Engineering calcium deposits on polycaprolactone scaffolds for intravascular applications using primary human osteoblasts.

Total atherosclerotic occlusions often include significant calcium deposits. Current animal models do not mimic the pathology of gradual occlusion of arteries and lack cell-mediated calcium. The primary goal of this project was to establish an animal model incorporating these features into chronic total occlusions, using biodegradable scaffolds. As the first step, this study sought to determine the optimal dosage of TGF-ß1 on polycaprolactone (PCL) scaffolds cultured with primary human osteoblasts (HOBs) to effectively induce in vitro calcification. HOBs were cultured in TGF-ß1 and dexamethsaone (Dex)-supplemented medium in well plates. Calcium in the cultures was visualized using alizarin red. The highest calcification was observed in groups with both TGF-ß1 (0.02 ng/ml) and Dex (10(-10) M) in the medium. Next, HOBs were cultured on PCL scaffolds with different loadings of TGF-ß1: 0 (control), 5, 10, 50 and 100 ng. These cultures were performed with or without Dex (10(-10) M) in the medium. DNA content, ALP activity and the amount and distribution of calcium were examined at 7, 14, 21 and 28 days. TGF-ß1 appeared to have an inhibitory effect on scaffold calcification when grown in Dex-supplemented medium. When cultured without Dex, the lower amount of TGF-ß1 loading (5 ng) showed the most calcification, high DNA synthesis and high ALP activity on scaffolds. This study demonstrates the potential of implanting a PCL-HOB construct in an animal artery to establish a model of atherosclerotic occlusion with calcification.

Delivery of paclitaxel from cobalt-chromium alloy surfaces without polymeric carriers.

Polymer-based carriers are commonly used to deliver drugs from stents. However, adverse responses to polymer coatings have raised serious concerns. This research is focused on delivering drugs from stents without using polymers or any carriers. Paclitaxel (PAT), an anti-restenotic drug, has strong adhesion towards a variety of material surfaces. In this study, we have utilized such natural adhesion property of PAT to attach these molecules directly to cobalt-chromium (Co-Cr) alloy, an ultra-thin stent strut material. Four different groups of drug coated specimens were prepared by directly adding PAT to Co-Cr alloy surfaces: Group-A (PAT coated, unheated, and ethanol cleaned); Group-B (PAT coated, heat treated, and ethanol cleaned); Group-C (PAT coated, unheated, and not ethanol cleaned); and Group-D (PAT coated, heat treated and not ethanol cleaned). In vitro drug release of these specimens was investigated using high performance liquid chromatography. Groups A and B showed sustained PAT release for up to 56 days. A simple ethanol cleaning procedure after PAT deposition can remove the loosely bound drug crystals from the alloy surfaces and thereby allowing the remaining strongly bound drug molecules to be released at a sustained rate. The heat treatment after PAT coating further improved the stability of PAT on Co-Cr alloy and allowed the drug to be delivered at a much slower rate, especially during the initial 7 days. The specimens which were not cleaned in ethanol, Groups C and D, showed burst release. PAT coated Co-Cr alloy specimens were thoroughly characterized using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. These techniques were collectively useful in studying the morphology, distribution, and attachment of PAT molecules on Co-Cr alloy surfaces. Thus, this study suggests the potential for delivering paclitaxel from Co-Cr alloy surfaces without using any carriers.

Effect of post-deposition heating temperature and the presence of water vapor during heat treatment on crystallinity of calcium phosphate coatings.

In this study, radiofrequency sputtered calcium phosphate (CaP) coatings were evaluated after 1h post-deposition heat treatment at either 350 degrees C, 400 degrees C, 450 degrees C, 500 degrees C or 600 degrees C in the presence or absence of water vapor. X-ray diffraction analyses indicated the as-sputtered coatings to be amorphous. With different post-deposition heat treatments used, in this study, crystallinity of CaP coatings was observed to be in the range of 0-68%. The 400 degrees C and 450 degrees C heat-treated CaP coatings in the absence of water vapor were poorly crystalline, exhibiting a crystallinity of 2+/-1%. In comparison to heat treatments at 450 degrees C in the absence of water vapor, the presence of water vapor at 450 degrees C heat treatment resulted in a significant increase in coating crystallinity. However, this effect was not observed at higher temperatures. A coating crystallinity of 60-68% was observed for coatings heat treated at 450 degrees C in the presence of water vapor, and at 500 degrees C and 600 degrees C in the presence or absence of water vapor. In addition, increases in the degree of coating crystallinity were observed to be consistent with the increasing number of PO(4) peaks observed as a result of different post-deposition heat treatments. It was concluded that the presence of water vapor at 450 degrees C post-deposition heat treatment significantly affect the crystallinity of CaP coatings, whereas an increase to temperature higher than 450 degrees C and in the presence of water vapor has no significant effect on crystallinity.

Comparison of UHMWPE particles in synovial fluid and tissues from failed THA.

The size and morphology of ultra high molecular weight polyethylene (UHMWPE) wear particles isolated from synovial fluid and periprosthetic tissues from three failed total hip arthroplasties were evaluated. Hip capsule, femoral canal tissue, and synovial fluid were collected at the time of revision surgery. The polyethylene wear particles were isolated and then imaged using a scanning electron microscope. The size and morphology of the particles were quantified using an image analysis protocol. Five shape descriptors were defined for each particle: equivalent circle diameter (ECD, a measure of size having units of length), aspect ratio (AR), elongation (E), roundness (R), and form factor (FF). The size and shape of the polyethylene particles differed depending on the source. Femoral tissue particles had the lowest equivalent circle diameter (0.697 +/- 0.009 mm), aspect ratio (1.577 +/- 0.016), and elongation (1.912 +/- 0.030), but the highest values for roundness (0.715 +/- 0.005) and form factor (0.874 +/- 0.003). Hip capsule particles had the highest equivalent circle diameter (0.914 +/- 0.019 mm), aspect ratio (1.764 +/- 0.025), and elongation (2.488 +/- 0.053), but the lowest values for roundness (0.642 +/- 0.006) and form factor (0.803 +/- 0.005). The size and shape descriptors for synovial fluid particles (equivalent circle diameter: 0.763 +/- 0.012 mm; aspect ratio: 1.700 +/- 0.029; elongation: 2.212 +/- 0.054; roundness: 0.681 +/- 0.006; and form factor: 0.841 +/- 0.004) were intermediate among the femoral tissue and hip capsule particles. These data suggest that larger particles may become lodged in the hip capsule, while smaller particles may migrate to more distant tissues and subsequently cause aseptic loosening and osteolysis.