In vitro biostability evaluation of polyurethane composites in acidic, basic, oxidative, and neutral solutions

A passive biodegradable implant for subcutaneous soft-tissue trauma monitoring

In-body medical devices can play an important role in clinical monitoring and diagnosis of diseases. Wireless devices implanted within a patient have to be physically small, and must overcome the challenges of having a little or no onboard electrical power and the highly attenuating electromagnetic propagation environment which is the human body. In this paper, we investigate the use of biodegradable implant to monitor the healing of soft-tissue trauma and to allow early stage diagnosis of infection. The implantable tag is designed to degrade in a predetermined and controlled method, the stage of which can be measured from outside the body without the need for further surgical intervention. The speed of degradation of the tag depends on the temperature and acidity of the subcutaneous tissue in which the tag is implanted. We show that as the electrical length of the tag pattern increases due to degradation, the resonant frequency changes significantly, and this change in resonant frequency can be detected from outside the patient. Results are presented showing the tag's performance at normal and oblique incidence, and techniques for miniaturizing and enhancing the tag's response sensitivity are given. As the entire tag is biodegradable, there is no need for further postoperative surgery to remove it from the patient at the end of its useful life.

Degradation studies on segmented polyurethanes prepared with HMDI, PCL and different chain extenders

Biodegradable segmented polyurethanes (BSPUs) were prepared with poly(caprolactone) as a soft segment, 4,4'-methylene bis (cyclohexyl isocyanate) and either butanediol (BSPU1) or dithioerythritol (BSPU2) as a chain extender. BSPU samples were characterized in terms of their physicochemical properties and their hemocompatibility. Polymers were then degraded in acidic (HCl 2N), alkaline (NaOH 5M) and oxidative (H(2)O(2) 30wt.%) media and characterized by their mass loss, Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Undegraded BSPU1 and BSPU2 exhibited different properties, such as the glass transition temperature T(g) of the soft segment (-25 vs. 4 degrees C), mechanical properties (600% vs. 900% strain to break) and blood coagulating properties (clotting time=11.46 vs. 8.13min). After acidic and alkaline degradation, the disappearance of the 1728cm(-1) band of polycaprolactone (PCL) on both types of BSPU was detected by FTIR. However, the oxidative environment did not affect the soft segment severely as the presence of PCL crystalline domains were observed both by DSC (melting temperature T(m)=52.8 degrees C) and XRD (2theta=21.3 degrees and 23.7 degrees ). By TGA three decomposition temperatures were recorded for both BSPU samples, but the higher decomposition temperature was enhanced after acidic and alkaline degradation. The formation of the porous structure on BSPU1 was observed by SEM, while a granular surface was observed on BSPU2 after alkaline degradation.

Degradability of polymers for implantable biomedical devices

Many key components of implantable medical devices are made from polymeric materials. The functions of these materials include structural support, electrical insulation, protection of other materials from the environment of the body, and biocompatibility, as well as other things such as delivery of a therapeutic drug. In such roles, the stability and integrity of the polymer, over what can be a very long period of time, is very important. For most of these functions, stability over time is desired, but in other cases, the opposite–the degradation and disappearance of the polymer over time is required. In either case, it is important to understand both the chemistry that can lead to the degradation of polymers as well as the kinetics that controls these reactions. Hydrolysis and oxidation are the two classes of reactions that lead to the breaking down of polymers. Both are discussed in detail in the context of the environmental factors that impact the utility of various polymers for medical device applications. Understanding the chemistry and kinetics allows prediction of stability as well as explanations for observations such as porosity and the unexpected behavior of polymeric composite materials in some situations. In the last part, physical degradation such interfacial delamination in composites is discussed.