Bone induction by demineralized bone particles: long-term observations of the implant-connective tissue interface

In vivo studies on osteoinduction: A systematic review on animal models, implant site, and type and postimplantation investigation

Musculoskeletal diseases involving loss of tissue usually require management with bone grafts, among which autografts are still the gold standard. To overcome autograft disadvantages, the development of new scaffolds is constantly increasing, as well as the number of in vivo studies evaluating their osteoinductivity in ectopic sites. The aim of the present systematic review is to evaluate the last 10 years of osteoinduction in vivo studies. The review is focused on: (a) which type of animal model is most suitable for osteoinduction evaluation; (b) what are the most used types of scaffolds; (c) what kind of post-explant evaluation is most used. Through three websites (www.pubmed.com, www.webofknowledge.com and www.embase.com), 77 in vivo studies were included. Fifty-eight studies were conducted in small animal models (rodents) and 19 in animals of medium or large size (rabbits, dogs, goats, sheep, and minipigs). Despite the difficulty in establishing the most suitable animal model for osteoinductivity studies, small animals (in particular mice) are the most utilized. Intramuscular implantation is more frequent than subcutis, especially in large animals, and synthetic scaffolds (especially CaP ceramics) are preferred than natural ones, also in combination with cells and growth factors. Paraffin histology and histomorphometric evaluations are usually employed for postimplantation analyses.

Evaluation of osteoinduction properties of the demineralized bovine foetal growth plate powder as a new xenogenic biomaterial in rat

The aim of this study was evaluation of osteoinductive properties of demineralized bovine foetal growth plate in submuscular transplantation (ectopic osteoinduction) as a new xenogenic biomaterial in rat model. Demineralized bovine foetal growth plate was ectopically implanted in 18 male Sprague-Dawley rats. In 18 of the animals under aseptic conditions two submuscular pouches were created between external and internal oblique abdominal muscles in the two flanks: the right was left empty (sham) and the left was filled with 20mg of demineralized bovine foetal growth plate powder. Radiographs were taken in 2, 4 and 6 weeks after the surgery, then six animals were pharmacologically euthanized after 2, 4 and 6 weeks for histopathological evaluation. Results showed: (1) osteoinductivity of xenogenic demineralized bovine foetal growth plate powder, and (2) earlier mineralization of ectopically implanted demineralized bovine foetal growth plate in the submuscular implanted area. Our results show that submuscular implantation of xenogenic demineralized bovine foetal growth plate has osteoinductive properties in a rat model.

Augmentation of demineralized bone matrix (DBM) mineralization by a synthetic growth factor mimetic

These studies evaluated whether F2A4-K-NS, a peptide mimetic of FGF-2, could augment ectopic bone production following the subcutaneous implant of human demineralized bone matrix (DBM). DBM was formulated into a gel with and without F2A4-K-NS, and injected subcutaneously into athymic rats. After 28 days the resultant tissue was excised and fixed. The tissue was examined with soft X-rays and microcomputerized tomography (micro-CT), and by histological methods. Inclusion of F2A4-K-NS with DBM resulted in an increased mineral deposition as determined by soft X-ray and micro-CT analysis and von Kossa staining. DBM-containing tissues showed extensive mineralization compared to the carrier alone, which was poorly mineralized. The mineralization was qualitatively and quantitatively the most extensive in the samples containing F2A4-K-NS plus DBM. Additionally, the highest amount of von Kossa staining for calcium was observed in tissues from animals that had received DBM plus F2A4-K-NS. In these studies, 100 ng of peptide per 0.2 mL of injectable DBM gel generated the most optimal results. The synthetic peptide F2A4-K-NS augmented DBM-induced ectopic mineralization in athymic animals.

Quantitative microcomputed tomography analysis of mineralization within three-dimensional scaffoldsin vitro

Synthetic and naturally derived scaffold biomaterials in combination with osteogenic cells or bioactive factors have the potential to serve as bone graft substitutes. Porous poly(l-lactide-co-dl-lactide) (PLDL) scaffolds with mechanical properties comparable to trabecular bone and an oriented, interconnected porosity designed to enhance internal mass transport were recently developed. In this study, PLDL scaffolds were seeded with rat calvarial or rat stromal cells and cultured up to 8 weeks in media containing osteogenic supplements. Cell-seeded human demineralized trabecular bone matrix (DTBM) scaffolds were included for comparison. All constructs were imaged weekly from 4 to 8 weeks using microcomputed tomography (micro-CT) to nondestructively quantify the amount and distribution of mineralized matrix formation. The total mineralized matrix volume increased with time in culture for all construct groups. DTBM constructs contained significantly more mineralized matrix than PLDL constructs. However, an analysis of the acellular DTBM scaffolds exposed to osteogenic media revealed partial remineralization of the demineralized matrix whereas no mineralization was detected in acellular PLDL scaffolds. Differences in mineral distribution were also evident with cell-mediated mineralization found throughout the PLDL constructs but localized to the periphery of the DTBM constructs for both cell types. Expression of bone marker genes indicating osteoblast differentiation was demonstrated in all groups at 8 weeks using a quantitative reverse transcription polymerase chain reaction. Osteocalcin expression was significantly higher for calvarial cell constructs compared to stromal cell constructs, regardless of the type of scaffold. This study demonstrated that micro-CT imaging may be used to nondestructively and quantitatively monitor mineralization within three-dimensional scaffolds in vitro. PLDL scaffolds with an oriented microarchitecture were shown to support cell attachment, differentiation, and cell-mediated mineralization comparable to natural DTBM scaffolds.

Arthrodesis of lumbar spine transverse processes using nacre in rabbit

This study compares the osteogenic effects of nacre and autogenous bone grafts in a rabbit model of lumbar spine transverse process arthrodesis. A total of 15 rabbits were processed for arthrodesis between the fifth and sixth lumbar vertebrae using nacre powder mixed with autologous blood or autogenous iliac crest bone. Control rabbits were sham operated. Sample vertebrae were removed from the nacre-implanted rabbits at 2, 5, and 11 weeks postsurgery. The autogenous bone graft and sham-operated groups were processed for histological study 11 weeks postsurgery. The results for the three groups were compared at 11 weeks. The nacre-implanted samples taken at 2 weeks showed that the nacre was well tolerated by the host tissue. Endochondral bone formation was seen in the region of the dissolving nacre particles by 5 weeks. The newly formed bone formed a solid fusion between the transverse processes in one-third of the rabbits. There was still new bone formation at 11 weeks at the nacre implant site. Two-thirds of the rabbits had formed a solid fusion. Light microscopy also showed new bone formation 11 weeks after the autologous bone graft. All rabbits had a solid fusion. This initial study indicates that nacre can induce spinal fusion in an acceptable percentage of cases.

Mineralization processes in demineralized bone matrix grafts in human maxillary sinus floor elevations

For reconstruction of the severely resorbed lateral maxilla for dental implant placement, one of the successful procedures is to elevate the maxillary sinus floor by implanting demineralized bone matrix (DBM). We studied bone formation in DBM grafts in the lateral maxilla in humans by means of histology and histomorphometry. Six months after grafting, at the time of dental implantation biopsies were taken from the grafted areas of seven patients. All biopsies contained mineralized matrix (MM) in the grafted area. At close inspection, three types of mineralization were found. First, lamellar biomineralization was seen in and near the maxillary host bone. Second, remineralization was observed in some particles that probably had not been completely demineralized. In the area connecting the graft and host bone, where woven bone was formed against DBM particles, a third mechanism was detected. In this case many dotlike foci of remineralization appeared close to the bone-DBM interface. The remineralized DBM and woven bone were both subsequently remodeled. Bone formation was most active in the area adjoining the maxillary host bone. We conclude that in human sinus floor elevation, allogenic DBM increases mineralized tissue volume by osteoconduction that is supported by the remineralization processes. Osteoinduction by this material seems questionable.

Repair of human skull defects using osteoinductive bone alloimplants

To estimate the efficacy of cranioplasty in clinical practice, autolyzed, antigen-extracted, allogenic (AAA) bone was prepared from cortical bones of human organ donors. AAA bone implants consisted of completely demineralized bone powder, completely demineralized pliable bone chips, surface-demineralized bone chips with pliable crevices, surface-demineralized rigid bone chips, or combinations thereof. 21 patients received AAA bone cranioplasties and were followed-up for between 12 and 58 months (average: 29 months). No infection or rejection of any of the AAA bone implants occurred. X-ray assessments as well as bone scintigraphies revealed osseous integration and remodelling of the AAA bone implants with minimal resorption, with the exception of completely demineralized AAA bone chips which showed partial resorption (2 cases). However, the partial resorption of completely demineralized AAA bone chips ceased after the implants had been remodelled. In 4 cases, the osteosynthesis material was removed between 10 and 18 months after the cranioplasty. In another case, a re-entry was necessary because of recurrence of an intracranial tumor. All of these five AAA bone reconstructions showed bleeding surfaces and osseous consolidations at the time of re-entry. A bone biopsy taken from one of these cranioplasties showed osteoinduction on the surface of the AAA bone implants. This first clinical review of cranial reconstructions using osteoinductive AAA bone implants emphasizes the therapeutical application of AAA bone for cranioplasty. Large AAA bone chips from human skull bones facilitate the reproduction of the skull's convexity especially when combined with preoperative stereolithography-based planning.

Bone defect healing in the absence and presence of a plastic catheter: an experimental study in the rabbit

The healing pattern of small, round, cortical defects, drilled in the upper tibial diaphysis of rabbits, was studied histologically and histomorphometrically. Group I rabbits were not further handled. In groups II and III animals, a polyethylene catheter was introduced into the medullary cavity by way of a second cortical hole and driven forward until its tip was close to the first cortical defect. Group II rabbits were not further handled. The cortical defect of group III animals was irradiated from a diode source via a fiber optic cable in the catheter. Assessment of the osseous healing of the cortical defects revealed neither qualitatively nor quantitatively significant differences among the three groups. The morphological catheter, which abuts on a cortical defect, does not hinder the normal progression of osseous bridging of the gap.