Carlos Valencia

Effects of calcium phosphate/chitosan composite on bone healing in rats: calcium phosphate induces osteon formation.

Vascularization of an artificial graft represents one of the most significant challenges facing the field of bone tissue engineering. Over the past decade, strategies to vascularize artificial scaffolds have been intensively evaluated using osteoinductive calcium phosphate (CaP) biomaterials in animal models. In this work, we observed that CaP-based biomaterials implanted into rat calvarial defects showed remarkably accelerated formation and mineralization of new woven bone in defects in the initial stages, at a rate of ∼60 μm/day (0.8 mg/day), which was considerably higher than normal bone growth rates (several μm/day, 0.1 mg/day) in implant-free controls of the same age. Surprisingly, we also observed histological evidence of primary osteon formation, indicated by blood vessels in early-region fibrous tissue, which was encapsulated by lamellar osteocyte structures. These were later fully replaced by compact bone, indicating complete regeneration of calvarial bone. Thus, the CaP biomaterial used here is not only osteoinductive, but vasculogenic, and it may have contributed to the bone regeneration, despite an absence of osteons in normal rat calvaria. Further investigation will involve how this strategy can regulate formation of vascularized cortical bone such as by control of degradation rate, and use of models of long, dense bones, to more closely approximate repair of human cortical bone.

[Enteric Gram negative rods and unfermented of glucose bacteria in patients with peri-implant disease].

INTRODUCTION Implants can be colonized by microorganisms from oral biofilms and may affect peri-implant tissues health. Among these bacteria, pathogens typically associated with periodontitis can be found, such as Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis, as well as Gram negative enteric bacilli not typically associated with periodontal diseases. OBJECTIVE Superinfecting bacteria were characterized from peri-implant lesions in patients with history of periodontitis. MATERIALS AND METHODS Sixty-eight implants were studied in 55 patients; the average patient age was 56 years. Forty-nine implants had peri-implant lesions and 19 were considered stable. Subgingival samples were obtained in affected and stable implants. The samples were streaked on Mac-Conkey agar and incubated at 37°C for 24 hours. The colonies were identified with the kit-BD BBL Crystal E/NF®. RESULTS Superinfecting organisms were detected in 20 patients--they were seen more frequently at diseased implants (n=15) than at healthy implants (n=5). The prevalence of superinfecting bacteria on the selected implants was 33.8% (n=23/68). These bacteria were more prevalent among affected implants (n=17 or 25%) than those with stable implants n=6 (8.8%). Klebsiella pneumoniae was the most frequent Gram negative rod detected (n=12). CONCLUSIONS One-third of the implants had superinfecting organisms. Implants with a peri-implant lesion had a higher frequency of superinfecting bacteria. Klebsiella pneumoniae was the most common superinfecting organism isolated. A multiple infection caused by superinfecting bacteria was present only at diseased implants. These microbial agents potentially affect implant stability.

Synthesis and Application of Scaffolds of Chitosan-Graphene Oxide by the Freeze-Drying Method for Tissue Regeneration

Several biomaterials, including natural polymers, are used to increase cellular interactions as an effective way to treat bone injuries. Chitosan (CS) is one of the most studied biocompatible natural polymers. Graphene oxide (GO) is a carbon-based nanomaterial capable of imparting desired properties to the scaffolds. In the present study, CS and GO were used for scaffold preparation. CS was extracted from the mycelium of the fungus Aspergillus niger. On the other hand, GO was synthesized using an improved Hummers-Offemann method and was characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), and dynamic light scattering (DLS). Subsequently, three formulations (GO 0%, 0.5%, and 1%) were used to prepare the scaffolds by the freeze-drying technique. The scaffolds were characterized by FTIR, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), to determine their thermal stability and pore size, demonstrating that their stability increased with the increase of GO amount. Finally, the scaffolds were implanted, recollected 30 days later, and studied with an optical microscope, which evidenced the recovery of the tissue architecture and excellent biocompatibility. Hence, these results strongly suggested the inherent nature of chitosan/graphene oxide (CS/GO) scaffolds for their application in bone tissue regeneration.

Synthesis of Poly (Lactic Acid) and Production of Scaffolds by Electrospinning

In this research, the synthesis of L-lactide (L-Lc), the cyclic dimer of poly (L-lactic acid) (PLLA) with a 55.20% yield and its polymerization to PLLA with different molecular weights is reported. The product was used to produce fibrous scaffolds by electrospinning using variations in concentration, distance, flow and voltage. A high-resolution stereoscope was employed to find fiber diameter (500 y 1000 μm); PLLA with 295,000 g/mol molecular weight (viscometry) was obtained after 96 hours of reaction and yielded the best results in the electrospinning process. These scaffolds were evaluated in vitrofor cell growth and cytotoxicity with human skin fibroblasts. None of the samples were cytotoxic above the permitted threshold of 50%. This study provides an important increase in performance for the synthesis of poly (L-lactic acid) (PLLA) and further development in the manufacturing of scaffolds which have multiple uses.