Mads Bruun Hovgaard

Bovine serum albumin adsorption on nano-rough platinum surfaces studied by QCM-D

The adsorption of bovine serum albumin (BSA) on platinum surfaces with a root-mean-square roughness ranging from 1.49nm to 4.62nm was investigated using quartz crystal microbalance with dissipation (QCM-D). Two different BSA concentrations, 50microg/ml and 1mg/ml, were used, and the adsorption studies were complemented by monitoring the antibody interaction with the adsorbed BSA layer. The adsorption process was significantly influenced by the surface nano-roughness, and it was observed that the surface mass density of the adsorbed BSA layer is enhanced in a non-trivial way with the surface roughness. From a close examination of the energy dissipation vs. frequency shift plot obtained by the QCM-D technique, it was additionally observed that the BSA adsorption on the roughest surface is subject to several distinct adsorption phases revealing the presence of structural changes facilitated by the nano-rough surface morphology during the adsorption process. These changes were in particular noticeable for the adsorption at the low (50microg/ml) BSA concentration. The results confirm that the nano-rough surface morphology has a significant influence on both the BSA mass uptake and the functionality of the resulting protein layer.

In Vivo Toxicity of Silver Nanoparticles and Silver Ions in Zebrafish (Danio rerio)

The influence of water chemistry on characterised polyvinyl pyrrolidone- (PVP-) coated silver nanoparticles (81 nm) was investigated. NaCl solution series of 100–800 mg L−1 lead to initial and temporal increase in nanoparticles size, but agglomeration was limited. pH variation (5–8) had only minor influence on the hydrodynamic particle size. Acute toxicity of nanosivler to zebrafish (Danio rerio) was investigated in a 48-hour static renewal study and compared with the toxicity of silver ions (AgNO3). The nanosilver and silver ion 48-hour median lethal concentration (LC50) values were 84 μg L−1 and 25 μg L−1, respectively. To investigate exposure-related stress, the fish behaviour was observed visually after 0, 3, 6, 12, 24, 27, 30, and 48 hours of both nanosilver and ionic silver treatments. These observations revealed increased rate of operculum movement and surface respiration after nanosilver exposure, suggesting respiratory toxicity. The present study demonstrates that silver nanoparticles are lethal to zebrafish.

Fibronectin adsorption on tantalum: the influence of nanoroughness.

The complex mechanisms of protein adsorption at the solid-liquid interface is of great importance in many research areas, including protein purification, biocompatibility of medical implants, biosensing, and biofouling. The protein adsorption process depends crucially on both the nanoscale chemistry and topography of the interface. Here, we investigate the adsorption of the cell-binding protein fibronectin on flat and nanometer scale rough tantalum oxide surfaces using ellipsometry and quartz crystal microbalance with dissipation (QCM-D). On the flat tantalum oxide surfaces, the interfacial protein spreading causes an increase in the rigidity and a decrease in the thickness of the adsorbed fibronectin layer with decreasing bulk protein concentration. For the tantalum oxide surfaces with well-controlled, stochastic nanometer scale roughness, similar concentration effects are observed for the rigidity of the fibronectin layer and saturated fibronectin uptake. However, we find that the nanorough tantalum oxide surfaces promote additional protein conformational changes, an effect especially apparent from the QCM-D signals, interpreted as an additional stiffening of the formed fibronectin layers.

AFM-based force spectroscopy measurements of mature amyloid fibrils of the peptide glucagon

We report on the mechanical characterization of individual mature amyloid fibrils by atomic force microscopy (AFM) and AFM-based single-molecule force spectroscopy (SMFS). These self-assembling materials, formed from the 29-residue amphiphatic peptide hormone glucagon, were found to display a reversible elastic behaviour. Based on AFM morphology and SMFS studies, we suggest that the observed elasticity is due to a force-induced conformational transition which is reversible due to the β-helical conformation of protofibrils, allowing a high degree of extension. The elastic properties of such mature fibrils contribute to their high stability, suggesting that the internal hydrophobic interactions of amyloid fibrils are likely to be of fundamental importance in the assembly of amyloid fibrils and therefore for the understanding of the progression of their associated pathogenic disorders. In addition, such biological amyloid fibril structures with highly stable mechanical properties can potentially be used to produce nanofibres (nanowires) that may be suitable for nanotechnological applications.

Tantalum films with well-controlled roughness grown by oblique incidence deposition

We have investigated how tantalum films with well-controlled surface roughness can be grown by e-gun evaporation with oblique angle of incidence between the evaporation flux and the surface normal. Due to a more pronounced shadowing effect the root-mean-square roughness increases from about 2 to 33 nm as grazing incidence is approached. The exponent, characterizing the scaling of the root-mean-square roughness with length scale (α), varies from 0.75 to 0.93, and a clear correlation is found between the angle of incidence and root-mean-square roughness.

Influence of surface roughness on quartz crystal microbalance measurements in liquids

The influence of nanometer scale surface roughness on the frequency and dissipation responses of a quartz crystal microbalance operating in a liquid environment has been investigated by exposing quartz crystals, with a rough tantalum coating, to water solutions with varying concentrations of sucrose. A clear correlation between the measured surface roughness and the frequency shift is observed, while the shift in the dissipation factor is nearly unaffected by an increase in surface roughness. The experimental results are compared to published theoretical models for the frequency shift and shift in dissipation factor which incorporate roughness effects. For a high surface roughness the data cannot be satisfactorily explained by a model where the only effect of roughness is rigidly coupled liquid. A more advanced model, taking pressure gradients into account, provides a better description of the data.

Hydroxyapatite nanoparticles in poly-D,L-lactic acid coatings on porous titanium implants conducts bone formation.

It is well established in the field of biomaterials that hydroxyapatite (HA) may provide interesting osteoconductive properties. In this study, we investigated the osseointegrational effect of a 50/50 vol % composite of HA nanoparticles and poly-D,L-lactic acid (PDLLA) coated on model titanium bone implants in an in vivo animal model. The aim is to evaluate how the addition of HA to PDLLA may improve the bone formation and initial fixation of the implant. Two titanium implants coated with the PDLLA/HA composite and pure PDLLA, respectively, were implanted bilaterally in proximal part of humeri with a 2-mm peri-implant gap in 10 sheep. After 12 weeks, the remains of the coatings were present on 20.3 and 19.8% of PDLLA/HA composite- and PDLLA-coated implants, respectively. It was observed that newly formed bone (39.3%) and fibrous tissue (58.3%) had replaced the PDLLA/HA composite, whereas pure PDLLA was replaced almost completely by fibrous tissue (96.2%). Consequently, the PDLLA/HA composite-coated implants were better fixated as confirmed by push-out tests. Using quantification of peri-implant tissue and implant fixation as parameters, the present findings, therefore, clearly reveal that the addition of nanoparticulate HA to a PDLLA coating on titanium implants increases osseointegration.

Deposition at Glancing Angle, Surface Roughness, and Protein Adsorption : Monte Carlo Simulations

To generate rough surfaces in Monte Carlo simulations, we use the 2 + 1 solid-on-solid model of deposition with rapid transient diffusion of newly arrived atoms supplied at glancing angle. The surfaces generated are employed to scrutinize the effect of surface roughness on adsorption of globular and anisotropic rodlike proteins. The obtained results are compared with the available experimental data for Ta deposition at glancing angle and for the bovine serum albumin and fibrinogen uptake on the corresponding Ta films.

Self-assembled porphyrin microrods and observation of structure-induced iridescence

Self-assembled microrods {based on 5-nitro-10,15,20-trialkylporphyrins [(CnH2n+1)3-NO2P]} and microplates {based on 5,10,15,20-tetraheptylporphyrin [(C7H15)4-P]} are fabricated and characterised using optical microscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The length of the alkyl chains and the deposition surface are found to influence the optical properties and microrod self-assembly. When the deposition surface is silica (α-quartz), 5-nitro-trialkylporphyrins, (C5H11)3-NO2P, (C7H15)3-NO2P and (C11H23)3-NO2P all form microrods of 0.7–0.8 micron diameter; the average length of the microrods varies from 170 microns for (C5H11)3-NO2P to about 11 microns for (C7H15)3-NO2P and (C11H23)3-NO2P, whereas (C19H39)3-NO2P with much longer alkyl chains only gives powders. Controlling the precipitation is crucial in preventing the disordered aggregation of assembled layers observed in the bulk. Very interestingly, the microrods formed from (C7H15)3-NO2P show marked iridescent character. When (C7H15)3-NO2P is deposited on silicon, however, longer curved microrods which do not show iridescence are produced. Single crystal X-ray crystallography of (C7H15)3-NO2P reveals the packing of the bulk material which explains the packing topology of the layers observed by AFM but not the iridescence. The observed structural colour of the (C7H15)3-NO2P microrods is explained by staggering of the layers to produce a corrugated surface with a period of 125 nm, as measured by AFM.

Self-assembled photonic wires

The fabrication of ultra long molecular wires with photonic properties based on ionic self assembly of porphyrins are demonstrated.