Evaluation of the effectiveness of a bMSC and BMP-2 polymeric trilayer system in cartilage repair.

In this study a poly(lactide-co-glycolide) acid (PLGA) tri-layer scaffold is proposed for cartilage repair. The trilayer system consists of a base layer formed by a tablet of PLGA microspheres, a second layer composed of a microsphere suspension placed on top of the tablet, and the third layer, which constitutes an external electrospun PLGA thin polymeric membrane. Combinations of bone morphogenetic protein-2 (BMP-2) encapsulated in the microspheres of the suspension layer, and bone marrow mesenchymal stem cells (bMSC) seeded on the electrospun membrane, are evaluated by histologic analyses and immunohistochemistry in a critical size osteochondral defect in rabbits. Five experimental groups, including a control group (empty defect), a blank group (blank scaffold), a bMSC treated group, two groups treated with 2.5 µg or 8.5 µg of BMP-2 and another two groups implanted with bMSC-BMP-2 combination are evaluated. The repair area increases throughout the experimental time (24 weeks). The repair observed in the treated groups is statistically higher than in control and blank groups. However, the bMSC-BMP-2 combination does not enhance the BMP-2 response. In conclusion, BMP-2 and bMSC repaired effectively the osteochondral defect in the rabbits. The bMSC-BMP-2 combination did not produce synergism.

Biodistribution of radiolabeled polyglutamic acid and PEG-polyglutamic acid nanocapsules.

Recently we reported the development of 100nm polyglutamic acid (PGA)-based nanocapsules, which were intended to carry anticancer drugs to the lymphatic system (Abellan-Pose et al., 2016). In this work, the objective was to further assess the potential "lympho-targeting" properties of radiolabeled 111In-PGA and 111In-PGA-PEG, following intravenous or subcutaneous administration. The results indicate that, following intravenous administration, both types of nanocapsules exhibit a modest accumulation in the lymph nodes (⩽2.3% ID/g). On the contrary, following subcutaneous administration, and irrespective of the presence of PEG on their surface, the nanocapsules were found to form a reservoir at the injection site, from which they drained slowly into the popliteal and the iliac lymph nodes. The significant accumulation of the radiolabeled nanocapsules in the lymph nodes was attained at 24 and 48h post-injection, reaching values comprised between 70% and 187% ID/g in the popliteal lymph nodes. Altogether, the results led us to validate our hypothesis about the ability of the PGA and PGA-PEG nanocapsules to reach the lymphatic system, especially following subcutaneous administration.

BMP-2, PDGF-BB, and bone marrow mesenchymal cells in a macroporous ß-TCP scaffold for critical-size bone defect repair in rats.

The aim of this work was to study the bone repair induced by bone morphogenetic protein-2 (BMP-2), rat mesenchymal stem cells (rMSCs), and platelet-derived growth factor (PDGF-BB) incorporated in a macroporous beta-tricalcium phosphate (ß-TCP) system fabricated by robocasting, and to identify the most beneficial combination in a critical rat calvaria defect. BMP-2 was formulated in microspheres to provide a prolonged, local concentration, whereas PDGF-BB, which acts during the initial stage of defect repair, was incorporated in a thin layer of crosslinked alginate. Approximately 80% of PDGF-BB and 90% of BMP-2 were released into the defect during the first 2 d and 3 weeks, respectively. Histological analyses indicated a minor synergistic effect in the BMP-2-MSC groups. In contrast, significant antagonism was found with combined BMP-2 and PDGF-BB defect treatment. The high-grade repair induced by BMP-2 rules out any advantage from combining BMP-2 with PDGF-BB or MSCs, at least with this scaffold and defect model.

Evaluation of nanostructure and microstructure of bone regenerated by BMP-2-porous scaffolds.

In this study, three systems containing BMP-2 were fabricated, including two electrospun sandwich-like-systems of PLGA 75:25 and PLGA 50:50 and a microsphere system of PLGA 50:50 to be implanted in a critical size defect in rat calvaria. The in vivo BMP-2 release profiles of the three systems were similar. The total dose was released during the first two weeks. To evaluate the nano and microstructure of the regenerated bone a multi-technique analysis was used, including stereo microscope, X-Ray; AFM, micro-CT, and histological analyses. The progression of bone regeneration was followed at 4, 8, and 12 weeks after the microsphere system implantation whereas the two electrospun systems were evaluated at fixed 12 weeks. All the techniques applied showed high bone regeneration. The average values of bone volume density, bone mineral density, Young's modulus, and the percent of bone repair were ∼70% of the values of the native bone. Besides, SEM-EDX analysis indicated that the main chemical elements in the new bone were oxygen, calcium, and phosphorus in a ratio similar to that of native bone. In comparison, the micro-CT may provide an alternative to histology for the evaluation of bone formation at the defect size.

Smurf1 knocked-down, mesenchymal stem cells and BMP-2 in an electrospun system for bone regeneration.

A sandwich-like system, fabricated with electrospun, poly(lactic-co-glycolic-acid) (PLGA) membranes incorporating either human recombinant bone morphogenetic protein 2 (BMP-2) enriched microspheres, rat bone marrow mesenchymal stem cells (rMSC), or rMSC with their Smurf1 (SMAD ubiquitin regulatory factor-1) expression knocked down by means of siRNA (rMSC573) at varying densities was evaluated in a rat calvarial, critical-size defect. The behavior of four membrane varieties, fabricated with different PLGA copolymers, was initially studied in rMSC cultures to decide on optimal membrane degradation and cell proliferation and differentiation characteristics. PLGA75:25 provided the most stable structure, and favored the cell environment. Radiological and histological analyses indicated bone repair in animals treated with the PLGA75:25 bioactivated systems. We found no synergist interaction between BMP-2 and rMSC 8 to 12 weeks postimplantation. By contrast, synergistic defect repair of around 85% was detected after 8 weeks of combined BMP-2 and rMSC573 treatment.

In vivo osteogenic response to different ratios of BMP-2 and VEGF released from a biodegradable porous system.

Bone regeneration and vascularization with porous PLGA scaffolds loaded with VEGF (0.35 and 1.75 µg) and BMP-2 (3.5 and 17.5 µg), incorporated in PLGA microspheres, or the combination of either dose of BMP-2 with the low dose of VEGF were investigated in an intramedullary femur defect in rabbits. The system was designed to control growth factor (GF) release and maintain the GFs localized within the defect. An incomplete release was observed in vitro whereas in vivo VEGF and BMP-2 were totally delivered during 3 and 4 weeks, respectively. A weak synergistic effect of the dual delivery of VEGF and BMP-2 (high dose) was found by 4 weeks. However, the absence of an apparent synergistic long-term effect (12 weeks) of the combination over BMP-2 alone suggests that more work has to be done to optimize VEGF dose, sequential presentation, and the ratio of the two GFs to obtain a beneficial bone repair response.