A biocompatible hydrogel consisting of extracellular matrix (ECM) from human tendons is described as a potential scaffold for guided tissue regeneration and tissue engineering purposes. Lyophilized decellularized tendons were milled and enzymatically digested to form an ECM solution. The ECM solution properties are assessed by proteome analysis with mass spectrometry, and the material's rheological properties are determined as a function of frequency, temperature, and time. In vivo application of the gel in a rat model is assessed for remodeling and host cell repopulation. Histology for macrophage invasion, fibroblast repopulation, and nanoscale properties of the gel is assessed. Gel interaction with multipotent adipoderived stem cells (ASCs) is also addressed in vitro to assess possible cytotoxicity and its ability to act as a delivery vehicle for cells. Proteome analysis of the ECM-solution and gel mass spectroscopy identified the most abundant 150 proteins, of which two isoforms of collagen I represented more than 55% of the sample. Rheology showed that storage (G') and loss (G″) of the ECM solution were stable at room temperature but displayed sigmoidal increases after ∼15 min at 37°C, matching macroscopic observations of its thermo responsiveness. G' and G″ of the gel at 1 rad/s were 213.1±19.9 and 27.1±2.4 Pa, respectively. Electron microscopy revealed fiber alignment and good structural porosity in the gel, as well as invasion of cells in vivo. Histology also showed early CD68(+) macrophage invasion throughout the gel, followed by increasing numbers of fibroblast cells. ASCs mixed with the gel in vitro proliferated, indicating good biocompatibility. This ECM solution can be delivered percutaneously into a zone of tendon injury. After injection, the thermoresponsive behavior of the ECM solution allows it to polymerize and form a porous gel at body temperature. A supportive nanostructure of collagen fibers is established that conforms to the three-dimensional space of the defect. This hydrogel holds the distinctive composition specific for tendon ECM, where tissue-specific cues facilitate host cell infiltration and remodeling. The results presented indicate that injectable ECM materials from tendon may offer a promising alternative in the treatment of tendinopathies and acute tendon injuries.

SummaryIncreasing evidence suggests that local blood flow should be monitored during microdialysis (MD) as the recovery of analytes is affected by local blood flow. At present ethanol clearance is the standard technique for this purpose, but it is not functional at very low perfusion velocities. Here, we introduce a technique for MD whereby local tissue blood flow is recorded by the use of urea clearance (changes inflow⁄outflow concentration), in conjunction with measurements of tissue metabolism (glucose, lactate and puruvate). MD probes were inserted into the gracilis muscle of 15 rats and perfused with a medium containing urea (20 mmol l )1 ). Changes in muscle blood flow were made by addition of noradrenaline (5 lg ml) to the perfusion medium at two perfusion velocities (0AE6 and 0AE4 ll min )1 ). The clearance of urea from the perfusion medium was then calculated and examined in relation to the dose of noradrenaline and to the coexisting changes in extracellular metabolites. The results showed reproducible and dose-dependent changes in blood flow that were induced by noradrenaline. These were characterized by dose-dependent changes in the urea clearance as well as blood-flow-specific changes in the MD metabolic markers (reduction in glucose and increase in lactate). The sensitivity for blood flow changes as assessed by urea clearance (MD) was increased at 0AE4 compared with the 0AE6 ll min )1 perfusion speed. The results indicate that inclusion of urea to the perfusion medium may be used to monitor changes in skeletal muscle blood flow at low perfusion velocities and in parallel assess metabolic variables with a high recovery (>90%).

Objective. Electrical stimulation of the peripheral nervous system (PNS) can treat various diseases and disorders, including the healing process after nerve injury. A major challenge when designing electrodes for PNS stimulation is the mechanical mismatch between the nerve and the device, which can lead to non-conformal contact, tissue damage and inefficient stimulation due to current leakage. Soft and stretchable cuff electrodes promise to tackle these challenges but often have limited performance and rely on unconventional materials. The aim of this study is to develop a high performance soft and stretchable cuff electrode based on inert materials for low-voltage nerve stimulation. Approach. We developed 50 µm thick stretchable cuff electrodes based on silicone rubber, gold nanowire conductors and platinum coated nanowire electrodes. The electrode performance was characterized under strain cycling to assess the durability of the electrodes. The stimulation capability of the cuff electrodes was evaluated in an in vivo sciatic nerve rat model by measuring the electromyography response to various stimulation pulses. Main results. The stretchable cuff electrodes showed excellent stability for 50% strain cycling and one million stimulation pulses. Saturated homogeneous stimulation of the sciatic nerve was achieved at only 200 mV due to the excellent conformability of the electrodes, the low conductor resistance (0.3 Ohm sq−1), and the low electrode impedance. Significance. The developed stretchable cuff electrode combines favourable mechanical properties and good electrode performance with inert and stable materials, making it ideal for low power supply applications within bioelectronic medicine.

IntroductionMicrovascular changes in the skin due to pharmacological and physiological provocations can be used as a marker for vascular function. While laser Doppler flowmetry (LDF) has been used extensively for measurement of skin microvascular responses, Laser Speckle Contrast Imaging (LSCI) and Tissue Viability Imaging (TiVi) are novel imaging techniques. TiVi measures red blood cell concentration, while LDF and LSCI measure perfusion. Therefore, the aim of this study was to compare responses to provocations in the skin using these different techniques.MethodChanges in skin microcirculation were measured in healthy subjects during (1) iontophoresis of sodium nitroprusside (SNP) and noradrenaline (NA), (2) local heating and (3) post-occlusive reactive hyperemia (PORH) using LDF, LSCI and TiVi.ResultsIontophoresis of SNP increased perfusion (LSCI: baseline 40.9±6.2 PU; 10-min 100±25 PU; p<0.001) and RBC concentration (TiVi: baseline 119±18; 10-min 150±41 AU; p = 0.011). No change in perfusion (LSCI) was observed after iontophoresis of NA (baseline 38.0±4.4 PU; 10-min 38.9±5.0 PU; p = 0.64), while RBC concentration decreased (TiVi: baseline 59.6±11.8 AU; 10-min 54.4±13.3 AU; p = 0.021). Local heating increased perfusion (LDF: baseline 8.8±3.6 PU; max 112±55 PU; p<0.001, LSCI: baseline 50.8±8.0 PU; max 151±22 PU; p<0.001) and RBC concentration (TiVi: baseline 49.2±32.9 AU; max 99.3±28.3 AU; p<0.001). After 5 minutes of forearm occlusion with prior exsanguination, a decrease was seen in perfusion (LDF: p = 0.027; LSCI: p<0.001) and in RBC concentration (p = 0.045). Only LSCI showed a significant decrease in perfusion after 5 minutes of occlusion without prior exsanguination (p<0.001). Coefficients of variation were lower for LSCI and TiVi compared to LDF for most responses.ConclusionLSCI is more sensitive than TiVi for measuring microvascular changes during SNP-induced vasodilatation and forearm occlusion. TiVi is more sensitive to noradrenaline-induced vasoconstriction. LSCI and TiVi show lower inter-subject variability than LDF. These findings are important to consider when choosing measurement techniques for studying skin microvascular responses.