Adsorption of drugs on nanodiamond: toward development of a drug delivery platform.

Nanodiamond particles produced by detonation synthesis and having ∼5 nm diameter possess unique properties, including low cell toxicity, biocompatibility, stable structure, and highly tailorable surface chemistry, which render them an attractive material for developing drug delivery systems. Although the potential for nanodiamonds in delivery and sustained release of anticancer drugs has been recently demonstrated, very little is known about the details of adsorption/desorption equilibria of these and other drugs on/from nanodiamonds with different purity, surface chemistry, and agglomeration state. Since adsorption is the basic mechanism most commonly used for the loading of drugs onto nanodiamond, the fundamental studies into the details of adsorption and desorption on nanodiamond are critically important for the rational design of the nanodiamond drug delivery systems capable of targeted delivery and triggered release, while minimizing potential leaks of dangerous drugs. In this paper we report on a physical-chemical study of the adsorption of doxorubicin and polymyxin B on nanodiamonds, analyzing the role of purification and surface chemistry of the adsorbent.

Raman spectroscopy study of the nanodiamond-to-carbon onion transformation.

Here, we present a comprehensive study analyzing early stages of the transformation of detonation nanodiamond (ND) powder to graphitic carbon onions via thermal annealing in argon atmosphere. Raman spectroscopy was employed to monitor this transformation, starting with the sp³-to-sp² conversion of the ND surface at the onset of the graphitization process. Additionally, transmission electron microscopy, x-ray diffraction, and thermogravimetric analysis were used to supplement the structural information obtained from Raman spectroscopy and allow for an accurate interpretation of the obtained Raman data. The effect of the annealing time on the transformation process was also studied to determine the kinetics of the conversion at low temperatures. The results presented in this study complement previous work on ND annealing and provide deeper insight into the nanodiamond-to-carbon onion conversion mechanism, in particular the time and size dependence. We present further evidence for the existence of a disordered sp² phase as an intermediate step in the transformation process.

Multifrequency imaging in the intermittent contact mode of atomic force microscopy: beyond phase imaging.

The cantilever dynamics in single-frequency scanning probe microscopy (SPM) are undefined due to having only two output variables, which leads to poorly understood image contrast. To address this shortcoming, generalized phase imaging scanning probe microscopy (GP-SPM), based on broad band detection and multi-eigenmode operation, is developed and demonstrated on diamond nanoparticles with different functionalization layers. It is shown that rich information on tip-surface interactions can be acquired by separating the response amplitude, instant resonance frequency, and quality factor. The obtained data allow high-resolution imaging even in the ambient environment. By tuning the strength of tip-surface interaction, different surface functionalizations can be discerned.

Mechanical properties and biomineralization of multifunctional nanodiamond-PLLA composites for bone tissue engineering.

Multifunctional bone scaffold materials have been produced from a biodegradable polymer, poly(L-lactic acid) (PLLA), and 1-10% wt of octadecylamine-functionalized nanodiamond (ND-ODA) via solution casting followed by compression molding. By comparison to pure PLLA, the addition of 10% wt of ND-ODA resulted in a significant improvement of the mechanical properties of the composite matrix, including a 280% increase in the strain at failure and a 310% increase in fracture energy in tensile tests. The biomimetic process of bonelike apatite growth on the ND-ODA/PLLA scaffolds was studied using microscopic and spectroscopic techniques. The enhanced mechanical properties and the increased mineralization capability with higher ND-ODA concentration suggest that these biodegradable composites may potentially be useful for a variety of biomedical applications, including scaffolds for orthopedic regenerative engineering.

Covalent incorporation of aminated nanodiamond into an epoxy polymer network.

Outstanding mechanical and optical properties of diamond nanoparticles in combination with their biocompatibility have recently attracted much attention. Modification of the surface chemistry and incorporation into a polymer is required in many applications of the nanodiamond. Nanodiamond powder with reactive amino groups (∼20% of the number of surface carbon atoms in each 5 nm particle) was produced in this work by covalent linking of ethylenediamine to the surface carboxyl groups via amide bonds. The synthesized material was reacted with epoxy resin, yielding a composite, in which nanodiamond particles are covalently incorporated into the polymer matrix. The effect of amino groups grafted on the nanodiamond on the curing chemistry of the epoxy resin was analyzed and taken into consideration. Covalently bonded nanodiamond-epoxy composites showed a three times higher hardness, 50% higher Young's modulus, and two times lower creep compared to the composites in which the nanodiamond was not chemically linked to the matrix. Aminated nanodiamond produced and characterized in the present study may also find applications beyond the composites, for example, as a drug, protein, and gene delivery platform in biology and medicine, as a solid support in chromatography and separation science, and in solid state peptide synthesis.

Fluorescent PLLA-nanodiamond composites for bone tissue engineering.

Superior mechanical properties, rich surface chemistry, and good biocompatibility of diamond nanoparticles make them attractive in biomaterial applications. A multifunctional fluorescent composite bone scaffold material has been produced utilizing a biodegradable polymer, poly(l-lactic acid) (PLLA), and octadecylamine-functionalized nanodiamond (ND-ODA). The uniform dispersion of nanoparticles in the polymer led to significant increase in hardness and Young's modulus of the composites. Addition of 10%wt of ND-ODA resulted in more than 200% increase in Young's modulus and 800% increase in hardness, bringing the nanocomposite properties close to that of the human cortical bone. Testing of ND-ODA/PLLA as a matrix supporting murine osteoblast (7F2) cell growth for up to 1 week showed that the addition of ND-ODA had no negative effects on cell proliferation. ND-ODA serves as a multifunctional additive providing improved mechanical properties, bright fluorescence, and options for drug loading and delivery via surface modification. Thus ND-ODA/PLLA composites open up numerous avenues for their use as components of bone scaffolds and smart surgical tools such as fixation devices in musculoskeletal tissue engineering and regenerative medicine. Intense fluorescence of ND-ODA/PLLA scaffolds can be used to monitor bone re-growth replacing the implant in vivo.