Bone regeneration

Keywords Chitosan Nanoparticles Microspheres Chemically modified chitosans Polyelectrolyte complexes Oral and nasal administration Nerve, cartilage and bone regeneration Wound dressing... 

In concentrated NaOH, chitin becomes alkali chitin which reacts with 2-chloroethanol to yield 0-(2-hydroxyethyl) chitin, known as glycol chitin this compoimd was probably the first derivative to find practical use (as the recommended substrate for lysozyme). Alkali chitin with sodium monochloroacetate yields the widely used water-soluble 0-carboxymethyl chitin sodium salt [118]. The latter is also particularly susceptible to lysozyme, and its oUgomers are degraded by N-acetylglucosaminidase, thus it is convenient for medical appHcations, including bone regeneration. 

The reconstruction of the periodontal tissue with chitosan was a prelude to the discovery of the osteoinductive properties of chitosan [331]. Surgical wounds from wisdom tooth avulsions were treated with freeze-dried methylpyrrolidinone chitosan that promoted bone regeneration. Methyl-pyrrolidinone chitosan was useful in apicoectomy as well. None of the patients reported adverse effects over three years of observation [332]. 

Chitosan membranes can also be superficially modified, for instance with 3-isocyanatopropyl triethoxysilane. Silanol groups and calcium salt acted as nucleation sites and accelerator, respectively, for the formation of apatite crystals therefore, this chitosan membrane is a bioactive guided bone-regeneration material thanks to its apatite-forming ability [341]. 

Concurrent with these investigations, polyphosphazene matrices, functionalized with aminoacid esters or with imidazole groups, became of importance because of their tissue engineering aspects in bone regeneration [655,656,679], treatment of periodontal diseases [657], and nerve reconstruction problems [680-682] in which the remarkable bio compatibility of POP matrices was coupled with their tuneable bio degradability. 

Most of the bio-nanocomposites tested as implants for bone regeneration are based on the assembly of HAP nanoparticles with collagen, trying to reproduce the composition, biocompatibility and suitable mechanical properties of natural bone. 

Bio-nanocomposites based on calcium phosphates can perform other innovative fundions such as acting as a reservoir for the controlled release of bioadive compounds once the material is implanted in the bone defect. For instance, the incorporation of a morphogenetic protein that promotes bone regeneration in an HAP-alginate-collagen system [110] or a vitamin in a Ca-deficient HAP-chitosan nanocomposite [111] are recent examples of this kind of application. 

Bioactive materials can be used as powders for filling small defects and as coatings that enhance metallic prosthesis fixation. However, when considering bioactive materials for bone regeneration in medium and large defects, bioactive pieces with appropriate mechanical properties are required. At this point, the key is to keep the properties provided by the nanostructure when processing a piece at the macroscopic... 

BONE REGENERATION, 52 BORON NITRIDE, 201 298 BOUNDARY CONDITION, 299 314 345 359... 

Bruder SP, Kurth AA, Shea M, Hayes WC, Jaiswal N, Kadiyala S. Bone regeneration by implantation of purified, culture-expanded human mesenchymal stem cells. J Orthop Res 1998 16 155-162. 

When this fracture repair system fails or is not expected to work, then an attempt must be made to induce bone regeneration for skeletal repair or reconstruction. The surgeon endeavors to make local skeletal conditions mimic those that the body would expect to encounter in a situation that requires fracture repair. In a very real sense, he or she tries to trick the body into initiating the fracture repair system. Current surgical options to accomplish this... 

This discussion has introduced the problem of bone regeneration clinical situations where the body s fracture repair system either has failed or has not been induced to action. The overall strategy to address this problem includes... 

All the various types of chitosans were degraded with time, in conjunction with the bone regeneration (Ikeda et al., 2002). However, it takes about 9 months after the implantation for the almost complete disappearance of chitosan in the bone tissue. Only the monomer type of chitosan, d-glucosamine which is effective to relieve the signs of osteoarthritis, is easy to completely dissolve immediately in vitro and in vivo. 

Vardaxis, N. J., Boon, M. E., and Ruijgrok, J. M. (1996). Calcification of cross-linked collagen-elastin membrane implants in vivo and their proposed use in bone regeneration. Biomaterials 17, 1489-1497. 

Laurencin and coworkers213 have used a different approach to control the rate of bioerosion of polymers with amino acid ester side groups. They used hydrophobic 4-methylphenoxy cosubstituents ( 50%) to slow the rate of hydrolysis, and these polymers were employed to study the rate of release of inulin. Similar polymers are also being developed by the same investigators as tissue engineering substrates for bone regeneration.214"218... 

Moutsatsos, I.K., Turgeman, G., Zhou, S., Kurkalli, B.C., Pelled, G., Tzur, L. et al. (2001) Exogenously regulated stem cell-mediated gene therapy for bone regeneration. Mol. Ther., 3,449 161. 

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