Polyether ether ketone implants achieve increased bone fusion when coated with nano-sized hydroxyapatite: a histomorphometric study in rabbit bone.

Polyether ether ketone (PEEK) possesses excellent mechanical properties similar to those of human bone and is considered the best alternative material other than titanium for orthopedic spine and trauma implants. However, the deficient osteogenic properties and the bioinertness of PEEK limit its fields of application. The aim of this study was to limit these drawbacks by coating the surface of PEEK with nano-scaled hydroxyapatite (HA) minerals. In the study, the biological response to PEEK, with and without HA coating, was investigated. Twenty-four screw-like and apically perforated implants in the rabbit femur were histologically evaluated at 3 weeks and 12 weeks after surgery. Twelve of the 24 implants were HA coated (test), and the remaining 12 served as uncoated PEEK controls. At 3 weeks and 12 weeks, the mean bone-implant contact was higher for test compared to control (P<0.05). The bone area inside the threads was comparable in the two groups, but the perforating hole showed more bone area for the HA-coated implants at both healing points (P<0.01). With these results, we conclude that nano-sized HA coating on PEEK implants significantly improved the osteogenic properties, and in a clinical situation this material composition may serve as an implant where a rapid bone fusion is essential.

Precipitation of Calcium Phosphates in the Presence of Collagen Type I on Four Different Bioactive Titanium Surfaces: an in Vitro Study.

OBJECTIVES: To compare the properties of calcium phosphate precipitation on four different bioactive surface preparations and one control surface in the simulated body fluid model with added collagen type I. MATERIAL AND METHODS: Blasted titanium discs were treated with four different surface modifications, alkali and heat, sodium fluoride, anodic oxidation and hydroxyapatite coating. The discs were divided into five groups where one group, the blasted, served as control. The discs were immersed in simulated body fluid and collagen for 24 h, 3 days, 1 week and 2 weeks and then analysed by optical interferometry, scanning electron microscopy/energy dispersive X-ray analysis and X-ray photoelectron spectroscopy. RESULTS: All surfaces show small precipitates after 3 days which with longer immersion times increase. After 2 weeks the surfaces were completely covered with precipitates, and Ca/P ratios were approximately 1.3, independently on surface preparation. The fluoridated discs showed significantly (P ≤ 0.05) higher degree of CaP after one week of immersion as compared to the other surface preparations. The collagen type I content increased with time, as reflected by increased nitrogen content. CONCLUSIONS: The results from this study indicate that a fluoridated titanium surface may favour precipitation of calcium phosphate in the presence of collagen type I, as compared to the other surface treatments of the present study.

Nanosized Hydroxyapatite Coating on PEEK Implants Enhances Early Bone Formation: A Histological and Three-Dimensional Investigation in Rabbit Bone.

Polyether ether ketone (PEEK) has been frequently used in spinal surgery with good clinical results. The material has a low elastic modulus and is radiolucent. However, in oral implantology PEEK has displayed inferior ability to osseointegrate compared to titanium materials. One idea to reinforce PEEK would be to coat it with hydroxyapatite (HA), a ceramic material of good biocompatibility. In the present study we analyzed HA-coated PEEK tibial implants via histology and radiography when following up at 3 and 12 weeks. Of the 48 implants, 24 were HA-coated PEEK screws (test) and another 24 implants served as uncoated PEEK controls. HA-coated PEEK implants were always osseointegrated. The total bone area (BA) was higher for test compared to control implants at 3 (p < 0.05) and 12 weeks (p < 0.05). Mean bone implant contact (BIC) percentage was significantly higher (p = 0.024) for the test compared to control implants at 3 weeks and higher without statistical significance at 12 weeks. The effect of HA-coating was concluded to be significant with respect to early bone formation, and HA-coated PEEK implants may represent a good material to serve as bone anchored clinical devices.

Biomechanical evaluation and surface characterization of a nano-modified surface on PEEK implants: a study in the rabbit tibia.

Polyether ether ketone (PEEK) is today frequently used as a biomaterial in different medical operations due to its excellent mechanical and chemical properties. However, the untreated surface of PEEK is bioinert and hydrophobic, and it does not osseointegrate in its pure form. The aim of this study was to evaluate a unique nano-modified surface of PEEK with respect to osseointegration. Forty-eight threaded, non-cutting PEEK implants were inserted bilaterally in the tibia of 24 rabbits. Half of the implants (n=24) were coated with nanocrystalline hydroxyapatite (test) and the remaining implants (n=24) were left uncoated (control). Half of the animals (n=12) were euthanized after 3 weeks of healing and the remaining (n=12) after 12 weeks. The implant retention was measured with a removal torque apparatus. Surface analysis was performed with interferometry, scanning electron microscopy, and X-ray photon spectroscopy to relate the removal torque to the applied surface. The test implants revealed a significantly higher retention after 3 weeks (P=0.05) and 12 weeks (P=0.028) compared to controls. The result of the present study proves that the addition of nanocrystalline hydroxyapatite coating to PEEK surfaces significantly increases its removal torque and biocompatibility.

Evaluation of bone healing on sandblasted and Acid etched implants coated with nanocrystalline hydroxyapatite: an in vivo study in rabbit femur.

This study aimed at investigating if a coating of hydroxyapatite nanocrystals would enhance bone healing over time in trabecular bone. Sandblasted and acid etched titanium implants with and without a submicron thick coat of hydroxyapatite nanocrystals (nano-HA) were implanted in rabbit femur with healing times of 2, 4, and 9 weeks. Removal torque analyses and histological evaluations were performed. The torque analysis did not show any significant differences between the implants at any healing time. The control implant showed a tendency of more newly formed bone after 4 weeks of healing and significantly higher bone area values after 9 weeks of healing. According to the results from this present study, both control and nano-HA surfaces were biocompatible and osteoconductive. A submicron thick coating of hydroxyapatite nanocrystals deposited onto blasted and acid etched screw shaped titanium implants did not enhance bone healing, as compared to blasted and etched control implants when placed in trabecular bone.

The biological response to three different nanostructures applied on smooth implant surfaces.

OBJECTIVE: To evaluate the biological effects of three calcium phosphate (CaP) coatings with nanostructures on relatively smooth implant surfaces. MATERIAL AND METHODS: Stable CaP nanoparticle suspensions of different particle sizes and structures were coated onto implants by immersion and subsequent heat treatment. An uncoated implant was used as the control. After topographical and chemical characterizations, implants were randomly inserted into rabbit tibiae for removal torque (RTQ) testing. To confirm the biological reaction, implants were placed in the bilateral femurs of three rabbits. RESULTS: The topographical characterization showed that each surface had different nanostructural characteristics and X-ray photon spectroscopy showed various CaP compositions. The control and test groups had different nanotopographies; however, the differences among the test groups were only significant for Surfaces B and C and the rest were insignificant. The RTQ tests showed significantly higher values in two test groups (Surface A and Surface C). Histologically, no adverse effects were seen in any group. Histomorphometrical evaluation showed comparable or better osseointegration along the implant threads in the test groups. CONCLUSION: The three different CaP coatings with nanostructures on the implant surfaces had enhancing effects on osseointegration. Along with the surface nanotopography, the CaP chemistry might have influenced the biological outcomes.

Laminin Coating Promotes Calcium Phosphate Precipitation on Titanium Discs in vitro.

OBJECTIVES: The objective of this study was to investigate the effect of a laminin coating on calcium phosphate precipitation on three potentially bioactive titanium surfaces in simulated body fluid. MATERIAL AND METHODS: Blasted titanium discs were prepared by alkali and heat treatment (AH), anodic oxidation (AO) or hydroxyapatite coating (HA) and subsequently coated with laminin. A laminin coated blasted surface (B) served as a positive control while a blasted non coated (B-) served as a negative control. Surface morphology was examined by Scanning Electron Microscopy (SEM). The analysis of the precipitated calcium and phosphorous was performed by Energy Dispersive X-ray Spectroscopy (EDX). RESULTS: The thickness of the laminin coating was estimated at 26 Å by ellipsometry. Interferometry revealed that the coating process did not affect any of the tested topographical parameters on µm level when comparing B to B-. After 2 weeks of incubation in SBF, the alkali-heat treated discs displayed the highest calcium phosphate deposition and the B group showed higher levels of calcium phosphate than the B- group. CONCLUSIONS: Our results suggest that laminin may have the potential to be used as a coating agent in order to enhance the osseoinductive performance of biomaterial surfaces, with the protein molecules possibly functioning as nucleation centres for apatite formation. Nevertheless, in vivo studies are required in order to clarify the longevity of the coating and its performance in the complex biological environment.

Early interactions between leukocytes and three different potentially bioactive titanium surface modifications.

The aim of the present study was to compare the early interactions between leukocytes and three different surface modifications, suggested as bioactive. Blasted titanium discs were modified by alkali and heat treatment, sodium fluoride treatment, or hydroxyapatite coating. A number of these discs were also immersed in simulated body fluid (SBF) for a week, a treatment which yielded high levels of calcium and phosphate on each surface type. The specimens were exposed for human venous blood for 32 minutes and the respiratory burst response was measured in terms of reactive oxygen species with a luminometer, and coverage of viable cells with a fluorescence microscope after staining steps. The topography, morphology, and chemistry of the surfaces were evaluated with optical interferometry and scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX). A high respiratory burst response was found for HA coated titanium in comparison with the other surface groups (p < 0.0005). The SBF immersion resulted in an increased respiratory burst response (p < 0.0005) and removed statistically significant differences between the surface groups. Thus, the results in the present study indicate that different titanium surface modifications influence the early inflammatory response differently, and that calcium phosphate compounds increase the inflammatory response.

In vitro Evaluation of Calcium Phosphate Precipitation on Possibly Bioactive Titanium Surfaces in the Presence of Laminin.

OBJECTIVES: The aim of the present study was to evaluate calcium phosphate precipitation and the amount of precipitated protein on three potentially bioactive surfaces when adding laminin in simulated body fluid. MATERIAL AND METHODS: BLASTED TITANIUM DISCS WERE PREPARED BY THREE DIFFERENT TECHNIQUES CLAIMED TO PROVIDE BIOACTIVITY: alkali and heat treatment (AH), anodic oxidation (AO) or hydroxyapatite coating (HA). A blasted surface incubated in laminin-containing simulated body fuid served as a positive control (B) while a blasted surface incubated in non laminin-containing simulated body fuid served as a negative control (B-). The immersion time was 1 hour, 24 hours, 72 hours and 1 week. Surface topography was investigated by interferometry and morphology by Scanning Electron Microscopy (SEM). Analysis of the precipitated calcium and phosphorous was performed by Energy Dispersive X-ray Spectroscopy (EDX) and the adsorbed laminin was quantified by iodine ((125)I) labeling. RESULTS: SEM demonstrated that all specimens except for the negative control were totally covered with calcium phosphate (CaP) after 1 week. EDX revealed that B- demonstrated lower sum of Ca and P levels compared to the other groups after 1 week. Iodine labeling demonstrated that laminin precipitated in a similar manner on the possibly bioactive surfaces as on the positive control surface. CONCLUSIONS: Our results indicate that laminin precipitates equally on all tested titanium surfaces and may function as a nucleation center thus locally elevating the calcium concentration. Nevertheless further studies are required to clarify the role of laminin in the interaction of biomaterials with the host bone tissue.

Nucleation and growth of calcium phosphates in the presence of fibrinogen on titanium implants with four potentially bioactive surface preparations. An in vitro study.

The aim of this study was to compare the nucleating and crystal growth behaviour of calcium phosphates on four types of potentially bioactive surfaces, using the simulated body fluid (SBF) model with added fibrinogen. Blasted titanium discs were modified by alkali and heat treatment, anodic oxidation, fluoride treatment, or hydroxyapatite coating. The discs were immersed in SBF with fibrinogen for periods of 3 days and 1, 2, 3 and 4 weeks. The topography, morphology, and chemistry of the surfaces were evaluated with optical interferometry, scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), and x-ray photoelectron spectroscopy (XPS), respectively. All surface modifications showed early calcium phosphate formation after 3 days, and were almost completely covered by calcium phosphates after 2 weeks. After 4 weeks, the Ca/P ratio was approximately 2.0 for all surface groups except the fluoride modified surface, which had a Ca/P ratio of 1.0-1.5. XPS measurements of the nitrogen concentration, which can be interpreted as an indirect measure of the protein content, reached a peak value after 3 days immersion and decreased thereafter. In conclusion, the results in the present study, when compared to earlier SBF studies without proteins, showed that fibrinogen stimulates calcium phosphates formation. Furthermore, no pronounced differences could be detected between blasted controls and the potentially bioactive specimens.

The effect of chemical and nanotopographical modifications on the early stages of osseointegration.

PURPOSE: To investigate the effect of chemically modified implants with similar microtopographies but different nanotopographies on early stages of osseointegration. MATERIALS AND METHODS: Forty screw-shaped implants were placed in 10 New Zealand white rabbits. The implant surface modifications investigated in the present study were (1) blasting with TiO2 and further (2) fluoride treatment or (3) modification with nano-hydroxyapatite. Surface evaluation included topographical analyses with interferometry, morphologic analyses with scanning electron microscopy, and chemical analyses with x-ray photoelectron spectroscopy. Bone response was investigated with the removal torque test, and histologic analyses were carried out after a healing period of 4 weeks. RESULTS: Surface roughness parameters showed a slight decrease of the average height deviation for the fluoride-treated compared to the blasted (control) and nano-hydroxyapatite implants. Scanning electron microscopic images at high magnification indicated the presence of nanostructures on the chemically modified implants. Chemical analyses revealed the presence of titanium, oxygen, carbon, and nitrogen in all implant groups. The blasted-fluoride group revealed fluoride, and the blasted-nano HA group calcium and phosphorus with simultaneous decrease of titanium and oxygen. Removal torque values revealed an increased retention for the chemically modified implants that exhibit specific nanotopography. The histologic analyses demonstrated immature bone formation in contact with the implant surface in all groups, according to the healing period of the experiment. CONCLUSION: Chemical modifications used in the present study were capable of producing a particular nanotopography, and together with the ions present at the implant surface, may explain the increased removal torque values after a healing period of 4 weeks.

Effect of hydroxyapatite and titania nanostructures on early in vivo bone response.

PURPOSE: Hydroxyapatite (HA) or titania nanostructures were applied on smooth titanium implant cylinders. The aim was to investigate whether nano-HA may result in enhanced osseointegration compared to nano-titania structures. MATERIALS AND METHODS: Surface topography evaluation included detailed characterization of nano-size structures present at the implant surface combined with surface roughness parameters at the micro- and nanometer level of resolution. Microstructures were removed from the surface to ensure that bone response observed was dependent only on the nanotopography and/or chemistry of the surface. Early in vivo histological analyses of the bone response (4 weeks) were investigated in a rabbit model. RESULTS: In the present study, nano-titania-coated implants showed an increased coverage area and feature density, forming a homogenous layer compared to nano-HA implants. Bone contact values of the nano-titania implants showed a tendency to have a higher percentage as compared to the nano-HA implants (p = .1). CONCLUSION: Thus, no evidence of enhanced bone formation to nano-HA-modified implants was observed compared to nano-titania-modified implants. The presence of specific nanostructures dependent on the surface modification exhibiting different size and distribution did modulate in vivo bone response.

Bone reaction to nano hydroxyapatite modified titanium implants placed in a gap-healing model.

Nanohydroxyapatite materials show similar chemistry to the bone apatite and depending on the underlying topography and the method of preparation, the nanohydroxyapatite may simulate the specific arrangement of the crystals in bone. Hydroxyapatite (HA) and other CaP materials have been indicated in cases in which the optimal surgical fit is not achievable during surgery, and the HA surface properties may enhance bone filling of the defect area. In this study, very smooth electropolished titanium implants were used as substrata for nano-HA surface modification and as control. One of each implant (control and nano HA) was placed in the rabbit tibia in a surgical site 0.7 mm wider than the implant diameter, resulting in a gap of 0.35 mm on each implant side. Implant stability was ensured by a fixating plate fastened with two side screws. Topographical evaluation performed with an optical interferometer revealed the absence of microstructures on both implants and higher resolution evaluation with AFM showed similar nanoroughness parameters. Surface pores detected on the AFM measurements had similar diameter, depth, and surface porosity (%). Histological evaluation demonstrated similar bone formation for the nano HA and electropolished implants after 4 weeks of healing. These results do not support that nano-HA chemistry and nanotopography will enhance bone formation when placed in a gap-healing model. The very smooth surface may have prevented optimal activity of the material and future studies may evaluate the synergic effects of the surface chemistry, micro, and nanotopography, establishing the optimal parameters for each of them.

Micellar induced regioselectivity in the two-step consecutive reaction of SO3(2-) with Br-(CH2CH2)n-Br (n=2-5).

High field (800 MHz) (1)H NMR was used to monitor the two-step consecutive reaction of excess SO(3)(2-) with symmetrical bifunctional alpha,omega-dibromoalkanes with butane (DBB), hexane (DBH), octane (DBO), and decane (DBD) chains in CTAB micelles at 25 degrees C. The first-order rate constant for the first substitution step for DBB and DBH is about 5 times faster than for the second, but the kinetics for DBO and DBD were not cleanly first-order. After 40 min, the solution contained about 80% of the intermediate bromoalkanesulfonate from DBB and DBH and the remainder is alkanedisulfonate and unreacted starting material. The same reactions were carried out in homogeneous MeOH/D(2)O solutions at 50 degrees C. The rate constants for all four alpha,omega-dibromoalkanes were first-order throughout the time course of the reaction and the same within +/-10%. However, because micellar solutions are organized on the nanoscale and bring together lipophilic and hydrophilic reactants into a small reaction volume at the micellar interface, they speed this substitution reaction considerably compared to reaction in MeOH/D(2)O. The CTAB micelles also induce a significant regioselectivity in product formation by speeding the first step of the consecutive reaction more than the second. The results are consistent with the bromoalkanesulfonate intermediates having a radial orientation within the micelles with the -CH(2)SO(3)(-) group in the interfacial region and the -CH(2)Br group directed into the micellar core such that the concentration of -CH(2)Br groups in the reactive zone, i.e., the micellar interface, is significantly reduced. These results provide the first example of self-assembled surfactant system altering the relative rates of the reaction steps of a consecutive reaction and, in doing so, enhancing monosubstitution of a symmetrically disubstituted species.

Use of self-assembled surfactant systems as media for a substitution reaction.

The reaction between 3-bromo-1-propanol and phenol and a series of phenols carrying substituents in 4-position was studied in micellar media and in microemulsions based on either a cationic or a nonionic surfactant. The reactivity and the yield were evaluated and compared to those obtained in a microhomogeneous medium, methanol-water. It was found that the micellar system based on the cationic surfactant dodecyltrimethylammonium bromide was particularly efficient as reaction medium in giving the highest yields. The high reactivity obtained in this system was attributed to formation of a pi-cation complex between the benzene ring of the phenol and the headgroup of the cationic surfactant, resulting in exposure of the phenolate oxygen to the aqueous subvolume where the substrate, 3-bromo-1-propanol, was situated. A highly distorted NMR spectrum of the cationic surfactant gave evidence for this hypothesis.

Oxidation of self-organized nonionic surfactants.

Nonionic surfactants containing a polyoxyethylene headgroup are known to slowly undergo oxidative degradation when exposed to air. The oxidation, which starts by abstraction of a hydrogen atom from a methylene group in alpha-position to an ether oxygen, is accelerated by metal ions. Silver ion mediated oxidation of a technical grade surfactant of this type, Brij 30, was investigated in two types of self-assembled systems, a water-in-oil microemulsion and a liquid crystalline phase. It was found that in both systems the longer homologues, i.e., the surfactant homologues that carry a longer polyoxyethylene chain, decompose faster than the shorter homologues. This trend was found to be more pronounced when the surfactant is present in a liquid crystal than in a microemulsion. The difference is explained in terms of differences in accessibility of the polyoxyethylene chains to the silver ions.