Hydrogels, due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics, have been the material of choice for many applications in regenerative medicine. They can serve as scaffolds that provide structural integrity to tissue constructs, control drug and protein delivery to tissues and cultures, and serve as adhesives or barriers between tissue and material surfaces. In this work, the properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed. Recent research involving several different hydrogels polymerized from a variety of synthetic and natural monomers using typical and novel synthetic methods are highlighted. Finally, special attention is given to the microfabrication techniques that are currently resulting in important advances in the field.

/pdf/hydrogels-in-regenerative-medicine-lx1cllc4g8.pdf

Hydrogels in regenerative medicine

An analyte monitor includes a sensor, a sensor control unit, and a display unit. The sensor has, for example, a substrate, a recessed channel formed in the substrate, and conductive material disposed in the recessed channel to form a working electrode. The sensor control unit typically has a housing adapted for placement on skin and is adapted to receive a portion of an electrochemical sensor. The sensor control unit also includes two or more conductive contacts disposed on the housing and configured for coupling to two or more contact pads on the sensor. A transmitter is disposed in the housing and coupled to the plurality of conductive contacts for transmitting data obtained using the sensor. The display unit has a receiver for receiving data transmitted by the transmitter of the sensor control unit and a display coupled to the receiver for displaying an indication of a level of an analyte. The analyte monitor may also be part of a drug delivery system to alter the level of the analyte based on the data obtained using the sensor.

Analyte Monitoring Device And Methods Of Use

Current strategies of regenerative medicine are focused on the restoration of pathologically altered tissue architectures by transplantation of cells in combination with supportive scaffolds and biomolecules. In recent years, considerable interest has been given to biologically active scaffolds which are based on similar analogs of the extracellular matrix that have induced synthesis of tissues and organs. To restore function or regenerate tissue, a scaffold is necessary that will act as a temporary matrix for cell proliferation and extracellular matrix deposition, with subsequent ingrowth until the tissues are totally restored or regenerated. Scaffolds have been used for tissue engineering such as bone, cartilage, ligament, skin, vascular tissues, neural tissues, and skeletal muscle and as vehicle for the controlled delivery of drugs, proteins, and DNA. Various technologies come together to construct porous scaffolds to regenerate the tissues/organs and also for controlled and targeted release of bioactive agents in tissue engineering applications. In this paper, an overview of the different types of scaffolds with their material properties is discussed. The fabrication technologies for tissue engineering scaffolds, including the basic and conventional techniques to the more recent ones, are tabulated.

/pdf/polymeric-scaffolds-in-tissue-engineering-application-a-2sbenjc1po.pdf

Polymeric scaffolds in tissue engineering application: a review

Since its inception just over a half century ago, the field of biomaterials has seen a consistent growth with a steady introduction of new ideas and productive branches. This review describes where we have been, the state of the art today, and where we might be in 10 or 20 years. Herein, we highlight some of the latest advancements in biomaterials that aim to control biological responses and ultimately heal. This new generation of biomaterials includes surface modification of materials to overcome nonspecific protein adsorption in vivo, precision immobilization of signaling groups on surfaces, development of synthetic materials with controlled properties for drug and cell carriers, biologically inspired materials that mimic natural processes, and design of sophisticated three-dimensional (3-D) architectures to produce well-defined patterns for diagnostics, e.g., biological microelectromechanical systems (bioMEMs), and tissue engineering.

BIOMATERIALS: Where We Have Been and Where We Are Going

Recent developments in the application of micro- and nanosystems for drug administration include a diverse range of new materials and methods. New approaches include the on-demand activation of molecular interactions, novel diffusion-controlled delivery devices, nanostructured 'smart' surfaces and materials, and prospects for coupling drug delivery to sensors and implants. Micro- and nanotechnologies are enabling the design of novel methods such as radio-frequency addressing of individual molecules or the suppression of immune response to a release device. Current challenges include the need to balance the small scale of the devices with the quantities of drugs that are clinically necessary, the requirement for more stable sensor platforms, and the development of methods to evaluate these new materials and devices for safety and efficacy.

Small-scale systems for in vivo drug delivery.

Transplantation of tissues enclosed within a membrane device designed to protect the cells from immune rejection (immunoisolation) provides an opportunity to treat a variety of disease conditions. Successful implementation of immunoisolation has been hampered by the foreign-body reaction to biomaterials. We screened a variety of commercially available membranes for foreign-body reactions following implantation under the skin of rats. Histologic analysis revealed that neovascularization at the membrane-tissue interface occurred in several membranes that had pore sizes large enough to allow complete penetration by host cells (0.8-8 microns pore size). When the vascularization of the membrane-tissue interface of 5-microns-pore-size polytetrafluoroethylene (PTFE) membranes was compared to 0.02-microns-pore-size PTFE membranes, it was found that the larger pore membranes had 80-100-fold more vascular structures. The increased vascularization was observed even though the larger pore membrane was laminated to a smaller pore inner membrane to prevent cell entry into the prototype immunoisolation device. This significantly higher level of vascularization was maintained for 1 year in the subcutaneous site in rats.

Neovascularization of synthetic membranes directed by membrane microarchitecture

An implantable sensor for use in measuring a concentration of an analyte such as glucose in a bodily fluid, including a body with a sensing region adapted for transport of analytes between the sensor and the bodily fluid, wherein the sensing region is located on a curved portion of the body such that when a foreign body capsule forms around the sensor, a contractile force is exerted by the foreign body capsule toward the sensing region The body is partially or entirely curved, partially or entirely covered with an anchoring material for supporting tissue ingrowth, and designed for subcutaneous tissue implantation The geometric design, including curvature, shape, and other factors minimize chronic inflammatory response at the sensing region and contribute to improved performance of the sensor in vivo

Optimized sensor geometry for an implantable glucose sensor

A device for implantation in a host having a material at an interface between the host and the device, said material having a conformation which results in growth of vascular structures by the host close to the interface.

Close vascularization implant material

Polymer membrane structures are microfabricated from polyimide film by lithography or etching. The microfabricated structures have systematically varied dimensions and geometries conducive to implanting in host tissue and the promotion, when implanted, of new vascular structures.

Porous microfabricated polymer membrane structures

Implant assemblies (10) and methodologies provide immuno-protection for implanted allografts, xenografts, and isografts. The assemblies and methodologies establish an improved boundary between the host and the implanted cells (12). The boundary has a pore size, an ultimate strength, and a metabolic transit value that assures the survival of the cells (12) during the critical ischemic period and afterward. The boundary allows the fabrication and clinical use of implant assemblies and methodologies that can carry enough cells (12) to be of therapeutic value to the host, yet occupy a relatively small, compact area within the host.

Laura A. Martinson

Papers

Neovascularization of synthetic membranes directed by membrane microarchitecture

Optimized sensor geometry for an implantable glucose sensor

Close vascularization implant material

Porous microfabricated polymer membrane structures

Angiogenic tissue implant systems and methods