Microfabricated PLGA scaffolds: a comparative study for application to tissue engineering

The Study of Properties and Structure of Polylactide–Graphite Nanoplates Compositions

Composites of polylactide containing graphite nanoplates as a filler in the concentration range 1–20 wt% were prepared in methylene chloride using the sonication technique. The thermal characteristics and phase transitions were studied by DSC and TGA methods. The temperatures and heats of glass transition, crystallization, and melting were determined, and the degree of crystallinity during primary and secondary heating was calculated. It is shown that the introduction of graphite nanoplates leads to an increase in the elastic modulus and a decrease in the breaking stress and elongation at break. These changes are especially pronounced at 20% GNP content in the composition, when the corresponding mechanical parameters are characteristics of brittle polymer systems. The study of the electrical properties of the composites showed that the percolation threshold in these materials is close to 7 wt%, which is significantly lower than in the case of spherical particles of comparable density. The SEM study of the filled composites showed a system of pores, which were apparently formed during the evaporation of solvent in the process of their preparation. Diverse structures of PLA/GNP composites films after hot pressure were established by the SEM method.

A review of wound dressing materials and its fabrication methods: emphasis on three-dimensional printed dressings

A wound is a trauma caused by some adverse external or blunt forces that can damage the body tissues. Wound healing is a complex process that occurs post-injury which involves the revamping of the structure and function of damaged tissues. Scaffolds are engineered tissue structures manufactured using different materials and methods for facilitating the wound healing process. For external wounds, the antimicrobial property and ability to absorb moisture play an important role in the material selection of the scaffold. Among different methods that exist for designing scaffolds, three-dimensional printing has emerged as a promising technique wherein customised scaffolds can be designed. However, the literature on three-dimensional printed dressings is very much limited compared to conventional ones. Therefore, this review specifically focuses on the methods used to design the scaffolds with special emphasis on different three-dimensional printing techniques. It covers the process of external wound healing, different materials used in the fabrication of scaffolds, and their advantages and drawbacks.

Innovations in Craniofacial Bone and Periodontal Tissue Engineering - From Electrospinning to Converged Biofabrication

From a materials perspective, the pillars for the development of clinically translatable scaffold-based strategies for craniomaxillofacial (CMF) bone and periodontal regeneration have included electrospinning and 3D printing (biofabrication) technologies. Here, we offer a detailed analysis of the latest innovations in 3D (bio)printing strategies for CMF bone and periodontal regeneration and provide future directions envisioning the development of advanced 3D architectures for successful clinical translation. First, the principles of electrospinning applied to the generation of biodegradable scaffolds are discussed. Next, we present on extrusion-based 3D printing technologies with a focus on creating scaffolds with improved regenerative capacity. In addition, we offer a critical appraisal on 3D (bio)printing and multitechnology convergence to enable the reconstruction of CMF bones and periodontal tissues. As a future outlook, we highlight future directions associated with the utilization of complementary biomaterials and (bio)fabrication technologies for effective translation of personalized and functional scaffolds into the clinics.

Double-Framed Thin Elastomer Devices

Elastomers and, in particular, polydimethylsiloxane (PDMS) are widely adopted as biocompatible mechanically compliant substrates for soft and flexible micro-nanosystems in medicine, biology, and engineering. However, several applications require such low thicknesses (e.g., <100 μm) that make peeling-off critical because very thin elastomers become delicate and tend to exhibit strong adhesion with carriers. Moreover, microfabrication techniques such as photolithography use solvents which swell PDMS, introducing complexity and possible contamination, thus limiting industrial scalability and preventing many biomedical applications. Here, we combine low-adhesion and rectangular carrier substrates, adhesive Kapton frames, micromilling-defined shadow masks, and adhesive-neutralizing paper frames for enabling fast, easy, green, contaminant-free, and scalable manufacturing of thin elastomer devices, with both simplified peeling and handling. The accurate alignment between the frame and shadow masks can be further facilitated by micromilled marking lines on the back side of the low-adhesion carrier. As a proof of concept, we show epidermal sensors on a 50 μm-thick PDMS substrate for measuring strain, the skin bioimpedance and the heart rate. The proposed approach paves the way to a straightforward, green, and scalable fabrication of contaminant-free thin devices on elastomers for a wide variety of applications.

Construction of polyphosphoesters with the main chain of rigid backbones and stereostructures via organocatalyzed ring-opening polymerization

A highly stereoregular polyphosphoester with a rigid cyclohexylene structure in the main chain was constructed via ring-opening polymerization (ROP) in the presence of an organic catalyst system.

Three dimensional extrusion printing induces polymer molecule alignment and cell organization within engineered cartilage

Proper cell-material interactions are critical to remain cell function and thus successful tissue regeneration. Many fabrication processes have been developed to create microenvironments to control cell attachment and organization on a three-dimensional (3D) scaffold. However, these approaches often involve heavy engineering and only the surface layer can be patterned. We found that 3D extrusion based printing at high temperature and pressure will result an aligned effect on the polymer molecules, and this molecular arrangement will further induce the cell alignment and different differentiation capacities. In particular, articular cartilage tissue is known to have zonal collagen fiber and cell orientation to support different functions, where collagen fibers and chondrocytes align parallel, randomly, and perpendicular, respectively, to the surface of the joint. Therefore, cell alignment was evaluated in a cartilage model in this study. We used small angle X-ray scattering analysis to substantiate the polymer molecule alignment phenomenon. The cellular response was evaluated both in vitro and in vivo. Seeded mesenchymal stem cells (MSCs) showed different morphology and orientation on scaffolds, as a combined result of polymer molecule alignment and printed scaffold patterns. Gene expression results showed improved superficial zonal chondrogenic marker expression in parallel-aligned group. The cell alignment was successfully maintained in the animal model after 7 days with distinct MSC morphology between the casted and parallel printed scaffolds. This 3D printing induced polymer and cell alignment will have a significant impact on developing scaffold with controlled cell-material interactions for complex tissue engineering while avoiding complicated surface treatment, and therefore provides new concept for effective tissue repairing in future clinical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2190-2199, 2018.

Modeling gold nanoparticle-eluting spacer degradation during brachytherapy application with in situ dose painting

OBJECTIVE

To investigate the dosimetric impact of slow vs burst release of gold nanoparticles (GNPs) from biodegradable brachytherapy spacers loaded with GNPs, which has been proposed to increase therapeutic efficacy during brachytherapy application with in situ dose painting.

METHODS

Mathematical models were developed based on experimental data to study the release of GNPs from a spacer designed with poly(lactic-co-glycolic acid) polymer. The models addressed diffusion controlled-release process and poly(lactic-co-glycolic acid) degradation kinetics that were used to determine GNP concentration profiles in tumour and the corresponding dose enhancement.

RESULTS

The results show a significant delay of GNP diffusion in the tumour in comparison to burst release assumed in previous studies. The model for diffusion controlled-release process and the model for combined processes of both diffusion and polymer degradation indicated that it may take about 25 and 45 days, respectively, for all GNPs to release from the spacer. Based on tumour concentration profiles, a significant dose enhancement factor (>2) could be attained at a tumour distance of 5 mm from a spacer loaded with 2-, 5- and 10-nm GNP sizes.

CONCLUSION

The results highlight the need to account for the slow release of GNPs from spacers and polymer biodegradation in research development of the GNP-eluting spacers. The findings suggest the use of radioisotopes with longer half-lives, such as iodine-125, in comparison with others with shorter half-lives such as Pd-103 and Cs-131. Advances in knowledge: The study provides a scientific platform and basis for research development of GNP-eluting spacers that can be used during brachytherapy to boost dose to tumour subvolumes, towards enhancing therapeutic efficacy. It concludes that the use of iodine-125 would be more feasible.

Hope versus hype: what can additive manufacturing realistically offer trauma and orthopedic surgery?

Additive manufacturing (AM) is a broad term encompassing 3D printing and several other varieties of material processing, which involve computer-directed layer-by-layer synthesis of materials. As the popularity of AM increases, so to do expectations of the medical therapies this process may offer. Clinical requirements and limitations of current treatment strategies in bone grafting, spinal arthrodesis, osteochondral injury and treatment of periprosthetic joint infection are discussed. The various approaches to AM are described, and the current state of clinical translation of AM across these orthopedic clinical scenarios is assessed. Finally, we attempt to distinguish between what AM may offer orthopedic surgery from the hype of what has been promised by AM.

A sacrificial process for fabrication of biodegradable polymer membranes with submicron thickness

A new sacrificial molding process using a single mask has been developed to fabricate ultrathin 2-dimensional membranes from several biocompatible polymeric materials. The fabrication process is similar to a sacrificial microelectromechanical systems (MEMS) process flow, where a mold is created from a material that can be coated with a biodegradable polymer and subsequently etched away, leaving behind a very thin polymer membrane. In this work, two different sacrificial mold materials, silicon dioxide (SiO2 ) and Liftoff Resist (LOR) were used. Three different biodegradable materials; polycaprolactone (PCL), poly(lactic-co-glycolic acid) (PLGA), and polyglycidyl methacrylate (PGMA), were chosen as model polymers. We demonstrate that this process is capable of fabricating 200-500 nm thin, through-hole polymer membranes with various geometries, pore-sizes and spatial features approaching 2.5 µm using a mold fabricated via a single contact photolithography exposure. In addition, the membranes can be mounted to support rings made from either SU8 or PCL for easy handling after release. Cell culture compatibility of the fabricated membranes was evaluated with human dermal microvascular endothelial cells (HDMECs) seeded onto the ultrathin porous membranes, where the cells grew and formed confluent layers with well-established cell-cell contacts. Furthermore, human trabecular meshwork cells (HTMCs) cultured on these scaffolds showed similar proliferation as on flat PCL substrates, further validating its compatibility. All together, these results demonstrated the feasibility of our sacrificial fabrication process to produce biocompatible, ultra-thin membranes with defined microstructures (i.e., pores) with the potential to be used as substrates for tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1192-1201, 2016.

Tissue engineering of the penis

Congenital disorders, cancer, trauma, or other conditions of the genitourinary tract can lead to significant organ damage or loss of function, necessitating eventual reconstruction or replacement of the damaged structures. However, current reconstructive techniques are limited by issues of tissue availability and compatibility. Physicians and scientists have begun to explore tissue engineering and regenerative medicine strategies for repair and reconstruction of the genitourinary tract. Tissue engineering allows the development of biological substitutes which could potentially restore normal function. Tissue engineering efforts designed to treat or replace most organs are currently being undertaken. Most of these efforts have occurred within the past decade. However, before these engineering techniques can be applied to humans, further studies are needed to ensure the safety and efficacy of these new materials. Recent progress suggests that engineered urologic tissues and cell therapy may soon have clinical applicability.

PLGA/hydrogel biopapers as a stackable substrate for printing HUVEC networks via BioLP

Two major challenges in tissue engineering are mimicking the native cell-cell arrangements of tissues and maintaining viability of three-dimension (3D) tissues thicker than 300 µm. Cell printing and prevascularization of engineered tissues are promising approaches to meet these challenges. However, the printing technologies used in biofabrication must balance the competing parameters of resolution, speed, and volume, which limit the resolution of thicker 3D structures. We suggest that high-resolution conformal printing techniques can be used to print 2D patterns of vascular cells onto biopaper substrates which can then be stacked to form a thicker tissue construct. Towards this end we created 1 cm × 1 cm × 300 µm biopapers to be used as the transferable, stackable substrate for cell printing. 3.6% w/v poly-lactide-co-glycolide was dissolved in chloroform and poured into molds filled with NaCl crystals. The salt was removed with DI water and the scaffolds were dried and loaded with a Collagen Type I or Matrigel. SEM of the biopapers showed extensive porosity and gel loading throughout. Biological laser printing (BioLP) was used to deposit human umbilical vein endothelial cells (HUVEC) in a simple intersecting pattern to the surface of the biopapers. The cells differentiated and stretched to form networks preserving the printed pattern. In a separate experiment to demonstrate "stackability," individual biopapers were randomly seeded with HUVECs and cultured for 1 day. The mechanically stable and viable biopapers were then stacked and cultured for 4 days. Three-dimensional confocal microscopy showed cell infiltration and survival in the compound multilayer constructs. These results demonstrate the feasibility of stackable "biopapers" as a scaffold to build 3D vascularized tissues with a 2D cell-printing technique.

Advanced material strategies for tissue engineering scaffolds

Tissue engineering seeks to restore the function of diseased or damaged tissues through the use of cells and biomaterial scaffolds. It is now apparent that the next generation of functional tissue replacements will require advanced material strategies to achieve many of the important requirements for long-term success. Here we provide representative examples of engineered skeletal and myocardial tissue constructs in which scaffolds were explicitly designed to match native tissue mechanical properties as well as to promote cell alignment. We discuss recent progress in microfluidic devices that can potentially serve as tissue engineering scaffolds, since mass transport via microvascular-like structures will be essential in the development of tissue engineered constructs on the length scale of native tissues. Given the rapid evolution of the field of tissue engineering, it is important to consider the use of advanced materials in light of the emerging role of genetics, growth factors, bioreactors, and other technologies.

Curative effect and histocompatibility evaluation of reconstruction of traumatic defect of rabbit urethra using extracellular matrix

OBJECTIVE

To investigate the curative effect and histocompatibility of reconstruction of traumatic urethral defect of rabbit using urethral extracellular matrix (ECM).

METHODS

Urethral ECM was obtained by excision of the urethra in 20 donor rabbits. In experimental group, 20 rabbits were resected a 1.0 cm-1.5 cm segment of the urethra and artificially made a model of traumatic urethral defect, then reconstructed by the urethral extracellular matrix of the same length. The rabbit immunity response was assessed by lymphocyte transformation test and serum TNF-alpha level. The reconstructed urethral segments were stained with hematoxylin-eosin and Van Gieson stain and observed by histological examination postoperatively. The urethrography, urethroscopy and urodynamic examinations were performed.

RESULTS

There was no significant difference in stimulative index of lymphocyte transformation between ECM group and control group. The serum TNF-alpha levels of ECM group slightly rose, but the increase was not significant as compared with control group. On postoperative day 10, epithelial cell had migrated from each side and small vessels were found in the extracellular matrix. In the 3rd week, several layers of urothelium covered the whole surface of the matrix tube. In the 6th week, the disorganized arrangements of smooth muscle fibers were firstly observed by Van Gieson staining. In the 24th week, the smooth muscle cells increased and the matrix tube appeared fairly similar to normal urethral wall components. The urethroscopy and urodynamic evaluation revealed that the surface of reconstructed urethra was smooth and emiction was unobstructed.

CONCLUSION

The urethral extracellular matrix might be an ideal and safe biomaterial for the reconstruction of urethral traumatic defect.

Genipin-crosslinked chitosan/gelatin blends for biomedical applications

Blends between chitosan (CS) and gelatin (G) with various compositions (CS/G 0/100 20/80, 40/60, 60/40 100/0 w/w) were produced, as candidate materials for biomedical applications. Different amounts of genipin (0.5 wt.% and 2.5 wt.%) were used to crosslink CS/G blends, promoting the formation of amide and tertiary amine bonds between the macromolecules and the crosslinker. The effects of composition and crosslinking on the physico-chemical properties of samples were evaluated by infrared analysis, thermogravimetry, contact angle measurements, dissolution and swelling tests. Mechanical properties of crosslinked samples were also determined through stress-strain and creep tests: samples stiffness increased with increasing the crosslinker amount and the CS content. Blend composition affected mouse fibroblasts adhesion and proliferation on substrates, depending on the crosslinker amount. Finally, crosslinked CS/G blends containing 80 wt.% G were found to support neuroblastoma cells adhesion and proliferation which made them promising candidates for uses in the field of nerve regeneration.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(ε-caprolactone) blends for tissue engineering applications in the form of hollow fibers

In this work, hollow fibers to be used as guides for tissue engineering applications were produced by dry-jet-wet spinning of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(epsilon-caprolactone) (PHBHV/PCL) solutions in chloroform with various weight ratios between the components (PHBHV/PCL 100/0; 80/20; 60/40; 50/50; 40/60; 20/80; 0/100 w/w). Fibers obtained from PHBHV/PCL blends had a low degree of surface and bulk porosity, depending on composition. Physicochemical characterization involving scanning electron microscopy and differential scanning calorimetry (DSC) showed that PHBHV/PCL blends are compatible. Interactions between blend components were studied by Fourier transform infrared total reflectance spectroscopy, DSC analysis, and polarized optical microscopy analysis. Homogeneity of blend composition was assessed by IR-chemical imaging analysis. PHBHV/PCL samples were found to be weakly hydrophilic and their biocompatibility was proved by in vitro tests using mouse fibroblasts. Mechanical properties of PHBHV/PCL blends were investigated by stress-strain tests, showing an increasing ductility of blend samples with increasing PCL amount. Hollow fibers supported fibroblasts attachment and proliferation depending on composition and porosity degree.

Degradable block polyurethanes from nontoxic building blocks as scaffold materials to support cell growth and proliferation

Linear degradable polyurethanes were prepared and proposed for tissue engineering applications. Biocompatible segments were selected for the synthesis to promote their integration with the biological environment. Physicochemical and morphological characterization (SEC, DSC, DMTA, AFM) revealed that the properties of these polymeric systems can be easily tuned by varying the nature and the composition of the constituent segments. In vitro biological assays (citotoxicity, fibroblast adhesion, and proliferation) showed that all polymers are not toxic, promoting the adhesion and proliferation of fibroblast cells, with slight differences depending on the material hydrophilicity.

Generation of static and dynamic patterned co-cultures using microfabricated parylene-C stencils

Many biological processes, such as stem cell differentiation, wound healing and development, involve dynamic interactions between cells and their microenvironment. The ability to control these dynamic processes in vitro would be potentially useful to fabricate tissue engineering constructs, study biological processes, and direct stem cell differentiation. In this paper, we used a parylene-C microstencil to develop two methods of creating patterned co-cultures using either static or dynamic conditions. In the static case, embryonic stem (ES) cells were co-cultured with fibroblasts or hepatocytes by using the reversible sealing of the stencil on the substrate. In the dynamic case, ES cells were co-cultured with NIH-3T3 fibroblasts and AML12 hepatocytes sequentially by engineering the surface properties of the stencil. In this approach, the top surface of the parylene-C stencil was initially treated with hyaluronic acid (HA) to reduce non-specific cell adhesion. The stencil was then sealed on a substrate and seeded with ES cells which adhered to the underlying substrate through the holes in the membrane. To switch the surface properties of the parylene-C stencils to cell adhesive, collagen was deposited on the parylene-C surfaces. Subsequently, a second cell type was seeded on the parylene-C stencils to form a patterned co-culture. This group of cells was removed by peeling off the parylene-C stencils, which enabled the patterning of a third cell type. Although the static patterned co-culture approach has been demonstrated previously with a variety of methods, layer-by-layer modification of microfabricated parylene-C stencils enables dynamic patterning of multiple cell types in sequence. Thus, this method is a promising approach to engineering the complexity of cell-cell interactions in tissue culture in a spatially and temporally regulated manner.

Comparative in vitro study of the cell proliferation of ovine and human osteoblast‐like cells on conventionally and rapid prototyping produced scaffolds tailored for application as potential bone replacement material

Reconstruction of bone defects in the field of craniomaxillofacial surgery is a relevant problem. In regenerative medicine, autologous bone is not available sufficiently. The full replacement of autologous bone grafts is required. A promising research field is the bone engineering. Especially the application of rapid prototyping (RP) enables new perspectives concerning the scaffold design. The aim of the study was to compare scaffolds produced by RP-technology (native and plasma-coated PLGA-scaffolds) with conventionally produced scaffolds (agar plates with hydroxyapatite and hyaluronic acid coated agar plates with hydroxyapatite) relating to proliferation, adhesion, and morphology of osteoblasts to get knowledge about the application potential of such 3D-manufactured matrices for bone engineering. TissueFoil E served as reference. To compare the scaffolds, 12 ovine and 12 human osteoblast-like cell cultures of the skull were used. Results were obtained by EZ4U, scanning electron microscopy, and light microscopy. The highest cell proliferation rate of human osteoblast-like cells was measured on TissueFoil E followed by plasma-coated PLGA-scaffolds and uncoated PLGA-scaffolds, whereas of ovine osteoblast-like cells on plasma-coated PLGA-scaffolds followed by TissueFoil E and uncoated PLGA-scaffolds. Human and ovine osteoblast-like cells on coated and uncoated agar plates had significant lower proliferation rates compared with TissueFoil E and PLGA-scaffolds. These results showed the potential of RP in the field of bone engineering. Mechanical properties of such scaffolds and in vivo studies should be investigated to examine if the scaffolds hold up the pressure it will undergo long enough to allow regrowth of bone and to examine the revascularization.

Guidance of liver and kidney organotypic cultures inside rectangular silicone microchannels

We have studied the effect of rectangular polydimethylsiloxane (PDMS) microchannels on the behavior of embryonic liver and kidney explants maintained in contact with these microchannels. The microchannel widths were varied from 35 to 300 microm and depth from 45 to 135 microm. The growth of these tissue types were compared to the development on flat silicone and plastic control material. At seeding, due to the viscoelastic properties of both organs, "capillary-like filling" was observed inside the narrowest microchannels. In those cases, the tissues grew to a confluent layer joining the microchannels with no cell migration and proliferation inside the microchannels. In the largest microchannels, only a weak migration was observed and the cellular behavior appears quite similar to that of PDMS flat culture conditions. In intermediate geometries, we observed different tissue growth progressed inside those microchannels with an average growth properties inside the microchannels when compared to other sizes. The liver tissues velocity of up to 72 microm/day resulting to form a dense three-dimensional multicellular 'liver-like tissue'. Scanning electron microscopy (SEM) observations demonstrated that the tissue was organized like an epithelial layer with round cells embedded in an extracellular matrix. Liver cell mobility may result primarily from the activity of the marginal cells, whereas the sub-marginal cells appeared passively dragged. Parenchymal organization demonstrating differentiated states was also observed. Kidney grew mainly on the microchannel walls and the tissues never appeared dense and organized as the liver ones.

Phenomenological model of bone remodeling cycle containing osteocyte regulation loop

Biological parameters, such as bone resorption and formation constants, are important variables to achieve optimised hard tissue scaffolds design. To help to understand the modelling process that occurs when a scaffold is implanted it is vital to understand the rather complex bone remodeling process prevalent in native bone. One approach to developing a mathematical model that predicts osteoactivity both in scaffolds, as well as in bone in vivo, is based on a bio-cybernetic vision of basic multicellular unit (BMU) action -. In the case of the model presented in this paper, an additional loop of regulation based on osteocyte activity has been added. This approach has resulted in a four-dimensional system, which shows steady-quasi-cyclic behaviour using a particular range of constants with real biological meaning. The initial findings suggesting that the basic steady-state appears as a torus in multidimensional phase space have been discussed. The existence of this surface in the osteoclasts-osteoblasts-osteocytes-bone subspace indicates that there is a first integral for this dynamic system. Biological and physical interpretation of this integral as a conservative value has been proposed. It is possible to draw an analogy between this conservative value, as a kind of substrate-energy regenerative potential of the bone remodeling system with a molecular nature, to the classical physical value (energy). There are clear indications that there is recovering potential within the BMU that results in a steady operating genetically predominated bone remodeling process. This recovering potential is directed against both mechanical and biomechanical damage to the bone. The current model has credibility when compared to the normal bone remodeling process. However, additional work is required to study a wider range of constants.

Preparation of macroporous polymer scaffolds using calcined cancellous bone as a template

A technique for preparing porous polymeric scaffolds using calcined cancellous bone as template has been developed. The scaffolds prepared by this method were morphologically similar to the structure of the demineralized bone matrix (DBM), i.e. scaffolds prepared by this novel method possessed high porosity, interconnected pores and uniform pore distribution. In addition, the mechanical properties of the scaffolds prepared by this novel method were significantly improved as compared to that of the scaffolds prepared by conventional solvent cast-particle leaching (SC-PL) method. The effects of concentration of the polymer solution on the structure, porosity and mechanical properties of the scaffolds were evaluated and the results showed that the mechanical properties of the scaffolds could be controlled by adjusting the concentration of the polymer solution. The advantages mentioned above suggest that this novel method might be a useful technique to prepare polymer scaffolds for tissue engineering.

Materials for Peripheral Nerve Regeneration

Recent efforts in scientific research in the field of peripheral nerve regeneration have been directed towards the development of artificial nerve guides. We have studied various materials with the aim of obtaining a biocompatible and biodegradable two layer guide for nerve repair. The candidate materials for use as an external layer for the nerve guides were poly(caprolactone) (PCL), a biosynthetic blend between PCL and chitosan (CS) and a synthesised poly(ester-urethane) (PU). Blending PCL, which is a biocompatible synthetic polymer, with a natural polymer enhanced the system biocompatibility and biomimetics, fastened the degradation rates and reduced the production costs. Various novel block poly(ester-urethane)s are being synthesised by our group with tailored properties for specific tissue engineering applications. One of these poly(ester-urethane)s, based on a low molecular weight poly(caprolactone) as the macrodiol, cycloesandimethanol as the chain extender and hexamethylene diisocyanate as the chain linker, was investigated for the production of melt extruded nerve guides. We studied natural polymers such as gelatin (G), poly(L-lysine) (PL) and blends between chitosan and gelatin (CS/G) as internal coatings for nerve guides. In vitro and in vivo tests were performed on PCL guides internally coated either with G or PL to determine the differences in the quality of nerve regeneration associated with the type of adhesion protein. CS/G natural blends combined the good cell adhesion properties of the protein phase with the ability to promote nerve regeneration of the polysaccharide phase. Natural blends were crosslinked both by physical and chemical crosslinking methods. In vitro neuroblast adhesion tests were performed on CS/G film samples, PCL/CS and PU guides internally coated with G to evaluate the ability of such materials towards nerve repair.

Microrobotics and MEMS-Based Fabrication Techniques for Scaffold-Based Tissue Engineering

Scaffold based tissue engineering strategies use cells, biomolecules and a scaffold to promote the repair and regeneration of tissues. Although scaffold-based tissue engineering approaches are being actively developed, most are still experimental, and it is not yet clear what defines an ideal scaffold/cell construct. Solid free form fabrication (SFF) techniques can precisely control matrix architecture (size, shape, interconnectivity, branching, geometry and orientation). The SFF methods enable the fabrication of scaffolds with various designs and material compositions, thus providing a control of mechanical properties, biological effects and degradation kinetics. This paper reviews the application of micro-robotics and MEMS-based fabrication techniques for scaffold design and fabrication. It also presents a novel robotic technique to fabricate scaffold/cell constructs for tissue engineering by the assembly of microscopic building blocks.

A reusable microfluidic plate with alternate-choice architecture for assessing growth preference in tissue culture

We present the design of a chamber to evaluate in vitro how species and concentrations of soluble molecules control features of cell growth-potentially including cell proliferation, cell motility, process extension, and process termination. We have created a reusable cell culture plate that integrates a microfluidic media delivery network with standard cell culture environment. The microfluidic network delivers a stream of cell culture media with a step-like concentration gradient down a 50-100 microm wide microchannel called the presentation region. Migrating cells or growing cell processes freely choose between the two distinct chemical environments in the presentation region, but they are forced to exclusively choose either one environment or the other when they grow past a physical barrier acting as a decision point. Our fabrication technique requires little specialized equipment, and can be carried out in approximately 4 days per plate. We demonstrate the effectiveness of our plates as neurites from spiral ganglion explants preferentially grow in media containing neurotrophin-3 (NT-3) as opposed to media without NT-3. Our design could be used without modification to study dissociated cell responses to soluble growth cues, and for behavioral screening of small motile organisms.

Dynamics of Chain Exchange Between Self-Assembled Diblock Copolymer Micelles of Poly(ethylene oxide)-block-Polylactide Studied by Direct Nonradiative Excitation Energy Transfer

A series of diblock poly(ethylene oxide)-block-polylactide copolymers with fairly narrow distribution of molar masses and compositions was prepared and characterized. The copolymers form multimolecular spherical micelles in 1,4-dioxane-water mixtures. The chain exchange between micelles formed by fluorescence-labeled copolymers was studied by direct nonradiative excitation energy transfer (NRET) fluorescence measurements in water-rich media containing 10 vol.% of 1,4-dioxane. The equilibration rate, i.e., the rate of unimer chain exchange between micelles obeys basically the theoretically predicted scaling relations. It slows down with the length of soluble blocks (a quadratic decrease) and considerably (an exponential decrease) with the length of insoluble chains. Scaling exponents were found lower than those predicted. The study shows that nanoparticle systems based on poly(ethylene oxide)-block-polylactide copolymers with required properties for various biomedical applications can be designed, prepared and their properties can be optimized.