Nano-crystalline diamond-coated titanium dental implants – A histomorphometric study in adult domestic pigs

Nanotechnology for Dentistry: Prospects and Applications

In the XXI century, application of nanostructures in oral medicine has become common. In oral medicine, using nanostructures for the treatment of dental caries constitutes a great challenge. There are extensive studies on the implementation of nanomaterials to dental composites in order to improve their properties, e.g., their adhesive strength. Moreover, nanostructures are helpful in dental implant applications as well as in maxillofacial surgery for accelerated healing, promoting osseointegration, and others. Dental personal care products are an important part of oral medicine where nanomaterials are increasingly used, e.g., toothpaste for hypersensitivity. Nowadays, nanoparticles such as macrocycles are used in different formulations for early cancer diagnosis in the oral area. Cancer of the oral cavity-human squamous carcinoma-is the sixth leading cause of death. Detection in the early stage offers the best chance at total cure. Along with diagnosis, macrocycles are used for photodynamic mechanism-based treatments, which possess many advantages, such as protecting healthy tissues and producing good cosmetic results. Application of nanostructures in medicine carries potential risks, like long-term influence of toxicity on body, which need to be studied further. The introduction and development of nanotechnologies and nanomaterials are no longer part of a hypothetical future, but an increasingly important element of today's medicine.

Key Challenges in Diamond Coating of Titanium Implants: Current Status and Future Prospects

Over past years, the fabrication of Ti-based permanent implants for fracture fixation, joint replacement and bone or tooth substitution, has become a routine task. However, it has been found that some degradation phenomena occurring on the Ti surface limits the life or the efficiency of the artificial constructs. The task of avoiding such adverse effects, to prevent microbial colonization and to accelerate osteointegration, is being faced by a variety of approaches in order to adapt Ti surfaces to the needs of osseous tissues. Among the large set of biocompatible materials proposed as an interface between Ti and the hosting tissue, diamond has been proven to offer bioactive and mechanical properties able to match the specific requirements of osteoblasts. Advances in material science and implant engineering are now enabling us to produce micro- or nano-crystalline diamond coatings on a variety of differently shaped Ti constructs. The aim of this paper is to provide an overview of the research currently ongoing in the field of diamond-coated orthopedic Ti implants and to examine the evolution of the concepts that are accelerating the full transition of such technology from the laboratory to clinical applications.

Coating Ti6Al4V implants with nanocrystalline diamond functionalized with BMP-7 promotes extracellular matrix mineralization in vitro and faster osseointegration in vivo

The present study investigates the effect of an oxidized nanocrystalline diamond (O-NCD) coating functionalized with bone morphogenetic protein 7 (BMP-7) on human osteoblast maturation and extracellular matrix mineralization in vitro and on new bone formation in vivo. The chemical structure and the morphology of the NCD coating and the adhesion, thickness and morphology of the superimposed BMP-7 layer have also been assessed. The material analysis proved synthesis of a conformal diamond coating with a fine nanostructured morphology on the Ti6Al4V samples. The homogeneous nanostructured layer of BMP-7 on the NCD coating created by a physisorption method was confirmed by AFM. The osteogenic maturation of hFOB 1.19 cells in vitro was only slightly enhanced by the O-NCD coating alone without any increase in the mineralization of the matrix. Functionalization of the coating with BMP-7 resulted in more pronounced cell osteogenic maturation and increased extracellular matrix mineralization. Similar results were obtained in vivo from micro-CT and histological analyses of rabbit distal femurs with screws implanted for 4 or 12 weeks. While the O-NCD-coated implants alone promoted greater thickness of newly-formed bone in direct contact with the implant surface than the bare material, a further increase was induced by BMP-7. It can be therefore concluded that O-NCD coating functionalized with BMP-7 is a promising surface modification of metallic bone implants in order to improve their osseointegration.

Diamond in the Rough: Toward Improved Materials for the Bone-Implant Interface

The ability of an orthopedic implant to integrate successfully with the surrounding bone tissue is imperative for optimal patient outcomes. Here, the recent advances and future prospects for diamond-based coatings of conventional osteo-implant materials (primarily titanium) are explored. The ability of these diamond coatings to enhance integration into existing bone, improved implant mechanical properties, facilitate surface chemical functionalization, and provide anti-microbial properties are discussed in context of orthopedic implants. These diamond-based materials may have the additional benefit of providing an osteo-inductive effect, enabling better integration into existing bone via stem cell recruitment and bone regeneration. Current and timely research is highlighted to support the discussion and suggestions in further improving implant integration via an osseoinductive effect from the diamond composite materials.

The Effect of Coronal Implant Design and Drilling Protocol on Bone-to-Implant Contact: A 3-Month Study in the Minipig Calvarium

Background: Stress concentrated at an implant’s neck may affect bone-to-implant contact (BIC). The objective of this study was to evaluate four different implant neck designs using two different drilling protocols on the BIC. Methods: Ninety-six implants were inserted in 12 minipigs calvarium. Implants neck designs evaluated were: type 1–6 coronal flutes (CFs), 8 shallow microthreads (SMs); type 2–6 CFs,4 deep microthreads (DMs); type 3–4 DMs; type 4–2 CFs, 8 SMs. Two groups of forty-eight implants were inserted with a final drill diameter of 2.8 mm (DP1) or 3.2 mm (DP2). Animals were sacrificed after 1 and 3 months, total-BIC (t-BIC) and coronal-BIC (c-BIC) were evaluated by nondecalcified histomorphometry analysis. Results: At 1 month, t-BIC ranged from 85–91% without significant differences between implant types or drilling protocol. Flutes on the coronal aspect impaired the BIC at 3 m. c-BIC of implant types with 6 CFs was similar and significantly lower than that of implant types 3 and 4. c-BIC of implant type 4 with SMs was highest of all implant types after both healing periods. Conclusions: BIC was not affected by the drilling protocol. CFs significantly impaired the -BIC. Multiple SMs were associated with greater c-BIC.

Nanocomposites for Enhanced Osseointegration of Dental and Orthopedic Implants Revisited: Surface Functionalization by Carbon Nanomaterial Coatings

Over the past few decades, carbon nanomaterials, including carbon nanofibers, nanocrystalline diamonds, fullerenes, carbon nanotubes, carbon nanodots, and graphene and its derivatives, have gained the attention of bioengineers and medical researchers as they possess extraordinary physicochemical, mechanical, thermal, and electrical properties. Recently, surface functionalization with carbon nanomaterials in dental and orthopedic implants has emerged as a novel strategy for reinforcement and as a bioactive cue due to their potential for osseointegration. Numerous developments in fabrication and biological studies of carbon nanostructures have provided various novel opportunities to expand their application to hard tissue regeneration and restoration. In this minireview, the recent research trends in surface functionalization of orthopedic and dental implants with coating carbon nanomaterials are summarized. In addition, some seminal methodologies for physicomechanical and electrochemical coatings are discussed. In conclusion, it is shown that further development of surface functionalization with carbon nanomaterials may provide innovative results with clinical potential for improved osseointegration after implantation.

Surface Characteristics and Biological Evaluation of Si-DLC Coatings Fabricated Using Magnetron Sputtering Method on Ti6Al7Nb Substrate

Diamond-like carbon (DLC) coatings are well known as protective coatings for biomedical applications. Furthermore, the incorporation of different elements, such as silicon (Si), in the carbon matrix changes the bio-functionality of the DLC coatings. This has also been proven by the results obtained in this work. The Si-DLC coatings were deposited on the Ti6Al7Nb alloy, which is commonly used in clinical practice, using the magnetron sputtering method. According to the X-ray photoelectron spectroscopy (XPS) analysis, the content of silicon in the examined coatings varied from ~2 at.% up to ~22 at.%. Since the surface characteristics are key factors influencing the cell response, the results of the cells’ proliferation and viability assays (live/dead and XTT (colorimetric assays using tetrazolium salt)) were correlated with the surface properties. The surface free energy (SFE) measurements, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the polarity and wettability of the surfaces examined increase with increasing Si concentration, and therefore the adhesion and proliferation of cells was enhanced. The results obtained revealed that the biocompatibility of Si-doped DLC coatings, regardless of the Si content, remains at a very high level (the observed viability of endothelial cells is above 70%).

Enhanced osteoconductivity on electrically charged titanium implants treated by physicochemical surface modifications methods

Biomimetic design is a key tenet of orthopedic device technology, and in particular the development of responsive surfaces that promote ion exchange with interfacing tissues, facilitating the ionic events that occur naturally during bone repair, hold promise in orthopedic fixation strategies. Non-bioactive nanostructured titanium implants treated by shot-blasting and acid-etching (AE) induced higher bone implant contact (BIC=52% and 65%) compared to shot-blasted treated (SB) implants (BIC=46% and 47%) at weeks 4 and 8, respectively. However, bioactive charged implants produced by plasma (PL) or thermochemical (BIO) processes exhibited enhanced osteoconductivity through specific ionic surface-tissue exchange (PL, BIC= 69% and 77% and BIO, BIC= 85% and 87% at weeks 4 and 8 respectively). Furthermore, bioactive surfaces (PL and BIO) showed functional mechanical stability (resonance frequency analyses) as early as 4 weeks post implantation via increased total bone area (BAT=56% and 59%) ingrowth compared to SB (BAT=35%) and AE (BAT=35%) surfaces.

Comparing the effect of strontium-functionalized and fluoride-modified surfaces on early osseointegration

BACKGROUND

Studies have shown that medical devices comprising strontium contribute to bone healing and osseointegration. The aim of this study was to evaluate the in vivo performance of surface-functionalized implants (Ti-Sr-O) showing predictable release characteristics of strontium and compare it to performance a commercially available fluoride-modified surface.

METHODS

Ti-Sr-O functionalized, fluoride-modified,  Grade 4 titanium implants were inserted in the femoral condyle of adult male New Zealand white rabbits. Atomic absorption spectrometry (AAS) was utilized to monitor strontium blood serum levels. Two weeks after insertion, histomorphometric evaluation was performed with respect to bone-to-implant contact (BIC%) and bone formation (BF%) using defined regions of interest.

RESULTS

Mean values for BIC% showed a comparable degree of osseointegration for Ti-Sr-O and the fluoride-modified surface, while BF% revealed a significant difference in increased BF with Ti-Sr-O. AAS measurements did not indicate any influence of the Ti-Sr-O modified implants on the strontium blood serum concentrations.

CONCLUSIONS

Within the limitations of this study, it was shown that the Ti-Sr-O coating, with sustained release characteristics of strontium, enhanced bone apposition and, thus, could find practical applications, e.g., within the field of medical implantology.

Polycrystalline Diamond Coating of Additively Manufactured Titanium for Biomedical Applications

Additive manufacturing using selective laser melted titanium (SLM-Ti) is used to create bespoke items across many diverse fields such as medicine, defense, and aerospace. Despite great progress in orthopedic implant applications, such as for "just in time" implants, significant challenges remain with regards to material osseointegration and the susceptibility to bacterial colonization on the implant. Here, we show that polycrystalline diamond coatings on these titanium samples can enhance biological scaffold interaction improving medical implant applicability. The highly conformable coating exhibited excellent bonding to the substrate. Relative to uncoated SLM-Ti, the diamond coated samples showed enhanced mammalian cell growth, enriched apatite deposition, and reduced microbial S. aureus activity. These results open new opportunities for novel coatings on SLM-Ti devices in general and especially show promise for improved biomedical implants.

In vitro cytotoxicity assessment of nanodiamond particles and their osteogenic potential

Scaffolds functionalized with nanodiamond particles (nDP) hold great promise with regard to bone tissue formation in animal models. Degradation of the scaffolds over time may leave nDP within the tissues, raising concerns about possible long-term unwanted effects. Human SaOS-2 osteoblast-like cells and U937 monoblastoid cells were exposed to five different concentrations (0.002-2 mg/L) of nDP (size range: 2.36-4.42 nm) for 24 h. Cell viability was assessed by impedance-based methods. The differential expression of stress and toxicity-related genes was evaluated by polymerase chain reaction (PCR) super-array, while the expression of selected inflammatory and cell death markers was determined by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR). Furthermore, the expression of osteogenic genes by SaOS-2 cells, alkaline phosphatase activity and the extracellular calcium nodule deposition in response to nDP were determined in vitro. Cells responded differently to higher nDP concentrations (≥0.02 mg/L), that is, no loss of viability for SaOS-2 cells and significantly reduced viability for U937 cells. Gene expression showed significant upregulation of several cell death and inflammatory markers, among other toxicity reporter genes, indicating inflammatory and cytotoxic responses in U937 cells. Nanodiamond particles improved the osteogenicity of osteoblast-like cells with no evident cytotoxicity. However, concentration-dependent cytotoxic and inflammatory responses were seen in the U937 cells, negatively affecting osteogenicity in co-cultures. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1697-1707, 2018.

Nanomaterials in dentistry: a cornerstone or a black box?

Aim: The studies on tooth structure provided basis for nanotechnology-based dental treatment approaches known as nanodentistry which aims at detection and treatment of oral pathologies, such as dental caries and periodontal diseases, insufficiently being treated by conventional materials or drugs. This review aims at defining the role of nanodentistry in the medical area, its potential and hazards. Materials & methods: To validate these issues, current literature on nanomaterials for dental applications was critically reviewed. Results: Nanomaterials for teeth restoration, bone regeneration and oral implantology exhibit better mechanical properties and provide more efficient esthetic outcome. However, still little is known about influence of long-term function of such biomaterials in the living organism. Conclusion: As application of nanomaterials in industry and medical-related sciences is still expanding, more information is needed on how such nano-dental materials may interfere with oral cavity, GI tract and general health.

Biological evaluation of ultrananocrystalline and nanocrystalline diamond coatings

Nanostructured biomaterials have been investigated for achieving desirable tissue-material interactions in medical implants. Ultrananocrystalline diamond (UNCD) and nanocrystalline diamond (NCD) coatings are the two most studied classes of synthetic diamond coatings; these materials are grown using chemical vapor deposition and are classified based on their nanostructure, grain size, and sp³ content. UNCD and NCD are mechanically robust, chemically inert, biocompatible, and wear resistant, making them ideal implant coatings. UNCD and NCD have been recently investigated for ophthalmic, cardiovascular, dental, and orthopaedic device applications. The aim of this study was (a) to evaluate the in vitro biocompatibility of UNCD and NCD coatings and (b) to determine if variations in surface topography and sp³ content affect cellular response. Diamond coatings with various nanoscale topographies (grain sizes 5-400 nm) were deposited on silicon substrates using microwave plasma chemical vapor deposition. Scanning electron microscopy and atomic force microscopy revealed uniform coatings with different scales of surface topography; Raman spectroscopy confirmed the presence of carbon bonding typical of diamond coatings. Cell viability, proliferation, and morphology responses of human bone marrow-derived mesenchymal stem cells (hBMSCs) to UNCD and NCD surfaces were evaluated. The hBMSCs on UNCD and NCD coatings exhibited similar cell viability, proliferation, and morphology as those on the control material, tissue culture polystyrene. No significant differences in cellular response were observed on UNCD and NCD coatings with different nanoscale topographies. Our data shows that both UNCD and NCD coatings demonstrate in vitro biocompatibility irrespective of surface topography.

Effects of nanotopography on the in vitro hemocompatibility of nanocrystalline diamond coatings

Nanocrystalline diamond (NCD) coatings have been investigated for improved wear resistance and enhanced hemocompatibility of cardiovascular devices. The goal of this study was to evaluate the effects of NCD surface nanotopography on in vitro hemocompatibility. NCD coatings with small (NCD-S) and large (NCD-L) grain sizes were deposited using microwave plasma chemical vapor deposition and characterized using scanning electron microscopy, atomic force microscopy, contact angle testing, and Raman spectroscopy. NCD-S coatings exhibited average grain sizes of 50-80 nm (RMS 5.8 nm), while NCD-L coatings exhibited average grain sizes of 200-280 nm (RMS 23.1 nm). In vitro hemocompatibility testing using human blood included protein adsorption, hemolysis, nonactivated partial thromboplastin time, platelet adhesion, and platelet activation. Both NCD coatings demonstrated low protein adsorption, a nonhemolytic response, and minimal activation of the plasma coagulation cascade. Furthermore, the NCD coatings exhibited low thrombogenicity with minimal platelet adhesion and aggregation, and similar morphological changes to surface-bound platelets (i.e., activation) in comparison to the HDPE negative control material. For all assays, there were no significant differences in the blood-material interactions of NCD-S versus NCD-L. The two tested NCD coatings, regardless of nanotopography, had similar hemocompatibility profiles compared to the negative control material (HDPE) and should be further evaluated for use in blood-contacting medical devices. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 253-264, 2017.

Evaluating the osseointegration of nanostructured titanium implants in animal models: Current experimental methods and perspectives (Review)

The aim of this paper is to review the experimental methods currently being used to evaluate the osseointegration of nanostructured titanium implants using animal models. The material modifications are linked to the biocompatibility of various types of oral implants, such as laser-treated, acid-etched, plasma-coated, and sand-blasted surface modifications. The types of implants are reviewed according to their implantation site (endoosseous, subperiosteal, and transosseous implants). The animal species and target bones used in experimental implantology are carefully compared in terms of the ratio of compact to spongy bone. The surgical technique in animal experiments is briefly described, and all phases of the histological evaluation of osseointegration are described in detail, including harvesting tissue samples, processing undemineralized ground sections, and qualitative and quantitative histological assessment of the bone-implant interface. The results of histological staining methods used in implantology are illustrated and compared. A standardized and reproducible technique for stereological quantification of bone-implant contact is proposed and demonstrated. In conclusion, histological evaluation of the experimental osseointegration of dental implants requires careful selection of the experimental animals, bones, and implantation sites. It is also advisable to use larger animal models and older animals with a slower growth rate rather than small or growing experimental animals. Bones with a similar ratio of compact to spongy bone, such as the human maxilla and mandible, are preferred. A number of practical recommendations for the experimental procedures, harvesting of samples, tissue processing, and quantitative histological evaluations are provided.

Establishment of a new pull-out strength testing method to quantify early osseointegration-An experimental pilot study

OBJECTIVES

The animal study aims to evaluate a new experimental model for measuring sole the influence of the surface characteristics independent from implant macro-design on the level of osseointegration by registering the pull-out strength needed for removal of experimental devices with different surfaces from artificial defects.

MATERIAL AND METHODS

Seventy-two test bodies (36 with the FRIADENT(®) plus surface, 36 with the P15/HAp biofunctionalized surface) were inserted in six adult domestic pigs with artificial calvarial defects. The experimental devices were designed to fit in the defects leaving a gap between the test body and the local bone. After 21 days of healing, the animals were sacrificed and the test bodies were pulled out with a standardised reproducible pull-out device measuring the pull-out strength. The pull-out strength for both groups was compared.

RESULTS

Twenty-one days after insertion a mean force of 412 ± 142 N for the P15/HAp group and 183 ± 105 N for the FRIADENT(®) plus group was measured for the removal of the specimens from the calvarial bone. The difference between the groups was statistically significant (p < 0.0001).

CONCLUSION

The experimental set-up seems to be a suitable method when measuring the impact of implant surfaces on the early stage of osseointegration.

Analysis of implant-failure predictors in the posterior maxilla: a retrospective study of 1395 implants

The aim of this study was to analyze predictors for dental implant failure in the posterior maxilla. A database was created to include patients being treated with dental implants posterior to the maxillary cuspids. Independent variables thought to be predictive of potential implant failure included (1) sinus elevation, (2) implant length, (3) implant diameter, (4) indication, (5) implant region, (6) timepoint of implant placement, (7) one-vs. two-stage augmentation, and (8) healing mode. Cox regression analysis was used to evaluate the influence of predictors 1-3 on implant failure as dependent variable. The predictors 4-9 were analyzed strictly descriptively. The final database included 592 patients with 1395 implants. The overall 1- and 5-year implant survival rates were 94.8% and 88.6%, respectively. The survival rates for sinus elevation vs. placement into native bone were 94.4% and 95.4%, respectively (p = 0.33). The survival rates for the short (<10 mm), the middle (10-13 mm) and the long implants (>13 mm) were 100%, 89% and 76.8%, respectively (middle-vs. long implants p = 0.62). The implant survival rates for the small- (<3.6 mm), the middle- (3.6-4.5 mm) and the wide diameter implants (>4.5 mm) were 92.5%, 87.9% and 89.6%, respectively (p = 0.0425). None of the parameters evaluated were identified as predictor of implant failure in the posterior maxilla.

Carbon-based smart nanomaterials in biomedicine and neuroengineering

The search for advanced biomimetic materials that are capable of offering a scaffold for biological tissues during regeneration or of electrically connecting artificial devices with cellular structures to restore damaged brain functions is at the forefront of interdisciplinary research in materials science. Bioactive nanoparticles for drug delivery, substrates for nerve regeneration and active guidance, as well as supramolecular architectures mimicking the extracellular environment to reduce inflammatory responses in brain implants, are within reach thanks to the advancements in nanotechnology. In particular, carbon-based nanostructured materials, such as graphene, carbon nanotubes (CNTs) and nanodiamonds (NDs), have demonstrated to be highly promising materials for designing and fabricating nanoelectrodes and substrates for cell growth, by virtue of their peerless optical, electrical, thermal, and mechanical properties. In this review we discuss the state-of-the-art in the applications of nanomaterials in biological and biomedical fields, with a particular emphasis on neuroengineering.