Nimet Bölgen

Three-Dimensional Ingrowth of Bone Cells Within Biodegradable Cryogel Scaffolds in Bioreactors at Different Regimes

Three-dimensional cell ingrowth within biodegradable cryogel scaffolds made of cross-linked 2-hydroxyethyl methacrylate (HEMA)-lactate-dextran with interconnected macropores was studied in bioreactors at different regimes (static, perfusion, and compression-perfusion). An osteoblast-like cell line (MG63) was used in these studies. The samples taken after selected times from the bioreactors were examined by microscopy techniques (light, SEM, TEM, and laser scanning confocal). The cell culture conditions were found to have a significant impact not only on the cell morphology, such as the extent of cell attachment and ingrowth, but also on cellular activities. Dynamic conditions (perfusion and/or compression) greatly improved cell ingrowth and extracellular matrix (ECM) synthesis. Alkaline phosphatase activity results confirmed the positive effect of dynamic conditions on bone cells.

Electrospun matrices made of poly(α-hydroxy acids) for medical use

Biomaterials are widely used in diverse applications as substances, materials or important elements of biomedical devices. Biodegradable polymers, both natural and synthetic, have been utilized in applications in which they act as temporary substitutes. Poly(alpha-hydroxy acids), especially lactic acids and glycolic acid and their copolymers with epsilon-caprolactone, are the most widely known and used among all biodegradable polymers. They degrade in vivo into safe end products mainly by hydrolysis in a few weeks to several months, depending on several factors, including molecular structure/morphology, average molecular weight, size and shape. They are processed into tailor-made materials for diverse applications, although mainly for soft and hard tissue repair. Electrospinning is a method of producing nanofibers and nonwoven matrices from their solutions and melts. Several factors affect fiber diameter and resulting nonwoven structures/morphologies. Recently, electrospun matrices made of lactic acids, glycolic acid and epsilon-caprolactone homo- and co-polymers have been attracting increasing attention for fabrication of novel materials for medical use. This review briefly describes poly(alpha-hydroxy acids) and the elecrospinning process, and gives some selected recent applications of electrospun matrices made from these polymers.

Cryogelation for preparation of novel biodegradable tissue-engineering scaffolds

2-Hydroxyethyl methacrylate-L-lactate (HEMA-LLA) and HEMA-L-lactate-dextran (HEMA-LLA-D) were synthesized. 1H-NMR confirmed the formation of these oligomers and macromers. Cryogels with different pore structures were prepared using different amounts of HEMA, HEMA-LLA and HEMA-LLA-D by a cryogelation technique. SEM micrographs exhibited pore morphologies. Cryogels were highly porous with interconnected pore structures, opaque, spongy and highly elastic. It was possible to compress them to remove the water in the pores and to return to their original form just by immersing them in water in few minutes, which was quite reproducible. Their swelling abilities, compressive strengths and degradation in buffer solutions were found to be related with their structural properties which was controlled by changing the cryogelation recipe.

Tissue responses to novel tissue engineering biodegradable cryogel scaffolds: An animal model

Biodegradable macroporous cryogels with highly open and interconnected pore structures were produced from dextran modified with oligo L-lactide bearing hydroxyethylmethacrylate (HEMA) end groups in moderately frozen solutions. Tissue responses to these novel scaffolds were evaluated in rats after dorsal subcutaneous implantation, iliac submuscular implantation, auricular implantation, or in calvarial defect model. In no case, either necrosis or foreign body reaction was observed during histological studies. The cryogel scaffolds integrated with the surrounding tissue and the formation of a new tissue were accompanied with significant ingrowth of connective tissue cells and new blood vessels into the cryogel. The tissue responses were significantly lower in auricular and calvarial implantations when compared with the subcutanous and the submuscular implantations. The degradation of the scaffold was slower in bone comparing to soft tissues. The biodegradable cryogels are highly biocompatible and combine extraordinary properties including having soft and elastic nature, open porous structure, and very rapid and controllable swelling. Therefore, the cryogels could be promising candidates for further clinical applications in tissue regeneration.

Gelatin- and hydroxyapatite-based cryogels for bone tissue engineering: synthesis, characterization, in vitro and in vivo biocompatibility.

The aim of this study was the synthesis and characterization of gelatin‐ and hydroxyapatite (osteoconductive component of bone)‐based cryogels for tissue‐engineering applications. Preliminary in vitro and in vivo biocompatibility tests were conducted. Gelatin‐ and hydroxyapatite‐based cryogels of varying concentrations were synthesized using glutaraldehyde as the crosslinking agent. Chemical structure, pore morphology, pore size distribution, mechanical properties, swelling characteristics and degradation profiles of the synthesized cryogels were demonstrated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), mercury porosimetry, a mechanical test device, swelling ratio tests and weight loss measurements, respectively. In vitro cell viability and in vivo biocompatility tests were performed in order to show the performance of the cryogels in the biological environment. Changing the concentrations of gelatin, hydroxyapatite and crosslinker changed the chemical structure, pore size and pore size distribution of the cryogels, which in turn resulted in the ultimate behaviour (mechanical properties, swelling ratio, degradation profile). In vitro cell culture tests showed the viability of the cells. The cryogels did not show any cytotoxic effects on the cells. Clinical outcomes and the gross pathological results demonstrated that there was no necrosis noted in the abdominal and thoracic regions at the end of implantation and the implanted cryogel was found to be non‐irritant and non‐toxic at 12 weeks of implantation. Copyright

Stem cell suspension injected HEMA-lactate-dextran cryogels for regeneration of critical sized bone defects

Abstract HEMA-Lactate-Dextran cryogel scaffolds were produced by cryogelation. Mesencyhmal stem cells (MSC) were isolated from rat bone marrow. Critical sized cranial bone defects were created in rat cranium. Stem cells were injected inside the macropores of the cryogel scaffolds prepared from HEMA-Lactate-Dextran possessing the same dimensions with the defect and placed in the cranial bone. The cryogels placed in the defect without stem cells served as control. After selected time intervals the experimental sites were removed from the animals and new bone formation and tissue integration were investigated by histological analysis. The in vivo results exhibited osseous tissue integration within the implant and mineralized functionally stable bone restoration of the cranial defects. Tissue formation started in the macrospores of the scaffold starting from periphery to the center. A significant ingrowth of connective tissue cells and new blood vessels allowed new bone formation. Histological data demonstrated that new bone per total defect area ratio, were not significantly different in “scaffold-stem cells” group compared to that of “scaffold only” group on all time points. However, the blood vessel density was significantly higher in “scaffold-stem cells” group comparing to that of the “scaffold only” group on day 30. “Scaffold-stem cells” given group gave better tissue response score when compared to “scaffold only” group on day 180.

Thermoresponsive biodegradable HEMA-lactate-Dextran-co-NIPA cryogels for controlled release of simvastatin

Abstract NIPA and HEMA–lactate–Dextran-based biodegradable and thermoresponsive cryogels were synthesized at different compositions by cryogelation. Chemical and morphological properties of the HEMA–lactate–Dextran-co-NIPA cryogel matrices were demonstrated by FTIR, SEM, and ESEM. Thermoresponsivity of the prepared cryogels was investigated by DSC, imaging NMR, and swelling studies. For possible use of the cryogels in potential bone tissue engineering applications, either hydrophobic simvastatin was embedded, or hydrophilic simvastatin was incorporated in the cryogels. Release profiles of simvastatin delivering cryogel scaffolds depending on their composition, hydrophobicity or hydrophilicity of loaded simvastatin and the medium temperature were demonstrated.

Nanofibers for Tissue Engineering and Regenerative Medicine

Electrospinning is a process in which polymer fibers are produced with diameters down to the nanometer range through the action of an electric field imposed on a polymer solution/melt. Distinct properties that make electrospun nanofibrous materials unique are their high surface area, porosity, tensile strength and high extensibility. Indeed the size of the fibers down to nanometer scale make the final structures unique. And since the structure of the nanofibers is very similar to the extracellular matrix, many applications of them are proposed to be used in biomedicine especially for tissue engineeri2ng applications. Many polymers were used to prepare electrospun nanofibers including natural and synthetic ones. Poly(e-caprolactone) (PCL) was used extensively in the tissue engineering field as a synthetic polymer and alternative to natural polymers. The relatively inexpensive production routes, FDA approval, tailorable biodegradability, biocompatibility and easy manipulation make this polymer promising for electrospinning applications. Therefore PCL based electrospun matrices were used in several tissue engineering attempts including skin, bone, vascular and nerve regeneration. This review summarizes the use of electrospun PCL nanofibers in tissue engineering and regenerative medicine applications.

Comparison of additive effects on the PVA/starch cryogels: Synthesis, characterization, cytotoxicity, and genotoxicity studies

ABSTRACT The research goal of this study is to produce suitable scaffolds for tissue engineering applications. Different ratios of polyvinyl alcohol (PVA)/starch (90:10, 70:30, 50:50) and crosslinking methods have been used to prepare cryogels. Chemically crosslinked cryogels were synthesized using glutaraldehyde as the crosslinking agent. For the physically crosslinked cryogels, sodium dodecyl sulfate was used during cryogelation as the foaming agent. Chemical structure and pore morphology were demonstrated by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). Swelling ratio and degradation profile of the scaffolds were also determined. 3-(4,5-dimethylthiazoyl-2-yl)-2,5-diphenyltetrazolium bromide assay and SEM were used to investigate the biocompatibility of the scaffolds and cell morphology. Genotoxicity test was performed to show DNA fragmentation. The overall results demonstrated that PVA/starch cryogels could have potentially appealing application as scaffolds for tissue engineering applications and additives affect the architecture and characteristic properties of the cryogels. GRAPHICAL ABSTRACT

A novel strategy for cartilage tissue engineering: Collagenase-loaded cryogel scaffolds in a sheep model

ABSTRACT In this study, we developed a novel strategy, through which cartilage tissue pieces were placed in a sheep cartilage defect model and covered with a collagenase incorporated cryogel scaffold (in vivo cartilage tissue engineering, IVCTE group). While applying this strategy, the chondrocytes could be isolated inside the body and the treatment could be accomplished in one session. To compare our strategy, to another group, in which we used cultured cells and Chondro-gide, standard matrix-induced autologous chondrocyte implantation (MACI) was applied. Although the MACI applied group demonstrated better healing than IVCTE, the type II collagen synthesis was better in the IVCTE group compared to MACI applied group. Collagenase did not have detrimental effect on surrounding cartilage in IVCTE group. The preliminary results of the novel strategy applied group (IVCTE) were promising. GRAPHICAL ABSTRACT