Medical Devices : Orthopedics


Calibrated Drill Sleeve Also Protects Soft Tissue

UW–Madison researchers have developed a separable drill sleeve that provides braking resistance and can be used with conventional orthopedic drills and bits. The sleeve protects soft tissue from the drill bit, measures the depth of the bore hole and prevents the drill from plunging through the far side of the bone.

The sleeve features upper and lower tube segments. At the lower end is a base that contacts bone and provides a passage for the drill bit. The upper segment is able to slide relative to the base and indicate bore depth. In between the segments is a fluid damper that resists sudden acceleration of the drill bit as it pushes beyond the bone.

Bone Tissue Regeneration System That Provides Spatial and Temporal Control Over the Release of Growth Factors

UW–Madison researchers have developed a tissue regeneration system that utilizes porous scaffolds to localize and temporally control the release of multiple growth factors.  In this system, porous beta tricalcium phosphate (β-TCP) templates are coated with one or more extracellular matrix layers.  The layers include at least one thin, degradable mineral layer that is similar to bone mineral.  Because the coating process does not require high temperatures or organic solvents, biologically active growth factors such as vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) can be incorporated in the layers. 

To control dissolution order, and ultimately, delivery of the biologically active molecules, multiple distinct layers are deposited on the β-TCP scaffold.  Each layer may contain one or more active biomolecules and is designed to dissolve at a separate rate. As the matrix material gradually breaks down, the growth factors are delivered sequentially.  This provides temporal control of growth factor signaling, thereby directing the activities of associated cells, to enable the growth of new bone tissue.

Biologically Active Sutures Enhance Tissue Healing Following Surgical Procedures

UW-Madison researchers have developed a method of coating the surface of commonly used suture materials and other orthopedic devices with a biodegradable layer containing molecules that can induce tissue growth and limit bacterial infection.  The rate at which the coating degrades can be modified to control the release of the molecules. 

Specifically, a suture is coated with a mineral layer under physiological temperature and pH, resulting in a nano-porous structure with high surface area for protein binding.  Then biologically active molecules are bound to the surface of the suture for subsequent release in vivo.  Protein binding can be achieved rapidly in the operating room, and the process can be adapted to enable the incorporation of a wide range of other therapeutic molecules, in addition to proteins.

An Orthopedic Implant Coating for Enhanced Bone Growth

UW-Madison researchers have developed a biomaterial-based approach for directing bone regeneration to treat bony defects. This approach uses a biologically active calcium phosphate-based coating to target and control delivery of a bound growth factor molecule capable of inducing bone growth. This coating can be applied to all bioresorbable materials commonly used in orthopedic surgery, including nails, pins, anchors, screws, plates and scaffolds.

Under physiological conditions, the solubility of different calcium phosphate materials can vary by more than 5000 percent. To take advantage of this broad range of dissolution rates, the coating consists of several layers of calcium phosphate materials with distinct dissolution profiles. Bone growth factors are bound to the calcium phosphate and released based on the dissolution profile of each layer. To provide a delayed release, calcium phosphate layers that do not contain a growth factor or drug can be incorporated into the coating. This approach can be easily integrated with existing implants and surgical procedures in clinics.

Bioactive and Biocompatible Copolymers for Use in Medical Implants

UW-Madison researchers have combined polyurethane with naturally-occurring glycosaminoglycans, such as hyaluronic acid and dermatan sulfate, to create a new class of biomaterials with improved properties. The resulting copolymers combine the elasticity and mechanical strength of polyurethane with the biological properties of glycosaminoglycans. They have excellent hemocompatibility and biocompatibility for use in medical implant devices.

In addition, selecting the appropriate glycosaminoglycan allows the biological properties of the copolymer to be tailored to elicit specific physiological responses. For instance, the polyurethane-dermatan sulfate copolymer formulation is non-biofouling, while one version of the polyurethane-hyaluronic acid copolymer permits the growth of endothelial cells only.

Biomaterial Scaffolds for the Repair and Regeneration of Intervertebral Discs and Articulating Joints

Researchers from UW-Madison and elsewhere have developed methods for engineering and preparing scaffolds for repairing intervertebral discs and articulating joints.  These scaffolds have internal porous architectures that meet the need for mechanical stiffness and strength as well as connected porosity for cell migration and tissue regeneration. 

The methods utilize images prepared with magnetic resonance (MR) or a combination of MR and computed tomography (CT) as a template for creating the scaffolds as well as the fixation for the scaffolding into adjacent tissue or bone.  Their advantages include the ability to design microstructures that mimic intervertebral load carrying capability and the potential to provide directed nutrients to migrated cells within the disc.  Furthermore, the ability to create structures that can regrow natural tissue could be an improvement upon current artificial discs made of synthetic materials which are subject to greater wear and tear.

Injection Molding of Biodegradable Tissue Engineering Scaffolds

UW-Madison researchers have developed a simple and inexpensive method of mass producing biodegradable structures for tissue engineering and drug delivery applications. The method starts with a composite blend of a salt, a water-soluble polymer and a biodegradable polymer. A foaming agent and/or supercritical fluid may be added to the composite, which is injected into a mold to form components with complex geometries. After molding, the salt and water-soluble polymer are removed to result in a low density, biodegradable structure.