Showing papers in "Comprehensive Biomaterials in 2011"

1.111 – Bioactive Ceramics: Physical Chemistry

Abstract: The chapter mainly discusses the physical–chemical properties of calcium phosphates (Ca-P), among the most important and most used bioactive ceramics. The main calcium phosphate compounds are presented with a brief description of their synthesis methods. Their characterization, using different techniques, including chemical analyses, X-ray diffraction, Fourier transform infrared (FTIR), Raman and solid-state nuclear magnetic resonance (NMR) spectrometries, and scanning and transmission electron microscopies (SEM and TEM), is reviewed and the different information obtained are discussed. The thermal stability and the relationships between different Ca-P phases are then described. The biological properties of Ca-P are related to their behavior in solution; their solubility, transformations and hydrolysis, nucleation ability, and surface properties and reactivity (ion exchange, adsorption) are presented especially in the case of apatites. The biological response regarding bioactivity, biodegradation, and simulated body fluid (SBF) testing is discussed from the point of view of the Ca-P physical chemistry. Several examples of applications are then proposed as ceramics, coatings, cements, and composite materials. A brief presentation of other bioactive mineral compounds follows (oxides and hydroxides, calcium carbonate, calcium sulfate).

Tissue Engineering of the Temporomandibular Joint

Abstract: Temporomandibular joint (TMJ) morbidities affect around a quarter of the US population, yet there are no consistently successful treatment solutions. The TMJ comprises the articulating tissues between the mandibular condyle and the temporal fossa. Its fibrocartilaginous components form the articulating surfaces, with the biconcave TMJ disc allowing for smooth movement between the condyle and fossa during normal mastication. Each tissue within the joint displays unique cellular, biochemical, and biomechanical characteristics. These characteristics are important for the tissue engineer to understand, given the joint's limited ability for self-repair following injury. The TMJ is susceptible to pathologies such as osteoarthritis and internal derangement of the disc, which are extremely painful and often require clinical intervention. Current therapies include anti-inflammatory measures, occlusal splints, and in extreme cases, total joint replacement. These therapies, however, are only semipermanent and fail to restore full functionality to the joint. Tissue engineering may provide functional biological replacements for TMJ tissues, resulting in a long-term solution to TMJ pathologies. Research using alternate cell sources, scaffolds, bioactive factors, and mechanical stimulation has shown promise, but more research must be done to determine optimal combinations of these factors.

2.204 – Peptoids: Synthesis, Characterization, and Nanostructures

Abstract: Oligomers of N -substituted glycine, or peptoids, are versatile tools to create functional molecules in biological and materials science research. Peptoids are a bioinspired sequence-specific polymer, whose properties lie between biopolymers and nonnatural synthetic polymers. Their convenient synthesis and availability of highly diverse monomers enable the precise tailoring of properties. Extensive compound libraries can be readily generated and can be screened to identify novel molecules with desired activities. The relationship between peptoid sequence, structure, and function has been actively investigated, and we are now capable of creating higher-order peptoid structures ranging from precisely defined secondary and tertiary structures to self-assembled nanostructures. The synthetic feasibility, excellent stability, and structural control provide an excellent platform for novel materials discovery. In this chapter, we review peptoid synthesis, structure, and their functionalities in the fields of drug discovery, drug delivery, and biomaterials, which have been investigated over the past 2 decades.

Electrochemical Behavior of Metals in the Biological Milieu

Abstract: Corrosion in the biological milieu presents the basic science background to understand the nature of corrosion processes associated with medical devices and the metallic biomaterials from which they are made. This chapter introduces the concepts of corrosion, the factors that affect corrosion (oxidation and reduction reactions), and the role of passive oxide films in the behavior of metallic biomaterials. Links between the environmental conditions, including biological molecules and mechanical factors, and interactions between the biological system and the metal–oxide surface are described. Current state-of-the-art corrosion testing methods including polarization testing, scratch testing, and impedance spectroscopy are described and related to currently used materials. The importance of the biological environment is also presented to provide a better understanding of how inflammation, infection, or other local conditions may enhance or alter corrosion behavior. Finally, aspects of corrosion that are not typically considered, including the reduction half-cells, are presented and shown to significantly affect cell behavior. Overall, much is known about corrosion in the biological milieu; however, there is also much that is not yet understood. This chapter lays the foundation upon which additional studies could be designed.

Development of contact lenses from a biomaterial point of view - materials, manufacture, and clinical application

Abstract: Rigid lenses, which were originally made from glass (between 1888 and 1940) and later from polymethyl methacrylate or silicone acrylate materials, are uncomfortable to wear and are now seldom fitted to new patients. Contact lenses became a popular mode of ophthalmic refractive error correction following the discovery of the first hydrogel material – hydroxyethyl methacrylate – by Czech chemist Otto Wichterle in 1960. To satisfy the requirements for ocular biocompatibility, contact lenses must be transparent and optically stable (for clear vision), have a low elastic modulus (for good comfort), have a hydrophilic surface (for good wettability), and be permeable to certain metabolites, especially oxygen, to allow for normal corneal metabolism and respiration during lens wear. A major breakthrough in respect of the last of these requirements was the development of silicone hydrogel soft lenses in 1999 and techniques for making the surface hydrophilic. The vast majority of contact lenses distributed worldwide are mass-produced using cast molding, although spin casting is also used. These advanced mass-production techniques have facilitated the frequent disposal of contact lenses, leading to improvements in ocular health and fewer complications. More than one-third of all soft contact lenses sold today are designed to be discarded daily (i.e., ‘daily disposable’ lenses).

Electrospinning and Polymer Nanofibers: Process Fundamentals

Abstract: Electrospinning is a popular technique for manufacturing nanofibers using an electrified jet of a polymeric fluid. The fibrous, nonwoven mat that typically results from electrospinning finds applications in a wide range of industries. While setting up an electrospinning experiment is relatively simple, controlling the attributes of the end-products, such as the diameter and morphology of the fiber formed, the orientation of the deposited fiber, the porosity, and the surface properties of the resultant mat, etc., is considerably more challenging. Significant progress has been made in recent years in understanding the physical mechanisms that govern the process of fiber formation through electrospinning. This chapter reviews these advances and provides an overview of the present status of the technology. The process of electrospinning is outlined and the mathematical framework for studying the mechanics involved is discussed. The relevant electrical and the rheological aspects of polymeric fluids are also reviewed. An account of the advances in controlling the fiber diameter, morphology, and surface properties, as well as in controlling the properties of the mat, is provided. This chapter also discusses the limitations of the current technology and provides a perspective for future developments.

4.410 – Sterilization of Biomaterials of Synthetic and Biological Origin

Abstract: Sterilization is a critical step in medical device manufacturing which affects the safety and efficacy of the medical devices. Sterilization of medical devices is accomplished by the use of physical or chemical processes that inactivate all forms of microbial life. This chapter reviews the sterilization methods that are being used on medical devices and biomaterials, followed by more comprehensive review and discussions on their specific applications for sterilization of different synthetic and biological materials. The approaches for selection of sterilization methods for different types of biomaterials, and evaluation of sterilization effects on biomaterials are also included.

Polymer Fundamentals: Polymer Synthesis

Abstract: Polymers can be of biological and synthetic origin, and are very important in our daily lives. They are used in all the major industries including textile, automotive, household goods, medical devices and products, etc. The significant difference between the requirements of these applications necessitates the availability of a large variety of polymers to choose from. Synthetic polymers can be prepared by addition and condensation polymerization using a variety of polymerization processes to yield polymers with differences in their stereoregularity, organization of their constituents, molecular weight, and crystallinity. All these differences yield polymers with different mechanical properties. Since the number of monomers available is very high, the variety of the polymers theoretically possible is also high. Some become viscoelastic and some are just plastic. Polymers are not always linear like noodles but can be made to have branches either of the same monomer or by adding other monomers to change the chemistry and the crystallinity of the product. They can be further branched or cross-linked so that the polymer becomes insoluble, and just swells in its linear polymer's solvents creating the gels. Or, a number of monomers can be used simultaneously to prepare macromolecules with properties that can be tailored to the needs of the application. All these play a deciding role on whether a polymer is suitable for load-bearing applications or in replacing the soft tissues in the human body. In this chapter, the main approaches to polymer synthesis and the parameters influencing the properties of the final product are discussed.

4.6 Protein Interactions With Biomaterials

Abstract: Proteins adsorb to biomaterial surfaces from body fluids. The result is activation of complex cascade events such as coagulation, immune complement, and cell recruitment to a wound site. The events are of special importance in direct blood-contacting applications and eventually for tissue healing around biomaterials. The events are rapid or slow and proceed during seconds to hours and determine cell differentiation, proliferation, cytoskeleton organization as well as the wound healing processes at large. Desorbed surface deposited proteins display more than 150 electrophoretic bands and indicate these bands are comprised of thousands of proteins. The vast majority of performed protein adsorption studies deal with the most abundant plasma proteins, “The Big Twelve,” because these compete effectively for the interfacial space. This article reviews basics of protein adsorption and surface properties, protein-resistant surfaces, and complex cascade reactions with specific emphasis on coagulation- and immune complement activation. Finally, a short review of consequences of protein adsorption is discussed.

4.407 – Bacterial Adhesion and Biomaterial Surfaces

Abstract: One of the most common and serious complications associated with the implantation of any biomaterial into a biological system such as the human body is bacterial infection. The presence and growth of bacteria in the vicinity of any implanted biomaterial represents failure of the device, despite the fact that the device may otherwise be free of any material or functional defect. The focus of this chapter is this first step in the colonization/infection process: the adhesion of bacteria to biomaterials. The number of bacteria that may adhere and their ability to grow and spread on the biomaterial surface is greatly influenced by the physicochemical properties of both the biomaterial and the bacteria. The laboratory methods used to measure bacterial adhesion, the theories developed to explain it, and the biomaterial parameters, which influence bacterial adhesion will all be discussed in this chapter. Finally, surface modification has become a major field of work in biomaterial science to improve various aspects of currently available biomaterials, and we will describe the impact of numerous modifications of biomaterial surfaces on bacterial adhesion as well as a brief description of some biomaterial modifications designed to create so-called bacteria-repellent biomaterials.

Peripheral Nerve Regeneration

Abstract: Several advances in nerve cell culture, development of new biomaterials, and genetic techniques have led to the introduction to innovative techniques for nerve regeneration. Analytically, natural or artificial grafts used to bridge nerve gaps have four central components germane to regeneration: scaffold/substrate, growth factors, extracellular matrix (ECM) molecules, and cells. A graft might have a combination or all of the four components. The grafts are classified as isotropic or anisotropic on the basis of distribution of these four components within the graft. In isotropic grafts, the components are distributed uniformly within the graft, with no directional cues. In anisotropic grafts one or more of these components are distributed anisotropically, usually along the direction of regeneration, to direct the axonal growth towards the distal target. Isotropic natural materials used as scaffolds include veins, skeletal muscle fibers, and collagen, and synthetic scaffolds are advantageous because they can be tailored in terms of their mechanical, chemical, and structural properties to augment nerve regeneration. Several anisotropic scaffolds are fabricated to affect neuronal behavior. Neuronal-growth supporting cells could be incorporated with longitudinally aligned filaments and gels in nerve guidance conduits (NGCs) to enhance nerve regeneration. Biodegradable conduits of a copolymer of lactic and glycolic acids (PLGA) with longitudinally aligned channels are used for nerve regeneration. The channels, with the lumen coated with laminin, and seeded with Schwann cells, show regeneration comparable to nerve autografts over a 7-mm nerve gap in rats.

3.331 – Conjugated Polymers for Biosensor Devices

Abstract: Conjugated polymers (CPs), or polymers having a conjugated π-electron backbone, have recently attracted much attention from the biosensors research community due to the many promises and advantages that CPs hold for signal amplification in biosensor devices. In this chapter, the use of CPs for biosensor devices has been reviewed and the contents have been broken down into three parts. Part 1 commences with a brief definition of a ‘biosensor’ and why CPs are promising candidates that can facilitate a new generation of biosensors. Subsequently, a brief description covering the synthesis methods of CPs and how CPs can be used for electrochemical and optical biosensors is provided. In Part 2, the use of CPs in electrochemical biosensors is described. Focusing more on the ‘sensing’ component of biosensors, different possibilities to immobilize biological sensing elements (BSEs) onto electrodes of electrochemical CP based biosensors are covered. The choice of immobilization strategy (depending on the type of BSEs utilized) and current research direction of electrochemical CP-based biosensors are discussed. Due to the unique conjugated π-electron backbone system, CPs exhibit different optical properties depending on their adopted state, for example, linear or random coiled. The last part describes different optical sensing approaches, through the use of CPs, for biological analytes that have been demonstrated. Special attention is given to works describing biosensing approaches performed on solid support as these works may be further evolved and employed into biosensor devices.

2.213 – Chitosan

Abstract: Chitosan is a linear copolymer of d-glucosamine and N-acetyl d-glucosamine in a β-(1-4) linkage, in which glucosamine is the predominant repeating unit It is easily processed into films, 3D-scaffolds, nanofibers, and nanoparticles It forms polyelectrolyte complexes with polysacharides, polyamino acids, proteins, and glycosoaminoglycans (GAGs) Its degree of acetylation influences many properties, including ability to support cell attachment, proliferation and differentiation, inflammatory response, and degradation rate Its structural similarity with GAGs, which are constituents of the extracellular matrix (ECM), makes it a natural candidate for being a component of ECM-like matrices used for tissue repair/regeneration

Bioactive Ceramics: Cements

Abstract: Bioactive cement may be a breakthrough for the biomaterials aimed at the reconstruction of bone defect as they set in situ and form bioactive set mass. As a result of the setting reaction, the bone defect can be filled with the bioactive materials without leaving a gap between the cement and surrounding bone. Also, the setting reaction allows minimum invasive surgery when the bone cement is injected to the bone defects using a syringe. On the contrary, bioactive cements show an inflammatory response when they fail to set. Therefore, understanding the setting reaction is key to their clinical use. The setting reaction of apatite cement, brushite cement, and gypsum is classified as a dissolution–precipitation reaction, where components of the powder phase dissolve into their mixing liquid, and the dissolved compounds precipitate as other compounds. Due to the interlocking of precipitated crystals, the cement sets. Portland cement and mineral trioxide set based on hydration reaction and the resulting formation of amorphous calcium silicate hydrate and calcium hydroxide. Further improvement of bioactive cement is also awaited, based on the understanding of the setting reaction.

4.426 – Electrospun Fibers for Drug Delivery

Abstract: The past decade has seen a remarkable surge of interest in the electrostatic drawing of fibers (electrospinning), particularly for biomedical applications in regenerative medicine. The inexpensive nature of electrospinning has enabled biomedical researchers to use ultrafine diameter fibers for tissue engineering and drug delivery purposes. Research in electrospun fibers for drug delivery is exponentially increasing, and often accompanied by the need to make these fibrous materials cell invasive for tissue engineering. This and other challenges for biomedical electrospinning are being identified and tackled within the research community. The result is an increasingly diverse approach to electrospinning, with numerous options for both scaffold manufacture and drug release. For example, coaxial electrospinning is altering the release profiles of drugs, while improvements in surface modification incorporated specific bioactive compounds with reduced fouling by nonspecific protein adsorption. While challenges remain, approaches for cell-invasive electrospun materials are maturing so that this technique can become a powerful new tool in regenerative medicine. The potential and huge interest generated after less than 10 years of electrospinning research indicates that the next decade will also be dynamic for this technique.

Finite Element Analysis in Bone Research: A Computational Method Relating Structure to Mechanical Function

Abstract: Bone is probably the most frequently investigated biological material and finite element analysis (FEA) is the computational tool most commonly used for the analysis of bone biomechanical function. FEA has been used in bone research for more than 30 years and has had a substantial impact on our understanding of the complex behavior of bone. Bone is structured in a hierarchical way covering many length scales and this chapter reflects this hierarchical organization. In particular, the focus is on the applications of FEA for understanding the relationship between bone structure and its mechanical function at specific hierarchical levels. Depending on the hierarchical level, different issues have been investigated with FEA ranging from more clinically oriented topics related to bone quality (e.g., predicting bone strength and fracture risk) to more fundamental problems dealing with the mechanical aspects of biological processes (e.g., stress and strain around osteocyte lacunae) as well as with the micromechanical behavior of bone at its ultrastructure. A better understanding of the relationship between structure and mechanical function is expected to be important for the current trends in (bio)materials design, where the structure of biological materials is considered as a possible source of inspiration, as well as for more successful approaches in the prevention and treatment of age- and disease-related fractures.

1.8 Wear-Resistant Ceramic Films and Coatings

Abstract: Optimizing the bearing surfaces of joint replacements is an urgent socioeconomic need because of the increasing life expectancy and increased performance demands from the growing number of younger patients to whom the surgery is indicated. Ceramic surface films have a great potential to improve the tribological performance and longevity of artificial joints as they provide the metallic components with a hard, wear-resistant surface while preserving their toughness and fracture resistance. Although simple in concept, providing a clinically and commercially successful coating–substrate combination has proven challenging. A critical feature for alternative technology is the adhesion of the coating to the substrate. Not only would adhesive failure of the ceramic film negate its potential wear advantages, but also it would liberate hard third-body particles that could increase abrasive wear of the bearing surfaces. Superficial films formed by physical vapor deposition or chemical vapor deposition of titanium nitride (TiN) and diamond-like carbon, as well as zirconium oxide (ZrO 2 ) produced by controlled oxidation of a zirconium alloy substrate, are the most extensively studied hard coatings for orthopedic applications. In this article, the structure, durability, tribological behavior, and clinical performance of these and alternative hard ceramic coatings are discussed.

Bone Tissue Grafting and Tissue Engineering Concepts

Abstract: This chapter addresses bone tissue grafting and tissue engineering approaches, beginning with use of bone graft and bone graft substitutes and their functions as bioactive scaffolds for bone regeneration. How bone tissue engineering has evolved from bone substitutes to resorbable polymeric scaffolds is discussed. Differences in strategies that promote autologous healing by providing a bioactive scaffold, provide autologous or allogeneic cells to assist in autologous healing, or jump-start healing by growing tissue ex vivo, are discussed. A review of preclinical and clinical models to assess the effectiveness of bone tissue engineering strategies is included.

Bacterial Cellulose as Biomaterial

Abstract: Cellulose is a biopolymer that has long been used as a biomedical material and is still used in a modified form in hemodialysis membranes and as a carrier material in drug release systems. The different sources of cellulose that have not yet been fully explored, for example, bacterial cellulose (BC), might possess properties that are needed for some very specific biomedical applications. BC differs considerably from other sources of cellulose and still requires a great deal of research to be understood completely.

Phosphate-Based Glasses

Abstract: This chapter reviews the development of phosphate-based glasses for biomedical use. Phosphate-based glasses are unique in that they are degradable and also their degradation rate can be controlled. The chapter commences with the basic concepts of glass structure that are pertinent to phosphate-based glasses and how the addition of other components affects glass structure at both the atomic and the bulk levels. In particular, an understanding of the role of bridging and nonbridging oxygens in the phosphate network, and their measurement by 31 P magic angle spinning nuclear magnetic resonance (MAS-NMR) will be addressed. The chapter goes on to describe the methods of synthesis, both conventional melt quenching and the more recently developed sol–gel derived synthesis routes. The conversion of these glasses to a fiber form is also discussed. The role of dopants in these glasses is clearly important and is highlighted in this chapter. The dopants can play two roles; they can either control the degradation rate and/or act as an active species that can either improve the bioactivity or act as an antibacterial ion. The chapter finishes with a section on the possible therapeutic uses, both in the medical and veterinary arenas.

5.534 – Skin Tissue Engineering

Abstract: The integration of healing, cell biology, and skin tissue engineering research has been ongoing for almost 60 years. In this chapter, we provide an eagle's eye view of skin anatomy and functions, wound healing processes, and the challenges related to wound healing that tissue engineers face. Several biomaterials have been examined for their potential use in skin substitutes to replace/regenerate skin with normal structure and function. However, it is obvious that the ideal skin substitute does not exist. The problems and challenges in the skin substitutes currently available include low mechanical properties, lack of biocompatibility, minimal structural differentiation, limited vascularization (low take rate), and scar development. However, an articulation between skin tissue engineering and regenerative medicine may bring transforming advances in this field that may lead to the ability to restore skin structure and function. Through the combination of stem cell manipulation, angiogenesis control, advanced bioactive molecules, and smart biomaterials development, it may be possible to design an authentic skin substitute or an engineered composite that induces skin regeneration.

7.38 Suture Material: Conventional and Stimuli Responsive☆

Abstract: Suture materials and staples play an important role in wound repair by providing support to healing tissues. There is no ideal suture material. Important properties to consider when selecting a suture material are tensile strength, diameter, tissue absorption, coefficient of friction, knot security and strength, elasticity and plasticity, memory, handling, tissue reactivity, capillarity, fluid absorption, and ease of removal. Sutures are generally classified as absorbable or nonabsorbable. Commonly available absorbable sutures include gut, polyglactin 910, polyglycolic acid, poliglecaprone, polydioxanone, polyglycolide–trimethylene carbonate, and caprosyn. Nonabsorbable sutures include silk, polybutester, braided polyester, nylon, polypropylene, goretex, and stainless steel. Barbed sutures are available in absorbable and nonabsorbable forms. Staples provide a strong and biologically inert alternative method of skin closure. Specific stapling devices have also been developed for vessel ligation and for thoracic and abdominal surgery. Selection of the most suitable suture material is made by the surgeon and is based on the physical and biological properties of the material, assessment of the wound, the healing properties of the tissue, and the patient's physical condition. Continued technological improvement in suture material and needles has enabled an enormous increase in the variety of materials available. The greatest challenge for surgeons is to stay abreast of new technology.

3.311 – Molecular Simulation Methods to Investigate Protein Adsorption Behavior at the Atomic Level

Abstract: Although protein adsorption to biomaterial surfaces is widely recognized as being an important mediator of biological response, a molecular-level understanding of protein–surface interactions is still lacking. Molecular simulation provides a means to study and understand these types of processes at the molecular level. Before this potential can be realized, however, appropriate methods must first be developed to enable protein adsorption behavior to be accurately represented in a molecular simulation. This chapter begins with an overview of some of the fundamentals of protein adsorption. It then introduces the field of molecular simulation and covers a series of topics regarding how molecular simulations are performed, with specific focus on three of the most important issues for the simulation of protein adsorption behavior: force field parameterization, representation of solvent effects, and sampling of the molecular system. A summary is then presented regarding how these methods have been developed and applied to simulate protein–surface interactions over the past two decades. This is followed by a discussion of the key areas for the continued development of molecular simulation methods toward the goal of providing these methods as powerful tools to guide the design of biomaterial surfaces to control protein adsorption behavior for a broad range of applications in biomedical engineering and biotechnology.

4.416 – Growth Factors and Protein-Modified Surfaces and Interfaces

Abstract: Designing biomaterials that specifically regulate cell behaviors is significant to biomedical device performance. Many functions of cells are regulated by three interactions, namely, with (1) extracellular matrices (ECMs), (2) neighboring cells, and (3) soluble biosignals such as growth factors. Biomaterial researchers have immobilized ECM, cell adhesion factors, and growth factors to regulate the cell functions. Here, the biosignaling of ECM, cell adhesion factors, and growth factors are reviewed and biomaterial designs using the biosignaling mechanisms are discussed. First, proteins employed for surface modification are summarized. For cell adhesion, ECM, cell adhesion protein, and cell adhesion peptides are explained. Growth factor proteins for enhancement of cell growth are exemplified and their action mechanisms are reviewed. The importance of these proteins is also discussed. Second, as protein-immobilized surfaces, immobilization of ECM, biomimetic peptides, molecules corresponding to cell–cell interactions, and growth factors are reviewed. Finally, biomaterials design using immobilization of protein is discussed as summary and future directions.

Imaging Mineralized Tissues in Vertebrates

Abstract: Mineralized tissues are hierarchically organized and many of them are temporally and spatially heterogeneous because of continuous (re)modeling. Their mechanical properties depend on shape/geometry at the macro scale, on microarchitecture, as well as on material characteristics at the micro- to nanometer scale. This is particularly important for the understanding of the structure–function relationship in normal, ageing, and diseased bone. Several imaging techniques are available today which give access to structure and composition of the mineralized tissue with a spatial resolution even below the submicron range. Bone biopsy samples are becoming widely used to monitor the effects on trabecular architecture and mineralization in clinical studies during the treatment of bone diseases. Furthermore, bone biopsy samples provide the possibility to study the lamellar structure, the mineral content, the elastic properties, the organic matrix (e.g., collagen cross-linking), and the structural characteristics (arrangement, shape, size, and orientation distribution of the hydroxyapatite particles in the organic matrix) of the nanocomposite material. This article gives a brief description of the physical background, the usage, and the limitations of a wide selection of methods to image mineralized tissues and to map their physical properties.

2.212 – Silk Biomaterials

Abstract: Silk is a versatile protein polymer spun as fibers by silkworms and spiders. Silks have played a major role in the history of textures for thousands of years. Silk proteins are of high molecular weight and have been formulated into many biomedical applications. Previous medical uses of silks focused on sutures, while the newer processed forms of silks are expanding biomedical utility into many areas of tissue repair and regeneration and medical device needs. These applications include ligaments, cartilage and bone, optical and microfluidic devices, nanofiber mats for skin wound healing, microspheres/nanoparticles for drug delivery, and hydrogels, among others. Through processing control of beta-sheet crystalline content of silk biomaterials, biological, mechanical, optical, thermal, and electromagnetic properties can be tailored to specific needs. This control can be achieved in all aqueous systems or in organic solvents, offering further versatility to the materials. This chapter provides a broad review of silk-based biomaterials that have been pursued in recent years.

6.616 – Materials in Fracture Fixation

Abstract: Fracture fixation has presented a challenge to orthopedic surgeons since fixation methods were first available. Understanding current concepts of fracture fixation including load-bearing and load-sharing devices is important for selecting the optimal fixation device for each individual. Biomaterial properties of each implant play a major role in the success of fracture treatment. Biomaterials used for orthopedic applications have unique functional and safety requirements. Ideally materials should be biocompatible, resistant to corrosion, and have adequate mechanical properties to protect the bone until the fracture is healed. The major principles to treat fracture include stable fixation and preferable load-sharing devices to reduce stress shielding phenomenon. In the settings where bone quality is suboptimal such as osteoporosis, biomaterials such as ceramics are important to augment bone defects and enhance rigidity of fixation devices to bone. Advancements in the development of new biomaterials as well as coatings for the treatment of fracture have been attempted and undergone tremendous researches. Moving forward, clinicians and manufacturers must look beyond the mechanical properties as the main focus of fracture healing and toward combined mechanical and biological constructs that can enhance bone healing not only on a structural level but also on a cellular level.

3.319 – Characterization of Nanoparticles in Biological Environments

Abstract: Deliberate and accidental exposure of the ecosystem including humans to nanoparticles becomes inevitable as nanomaterials are increasingly used. In biological fluids, biomolecules associate with nanoparticles, leading to the formation of a dynamic biomolecule “corona” that critically defines the biological identity of the particle. As the bio-physical properties of such a decorated particle often differ significantly from those of the formulated particle a detailed characterization of nanoparticles in biological environments becomes increasingly important though, nevertheless also technically challenging. Here, we introduce experimental methods currently employed for nanoparticle characterization, present examples underlining the complexity of the nano-bio interface, and discuss the need for further technical and conceptual developments. A deep and mechanistic bio-physical understanding of the nano-bio interface is a challenge but also fundamental prerequisite for future applications in nanobiology, nanomedicine and nano(eco)toxicology.

4.413 – Patterned Biointerfaces

Abstract: This chapter introduces the concept of biointerface engineering. The topology, chemical composition, and physicochemical properties of material surfaces strongly impact their interactions with biomolecules, tissue cells, bacteria, or viruses. Adhesion, shape, motility, differentiation, and ultimately, cell function or apoptosis, can be steered by engineered surfaces. In this context, patterned surfaces and interfaces with dimensions from the macro- to the micro- and nanoscale, presenting biochemical cues in a spatially controlled manner, have made major contributions to interrogating the various fundamental processes that steer the response of biomacromolecular and cellular entities to materials. A wide range of patterning techniques are now at hand that rely on either processes originally developed by the microelectronics industry and/or the self-organization of macromolecules, colloids, vesicles, or viruses, ultimately allowing for the positioning of objects down to molecular dimensions. Engineering of patterned surfaces is also becoming a key technology in the fields of biosensing, bioanalytics, medical diagnostics, lab-on-chip devices, drug discovery and screening, and tissue engineering. This chapter covers an introduction and overview of a range of micro- and nanopatterning techniques of interest to the biointerface community as well as selected examples of applications toward a variety of biologically relevant scientific studies.

1.125 – Polyurethanes and Silicone Polyurethane Copolymers

Abstract: Polyurethanes and silicone-containing polyurethanes have a long history of use in medical devices and prosthetic implants. Initially, device designers adopted commercially available polymers that were developed for a variety of industrial applications including textiles and even shoe soles. One first-generation silicone–urethane hybrid (Avcothane™-51), used in clinical intraaortic balloons starting c . 1969, may have been the first polymer ever developed to be a ‘biomaterial.’ As the versatility of certain members of this huge family of polymers became appreciated, scientists and engineers began to modify and improve polyurethanes for use in medical applications. Today, there exists, a large body of scientific and patent literature about structure-versus-property relationships in polyurethanes. It provides the foundation for systematic development of high-performance polyurethanes tailored for specific biomedical applications. This increasing knowledge base and their successful history in a number of critical, life supporting devices suggests that (silicone)polyurethanes will continue to be important biomaterials for many years to come.