Surface modification of polymeric biomaterials

The self-assembly and inhibition of protein adsorption by thiolated dextran monolayers at hydrophobic metal surfaces. In Ratner BD, Castner DG (eds) Surface modification of polymeric biomaterials. Plenum, New York, p 117... 

AMUI PARK Surface Modification of Polymeric Biomaterials... 

Surface modification of polymeric biomaterials is becoming an increasingly popular method to improve material multifunctional, biological... 

Amiji M, Park K. Surface modification of polymeric biomaterials with poly(ethylene oxide), albumin, and heparin for reduced thrombogenicity. J Biomater Sci Polym Ed 1993 4(3) 217-34. 

Guney, A., Kara, R, Ozgen, O., Aksoy, E.A., Hasirci, V., Hasird, N. Surface Modification of Polymeric Biomaterials. Biomaterials Surface Sdence. WQey-VCH Verlag/GmbH Co... 

In dentistry, silicones are primarily used as dental-impression materials where chemical- and bioinertness are critical, and, thus, thoroughly evaluated.546 The development of a method for the detection of antibodies to silicones has been reviewed,547 as the search for novel silicone biomaterials continues. Thus, aromatic polyamide-silicone resins have been reviewed as a new class of biomaterials.548 In a short review, the comparison of silicones with their major competitor in biomaterials, polyurethanes, has been conducted.549 But silicones are also used in the modification of polyurethanes and other polymers via co-polymerization, formation of IPNs, blending, or functionalization by grafting, affecting both bulk and surface characteristics of the materials, as discussed in the recent reviews.550-552 A number of papers deal specifically with surface modification of silicones for medical applications, as described in a recent reference.555 The role of silicones in biodegradable polyurethane co-polymers,554 and in other hydrolytically degradable co-polymers,555 was recently studied. 

Surface modification with hydrophilic polymers, such as poly(ethylene oxide) (PEO), has been beneficial in improving the blo( compatibility of polymeric biomaterials. Surface-bound PEO is expected to prevent plasma protein adsoiption, platelet adhesion, and bacterial adhesion by the steric repulsion mechanism. PEO-rich surfaces have been prepared either by physical adsorption, or by covalent grafting to the surface. Physically adsorbed PEO homopolymers and copolymers are not very effective since they can be easily displaced from the surface by plasma proteins and cells. Covalent grafting, on the other hand, provides a permanent layer of PEO on the surface. Various methods of PEO grafting to the surface and their effect on plasma protein adsorption, platelet adhesion, and bacterial adhesion is discussed. 

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). 

The important material properties which can influence protein and cell interactions at the biomaterial-biologic interface are listed in Table 2. It is probable that surface composition and topography most strongly influence the composition and organization of the initial adsorbed protein layer It is this layer which mediates subsequent cellular events at that interface. Thus, a great deal of effort has gone into surface modifications and characterization of polymeric biomaterials. 

The surface modification of biomaterials is also frequently achieved using plasmas. The physico-chemical properties of the material surface may be modified using plasma discharge in different gases, or a polymer coating may be deposited using plasma polymerization (cf. the section on Data Interpretation Through Simulation). A well-known example of the first approach is tissue-culture polystyrene (TCPS), which is commonly used to culture cells in vitro (Fig. 19). XPS shows that plasma... 

Plasma treatment and plasma deposition polymerization provides a unique and powerful method for the surface chemical modification of polymeric materials without altering their bulk properties. (7-5) These techniques offer the possibility to improve the performance of existing biomaterials and medical devices and for developing new biomaterials-(- -6)... 

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. 

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. 

One strategy is to fabricate a template structure using polymeric material (thus, using the same chemistry as described in Sects. 5.2 and 5.3) and back-fill or coat this structure with inorganic materials. For example, surface modification, followed by electroless deposition of Ag [217-219] or Cu [220], or by chemical reduction of Au solutions by surface functionalities [220], has been used to obtain metallized structures, while infiltration of polymeric photonic bandgap-type structures with Ti(0 Pr)4 solution, followed by hydrolysis and calcination, has been used to obtain highly refractive inverted Xi02 structures [221]. Au has also been deposited onto multiphoton-patterned matrices of biomaterials [194]. 

K. Fujimoto, H. Tadokoro, Y. Ueda, Y. Ikada, Polyurethane surface modification by graft polymerization of acrylamide for reduced protein adsorption and platelet adhesion. Biomaterials 14 (6) (1993) 442-448. 

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