Bone Regeneration Based on Tissue Engineering Conceptions – A 21st Century Perspective

The role of Bone Tissue Engineering in the field of Regenerative Medicine has been the topic of substantial research over the past two decades. Technological advances have improved orthopaedic implants and surgical techniques for bone reconstruction. However, improvements in surgical techniques to reconstruct bone have been limited by the paucity of autologous materials available and donor site morbidity. Recent advances in the development of biomaterials have provided attractive alternatives to bone grafting expanding the surgical options for restoring the form and function of injured bone. Specifically, novel bioactive （second generation） biomaterials have been developed that are characterised by controlled action and reaction to the host tissue environment, whilst exhibiting controlled chemical breakdown and resorption with an ultimate replacement by regenerating tissue. Future generations of biomaterials （third generation） are designed to be not only osteo- conductive but also osteoinductive, i.e. to stimulate regeneration of host tissues by combining tissue engineer- ing and in situ tissue regeneration methods with a focus on novel applications. These techniques will lead to novel possibilities for tissue regeneration and repair. At present, tissue engineered constructs that may find future use as bone grafts for complex skeletal defects, whether from post-traumatic, degenerative, neoplastic or congenital/developmental ＂origin＂ require osseous reconstruction to ensure structural and functional integrity. Engineering functional bone using combinations of cells, scaffolds and bioactive factors is a promising strategy and a particular feature for future development in the area of hybrid materials which are able to exhibit suitable biomimetic and mechanical properties. This review will discuss the state of the art in this field and what we can expect from future generations of bone regeneration concepts.

A New Model to Study Healing of a Complex Femur Fracture with Concurrent Soft Tissue Injury in Sheep

High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact. There is evidence that such closed soft tissue injuries affect the healing of bone fractures, and vice versa. Despite this knowledge, most impact trauma studies in animals have focussed on bone fractures or soft tissue trauma in isolation. However, given the simultaneous impact on both tissues a better understanding of the interaction between these two injuries is necessary to optimise clinical treatment. The aim of this study was therefore to develop a new experimental model and characterise, for the first time, the healing of a complex fracture with concurrent closed soft tissue trauma in sheep. A pendulum impact device was designed to deliver a defined and standardised impact to the distal thigh of sheep, causing a reproducible contusion injury to the subcutaneous soft tissues. In a subsequent procedure, a reproducible femoral butterfly fracture (AO C3-type) was created at the sheep’s femur, which was initially stabilised for 5 days by an external fixator construct to allow for soft tissue swelling to recede, and ultimately in a bridging construct using locking plates. The combined injuries were applied to twelve sheep and the healing observed for four or eight weeks (six animals per group) until sacrifice. The pendulum impact led to a moderate to severe circumferential soft tissue injury with significant bruising, haematomas and partial muscle disruptions. Posttraumatic measurements showed elevated intra-compartmental pressure and circulatory tissue breakdown markers, with recovery to normal, pre-injury values within four days. Clinically, no neurovascular deficiencies were observed. Bi-weekly radiological analysis of the healing fractures showed progressive callus healing over time, with the average number of callus bridges increasing from 0.4 at two weeks to 4.2 at eight weeks. Biomechanical testing after sacrifice showed in- creasing torsional stiffness between four and eight weeks healing time from 10% to 100%, and increasing ultimate torsional strength from 10% to 64% (relative to the contralateral control limb). Our results demonstrate the robust healing of a complex femur fracture in the presence of a severe soft tissue contusion injury in sheep and demonstrate the establishment of a clinically relevant experimental model, for research aimed at improving the treatment of bone fractures accompanied by closed soft tissue injuries.

Prevention of Staphylococcus aureus biofilm formation on metallic surgical implants via controlled release of gentamicin

Implant associated infections are a critical health concern following orthopaedic surgery. Sustained local delivery of antibiotics has been suggested as a means of preventing these infections. Poly(D,L-lactide) (PDLLA) is a biodegradable polymer that has been used to coat implants for the delivery of antibiotics and other bioactive molecules. While effective, these studies show that antibiotics are released in a burst profile. Here we evaluated a method for controlled release of gentamicin from implant surfaces using the palmitate alkyl salt to decrease its solubility in aqueous solution. Steel Kirschner wires (K-wires) were coated with Gentamicin-palmitate (GP)-PDLLA, gentamicin sulphate (GS)-PDLLA or vancomycin sulphate (VS)-PDLLA, and elution of antibiotics from coated K-wires investigated using HPLC/MS/ MS. In contrast to burst antibiotic release from the GS-PDLLA and VS-PDLLA groups, GP was released in a slower sustained manner. Colonisation and initial attachment of Staphylococcus aureus Xen29 to gentamicin-coated K-wires was reduced by 90% when compared to the non-coated control group. However there was no statistical difference in recovery of bacteria from GS or GP groups. Bacteria recovered from VS-PDLLA coated K-wires decreased by 36%. Bioluminescence emitted by S. aureus Xen29 was also reduced over seven days in the antibiotic control groups, demonstrating that growth and biofilm development over the longer term was impaired by antibiotic-PDLLA coating. These results indicate that using alkyl salts of antibiotics may be an effective strategy for controlling the release of antibiotics from implants.