Biocompatibility of Injectable Materials

Biomaterials considered for use in regenerative medicine must possess certain basic requirements, including biocompatibility, biodegradation at a controlled rate to non-toxic breakdown products, support of cellular infiltration and tissue ingrowth, mechanical properties consistent with the requirements of the host tissue, and handling properties that facilitate ease of use in a clinical environment. Injectable biomaterials present significant advantages relative to implants, such as the ability to conform to complex anatomical defects and to be administered using minimally invasive techniques. For example, in the field of orthopedics, injectable biomaterials are of interest for a number of clinical indications, including filling of defects in trabecular bone at sites that are not weight-bearing and in contained defects where the structural bone is intact. However, injectable biomaterials also present additional challenges beyond the basic requirements for biomedical implants described above. A primary concern is the toxicity and ultimate fate of reactive intermediates that are not incorporated in the final cured product. Additionally, the injected material may have adverse effects on surrounding host tissue due to the reactivity of specific components or to the release of heat through a reaction exotherm. In some cases, the viscosity of the injected material may be too low, resulting in extravasation of the material into surrounding tissues where it has an adverse effect. Injectable biomaterials that are currently being investigated and developed as therapies for tissue engineering and regenerative medicine.

The role of Bioreactors in Tissue Engineering :

Ex vivo engineering of living tissues is a rapidly developing area with the potential to impact significantly on a wide-range of biomedical applications. Major obstacles to the generation of functional tissues and their widespread clinical use are related to a limited understanding of the regulatory role of specific physicochemical culture parameters on tissue development, and the high manufacturing costs of the few commercially available engineered tissue products. By enabling reproducible and controlled changes of specific environmental factors, bioreactor systems provide both the technological means to reveal fundamental mechanisms of cell function in a 3D environment, and the potential to improve the quality of engineered tissues. In addition, by automating and standardizing tissue manufacture in controlled closed systems, bioreactors could reduce production costs, thus facilitating a wider use of engineered tissues.

Bioactive Glass in Tissue Engineering:

Bioactive glass has several appealing characteristics as a scaffold material for bone tissue engineering. New bioactive glasses based on borate and borosilicate compositions have shown the ability to enhance new bone formation when compared to silicate bioactive glass. Borate-based bioactive glasses also have controllable degradation rates, so the degradation of the bioactive glass implant can be more closely matched to the rate of new bone formation. Bioactive glasses can be doped with trace quantities of elements such as Cu, Zn and Sr, which are known to be beneficial for healthy bone growth. In addition to the new bioactive glasses, recent advances in biomaterials processing have resulted in the creation of scaffold architectures with a range of mechanical properties suitable for the substitution of loaded as well as non-loaded bone. While bioactive glass has been extensively investigated for bone repair, there has been relatively little research on the application of bioactive glass to the repair of soft tissues. However, recent work has shown the ability of bioactive glass to promote angiogenesis, which is critical to numerous applications in tissue regeneration, such as neovascularization for bone regeneration and the healing of soft tissue wounds. Bioactive glass has also been shown to enhance neocartilage formation during in vitro culture of chondrocyte-seeded hydrogels, and to serve as a subchondral substrate for tissue-engineered osteochondral constructs. Methods used to manipulate the structure and performance of bioactive glass in these tissue engineering applications are analyzed.

Supramolecular Biomaterials in kidney regeneration and replacement strategies :

The kidney is the primary organ involved in the filtration and excretion of waste, and toxic compounds from the blood. The nephron is the kidney’s functional component which is damaged or impaired in most renal diseases. In the Dutch population around 11% is suffering of mild to severe renal disease, with an increasing prevalence as the population ages.

As of yet there are only two treatment options for end stage kidney disease; dialysis, and kidney transplantation. Both options are far from ideal. Dialysis requires frequent visits to the clinic, and is incapable of clearing protein bound uremic toxins. Organ transplantation is limited by donor shortage, acute rejection, and a lifelong need for immunosuppressive therapy. Therefore, improvements are needed in kidney regeneration and replacement strategies.

In our previous research we have shown that supramolecular biomaterials can be created, mimicking the renal basement membrane. It was shown that these biomaterials are able to control in-vitro functioning of renal epithelial cells. Important in the further development of functional biomaterials, is their interaction with cells via bioactive functionalities, such as peptides. In the current research we aim at resolving the interactions of the cell with the bioactive supramolecular biomaterial at a microscopic and molecular level. Combination of these insights with established renal cell function assays is proposed to gain fundamental insights in renal cell behavior on supramolecular surfaces. This is proposed to lead to the development of materials that can be applied to ameliorate dialysis and possibly to in-situ regenerate renal tissue.

DNA delivery from polymer matrices for Tissue Engineering : 

Engineered tissues by the incorporation and sustained release of plasmids encoding tissue-inductive proteins from polymer matrices. Matrices of poly(lactide-co-glycolide) (PLG) were loaded with plasmid, which was subsequently released over a period ranging from days to a month in vitro. Sustained delivery of plasmid DNA from matrices led to the transfection of large numbers of cells. Furthermore, in vivo delivery of a plasmid encoding platelet-derived growth factor enhanced matrix deposition and blood vessel formation in the developing tissue. This contrasts with direct injection of the plasmid, which did not significantly affect tissue formation. This method of DNA delivery may find utility in tissue engineering and gene therapy applications.

Bladder Biomechanics and the use of Scaffolds for Regenerative Medicine in the Urinary Bladder : 

The urinary bladder is a complex organ with the primary functions of storing urine under low and stable pressure and micturition. Many clinical conditions can cause poor bladder compliance, reduced capacity, and incontinence, requiring bladder augmentation or use of regenerative techniques and scaffolds. To replicate an organ that is under frequent mechanical loading and unloading, special attention towards fulfilling its biomechanical requirements is necessary. Several biological and synthetic scaffolds are available, with various characteristics that qualify them for use in bladder regeneration in vitro and in vivo, including in the treatment of clinical conditions. The biomechanical properties of the native bladder can be investigated using a range of mechanical tests for standardized assessments, as well as mathematical and computational bladder biomechanics. Despite a large body of research into tissue engineering of the bladder wall, some features of the native bladder and the scaffolds used to mimic it need further elucidation.

Characteristics and applications of titanium oxide as a Biomaterial for medical implants : 

There is considerable interest in TiO2 for a wide range of applications; however, it mainly focuses on its uses as a biomaterial, particularly for biomedical implant devices. The main characteristics required for this application have been considered. Methods for producing TiO2 and Ag doped TiO2 films are summarized. The interactions of the films containing body fluids, mainly with blood components such as proteins, are discussed. Various techniques, including surface analysis methods, have been employed to characterize the undoped and Ag doped TiO2 films. Their behaviour under normal conditions inside the body, such as physiological pH, has been investigated.

Biomaterials for Wound healing : 

The advantageous biocompatibility and cell proliferative effects of synthetic and natural biomaterials have promoted their broad use in various medical areas, including wound healing. Most synthetic biomaterials show excellent physical properties but are, in general, complicated to fabricate, whereas natural biomaterials normally show no cell toxicity or elicit foreign body responses but show high natural variability. Existent biomaterials used for wound healing purposes, the naturally obtained categories such as polysaccharide-based, protein-based, nanofiber-based, and marine biomaterials, which have been investigated in depth in vivo and in clinical studies.

Surface modification of Biomaterials by heparinisation to improve Blood Compatibility : 

Blood compatibility is mainly influenced by the surface properties of the materials. The interaction of the surface and blood leads to a blood coagulation which is not desirable for some medical applications. In order to create a blood compatible material with an anti-thromobogenic or non-thromobogenic surface, many theoretical hypotheses have been postulated. In practice, surface modification by utilisation of heparin is one of the mostly widely accepted approaches for improvement of blood compatibility. In this chapter, some of the immobilisation methodologies are reviewed and the effects of heparinisation on blood compatibility both in vitro and in vivo are also assessed including protein adsorption, platelet adhesion, thrombus formation and other factors which influence blood compatibility.