Primary cancellous bone formation with BMP and micro-chambered beads: experimental study on sheep

Bone augmentation by replica-based bone formation

OBJECTIVE

The sources of iliac crest bone grafts are limited. Alternatives are evaluated due to the progress in biomaterial sciences. Synthetical hydroxyapatite (HA), ß-tricalcium phosphate (ß-TCP) or biphasic compounds, or even a mélange of HA and ß-TCP will replace bovine ceramics. The goal is maintenance of replica-based-bone formation (RBBF) for bone augmentation.

METHODS

2 female and 2 male patients between 41 and 73 years with 5 sinus elevations were evaluated. Sinus elevations with lateral fenestration, trapezoidal-muco-periosteal flaps and filling with micro-chambered beads (1.5 mm) was performed. A porcine-collagenous membrane and the refixated flap covered the defect. A biopsy program over 20 months was confirm confirm the maintenance of the newly formed bone.

RESULTS

A fast bone formation was pronounced. The biopsies revealed mature lamellar bone and full osseointegration of the ß-TCP implant. The biopsy after 20 months showed compact bone with osseointegration of minor rests of the ceramic implant. The defect revealed a mature bone stock already after 5 weeks.

SIGNIFICANCE

The introduction of the replica-based-bone formation (RBBF) around micro-chambered beads will change the paradigm of bone augmentation. The next step of the ongoing study has to redefine the interval for implant insertion. The clinical approach confirms the breakthrough to primary mature lamellar bone formation and will permit reduction of placement time for a dental implant.

Bone Morphogenetic Protein-7 Enhances Degradation of Osteoinductive Bioceramic Implants in an Ectopic Model

BACKGROUND

The aim of the present study was to evaluate the degradation pattern of highly porous bioceramics as well as the bone formation in presence of bone morphogenetic protein 7 (BMP-7) in an ectopic site.

METHODS

Novel calcium phosphate ceramic cylinders sintered at 1,300°C with a total porosity of 92-94 vol%, 45 pores per inch, and sized 15 mm (Ø) × 5 mm were grafted on the musculus latissimus dorsi bilaterally in 10 Göttingen minipigs: group I (n = 5): hydroxyapatite (HA) versus biphasic calcium phosphate (BCP), a mixture of HA and tricalcium phosphate (TCP) in a ratio of 60/40 wt%; group II (n = 5): TCP versus BCP. A test side was supplied in situ with 250 μg BMP-7. Fluorochrome bone labeling and computed tomography were performed in vivo. Specimens were evaluated 14 weeks after surgery by environmental scanning electron microscopy, fluorescence microscopy, tartrate-resistant acid phosphatase, and pentachrome staining.

RESULTS

Bone formation was enhanced in the presence of BMP-7 in all ceramics (P = 0.001). Small spots of newly formed bone were observed in all implants in the absence of BMP-7. Degradation of HA and BCP was enhanced in the presence of BMP-7 (P = 0.001). In those ceramics, osteoclasts were observed. TCP ceramics were almost completely degraded independently of the effect of BMP-7 after 14 weeks (P = 0.76), osteoclasts were not observed.

CONCLUSIONS

BMP-7 enhanced bone formation and degradation of HA and BCP ceramics via osteoclast resorption. TCP degraded via dissolution. All ceramics were osteoinductive. Novel degradable HA and BCP ceramics in the presence of BMP-7 are promising bone substitutes in the growing individual.

Gene delivery nanocarriers of bioactive glass with unique potential to load BMP2 plasmid DNA and to internalize into mesenchymal stem cells for osteogenesis and bone regeneration

The recent development of bioactive glasses with nanoscale morphologies has spurred their specific applications in bone regeneration, for example as drug and gene delivery carriers. Bone engineering with stem cells genetically modified with this unique class of nanocarriers thus holds great promise in this avenue. Here we report the potential of the bioactive glass nanoparticle (BGN) system for the gene delivery of mesenchymal stem cells (MSCs) targeting bone. The composition of 15% Ca-added silica, proven to be bone-bioactive, was formulated into surface aminated mesoporous nanospheres with enlarged pore sizes, to effectively load and deliver bone morphogenetic protein-2 (BMP2) plasmid DNA. The enlarged mesopores were highly effective in loading BMP2-pDNA with an efficiency as high as 3.5 wt% (pDNA w.r.t. BGN), a level more than twice than for small-sized mesopores. The BGN nanocarriers released the genetic molecules in a highly sustained manner (for as long as 2 weeks). The BMP2-pDNA/BGN complexes were effectively internalized to rat MSCs with a cell uptake level of ∼73%, and the majority of cells were transfected to express the BMP2 protein. Subsequent osteogenesis of the transfected MSCs was demonstrated by the expression of bone-related genes, including bone sialoprotein, osteopontin, and osteocalcin. The MSCs transfected with BMP2-pDNA/BGN were locally delivered inside a collagen gel to the target calvarium defects. The results showed significantly improved bone regeneration, as evidenced by the micro-computed tomographic, histomorphometric and immunohistochemical analyses. This study supports the excellent capacity of the BGN system as a pDNA-delivery nanocarrier in MSCs, and the engineered system, BMP2-pDNA/BGN with MSCs, may be considered a new promising candidate to advance the therapeutic potential of stem cells through genetic modification, targeting bone defects and diseases.

[Primary cancellous bone formation around micro-chambered beads]

OBJECTIVES

The question has been raised whether benign bone defects in patients can be treated with bone forming osteoconductive ceramics achieving primarily a cancellous bone scaffold, which is under load from the beginning.

MATERIAL AND METHODS

Ten reconstructions were performed in 9patients (6women and 3male), with a mean age of 49 (25-65)years, suffering a high variety of epi- and metaphyseal defects, four tibial fractures, two calcaneal fractures, one pathological phalangeal fracture, one chondroma of the distal femur and two open-wedge osteotomies were filled with micro-chambered ceramic beads of 4 and 6mm in diameter. The mean follow up was 22 (7- 8)months. X-rays and CT-scans formed the basis for the evaluation of the reconstruction of the cancellous bone scaffolds.

RESULTS

All cancellous structures were rebuilt, if completely filled with bone-forming elements. If the filling was incomplete, no physiological cancellous bone scaffold resulted. The β-TCP micro-chambered beads were completely reabsorbed or sandwich-like incorporated at the time of evaluation. The HA micro-chambered beads revealed a contrast enhancement and were integrated in the osseous construction of the bone scaffold.

CONCLUSION

Primary cancellous bone formation can be achieved with osteoconductive ceramic micro-chambered beads and can be combined with any osteosynthesis for stable fixation.

ε-Caprolactone in micro-chambered ceramic beads--a new carrier for gentamicin

PURPOSE

The purpose of this preliminary and descriptive study was to evaluate a biodegradable drug delivery system in combination with an innovative ceramic implant.

METHODS

The delivery of gentamicin of standardized samples was measured in the laboratory using ultra-high-performance liquid chromatography. Biocompatibility and biodegradation of the materials was investigated in an animal experiment in sheep up to 14 months. As carrier ε-caprolactone, 1:1 mixed with gentamicin, intruded into micro-chambered β-tricalcium-phosphate beads (MCB®) was studied.

RESULTS AND DISCUSSION

Gentamicin was released in calculable concentrations during the first 30 days. The release from ε-caprolactone was higher than that from polymethylmethacrylate and more predictable. The caprolactone carrier was reabsorbed by osteoclasts.

Long-term controlled release of 125I-tagged BMP-2 by mesoporous bioactive glass with ordered nanopores

The aim of this study was to investigate the ability of mesoporous bioactive glass with ordered nanopores (80S MBG) to adsorb and provide the delayed release of ¹²⁵I-tagged bone morphogenetic protein-2 (BMP-2). A 50 mg piece of 80S MBG was produced, which comprised SiO₂, CaO and P₂O₅ in a component molar ratio of 80:15:5. Each MBG piece adsorbed 30 μg ¹²⁵I-BMP-2. Persistent radioactivity in the MBG was periodically measured in simulated body fluid. The total amount of BMP-2 released and the mean amount released per day were calculated. A delayed release curve of BMP-2 was constructed. SPSS 15.0 software was used to perform a statistical analysis. The amount of BMP-2 released in the first two days was one-quarter of the total load. A line equation, y = 490.55×^1/2 + 7268.82, was obtained from the square root of protein release doses value at 3–94 days. The total amount of BMP-2 released over 94 days was 11.894 μg, which was ~39.6% of the total load. The half-life of the release time was 248 days. From the second week, the rate of BMP release had stabilized to a mean of 37.42±18.67 ng/day and the difference of the mean amount released per day had no statistical significance (P>0.05). High adsorption and delayed release effects of BMP-2 were observed in 80S MBG. The delayed release conforms to the Higuchi equation, which indicates possible applications in promoting bone healing.