A novel processing method for injection-molded polyether–urethane scaffolds. Part 1: Processing

Design and fabrication of porous biodegradable scaffolds: a strategy for tissue engineering

Current strategies of tissue engineering are focused on the reconstruction and regeneration of damaged or deformed tissues by grafting of cells with scaffolds and biomolecules. Recently, much interest is given to scaffolds which are based on mimic the extracellular matrix that have induced the formation of new tissues. To return functionality of the organ, the presence of a scaffold is essential as a matrix for cell colonization, migration, growth, differentiation and extracellular matrix deposition, until the tissues are totally restored or regenerated. A wide variety of approaches has been developed either in scaffold materials and production procedures or cell sources and cultivation techniques to regenerate the tissues/organs in tissue engineering applications. This study has been conducted to present an overview of the different scaffold fabrication techniques such as solvent casting and particulate leaching, electrospinning, emulsion freeze-drying, thermally induced phase separation, melt molding and rapid prototyping with their properties, limitations, theoretical principles and their prospective in tailoring appropriate micro-nanostructures for tissue regeneration applications. This review also includes discussion on recent works done in the field of tissue engineering.

Recent developments in micro- and nanofabrication techniques for the preparation of amorphous pharmaceutical dosage forms

Nano- and microfabrication techniques have been widely explored in the textile, polymer and biomedical arenas, although more recently these systems have attracted considerable interest as drug delivery vehicles with concomitant considerations of physical characterization, scalability, stability and drug release. In this review, the current thinking with regards to the manufacture of solid amorphous pharmaceutical materials using electrohydrodynamic and gyration-based approaches, melt-spinning approaches, thermal moulding, inkjet printing and 3D printing will be examined in the context of their potential and actual viability as dosage forms. A series of practical examples will be discussed as to how these approaches have been used as means of producing drug delivery systems for a range of delivery systems and treatments.

Polylactic Acid Based Nanocomposites: Promising Safe and Biodegradable Materials in Biomedical Field

Polylactic acid (PLA) is widely used in biological areas due to its excellent compatibility, bioabsorbability, and degradation behavior in human bodies. Pure polylactic acid has difficulty in meeting all the requirements that specific field may demand. Therefore, PLA based nanocomposites are extensively investigated over the past few decades. PLA based nanocomposites include PLA based copolymers in nanometer size and nanocomposites with PLA or PLA copolymers as matrix and nanofillers as annexing agent. The small scale effect and surface effect of nanomaterials help improve the properties of PLA and make PLA based nanocomposites more popular compared with pure PLA materials. This review mainly introduces different kinds of PLA based nanocomposites in recent researches that have great potential to be used in biomedical fields including bone substitute and repair, tissue engineering, and drug delivery system.

Fabrication of porous synthetic polymer scaffolds for tissue engineering

Tissue engineering provides a novel and promising approach to replace damaged tissue with an artificial substitute. Porous synthetic biodegradable polymers are the preferred materials for this substitution due to their microstructure, biocompatibility, biodegradability, and low cost. As a crucial element in tissue engineering, a scaffold acts as an artificial extracellular matrix (ECM) and provides support for cell migration, differentiation, and reproduction. The fabrication of viable scaffolds, however, has been a challenge in both clinical and academic settings. Methods such as solvent casting/particle leaching, thermally induced phase separation (TIPS), electrospinning, gas foaming, and rapid prototyping (additive manufacturing) have been developed or introduced for scaffold fabrication. Each method has its own advantages and disadvantages. In this review, the commonly used synthetic polymer scaffold fabrication methods will be introduced and discussed in detail, and recent progress regarding scaffold fabrication—such as combining different scaffold fabrication methods, combining various materials, and improving current scaffold fabrication methods—will be reviewed as well.

Supercritical CO2 in injection molding can produce open porous polyurethane scaffolds – a parameter study

There are several methods of producing open porous polymer structures for medical use. However, very few are applicable to industries and are therefore limited to both number of samples and batch variations. This study presents an industrial microcellular injection molding process, known as MuCell® technology, which was used to produce highly porous scaffolds of thermoplastic polyurethane. A parameter study was performed to quantify and analyze the effect of the processing parameters on the porous structure. Six key parameters (gas content, weight reduction, injection speed, mold temperature, plasticizing pressure, and temperature) were tested with an iteration method. The pore structure was determined with advanced micro Computer Tomography algorithm. All key processing parameters were identified. Gas content and weight reduction showed a more profound effect on the pore morphology than other parameters on the pore structure. It was possible to produce scaffolds with open porosity as high as 71%. The study concludes that MuCell® technology is an accurate and liable production method for large-scale production of open porous thermoplastic polyurethane scaffolds, and supercritical fluid could, therefore, be a potential production method for polymer scaffolds.

An injection molding process for manufacturing highly porous and interconnected biodegradable polymer matrices for use as tissue engineering scaffolds

In this research, injection molding was combined with a novel material combination, supercritical fluid processing, and particulate leaching techniques to produce highly porous and interconnected structures that have the potential to act as scaffolds for tissue engineering applications. The foamed structures, molded with polylactide (PLA) and polyvinyl alcohol (PVOH) with salt as the particulate, were processed without the aid of organic solvents, which can be detrimental to tissue growth. The pore size in the scaffolds is controlled by salt particulates and interconnectivity is achieved by the co-continuous blending morphology of biodegradable PLA matrix with water-soluble PVOH. Carbon dioxide (CO(2)) at the supercritical state is used to serve as a plasticizer, thereby imparting moldability of blends even with an ultra high salt particulate content, and allows the use of low processing temperatures, which are desirable for temperature-sensitive biodegradable polymers. Interconnected pores of approximately 200 microm in diameter and porosities of approximately 75% are reported and discussed.

Open-pore biodegradable foams prepared via gas foaming and microparticulate templating

Open-pore biodegradable foams with controlled porous architectures were prepared by combining gas foaming and microparticulate templating. Microparticulate composites of poly(epsilon-caprolactone) (PCL) and micrometric sodium chloride particles (NaCl), in concentrations ranging from 70/30 to 20/80 wt.-% of PCL/NaCl were melt-mixed and gas-foamed using carbon dioxide as physical blowing agent. The effects of microparticle concentration, foaming temperature, and pressure drop rate on foam microstructure were surveyed and related to the viscoelastic properties of the polymer/microparticle composite melt. Results showed that foams with open-pore networks can be obtained and that porosity, pore size, and interconnectivity may be finely modulated by optimizing the processing parameters. Furthermore, the ability to obtain a spatial gradient of porosity embossed within the three-dimensional polymer structure was exploited by using a heterogeneous microparticle filling. Results indicated that by foaming composites with microparticle concentration gradients, it was also possible to control the porosity and pore-size spatial distribution of the open-pore PCL foams.

Coating of polyurethane scaffolds with collagen: comparison of coating and cross-linking techniques

Collagen has been coated successfully onto numerous hydrophilic polymer scaffolds to improve cell adhesion. Due to the hydrophobic nature of thermoplastic polyurethane (TPU), coating with aqueous collagen solution is problematic for such scaffolds. This study facilitated the coating of TPU with collagen and compared cross-linking and coating techniques. Three different cross-linking methods were compared. Both thermal and glutaraldehyde methods showed proof of cross-linking; however glutaraldehyde seemed to be superior to the other methods. The use of human urine as a wetting agent and the chemical glutaraldehyde had no effect on a cytotoxicity test performed by means of a WST-1 assay with a fibroblastic cell line. Three different coating techniques for porous TPU scaffolds were also investigated: ultrasound, pressurized air and injection. Of these, injection performed best. This method facilitated a coating of 100% of the porous scaffolds examined, which was verified by staining, FTIR and SEM.

Preparation of porous apatite granules from calcium phosphate cement

A versatile method for preparing spherical, micro- and macroporous (micro: 2-10 and macro: 150-550 microm pores), carbonated apatitic calcium phosphate (Ap-CaP) granules (2-4 mm in size) was developed by using NaCl crystals as the porogen. The entire granule production was performed between 21 and 37 degrees C. A CaP cement powder, comprising alpha-Ca3(PO4)2 (61 wt.%), CaHPO4 (26%), CaCO3 (10%) and precipitated hydroxyapatite, Ca10(PO4)6(OH)2 (3%), was dry mixed with NaCl crystals varying in size from 420 microm to 1 mm. Cement powder (35 wt.%) and NaCl (65 wt.%) mixture was kneaded with an ethanol-Na2HPO4 initiator solution, and the formed dough was immediately agitated on an automatic sieve shaker for a few minutes to produce the spherical granules. Embedded NaCl crystals were then leached out of the granules by soaking them in deionized water. CaP granules were micro- and macroporous with a total porosity of 50% or more. Granules were composed of carbonated, poorly crystallized, apatitic CaP phase. These were the first spherical and porous CaP granules ever produced from a self-setting calcium phosphate cement. The granules reached their final handling strength at the ambient temperature through the cement setting reaction, without having a need for sintering.