Thomas Boland

HUMAN MICROVASCULATURE FABRICATION USING THERMAL INKJET PRINTING TECHNOLOGY

The current tissue engineering paradigm is that successfully engineered thick tissues must include vasculature. As biological approaches alone, such as VEGF, have fallen short of their promises, one may look for an engineering approach to build microvasculature. Layer-by-layer approaches for customized fabrication of cell/scaffold constructs have shown some potential in building complex 3D structures. With the advent of cell printing, one may be able to build precise human microvasculature with suitable bio-ink. Human microvascular endothelial cells (HMVEC) and fibrin were studied as bio-ink for microvasculature construction. Endothelial cells are the only cells to compose the human capillaries and also form the entire inner lining of cardiovascular system. Fibrin has been already widely recognized as tissue engineering scaffold for vasculature and other cells, including skeleton/smooth muscle cells and chondrocytes. In our study, we precisely fabricated micron-sized fibrin channels using a drop-on-demand polymerization. This printing technique uses aqueous processes that have been shown to induce little, if any, damage to cells. When printing HMVEC cells in conjunction with the fibrin, we found the cells aligned themselves inside the channels and proliferated to form confluent linings. The 3D tubular structure was also found in the printed patterns. We conclude that a combined simultaneous cell and scaffold printing can promote HMVEC proliferation and microvasculature formation.

Cell damage evaluation of thermal inkjet printed Chinese hamster ovary cells.

Thermal inkjet printing technology has been applied successfully to cell printing. However, there are concerns that printing process may cause cell damages or death. We conducted a comprehensive study of thermal inkjet printed Chinese hamster ovary (CHO) cells by evaluating cell viability and apoptosis, and possible cell membrane damages. Additionally, we studied the cell concentration of bio‐ink and found optimum printing of concentrations around 8 million cells per mL. Printed cell viability was 89% and only 3.5% apoptotic cells were observed after printing. Transient pores were developed in the cell membrane of printed cells. Cells were able to repair these pores within 2 h after printing. Green fluorescent protein (GFP) DNA plasmids were delivered to CHO‐S cells by co‐printing. The transfection efficiency is above 30%. We conclude that thermal inkjet printing technology can be used for precise cell seeding with minor effects and damages to the printed mammalian cells. The printing process causes transient pores in cell membranes, a process which has promising applications for gene and macroparticles delivery to induce the biocompatibility or growth of engineered tissues. Biotechnol. Bioeng. 2010;106: 963–969.

Thermal inkjet printing in tissue engineering and regenerative medicine.

With the advantages of high throughput, digital control, and highly accurate placement of cells and biomaterial scaffold to the desired 2D and 3D locations, bioprinting has great potential to develop promising approaches in translational medicine and organ replacement. The most recent advances in organ and tissue bioprinting based on the thermal inkjet printing technology are described in this review. Bioprinting has no or little side effect to the printed mammalian cells and it can conveniently combine with gene transfection or drug delivery to the ejected living systems during the precise placement for tissue construction. With layer-by-layer assembly, 3D tissues with complex structures can be printed using scanned CT or MRI images. Vascular or nerve systems can be enabled simultaneously during the organ construction with digital control. Therefore, bioprinting is the only solution to solve this critical issue in thick and complex tissues fabrication with vascular system. Collectively, bioprinting based on thermal inkjet has great potential and broad applications in tissue engineering and regenerative medicine. This review article introduces some important patents related to bioprinting of living systems and the applications of bioprinting in tissue engineering field.

Biofabrication: reappraising the definition of an evolving field

Biofabrication is an evolving research field that has recently received significant attention. In particular, the adoption of Biofabrication concepts within the field of Tissue Engineering and Regenerative Medicine has grown tremendously, and has been accompanied by a growing inconsistency in terminology. This article aims at clarifying the position of Biofabrication as a research field with a special focus on its relation to and application for Tissue Engineering and Regenerative Medicine. Within this context, we propose a refined working definition of Biofabrication, including Bioprinting and Bioassembly as complementary strategies within Biofabrication.

Minimally invasive tissue engineering composites and cell printing

Injectable composites combined with tissue-printing technology for improved bioengineered devices. The invisible engineering problem, the one often ignored, is the design of a readily implantable, precisely assembled cellular construct. Previous studies have consistently shown that composite tissue-engineered devises are readily implanted via minimally invasive means and, in the systems tested, produce minimal inflammation and fibrous encapsulation. Gels of optimal viscosity are able to maintain separation between the cellular scaffold and allow tissue growth. Studies with the cell/substrate printing system have shown that it is possible to define, in a controlled manner, spatial arrangement of cells within a gel substrate.

Loading dependent swelling and release properties of novel biodegradable, elastic and environmental stimuli-sensitive polyurethanes

A novel degradable, elastic, anionic, and linear polyurethane was synthesized from hexamethylene diisocyanate, polycaprolactone diol, and a bicine chain extender. The chemical structure, mechanical properties, degradation rate, and swelling ratio were characterized by comparing the polymer with a polyurethane containing a 2,2-(methylimino) diethanol chain extender. Due to the incorporation of negatively charged carboxyl side groups, the bicine extended polymers exhibited higher micro-phase separation, better mechanical properties in dry condition, and better sensitivity to environmental stimuli than controls, as demonstrated by its high swelling ratio at elevated pH, lower ionic strength, or higher temperature. The swelling ratio of membranes showed reversible change as the function of pH at 37 degrees C, the membranes becoming fully water soluble at pH above 8.3. Nile blue chloride and lysozyme were selected to study their release from this polymer. The release rates of both compounds were significantly influenced by the pH and ionic strength. The swelling ratios were also influenced by lysozyme loading at low pH. The pH dependent properties were used to fabricate scaffolds by drop-on-demand printing. Bicine extended polyurethanes may be of interest for possible drug delivery applications, customizable scaffold fabrication and other potential biomedical applications.

Design and implementation of a two-dimensional inkjet bioprinter

Tissue engineering has the potential to improve the current methods for replacing organs and tissues and for investigating cellular process within the scope of a tissue test system. Bioprinting technology can aid in the difficult task of arranging live mammalian cells and biomaterials in viable structures for tissue engineering purposes. This paper describes a system, based on HP26 series print cartridge technology, capable of precisely depositing multiple cell types in precise patterns. The paper discusses the research, design, and implementation of the printing system, which permits control of droplet firing parameters, including firing energy, speed, and spacing. The results demonstrate the system’s fine patterning ability of viable cells, including two-dimensional patterned co-cultures of two cell types. The system has been specifically designed with the flexibility to be extended to print more than two cell types and/or materials simultaneously and to layer printed patterns to form three-dimensional constructs. With these features, the printing system will serve as the foundation for a biofabrication system capable of three-dimensional cell co-cultures, i.e. tissue test systems.

Molecular Basis of Bacterial Adhesion

Bacterial infections are responsible for a broad spectrum of human illnesses and medical device complications. For example, urinary tract infections caused by Escherichia coli affect over 7 million people annually and are among the most common infectious diseases acquired by humans.39 Enteropathogenic E. coli (EPEC) and shiga toxin-producing E. coli (STIC) are diarrhoegenic pathogens causing serious health problems in both industrialized and developing countries.26,15 Helicobacter pylori have been found to be a main factor in the development of gastric and duodenal ulcers and are believed to be a causitive factor of gastic cancer.34 Staphylococcus aureus and Staphylococcus epidermidis are major causes of infections associated with wounds, indwelling catheters, and cardiovascular and orthopedic implant devices.1,19,24,25,35,49,56,59

Nanoindentation properties of compression-moulded ultra-high molecular weight polyethylene

Abstract This paper investigates the elastic modulus and hardness of untreated and treated compression-moulded ultra-high molecular weight polyethylene (UHMWPE) tibial inserts of a total knee replacement (TKR) prosthesis. Investigations were carried out at a nanoscale using a Nanoindenter™ at penetration depths of 100, 250 and 500 nm. The nanomechanical properties of surface and subsurface layers of the compression-moulded tibial inserts were studied using the untreated UHMWPE. The nanomechanical properties of intermediate and core layers of the compression-moulded tibial insert were studied using the cryoultrasectioned and etched UHMWPE treated samples. The cryoultrasectioning temperature (-150°C) of the samples was below the glass transition temperature, T g(-122± 2°C), of UHMWPE. The measurement of the mechanical response of crystalline regions within the nanostructure of UHMWPE was accomplished by removing the amorphous regions using a time-varying permanganic-etching technique. The percentage crystallinity of UHMWPE was measured using differential scanning calorimetry (DSC) and the T g of UHMWPE was determined by dynamic mechanical analysis (DMA). Atomic force microscopy (AFM) was used to assess the effect of surface preparation on the samples average surface roughness, R a. In this study, it was demonstrated that the untreated UHMWPE samples had a significantly lower (p<0.0001) elastic modulus and hardness relative to treated UHMWPE cryoultrasectioned and etched samples at all penetration depths. No significant difference (p > 0.05) in elastic modulus and hardness between the cryoultrasectioned and etched samples was observed. These results suggest that the surface nanomechanical response of an UHMWPE insert in a total joint replacement (TJR) prosthesis is significantly lower compared with the bulk of the material. Additionally, it was concluded that the nanomechanical response of material with higher percentage crystallinity (67 per cent) was predominantly determined by the crystalline regions within the semi-crystalline UHMWPE nanostructure.

Collagen Matrix Alignment Using Inkjet Printer Technology

Collagen fiber orientation plays an important role in many cell properties and actions in vivo. While it is easy to replicate randomly oriented collagen in vitro, it is much more difficult to create aligned collagen matrices for cell culture. In this work, a novel inkjet printer-based collagen alignment technique was established. A collagen type I solution was printed in a line pattern onto glass substrates using a modified inkjet printer. Staining studies indicated that the heat involved in the printing process is not great enough to denature the collagen. The extent of alignment was observed using light microscopy, atomic force microscopy (AFM), and polarized light microscopy. Additionally, cardiomyocytes, which require extracellular matrix alignment to maintain their in vivo phenotype, were cultured on the aligned matrices. The cells grew along the lines of collagen and coordinated beating, indicating the success of the aligned matrix. This collagen alignment technique is cheap, fast, precise, and easy to use in comparison to other current techniques. It may be used to align other extracellular matrix proteins and could even be used to create a three dimensional construct with varying fiber orientations.