The effect of alkaline phosphatase coated onto titanium alloys on bone responses in rats

Implantation of heat treatment Ti6al4v alloys in femoral bone of Wistar rats

Two heat treatments were carried out at below (Ti6Al4V₈₀₀) and above (Ti6Al4V₁₀₅₀) the beta-phase transformation temperature (T_TRANSUS = 980 °C), to study the effect of microstructural changes on osseointegration. The alloys were implanted in the femurs of hind legs of Wistar rats for 15, 30, and 60 days. Histology of the femur sections obtained for the first 15 days showed inflammatory tissue surrounding the implants and tissue contraction, which prevented osseointegration in early stages. After 30 days, trabecular bone, reduction of inflammatory tissue around the implants, and osseointegration were observed in Ti6Al4V as received and Ti6Al4V₁₀₅₀ alloys, while osseointegration was detected for the three alloys after 60 days. These results were supported through morphometric studies based on the analysis of Bone Implant Contact (BIC), where there was a larger bone contact after 60 days for the Ti6Al4V₁₀₅₀ alloy; indicating that microstructural features of the Ti6Al4V alloys influence their osseointegration, with the lamellar microstructure (Ti6Al4V₁₀₅₀), being the most responsive. Graphical abstract.

Histological evaluation of titanium fiber mesh-coated implants in a rabbit femoral condyle model

OBJECTIVES

This study was aimed to comparatively evaluate new bone formation into the pores of a flexible titanium fiber mesh (TFM) applied on the surface of implant.

METHODS

Twenty-eight custom made cylindrical titanium implants (4 ×10 mm) with and without a layer of two different types of TFM (fiber diameter of 22 µm and 50 µm, volumetric porosity ~70%) were manufactured and installed bilaterally in the femoral condyles of 14 rabbits. The elastic modulus for these two TFM types was ~20 GPa and ~5 GPa respectively, whereas the solid titanium was ~110 GPa. The implants (Control, TFM-22, TFM-50) were retrieved after 14 weeks of healing and prepared for histological assessment. The percentage of the bone area (BA%), the bone-to-implant contact (BIC%) and amount were determined.

RESULTS

Newly formed bone into mesh porosity was observed for all three types of implants. Histomorphometric analyses revealed significantly higher (~2.5 fold) BA% values for TFM-22 implants (30.9 ± 9.5%) compared to Control implants (12.7 ± 6.0%), whereas BA% for TMF-50 did not significantly differ compared with Control implants. Furthermore, both TFM-22 and TFM-50 implants showed significantly higher BIC% values (64.9 ± 14.0%, ~2.5 fold; 47.1 ± 14.1%, ~2 fold) compared to Control (23.6 ± 17.4%). Finally, TFM-22 implants showed more and thicker trabeculae in the peri-implant region.

SIGNIFICANCE

This in vivo study demonstrated that implants with a flexible coating of TFM improve bone formation within the inter-fiber space and the peri-implant region.

Negative Pressure Irrigation Presents Mineralizing Potential in Dogs' Immature Teeth with Periapical Lesion

The objective of this in vivo study was to assess the effect of the root canal irrigation by negative and positive apical pressure on the expression of molecules that are an indicative of cell differentiation with mineralizing phenotype in teeth of dogs with incomplete rhizogenesis and induced periapical lesion. A total of 30 teeth (60 roots) were distributed into 3 groups (n=20): EndoVac®, Conventional and Control. After 90 days, the routine histotechnical procedures were performed and the sections were submitted to immunohistochemical technique for the staining of osteopontin (OPN), alkaline phosphatase (ALP) and the RUNX2 transcription factor in the apical and periapical regions of the roots. A semi-quantitative analysis of the positive immunostaining was performed and the intensity of the expression was classified in absent (0), mild (1), moderate (2), or intense (3). Scores data were statistically analyzed by the Kruskal-Wallis non-parametric test and Dunn post-test, and the significance level was set at 5%. RUNX2 immunostaining revealed that in the negative pressure group there was a significantly stronger (p<0.05) immunostaining in comparison to the control group. Regarding the OPN expression, it was not possible to detect a statistically significant difference between the groups (p>0.05). After analyzing ALP immunostaining, a statistically significant difference was observed between the groups (p<0.05), and the negative pressure group showed a markedly stronger mark immunostaining than the control group. The results of the present in vivo study allowed concluding that negative apical pressure irrigation presents mineralizing potential in immature teeth with apical periodontitis.

Histopathological, histoenzymological, immunohistochemical and immunofluorescence analysis of tissue response to sealing materials after furcation perforation

AIM

To evaluate in vivo tissue responses after sealing furcation perforations in dog's teeth with either Biodentine™, mineral trioxide aggregate (MTA) or gutta-percha, by means of histopathological, histoenzymological, immunohistochemical and immunofluorescence analysis.

METHODOLOGY

After root canal treatment, perforations were created in the central region of the pulp chamber floor using a round diamond bur and filled with one or other of the materials. The animals were euthanized after 120 days, and the teeth (n = 30) were processed for histopathological analysis of new mineralized tissue formation and collagen fibre reinsertion, immunohistochemical analysis of osteopontin (OPN) and alkaline phosphatase (ALP) and immunofluorescence analysis for bone morphogenetic protein (BMP-2), cementum attachment protein (CAP), bone sialoprotein (BSP), osteocalcin (OCN) and cementum protein1 (CEMP1). Histoenzymology was performed for TRAP activity and osteoclast count. Data were analysed statistically (α = 0.05) using chi-square and Kruskal-Wallis tests.

RESULTS

Gutta-percha did not induce mineralized tissue formation. MTA and Biodentine^TM formed mineralized tissue in 88% and 92% of specimens, respectively, with no significant difference (P > 0.05). Gutta-percha was associated with scattered collagen fibres parallel to the perforations. Groups treated with MTA or Biodentine^TM had partial fibre reinsertion perpendicular to the newly formed mineralized tissue. All materials induced OPN and ALP expression, weakest for gutta-percha and strongest for MTA (P < 0.05). Only MTA induced BMP-2, BSP, OCN, CAP and CEMP1 expression. Osteoclast counts were similar in all groups (P = 0.97).

CONCLUSIONS

Mineral trioxide aggregate and Biodentine^TM were biocompatible, with formation of mineralized tissue and partial reinsertion of collagen fibres. In addition, the participation of several molecules by which calcium silicate-based materials induce the formation of mineralized tissue were noted, with expression of ALP and OPN mineralization markers, without interference in the number of osteoclasts. Only MTA stimulated the expression of proteins associated with the formation of a cementum-like mineralized tissue.

Effect of surface alkali-based treatment of titanium implants on ability to promote in vitro mineralization and in vivo bone formation

This study investigated whether a novel alkali-based surface modification enhances in vitro mineralization as well as in vivo bone formation around titanium (Ti) implants in a femoral condyle model of 36 male Wister rats. All implant surfaces were grit-blasted and then received either acid-etching treatment, alkali-based treatment, or were left untreated (controls). Histological and histomorphometrical analyses were performed on retrieved specimens after 4 and 8weeks of healing to assess peri-implant bone formation. Results of implants surface characterisation showed notable differences in the topography and composition of alkali-treated surfaces, reflecting the formation of submicron-structured alkali-titanate layer. In the in vitro test, alkali-treated Ti surfaces showed the ability to stimulate mineralization upon soaking in simulated body fluid (SBF). In vivo histomorphometrical analyses showed similar values for bone area (BA%) and bone-to-implant contact (BIC%) for all experimental groups after both 4- and 8-week implantation periods. In conclusion, the surface topography and composition of the grit-blasted Ti implants was significantly modified using alkali-based treatment. With respect to the present in vivo model, the biological performance of alkali-treated Ti implants is comparable to the commercially available, grit-blasted, acid-etched Ti implants.

STATEMENT OF SIGNIFICANCE

Since success rate of dental implants might be challenged in bone of low density, an optimum implant surface characteristic is demanding. In this work, alkali treatment of Ti implants showed significant advantage of surface mineralization upon soaking in simulated body fluid. Using an in vivo rat model, Ti surfaces with either acid-etching treatment or alkali-based treatment evoked robust bone formation around Ti implants. Such information may be utilized for the advancement of biomaterials research for bone implants in future.

Osteophilic properties of bone implant surface modifications in a cassette model on a decorticated goat spinal transverse process

This study comparatively evaluated the osteophilic capacity of 17 different surface modifications (i.e. fourteen different chemical modifications via ceramic coatings and three different physical modifications via surface roughness) for titanium (Ti) surfaces. All surface modifications were subjected to physico-chemical analyses and immersion in simulated body fluid (SBF) for coating stability assessment. Subsequently, a bone conduction chamber cassette model on the goat transverse process was used for comparative in vivo analysis based on bone responses to these different surface modifications after twelve weeks. Histological and histomorphometrical analyses in terms of longitudinal bone-to-implant contact percentage (BIC%), relative bone area (BA%) were investigated within each individual channel and maximum bone height (BH). Characterization of the surface modifications showed significant differences in surface chemistry and surface roughness among the surface modifications. Generally, immersion of the coatings in SBF showed net uptake of calcium by thick coatings (>50μm; plasma-sprayed and biomimetic coatings) and no fluctuations in the SBF for thin coatings (<50μm). The histomorphometrical data set demonstrated that only plasma-sprayed CaP coatings performed superiorly regarding BIC%, BA% and BH compared to un-coated surfaces, irrespective of surface roughness of the latter. In conclusion, this study demonstrated that the deposition of plasma-sprayed CaP coating with high roughness significantly improves the osteophilic capacity of titanium surfaces in a chamber cassette model.

STATEMENT OF SIGNIFICANCE

For the bone implant market, a large number of surface modifications are available on different types of (dental and orthopedic) bone implants. As the implant surface provides the interface at which the biomaterial interacts with the surrounding (bone) tissue, it is of utmost importance to know what surface modification has optimal osteophilic properties. In contrast to numerous earlier studies on bone implant surface modifications with limited number of comparison surfaces, the manuscript by van Oirschot et al. describes the data of in vivo experiments using a large animal model that allows for direct and simultaneous comparison of a large variety of surface modifications, which included both commercially available and experimental surface modifications for bone implants. These data clearly show the superiority of plasma-sprayed hydroxyapatite coatings regarding bone-to-implant contact, bone amount, and bone height.

Composites of gellan gum hydrogel enzymatically mineralized with calcium-zinc phosphate for bone regeneration with antibacterial activity

Gellan gum hydrogels functionalized with alkaline phosphatase were enzymatically mineralized with phosphates in mineralization medium containing calcium (Ca) and zinc (Zn) to improve their suitability as biomaterials for bone regeneration. The aims of the study were to endow mineralized hydrogels with antibacterial activity by incorporation of Zn in the inorganic phase, and to investigate the effect of Zn incorporation on the amount and type of mineral formed, the compressive modulus of the mineralized hydrogels and on their ability to support adhesion and growth of MC3T3-E1 osteoblast-like cells. Mineralization medium contained glycerophosphate (0.05 m) and three different molar Ca:Zn ratios, 0.05:0, 0.04:0.01 and 0.025:0.025 (all mol/dm³ ), hereafter referred to as A, B and C, respectively. FTIR, SAED and TEM analysis revealed that incubation for 14 days caused the formation of predominantly amorphous mineral phases in sample groups A, B and C. The presence of Zn in sample groups B and C was associated with a drop in the amount of mineral formed and a smaller mineral deposit morphology, as observed by SEM. ICP-OES revealed that Zn was preferentially incorporated into mineral compared to Ca. Mechanical testing revealed a decrease in compressive modulus in sample group C. Sample groups B and C, but not A, showed antibacterial activity against biofilm-forming, methicillin-resistant Staphylococcus aureus. All sample groups supported cell growth. Zn incorporation increased the viable cell number. The highest values were seen on sample group C. In conclusion, the sample group containing the most Zn, i.e. group C, appears to be the most promising. Copyright © 2015 John Wiley & Sons, Ltd.

Generation of composites for bone tissue-engineering applications consisting of gellan gum hydrogels mineralized with calcium and magnesium phosphate phases by enzymatic means

Mineralization of hydrogels, desirable for bone regeneration applications, may be achieved enzymatically by incorporation of alkaline phosphatase (ALP). ALP-loaded gellan gum (GG) hydrogels were mineralized by incubation in mineralization media containing calcium and/or magnesium glycerophosphate (CaGP, MgGP). Mineralization media with CaGP:MgGP concentrations 0.1:0, 0.075:0.025, 0.05:0.05, 0.025:0.075 and 0:0.1 (all values mol/dm³ , denoted A, B, C, D and E, respectively) were compared. Mineral formation was confirmed by IR and Raman, SEM, ICP-OES, XRD, TEM, SAED, TGA and increases in the the mass fraction of the hydrogel not consisting of water. Ca was incorporated into mineral to a greater extent than Mg in samples mineralized in media A-D. Mg content and amorphicity of mineral formed increased in the order A < B < C < D. Mineral formed in media A and B was calcium-deficient hydroxyapatite (CDHA). Mineral formed in medium C was a combination of CDHA and an amorphous phase. Mineral formed in medium D was an amorphous phase. Mineral formed in medium E was a combination of crystalline and amorphous MgP. Young's moduli and storage moduli decreased in dependence of mineralization medium in the order A > B > C > D, but were significantly higher for samples mineralized in medium E. The attachment and vitality of osteoblastic MC3T3-E1 cells were higher on samples mineralized in media B-E (containing Mg) than in those mineralized in medium A (not containing Mg). All samples underwent degradation and supported the adhesion of RAW 264.7 monocytic cells, and samples mineralized in media A and B supported osteoclast-like cell formation. Copyright © 2014 John Wiley & Sons, Ltd.

A theranostic agent to enhance osteogenic and magnetic resonance imaging properties of calcium phosphate cements

With biomimetic biomaterials, like calcium phosphate cements (CPCs), non-invasive assessment of tissue regeneration is challenging. This study describes a theranostic agent (TA) to simultaneously enhance both imaging and osteogenic properties of such a bone substitute material. For this purpose, mesoporous silica beads were produced containing an iron oxide core to enhance bone magnetic resonance (MR) contrast. The same beads were functionalized with silane linkers to immobilize the osteoinductive protein BMP-2, and finally received a calcium phosphate coating, before being embedded in the CPC. Both in vitro and in vivo tests were performed. In vitro testing showed that the TA beads did not interfere with essential material properties like cement setting. Furthermore, bioactive BMP-2 could be efficiently released from the carrier-beads. In vivo testing in a femoral condyle defect rat model showed long-term MR contrast enhancement, as well as improved osteogenic capacity. Moreover, the TA was released during CPC degradation and was not incorporated into the newly formed bone. In conclusion, the described TA was shown to be suitable for longitudinal material degradation and bone healing studies.

Femtosecond laser-induced micropattern and Ca/P deposition on Ti implant surface and its acceleration on early osseointegration

Surface microstructure and chemical composition of the implant are very important for its osseointegration in vivo. In this paper, a hierarchical micropattern covered with calcium phosphate (Ca/P phase) was obtained on titanium (Ti) implant surface by femtosecond lasers (FSL) irradiation in hydroxyapatite suspension. The hierachical micropattern as well as Ca/P phase increased osteoblastic cell adhesion. Higher expression of osteogenic markers (osteocalcin, osteopontin, and runt related transcription factor-2) on the surface treated by FSL of 2.55 J/cm(2) indicated the favorable effect of laser treatment on cell differentiation. In vivo studies were carried out to evaluate the effect of laser treatment and Ca/P deposition on the osseointegration. It showed that the binding capacity between bone and FSL-treated Ti implants was obviously stronger than that between bone and polished or sand blasting and acid etching (SLA) Ti implants. Bone trabecula surrounded the FSL-treated implants without fibrous tissue after 8-week implantation. Also, higher bone mineral density was seen surrounding the FSL-treated implants. Our in vitro and in vivo studies demonstrated that the FSL induced micropattern and Ca/P phase had positive effects on the acceleration of early osseointegration of Ti implants with bone tissue.

Alginate-hydroxypropylcellulose hydrogel microbeads for alkaline phosphatase encapsulation

There is a growing interest in using proteins as therapeutics agents. Unfortunately, they suffer from limited stability and bioavailability. We aimed to develop a new delivery system for proteins. ALP, a model protein, was successfully encapsulated in the physically cross-linked sodium alginate/hydroxypropylcellulose (ALG-HPC) hydrogel microparticles. The obtained objects had regular, spherical shape and a diameter of ∼4 µm, as confirmed by optical microscopy and SEM analysis. The properties of the obtained microbeads could be controlled by temperature and additional coating or crosslinking procedures. The slow, sustained release of ALP in its active form with no initial burst effect was observed for chitosan-coated microspheres at pH = 7.4 and 37 °C. Activity of ALP released from ALG/HPC microspheres was confirmed by the occurance of effectively induced mineralization. SEM and AFM images revealed formation of the interpenetrated three-dimensional network of mineral, originating from the microbeads' surfaces. FTIR and XRD analyses confirmed formation of hydroxyapatite.

Dual contrast agent for computed tomography and magnetic resonance hard tissue imaging

Calcium phosphate cements (CPCs) are commonly used bone substitute materials, which closely resemble the composition of the mineral phase of bone. However, this high similarity to natural bone also results in difficult discrimination from the bone tissue by common imaging modalities, that is, plain X-ray radiography and three-dimensional computed tomography (CT). In addition, new imaging techniques introduced for bone tissue visualization, like magnetic resonance imaging (MRI), face a similar problem. Even at high MRI resolution, the lack of contrast between CPCs and surrounding bone is evident. Therefore, this study aimed to evaluate the feasibility of a dual contrast agent, traceable with both CT and MRI as enhancers of CPC/bone tissue contrast. Our formulation is based on the use of silica beads as vectors, which encapsulate and carry contrast-enhancing nanoparticles, in our case, colloidal Gold and Superparamagnetic Iron oxide particles (SPIO). The bead suspension was incorporated within a calcium phosphate powder. The resultant cements were then tested both in vitro and in vivo in a femoral condyle defect model in rats. Results showed that the mechanical properties of the cement were not significantly affected by the inclusion of the beads. Both in vitro and in vivo data proved the homogeneous incorporation of the contrast within the cement and its visual localization, characterized by a short-term CT contrast enhancement and a long-term MR effect recognizable by the characteristic blooming shape. Finally, no signs of adverse tissue reactions were noticed in vivo. In conclusion, this study proved the feasibility of a multimodal contrast agent as an inert and biocompatible enhancer of CaP cement versus bone tissue contrast.

Enzymatic mineralization of hydrogels for bone tissue engineering by incorporation of alkaline phosphatase

Alkaline phosphatase (ALP), an enzyme involved in mineralization of bone, is incorporated into three hydrogel biomaterials to induce their mineralization with calcium phosphate (CaP). These are collagen type I, a mussel-protein-inspired adhesive consisting of PEG substituted with catechol groups, cPEG, and the PEG/fumaric acid copolymer OPF. After incubation in Ca-GP solution, FTIR, EDS, SEM, XRD, SAED, ICP-OES, and von Kossa staining confirm CaP formation. The amount of mineral formed decreases in the order cPEG > collagen > OPF. The mineral:polymer ratio decreases in the order collagen > cPEG > OPF. Mineralization increases Young's modulus, most profoundly for cPEG. Such enzymatically mineralized hydrogel/CaP composites may find application as bone regeneration materials.

Biological response to titanium implants coated with nanocrystals calcium phosphate or type 1 collagen in a dog model

OBJECTIVE

The current study aimed to evaluate the osteogenic potential of electrosprayed organic and non-organic surface coatings in a gap-implant model over 4 and 12 weeks of implantation into the dog mandible.

MATERIAL AND METHODS

Sixteen Beagle dogs received experimental titanium implants in the mandible 3 months after removal of left premolars (P2, P3 and P4). Three types of implants were installed in each animal: non-coated implant, nano-CaP coated implant and implant with type 1 collagen coating. Both micro-CT and histomorphometry were used to evaluate peri-implant bone response after implantation periods of 4 and 12 weeks. The bone area percentage was assessed histomorphometrically in three different zones (inner: 0-300 μm; middle: 300-600 μm; and outer: 600-1000 μm) around the implant surface. Bone-bridging of the gap was also calculated for each sample.

RESULTS

Four weeks after implantation, nano-CaP and collagen-coated implants showed significantly higher bone volume (BV) in the inner zone compared with non-coated implants (P < 0.05 and P < 0.01). After 12 weeks, histomorphometric analysis showed comparable amounts of BV between all experimental groups. Also, no significant difference was found in the BV, as measured using micro-CT, between the implant groups. Absolute bone ingrowth measurements were highest for collagen-coated implants, but these differences were not significant.

CONCLUSION

The obtained data failed to provide a consistent favourable effect on bone formation of the collagen coating over 3 months of implantation. It is concluded that the source of the collagen as well as the limited osseous environment overshadowed a possible effect of the applied implant surface modifications. Similarly, the tested nano-apatite surface coating did not improve peri-implant bone ingrowth into a gap-implant model.

In vivo bone response and mechanical evaluation of electrosprayed CaP nanoparticle coatings using the iliac crest of goats as an implantation model

Recent trends in clinical implantology include the use of endosseous dental implant surfaces embellished with nano-sized modifications. The current study was initiated to evaluate the mechanical properties, as well as the potential beneficial effects, of electrosprayed CaP nanoparticle-coated (nano-CaP) implants on the in vivo osteogenic response, compared with grit-blasted, acid-etched (GAE) implant surfaces as controls. For this purpose nano-CaP coatings were deposited on cylindrical screw-type (St) implants and implanted bilaterally into the iliac crest of goats for 6weeks. In addition to histological and histomorphometrical analyses, insertion torque and removal torque values were measured on implant placement and retrieval, respectively. The present study showed similar insertion and removal torque values for nano-CaP-coated and GAE control implants, with no statistically significant increase in torque value during the implant period for either group. With regard to bone-implant contact and peri-implant bone volume, no significant differences were found between nano-CaP-coated and GAE implants after 6weeks implantation. In conclusion, this study has demonstrated that in situations in which implants are placed in a non-compromised situation using a standard press fit implantation strategy the performance of electrosprayed nano-CaP coatings is comparable with GAE implants, both with respect to implant fixation and bone healing response.