Metallic biocompatibility

Fig. 11.11 Various methods of bio-conjugation, (a) Direct immobilization of the linker molecule to the metal surface, (b) composite formation of the metal/biocompatible shell hybrids, (c) examples of direct immobilization to metal surface [77, 81, 82], (d) examples of active ester utilization [70, 80], and (e) an example of malelmide-based bio-conjugatlon [33]...

Key words degradable metals, biocompatibility, in vivo corrosion, in vitro corrosion, magnesium implant. 

M. Szycher, Biocompatible Polymers, Metals and Composites, Technomic Publishing Co., Inc., Lancaster, Pa., 1983. 

Hydroxyapaite, the mineral constituent of bone, is appHed to the surfaces of many dental implants for the purpose of increasing initial bone growth. Some iavestigators beHeve that an added benefit is that the hydroxyapatite shields the bone from the metal. However, titanium and its aHoy, Ti-6A1-4V, are biocompatible and have anchored successfuHy as dental implants without the hydroxyapatite coating. 

Nearly all synthetic pathways discussed in Section 3 can principally be applied to synthesize biocompatible metal... 

In a different way, metallic-core nanoparticles [346-349] (prepared cf. Section 3.10) equipped with biocompatible coats such as L-cysteine or dextrane may be exploited for highly efficient and cell-specific cancer cell targeting, i.e., for improving diagnosis and therapy of human cancer. In a recent proof-of-principle experiment an unexpectedly low toxicity of the L-cysteine-covered cobalt nanoparticles was demonstrated [433] For diagnostic purposes, it is expected to use the advantageous magnetic properties of the metallic-core nanoparticles to obtain a contrast medium for MRI with considerably increased sensitivity, capable to detect micro-metastases in the environment of healthy tissues [434 37]. 

In the past few years, a large number of experimental and theoretical studies have focused on metal oxide surfaces with the aim of gaining insight into their catalytic, photocatalytic, and gas-sensing activity [68]. Owing to its thermodynamic stability and relatively easy preparation, the rutile Ti02(l 10) surface has evolved into one of the key models for metal oxide surfaces. For example, it has been extensively used in the research of biocompatible materials, gas sensors, and photocatalysts [69]. 

Figure 2.3 SAM surface modification has been done using monothiol and dithiol compounds containing PEG linkers. Useful coatings typically contain mainly PEG-hydroxyl or PEG-monomethyl ether linkers that provide a biocompatible lawn, which prevents nonspecific binding of proteins to the metallic surface. About 10 percent of the surface modifications are done using a longer carboxylate-containing thiol-PEG linker that provides sites for attachment of affinity ligands.

Dendrimers can be used to effectively coat and passivate fluorescent quantum dots to make biocompatible surfaces for coupling proteins or other biomolecules. In addition, the ability of dendrimers to contain guest molecules within their three-dimensional structure also has led to the creation of dendrimer-metal nanoclusters having fluorescent properties. In both applications, dendrimers are used to envelop metal or semiconductor nanoparticles that possess fluorescent properties useful for biological detection. 

Figure 9.60 Many different thiol-containing linkers can be used to prepare water-soluble QDs. The monothiol compounds suffer from the deficiency of being easily oxidized or displaced off the surface, thus creating holes for potential nonspecific binding. The dithiol linkers are superior in this regard, as they form highly stable dative bonds with the semiconductor metal surface that do not get displaced. The PEG-based linkers are especially effective at creating a biocompatible surface for conjugation with biomolecules.

---