A microfluidic approach to studying the injection flow of concentrated albumin solutions

Subcutaneous injection by means of prefilled syringes allows patients to self-administrate high-concentration (100 g/L or more) protein-based drugs. Although the shear flow of concentrated globulins or monoclonal antibodies has been intensively studied and related to the injection force proper of SC processes, very small attention has been paid to the extensional behavior of this category of complex fluids. This work focuses on the flow of concentrated bovine serum albumin (BSA) solutions through a microfluidic “syringe-on-chip” contraction device which shares some similarities with the geometry of syringes used in SC self-injection. By comparing the velocity and pressure measurements in complex flow with rheometric shear measurements obtained by means of the “Rheo-chip” device, it is shown that the extensional viscosity plays an important role in the injection process of protinaceous drugs. Article Highlights A microfluidic “syringe on chip” device mimicking the injection flow of protinaceous drugs has been developed. The velocity field of concentrated BSA solutions through the “syringe on chip” is Newtonian-like. The extensional viscosity of concentrated protein solutions should also be considered when computing injection forces through needles.

Injectability of Thermosensitive, Low-Concentrated Chitosan Colloids as Flow Phenomenon through the Capillary under High Shear Rate Conditions

Low-concentrated colloidal chitosan systems undergoing a thermally induced sol–gel phase transition are willingly studied due to their potential use as minimally invasive injectable scaffolds. Nevertheless, instrumental injectability tests to determine their clinical utility are rarely performed. The aim of this work was to analyze the flow phenomenon of thermosensitive chitosan systems with the addition of disodium β-glycerophosphate through hypodermic needles. Injectability tests were performed using a texture analyzer and hypodermic needles in the sizes 14G–25G. The rheological properties were determined by the flow curve, three-interval thixotropy test (3ITT), and Cox–Merz rule. It was found that reducing the needle diameter and increasing its length and the crosshead speed increased the injection forces. It was claimed that under the considered flow conditions, there was no need to take into account the viscoelastic properties of the medium, and the model used to predict the injection force, based solely on the shear-thinning nature of the experimental material, showed very good agreement with the experimental data in the shear rate range of 200–55,000 s−1. It was observed that the increase in the shear rate value led to macroscopic structural changes of the chitosan sol caused by the disentangling and ordering of the polysaccharide chains along the shear field.

A Medium Viscous Acrylic Cement Enhances Uniformity of Cement Filling and Reduces Leakage in Cancellous Bone Augmentation

Vertebroplasty is an efficient procedure to treat osteoporotic vertebral fractures. Cement leakage is considered to be the most severe complication during vertebroplasty. At high cement viscosities, the risk of leakage is reduced. However, injection forces are highly increased, requiring the use of high force injection systems with the lack in tactile force feedback. Therefore, an acrylic cement was developed showing medium initial viscosity and which still allows to be manually applied using syringes. An established model favoring leakage was used to observe the filling pattern and leaked cement mass. The method used included the simulation of body temperature, and all materials submitted are approved medical products. When applied just after preparation, the medium viscous cement resulted in good cement filling and less cement leakage than low viscosity cement. The added clinical value of the new cement is that the waiting time for the physician will be shortened to zero minutes without compromising the safety for the procedure.