Functionally modified gelatin microspheres as a growth factor’s delivery system: development and characterization

Controlled Release of Vascular Endothelial Growth Factor from Heparin-Functionalized Gelatin Type A and Albumin Hydrogels

Bio-based release systems for pro-angiogenic growth factors are of interest, to overcome insufficient vascularization and bio-integration of implants. In this study, we investigated heparin-functionalized hydrogels based on gelatin type A or albumin as storage and release systems for vascular endothelial growth factor (VEGF). The hydrogels were crosslinked using carbodiimide chemistry in presence of heparin. Heparin-functionalization of the hydrogels was monitored by critical electrolyte concentration (CEC) staining. The hydrogels were characterized in terms of swelling in buffer solution and VEGF-containing solutions, and their loading with and release of VEGF was monitored. The equilibrium degree of swelling (EDS) was lower for albumin-based gels compared to gelatin-based gels. EDS was adjustable with the used carbodiimide concentration for both biopolymers. Furthermore, VEGF-loading and release were dependent on the carbodiimide concentration and loading conditions for both biopolymers. Loading of albumin-based gels was higher compared to gelatin-based gels, and its burst release was lower. Finally, elevated cumulative VEGF release after 21 days was determined for albumin-based hydrogels compared to gelatin A-based hydrogels. We consider the characteristic net charges of the proteins and degradation of albumin during release time as reasons for the observed effects. Both heparin-functionalized biomaterial systems, chemically crosslinked gelatin type A or albumin, had tunable physicochemical properties, and can be considered for controlled delivery of the pro-angiogenic growth factor VEGF.

Antibacterial activity and cytotoxycity of gelatine-conjugated lysine-based peptides

The effect of the coupling approach (chemical by using carbodiimide chemistry, and enzymatic by using transglutaminase) of a hydrophilic ɛ-poly-L-lysine (ɛPL) and a structurally-hydrophobic oligo-acyl-lysyl (OAK) to a gelatine (GEL) macromolecule, and their antibacterial activity against Gram-negative E. coli and Gram-positive S. aureus bacteria, as well as cytotoxicity to human osteoblast cells was studied as potential macromolecules for biomedical applications. Different spectroscopic (ultraviolet-visible, infrared, fluorescence, and electron paramagnetic resonance) and separation (size-exclusion chromatography and capillary zone electrophoresis) techniques, as well as zeta-potential analysis were performed to confirm the ɛPL/OAK covalent coupling and to determine their amount and orientation of the immobilization. The highest and kinetically the fastest reduction of bacteria (≥77% against E. coli vs. ≥82% against S. aureus) was achieved with GEL functionalized with ɛPL/OAK by the chemical grafting-to approach being correlated with conformationally the highly-flexible ˝brush-like˝ orientation linkage of peptides, enable its targeted and rapid interactions with bacteria membrane. The up to 400-fold lower yield of OAKs being immobilized may be related also to its cationic charge and hydrophobic alkyl chain moieties, compared to more hydrophilic ɛPL easily causing random polymerization and self-conjugation. The ɛPL/OAK-functionalized GEL did not induce citotoxicity to osteoblasts, even at ∼25-fold higher concentration than bacterial minimum inhibitory (MIC) concentration of ɛPL/OAK. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3110-3126, 2017.

Investigation of the changes of biophysical/mechanical characteristics of differentiating preosteoblasts in vitro

BACKGROUND

Topography, stiffness, and composition of biomaterials play a crucial role in cell behaviors. In this study, we have investigated biochemical (gene markers), biophysical (roughness), and biomechanical (stiffness) changes during the osteogenic differentiation of preosteoblasts on gelatin matrices.

RESULTS

Our results demonstrate that gelatin matrices offer a favorable microenvironment for preosteoblasts as determined by focal adhesion and filopodia formation. The osteogenic differentiation potential of preosteoblasts on gelatin matrices is confirmed by qualitative (Alizarin red, von kossa staining, immunofluorescence, and gene expression) and quantitative analyses (alkaline phosphatase activity and calcium content). The biomechanical and biophysical properties of differentiating preosteoblasts are analyzed using atomic force microscopy (AFM) and micro indentation. The results show sequential and significant increases in preosteoblasts roughness and stiffness during osteogenic differentiation, both of which are directly proportional to the progress of osteogenesis. Cell proliferation, height, and spreading area seem to have no direct correlation with differentiation; however, they may be indirectly related to osteogenesis.

CONCLUSIONS

The increased stiffness and roughness is attributed to the mineralized bone matrix and enhanced osteogenic extracellular matrix protein. This report indicates that biophysical and biomechanical aspects during in vitro cellular/extracellular changes can be used as biomarkers for the analysis of cell differentiation.