INJECTABLE HYBRID SYSTEM FOR STRONTIUM LOCAL DELIVERY TO PROMOTE BONE REGENERATION

In bone tissue regeneration strategies, injectable bone substitutes are very attractive since they can be applied with minimally invasive surgical procedures and can perfectly fill irregular defects created in cases of trauma, infection or tumor resection. These materials must combine adequate mechanical properties with the ability to induce new bone formation. Incorporating strontium (Sr) in bone substitute biomaterials may be a strategy to achieve high Sr concentrations, not in a systemic but in a local environment, taking advantage of the osteoanabolic and anti-osteoclastic activity of Sr, for the enhancement of new bone formation. In this context, the aim of the present work was to evaluate the response of a Sr-hybrid injectable system for bone regeneration, designed by our group, consisting of hydroxyapatite microspheres doped with Sr and an alginate vehicle crosslinked in situ with Sr, in an in vivo scenario. Two different animal models were used, rat (Wistar) and sheep (Merino Branco) critical sized bone defect. Non Sr-doped similar materials (Ca-hybrid) or empty defects were used as control. Sr-hybrid system led to an increased bone formation in both center and periphery of a rat critical sized defect compared to a non Sr–doped similar system, where new bone formation was restricted to the periphery. Moreover newly formed bone was identified as early as one week after its implantation in a sheep model. After eight weeks, the bone surrounded the microspheres, both in the periphery and in the center of the defect. Most importantly, the hybrid system provided a scaffold for cell migration and tissue ingrowth and offered structural support, as observed in both models. The effective improvement of local bone formation suggests that this might be a promising approach for bone regeneration, especially in osteoporotic conditions

Tiludronate and clodronate do not affect bone structure or remodeling kinetics over a 60 day randomized trial

Background Tiludronate and clodronate are FDA-approved bisphosphonate drug therapies for navicular disease in horses. Although clinical studies have determined their ability to reduce lameness associated with skeletal disorders in horses, data regarding the effect on bone structure and remodeling is lacking. Additionally, due to off-label use of these drugs in young performance horses, effects on bone in young horses need to be investigated. Therefore, the purpose of this randomized, experimental pilot study was to determine the effect of tiludronate and clodronate on normal bone cells, structure and remodeling after 60 days in clinically normal, young horses. Additionally, the effect of clodronate on bone healing 60 days after an induced defect was investigated. Results All horses tolerated surgery well, with no post-surgery lameness and all acquired biopsies being adequate for analyses. Overall, tiludronate and clodronate did not significantly alter any bone structure or remodeling parameters, as evaluated by microCT and dynamic histomorphometry. Tiludronate did not extensively impact bone formation or resorption parameters as evaluated by static histomorphometry. Similarly, clodronate did not affect bone formation or resorption after 60 days. Sixty days post-defect, healing was minimally affected by clodronate. Conclusions Tiludronate and clodronate do not appear to significantly impact bone tissue on a structural or cellular level using standard dose and administration schedules

A method to assess primary stability of acetabular components in association with bone defects

The objectives of this study were to develop a simplified acetabular bone defect model based on a representative clinical case, derive four bone defect increments from the simplified defect to establish a step‐wise testing procedure, and analyze the impact of bone defect and bone defect filling on primary stability of a press‐fit cup in the smallest defined bone defect increment. The original bone defect was approximated with nine reaming procedures and by exclusion of specific procedures, four defect increments were derived. The smallest increment was used in an artificial acetabular test model to test primary stability of a press‐fit cup in combination with bone graft substitute (BGS). A primary acetabular test model and a defect model without filling were used as reference. Load was applied in direction of level walking in sinusoidal waveform with an incrementally increasing maximum load (300 N/1000 cycles from 600 to 3000 N). Relative motions (inducible displacement, migration, and total motion) between cup and test model were assessed with an optical measurement system. Original and simplified bone defect volume showed a conformity of 99%. Maximum total motion in the primary setup at 600 N (45.7 ± 5.6 µm) was in a range comparable to tests in human donor specimens (36.0 ± 16.8 µm). Primary stability was reduced by the bone defect, but could mostly be reestablished by BGS‐filling. The presented method could be used as platform to test and compare different treatment strategies for increasing bone defect severity in a standardized way

Bone marrow seeded bone graft versus bone graft; compact bone critical sized defect healing pattern in rabbit

The main aim of the present study was to investigate the effect of combination of bone marrow as the primary origin of osteoblast and at the same time as the seed cell and corticocancellous bone graft as the natural scaffold in repair of compact bone full thickness segmental critical sized defect in rabbits. Twelve rabbits had been divided into two groups; In Group one, fresh autogenous bone marrow aspirate has been seeded into the scaffold of autogenous corticocancellous bone graft which was utilized to repair critical size compact bone defect in mid shaft of radius. Corticocancellous bone graft alone was used as the Group 2 or control group. Up to 8 weeks, radiographs were taken to evaluate the level of osteogenicity in both groups. Rabbits were euthanized on week eight postoperative and the implants were harvested for gross, histological and scanning electron microscope observations. New bone formation and osteogenesis was observed at the margins and centre of the Group 1. Combination of mature and immature trabecullae covered the defect and bone formation pattern included osteogenesis, osteoinduction and osteocunduction. In the implant of corticocancellous bone graft alone or group 2, the major new bone formation was at the margins of the defect and osteogenesis was not observed at the centre of the defect and the major bone formation pattern was creeping substitution. As the conclusion, combination of bone marrow and corticocancellous bone graft had better results than corticocancellous bone graft alone in osteogenesis potential. Bone formation capability and critical sized defect repair was faster and more efficient and successful in Group 2 defect

Early Clinical and Radiological Experience with a Ceramic Bone Graft Substitute in the Treatment of Benign and Borderline Bone Lesions

Abstract Substitutes for bone grafts experience increasing popularity, but the need for defect-filling following simple curettage of benign bone lesions is controversial. In this study, we wish to objectively report the radiological changes following bone defect-filling using a composite ceramic bone graft substitute, as well as the clinical results and complications. We evaluated 35 surgically treated benign bone lesions with subsequent defect-filling using two variants of a composite ceramic bone graft substitute (CERAMENT|BONE VOID FILLER or CERAMENT|G, BONESUPPORT AB, SWEDEN). After one year, a normal cortical thickness surrounding the defect was seen in approximately 80% of patients. Inside the defect-cavity, an almost complete product-resorption was seen after one year. The most common complication was a post-operative inflammatory soft-tissue reaction, seen in 7 patients (20%), which resolved without further treatment, although short-term antibiotic treatment was initiated at a local hospital in 6 patients, due to suspected wound infection. In summary, cortical thickness most commonly normalizes after bone tumor removal and filling of the bone defect using this particular composite ceramic bone graft substitute. The ceramic substitute undergoes resorption, which causes progressive changes in the radiological appearance inside the bone defect

Comparison of nanoparticular hydroxyapatite pastes of different particle content and size in a novel scapula defect model

Nanocrystalline hydroxyapatite (HA) has good biocompatibility and the potential to support bone formation. It represents a promising alternative to autologous bone grafting, which is considered the current gold standard for the treatment of low weight bearing bone defects. The purpose of this study was to compare three bone substitute pastes of different HA content and particle size with autologous bone and empty defects, at two time points (6 and 12 months) in an ovine scapula drillhole model using micro-CT, histology and histomorphometry evaluation. The nHA-LC (38% HA content) paste supported bone formation with a high defect bridging-rate. Compared to nHA-LC, Ostim(®) (35% HA content) showed less and smaller particle agglomerates but also a reduced defect bridging-rate due to its fast degradation The highly concentrated nHA-HC paste (48% HA content) formed oversized particle agglomerates which supported the defect bridging but left little space for bone formation in the defect site. Interestingly, the gold standard treatment of the defect site with autologous bone tissue did not improve bone formation or defect bridging compared to the empty control. We concluded that the material resorption and bone formation was highly impacted by the particle-specific agglomeration behaviour in this study

Histomorphometric evaluation of bone regeneration induced by biodegradable scaffolds as carriers for dental pulp stem cells in a rat model of calvarial "critical size" defect

Objective: The aim of this study was to test specific stem cells that could enhance bone formation in combination with specific scaffolds. Methods: Dental Pulp Stem Cells (DPSCs) were seeded with Granular Deproteinized Bovine Bone (GDPB) or Beta-Tricalcium Phosphate (ß-TCP) in a rat model of calvarial "critical size" defect. DPSCs were isolated from permanent human teeth, obtained and characterized using specific stem cells markers (Nanog and Oct-4) by real time-PCR and immunofluorescence. Cells were differentiated for 10-15 days towards the osteoblastic phenotype with 100μM L-ascorbic acid, added every day in culture medium and 20 vol. percentage of FBS in α-MEM medium. Osteogenic commitment was evaluated with real time-PCR by measuring the expression of specific markers (osteonectin and runx2). When a sufficient cell number was obtained, DPSCs were trypsinized, washed in culture medium and seeded onto the GDPB and ß-TCP scaffold sat a density of 0.5-1×106 cells/scaffold. Two bilateral critical-size circular defects (5 mm diameter; 1 mm thickness) were created from the parietal bone of the 8 athymic T-cell deficient nude rats. One cranial defect for each rat was filled with the scaffold alone and the other defect with the scaffold seeded with stem cells. After 12 weeks post-surgery animals were euthanized and histomorphometric analysis was performed. Differences between groups were analyzed by one-way analysis of variance (ANOVA) followed by Fisher's Protected Least Significant Difference (PLSD) post-hoc test. A p-value <0.05 was considered statistically significant. Results: GDPB group presented higher percentage of lamellar bone than that of GDPB/DPSC, ß-TCP alone had lower levels as compared to ß-TCP/DPSC. The addition of stem cells significantly increased woven bone formation in both scaffold-based implants, although still higher in GDPB based implants. Conclusion: Our findings indicate that GDPB and ß-TCP used as scaffold to induce bone regeneration may benefit from adding DPSC to tissue-engineered constructs

Weightbearing ovine osteochondral defects heal with inadequate subchondral bone plate restoration: implications regarding osteochondral autograft harvesting

PURPOSE: It is unknown what causes donor site morbidity following the osteochondral autograft transfer procedure or how donor sites heal. Contact pressure and edge loading at donor sites may play a role in the healing process. It was hypothesized that an artificially created osteochondral defect in a weightbearing area of an ovine femoral condyle will cause osseous bridging of the defect from the upper edges, resulting in incomplete and irregular repair of the subchondral bone plate. METHODS: To simulate edge loading, large osteochondral defects were created in the most unfavourable weightbearing area of 24 ovine femoral condyles. After killing at 3 and 6 months, osteochondral defects were histologically and histomorphometrically evaluated with specific attention to subchondral bone healing and subchondral bone plate restoration. RESULTS: Osteochondral defect healing showed progressive osseous defect bridging by sclerotic circumferential bone apposition. Unfilled area decreased significantly from 3 to 6 months (P = 0.004), whereas bone content increased (n.s.). Complete but irregular subchondral bone plate restoration occurred in ten animals. In fourteen animals, an incomplete subchondral bone plate was found. Further common findings included cavitary lesion formation, degenerative cartilage changes and cartilage and subchondral bone collapse. CONCLUSIONS: Osteochondral defect healing starts with subchondral bone plate restoration. However, after 6 months, incomplete or irregular subchondral bone plate restoration and subsequent failure of osteochondral defect closure is common. Graft harvesting in the osteochondral autograft transfer procedure must be viewed critically, as similar changes are also present in humans. LEVEL OF EVIDENCE: Prognostic study, Level III

Defect-related luminescent nanostructured hydroxyapatite promotes mineralization through both intracellular and extracellular pathways

Hydroxyapatite (HAP) is a widely used biomaterial for bone tissue substitution due to its chemical similarity with the natural bone. Defect-related luminescent HAP materials have the same chemical composition as normal HAP and excellent biocompatibility. However, only few works have focused on the defect-related luminescent HAP materials on bone regeneration. In this work, we systematically investigated the bone regeneration pathway induced by nanostructured particles using defect-related luminescent hydroxyapatite (S2) materials. We monitored the subcellular distribution and location of S2 during osteoblast differentiation with the property of defect-related luminescence. Nano-scale S2 could be internalized by osteoblasts (OBs) via caveolae-mediated endocytosis and macropinocytosis. S2 incorporated into the lysosomes dissolved and released calcium ions for the formation of mineralized nodules. Extracellular S2 also promoted bone regeneration as a nucleation site. Taken together, the physical properties of hydroxyapatite control the bone regeneration pathway in osteoblasts