In vitro studies of biocompatible thermo-responsive hydrogels with controlled-release basic fibroblast growth factor

Endothelial progenitor cells for fabrication of engineered vascular units and angiogenesis induction

The promotion of vascularization and angiogenesis in the grafts is a crucial phenomenon in the healing process and tissue engineering. It has been shown that stem cells, especially endothelial progenitor cells (EPCs), can stimulate blood vessel formation inside the engineered hydrogels after being transplanted into the target sites. The incorporation of EPCs into the hydrogel can last the retention time, long-term survival, on-target delivery effects, migration and differentiation into mature endothelial cells. Despite these advantages, further modifications are mandatory to increase the dynamic growth and angiogenesis potential of EPCs in in vitro and in vivo conditions. Chemical modifications of distinct composites with distinct physical properties can yield better regenerative potential and angiogenesis during several pathologies. Here, we aimed to collect recent findings related to the application of EPCs in engineered vascular grafts and/or hydrogels for improving vascularization in the grafts. Data from the present article can help us in the application of EPCs as valid cell sources in the tissue engineering of several ischemic tissues.

Encapsulation of the growth factor neurotrophin-3 in heparinised poloxamer hydrogel stabilises bioactivity and provides sustained release

Poloxamer-based hydrogels show promise to stabilise and sustain the delivery of growth factors in tissue engineering applications, such as following spinal cord injury. Typically, growth factors such as neurotrophin-3 (NT-3) degrade rapidly in solution. Similarly, poloxamer hydrogels also degrade readily and are, therefore, only capable of sustaining the release of a payload over a small number of days. In this study, we focused on optimising a hydrogel formulation, incorporating both poloxamer 188 and 407, for the sustained delivery of bioactive NT-3. Hyaluronic acid blended into the hydrogels significantly reduced the degradation of the gel. We identified an optimal hydrogel composition consisting of 20 % w/w poloxamer 407, 5 % w/w poloxamer 188, 0.6 % w/w NaCl, and 1.5 % w/w hyaluronic acid. Heparin was chemically bound to the poloxamer chains to enhance interactions between the hydrogel and the growth factor. The unmodified and heparin-modified hydrogels exhibited sustained release of NT-3 for 28 days while preserving the bioactivity of NT-3. Moreover, these hydrogels demonstrated excellent cytocompatibility and had properties suitable for injection into the intrathecal space, underscoring their suitability as a growth factor delivery system. The findings presented here contribute valuable insights to the development of effective delivery strategies for therapeutic growth factors for tissue engineering approaches, including the treatment of spinal cord injury.

Temperature-Induced Mechanomodulation of Interpenetrating Networks of Star Poly(ethylene glycol)-Heparin and Poly(N-isopropylacrylamide)

Thermoresponsive interpenetrating networks (IPNs) were prepared by sequential synthesis of a biohybrid network of star-shaped poly(ethylene glycol) [starPEG] and heparin and a poly(N-isopropylacrylamide)-polymer network. Amide bond formation was used for cross-linking of the starPEG-heparin network and photo-cross-linking with N,N'-methylenebis(acrylamide) was applied for the formation of the second polymer network. Both networks were linked by chain entanglements and hydrogen bonds only. The obtained sequential IPNs (seq-IPNs) showed temperature-dependent network properties as reflected by swelling and elasticity data as well as by the release of glycosaminoglycan-binding growth factors. The elastic modulus of the seq-IPNs was found to be amplified up to 50-fold upon temperature change from 22 to 37 °C compared to the intrinsic elastic moduli of the two combined networks. The heparin concentration (as well as the complexation of growth factors with the hydrogel-contained heparin) was demonstrated to be variably independent from the mechanical properties (elastic moduli) of the hydrogels. Illustrating the usability of the developed seq-IPN platform for cell fate control, the thermo-modulation of the release of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP-2) is shown as well as the osteogenic differentiation of human mesenchymal stem cells exposed to stiff and BMP-2 releasing seq-IPNs.

The Influence of Anionic Initiator on the Selected Properties of Poly-N-Isopropyl Acrylamide Evaluated for Controlled Drug Delivery

The aim of the study was to monitor the influence of increasing initiator concentrations on the properties of poly-N-isopropylacrylamide (polyNIPA) nanoparticles obtained via surfactant free precipitation polymerization (SFPP). In all studied systems P-001 to P-1, the same amount of monomer was used, and increasing amounts of potassium persulphate (KPS). The course of each reaction was monitored by measuring the conductivity of the whole system. The resulting composition of products was confirmed by attenuated total reflectance within Fourier transformed infrared spectroscopy (ATR-FTIR) measurements. The hydrodynamic diameters with polydispersity index (PDI) and zeta potential (ZP) were measured in aqueous dispersions of the synthesized polymers in dynamic light scattering (DLS) device (λ = 678 nm), and were found to be for P-1: 20.33 nm (PDI = 0.49) and −7 mV, for P-05: 22.24 nm (PDI = 0.39) and −5 mV, for P-01: 50.14 nm (PDI = 0.49) and −3 mV, for P-005: 62.75 nm (PDI = 0.54) and −3 mV and for P-001: 509.4 nm (PDI = 0.61) and −12 mV at 18 °C, respectively. Initiator concentration affects the size and ZP of particles. The hydrodynamic diameter decreases with initiator concentration increase, whereas the time of the reaction decreases when the initiator concentration increases. This fact is reflected in the observed values of conductivity in the course of the performed reaction. Evaluated volume phase transition temperature in the range of 32 °C enables further research of the nanoparticles as thermosensitive drug carriers.