Local treatment of mixed osteolytic/osteoblastic spinal metastases: is photodynamic therapy effective?

The widespread use of systemic and local therapies aimed at spinal metastatic lesions secondary to breast cancer has increased the incidence of mixed osteolytic/osteoblastic patterns of bony disease. The complex structure of these lesions requires novel therapeutic approaches to both reduce tumor burden and restore structural stability. In photodynamic therapy (PDT), a minimally invasive approach can be used to employ light to activate a photosensitizing agent that preferentially accumulates in tumor tissue, leading to cell toxicity and death. Previous work in an osteolytic rat model (MT-1) demonstrated that PDT effectively ablates tumor and improves vertebral structural properties. The aim of this study was to assess the efficacy of PDT in a rat model of mixed osteolytic/osteoblastic spinal metastases. Mixed spinal metastases were generated through intracardiac injection of Ace-1 canine prostate cancer cells into female athymic rats (day 0). A single PDT treatment was applied to lumbar vertebra L2 of tumor-bearing and healthy control rats (day 14). PDT-treated and untreated control rats were euthanized and excised spines imaged with µCT to assess bone quality (day 21). Spines were mechanically tested or histologically processed to assess mechanical integrity, tumor burden, and remodelling properties. Untreated tumor-bearing vertebrae showed large areas of osteolysis and areas of immature, new bone formation. The overall bone quality resulting from these lesions consisted of decreased structural properties but without a significant reduction in mechanical integrity. PDT was shown to significantly decrease tumor burden and osteoclastic activity, thereby improving vertebral bone structural properties. While non-tumor-bearing vertebrae exhibited significantly more new bone formation following PDT, the already heightened level of new bone formation in the mixed tumor-bearing vertebrae was not further increased. As such, the effect of PDT on mixed metastases may be more influenced by suppression of osteoclastic resorption as opposed to the triggering of new bone formation.

First-principles study of the structural, elastic, and electronic properties of C(20), C(12)B(8), and C(12)N(8).

First-principles calculations were performed to study the structural, elastic, and electronic properties of the crystalline form of C(20), C(12)B(8), and C(12)N(8). These compounds exhibit very different elastic and electronic properties. The shear modulus of C(12)N(8) is much higher than those of C(20) and C(12)B(8). The strong covalent C-N interaction plays an important role in this high shear modulus. Compared with C(20), the relatively small Zener anisotropy of C(12)N(8) is mainly due to its large elastic constant (C(11) - C(12)). The calculated band structure shows that C(12)N(8) is an insulator with a direct band gap of 3 eV and the other two compounds (C(20) and C(12)B(8)) are metallic. Analysis of the band structure, density of states, and charge density show that the degree of filling in the non-bonding 2p(z) strongly affects the electronic properties. The full filling of the non-bonding orbital for C(12)N(8) results in its insulating behavior.

Dynamics of an ultrasonic transducer used for wire bonding.

The vibration displacement distributions along a transducer used in ultrasonic wire bonding were measured using a heterodyne interferometer, and many nodes and anti-nodes were found. A mechanical finite element method (FEM) was used to compute the resonant frequencies and vibration mode shapes. The displacement distributions of the dominant 2nd axial mode agreed well with the measured values. Undesirable nonaxial modes, including the higher order flexural and torsional modes, also were excited at frequencies very close to the working frequency (2nd axial mode) of the transducer. Hence, the measured displacements were the resultant of all the allowable modes being excited. However, the excitation of these nonaxial modes were small enough not to affect the formation of consistent and high quality wire bonds. Results of the present study were used to determine a suitable location for installing a piezoelectric sensor to monitor the bond quality.