Biology subjects

Lamont, C.

Publications and source records attributed to Lamont, C..

3 recordsLinked to original sources

bioRxiv2025

On the Stability of Silicone-Encapsulated CMOS ICs for Active Implantable Devices: 4.3 Years of Accelerated Life Testing

The reliability of polymer-encapsulated CMOS integrated circuits (ICs) is critical for the development of miniaturised active implantable medical devices (AIMDs). Traditional hermetic packaging methods become impractical as implant sizes decrease, necessitating alternative methods of protection from body fluids. This study evaluates the long-term stability of silicone-encapsulated CMOS ICs through accelerated life testing using electrical impedance spectroscopy (EIS) and visual inspection. CMOS interdigitated combs (IDCs) were encapsulated in medical grade silicone rubber, subjected to immersion in phosphate-buffered saline (PBS), and tested at elevated temperatures (47{degrees}C, 67{degrees}C, and 87{degrees}C) under both 5V DC and biphasic voltage biases for up to 4.3 years. Remarkably, no insulation failures were observed in the IDCs, with no significant water ingress detected through impedance changes. Failures at the ICs were limited to wire bond open-circuits, though there was some pad discolouration/corrosion. Other failures were elsewhere, not at the ICs. This highlights the stability of modern silicon oxide/silicon nitride bilayer passivation when encapsulated in adhesive silicone rubber. Visual analysis revealed occasional solder and aluminium pad corrosion, particularly at higher temperatures, but these changes did not correlate with EIS failures. The findings suggest that silicone encapsulation, combined with passivation and shielding strategies, enables long-term IC reliability in biofluid environments. To our knowledge, this paper presents the longest reported accelerated ageing study of test structures for implantable devices, laying the groundwork for the integration of silicone-encapsulated ICs into next-generation chip-scale bioelectronic implants.

biochemistry↗

bioRxiv2024

Longevity of Implantable Silicon-ICs for Emerging Neural Applications: Evaluation of Bare Die and PDMS-Coated ICs After Accelerated Aging and Implantation Studies

Silicon integrated circuits (ICs) are central to the next-generation miniature active neural implants, whether packaged in soft polymers for flexible bioelectronics or implanted as bare die for neural probes. These emerging applications bring the IC closer to the corrosive body environment, raising reliability concerns, particularly for long-term clinical use. Here, we evaluated the long-term electrical and material stability of silicon-ICs from two foundries, after one-year accelerated in vitro and in vivo animal studies. The ICs featured various custom-designed test structures and were partially PDMS coated, creating two regions on each chip, uncoated "bare die" and "PDMS-coated". During the accelerated in vitro study, ICs were electrically biased and periodically monitored. Results demonstrated stable electrical performance for at least a year, suggesting that bare die ICs can function in the body for months. Despite electrical stability, material analysis revealed chemical and electrically driven degradation of the IC passivation in the bare die regions. In contrast, PDMS-coated regions revealed no such degradation, making PDMS a highly suitable encapsulant for ICs intended for years-long implantation. Based on the new insights, guidelines are proposed that may enhance the longevity of implantable ICs, significantly broadening their applications in the biomedical field.

neuroscience↗

bioRxiv2017

Mathematical modeling of tumor-tumor distant interactions supports a systemic control of tumor growth

Interactions between different tumors within the same organism have major clinical implications, especially in the context of surgery and metastatic disease. Three main explanatory theories (competition, angiogenesis inhibition and proliferation inhibition) have been proposed but precise determinants of the phenomenon remain poorly understood. Here we formalized these theories into mathematical models and performed biological experiments to test them with empirical data. In syngeneic mice bearing two simultaneously implanted tumors, growth of only one of the tumors was significantly suppressed (61% size reduction at day 15, p<0.05). The competition model had to be rejected while the angiogenesis inhibition and proliferation inhibition models were able to describe the data. Additional models including a theory based on distant cytotoxic log-kill effects were unable to fit the data. The proliferation inhibition model was identifiable and minimal (4 parameters), and its descriptive power was validated against the data, including consistency in predictions of single tumor growth when no secondary tumor was present. This theory may also shed new light on single cancer growth insofar as it offers a biologically translatable picture of how local and global action may combine to control local tumor growth, and in particular, the role of tumor-tumor inhibition. This model offers a depiction of concomitant resistance that provides an improved theoretical basis for tumor growth control and may also find utility in therapeutic planning to avoid post-surgery metastatic acceleration.

cancer biology↗