Tissue engineering and the trauma surgeon

The demands for repair and renewal of worn out or injured human tissue grow year on year<Eth> it is a demand that cannot be met from live human donors. A partial solution may be found from cadaveric or trans-species transplantation of tissue, but these approaches are steeped in the problems of disease transfer and ethical dilemma. Tissue engineering is a new technology that seeks to meet these increasing demands by utilizing novel cell culture methods in vitro to provide tissue replacements in vivo. This article reviews the current state of tissue engineering and its potential for use in the realms of trauma surgery.

Stem cell applications and tissue engineering approaches in surgical practice

There has been an increasing interest in stem cell applications and tissue engineering approaches in surgical practice to deal with damaged or lost tissue. Although there have been developments in almost all surgical disciplines, the greatest advances are being made in orthopaedics, especially in bone repair. Significant hurdles however remain to be overcome before tissue engineering becomes more routinely used in surgical practice.

Addressing thrombogenicity in vascular graft construction

Thrombosis is a major cause of poor patency in synthetic vascular grafts for small diameter vessel (< 6 mm) bypass. Arteries have a host of structural mechanisms by which they prevent triggering of platelet activation and the clotting cascade. Many of these are present in vascular endothelial cells. These mechanisms act together with perpetual feedback at different levels, providing a constantly fine-tuned non-thrombogenic environment. The arterial wall anatomy also serves to promote thrombosis as a healing mechanism when it has been severely injured. Surface modification of synthetic graft surfaces to attenuate the coagulation cascade has reduced thrombosis levels and improved patency in vitro and in animal models. Success in this endeavor is critically dependent on the methods used to modify the surface. Platelets adhere to positively charged surfaces due to their own negative charge. They also preferentially attach to hydrophobic surfaces. Therefore synthetic graft development is concerned with hydrophilic materials with negative surface charge. However, fibrinogen has both hydrophilic and hydrophobic binding sites-amphiphilic materials reduce its adhesion and subsequent platelet activation. The self-endothelializing synthetic graft is an attractive proposition as a confluent endothelial layer incorporates many of the anti-thrombogenic properties of arteries. Surface modification to promote this has shown good results in animal models. The difficulties experienced in achieving spontaneous endothelialisation in humans have lead to the investigation of pre-implantation in vitro endothelial cell seeding. These approaches ultimately aim to result in novel synthetic grafts which are anti-thrombogenic and hence suitable for coronary and distal infrainguinal bypass.

Electrospun nanofibres: Biomedical applications

Synthetic and semi-synthetic polymeric materials were originally developed for their durability and resistance to all forms of degradation, including biodegradation. Nanotechnology has the potential to revolutionize many sectors, including pharmaceuticals, information technology, medical devices, materials science, chemicals, and energy. Nanofibres provide a connection between the nanoscale world and the macroscale world, since their diameters are in the range of 1 to 100 nanometres and several metres in length. Therefore, the current emphasis of research is to exploit such properties and focus on determining appropriate conditions for electrospinning various polymers and biopolymers for eventual applications including: multifunctional membranes; biomedical structural elements (scaffolds used in tissue engineering, wound dressing, drug delivery, artificial organs, vascular grafts); protective shields in specialty fabrics; and filter media for submicron particles in the separation industry. This paper reviews the research on recent biomedical applications of electrospun nanofibres.

Tissue Engineering für Herzklappen und Gefäße

Current prosthetic substitutes for heart valves and blood vessels have numerous limitations such as limited durability (biological valves), susceptibility to infection, the necessity of lifelong anticoagulation therapy (prosthetic valves), and reduced patency in small-caliber grafts, for example. Tissue engineering using either polymers or decellularized native allogeneic or xenogenic heart valve/vascular matrices may provide the techniques to develop the ideal heart valve or vascular graft. The matrix scaffold serves as a basis on which seeded cells can organise and develop into the valve or vascular tissue prior to or following implantation. The scaffold is either degraded or metabolised during the formation and organisation of the newly generated matrix, leading to vital living tissue. This paper summarises current research and first clinical developments in the tissue engineering of heart valves and vascular grafts.

Synthesis and characterization of acrylic terpolymers with RGD peptides for biomedical applications

The goal of this research was to design a biomaterial, using acrylic terpolymers, which could support endothelial cells and function in small diameter vascular graft applications. Hexyl methacrylate (HMA) and octyl methacrylate (OMA) were used as comonomers to produce a material with a low glass transition temperature (T(g)). Methacrylic acid (MAA) was used to provide ionic character, and methyl methacrylate (MMA) was selected because of its wide usage in biomedical applications. Cation neutralization was employed to modify the mechanical properties. RGD-based peptide sequences were attached to promote endothelial cell adhesion, because vascular grafts seeded with endothelial cells have fewer problems with thrombosis. The two methods used to incorporate peptide sequences were a chain transfer reaction during polymerization, and a coupling reaction attaching the peptides to carboxyl groups on the polymer after polymerization. The compositions that produced T(g)s of approximately 0 degrees C were 75 mol% OMA and 92 mol% HMA. The Young's modulus of the HMA copolymer was approximately 0.37 MPa, well below the desired value of 0.9 MPa. Likewise, the Young's modulus of approximately 0.50 MPa for the OMA copolymer was also below the desired value. After partial neutralization with sodium cations, the Young's moduli increased to approximately 0.93 and 0.99 MPa, respectively. The chain transfer reaction lowered the molecular weights and mechanical properties of the copolymers, while the coupling reaction method had little effect on these properties. The chain transfer method appears to be a promising one-step method to produce polymers with a wide range of peptide concentrations.

Tissue engineering in surgery

The demands for repair and renewal of worn out or injured human tissue continue to increase and it is now apparent that this demand cannot be met from human donors. A partial solution may be found in living related and trans-species transplantation but these approaches invoke the problems of disease transfer and ethical dilemmas. Tissue engineering is a new technology that seeks to meet these increasing demands by utilising novel cell culture methods in vitro to provide tissue replacements in vivo. This article reviews the current state of tissue engineering and its potential for use in surgery.

Endothelial cell adhesion on RGD-containing methacrylate terpolymers

Hexyl methacrylate (HMA), methyl methacrylate (MMA), and methacrylic acid (MAA) were used as comonomers to produce a low glass transition temperature material, potentially useful in fabricating a small diameter vascular graft. Because it has been shown that grafts seeded with endothelial cells have better resistance to thrombosis, RGD-based peptide sequences were incorporated into the terpolymer. The two methods used for incorporating peptide sequences were a chain transfer reaction during polymerization, and a coupling reaction between the amine terminus of the peptide and the carboxyl groups of the MAA. Polymers were synthesized using the chain transfer reaction with peptide concentrations ranging from 1.7 to 7.0 micromol/g. Weight-average molecular weights decreased with increasing peptide concentration from 310,000 g/mol for the terpolymer without peptide, to 110,000 g/mol for a peptide concentration of 7.0 micromol/g. As a result, Young's modulus decreased with increasing peptide concentration. Terpolymers with peptides attached through a coupling reaction showed no decrease in molecular weight or mechanical properties. Confocal microscopy showed cells seeded on the RGD surfaces adhered and spread, while terpolymers with RGE sequences showed cells that were rounded and not spreading. Cell density on RGD surfaces increased with increasing peptide concentration up to a bulk peptide concentration of approximately 5 micromol/g and reached a plateau, which indicated the minimum peptide concentration necessary for maximum cell adhesion.

Improving the clinical patency of prosthetic vascular and coronary bypass grafts: the role of seeding and tissue engineering

In patients requiring coronary or peripheral vascular bypass procedures, autogenous vein is currently the conduit of choice. If this is unavailable, then a prosthetic material is used. Prosthetic graft is liable to fail due to occlusion of the graft. To prevent graft occlusion, seeding of the graft lumen with endothelial cells is undertaken. Recent advances have also looked at developing a completely artificial biological graft engineered from the patient's cells with properties similar to autogenous vessels. This review encompasses the developments in the two principal technologies used in developing hybrid coronary and peripheral vascular bypass grafts, that is, seeding and tissue engineering.

Vascular tissue engineering

The development of a tissue-engineered blood vessel substitute has motivated much of the research in the area of cardiovascular tissue engineering over the past 20 years. Several methodologies have emerged for constructing blood vessel replacements with biological functionality. These include cell-seeded collagen gels, cell-seeded biodegradable synthetic polymer scaffolds, cell self-assembly, and acellular techniques. This review details the most recent developments, with a focus on core technologies and construct development. Specific examples are discussed to illustrate both the benefits and shortcomings of each methodology, as well as to underline common themes. Finally, a brief perspective on challenges for the future is presented.