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ObjectiveThis study investigated the effects of the inflammatory tissue response (ITR) to an insulin infusion set (IIS) on insulin bolus spread over wear time, as well as the effect of cannula insertion angle on the ITR, bolus shape, and pump tubing pressure.Research design and methodsAngled or straight IISs were inserted every other day for 14 days into the subcutaneous tissue of 11 swine and insulin was delivered continuously. Prior to euthanasia, a 70 µL bolus of insulin/X-ray contrast agent was infused while recording a pressure profile (peak tubing pressure, pmax; area under the pressure curve, AUC), followed by the excision of the tissue-catheter specimen. Bolus surface area (SA) and volume (V) were assessed via micro-CT. Tissue was stained to analyze total area of inflammation (TAI) and inflammatory layer thickness (ILT) surrounding the cannula.ResultsA bolus delivered through an angled IIS had a larger mean SA than a bolus delivered through a straight cannula (314.0±84.2 mm2 vs 229.0±99.7 mm2, p<0.001) and a larger volume (198.7±66.9 mm3 vs 145.0±65.9 mm3, p=0.001). Both decreased significantly over wear time, independent of angle. There was a significant difference in TAI (angled, 9.1±4.0 mm2 vs straight, 14.3±8.6 mm2, p<0.001) and ILT (angled, 0.7±0.4 vs straight, 1.2±0.7 mm, p<0.001). pmax (p=0.005) and AUC (p=0.014) were lower using angled IIS. As ILT increased, pmax increased, while SA and V decreased.ConclusionsThe progression of the ITR directly affected bolus shape and tubing pressure. Although straight insertion is clinically preferred, our data suggest that an angled IIS elicits lower grades of ITR and delivers a bolus with lower tubing pressure and greater SA and V. The subcutaneous environment plays a crucial role in IIS longevity, and the insertion angle needs to be considered in future IIS designs and clinical trials.

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The goal of this study was to better understand how analytical permeability models based on scaffold architecture can facilitate a non-invasive technique to real time monitoring of pressure drop in bioreactors. In particular, we evaluated the permeability equations for electrospun and freeze dried scaffolds via pressure drop comparison in an axial-flow bioreactor using computational fluid dynamic (CFD) and experimentation. The polycaprolactone-cellulose acetate fibers obtained by co-axial electrospinning technique and Chitosan-Gelatin scaffolds prepared using freeze-drying techniques were utilized. Initially, the structural properties (fiber size, pore size and porosity) and mechanical properties (elastic modulus and Poisson's ratio) of scaffolds in phosphate buffered saline at 37 °C were evaluated. The CFD simulations were performed by coupling fluid flow, described by Brinkman equation, with structural mechanics using a moving mesh. The experimentally obtained pressure drop values for both 1 mm thick and 2 mm thick scaffolds agreed with simulation results. To evaluate the effect of permeability and elastic modulus on pressure drop, CFD predictions were extended to a broad range of permeabilities spanning synthetic scaffolds and tissues, elastic moduli, and Poisson's ratio. Results indicated an increase in pressure drop with increase in permeability. Scaffolds with higher elastic modulus performed better and the effect of Poisson's ratio was insignificant. Flow induced deformation was negligible in axial-flow bioreactor. In summary, scaffold permeabilities can be calculated using scaffold microarchitecture and can be used in non-invasive monitoring of tissue regeneration.

This study evaluated the effect of scaffold processing methods on viscoelastic properties of polycaprolactone (PCL), a frequently explored biomaterial in tissue engineering. 80 kDa and 45 kDa PCL scaffolds were synthesized using salt leaching and electrospinning techniques. Also, films were formed by air drying. Scanning electron microscopy analysis confirmed that salt leached scaffolds had open pore architecture and electrospun scaffolds had randomly distributed uniform fibers. Using the tensile test results in phosphate buffered saline (pH57.4) and 37 C, ramp-hold tests were performed for five stages by setting the strain rate to be 1%s 21 for 2 s followed by 58 s of hold. Also, tests were performed at various strain rates and total strain. Salt leached scaffolds of same MW showed less relaxation in each stage relative to electrospun scaffolds. 45 kDa salt leached scaffolds relaxed more than 80 kDa scaffolds. Stress accumulated in each stage was more in films than in scaffolds. However, relaxation function appeared similar between films and electrospun fibers. Strain rate and amount of applied strain had significant effect on relaxation characteristics; 0.6%s 21 strain rate had higher accumulated stress than 1%s 21 and 3%s 21 . Increased amount of loading had significant effect in the first stage with repetitive relaxation characteristics in subsequent stages. SEM analysis of tested samples showed no change in the microstructure with the exception of a few locations where pores oriented in the direction of the pull. In summary, viscoelastic characteristics vary based on the type of scaffold processing used, despite use of the same polymer. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4237-4244, 2013