Orthopedics, polymeric biomaterials

It has exceptionally good optical properties its transparency has made it a popular substitute for glass in apphcations where breakage must be avoided (plexiglass). It has a variety of industrial uses including automotive parts and glazings. PMMA was the first implanted synthetic polymeric biomaterial it was used as a hip prosthesis in 1947 (see USP XVIII, The Pharmacopia of the USA, (18th Revision), US Pharmacopoeia Convention, Inc., Rockville, MD, 1 September 1980). PMMA is currently used in orthopedic applications, as bone cement, and in intraocular lenses. 

This chapter addresses the application of polymeric biomaterials in the context of implantable devices intended for long-term functionality and permanent existence in the recipients. Basic concepts of biocompatibility as well as mechanical and structural compatibility are discussed to provide appropriate background for the understanding of polymer usage in cardiovascular, orthopedic, ophthalmologic, and dental prostheses. Furthermore, emerging classes... 

Table 19.1 summarizes some of the existing usage of polymeric biomaterials in a variety of implantable prostheses for cardiovascular, orthopedic, ophthalmologic, and dental applications. 

As it was previously mentioned, human body tissues and structures may suffer a variety of destructive processes, including fracture, infection and even cancer, causing pain and loss of function. Under these circumstances, it may be possible to remove the diseased tissue and replace it with some suitable synthetic material [20]. One of the most important applications of biomaterials in medicine are the orthopedic implant devices and the lost bone tissue replacement. In this sense, the most used polymeric biomaterial is PMMA. Due to its biocompatible nature and tuneable mechanical properties, it has been widely used as bone cements and as screws in bone fixation. This is one of the main reasons why PMMA and its derivatives have been successfully used in vertebroplasty and are the most common adhesive to anchor prostheses. 

As an extension to this surface-modification method, researchers have utilized plasma polymerization of acrylic acid to immobilize biologically active molecules, such as recombinant human bone formation protein-2 (rhBMP-2). rhBMP-2 is a signaling molecule that promotes bone formation by osteoinduction that has been utilized for various orthopedic tissue-engineering applications (Kim et al., 2013). One research group modified a PCL scaffold surface with plasma-polymerized acrylic acid (PPAA) and rhBMP-2 via electrostatic interactions (Kim et al., 2013) (which is outside of the scope of this chapter). This interesting approach may be apphed to the surface modification of solid fillers and provide additional benefits compared to the surface-modification techniques currently utihzed in orthopedic polymeric biocomposite development. The acrylic acid and rhBMP-2-modifled surface showed improved cell attachment and adhesion compared to the surface with acrylic acid alone. The ability to modify the surface of a solid-filler particle in a polymeric biocomposite with a bioactive molecule, such as rhBMP-2, provides a delivery vehicle for the bioactive molecule to the polymeric biocomposite and the eventual implantation site of this biomaterial. Such surface-modification and immobihzation approaches may provide a method to control the release kinetics of attached molecules to the localized bone-defect site. 

The world of biomaterials is diverse, encompassing ceramics and metals used for orthopedic implants (already discussed in Chapters 2 and 3), to artificial heart valves, blood vessel stents, and contact lenses. This sectiOTi will delve into those biomaterials apphcations that utihze soft polymeric-based materials. 

This chapter will focus on fundamental concepts related to surface modification of materials utilized within polymeric biocomposites for orthopedic applications. For this chapter, orthopedic applications are defined as medical indications or procedures that benefit from utilization of polymeric biocomposites and/or additional implanted therapeutic material to aid in bone regeneration at a localized site. The term surface modification refers to the physical attachment of molecules, predominantly silanes and/or polymers, to the surface of a solid-phase material. Polymeric biocomposites are a class of biomaterials that comprises a biocompatible bulk polymer and a particulated solid phase, often referred to as a binder and a filler, respectively. As there are vast combinations of polymers and solid materials that fit this definition, this chapter highlights solely those combinations that have been utilized for orthopedic applications, in either the acadenuc or the medical industry settings. 

Due to their tunable degradability, biocompatibility, processibility, and versatility, polymeric biocomposites are principal materials investigated for the development of synthetic bone scaffolds, cements, and composites (Porter et al., 2009). As previously defined, a polymeric biocomposite is composed of two or more bulk biomaterials (at least one a polymer) of different phases intended for use in the body. There are an unfathomable number of biocomposites that fit this broad criterion. Classic polymeric biocomposites for orthopedic applications are composed of a solid, synthetic ceramic phase that is osteoconductive or -inductive (Sepulveda et al., 2002) and a biocompatible polymer that was at one stage a liquid. 

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