Polymeric Materials for Bone and Cartilage Repair

Although, the drug delivery system (DDS) concept is not new, great progress has recently been made in the treatment of a variety of diseases. Targeting delivery of drugs to the diseased lesions is one of the most important aspects of DDS. To convey a sufficient dose of drug to the lesion, suitable carriers of drugs are needed. Nano and microparticle carriers have important potential applications for the administration of therapeutic molecules. The research in this area is being carried out all over the world at a great pace. Research areas cover novel properties that have been developed increased efficiency of drug delivery, improved release profiles and drug targeting. The purpose of this review is to take a closer look at nano/microparticles as drug delivery devices.

/pdf/nano-and-microparticles-as-controlled-drug-delivery-devices-wygizhqqug.pdf

Nano and microparticles as controlled drug delivery devices.

Slowly polymerizing hydrogels are provided which are useful as a means of delivering large numbers of isolated cells via injection. The gels promote engraftment and provide three dimensional templates for new cell growth. The resulting tissue is similar in composition and histology to naturally occurring tissue. This method can be used for a variety of reconstructive procedures, including custom molding of cell implants to reconstruct three dimensional tissue defects, as well as implantation of tissues generally. The polymers permit construction of muscle and cartilage tissues which are useful to repair defects such as reflux and incontinence.

Injectable hydrogel compositions

This chapter reviews recent developments in biodegradable synthetic polymers focusing on tailoring polymer structures to meet material specification for emerging applications such as tissue engineered products and therapies. Major classes and new families of synthetic polymers are discussed with regard to synthesis, properties and biodegradability, and known degradation modes and products are summarized based on studies reported during the past 10-15 years. Polyesters and their copolymers, polyurethanes, polyphosphazenes, polyanhydrides, polycarbonates, polyesteramides and recently developed injectable polymer systems based on polypropylenefumarates, polyurethanes and acrylate/urethane systems are reviewed. Polyesters such as polyglycolides, polylactides and their copolymers still remain as the major class of synthetic biodegradable polymers with products in clinical use. Although various copolymerization methods have addressed needs of different applications, release of acidic degradation products, processing difficulties and limited range of mechanical properties remains as major disadvantages of this family of polymers. Injectable polymers based on urethane and urethane/acrylate have shown great promise in developing delivery systems for tissue engineered products and therapies.

Recent developments in biodegradable synthetic polymers

A cell-scaffold composition is prepared in vitro for implanting to produce functional organ tissue in vivo. The scaffold is three-dimensional and is composed of hollow or solid fibers of a biocompatible, synthetic polymer which is biodegradable or non-biodegradable. The fibers of the scaffold may have a branched configuration extending outwardly from a central stem. Fibers of the scaffold are spaced apart such that the maximum distance over which diffusion of nutrients and gases must occur through a mass of cells attached to the fibers is between 200 and 300 microns. The diffusion provides free exchange of nutrients, gases and waste to and from cells proliferating throughout the scaffold in an amount effective to maintain cell viability throughout the scaffold in the absence of vascularization. Cells derived from vascularized organ tissue are attached in vitro to the surface of the fibers uniformly throughout the scaffold in an amount effective to produce functional vascularized organ tissue in vivo, the cells are grown on the scaffold in a nutrient solution in vitro to form the cell-scaffold composition which is implanted in a host at a location having adequate vascularization to allow growth of blood vessels into the cell-scaffold composition. Growth factors, compounds stimulating angiogenesis and immunomodulators may be provided in the cell-scaffold composition and the fibers may have a coating to enhance cell attachment. Combinations of cell-scaffold compositions containing different cell populations may be implanted.

Three-dimensional fibrous scaffold containing attached cells for producing vascularized tissue in vivo

Synthesis of Poly[(amino acid alkyl ester)phosphazenes]

Synthesis and Hydrolysis of Hexakis(imidazolyl)cyclotriphosphazene

: Hexa(p-lithiophenoxycyclotriphosphazene) has been synthesized as an intermediate for the covalent attachment of metallo-, phosphino, carboxylato, alkyl, or tertiary alcohol units to the side group structure. These reactions are models for the preparation of the corresponding phosphazene high polymers.

Small-molecule cyclic models for the synthesis of new polyphosphazenes: side-group construction via lithiophenoxy derivatives

: A new class of polyphosphazenes has been synthesized via the lithio-derivatives of aryloxyphosphazene high polymers. These were used as intermediates for the introduction of phosphine-, organotin-, gold-, or COOH- pendent units. (Author)

/pdf/side-group-construction-in-high-polymeric-phosphazenes-via-3u084fzbra.pdf

Side-Group Construction in High Polymeric Phosphazenes via Lithiophenoxy Intermediates

: The first example of a successful metal-halogen exchange reaction between n-butyllithium and a hexa(p-halogenophenoxy)cyclotriphosphazene is described. The hexalithio derivative was allowed to react with electrophiles to yield carboxylic acid, stannane, and phosphine-derivatives. (Author)

Preparation of [NP(p-OC6H4Li)2]3 by Metal-Halogen Exchange, and its Reactions with Electrophiles

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