Hila Bahar

Highly porous bioresorbable scaffolds with controlled release of bioactive agents for tissue-regeneration applications

Highly porous poly(DL-lactic-co-glycolic acid) films with controlled release of horseradish peroxidase (HRP) as a model protein have been successfully developed and studied. These films, which are prepared by freeze-drying inverted emulsions, are designed for use in tissue-regeneration applications. The effects of the emulsions formulation and host polymers characteristics on the films microstructure and HRP release profile over 4 weeks were investigated. A dual pore size population is characteristic for most films, with large 12-18 microm pores and small 1.5-7 microm pores, and porosity in the range of 76-92%. An increase in the polymer content and its initial molecular weight, organic/aqueous (O:A) phase ratio and lactic acid content, or a decrease in the HRP content, all resulted in a decreased burst effect and a more moderate release profile. A simultaneous change in two or three of these formulation parameters (compared to a reference formulation) resulted in a synergistic effect on the HRP release profile. A constant HRP release rate was achieved when a composite film was used. Human gingival fibroblast adhesion to the films indicated good biocompatibility. Appropriate selection of the emulsions parameters can therefore yield highly porous films with the desired protein-release behavior which can serve as scaffolds for bioactive agents in tissue-regeneration applications.

Commentary on: periodontally accelerated osteogenic orthodontics (PAOO) - a clinical dilemma.

It is apparent that tooth movement is enhanced by procedures that elevate the remodeling of alveolar bone, and of periodontal and gingival fibrous tissues. The periodontally accelerated osteogenic orthodontics (PAOO) also termed as Wilckodontics, involves full-thickness labial and lingual alveolar flaps accompanied with limited selective labial and lingual surgical scarring of cortical bone (corticotomy). Most of the authors suggest that the RAP is the major stimulus for alveolar bone remodeling, enabling the PAOO. However, we propose that detachment of the bulk of dentogingival and interdental fibers from coronal part of root surfaces by itself should suffice to stimulate alveolar bone resorption mainly on its PDL surfaces, leading to widening of the periodontal ligament space which largely attributes to accelerated osteogenic orthodontics. Moreover this limited fiberotomy also disrupts transiently the positional physical memory of dentition (PPMD), allowing accelerated tooth movement. During retention period, a new biological and physical connectivity is generated that could be termed as new positional memory of the dental arch.

Influence of bone-derived matrices on generation of bone in an ectopic rat model

Most bone regeneration experimental models that test bone‐derived matrices take place in conjunction with the native bone. Here, we compared the relative effectiveness of bone matrix components on bone‐marrow‐directed osteogenesis in an ectopic model. Cortical bone cylinders consisted of diaphysis of DA rat femurs. They were either demineralized (DBM), deproteinized (HABM), or nontreated (MBM). Fresh bone marrow was placed into cylinders and implanted at subcutaneous thoracic sites of 2‐month‐old DA rats. At designated times the cylinders were surgically removed from the animals. Microradiographs of DBM and histology of DBM and MBM cylinders demonstrated progressive increase in mineralized bone volume and its trabecular configuration. Bone filled the inner volume of DBM and MBM cylinders within 4 weeks, while in HABM cylinders mostly granulation tissue developed. In the DBM cylinders cartilage deposited within 10 days, while in the MBM cylinders bone was directly deposited. As early as day 3 after marrow transplantation, marrow cells interacting with DBM increased significantly the genes that express the cartilage and the bone phenotype. In conclusion, organic components of bone are needed for marrow‐directed osteogenesis.

Tissue Engineering of Bone: Critical Evaluation of Scaffold Selection

Itzhak Binderman1, Avinoam Yaffe2, Yuval Samuni3, Hila Bahar1, Joseph Choukroun4 and Philippe Russe5 1Department of Oral Biology, Maurice and Gabriela Goldschleger, School of Dental Medicine, Sackler Faculty of Medicine, Tel Aviv University, 2Department of Prosthodontics, Haddasah School of Dental Medicine, Hebrew University of Jerusalem, 3Department of Oral and Maxillofacial Surgery, Barzilai Medical Center, Ashkelon, 4Syfac, Nice, 5Private Practice, Reims, 1,2,3Israel 4,5France