Influence of scaffold pore size on collagen I development: A new in vitro evaluation perspective

Bone tissue engineering takes part in the complex process of bone healing by combining cells, chemical/physical signals, and scaffolds with the scaffolds providing an artificial extracellular matrix network. The role of the support template for cell activity is crucial to guide the healing process. This in vitro study compared three different poly(D,L-lactic acid) scaffolds obtained by varying the pore size generated by applying different salt leaching processes. The influence of pore dimensions on the extracellular matrix produced by human osteosarcoma-derived osteoblasts (MG63 cell line) seeded on these different materials was analyzed. This study is targeted on the intermediate stage of the bone healing process, where a collagen network is beginning to develop by the growing osteoblasts representing the template for the ultimate stage of bone formation. Imaging analyses assessed by confocal laser microscopy were combined with gene expression measurements of the most common genes involved in the bone healing process. Furthermore, in vitro evaluations were carried out to investigate cell morphology, proliferation, and viability. It was found that the different pore size matrixes can affect extracellular matrix development and that cell organization, collagen I assembly, and mineralization are strictly correlated.

Tissue engineering: from biology to biological substitutes

Tissue engineering is an emerging multidisciplinary and interdisciplinary field involving the development of bioartificial implants and/or the fostering of tissue remodeling with the purpose of repairing or enhancing tissue or organ function. Bioartificial constructs generally consist of cells and biomaterials, so tissue engineering draws from both cell and biomaterials science and technology. Successful applications require a thorough understanding of the environment experienced by cells in normal tissues and by cells in bioartificial devices before and after implantation. This paper reviews these topics, as well as the current status and future possibilities in the development of different bioartificial constructs, including bioartificial skin, cardiovascular implants, bioartificial pancreas, and encapsulated secretory cells. Issues that need to be addressed in the future are also discussed. These include, but are not limited to, the development of new cell lines and biomaterials, the evaluation of the optimal construct architecture, and the reproducible manufacture and preservation of bioartificial devices until ready for use.

Use of Matrix Assisted Pulsed Laser Evaporation (Maple) for the Growth of Organic Thin Films

A novel variation of conventional pulsed laser deposition, called matrix assisted pulsed laser evaporation, or MAPLE, has been utilized for growing organic thin films. The MAPLE technique is carried out in a vacuum chamber and involves directing a pulsed laser beam) onto a frozen target consisting of an organic compound dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target with both solvent and organic molecules being released into the chamber. The volatile solvent is pumped away, whereas the organic molecules coat the surface of a substrate. Very thin and uniform films (50 to 100 nm) of various organic materials, such as carbohydrates, have been deposited on Si(111) and NaCl substrates. The films prepared using this method have been examined by optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and electrospray mass spectrometry. Careful control of the processing conditions allowed carbohydrates such as sucrose and glucose, in addition to high molecular weight polymers such as dextran, to be transferred to the substrate as uniform films, without significant chemical decomposition. The use of MAPLE films for chemical and biological sensor applications is being investigated and the potential of this technique for producing high quality thin films of other organic compounds will be discussed.

Finite element analysis of a personalized femoral scaffold with designed microarchitecture

Tissue engineering scaffolds with intricate and controlled internal structure can be realized using computer-aided design (CAD) and layer manufacturing (LM) techniques. Design and manufacturing of scaffolds for load-bearing bone sites should consider appropriate biocompatibile materials with interconnected porosity, surface properties, and sufficient mechanical properties that match the surrounding bone, in order to provide adequate support, and to mimic the physiological stress—strain state so as to stimulate new tissue growth. The authors have previously published methods for estimating subject- and site-specific bone modulus using computed tomography (CT) data, CAD, and process planning for LM of controlled porous scaffolds. This study evaluates the mechanical performance of the designed porous hydroxyapite scaffolds in load-bearing sites using a finite element (FE) approach. A subject-specific FE analysis using femoral, defect site geometry and anisotropic material assignment based on CT data is employed. Mechanical behaviour of the femur with scaffold in stance-phase gait loading, which has been shown experimentally to produce clinically relevant results, is analysed. The comparison of results with simulation of healthy femur shows an overall correspondence in stress and strain state which will provide optimized mechanical properties for avoiding stress shielding, and adequate strength to avoid failure risk and for active bone tissue regeneration.

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.

Tissue engineering: a 21st century solution to surgical reconstruction

Tissue engineering has emerged as a rapidly expanding approach to address the organ shortage problem. It is an "interdisciplinary field that applies the principles and methods of engineering and the life sciences toward the development of biological substitutes that can restore, maintain, or improve tissue function." Much progress has been made in the tissue engineering of structures relevant to cardiothoracic surgery, including heart valves, blood vessels, myocardium, esophagus, and trachea.

Dynamic seeding and in vitro culture of hepatocytes in a flow perfusion system

Our laboratory has investigated hepatocyte transplantation using biodegradable polymer matrices as an alternative treatment to end-stage liver disease. One of the major limitations has been the insufficient survival of an adequate mass of transplanted cells. This study investigates a novel method of dynamic seeding and culture of hepatocytes in a flow perfusion system. In experiment I, hepatocytes were flow-seeded onto PGA scaffolds and cultured in a flow perfusion system for 24 h. Overall metabolic activity and distribution of cells were assessed by their ability to reduce MTT. DNA quantification was used to determine the number of cells attached. Culture medium was analyzed for albumin content. In Experiment II, hepatocyte/polymer constructs were cultured in a perfusion system for 2 and 7 days. The constructs were examined by SEM and histology. Culture medium was analyzed for albumin. In experiment I, an average of 4.4 X 10(6) cells attached to the scaffolds by DNA quantification. Cells maintained a high metabolic activity and secreted albumin at a rate of 13 pg/cell/day. In experiment II, SEM demonstrated successful attachment of hepatocytes on the scaffolds after 2 and 7 days. Cells appeared healthy on histology and maintained a high rate of albumin secretion through day 7. Hepatocytes can be dynamically seeded onto biodegradable polymers and survive with a high rate of albumin synthesis in the flow perfusion culture system.