for the bacteriostatic behavior of Si₃ N₄ are likely due to multivariate surface effects including submicron-topography, negative charging, and chemical interactions which form peroxynitrite (an oxidative agent). Si₃ N₄ is a new biomaterial with the apparent potential to inhibit biofilm formation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1521-1534, 2017.

High-Performance Polymers and Their Potential Application as Medical and Oral Implant Materials: A Review

PURPOSE

To review the literature on high-performance polymeric (HPP) materials used as medical and oral implants and make comparisons with the commonly used titanium.

MATERIAL AND METHODS

Original scientific articles published in English in MEDLINE (PubMed-NCBI) and Picarta literature databases between January 01, 1995 and June 01, 2013 were included in this review. Additional information was derived from scientific reports, medical and chemical textbooks, handbooks, product information, manufacturers' instructions, and Internet web sites of the manufacturers.

RESULTS

Based on the 7 animal studies and 1 clinical study, HPP polyetheretherketone (PEEK) consisting of a single monomer and featuring a low Young modulus may be advantageous. PEEK seems to lead to less osteolyses and healing problems and no scattering in radiation was observed. Some animal studies showed direct contact between PEEK and the bone with high biocompatibility and no evidence for cytotoxicity, mutagenicity, carcinogenicity, and immunogenicity to the present day.

CONCLUSION

The HPPs (ie, PEEK) may carry some potential to be an alternative material for titanium as medical and dental implants. Yet, clinical and animal studies are limited in the field of implantology with such materials.