Effects of a magnesium adhesive cement on bone stability and healing following a metatarsal osteotomy in horses

Research progress on biodegradable magnesium phosphate ceramics in orthopaedic applications

To overcome critical size bone defects, calcium phosphate (CaP)-based ceramics have been widely explored. The compositional similarity with bone matrix and degradability are the main reasons for their selection in orthopaedic biomaterials. However, the low solubility rate under in vivo conditions raises concerns about these CaP groups, particularly hydroxyapatite (HA) and tricalcium phosphate (TCP) ceramics. Therefore, reliable and suitable degradable ceramics for bone defect repair are always an important research direction for researchers. The magnesium phosphate (MgP) group of bioceramics has been studied for orthopaedic applications and is comparatively new compared to traditional CaP ceramics. The role of magnesium in different biochemical processes, such as DNA stabilization, bone density maintenance, regulating Ca and Na ion channels, and cell proliferation and differentiation enhancement, is a key parameter for the development of MgP bioceramics. This article aims to give a comprehensive review of MgP ceramics in bone tissue engineering. Here, we have highlighted several preparation techniques, the existence of porosity, and the impact of metal ion doping on MgP bioceramics. Finally, in vitro and in vivo responses of MgP bioceramics in bone formation are discussed.

Biological performance of a bioabsorbable magnesium-magnesium phosphate cement interbody fusion cage in a porcine lumbar interbody fusion model: a feasibility study

PURPOSE

The aim of the study was to evaluate the feasibility of a bioabsorbable cage consisting of magnesium and magnesium phosphate cement (MPC) in a porcine lumbar interbody fusion model.

METHODS

Twelve male Ba-Ma mini pigs underwent lumbar discectomy and fusion with an Mg-MPC cage or a PEEK cage at the L3/L4 and L4/L5 level. Computed tomography (CT) scans were made to evaluate the distractive property by comparing average disc space height (DSH) before and at 6, 12, and 24 weeks after the operation. After the lumbar spines were harvested at 6 or 24 weeks after the operation, micro-CT examination was conducted to analyze the fusion rate, and stiffness of motion segments was investigated through mechanical tests. A histological study was performed to evaluate the tissue type, inflammation, and osteolysis in the intervertebral space.

RESULTS

CT scans showed no significant difference between the two groups in average DSH at each time point. Micro-CT scans revealed an equal fusion rate in both groups (0% at 6 weeks, 83.3% at 24 weeks). Both groups showed time-dependent increases in stability, the Mg-MPC cages achieved an inferior stiffness at 6 weeks and a comparable stiffness at 24 weeks. Histologic evaluation showed the presence of newly formed bone in both groups. However, empty spaces were observed at the interface or around the Mg-MPC cages.

CONCLUSION

Compared with the PEEK cages, the Mg-MPC cages achieved comparable distraction, fusion rate, and spinal stability at 24 weeks after the operation. However, due to inferior stiffness at the early stage and fast degradation, further modification of material composition and design are necessary.

Improving bone defect healing using magnesium phosphate granules with tailored degradation characteristics

OBJECTIVES

Dental implant placement frequently requires preceding bone augmentation, for example, with hydroxyapatite (HA) or β-tricalcium phosphate (β-TCP) granules. However, HA is degraded very slowly in vivo and for β-TCP inconsistent degradation profiles from too rapid to rather slow are reported. To shorten the healing time before implant placement, rapidly resorbing synthetic materials are of great interest. In this study, we investigated the potential of magnesium phosphates in granular form as bone replacement materials.

METHODS

Spherical granules of four different materials were prepared via an emulsion process and investigated in trabecular bone defects in sheep: struvite (MgNH4PO4·6H2O), K-struvite (MgKPO4·6H2O), farringtonite (Mg3(PO4)2) and β-TCP.

RESULTS

All materials except K-struvite exhibited promising support of bone regeneration, biomechanical properties and degradation. Struvite and β-TCP granules degraded at a similar rate, with a relative granules area of 29% and 30% of the defect area 4 months after implantation, respectively, whereas 18% was found for farringtonite. Only the K-struvite granules degraded too rapidly, with a relative granules area of 2% remaining, resulting in initial fibrous tissue formation and intermediate impairment of biomechanical properties.

SIGNIFICANCE

We demonstrated that the magnesium phosphates struvite and farringtonite have a comparable or even improved degradation behavior in vivo compared to β-TCP. This emphasizes that magnesium phosphates may be a promising alternative to established calcium phosphate bone substitute materials.

NIR-responsive injectable magnesium phosphate bone cement loaded with icariin promotes osteogenesis

There were defects like limited osteogenesis and fast drug release in traditional magnesium phosphate bone cement (MPC). In this study, we loaded icariin in a mesoporous nano silica container modified by polydopamine and then added it and citric acid into MPC (IHP-CA MPCs). The results indicate that IHP-CA MPCs have a long curing time, almost neutral pH value, excellent injectability, and compressive strength. In vitro experiments have shown that IHP-CA MPCs have good biocompatibility and bone promoting ability. These improvements provide feasible solutions and references for the clinical application of MPCs as implants.

Bone adhesive materials: From bench to bedside

Biodegradable bone adhesives represent a highly sought-after type of biomaterial which would enable replacement of traditional metallic devices for fixation of bone. However, these biomaterials should fulfil an extremely large number of requirements. As a consequence, bone-adhesive biomaterials which meet all of these requirements are not yet commercially available. Therefore, this comprehensive review provides an extensive overview of the development of bone adhesives from a translational perspective. First, the definition, classification, and chemistry of various types of bone adhesives are highlighted to provide a detailed overview of this emerging class of biomaterials. In this review we particularly focused studies which describe the use of materials that are capable of gluing two pieces of bone together within a time frame of minutes to days. Second, this review critically reflects on i) the experimental conditions of commonly employed adhesion tests to assess bone adhesion and ii) the current state-of-the-art regarding their preclinical and clinical applicability.

Bioactive Hydroxyapatite-Magnesium Phosphate Coatings Deposited by MAPLE for Preventing Infection and Promoting Orthopedic Implants Osteointegration

In this study, we used the matrix-assisted pulsed laser evaporation (MAPLE) technique to obtain hydroxyapatite (Ca10(PO4)6(OH)2) and magnesium phosphate (Mg3(PO4)2) thin coatings containing bone morphogenetic protein (BMP4) for promoting implants osteointegration and further nebulized with the antibiotic ceftriaxone (CXF) to prevent peri-implant infections. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), infrared microscopy (IRM) and Fourier-transform infrared spectroscopy (FT-IR). Furthermore, the antimicrobial properties were evaluated on Staphylococcus aureus biofilms and the cytocompatibility on the MC3T3-E1 cell line. The obtained results proved the potential of the obtained coatings for bone implant applications, providing a significant antimicrobial and antibiofilm effect, especially in the first 48 h, and cytocompatibility in relation to murine osteoblast cells.

Characterization and Biomechanical Study of a Novel Magnesium Potassium Phosphate Cement

Magnesium potassium phosphate cement (MKPC) has attracted considerable attention as a bone regeneration material. However, there are only a few reports on its biomechanical properties. To evaluate the biomechanical properties of MKPC, we compared the mechanical parameters of pedicle screws enhanced with either MKPC or polymethyl methacrylate (PMMA) bone cement. The results show that the maximum pull-out force of the pedicle screws was 417.86 ± 55.57 and 444.43 ± 19.89 N after MKPC cement setting for 30 min and 12 h, respectively, which was better than that of the PMMA cement. In fatigue tests, the maximum pull-out force of the MKPC cement group was 435.20 ± 7.96 N, whereas that of the PMMA cement in the control group was 346.80 ± 7.66 N. Furthermore, the structural characterization analysis of the MKPC cement revealed that its microstructure after solidification was an irregular tightly packed crystal, which improved the mechanical strength of the cement. The maximum exothermic temperature of the MKPC reaction was 45.55 ± 1.35 °C, the coagulation time was 7.89 ± 0.37 min, and the compressive strength was 48.29 ± 4.76 MPa, all of which meet the requirements of clinical application. In addition, the MKPC cement did not significantly inhibit cell proliferation or increase apoptosis, thus indicating good biocompatibility. In summary, MKPC exhibited good biomechanical properties, high initial strength, good biocompatibility, and low exothermic reaction temperature, demonstrating an excellent application potential in the field of orthopedics.

Accelerated bone regeneration through rational design of magnesium phosphate cements

Results of several studies during past years suggested that magnesium phosphate cements (MPCs) not only show excellent biocompatibility and osteoconductivity, but they also provide improved regeneration capacity due to higher solubility compared to calcium phosphates. These findings also highlighted that chemical similarity of bone substitutes to the natural bone tissue is not a determinant factor in the success of regenerative strategies. The aim of this study was to further improve the degradation speed of MPCs for a fast bone ingrowth within a few months. We confirmed our hypothesis, that decreasing the powder-liquid ratio (PLR) of cement results in an increased content of highly soluble phases such as struvite (MgNH₄PO₄⋅6H₂O) as well as K-struvite (MgKPO₄⋅6H₂O). Promising compositions with a low PLR of 1 g ml^-1 were implanted in partially-loaded tibia defects in sheep. Both cements were partially degraded and replaced by bone tissue after 4 months. The degradation speed of the K-struvite cement was significantly higher compared to the struvite cement, initially resulting in the formation of a cell-rich resorption zone at the surface of some implants, as determined by histology. Overall, both MPCs investigated in this study seem to be promising as an alternative to the clinically well-established, but slowly degrading calcium phosphate cements, depending on defect size and desired degradation rate. Whereas the K-struvite cement might require further modification towards a slower resorption and reduced inflammatory response in vivo, the struvite cement appears promising for the treatment of bone defects due to its continuous degradation with simultaneous new bone formation. STATEMENT OF SIGNIFICANCE: Cold setting bone cements are used for the treatment of bone defects that exceed a critical size and cannot heal on their own. They are applied pasty into the bone defect and harden afterwards so that the shape adapts to the individual defect. Magnesium phosphates such as magnesium ammonium phosphate hexahydrate (struvite) belong to a new class of these cold setting bone cements. They degrade much faster than the clinically established calcium phosphates. In this study, a magnesium phosphate that has hardly been investigated so far was implanted into partially-loaded defects in sheeps: Potassium magnesium phosphate hexahydrate. This showed even faster resorption compared to the struvite cement: after 4 months, 63% of the cement was already degraded.

Elution properties of a resorbable magnesium phosphate cement

OBJECTIVE

This study tests the elution capabilities of a magnesium phosphate cement (MPC). Study objectives were to quantify the passive release of magnesium ions from MPC and to assess the effects of antibiotic-loaded MPC on bacterial growth and osteoblast viability.

METHODS

MPC constructs were created and incubated in fetal bovine serum (FBS). At 2, 4, and 17 weeks, a sample was collected for magnesium ion concentration analysis. Control and vancomycin-loaded (vanc) MPC beads were also created. Zone of inhibition was measured after incubating beads on Staphylococcus aureus agar plates for 24 h. Osteoblasts were seeded onto control and vanc beads and cultured for 9 days. Metabolic activity was measured via a resazurin assay. ANOVA with Tukey HSD post-hoc tests and t-tests were performed.

RESULTS

Magnesium ions were eluted at 2 and 4-week time points without significant difference, but demonstrated a significant spike at the 17-week time point. Zones of inhibition for the bacterial species was observed for Vanc-MPC beads, but not control beads. No cytotoxic effects on osteoblasts were noted.

CONCLUSION

MPC has potential to improve bone regeneration based on its ability to passively elute magnesium. Additionally, antibiotic-loaded MPC inhibits bacterial growth while avoiding osteoblast cytotoxicity.

Magnesium Phosphate Cement as Mineral Bone Adhesive

Mineral bone cements were actually not developed for their application as bone-bonding agents, but as bone void fillers. In particular, calcium phosphate cements (CPC) are considered to be unsuitable for that application, particularly under moist conditions. Here, we showed the ex vivo ability of different magnesium phosphate cements (MPC) to adhere on bovine cortical bone substrates. The cements were obtained from a mixture of farringtonite (Mg3(PO4)2) with different amounts of phytic acid (C6H18O24P6, inositol hexaphosphate, IP6), whereas cement setting occurred by a chelation reaction between Mg2+ ions and IP6. We were able to show that cements with 25% IP6 and a powder-to-liquid ratio (PLR) of 2.0 g/mL resulted in shear strengths of 0.81 ± 0.12 MPa on bone even after 7 d storage in aqueous conditions. The samples showed a mixed adhesive-cohesive failure with cement residues on the bone surface as indicated by scanning electron microscopy and energy-dispersive X-ray analysis. The presented material demonstrated appropriate bonding characteristics, which could enable a broadening of the mineral bone cements' application field to bone adhesives.

Development and Bone Regeneration Capacity of Premixed Magnesium Phosphate Cement Pastes

Magnesium phosphate cements (MPC) have been demonstrated to have a superior bone regeneration capacity due to their good solubility under in vivo conditions. While in the past only aqueous MPC pastes have been applied, the current study describes the fabrication and in vitro/in vivo testing of an oil-based calcium doped magnesium phosphate (CaMgP) cement paste. Premixed oil-based pastes with CaMgP chemistry combine the advantages of conventional MPC such as high mechanical strength and good resorbability with a prolonged shelf-life and an easier clinical handling. The pastes set in an aqueous environment and predominantly form struvite and achieve a compressive strength of ~8-10 MPa after setting. The implantation into a drill-hole defect at the distal femoral condyle of New Zealand white rabbits over a course of 6 and 12 weeks demonstrated good biocompatibility of the materials without the formation of soft connective tissue or any signs of inflammation. In contrast to a hydroxyapatite forming reference paste, the premixed CaMgP pastes showed subsequent degradation and bony regeneration. The CaMgP cement pastes presented herein are promising bone replacement materials with excellent material properties for an improved and facilitated clinical application.

Cell Therapies in Tendon, Ligament, and Musculoskeletal System Repair

In the last few decades, several techniques have been used to optimize tendon, ligament, and musculoskeletal healing. The evidence in favor of these techniques is still not proven, and level I studies are lacking. We performed an analysis of the therapeutic strategies and tissue engineering projects recently published in this field. Here, we try to give an insight into the current status of cell therapies and the latest techniques of bioengineering applied to the field of orthopedic surgery. The future areas for research in the management of musculoskeletal injuries are outlined. There are emerging technologies developing into substantial clinical treatment options that need to be critically evaluated. Mechanical stimulation of the constructs reproduces a more propitious environment for effective healing.

Magnesium-based bioceramics in orthopedic applications

Magnesium ions are directly involved in numerous biological mechanisms; for example, they play an important part in the regulation of ion channels, DNA stabilization, enzyme activation and stimulation of cell growth and proliferation. This alkaline earth metal has gained great popularity in orthopedic applications in recent years. Magnesium-based bioceramics include a large group of magnesium containing compounds such as oxides, phosphates and silicates, that are involved in orthopedic applications like bone cements, bone scaffolds or implant coatings. This article aims to give a comprehensive review on different magnesium-based bioceramics, e.g. magnesium phosphates (MgO-P₂O₅), calcium magnesium phosphates (CaO-MgO-P₂O₅), and magnesium glasses (SiO₂-MgO) with a strong focus on the chemistry and properties of magnesium phosphate containing cements as the main application form. In addition, the processing of magnesium phosphate minerals into macroporous scaffolds for tissue engineering applications by either using traditional porogens or by additive manufacturing approaches are reflected. Finally, the biological in vitro and in vivo properties of magnesium phosphates for bone regeneration are summarized, which show promising results regarding the application as bone replacement material, but still lack in terms of testing in large animal models, load-bearing application sites and clinical data.

STATEMENT OF SIGNIFICANCE

Though bone substitutes from calcium phosphates have been investigated for a long time, a new trend is visible in the biomaterials sector: magnesium based bioceramics from magnesium phosphates and silicates due to the special biological significance of magnesium ions in enzymatic activation, cell growth and proliferation, etc. In contrast to pure magnesium implants, such formulations do not release hydrogen during degradation. As with calcium based bioceramics, magnesium based bioceramics are used for the development of diverse applications such as cements, macroporous scaffolds and coatings. From this perspective, we present a systematic overview on diverse kinds of magnesium based bioceramics, their processing regimes for different clinical purposes and their behavior both in vitro and in vivo.

Biodegradable Magnesium Alloys Developed as Bone Repair Materials: A Review

Bone repair materials are rapidly becoming a hot topic in the field of biomedical materials due to being an important means of repairing human bony deficiencies and replacing hard tissue. Magnesium (Mg) alloys are potentially biocompatible, osteoconductive, and biodegradable metallic materials that can be used in bone repair due to their in situ degradation in the body, mechanical properties similar to those of bones, and ability to positively stimulate the formation of new bones. However, rapid degradation of these materials in physiological environments may lead to gas cavities, hemolysis, and osteolysis and thus, hinder their clinical orthopedic applications. This paper reviews recent work on the use of Mg alloy implants in bone repair. Research to date on alloy design, surface modification, and biological performance of Mg alloys is comprehensively summarized. Future challenges for and developments in biomedical Mg alloys for use in bone repair are also discussed.

Hydrolysis, setting properties and in vitro characterization of wollastonite/newberyite bone cement mixtures

Bone cements based on magnesium phosphates such as newberyite (N; MgHPO₄.3H₂O) have been shown as potential bone substitutes due to their biocompatibility, biodegradability and ability to support osteoblast differentiation and proliferation. Newberyite can hydrolyze to hydrated magnesium phosphate compounds (e.g. bobierite (Mg₃(PO₄)₂.8H₂O)) at alkaline conditions. In this study, 25 and 50 wt% of crystalline β -wollastonite (woll; CaSiO₃) was admixed to newberyite powder in order to both enhance the acid-base hydrolysis of newberyite and to produce a functional bone cement. The setting process of wollastonite/newberyite cement mixtures started with the hydrolysis of the wollastonite with further transformation of newberyite into bobierite and the formation of magnesium silicate phase. The results demonstrated that 25 wollastonite/newberyite and 50 wollastonite/newberyite cement pastes at optimal powder/liquid ratios had final setting times of ∼34 and 25 min and compressive strength values of 18 and 32 MPa after seven days setting, respectively. The tests of cytotoxicity of cement extracts on osteoblastic cells and contact cytotoxicity of the cement substrates showed different results. The osteoblasts cultured in cement extracts readily proliferated which confirmed the non-cytotoxic concentration of ions released from both cements. On the other hand, a strong cytotoxic character of 25 wollastonite/newberyite sample surface in contrary to high (∼80%) proliferation activity of cells on the 50 wollastonite/newberyite cement substrate was observed. The differences in cell proliferation activity was attributed to different surface topographies of cement substrates, where needle-like precipitated microcrystals of magnesium phosphate phase (in 25 wollastonite/newberyite cement) prevented the adhesion and proliferation of osteoblasts contrary to the smoother surface covered by extremely fine nanoparticles in the 50 wollastonite/newberyite cement.

A Bone Glue with Sustained Adhesion under Wet Conditions

Bone glues often suffer from low adhesion to bone under wet conditions. This study aims to improve wet adhesiveness of a bone glue based on a photocurable poly(ethylene glycol) dimethacrylate matrix through in situ interpenetrating network formation by addition of six-armed isocyanate functional star-shaped prepolymers (NCO-sP(EO-stat-PO)). Biodegradable ceramic fillers are added to adjust the paste workability. The 3-point bending strength of the bone glues is in the range of 3.5-5.5 MPa and not significantly affected by the addition of NCO-sP(EO-stat-PO). Storage in phosphate buffered saline (PBS) decreases the bending strength of all formulations to approximately 1 MPa but the adhesion to cortical bone increases from 0.15-0.2 to 0.3-0.5 MPa after adding 20-40 wt% NCO-sP(EO-stat-PO) to the matrix. Bone glues without the NCO-sP(EO-stat-PO) additive lose their adhesiveness to bone after aging in PBS for 7 days, whereas modified glues maintain a shear strength of 0.18-0.25 MPa demonstrating the efficacy of the approach. Scanning electron microscopy and energy-dispersive X-ray spectroscopy investigations of the fracture surfaces prove a high amount of residual adhesive on the bone surface indicating that adhesion to the bone under wet conditions is stronger than cohesion.

Magnesium Phosphate Cement Systems for Hard Tissue Applications: A Review

In the search for more ideal bone graft materials for clinical application, the investigation into ceramic bone cements or bone void filler is ongoing. Calcium phosphate-based materials have been widely explored and implemented for medical use in bone defect repair. Such materials are an excellent choice because the implant mimics the natural chemistry of mineralized bone matrix and in injectable cement form, can be implemented with relative ease. However, of the available calcium phosphate cements, none fully meet the ideal standard, displaying low strengths and acidic setting reactions or slow setting times, and are often very slow to resorb in vivo. The study of magnesium phosphates for bone cements is a relatively new field compared to traditional calcium phosphate bone cements. Although reports are more limited, preliminary studies have shown that magnesium phosphate cements (MPC) may be a strong alternative to calcium phosphates for certain applications. The goal of the present publication is to review the history and achievements of magnesium phosphate-based cements or bone void fillers to date, assess how these cements compare with calcium phosphate competitors and to analyze the future directions and outlook for the research, development, and clinical implementation of these cements.

Bone Graft Substitute Provides Metaphyseal Fixation for a Stemless Humeral Implant

Stemless humeral fixation has become an alternative to traditional total shoulder arthroplasty, but metaphyseal fixation may be compromised by the quality of the trabecular bone that diminishes with age and disease, and augmentation of the fixation may be desirable. The authors hypothesized that a bone graft substitute (BGS) could achieve initial fixation comparable to polymethylmethacrylate (PMMA) bone cement. Fifteen fresh-frozen human male humerii were randomly implanted using a stemless humeral prosthesis, and metaphyseal fixation was augmented with either high-viscosity PMMA bone cement (PMMA group) or a magnesium-based injectable BGS (OsteoCrete; Bone Solutions Inc, Dallas, Texas) (OC group). Both groups were compared with a control group with no augmentation. Initial stiffness, failure load, failure displacement, failure cycle, and total work were compared among groups. The PMMA and OC groups showed markedly higher failure loads, failure displacements, and failure cycles than the control group (P<.01). There were no statistically significant differences in initial stiffness, failure load, failure displacement, failure cycle, or total work between the PMMA and OC groups. The biomechanical properties of magnesium-based BGS fixation compared favorably with PMMA bone cement in the fixation of stemless humeral prostheses and may provide sufficient initial fixation for this clinical application. Future work will investigate the long-term remodeling characteristics and bone quality at the prosthetic-bone interface in an in vivo model to evaluate the clinical efficacy of this approach.

A simple method for the preparation of magnesium phosphate conversion coatings on a AZ31 magnesium alloy with improved corrosion resistance

A simple method has been proposed for the preparation of magnesium phosphate conversion coating on a magnesium alloy (AZ31) to achieve protection against fast degradation in an implant environment.

Antimicrobial properties and dentin bonding strength of magnesium phosphate cements

The main objective of this work was to assess the antimicrobial properties and the dentin-bonding strength of novel magnesium phosphate cements (MPC). Three formulations of MPC, consisting of magnesium oxide and a phosphate salt, NH4H2PO4, NaH2PO4 or a mixture of both, were evaluated. As a result of the setting reaction, MPC transformed into either struvite (MgNH4PO4·6H2O) when NH4H2PO4 was used or an amorphous magnesium sodium phosphate when NaH2PO4 was used. The MPC had appropriate setting times for hard tissue applications, high early compressive strengths and higher strength of bonding to dentin than commercial mineral trioxide aggregate cement. Bacteriological studies were performed with fresh and aged cements against three bacterial strains, Escherichia coli, Pseudomonas aeruginosa (planktonic and in biofilm) and Aggregatibacter actinomycetemcomitans. These bacteria have been associated with infected implants, as well as other frequent hard tissue related infections. Extracts of different compositions of MPC had bactericidal or bacteriostatic properties against the three bacterial strains tested. This was associated mainly with a synergistic effect between the high osmolarity and alkaline pH of the MPC. These intrinsic antimicrobial properties make MPC preferential candidates for applications in dentistry, such as root fillers, pulp capping agents and cavity liners.

Biocompatibility of magnesium phosphate minerals and their stability under physiological conditions

Magnesium phosphates such as newberyite (MgHPO(4)·3H(2)O) are formed in vivo and are known to be biodegradable and nontoxic after implantation. Indeed, magnesium apatites have been shown to support osteoblast differentiation and function, and bone formation can occur around metallic magnesium implants. However, very little is known regarding the precipitation and stability of magnesium phosphates in physiological environments. In order to address this, the aqueous formation of magnesium phosphate as a function of pH, temperature and ion concentration is reported. Physicochemical characterization of the precipitates was carried out; additionally, biocompatibility and gene expression of osteoblast differentiation markers for bone formation via an in vitro cell culture assay were determined. Precipitation conditions for newberyite, tribasic magnesium phosphate pentahydrate, holtedahlite, bobierrite and cattiite were determined. Under physiological conditions of pH, temperature and magnesium phosphate concentration, no precipitates were formed. However, at concentrations 10-100 times higher than physiological, magnesium phosphate precipitates of cattiite and newberyite were formed. These two minerals demonstrated biocompatibility with osteoblast cultures and induced osteoblast adhesion and differentiation. The pattern of expression of OCN and CollA1 genes in the presence of newberyite crystals was comparable to that of calcium phosphate bioceramics. In our experiments, we have shown that certain magnesium phosphate phases such as newberyite and cattiite are able to promote in vivo osteogenic activity in a similar way to calcium phosphates such as hydroxyapatite and brushite. This confirms the great potential of magnesium phosphate ceramics in the development of new biomaterials for bone regeneration.

Osteointegration of soft tissue grafts within the bone tunnels in anterior cruciate ligament reconstruction can be enhanced

Anterior cruciate ligament reconstruction with a soft tissue autograft (hamstring autograft) has grown in popularity in the last 10 years. However, the issues of a relatively long healing time and an inferior histological healing result in terms of Sharpey-like fibers connection in soft tissue grafts are still unsolved. To obtain a promising outcome in the long run, prompt osteointegration of the tendon graft within the bone tunnel is essential. In recent decades, numerous methods have been reported to enhance osteointegration of soft tissue graft in the bone tunnel. In this article, we review the current literature in this research area, mainly focusing on strategies applied to the local bone tunnel environment. Biological strategies such as stem cell and gene transfer technology, as well as the local application of specific growth factors have been reported to yield exciting results. The use of biological bone substitute and physical stimulation also obtained promising results. Artificially engineered tissue has promise as a solution to the problem of donor site morbidity. Despite these encouraging results, the current available evidence is still experimental. Further clinical studies in terms of randomized control trial in the future should be conducted to extrapolate these basic science study findings into clinical practice.

The effect of variable waveform low-intensity pulsed ultrasound in a fourth metacarpal osteotomy gap model in horses

The objective of this study was to evaluate the effects of variable waveform low-intensity ultrasound on the healing of a fracture gap of the fourth metacarpal bone in horses. A randomized, blinded, controlled trial was conducted in eight healthy adult horses. In each horse, a 1-cm osteotomy of the fourth metacarpal bone was created. One randomly selected metacarpal gap was treated daily with a 40-min session of ultrasound and the opposite gap was managed similarly with an inactive transducer. The fourth metacarpal bones were radiographed weekly. Fluorescent markers were administered at 14, 28, 56 and 70 d. At the completion of the study at day 84, the bones were harvested and evaluated with peripheral quantitative computed tomography (pQCT) and histology. There were no significant differences between treated and control bones for any of the radiographic, pQCT or histologic parameters evaluated. These findings suggested that low-intensity ultrasound did not affect bone formation in a fracture gap model in the horse.

Functional tissue engineering of ligament healing

Ligaments and tendons are dense connective tissues that are important in transmitting forces and facilitate joint articulation in the musculoskeletal system. Their injury frequency is high especially for those that are functional important, like the anterior cruciate ligament (ACL) and medial collateral ligament (MCL) of the knee as well as the glenohumeral ligaments and the rotator cuff tendons of the shoulder. Because the healing responses are different in these ligaments and tendons after injury, the consequences and treatments are tissue- and site-specific. In this review, we will elaborate on the injuries of the knee ligaments as well as using functional tissue engineering (FTE) approaches to improve their healing. Specifically, the ACL of knee has limited capability to heal, and results of non-surgical management of its midsubstance rupture have been poor. Consequently, surgical reconstruction of the ACL is regularly performed to gain knee stability. However, the long-term results are not satisfactory besides the numerous complications accompanied with the surgeries. With the rapid development of FTE, there is a renewed interest in revisiting ACL healing. Approaches such as using growth factors, stem cells and scaffolds have been widely investigated. In this article, the biology of normal and healing ligaments is first reviewed, followed by a discussion on the issues related to the treatment of ACL injuries. Afterwards, current promising FTE methods are presented for the treatment of ligament injuries, including the use of growth factors, gene delivery, and cell therapy with a particular emphasis on the use of ECM bioscaffolds. The challenging areas are listed in the future direction that suggests where collection of energy could be placed in order to restore the injured ligaments and tendons structurally and functionally.

Magnesium-based bone cement and bone void filler: preliminary experimental studies

Bone cement has great potential in craniofacial surgery in the repair of osseous defects secondary to surgery or trauma. This includes the use of bone cement as a bone void filler for full-thickness cranial defects and as augmentation of deficient bones. Ideally, this material should be easily available, biocompatible, resorbable, bone inductive, and have adhesive qualities to bone. Calcium-based bone cements have some of these qualities but have a higher than desirable failure rate. OsteoCrete, a new magnesium-based bone cement and bone void filler, was compared to Norian in critical-sized skull defects and cementing bone flaps in rabbits. Both materials were successful; however, OsteoCrete had a faster resorption and replacement by bone rate than Norian. Bone flap position and apparent stability were also superior with OsteoCrete. There were no adverse reactions to either cement. A magnesium-based bone cement presents with advantages when compared with a comparator calcium-based cement in craniofacial surgery.

SM, Necat H, H. GR. Use of a magnesium-based bone adhesive for flexor tendon-to-bone healing

PURPOSE

Our previous studies in a canine animal model demonstrated that the flexor tendon-to-bone insertion site has a poor capacity to heal. Magnesium-based adhesives have the potential to improve tendon-to-bone healing. Therefore, we hypothesized that magnesium-based bone adhesive (MBA) will improve the tendon-to-bone biomechanical properties initially and in the early period after repair.

METHODS

Flexor digitorum profundus tendons were injured and repaired into bone tunnels in the distal phalanges of dogs. The bone tunnels were either filled with MBA before completing the repair or left empty (control [CTL]). Histologic appearance, tensile properties, range of motion, and bone density were examined at time zero and 21 days after the repair.

RESULTS

There was no histologic evidence of acute inflammation. There appeared to be more mast cells in the MBA group than in the CTL group. Chronic inflammatory infiltrate and fibrosis was slightly higher in the MBA group compared with the CTL group. Tensile properties at time zero were significantly higher in the MBA group compared with the CTL group. However, tensile properties were significantly lower in the MBA group compared with the CTL group at 21 days. Range of motion and bone density were significantly lower in the MBA and CTL groups compared with normal (ie, uninjured) at 21 days; no differences were seen when comparing MBA with CTL.

CONCLUSIONS

We found that the initial biomechanical properties of flexor tendon-to-bone repairs can be improved with MBA. However, MBA use in vivo led to a decrease in the biomechanical properties of the repair. There was no effect of MBA on bone density or range of motion in the early period after repair. Our histologic analysis suggests that the poor healing in the MBA group may have been due to an allergic response or to increased chronic inflammation resulting from the foreign material.

Augmentation of tendon-to-bone healing with a magnesium-based bone adhesive

BACKGROUND

Healing of an anterior cruciate ligament graft in a bone tunnel occurs by formation of fibrous scar tissue, which is weaker than the normal fibrocartilaginous insertion.

HYPOTHESIS

We hypothesized that a magnesium-based bone adhesive would improve tendon-to-bone healing in a rabbit anterior cruciate ligament reconstruction model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-five New Zealand White rabbits underwent bilateral anterior cruciate ligament reconstructions with semitendinosus autografts. A total of 12.5 g of bone adhesive was placed in the intraosseous tunnel around the graft in one limb, while the tunnels in the contralateral limb received no implant. Sixteen animals each were sacrificed at 3 weeks and at 6 weeks (12 biomechanical testing/4 histology). Outcomes included semiquantitative histologic analyses for new cartilage formation and fibrous tissue formation in the tendon-bone interface, microcomputed tomography to quantify new bone formation along the bone tunnel, and biomechanical testing of load-to-failure and stiffness. Three animals were sacrificed at time 0 to confirm adequate tunnel fill with the bone adhesive on microcomputed tomography.

RESULTS

All specimens had adequate tunnel fill with the bone adhesive at time 0. Application of the bone adhesive resulted in more cartilage formation and less fibrous tissue formation at the tendon-bone interface at 6 weeks compared with controls (P < .05). There was significantly more bone formation in the tibia of the treated limbs at 6 weeks (P = .01). The load-to-failure was significantly higher in the treated group at 6 weeks (71.8 +/- 31.8 N vs 43.4 +/- 14.8 N; P = .04). There were no differences in stiffness at either time point, and there were no differences at 3 weeks in any outcome variable.

CONCLUSION

The magnesium-based bone adhesive improves tendon-to-bone healing based on histologic and biomechanical testing at 6 weeks in a rabbit model of anterior cruciate ligament reconstruction.

CLINICAL RELEVANCE

Further studies are needed to investigate the clinical potential of this bone adhesive to enhance healing and decrease recovery time in soft-tissue ligament reconstruction.

Osteogenic gene regulation and relative acceleration of healing by adenoviral-mediated transfer of human BMP-2 or -6 in equine osteotomy and ostectomy models

This study evaluated healing of equine metatarsal osteotomies and ostectomies in response to percutaneous injection of adenoviral (Ad) bone morphogenetic protein (BMP)-2, Ad-BMP-6, or beta-galactosidase protein vector control (Ad-LacZ) administered 14 days after surgery. Radiographic and quantitative computed tomographic assessment of bone formation indicated greater and earlier mineralized callus in both the osteotomies and ostectomies of the metatarsi injected with Ad-BMP-2 or Ad-BMP-6. Peak torque to failure and torsional stiffness were greater in osteotomies treated with Ad-BMP-2 than Ad-BMP-6, and both Ad-BMP-2- and Ad-BMP-6-treated osteotomies were greater than Ad-LacZ or untreated osteotomies. Gene expression of ostectomy mineralized callus 8 weeks after surgery indicated upregulation of genes related to osteogenesis compared to intact metatarsal bone. Expression of transforming growth factor beta-1, cathepsin H, and gelsolin-like capping protein were greater in Ad-BMP-2- and Ad-BMP-6-treated callus compared to Ad-LacZ-treated or untreated callus. Evidence of tissue biodistribution of adenovirus in distant organs was not identified by quantitative PCR, despite increased serum antiadenoviral vector antibody. This study demonstrated a greater relative potency of Ad-BMP-2 over Ad-BMP-6 in accelerating osteotomy healing when administered in this regimen, although both genes were effective at increasing bone at both osteotomy and ostectomy sites.