Investigation of the size effect for photonic crystals.

Three types of photonic crystal (PC) thin films have been prepared for the investigation of their deformation behaviors by nanoindentation tests at the microscale and nanoscale. Each type of PC thin film was composed of poly(methyl methacrylate) (PMMA) nanoparticles with a uniform size. Another type of thin film was prepared by assembling nanoparticles with three different sizes. It was exciting to observe that the hardness and Young's modulus were significantly improved (more than 15 times) in well-ordered PC thin films than disordered ones. Furthermore, size-dependent mechanical properties were observed for the three types of PCs. Such a size effect phenomenon can be attributed to the special polycrystalline material having a periodical face-centered cubic structure of PC thin films. Furthermore, the indentation size effect that shows that the indentation hardness decreases with an increasing indentation depth has also been observed for all four types of thin films. It is conjectured that the application of the PC structure to other functional materials may enhance their mechanical properties.

Ganglion of the Flexor Tendon Sheath at the A2 Pulley - Case Report.

There are few reported cases of flexor tendon sheath ganglion arising from the A2 pulley. We report a case of a flexor tendon sheath ganglion in a 17-year old female who presented with pain, triggering and a swelling at the base of her right ring finger. During the excision biopsy, a ganglion measuring 0.5×0.8×0.4 cm in size was removed from the A2 pulley area.

The development of silk fibroin scaffolds using an indirect rapid prototyping approach: morphological analysis and cell growth monitoring by spectral-domain optical coherence tomography.

To date, naturally derived biomaterials are rarely used in advanced tissue engineering (TE) methods despite their superior biocompatibility. This is because these native materials, which consist mainly of proteins and polysaccharides, do not possess the ability to withstand harsh processing conditions. Unlike synthetic polymers, natural materials degrade and decompose rapidly in the presence of chemical solvents and high temperature, respectively. Thus, the fabrication of tissue scaffolds using natural biomaterials is often carried out using conventional techniques, where the efficiency in mass transport of nutrients and removal of waste products within the construct is compromised. The present study identified silk fibroin (SF) protein as a suitable material for the application of rapid prototyping (RP) or additive manufacturing (AM) technology. Using the indirect RP method, via the use of a mould, SF tissue scaffolds with both macro- and micro-morphological features can be produced and qualitatively examined by spectral-domain optical coherence tomography (SD-OCT). The advanced imaging technique showed the ability to differentiate the cells and SF material by producing high contrasting images, therefore suggesting the method as a feasible alternative to the histological analysis of cell growth within tissue scaffolds.

Fabrication of channeled scaffolds with ordered array of micro-pores through microsphere leaching and indirect Rapid Prototyping technique.

Advanced scaffold fabrication techniques such as Rapid Prototyping (RP) are generally recognized to be advantageous over conventional fabrication methods in terms architectural control and reproducibility. Yet, most RP techniques tend to suffer from resolution limitations which result in scaffolds with uncontrollable, random-size pores and low porosity, albeit having interconnected channels which is characteristically present in most RP scaffolds. With the increasing number of studies demonstrating the profound influences of scaffold pore architecture on cell behavior and overall tissue growth, a scaffold fabrication method with sufficient architectural control becomes imperative. The present study demonstrates the use of RP fabrication techniques to create scaffolds having interconnected channels as well as controllable micro-size pores. Adopted from the concepts of porogen leaching and indirect RP techniques, the proposed fabrication method uses monodisperse microspheres to create an ordered, hexagonal closed packed (HCP) array of micro-pores that surrounds the existing channels of the RP scaffold. The pore structure of the scaffold is shaped using a single sacrificial construct which comprises the microspheres and a dissolvable RP mold that were sintered together. As such, the size of pores as well as the channel configuration of the scaffold can be tailored based on the design of the RP mold and the size of microspheres used. The fabrication method developed in this work can be a promising alternative way of preparing scaffolds with customized pore structures that may be required for specific studies concerning cell-scaffold interactions.

Esophageal tissue engineering: an in-depth review on scaffold design.

Treatment of esophageal cancer often requires surgical procedures that involve removal. The current approaches to restore esophageal continuity however, are known to have limitations which may not result in full functional recovery. In theory, using a tissue engineered esophagus developed from the patient's own cells to replace the removed esophageal segment can be the ideal method of reconstruction. One of the key elements involved in the tissue engineering process is the scaffold which acts as a template for organization of cells and tissue development. While a number of scaffolds range from traditional non-biodegradable tubing to bioactive decellularized matrix have been proposed to engineer the esophagus in the past decade, results are still not yet favorable with many challenges relating to tissue quality need to be met improvements. The success of new esophageal tissue formation will ultimately depend on the success of the scaffold being able to meet the essential requirements specific to the esophageal tissue. Here, the design of the scaffold and its fabrication approaches are reviewed. In this paper, we review the current state of development in bioengineering the esophagus with particular emphasis on scaffold design.

Investigation of the mechanical properties and porosity relationships in selective laser-sintered polyhedral for functionally graded scaffolds.

An important requirement for a bone tissue engineering scaffold is a stiffness gradient that mimics that of native bone. Such scaffolds can be achieved by controlling their structure and porosity and are termed functionally graded scaffolds (FGS). Currently, the main challenges in FGS fabrication include the iterative and tedious design process as well as a heavy reliance on the user's CAD/CAM skills. This work aims to bring automated FGS production a step closer by providing a database that correlates scaffold porosity values and the corresponding compressive stiffness and integrating it into the design process. To achieve this goal, scaffolds with different structural configurations were designed using CASTS (Computer Aided System for Tissue Scaffolds), an in-house developed library system consisting of 13 different polyhedral units that can be assembled into scaffold structures. Polycaprolactone (PCL) was chosen as the scaffold material, while selective laser sintering, a powder-based rapid prototyping or additive manufacturing system was employed to fabricate the scaffolds. Mathematical relations correlating scaffold porosity and compressive stiffness readings were formulated and compiled. In addition, cytotoxicity assessment was conducted to evaluate the toxicity of the fabricated PCL scaffolds. Lastly, a brief demonstration of how the formulated relations are used in the FGS design process is presented.

Porous polycaprolactone scaffold for cardiac tissue engineering fabricated by selective laser sintering.

An advanced manufacturing technique, selective laser sintering (SLS), was utilized to fabricate a porous polycaprolactone (PCL) scaffold designed with an automated algorithm in a parametric library system named the "computer-aided system for tissue scaffolds" (CASTS). Tensile stiffness of the sintered PCL strut was in the range of 0.43+/-0.15MPa when a laser power of 3W and scanning speed of 150 in s(-1) was used. A series of compressive mechanical characterizations was performed on the parametric scaffold design and an empirical formula was presented to predict the compressive stiffness of the scaffold as a function of total porosity. In this work, the porosity of the scaffold was selected to be 85%, with micropores (40-100mum) throughout the scaffold. The compressive stiffness of the scaffold was 345kPa. The feasibility of using the scaffold for cardiac tissue engineering was investigated by culturing C2C12 myoblast cells in vitro for 21days. Fluorescence images showed cells were located throughout the scaffold. High density of cells at 1.2x10(6)cellsml(-1) was recorded after 4days of culture. Fusion and differentiation of C2C12 were observed as early as 6days in vitro and was confirmed with myosin heavy chain immunostaining after 11days of cell culture. A steady population of cells was then maintained throughout 21days of culturing. This work demonstrated the feasibility of tailoring the mechanical property of the scaffold for soft tissue engineering using CASTS and SLS. The macroarchitecture of the scaffold can be modified efficiently to fabricate scaffolds with different macropore sizes or changing the elemental cell design in CASTS. Further process and design optimization could be carried out in the future to fabricate scaffolds that match the tensile strength of native myocardium, which is of the order of tens of kPa.

Melt flow behaviour of poly-epsilon-caprolactone in fused deposition modelling.

Fused deposition modelling (FDM) is an extrusion based Rapid prototyping (RP) technique which can be used to fabricate tissue engineering scaffolds. The present work focuses on the study of the melt flow behaviour (MFB) of Poly-epsilon-caprolactone (PCL) as a representative biomaterial, on the FDM. The MFB significantly affects the quality of the scaffold which depends not only on the pressure gradient, its velocity, and the temperature gradients but also physical properties like the melt temperature and rheology. The MFB is studied using two methods: mathematical modelling and finite element analysis (FEA) using Ansys(R). The MFB is studied using accurate channel geometry by varying filament velocity at the entry and by varying nozzle diameters and angles at the exit. The comparative results of both mathematical modelling and FEA suggest that the pressure drop and the velocities of the melt flow depend on the flow channel parameters. One inference of particular interest is the temperature gradient of the PCL melt, which shows that it liquefies within 35% of the channel length. These results are invaluable to better understand the MFB of biomaterials that affects the quality of the scaffold built via FDM and can also be used to predict the MFB of other biomaterials.

Engineering functionally graded tissue engineering scaffolds.

Tissue Engineering (TE) aims to create biological substitutes to repair or replace failing organs or tissues due to trauma or ageing. One of the more promising approaches in TE is to grow cells on biodegradable scaffolds, which act as temporary supports for the cells to attach, proliferate and differentiate; after which the scaffold will degrade, leaving behind a healthy regenerated tissue. Tissues in nature, including human tissues, exhibit gradients across a spatial volume, in which each identifiable layer has specific functions to perform so that the whole tissue/organ can behave normally. Such a gradient is termed a functional gradient. A good TE scaffold should mimic such a gradient, which fulfils the biological and mechanical requirements of the target tissue. Thus, the design and fabrication process of such scaffolds become more complex and the introduction of computer-aided tools will lend themselves well to ease these challenges. This paper reviews the needs and characterization of these functional gradients and the computer-aided systems used to ease the complexity of the scaffold design stage. These include the fabrication techniques capable of building functionally graded scaffolds (FGS) using both conventional and rapid prototyping (RP) techniques. They are able to fabricate both continuous and discrete types of FGS. The challenge in fabricating continuous FGS using RP techniques lies in the development of suitable computer aided systems to facilitate continuous FGS design. What have been missing are the appropriate models that relate the scaffold gradient, e.g. pore size, porosity or material gradient, to the biological and mechanical requirements for the regeneration of the target tissue. The establishment of these relationships will provide the foundation to develop better computer-aided systems to help design a suitable customized FGS.

Higher Order Spectral (HOS) analysis of epileptic EEG signals.

Epilepsy is a neurological condition, which affects the nervous system. Automatic seizure detection is very important in clinical practice and has to be achieved by analyzing the Electroencephalogram (EEG). Seizures are the clinical manifestations of excessive and hypersynchronous activity of the neurons in the cerebral cortex and represent one of the most frequent malfunctions of the human central nervous system. Therefore, the search for precursors and predictors of a seizure in the human EEG is of utmost clinical relevance and may even lead to a deeper understanding of the seizure generating mechanisms. In this paper, the normal, pre-ictal (background) and ictal (epileptic) EEG signals are studied using higher order spectra. HOS based measures are shown to be able to distinguish epileptic EEG from normal and background EEG with high confident level (p-value of less than 0.05).

Characterization of a poly-epsilon-caprolactone polymeric drug delivery device built by selective laser sintering.

Selective Laser Sintering (SLS), an established Rapid Prototyping (RP) process, is investigated for building controlled drug delivery devices (DDD). The drug and its matrix in a powder form were first mixed mechanically before being sintered on the SLS. Each cylindrical DDD is designed with a number of concentric rings separated from each other by a characteristic 'wall' created by the laser of the SLS. These rings act as diffusion obstacles to control the rate of release. Poly-epsilon-caprolactone (PCL) was used as the matrix and Methylene Blue (MB) as the drug model. Samples were built, characterized and tested for homogeneity using Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Fourier Transform Infrared Spectrophotometry (FTIR). Experimental results show that the matrices fabricated are not affected by sintering and the polymer and drug model are evenly distributed throughout the matrix. The initial burst effect has been reduced by the increase of the numbers of rings. The linear curve using the Higuchi equation confirmed that the DDD matrix release profile is by diffusion. These results show that the DDD matrix design has promising potential for application in controlled release drug delivery.

Compressive properties and degradability of poly(epsilon-caprolatone)/hydroxyapatite composites under accelerated hydrolytic degradation.

Hydroxyapatite (HA) was incorporated as filler into polycaprolactone (PCL) matrix to improve the bioactivity as well as the compressive properties of the polymer composites that can be typically used in tissue engineering scaffolds. The compressive properties of five PCL/HA composites of different compositions were investigated in conjunction with the study of their rate of degradation. As PCL has a slow degradation rate, the experiment was conducted in a concentrated 5M sodium hydroxide medium to accelerate the degradation process. The compressive strength and modulus of all PCL/HA compositions were observed to decrease as the degradation experiment progressed, with samples having high HA content degraded most significantly as compared with samples with lower HA content. Pure PCL samples, however, were found to retain their mechanical properties comparatively well in the same degradation experiments. Although the addition of HA as filler into the PCL matrix was shown to have improved mechanical properties and bioactivity initially, these results do raise concerns of material properties being compromise during hydrolytic degradation.

Poly-epsilon-caprolactone/hydroxyapatite for tissue engineering scaffold fabrication via selective laser sintering.

Rapid prototyping (RP) techniques are becoming more popular for fabricating tissue engineering (TE) scaffolds owing to their advantages over conventional methods, such as the ability to fabricate scaffolds with predetermined interconnected networks without the use of organic solvents. A versatile RP technique, selective laser sintering (SLS), offers good user control of scaffold microstructure by adjusting the process parameters. This research focuses on a the use of biocomposite material, consisting of poly-epsilon-caprolactone (PCL) and hydroxyapatite (HA), to fabricate TE scaffolds using SLS. Biocomposite blends with different percentage weights of HA were physically blended and sintered to assess their suitability for fabrication via SLS. Optimal sintering conditions for the powders were achieved by varying parameters such as laser power and scan speed. Studies of the sintered specimen morphology were performed by scanning electron microscopy. Thermogravimetric analysis confirmed the homogeneity of the biocomposite blend. Simulated body fluid (SBF) samples show the formation of hydroxy carbonate apatite, as a result of soaking HA in a SBF environment. Cell culture experiment showed that Saos-2 cells were able to live and replicate on the fabricated scaffolds. The results show the favorable potential of PCL/HA biocomposite as TE scaffolds that are fabricated via SLS.

Fabrication and characterization of three-dimensional poly(ether- ether- ketone)/-hydroxyapatite biocomposite scaffolds using laser sintering.

The ability to have precise control over porosity, scaffold shape, and internal pore architecture is critical in tissue engineering. For anchorage-dependent cells, the presence of three-dimensional scaffolds with interconnected pore networks is crucial to aid in the proliferation and reorganization of cells. This research explored the potential of rapid prototyping techniques such as selective laser sintering to fabricate solvent-free porous composite polymeric scaffolds comprising of different blends of poly(ether-ether-ketone) (PEEK) and hydroxyapatite (HA). The architecture of the scaffolds was created with a scaffold library of cellular units and a corresponding algorithm to generate the structure. Test specimens were produced and characterized by varying the weight percentage, starting with 10 wt% HA to 40 wt% HA, of physically mixed PEEK-HA powder blends. Characterization analyses including porosity, microstructure, composition of the scaffolds, bioactivity, and in vitro cell viability of the scaffolds were conducted. The results obtained showed a promising approach in fabricating scaffolds which can produce controlled microarchitecture and higher consistency.

Selective laser sintering of biocompatible polymers for applications in tissue engineering.

The ability to use biological substitutes to repair or replace damaged tissues lead to the development of Tissue Engineering (TE), a field that is growing in scope and importance within biomedical engineering. Anchorage dependent cell types often rely on the use of temporary three-dimensional scaffolds to guide cell proliferation. Computer-controlled fabrication techniques such as Rapid Prototyping (RP) processes have been recognised to have an edge over conventional manual-based scaffold fabrication techniques due to their ability to create structures with complex macro- and micro-architectures. Despite the immense capabilities of RP fabrication for scaffold production, commercial available RP modelling materials are not biocompatible and are not suitable for direct use in the fabrication of scaffolds. Work is carried out with several biocompatible polymers such as Polyetheretherketone (PEEK), Poly(vinyl alcohol) (PVA), Polycaprolactone (PCL) and Poly(L-lactic acid) (PLLA) and a bioceramic namely, Hydroxyapatite (HA). The parameters of the selective laser sintering (SLS) process are optimised to cater to the processing of these materials. SLS-fabricated scaffold specimens are examined using a Scanning Electron Microscope (SEM). Results observed from the micrographs indicate the viability of them being used for building TE scaffolds and ascertain the capabilities of the SLS process for creating highly porous scaffolds for Tissue Engineering applications.

Development of tissue scaffolds using selective laser sintering of polyvinyl alcohol/hydroxyapatite biocomposite for craniofacial and joint defects.

The growing interest in scaffold-guided tissue engineering (TE) to guide and support cell proliferation in the repair and replacement of craniofacial and joint defects gave rise to the quest for a precise technique to create such scaffolds. Conventional manual-based fabrication techniques have several limitations such as the lack of reproducibility and precision. Rapid prototyping (RP) has been identified as a promising technique capable of building complex objects with pre-defined macro- and microstructures. The research focussed on the viability of using the selective laser sintering (SLS) RP technique for creating TE scaffolds. A biocomposite blend comprising of polyvinyl alcohol (PVA) and hydroxyapatite (HA) was used in SLS to study the feasibility of the blend to develop scaffolds. The biocomposite blends obtained via spray-drying technique and physical blending were subjected to laser-sintering to produce test specimens. The SLS-fabricated test specimens were characterized using scanning electron microscopy and X-ray diffraction. The test specimens were also tested for bioactivity by immersing the samples in simulated body fluid environment. The results obtained ascertained that SLS-fabricated scaffolds have good potential for TE applications.

Scaffold development using selective laser sintering of polyetheretherketone-hydroxyapatite biocomposite blends.

In tissue engineering (TE), temporary three-dimensional scaffolds are essential to guide cell proliferation and to maintain native phenotypes in regenerating biologic tissues or organs. To create the scaffolds, rapid prototyping (RP) techniques are emerging as fabrication techniques of choice as they are capable of overcoming many of the limitations encountered with conventional manual-based fabrication processes. In this research, RP fabrication of solvent free porous polymeric and composite scaffolds was investigated. Biomaterials such as polyetheretherketone (PEEK) and hydroxyapatite (HA) were experimentally processed on a commercial selective laser sintering (SLS) RP system. The SLS technique is highly advantageous as it provides good user control over the microstructures of created scaffolds by adjusting the SLS process parameters. Different weight percentage (wt%) compositions of physically mixed PEEK/HA powder blends were sintered to assess their suitability for SLS processing. Microstructural assessments of the scaffolds were conducted using electron microscopy. The results ascertained the potential of SLS-fabricated TE scaffolds.

Solid freeform fabrication of three-dimensional scaffolds for engineering replacement tissues and organs.

Most tissue engineering (TE) strategies for creating functional replacement tissues or organs rely on the application of temporary three-dimensional scaffolds to guide the proliferation and spread of seeded cells in vitro and in vivo. The characteristics of TE scaffolds are major concerns in the quest to fabricate ideal scaffolds. This paper identifies essential structural characteristics and the pre-requisites for fabrication techniques that can yield scaffolds that are capable of directing healthy and homogeneous tissue development. Emphasis is given to solid freeform (SFF), also known as rapid prototyping, technologies which are fast becoming the techniques of choice for scaffold fabrication with the potential to overcome the limitations of conventional manual-based fabrication techniques. SFF-fabricated scaffolds have been found to be able to address most, if not all the macro- and micro-architectural requirements for TE applications. This paper reviews the application/potential application of state-of-the-art SFF fabrication techniques in creating TE scaffolds. The advantages and limitations of the SFF techniques are compared. Related research carried out worldwide by different institutions, including the authors' research are discussed.

Rapid manufacturing techniques in the development of an axial blood pump impeller.

This paper presents a comparison of manufacturing techniques used in the development of an axial blood pump impeller. In this development process the impeller was designed and its performance was evaluated with the aid of computational fluid dynamics (CFD). Prototypes of those designs where the CFD results show promise were needed in sufficient quantities at a low cost for experimental validation of the CFD results. As the impeller is less than 16 mm in diameter with a maximum blade thickness of about 1.5 mm, innovative manufacturing techniques are explored in this paper to determine the best process for quick fabrication of prototypes that are dimensionally accurate, structurally robust and low in cost. Four rapid prototyping techniques were explored. The completed parts were compared on the basis of manufacturing time, quality and strength of parts obtained, manufacturing cost and also in vitro performances. Based on these studies, it was concluded that selective laser sintering (SLS) is the most appropriate method for the quick production of prototype parts for evaluation of pump performance.

Characterization of microfeatures in selective laser sintered drug delivery devices.

From initial applications in the fields of prosthesis, implants, surgery planning, anthropology, paleontology and forensics, the scope of rapid prototyping (RP) biomedical applications has expanded to include areas in tissue engineering (TE) and controlled drug delivery. In the current investigation, the feasibility of utilizing selective laser sintering (SLS) to fabricate polymeric drug delivery devices (DDDs) that are difficult to make using conventional production methods was studied. Two features, namely porous microstructure and dense wall formation, inherent in SLS fabricated parts were investigated for their potential roles in drug storage and controlling the release of drugs through the diffusion process. A study to determine the influence of key SLS process parameters on dense wall formation and porous microstructure of SLS fabricated parts was carried out. Composite-type DDDs incorporating dense wall and porous matrix features were designed and fabricated using SLS. The characteristics of the fabricated devices were investigated through microstructural examination and in vitro release tests carried out using a drug model or dye in a simulated body environment.