Structure-Performance Relationships of Temperature-Responsive PLGA-PEG-PLGA Gels for Sustained Release of Bone Morphogenetic Protein-2.

PLGA (poly(lactic-co-glycolic) acid)-PEG (polyethylene glycol)-PLGA synthesis conditions have an impact on the physicochemical features of the copolymer and its usefulness as biomaterial. This study reports on an analysis of the composition and structural properties of PLGA-PEG-PLGA copolymers applying a variety of analytical techniques. Viscoelastic properties and particularly the temperature-responsive behavior of PLGA-PEG-PLGA showed a marked dependence on copolymer structural features. Physicochemical and biological properties, such as bioadhesion, biocompatibility and cell viability, of the raw copolymers and their gels were also evaluated. The most promising copolymer was chosen to formulate the osteoinductive protein bone morphogenetic protein-2 (125I-BMP-2), and the ability of its gels to sustain the release both in vitro and in vivo was monitored in situ using a gamma counter. In vitro diffusion studies were carried out using a bioinspired set-up that included a biorelevant receptor medium. In vivo release tests after implantation in a critical-size calvarial defect model showed an important burst, but then the release fitted well to the square-root kinetics. Importantly, the release rate constants recorded in vitro and in vivo matched each other suggesting close in vitro-in vivo correlation. Overall, the information gathered opens new perspectives in the biomedical application of these temperature-sensitive materials.

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.

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.

Lifelink: 3G-based mobile telemedicine system.

Current wired telemedicine systems encounter difficulties when implemented in archipelagic developing countries because of the high cost of fixed infrastructure. In this research, we devised Lifelink, a mobile real-time telemonitoring and diagnostic facility to command and control remote medical devices through mobile phones. The whole process is phone-based, effectively freeing offsite medical specialists from stationary monitoring consoles and endowing the system with the potential to increase the number participating consultants. The electrocardiogram (ECG) readings are analyzed using a detrended fluctuation technique and classified into pathological cases using an unassisted K-means clustering algorithm. We analyzed 30 batches of 2-hour ECG signals taken from cardiac patients (20 males, 10 females, mean age 46.7 years) with pre-diagnosed pathologies. The method successfully categorized the 30 subjects without user intervention into the following cases: normal (at 86.7% accuracy), congestive heart failure (86.7%), and atrial fibrillation (80.0%). The synergy of mobile monitoring and fluctuation analysis presents a powerful platform to reach remote, underserved communities with poor or nonexistent wired communication structures. It is likely to be essential in the development of new mobile diagnostic and prognostic measures.