Biomaterials polymeric surfaces

Biomedical materials include metals, ceramics, natural polymers (biopolymers), and synthetic polymers of simple or complex chemical and/or physical structure. This volume addresses, to a large measure, fundamental research on phenomena related to the use of synthetic polymers as blood-compatible biomaterials. Relevant research stems from major efforts to investigate clotting phenomena related to the response of blood in contact with polymeric surfaces, and to develop systems with nonthrombogenic behavior in short- and long-term applications. These systems can be used as implants or replacements, and they include artificial hearts, lung oxygenators, hemodialysis systems, artificial blood vessels, artificial pancreas, catheters, etc. 

Recently, plasma gas discharge [Khang et al., 1997a] and corona treatment [Khang et al., 1996d] with reactive groups introduced on the polymeric surfaces have emerged as other ways to modify biomaterial surfaces [Lee et al., 1991 1992]. 

In recent years, dental research has been focused on dental implants and artificial teeth rooted in a patient s jaw allowing for a permanent denture, as alternatives to bridges or false teeth. A wide array of materials including polymers such as UHMWPE, PTFE, and PET have been used in many types of existing dental implants [54,119]. Porous polymeric surfaces are now designed to facilitate bone integration [54], Other dental applications of polymeric biomaterials have been for the development of a dental bridge, meant as a partial denture or false teeth. In extreme cases, removable dentures fabricated from PMMA are used to overcome the loss of all teeth [203]. 

Both XPS and TOF-SIMS are nowadays standard analytical tools for the determination of biomaterials surface chemistry. Examples of the use of XPS or TOF-SIMS for the analysis of biomimetic polymers include the investigation of different protein " ° and phosphate group modified polymeric surfaces. 

A wide variety of natural and synthetic materials have been used for biomedical applications. These include polymers, ceramics, metals, carbons, natural tissues, and composite materials (1). Of these materials, polymers remain the most widely used biomaterials. Polymeric materials have several advantages which make them very attractive as biomaterials (2). They include their versatility, physical properties, ability to be fabricated into various shapes and structures, and ease in surface modification. The long-term use of polymeric biomaterials in blood is limited by surface-induced thrombosis and biomaterial-associated infections (3,4). Thrombus formation on biomaterial surface is initiated by plasma protein adsorption followed by adhesion and activation of platelets (5,6). Biomaterial-associated infections occur as a result of the adhesion of bacteria onto the surface (7). The biomaterial surface provides a site for bacterial attachment and proliferation. Adherent bacteria are covered by a biofilm which supports bacterial growth while protecting them from antibodies, phagocytes, and antibiotics (8). Infections of vascular grafts, for instance, are usually associated with Pseudomonas aeruginosa Escherichia coli. Staphylococcus aureus, and Staphyloccocus epidermidis (9). 

Apart from polyplexes, various nanoscale assemblies of cationic polysaccharides are also proposed to promote the surface-mediated delivery of DNA to cells. These approaches are classified into one of two broad categories (i) methods based upon the physical adsorption of preformed polyplex on polymeric surfaces like PLGA or collagen films and these polyplex functionalized films promoted surface-mediated transfection of cells in vitro and in vivof (ii) methods for layer-by-layer adsorption of DNA and cationic polymers on surfaces to fabricate multilayered thin films. Recently, degradable carbohydrate-based nanogels were proposed for codelivery of pDNA and therapeutic proteins. These systems were designed to possess stimuli-sensitive characteristics where the temperature-sensitive property of nanogels allowed the facile encapsulation of biomaterials, while... 

Andersen, M. Q., Howard, K. A., Paludan, S. R., Besenbacher, F., Kjems, J. 2008. Delivery of siRNA from lyophilized polymeric surfaces. Biomaterials 29 506-512. 

Monomers, which polymerize via a free radical mechanism, can be polymerized on the activated support to produce coatings of various thicknesses and depths of penetration. Ionizing radiation has been extensively used for modifying the surfaces of biomaterials via surface grafting reactions. " ... 

Makal U, Wood L, Ohman DE, Wynne KJ. Polyurethane biocidal polymeric surface modifiers. Biomaterials 2006 27 1316-26. http //dx.doi.Org/10.1016/j.biomaterials.2005.08.038. 

This chapter provides a brief overview of some of the recent developments in the field of polymeric biomaterials with a particular emphasis on the articles included in this book (2-22). The research being done in this field is diverse and takes on several directions due to its multi disciplinary nature. It helps to organize these developments broadly into three sections (a) Synthetic approaches to polymer based biomaterials (b) characterization related development and (c) polymeric surfaces and (d) other biomedical applications of polymers. 

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. 

Polymers, both synthetic and natural, are the most diverse class of biomaterials. Polymeric biomaterials are widely used in both medical and pharmaceutical applications, and contribute significantly to the quality and effectiveness of health care. They are available in a wide variety of compositions and properties. They can readily be processed to form complex shapes with any size according to their final application. In addition, their surface properties, which are important in biological applications, may be readily modified by physical, chemical, or biochemical means. Their main disadvantage is the extractables in their structures (remaining after synthesis or fabrication processes), which may leach out during the use, and may lead undesirable effects on the host. 

Section 7.3 will describe tools we developed to synthesize and characterize soft dendritic nanostructured TPE biomaterials via living carbocationic polymerization, and decorate their surfaces with tissue-friendly groups. 

---