Surface characteristics of holmium-loaded poly(L-lactic acid) microspheres.

Radioactive holmium-166-loaded poly(L-lactic acid) microspheres (Ho-PLLA-MS) are promising systems for the treatment of liver malignancies. The surface characteristics of Ho-PLLA-MS before and after both neutron and gamma irradiation were investigated in order to get insight into their suspending behaviour and to identify suitable surfactants for clinical application of these systems. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used for surface characterization. The residual amounts of poly(vinyl alcohol) (PVA) of the microspheres, which was used as an emulsifier during the solvent evaporation process, were determined using a colorimetric iodine-borate method and the wettability of microspheres and PLLA films with and without holmium (Ho) loading was tested using suspending experiments and contact angle measurements. XPS showed that the surface of Ho-PLLA-MS mainly consisted of PLLA, less than 10% of the surface was covered with PVA after several washing and sieving steps. A colorimetric assay showed that the microspheres contained 0.2-0.3% (w/w) PVA. Combined with XPS data, this assay demonstrates that the PVA is likely dissolved in the core of the microspheres. XPS analysis also showed that after neutron irradiation, some holmium appeared on the surface. Moreover, Ho-loaded PLLA films had a much higher contact angle (85 degrees) than non-loaded films (70 degrees). Therefore, the Ho on the surface of neutron-irradiated Ho-PLLA-MS is probably the reason for their poor suspending behaviour in saline. No surface changes were seen with XPS after gamma irradiation. Based on their surface characteristics, a pharmaceutically acceptable solvent (1% Pluronic F68 or F127 in 10% ethanol) was formulated with which a homogeneous suspension of radioactive Ho-PLLA-MS could be easily obtained, making these systems feasible for further clinical evaluation.

Stretch-mediated responses of osteoblast-like cells cultured on titanium-coated substrates in vitro.

Cyclic stretching experiments on osteoblast-like cells have proven to be a useful tool in understanding the underlying mechanisms of load transduction at the bone-implant surface. However, most experimental setups use silicone rubber substrates, which are atypical for orthopedic and dental implant materials. Therefore, we investigated the responses of osteoblast-like cells to loading on titanium (Ti)-coated versus plain silicone substrates. Ti-coated substrates were made by a radio-frequency magnetron sputtering process, and characterized using Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, and contact-angle measurements. Osteoblast-like cells cultured from rat bone marrow were seeded on both types of substrates and stretched for 1 h continuously. Subsequently, cell proliferation, alkaline phosphatase activity, and calcium content were measured for up to 24 days after seeding. In addition light-, scanning electron-, and confocal laser scanning micrographs were made. The results showed that our Ti coating had a thickness of 50 nm and contained Ti/oxygen as 1:1. However, further characterization proved that the silicone material had a tendency to resurface through the coating. Osteoblast-like cells proliferated faster on the Ti-coated substrates, but differentiation was slower compared with the silicone substrates. It was concluded that that there was a definitive influence of the substrate material in mechanical stress models. Therefore, extrapolation of results obtained using silicone substrates cannot be translated directly toward the situation of metallic implant materials.

Initial deposition of calcium phosphate ceramic on polyethylene and polydimethylsiloxane by rf magnetron sputtering deposition: the interface chemistry.

Calcium phosphate (CaP) coatings are well known for their bioactive nature. CaP coated polymeric materials can be used as implant material. For this, a strong adhesion between the coating and substrate is necessary. Because the chemical structure of the interface plays an important role in the coating adhesion, we studied the interface between CaP and the polymers polyethylene (PE) and polydimethylsiloxane (PDMS/silicone rubber). Both untreated and plasma pretreated polymers were used. On PE, a low Ca/P ratio nearby the interface and a high amount of C-O bonds were found on both untreated and plasma pretreated PE. This is the result of phosphate-like groups that are able to bind to the carbon of the PE. PDMS reacts towards the plasma pretreatment by losing CH(3) side groups. Compared to PE, a low amount of C-O bonds is found nearby the interface. Besides, a low Ca/P ratio is found nearby the interface. This is the result of phosphate groups that connect to Si atoms of the PDMS, thereby replacing the CH(3) side groups. The bombardment by negatively charged oxygen ions that are accelerated from the target during the deposition process makes the chemical interaction between the coating and the substrates possible.