Ioannis Neitzel

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 Youngs modulus of the composites. Addition of 10%wt of ND-ODA resulted in more than 200% increase in Youngs 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.

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 Youngs 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.

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.

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.

Electrical conductivity of thermally hydrogenated nanodiamond powders

Electrical properties of detonation diamond nanoparticles (NDs) with individual diameters of ∼5 nm are important for many applications. Although diamond is an insulator, it is known that hydrogen-terminated bulk diamond becomes conductive when exposed to water. We show that heating ND in hydrogen gas at 600–900 °C resulted in a remarkable decrease in resistivity from 107 to 105 Ω cm, while the resistivity was essentially unchanged after treatment at 400 °C and lower temperatures. Fourier Transform Infrared Spectroscopy and X-ray photoelectron spectroscopy (XPS) studies revealed that hydrogenation of ND occurs at 600–900 °C, suggesting that the decrease in resistivity is based on transfer doping at the hydrogenated ND surface. Oxidation of the hydrogenated sample at 300 °C recovers resistivity to its original value. The resistivity of treated ND as a function of the O/C atomic ratio showed a transition from resistive (O/C ratio > 0.033) to conductive (O/C ratio < 0.033) state. This is consistent with the i...

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.

Advances in Surface Chemistry of Nanodiamond and Nanodiamond-Polymer Composites

Nanodiamonds have excellent mechanical and optical properties, high surface areas and tunable surface structures. These properties make ND a highly promising material for nanocomposite applications, in particular, when used in polymer matrix composites. However, to take full advantage of nanodiamonds in composite applications, their purity, rational control of surface chemistry, dispersion in the matrix, and interface between the nanofiller and the matrix need to be considered. This chapter summarizes recent developments in the optimization of nanodiamond surface chemistry and application of this material in polymer matrix composites.

PLLA-Nanodiamond Composites and Their Application in Bone Tissue Engineering

Nanodiamond (ND) is an attractive nanomaterial for reinforcement of polymers [1] due to the ND’s superior mechanical and chemical properties, and low biotoxicity. A novel composite material has been produced for bone scaffolds utilizing the biodegradable polymer, poly(L-lactic acid) (PLLA), and octadecylamine-functionalized nanodiamond (ND-ODA) [2]. Composites were prepared by admixing to a PLLA/chloroform solution chloroform suspensions of ND-ODA at concentrations of 0, 1, 3, 5, 7, and 10 (w/w). Dispersion of ND-ODA in the composites was studied by transmission electron microscopy (TEM). The lower-resolution TEM micrograph of 1% wt ND-ODA/PLLA film (Fig. 1a) shows nanodiamond particles dispersed in PLLA film on amorphous carbon support. Due to long hydrocarbon chains of ODA the ND-ODA particles have good wettability with the PLLA so there is no segregation of ND-ODA and PLLA, and the polymer completely surrounds the particles. The high-resolution TEM image (Fig. 1b) shows ND crystals with attached organic material that can be ODA or PLLA. Nanoindentation tests show that the mechanical strength of ND-ODA/PLLA composites improves upon addition of ND (Table 1). Even at low concentrations (1% wt) the ND-ODA increased the hardness of the composite by 60% and Young’s modulus by 20% over neat PLLA. Based on our preliminary observations, we conclude that further additions of ND-ODA resulted in smaller changes with subsequent saturation in the mechanical properties at ∼7% wt (see Table 1). ND is relatively novel nanomaterial. Establishing its biocompatibility requires further studies, especially for modified ND. We studied the biocompatibility of 5–10nm ND and ND-ODA in experiments with a murine osteoblast cell line (7F2, from ATCC). Incubation of a cultured osteoblasts with 1–100μg/ml of ND or ND-ODA particles for 4 hours did not show much influence on the cell viability (Fig. 2), as inferred from an alamarBlue™ assay. To test the feasibility of ND-ODA/PLLA as a matrix material supporting cell growth, osteoblasts were cultured on the composites for 6 days. The attactment and proliferation of 7F2 cells on the scaffolds were assessed, respectively, by fluorescent nuclear staining with Hoechst 33258 and the alamarBlueTM assay. Our results showed that the addition of ND-ODA had only a negligibly small effect on cell proliferation, which is indicative of good biocompatibility of the composites (Fig. 3). The morphology of 7F2 cells growing on all ND-ODA/PLLA composite scaffolds was assessed by SEM. The data (not shown) confirm that the osteoblasts spread on the scaffolds similar to their spreading on TCP (tissue culture plastic). To summarize, the improved mechanical properties of the PLLA/ND-ODA composites and their good biocompatibility suggest that these materials may be suitable for applications in musculoskeletal tissue engineering.Copyright

Nanodiamonds in composites: polymer chemistry and tribology

Abstract Due to their versatile properties combined with a favorable strength-to-weight ratio, polymer composites find numerous applications in industry. To further improve their performance, new matrix and reinforcing materials are required. Nanocomposites, containing fillers with particle sizes smaller than 100 nm, hold a great potential to fulfill this demand. At these small length scales, the specific surface area becomes large and polymer–filler interactions, leading to the formation of an interphase with improved properties, can dominate the properties of the composite. Tailoring the properties of the interphase allows for creating new nanocomposite materials. The small size of detonation nanodiamond particles in combination with their superior mechanical properties (diamond properties) and rich surface chemistry makes nanodiamond the superior material for reinforcing and tuning polymer matrices, where it can act through changing the properties of the interphase as well as forming a strong covalent interface with the matrix. This chapter summarizes recent developments in applications of nanodiamond in polymer composites.