# Immobilization of Detonation Nanodiamonds on Macroscopic Surfaces
## 4 Discussion  
This work describes the next step of application-oriented research into NDs with respect to biomedical applications. The objective was to evaluate the combination of scalable coating techniques and the drug-delivery capabilities of NDs. Widely-used biomaterials were coated with NDs by applying dip-coating, electrophoretic deposition, and covalent immobilization, using macroscopic, amine-terminated, silanized surfaces. The pragmatic study of ND coating behaviour and a qualitative assessment using nanoindentation and secondary electron microscopy shows the strongest and densest coating in the case of amide-bonded NDs. APTES will immobilize NDs due to an amide formation, where the covalent bond shows higher adhesive properties compared to the electrostatic and van der Waals interactions of physisorbed NDs. The present study is able to enhance the adhesion properties of immobilized NDs on biopolymer scaffolds. Recently, ND-modified, polymer-based bio-scaffolds are discussed for clinical applications. [PERSON] et al. showed an increased seeding efficiency of bone marrow stromal cells, due to the nanotopographical features of NDs in copolymer bio-scaffolds [51]. It has been shown that immobilized and protein functionalized NDs have improved in vivo vascularization and bone formation [52]. Oxygen-terminated NDs are an effective design to maximize the biological activity of an implant. [PERSON] et al. proved this concept using NDs as additives in poly(LLA-co-CL) scaffolds [53]. In conclusion, NDs are promising candidates for surface engineering approaches to biomaterials, and this work provides the information on various immobilization techniques. The surface of biomaterials plays a significant role during osseointegration. Immobilized nanoparticles on macroscopic rough surfaces describe a hierarchical structure. Fast in vivo bone formation ability and in vitro functionality of structured surfaces are ascribed to the synergistic effects of a hierarchical hybrid micro/nano-topography, according to [PERSON] et al. [53]. The macroscopic rough surface, e.g., obtained through sand-blasting, is a recommended substrate for the immobilization of nanoparticles. The successful conjugation of NDs to ssDNA through thioester bridges has been confirmed using fluorescent microscopy, particle size distribution, and zeta potential measurements. These measurements approve thioesters as a valid alternative coupling strategy to the previously discussed EDC/NHS-mediated amide formation. Drug delivery is an immensely complex task. As an initial step for further drug delivery platforms, we provide evidence of facile conjugation steps. Based on our results, we propose a combination of ssDNA-functionalised ND with the partial entrapment of adsorbed nuclei acids on Ti-based materials, for further cleavable immobilization strategies for NDs. We expect that it is possible to produce implant surfaces with high wear and infection resistance through the combination of the functionalisation potential with the structural improvements derived from the NDs. The immobilized NDs offer a huge variety of further options to link drug molecules to the implant surface, especially at the critical interface of soft tissue and implant surface. Despite our results, further experiments are required to pass the preclinical trials. In order to use the described immobilization techniques of NDs on metallic implant materials, the osteoblast cell behaviour is recommended for further investigations. The outcomes of the present study prove the concept of covalent immobilization strategies for NDs. Further experiments conducting a combination of electrophoretic deposition of carboxylated NDs and silanized surfaces, as well as biocompatibility tests of the surfaces are recommended. In order to address the translational relevance of ND-based coatings for biomedical applications, environmental pH and drug adsorption mechanisms should be considered.