E. Di Maio

Design of porous polymeric scaffolds by gas foaming of heterogeneous blends

One of the challenges in tissue engineering scaffold design is the realization of structures with a pre-defined multi-scaled porous network. Along this line, this study aimed at the design of porous scaffolds with controlled porosity and pore size distribution from blends of poly(ε-caprolactone) (PCL) and thermoplastic gelatin (TG), a thermoplastic natural material obtained by de novo thermoplasticization of gelatin. PCL/TG blends with composition in the range from 40/60 to 60/40 (w/w) were prepared by melt mixing process. The multi-phase microstructures of these blends were analyzed by scanning electron microscopy and dynamic mechanical analysis. Furthermore, in order to prepare open porous scaffolds for cell culture and tissue replacement, the TG and PCL were selectively extracted from the blends by the appropriate combination of solvent and extraction parameters. Finally, with the proposed combination of gas foaming and selective polymer extraction technologies, PCL and TG porous materials with multi-scaled and highly interconnected porosities were designed as novel scaffolds for new-tissue regeneration.

Processing/structure/property relationship of multi-scaled PCL and PCL–HA composite scaffolds prepared via gas foaming and NaCl reverse templating

In this study, we investigated the processing/structure/property relationship of multi‐scaled porous biodegradable scaffolds prepared by combining the gas foaming and NaCl reverse templating techniques. Poly(ε‐caprolactone) (PCL), hydroxyapatite (HA) nano‐particles and NaCl micro‐particles were melt‐mixed by selecting different compositions and subsequently gas foamed by a pressure‐quench method. The NaCl micro‐particles were finally removed from the foamed systems in order to allow for the achievement of the multi‐scaled scaffold pore structure. The control of the micro‐structural properties of the scaffolds was obtained by the optimal combination of the NaCl templating concentration and the composition of the CO2–N2 mixture as the blowing agent. In particular, these parameters were accurately selected to allow for the fabrication of PCL and PCL–HA composite scaffolds with multi‐scaled open pore structures. Finally, the biocompatibility of the scaffolds has been assessed by cultivating pre‐osteoblast MG63 cells in vitro, thus demonstrating their potential applications for bone regeneration. Biotechnol. Bioeng. 2011; 108:963–976.

Engineered μ-bimodal poly(ε-caprolactone) porous scaffold for enhanced hMSC colonization and proliferation

The use of scaffold-based strategies in the regeneration of biological tissues requires that the design of the microarchitecture of the scaffold satisfy key microstructural and biological requirements. Here, we examined the ability of a porous poly(epsilon-caprolactone) (PCL) scaffold with novel bimodal-micron scale (mu-bimodal) porous architecture to promote and guide the in vitro adhesion, proliferation and three-dimensional (3-D) colonization of human mesenchymal stem cells (hMSCs). The mu-bimodal PCL scaffold was prepared by a combination of gas foaming (GF) and selective polymer extraction (PE) from co-continuous blends. The microarchitectural properties of the scaffold, in particular its morphology, porosity distribution and mechanical compression properties, were analyzed and correlated with the results of the in vitro cell-scaffold interaction study, carried out for 21days under static conditions. Alamar Blue assay, scanning electron microscopy, confocal laser scanning microscopy and histological analyses were performed to assess hMSC adhesion, proliferation and 3-D colonization. The results showed that the combined GF-PE technique allowed the preparation of PCL scaffold with a unique multiscaled and highly interconnected microarchitecture that was characterized by mechanical properties suitable for load-bearing applications. Study of the cell-scaffold interaction also demonstrated the ability of the scaffold to support hMSC adhesion and proliferation, as well as the possibility to promote and guide 3-D cell colonization by appropriately designing the microarchitectural features of the scaffold.

Thermoplastic Foams from Zein and Gelatin

Abstract The aim of this study was to characterize the foaming of natural proteins as thermoplastic polymers. In particular, two proteins, one of vegetal origin, zein, and one of animal origin, gelatin, were processed to achieve thermoplastic polymers, and subsequently foamed by a gas foaming batch process. The effects of suitable plasticizing additives and melt-mixing process on the thermal and mechanical properties of the thermoplasticized proteins were evaluated to assess the thermoplastic characteristics of these materials. Furthermore, selected protein/plasticizers systems were foamed with mixtures of CO2 and N2 as blowing agents, in a batch foaming apparatus, at different temperatures, pressures and pressure drop rates, to evaluate the processing window and the final properties of the foams. Foams with densities of 0.1 g/cm3 and morphologies characterized by uniform distributions of cells with 10 μm diameters were obtained. Results indicated the suitability of zein and gelatin for being processed with classical thermoplastic processing technologies including melt mixing and foaming and their potentials as biodegradable polymers.

Engineering of Foamed Structures for Biomedical Application

The aim of this study was to combine gas foaming (GF) and reverse templating techniques to prepare open-pore polymeric foams with pore structures specifically designed for tissue engineering. Poly(ε-caprolactone) (PCL) has been melt mixed with two different templating agents, NaCl microparticles and thermoplastic gelatin (TG), to prepare microparticulate composites and co-continuous blends, respectively. These heterogeneous systems have been subsequently gas foamed by using mixtures of N2 and CO2 as blowing agents. Finally, the foamed materials have been soaked in H2O to selectively extract the NaCl or TG from the polymeric matrices to achieve the final foamed structure. The presence of the different templating agents extensively affected the foaming process of PCL; these effects have been analyzed and the results gathered important information to design porous scaffolds with fine tuned open-pore architectures. In particular, the control of the overall porosity, pore size and shape, pore interconnectivity, and spatial distribution of PCL matrix has been achieved by optimizing the GF process parameters with respect to the specific templating system. Results demonstrated that the combination of the GF and reverse templating techniques allowed the preparation of PCL scaffolds with open-pore architectures and highly controlled porosity and pore size spatial distribution.

Tuning the microstructure and biodegradation of three-phase scaffolds for bone regeneration made of PCL, Zein, and HA:

The aim of this study has been the design of novel multi-phase porous scaffolds with bi-modal pore size distributions and controlled biodegradation rate for bone tissue engineering (bTE), via a gas foaming—leaching approach. Poly(ε-caprolactone) (PCL) has been melt mixed with thermoplastic zein (TZ) and hydroxyapatite particle, to prepare multi-phase PCL—TZ and PCL—TZ—HA composites suitable to be further processed for the fabrication of 3D porous scaffolds. To this aim, these systems have been gas foamed by using CO2 as blowing agent and, subsequently, soaked in H2O to leach out the plasticizer from the TZ. This combined process allows the formation of an interpenetrated micro- and macro-porosity network within the samples. The effect of the different formulations on the micro-structural properties and in vitro biodegradation of the scaffolds has been investigated, and the results correlated to the mechanisms involved in the formation of the bi-modal pore structure. Results demonstrated that the multi-phase nature of the biomaterials prepared as well as their composition significantly affect the micro-structural properties and biodegradation rate of the scaffolds. The optimal selection of the processing conditions may allow for the design of multi-phase 3D porous scaffolds suitable for bTE.

A novel lab-scale batch foaming equipment: The mini-batch

In this paper, we report the design of a new experimental apparatus for the study of the foaming process of thermoplastic polymers with physical blowing agents. The novel lab-scale batch foaming equipment is capable of achieving accurate control of the processing variables, namely, the temperature, the saturation pressure and the pressure drop rate and, furthermore, of allowing the achievement of very high pressure drop rates, the observation of the sample while foaming and the very fast extraction of the foamed sample. By recalling the considerations discussed by Muratani et al. (J Cell Plast 2005; 24: 15), the design converged into a simple, cheap, and very small pressure vessel, thereby denoted as mini-batch. We herein describe the overall design path of the mini-batch, its characteristics, configurations, together with some examples of use with polystyrene and CO2 as the blowing agent.

CONTROLLED PREPARATION OF POROUS SCAFFOLDS BY GAS FOAMING OF HETEROGENEOUS BLENDS

Blending two different immiscible polymers is one of the most efficient strategies to prepare materials with improved performances. Recently, this multi‐phase systems have been used in tissue engineering aiming at the preparation of porous scaffolds for cell culture. In this study, thermoplastic biodegradable and biocompatible multi‐phase blends with co‐continuous micro‐structures have been prepared by melt mixing poly(e‐caprolactone) (PCL) with thermoplastic gelatin (TG), a thermoplastic material prepared by mixing gelatin with glycerol. The blend have been prepared by selecting the composition into the 60/40 to 40/60 wt‐% PCL‐TG range. Dynamic mechanical analysis was performed in order to asses the achievement of an heterogeneous micro‐structure while, gravimetric measurements and scanning electron micrograph analysis, performed after the selective extraction of the different phases, were used to evaluate the co‐continuity of the different systems prepared. Finally, the PCL/TG blends have been further p...

Interferometric measurement of film thickness during bubble blowing

In this paper, we propose digital holography in transmission configuration as an effective method to measure the time-dependent thickness of polymeric films during bubble blowing. We designed a complete set of experiments to measure bubble thickness, including the evaluation of the refractive index of the polymer solution. We report the measurement of thickness distribution along the film during the bubble formation process until the bubble‘s rupture. Based on those data, the variation range and variation trend of bubble film thickness are clearly measured during the process of expansion to fracture is indicated.

Biodegradable biomedical foam scaffolds

Abstract: This chapter discusses the theoretical and experimental aspects related to the techniques for the preparation of scaffold by gas foaming of biodegradable polymers, of both natural and synthetic origin. Properties of polymer/gas solutions controlling nucleation and growth of gas bubbles are analysed in the first part of this chapter. In the second part, specific preparation methodologies and morphologies of foams based on selected biodegradable polymers will be presented. These include polysaccharides (starch, chitosan, alginates), vegetal (zein) and animal (gelatin) proteins, and polyesters (poly(lactic acid) (PLA), poly(glycolic acid) (PGA), and their copolymers PLGA, and poly-£-caprolactone (PCL)).