Izabela-Cristina Stancu

Synthesis of methacryloyloxyethyl phosphate copolymers and in vitro calcification capacity.

Methacryloyloxyethyl phosphate is a methacrylic monomer used to modify different substrates by copolymerisation, in order to enhance hydroxyapatite deposition onto their surfaces. We report the synthesis of two copolymers series using increasing concentrations of methacryloyloxyethyl phosphate with (diethylamino) ethyl methacrylate and 1-vinyl-2-pyrrolidinone. Reactivity ratios were evaluated for the two copolymer systems. The influence of phosphate content and distribution on the capacity to form a calcium-rich layer was evaluated after immersion for 15 days in a synthetic body fluid. Corresponding homopolymers were synthesised as controls. Calcium-phosphorus globules were developed only on samples containing (diethylamino) ethyl methacrylate, and presenting a low density of phosphate groups. The amounts of calcium increased when higher concentrations of methacryloyloxyethyl phosphate were used. The use of 1-vinyl-2-pyrrolidinone was associated with greater calcium amounts, (compared to (diethylamino) ethyl methacrylate). The amine groups may favour the attraction of phosphorus, thus creating another way for the nucleation of calcium/phosphate crystals.

Novel gelatin–PHEMA porous scaffolds for tissue engineering applications

In the present work, novel bicomponent polymeric hydrogels based on methacrylamide-modified gelatin (MAG) and 2-hydroxyethyl methacrylate (HEMA) have been prepared by cross-linking polymerization using photoinitiation. Five types of novel hydrogels have been prepared using different MAG/HEMA ratios between 1/0.5 and 1/10 w/w. Subsequently, porous scaffolds were obtained via a cryogenic treatment followed by freeze-drying. Physico-chemical measurements as well as in vitro degradation tests have been performed in order to correlate the material composition with the corresponding properties. Among the properties studied we have to mention the water uptake capacity, the rheological properties and the enzyme-mediated degradation behaviour. The results indicate that the HEMA content in the initial polymerization mixtures modulates the architecture of the porous scaffolds from straightforward, top-to-bottom oriented channels for hydrogels possessing the lowest HEMA content to a complex and dense internal porosity of the channels the case of higher HEMA loaded materials. While aiming at tissue engineering applications, it is important to notice that the covalently bound gelatin sequences significantly improve the biocompatibility of PHEMA based hydrogels.

Porous calcium alginate–gelatin interpenetrated matrix and its biomineralization potential

Artificial bone composites exhibit distinctive features by comparison to natural tissues, due to a lack of self-organization and intimate interaction apatite-matrix. This explains the need of “bio-inspired materials”, in which hydroxyapatite grows in contact with self-assembling natural polymers. The present work investigates the function of a rational design in the hydroxyapatite-forming potential of a common biopolymer. Gelatin modified through intrinsic interactions with calcium alginate led through freeze-drying to porous hydrogels, whose architecture, constitutive features and chemistry were investigated with respect to their role on biomineralization. The apatite-forming ability was enhanced by the porosity of the materials, while the presence of alginate-reinforced Gel elastic chains, definitely favored this phenomenon. Depending on the concentration, polysaccharide chains act as “ionic pumps” enhancing the biomineralization. The mineralization-promoting effect of the peptide-polysaccharide network strictly depends on the hydrogels structural, compositional and morphological features derived from the interaction between the above mentioned two components.

One-pot synthesis of superabsorbent hybrid hydrogels based on methacrylamide gelatin and polyacrylamide. Effortless control of hydrogel properties through composition design

BiocompatibLe methacryLamide-modified geLatin (GELMA) hydrogeLs with tuned characteristics, obtained through network-forming photopoLymerization, have recenty attracted increasing attention due to their wide range of possibLe appLications such as drug reLease, tissue regeneration and generation of bioartificiaL impLants. Due to the controlled number of C=C bonds, GELMA may simuLtaneousLy act as macromonomer and crossLinker Leading through poLymerization to hydrogeLs with rationally designed performances. This study provides effortess one-pot synthesis of hybrid hydrogeLs based on covaLenty Linked GELMA and poLyacryLamide (PM), using photo-induced network-forming poLymerization. ConventionaL synthesis of simiLar hydrogeLs Leads to interpenetrating geLatin and PAA networks, usually invoLving muLtistep crossLinking of the components and the use of toxic crossLinkers. Through the described one-pot chemistry, the synthetic water superabsorbent PM with its well-recognized advantages can rationally benefit from the high biocompatibiLity and cell-adherence of GELMA in a simpLe covaLent way. This work provides a correLation between the composition and the corresponding hydrogeL properties (incLuding swelling, pH influence, mechanicaL behaviour, abiLity to generate porous scaffoLds, enzymatic degradation). The addition of PM moduLated the network density and the water affinity allowing the controL of eLasticity and degradabiLity. SuppLementary crossLinking of the synthetic component provided additionaL controL over hydrophiLicity. The capacity of such hydrogeLs to generate porous scaffoLds was proved; interesting morphoLogies were deveLoped onLy by varying the composition. In vitro ceLLuLar studies indicated that the presence of GELMA conferred controlled cell-affinity properties to the bicomponent hydrogeLs. NevertheLess, the drug reLease potentiaL of such hydrogeLs was preLiminarlly investigated using sodium nafcillin. GELMA PM hydrogeLs may be usefuL for tissue regeneration due to effortess synthesis, compositionaL flexibiLity and variabLe properties.

Osteoblast-Like Cell Behavior on Porous Scaffolds Based on Poly(styrene) Fibers

Scaffolds of nonresorbable biomaterials can represent an interesting alternative for replacing large bone defects in some particular clinical cases with massive bone loss. Poly(styrene) microfibers were prepared by a dry spinning method. They were partially melted to provide 3D porous scaffolds. The quality of the material was assessed by Raman spectroscopy. Surface roughness was determined by atomic force microscopy and vertical interference microscopy. Saos-2 osteoblast-like cells were seeded on the surface of the fibers and left to proliferate. Cell morphology, evaluated by scanning electron microscopy, revealed that they can spread and elongate on the rough microfiber surface. Porous 3D scaffolds made of nonresorbable poly(styrene) fibers are cytocompatible biomaterials mimicking allogenic bone trabeculae and allowing the growth and development of osteoblast-like cells in vitro.

Porous Gelatin-Alginate-Polyacrylamide Scaffolds with Interpenetrating Network Structure: Synthesis and Characterization

We report for the first time a simple method for the synthesis of porous gelatin-alginate-polyacrylamide scaffolds with interpenetrating networks structure. The materials are obtained through a step-by-step procedure, starting with the polymerization of acrylamide and followed by the cross-linking of the natural components. Porosity was induced through freeze-drying. The composition of the resulting porous matrices is responsible for elastic properties, high water affinity, and mechanical behavior appropriate for drug delivery and soft tissue engineering use. All these properties can be modulated by slightly modifying the initial polymer mixtures. The in vitro degradation behavior can be also controlled via compositional approach.

Apatite formation on active nanostructured coating based on functionalized gold nanoparticles

In this work, we developed a simple method of surface functionalization of polymer substrates to provide them with the ability to form biomimetic hydroxyapatite (HA) when incubated in synthetic body fluids (SBF). In a first step, gold nanoparticles (AuNPs) were used as surface nanostructuring units for a biocompatible polymer, poly(2-hydroxyethyl methacrylate), known to not promote biomineralization in SBF, and under physiological conditions. The treatment of AuNPs-modified substrate with mercaptosuccinic acid leads to brushes of carboxyl-ended chains self-assembled onto the gold-polymer hybrid nanosurface. The main aim of this work was to demonstrate that these multianionic nanosurfaces would induce HA formation when incubated in solutions mimicking physiologic conditions. The formation of apatite and its morphology and composition were successfully investigated by means of high resolution scanning and transmission electron microscopy with energy dispersive X-ray microanalysis, infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Emphasis was put on the nucleation of HA in areas with agglomerated carboxyl-ended functionalized nanoparticles. The results obtained in this study may unlock new applications for smart active coatings based on functionalized AuNPs, such as the induction of biomineralization.

Repair of calvarial bone defects in mice using electrospun polystyrene scaffolds combined with β-TCP or gold nanoparticles.

Non-biodegradable porous polystyrene (PS) scaffolds, composed of microfibers, have been prepared by electrospinning for the reconstruction of large bone defects. PS microfibers were prepared by incorporating β-TCP grains inside the polymer or grafting gold nanoparticles surface functionalized with mercaptosuccinic acid. Cytocompatibility of the three types of scaffolds (PS, β-TCP-PS and Au-PS) was studied by seeding human mesenchymal stem cells. Biocompatibility was evaluated by implanting β-TCP-PS and Au-PS scaffolds into a critical size (4mm) calvarial defect in mice. Calvaria were taken 6, 9, and 12 weeks after implantation; newly formed bone and cellular response was analyzed by microcomputed tomography (microCT) and histology. β-TCP-PS scaffolds showed a significantly higher cell proliferation in vitro than on PS or Au-PS alone; clearly, the presence of β-TCP grains improved cytocompatibility. Biocompatibility study in the mouse calvaria model showed that β-TCP-PS scaffolds were significantly associated with more newly-formed bone than Au-PS. Bone developed by osteoconduction from the defect margins to the center. A dense fibrous connective tissue containing blood vessels was identified histologically in both types of scaffolds. There was no inflammatory foci nor giant cell in these areas. AuNPs aggregates were identified histologically in the fibrosis and also incorporated in the newly-formed bone matrix. Although the different types of PS microfibers appeared cytocompatible during the in vitro experiment, they appeared biotolerated in vivo since they induced a fibrotic reaction associated with newly formed bone.

Development and Characterization of Photoresponsive Polymers

Polymeric materials that respond to light stimulus represent an important research area in the field of biomaterials. Light-responsive biomaterials have received significant attention due to their ability to provide spatially and temporally control and their potential to be less invasive. In this book chapter, we highlight the exciting progress realized in the biomedical field in recent years on photoresponsive polymeric systems. More precisely, we discuss the rational design of photoactive compounds, the role they have in the photoresponsive systems, the underlying principles behind photoresponsive behavior, and the subsequent applications in the biomaterial field. We also present the progress made in the field of photopharmacology, photoregulated drug delivery, and bioimaging, emphasizing the advantages on the basis of different architectures such as micelles, hydrogels, nanoparticles, and photoresponsive supramolecular assemblies. Finally, analytical techniques used to characterize the photoresponsive materials are expound.

Nanocomposite particles with improved microstructure for 3D culture systems and bone regeneration

Nano-apatite and gelatin-alginate hydrogel microparticles have been prepared by a one-step synthesis combined with electrostatic bead generation, for the reconstruction of bone defects. Based on the analysis of bone composition, architecture and embryonic intramembranous ossification, a bio-inspired fabrication has been developed. Accordingly, the mineral phase has been in situ synthesized, calcifying the hydrogel matrix while the latter was crosslinked, finally generating microparticles that can assemble into a bone defect to ensure interconnected pores. Although nano-apatite—biopolymer composites have been widely investigated, microstructural optimization to provide improved distribution and stability of the mineral is rarely achieved. The optimization of the developed method progressively resulted in two types of formulations (15P and 7.5P), with 15 and 7.5 (wt%) phosphate content in the initial precursor. The osteolytic potential was investigated using differentiated macrophages. A commercially available calcium phosphate bone graft substitute (Eurocer 400) was incorporated into the hydrogel, and the obtained composites were in vitro tested for comparison. The cytocompatibility of the microparticles was studied with mouse osteoblast-like cell line MC3T3-E1. Results indicated the best in vitro performance have been obtained for the sample loaded with 7.5P. Preliminary evaluation of biocompatibility into a critical size (3 mm) defect in rabbits showed that 7.5P nanocomposite is associated with newly formed bone in the proximity of the microparticles, after 28 days.Graphical abstract