Thermophoretic manipulation of the mechanical properties of biomaterials in microfluidics

The optimization of cell-substrate and cell-cell interactions is a central objective in tissue engineering applications. There is great potential to modulate and improve such interactions using extra cellular matrices that exhibit a gradient of mechanical properties that mimic accurately the in vivo tissue microenvironment and modulate cell behavior especially at the microscale. Here we show that by applying temperature gradients across a microfluidic channel and exploiting thermophoretic transport effects, it is possible to fabricate biocompatible hydrogels with controllable stiffness and porosity gradients. The elasticity of the hydrogels was evaluated locally by Atomic Force Microscopy revealing values between 20-100 kPa. The hydrogel microstructure was investigated by Scanning Electron Microscopy after supercritical drying and confirms the concentration gradient induced by thermophoresis. Moreover, we show that the stiffness gradient of the biomaterials can be effectively modulated by regulating the temperature difference across the microfluidic device and altering the concentration of gellan gum. Furthermore, the proliferation and level of mineralization of MC3T3 osteoblasts, seeded on the surface of the biomaterial, was monitored over time at different stiffness areas and time points, using live/dead assays and X-Ray Fluorescence technique. Cells show a preferential migration and proliferation towards the stiffer side where they also produce a higher mineralization (i.e., phosphorus and calcium deposits). Taken together, these results establish a new route to controlling the microstructure of cell culture matrices

Fabrication of gradient hydrogels using a thermophoretic approach in microfluidics

The extracellular matrix presents spatially varying physical cues that can influence cell behavior in many processes. Physical gradients within hydrogels that mimic the heterogenous mechanical microenvironment are useful to study the impact of these cues on cellular responses. Therefore, simple and reliable techniques to create such gradient hydrogels are highly desirable. This work demonstrates the fabrication of stiffness gradient Gellan gum (GG) hydrogels by applying a temperature gradient across a microchannel containing hydrogel precursor solution. Thermophoretic migration of components within the precursor solution generates a concentration gradient that mirrors the temperature gradient profile, which translates into mechanical gradients upon crosslinking. Using this technique, GG hydrogels with stiffness gradients ranging from 20 to 90 kPa over 600 µm are created, covering the elastic moduli typical of moderately hard to hard tissues. MC3T3 osteoblast cells are then cultured on these gradient substrates, which exhibit preferential migration and enhanced osteogenic potential toward the stiffest region on the gradient. Overall, the thermophoretic approach provides a non-toxic and effective method to create hydrogels with defined mechanical gradients at the micron scale suitable for in vitro biological studies and potentially tissue engineering applications

Fabrication of gradient hydrogels using a thermophoretic approach in microfluidics

The extracellular matrix presents spatially varying physical cues that can influence cell behavior in many processes. Physical gradients within hydrogels that mimic the heterogenous mechanical microenvironment are useful to study the impact of these cues on cellular responses. Therefore, simple and reliable techniques to create such gradient hydrogels are highly desirable. This work demonstrates the fabrication of stiffness gradient Gellan gum (GG) hydrogels by applying a temperature gradient across a microchannel containing hydrogel precursor solution. Thermophoretic migration of components within the precursor solution generates a concentration gradient that mirrors the temperature gradient profile, which translates into mechanical gradients upon crosslinking. Using this technique, GG hydrogels with stiffness gradients ranging from 20 to 90 kPa over 600 µm are created, covering the elastic moduli typical of moderately hard to hard tissues. MC3T3 osteoblast cells are then cultured on these gradient substrates, which exhibit preferential migration and enhanced osteogenic potential toward the stiffest region on the gradient. Overall, the thermophoretic approach provides a non-toxic and effective method to create hydrogels with defined mechanical gradients at the micron scale suitable for in vitro biological studies and potentially tissue engineering applications

Fabrication of gradient hydrogels using a thermophoretic approach in microfluidics.

Funder: Biotechnology and Biological Sciences Research Council; doi: http://dx.doi.org/10.13039/501100000268Funder: Wellcome Trust; doi: http://dx.doi.org/10.13039/100010269The extracellular matrix presents spatially varying physical cues that can influence cell behavior in many processes. Physical gradients within hydrogels that mimic the heterogenous mechanical microenvironment are useful to study the impact of these cues on cellular responses. Therefore, simple and reliable techniques to create such gradient hydrogels are highly desirable. This work demonstrates the fabrication of stiffness gradient Gellan gum (GG) hydrogels by applying a temperature gradient across a microchannel containing hydrogel precursor solution. Thermophoretic migration of components within the precursor solution generates a concentration gradient that mirrors the temperature gradient profile, which translates into mechanical gradients upon crosslinking. Using this technique, GG hydrogels with stiffness gradients ranging from 20 to 90 kPa over 600µm are created, covering the elastic moduli typical of moderately hard to hard tissues. MC3T3 osteoblast cells are then cultured on these gradient substrates, which exhibit preferential migration and enhanced osteogenic potential toward the stiffest region on the gradient. Overall, the thermophoretic approach provides a non-toxic and effective method to create hydrogels with defined mechanical gradients at the micron scale suitable forin vitrobiological studies and potentially tissue engineering applications

Carboplatin and Paclitaxel versus Cisplatin, Paclitaxel and Doxorubicin for first-line chemotherapy of Advanced Ovarian Cancer: A Hellenic Cooperative Oncology Group (HeCOG) study

Introduction: The combination of Carboplatin and Paclitaxel is considered the standard of care as initial chemotherapy for Advanced Ovarian Cancer (AOC). We compared this regimen with the combination of Cisplatin, Paclitaxel and Doxorubicin. Patients and methods: Patients with AOC were randomised to either six courses of Paclitaxel 175 mg/m(2) plus Carboplatin 7AUC or Paclitaxel at the same dose plus Cisplatin 75 mg/m(2) plus Doxorubicin 40 mg/m(2). Results: Analysis was performed on 451 patients. The treatment groups were well balanced with regard to patient and disease characteristics. Performance status (PS) was better in the anthracycline arm. In terms of severe toxicity, the only significant difference between the two groups was the development of febrile neutropaenia in the anthracycline arm. Overall response rate was similar in both groups. With a median follow-up of 57.5 months, a marginal significance towards improved Progression-Free Survival (PFS) was noted in favour of the anthracycline arm, whilst there was no difference in overall survival. In multivariate analysis the hazard of disease progression at any time was significantly decreased by 25.5% for patients of the anthracycline arm. Conclusion: The combination of Cisplatin, Paclitaxel and Doxorubicin demonstrates a marginal PFS improvement, but no additional survival benefit when compared with the standard Carboplatin/Paclitaxel regimen. (c) 2008 Elsevier Ltd. All rights reserved