Effect of weight-bearing on bone-bonding behavior of strontium-containing hydroxyapatite bone cement

A Strontium-Modified Titanium Surface Produced by a New Method and Its Biocompatibility In Vitro

OBJECTIVE

To present a new and effective method of producing titanium surfaces modified with strontium and to investigate the surface characteristics and in vitro biocompatibility of titanium (Ti) surfaces modified with strontium (Sr) for bone implant applications.

MATERIALS AND METHODS

Sr-modified Ti surfaces were produced by sequential treatments with NaOH, strontium acetate, heat and water. The surface characteristics and the concentration of the Sr ions released from the samples were examined. Cell adhesion, morphology and growth were investigated using osteoblasts isolated from the calvaria of neonatal Sprague-Dawley rats. Expression of osteogenesis-related genes and proteins was examined to assess the effect of the Sr-modified Ti surfaces on osteoblasts.

RESULTS

The modified titanium surface had a mesh structure with significantly greater porosity, and approximately5.37±0.35at.% of Sr was incorporated into the surface. The hydrophilicity was enhanced by the incorporation of Sr ions and water treatment. The average amounts of Sr released from the Sr-modified plates subjected to water treatment were slight higher than the plates without water treatment. Sr promoted cellular adhesion, spreading and growth compared with untreated Ti surfaces. The Sr-modified Ti plates also promoted expression of osteogenesis-related genes,and expression of OPN and COL-І by osteoblasts. Ti plates heat treated at 700°C showed increased bioactivity in comparison with those treated at 600°C. Water treatment upregulated the expression of osteogenesis-related genes.

CONCLUSIONS

These results show that Sr-modification of Ti surfaces may improve bioactivity in vitro. Water treatment has enhanced the response of osteoblasts. The Sr-modified Ti heat-treated at 700°C exhibited better bioactivity compared with that heated at 600°C.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

Enhancing pedicle screw fixation in the aging spine with a novel bioactive bone cement: an in vitro biomechanical study

STUDY DESIGN

A paired biomechanical study of pedicle screws augmented with bone cement in a human cadaveric and osteoporotic lumbar spine model. OBJECTIVES.: To evaluate immediate strength and stiffness of pedicle screw fixation augmented with a novel bioactive bone cement in an osteoporotic spine model and compare it with polymethylmethacrylate (PMMA) cement.

SUMMARY OF BACKGROUND DATA

A novel bioactive bone cement, containing nanoscale particles of strontium and hydroxyapatite (Sr-HA), can promote new bone formation and osteointegration and provides a promising reinforcement to the osteoporotic spine. Its immediate mechanical performance in augmenting pedicle screw fixation has not been evaluated.

METHODS

Two pedicle screws augmented with Sr-HA and PMMA cement were applied to each of 10 isolated cadaveric L3 vertebrae. Each screw was subjected to a toggling test and screw kinematics were calculated. The pedicle screw was subjected to a pullout test until failure. Finally, the screw coverage with cement was measured on computed tomographic images.

RESULTS

Screw translations in the toggling test were consistently larger in the Sr-HA group than in the PMMA group (1.4 ± 1.2 mm vs. 1.0 ± 1.1 mm at 1000 cycles). The rotation center was located closer to the screw tip in the Sr-HA group (19% of screw length) than in the PMMA group (37%). The only kinematic difference between Sr-HA and PMMA cements was the screw rotation at 1000 cycles (1.5° ± 0.9° vs. 1.3° ± 0.6°; P = 0.0026). All motion parameters increased significantly with more loading cycles. The pullout force was higher in the PMMA group than the Sr-HA group (1.40 ± 0.63 kN vs. 0.93 ± 0.70 kN), and this difference was marginally significant (P = 0.051). Sr-HA cement covered more of the screw length than PMMA cement (79 ± 19% vs. 43 ± 19%) (P = 0.036).

CONCLUSION

This paired-design study identified some subtle but mostly nonsignificant differences in immediate biomechanical fixation of pedicle screws augmented with the Sr-HA cement compared with the PMMA cement.

The effect of strontium incorporation in hydroxyapatite on osteoblasts in vitro

The purpose of this study was to test the effects of a series of strontium-substituted HA (Sr-HA) ceramics (0, 1, 5, and 10 mol% Sr substitution) on osteoblasts, thereby demonstrating whether strontium incorporation with HA would favor osteoblast metabolism. Rat primary osteoblasts were cultured with culture media containing ions released from the Sr-HA ceramics as they dissolved. MTT test, alkaline phosphatase activity, osteoblast transcription factor gene (cbfa1) expression and Alizarin Red staining were conducted at different time-points. There is no significant difference in cell proliferation between groups. However, compared with HA group, Sr-HA groups presented significant enhancement with regard to ALP activity, cbfa1 mRNA expression, and mineralization nodules. Among Sr-HA groups, 5 and 10% groups showed much better performances in ALP activity, cbfa1 mRNA expression, and mineralization nodules than 1% group, however, no significant difference was found between 5 and 10% groups. This study has demonstrated that Sr incorporation in HA ceramic enhanced osteoblastic cell differentiation and mineralization. However, further detailed studies are needed to understand the mechanistic effects of this Sr incorporation on osteoblastic cells and the optimal percentage of calcium should be substituted with strontium in HA.

Osteoblast response and osseointegration of a Ti-6Al-4V alloy implant incorporating strontium

This study investigated the surface characteristics, in vitro and in vivo biocompatibility of Ti-6Al-4V alloy implants incorporating strontium ions (Sr), produced by hydrothermal treatment using a Sr-containing solution, for future biomedical applications. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, optical profilometry, contact angle and surface energy measurement and inductively coupled plasma-mass spectroscopy (ICP-MS). Human osteoblast-like cell (MG63) attachment, proliferation, alkaline phosphatase (ALP) activity, and quantitative analysis of osteoblastic gene expression on Sr-containing Ti-6Al-4V surfaces were compared with untreated Ti-6Al-4V surfaces. Fifty-six screw implants (28 control and 28 experimental) were placed in the tibiae and femoral condyles of seven New Zealand White rabbits. The osteoconductivity of Sr-containing Ti-6Al-4V implants was evaluated by removal torque testing and histomorphometric analysis after 4weeks implantation. Hydrothermal treatment produced a crystalline SrTiO(3) layer. ICP-MS analysis showed that Sr ions were released from treated surfaces into the solution. Significant increases in ALP activity (P=0.000), mRNA expressions of key osteoblast genes (osterix, bone sialoprotein, and osteocalcin), removal torque values (P<0.05) and bone-implant contact percentages (P<0.05) in both cortical and cancellous bone were observed for Sr-containing Ti-6Al-4V surfaces. The results indicate that the Sr-containing oxide layer produced by hydrothermal treatment may be effective in improving the osseointegration of Ti-6Al-4V alloy implants by enhancing differentiation of osteoblastic cells, removal torque forces and bone apposition in both cortical and cancellous bone.

Osteoconductivity of strontium-doped bioactive glass particles: a histomorphometric study in rats

There is accumulating evidence that strontium (Sr)-containing bioceramics have positive effects on bone tissue repair. The aims of the present study were to evaluate the osteoconductivity of Sr-doped bioactive glass (BG) particles implanted in rat tibia bone marrow, and characterize the neoformed bone tissue by SEM-energy-dispersive X-ray microanalysis. Melt-derived BGs were prepared from a base 45S5 BG. Sr-doped glass (45S5.6Sr) was prepared using 6 wt % SrO as a substitute for the CaO. Histological analysis using undecalcified sections showed that new lamellar bone had formed along the surface of both 45S5 and 45S5.6Sr BG particles within 4 weeks. To evaluate osteoconductivity, affinity indices were calculated. At 30 days after implantation, 45S5 and 45S5.6Sr BGs had almost identical affinity indices (88% +/- 7% and 87% +/- 9%; p > 0.05). Strontium was not detected in the neoformed bone tissue surrounding 45S5.6Sr BG particles. These results indicate that 45S5.6Sr BG particles are osteoconductive when implanted inside the intramedullary canal of rat tibiae, and no alterations in bone mineralization, in terms of Ca/P ratio, were observed in the neoformed bone tissue around 45S5.6Sr BG particles.

Calcium Orthophosphate Cements and Concretes

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are a bioactive and biodegradable grafting material in the form of a powder and a liquid. Both phases form after mixing a viscous paste that after being implanted, sets and hardens within the body as either a non-stoichiometric calcium deficient hydroxyapatite (CDHA) or brushite, sometimes blended with unreacted particles and other phases. As both CDHA and brushite are remarkably biocompartible and bioresorbable (therefore, in vivo they can be replaced with newly forming bone), calcium orthophosphate cements represent a good correction technique for non-weight-bearing bone fractures or defects and appear to be very promising materials for bone grafting applications. Besides, these cements possess an excellent osteoconductivity, molding capabilities and easy manipulation. Furthermore, reinforced cement formulations are available, which in a certain sense might be described as calcium orthophosphate concretes. The concepts established by calcium orthophosphate cement pioneers in the early 1980s were used as a platform to initiate a new generation of bone substitute materials for commercialization. Since then, advances have been made in the composition, performance and manufacturing; several beneficial formulations have already been introduced as a result. Many other compositions are in experimental stages. In this review, an insight into calcium orthophosphate cements and concretes, as excellent biomaterials suitable for both dental and bone grafting application, has been provided.