The concept of tissue expansion for surgical reconstruction was first reported over 50 years ago, although the technique did not gain popular acceptance until the 1980s, when it was used predominantly in delayed breast reconstruction.
Self-inflating tissue expanders were developed in parallel to balloon-type devices. However, their impact was hindered by their limited expansion volumes and potential complications. The adoption of biocompatible osmotically active hydrogels was a major advance in the evolution of self-inflating devices, although they were relatively crude in terms of their in vivo performance.
Traditional tissue expansion utilizes an implantable subcutaneous silicone balloon that is gradually inflated (usually on a weekly basis) by injecting saline solution through a buried filling port. Inflation continues until the desired degree of soft tissue expansion is obtained — usually a period of some months. Although widely used in a range of reconstructive applications, they have a number of inherent limitations. Firstly, they are bulky and therefore of limited use for intricate anatomical locations, particularly in the pediatric setting.
Percutaneous inflation can also be uncomfortable and is poorly tolerated by some patients, especially children. Furthermore, the balloon expands equally in all directions (i.e. is isotropic), while in certain clinical situations, directional expansion (i.e. anisotropy) may be desirable. Such instances might include dorsal digital skin expansion prior to syndactyly release in order to avoid the need for skin grafting or intra-oral vertical ridge augmentation preceding the use of osseo-integrated dental implants.
An intelligent hydrogel material for tissue expansion was developed as the result of a unique collaboration between two materials scientists (Jan Czernuszka, Lecturer in Materials at the University of Oxford, and David Bucknall, currently Professor of Materials Science at the Georgia Institute of Technology in the U.S.) and two plastic and reconstructive surgeons (Marc C. Swan and Tim Goodacre based at the John Radcliffe Hospital in Oxford).
Czernuszka says, “I was approached by Tim and Marc who described a problem they had had when treating children. Together with them and David Bucknall, we developed this novel medical device. This is a clear case of careful, precise processing of biocompatible materials to meet an immediate clinical need. We have taken hydrogels and processed them such that they expand unidirectionally, and in a controlled manner. This control at the appropriate length scale is crucial to the success of the device, and it is what makes it unique.”
Oxtex Limited (Oxford, United Kingdom), a spinout from Isis Innovation Ltd, the technology transfer office of the University of Oxford, secured £500,000 of seed funding to develop this intelligent hydrogel technology.
How it Works
For the first time, surgeons will be able to accurately and predictably control the direction, the timing, and rate of the material’s expansion in the body. This will significantly reduce the risk of soft tissue damage and associated complications. The level of control makes them ideal for use in delicate anatomical locations, particularly in the treatment of children.
The Oxtex device typically displays a triphasic swelling profile in vivo – see Fig. 1. Phase I represents the biodegradable ‘time switch’ which delays the onset of swelling following implantation for a period of typically two weeks (as dictated by the surgeon).
The rate of osmotic expansion during Phase II is carefully controlled either by an integral polymer scaffold or an external semipermeable membrane thus preventing the undesirable effects of excessive expansion which include pain and potential tissue necrosis.
The final degree of swelling achieved at Phase III can be precisely controlled (up to 1500% if necessary) and is determined by the hydrogel formulation used. The device is entirely inert and will remain quiescent during Phase III until surgically removed in order to perform the definitive reconstruction.
The Oxtex product range comprises implantable self-inflating tissue expanders available in a range of sizes and shapes to suit the specific needs of the clinician and the patient. Advantages of the Oxtex technology over existing balloon and hydrogel technologies include:
- removes the need for injection ports due to the self-inflating action of the technology;
- a delayed action device is available whereby swelling commences after a predetermined time period (normally one to two weeks) following implantation to facilitate wound healing prior to expansion;
- a precisely controlled expansion rate (ranging from six weeks to six months), which minimizes the likelihood of soft tissue necrosis and subsequent device extrusion;
- a choice of isotropic and anisotropic expansion profiles, which is hugely valuable for delicate anatomical locations and targeted directional expansion;
- specific devices in the Oxtex range allow bespoke intraoperative shaping by the surgeon — to ensure an optimal fit for each patient.
Where it Stands
The market for the product, which can be shaped by the surgeon prior to implantation, is broad. It includes scar reconstruction following trauma, burns, or cancer surgery. It also includes the treatment of congenital craniofacial conditions and limb deformities. However, the largest market may be in restorative dentistry. Trials in this area are scheduled to begin at the Harvard School of Dental Medicine.
Swan says, “There is always a clinical need for extra soft tissue in reconstructive plastic surgery, but until now there has been no reliable method of attaining the optimal amount through hydrogel technology. This device will allow clinicians to treat more cases, at a lower cost, and hopefully with a better patient outcome. We also expect new procedures and clinical indications to arise as a result of this breakthrough technology.”
For more information about the Oxtex Intelligent Tissue Expander, visit http://info.hotims.com/40434-160.