Formulations for modulation of protein release from large-size PLGA microparticles for tissue engineering.

In this study we present an approach to pre-program lysozyme release from large size (100-300 µm) poly(DL-lactic acid-co-glycolic acid) (PLGA) microparticles. This approach involved blending in-house synthesized triblock copolymers with a PLGA 85:15. In this work it is demonstrated that the lysozyme release rate and the total release are related to the mass of triblock copolymer present in polymer formulation. Two triblock copolymers (PLGA-PEG1500-PLGA and PLGA-PEG1000-PLGA) were synthesized and used in this study. In a like-for-like comparison, these two triblock copolymers appeared to have similar effects on the release of lysozyme. It was shown that blending resulted in the increase of the total lysozyme release and shortened the release period (70% release within 30 days). These results demonstrated that blending PLGA-PEG-PLGA triblock copolymer with PLGA 85:15 can be used as a method to pre-program protein release from microparticles. These microparticles with modulated protein release properties may be used to create microparticle-based tissue engineering constructs with pre-programmed release properties.

Growing bone tissue-engineered niches with graded osteogenicity: an in vitro method for biomimetic construct assembly.

The traditional bone tissue-engineering approach exploits mesenchymal stem cells (MSCs) to be seeded once only on three-dimensional (3D) scaffolds, hence, differentiated for a certain period of time and resulting in a homogeneous osteoblast population at the endpoint. However, after achieving terminal osteodifferentiation, cell viability is usually markedly compromised. On the other hand, naturally occurring osteogenesis results from the coexistence of MSC progenies at distinct differentiative stages in the same microenvironment. This diversification also enables long-term viability of the mature tissue. We report an easy and tunable in vitro method to engineer simple osteogenic cell niches in a biomimetic fashion. The niches were grown via periodic reseeding of undifferentiated MSCs on MSC/scaffold constructs, the latter undergoing osteogenic commitment. Time-fractioning of the seeded cell number during differentiation time of the constructs allowed graded osteogenic cell populations to be grown together on the same scaffolds (i.e., not only terminally differentiated osteoblasts). In such cell-dynamic systems, the overall differentiative stage of the constructs could also be tuned by varying the cell density seeded at each inoculation. In this way, we generated two different biomimetic niche models able to host good reservoirs of preosteoblasts and other osteoprogenitors after 21 culture days. At that time, the niche type resulting in 40.8% of immature osteogenic progenies and only 59.2% of mature osteoblasts showed a calcium content comparable to the constructs obtained with the traditional culture method (i.e., 100.03 ± 29.30 vs. 78.51 ± 28.50 pg/cell, respectively; p=not significant), the latter colonized only by fully differentiated osteoblasts showing exhausted viability. This assembly method for tissue-engineered constructs enabled a set of important parameters, such as viability, colonization, and osteogenic yield of the MSCs to be balanced on 3D scaffolds, thus achieving biomimetic in vitro models with graded osteogenicity, which are more complex and reliable than those currently used by tissue engineers.

Urease loaded alginate microspheres for blood purification.

In this paper a device, based on urease-loaded microspheres, is presented. The first task of this work was the optimization of a procedure for the alginate microspheres realization, having a radius as close as possible to the optimal one necessary to achieve the maximum enzyme exploitation. This optimal radius was calculated theoretically through a mathematical model which describes the concentration of substrate (urea) inside the microspheres on the assumption of a diffusion-reaction mechanism. The enzyme-loaded microspheres were successfully tested in a prototypal device aimed at the depletion of urea from a circulating fluid simulating blood flow: the results showed that urea concentration in the circulating fluid drops down to less than 25% of the initial value after 5 h.

Interaction of human gingival fibroblasts with PVA/gelatine sponges.

Tissue engineering scaffolds should be able to reproduce optimal microenvironments in order to support cell attachment, three-dimensional growth, migration and, regarding fibroblasts, must also promote extracellular matrix production. Various bioactive molecules are employed in the preparation of spongy scaffolds to obtain biomimetic matrices by either surface-coating or introducing them into the bulk composition of the biomaterial. The biomimetic properties of a spongy matrix composed of PVA combined with the natural component gelatine were evaluated by culturing human gingival fibroblasts on the scaffold. Cell adhesion, morphology and distribution within the scaffold were assessed by histology and electron microscopy; viability and metabolic activity as well as extracellular matrix production were analyzed by MTT assay, cytochemistry and immunocytochemistry. Fibroblasts interacted positively with PVA/gelatine. They adhered to the PVA/gelatine matrix in which they had good spreading activity and active metabolism; fibroblasts were also able to produce extracellular matrix molecules (type I collagen, fibronectin and laminin) compared to bi-dimensionally grown cells. The in situ creation of a biological matrix by human fibroblasts together with the ability to produce growth factor TGF-beta1 and the intracellular signal transduction molecule RhoA, suggests that this kind of PVA/gelatine sponge may represent a suitable support for in vitro extracellular matrix production and connective tissue regeneration.

Gelatine/PLLA sponge-like scaffolds: morphological and biological characterization.

Biodegradable synthetic polymers such as poly(lactic acid) (PLA) are widely used to prepare scaffolds for cell transplantation and tissue growth, using different techniques set up for the purpose. However the poor hydrophilicity of these polymers represents the main limitation to their use as scaffolds because it causes a low affinity for the cells. An effective way to solve this problem could be represented by the addition of biopolymers that are in general highly hydrophilic. The present work concerns porous biodegradable sponge-like systems based on poly(L-lactic acid) (PLLA) and gelatine. Morphology and porosity characteristics of the sponges were studied by scanning electron microscopy and mercury intrusion porosimetry respectively. Blood compatibility was investigated by bovine plasma fibrinogen (BPF) adsorption test and platelet adhesion test (PAT). The cell culture method was used in order to evaluate the ability of the matrices to work as scaffolds for tissue regeneration. The obtained results indicate that the sponges have interesting porous characteristics, good blood compatibility and above all good ability to support cell adhesion and growth. In fact viable and metabolically active animal cells were found inside the sponges after 8 weeks in culture. On this basis the systems produced seem to be good candidates as scaffolds for tissue regeneration.

Gelatine/PLLA sponge-like scaffolds: morphological and biological characterization.

Biodegradable synthetic polymers such as poly(lactic acid) are widely used to prepare scaffolds for cell transplantation and tissue growth, using different techniques set up for the purpose. However the poor hydrophilicity of these polymers represents the main limitation to their use as scaffolds because it causes a low affinity for the cells. An effective way to solve this problem could be represented by the addition of biopolymers that are in general highly hydrophilic. The present work concerns porous biodegradable sponge-like systems based on poly(L-lactic acid) and gelatine. Morphology and porosity characteristics of the sponges were studied by scanning electron microscopy and mercury intrusion porosimetry respectively. Blood compatibility was investigated by bovine plasma fibrinogen adsorption test and platelet adhesion test. The cell culture method was used in order to evaluate the ability of the matrices to work as scaffolds for tissue regeneration. The obtained results indicate that the sponges have interesting porous characteristics, good blood compatibility and above all good ability to support cell adhesion and growth. In fact viable and metabolically active animal cells were found inside the sponges after 8 weeks in culture. On this basis the systems produced seem to be good candidates as scaffolds for tissue regeneration.

Anticancer drug delivery with nanoparticles.

Nanotechnology provides a variety of nanoscale tools for medicine. Among them nanoparticles are revolutionizing the field of drug delivery. These drug nanocarriers have the potential to enhance the therapeutic efficacy of a drug, since they can be engineered to modulate the release and the stability and to prolong the circulation time of a drug, protecting it from elimination by phagocytic cells or premature degradation. Moreover, nanoscale carriers can be tailored to accumulate in tumour cells and tissues, due to enhanced permeability and a retention effect or by active targeting using ligands designed to recognize tumour-associated antigens. Could these nanomedicine tools mark an end to the necessity for loco-regional drug delivery?

Morphological evaluation of bioartificial hydrogels as potential tissue engineering scaffolds.

Poly(vinyl alcohol) hydrogels prepared by freeze-thawing procedure represent synthetic systems widely investigated as non-biodegradable scaffolds for tissue regeneration. In order to improve the biocompatibility properties of pure poly(vinyl alcohol) (PVA) hydrogels, blends of PVA with different biological macromolecules, such hyaluronic acid, dextran, and gelatin were prepared and used to produce "bioartificial hydrogels". The porosity characteristics of these hydrogels were investigated by scanning electron microscopy and mercury intrusion porosimetry. The morphology of bioartificial hydrogels was evaluated and compared with that of pure PVA hydrogels. In particular the effect exerted by each biological component on pore size and distribution was investigated. The obtained results indicate that when a natural macromolecule is added to PVA the internal structure of the material changes. A small amount of biopolymer induces the structural elements of PVA matrix to take on a well evident lamellar appearance and an apparent preferential orientation. Comparing the results of SEM and mercury intrusion porosimetry it was concluded that hydrogels containing 20% of biological component have the most regular structure and at the same time the lowest total porosity. On the contrary samples with the highest content of natural polymer (40%) show the less regular structure and the highest total porosity.