Recent Advances in Tissue Engineering.

Tissue formation within the body, as part of a development or repair process, is a complex event in which cell populations self-assemble into functional units. There is intense academic, medical, and commercial interest in finding methods of replicating these events outside the body. This interest has accelerated with the demonstration of the engineering of skin and cartilage tissue in the laboratory and there is now worldwide activity in the in vitro regeneration of tissues including nerve, liver, bone, heart valves, blood vessels, bladder, and kidney. Approaches to tissue engineering center on the need to provide signals to cell populations to promote cell proliferation and differentiation. This review considers recent advances in methods of providing these signals to cells using examples of progress in the engineering of complex tissues.

A biodegradable antibiotic-impregnated scaffold to prevent osteomyelitis in a contaminated in vivo bone defect model.

Open fractures are at risk of serious infection and, if infected, require several surgical interventions and courses of systemic antibiotics. We investigated a new injectable formulation that simultaneously hardens in vivo to form a porous scaffold for bone repair and delivers antibiotics at high concentrations to the local site of infection. Duration of antimicrobial activity against Staphylococcus aureus was determined using the serial plate transfer test. Ultimate compressive strength and porosity of the material was measured with and without antibiotics. The material was evaluated in vivo in an ovine medial femoral condyle defect model contaminated with S. aureus. Sheep were sacrificed at either 2 or 13 weeks and the defect and surrounding bone assessed using micro-computed tomography and histology. Antimicrobial activity in vitro persisted for 19-21 days. Sheep with antibiotic-free material and bacteria became infected, while those with antibiotic-containing material and bacteria did not. Similarly, new bone growth was seen in uninoculated animals with plain polymer, and in those with antibiotic polymer with bacteria, but not in sheep with plain polymer and bacteria. The antibiotic-impregnated scaffolds were effective in preventing S. aureus infections whilst supporting bone growth and repair. If translated into clinical practice, this approach might reduce the need for systemic antibiotics.

Recent advances in tissue engineering: an invited review.

Tissue formation within the body, as part of a development or repair process, is a complex event in which cell populations self-assemble into functional units. There is intense academic, medical, and commercial interest in finding methods of replicating these events outside the body. This interest has accelerated with the demonstration of the engineering of skin and cartilage tissue in the laboratory and there is now worldwide activity in the in vitro regeneration of tissues including nerve, liver, bone, heart valves, blood vessels, bladder, and kidney. Approaches to tissue engineering center on the need to provide signals to cell populations to promote cell proliferation and differentiation. This review considers recent advances in methods of providing these signals to cells using examples of progress in the engineering of complex tissues.

Growth factor release from tissue engineering scaffolds.

Synthetic scaffold materials are used in tissue engineering for a variety of applications, including physical supports for the creation of functional tissues, protective gels to aid in wound healing and to encapsulate cells for localized hormone-delivery therapies. In order to encourage successful tissue growth, these scaffold materials must incorporate vital growth factors that are released to control their development. A major challenge lies in the requirement for these growth factor delivery mechanisms to mimic the in-vivo release profiles of factors produced during natural tissue morphogenesis or repair. This review highlights some of the major strategies for creating scaffold constructs reported thus far, along with the approaches taken to incorporate growth factors within the materials and the benefits of combining tissue engineering and drug delivery expertise.

Poly(L-lysine)-GRGDS as a biomimetic surface modifier for poly(lactic acid).

The immobilization of adhesion peptide sequences (such as RGD) at the surfaces of poly(alpha-hydroxyacid)s, including poly(lactic acid) (PLA), is complicated by an absence of functional groups to support covalent attachment. We demonstrate a method to overcome this problem, by attaching the peptide to poly(L-lysine) (PLL), which immobilizes the sequence through adsorption at the poly(alpha-hydroxyacid) surface. When coated using a 0.01% w/v solution of PLL-GRGDS, bovine aortic endothelial cells seeded upon the modified PLA showed a marked increase in spreading over unmodified PLA. However, inhibition of the cell-spreading effect occurred when using higher concentrations of PLL-GRGDS, which we attribute to the PLL component. This inhibitory effect can be challenged by increasing the amount of GRGDS attached to each PLL molecule. Potentially, this is a flexible method of surface modification that can engineer many different types of tissue engineering scaffolds with a variety of biomolecules, thus allowing initial cell adhesion to be controlled.

Cell function and viability in glucose polymer peritoneal dialysis fluids.

OBJECTIVE: To investigate the biocompatibility profile of a new peritoneal dialysis fluid containing glucose polymer (GPF). DESIGN: Viability and function of peripheral neutrophils (PMN) from healthy donors and cultured human peritoneal mesothelial cells were assessed in vitro after exposure to dialysis fluids. Phagocytosis, leukotriene B4 synthesis, and respiratory burst activation were measured following stimulation with serum-treated zymosan (STZ) or opsonized Staphylococcus epidermidis (S. epidermidis). Bacterial growth in the fluids was also investigated. In vivo pH equilibration of GPF and subsequent respiratory burst activation following incubation in spent dialysate were studied. RESULTS: For all the host defense parameters measured, commercial dialysis fluids (Dianeal; 1.36% and 3.86% glucose) and GPF (pH 5.2) were significantly more inhibitory than the control buffer (pH 7.3). Mesothelial cell viability was reduced by all the fluids tested irrespective of pH. Glucose polymer fluid was significantly more inhibitory than Dianeal 1.36% for STZ phagocytosis and respiratory burst activation. In contrast, it was less suppressive than Dianeal 3.86% for LTB4 synthesis. For all parameters tested, except LTB4 generation, there was a marked effect of pH, with GPF being significantly more inhibitory at pH 5.2 than at pH 7.3. None of the fluids tested supported the growth of S. epidermidis, although the viable counts in GFP were significantly higher than in Dianeal. Fluid inhibition of PMN respiratory burst activation and cytotoxicity were reduced in a time-dependent manner following increasing dwell time in vivo. CONCLUSIONS: GPF does not appear to be significantly different from Dianeal as far as host defense parameters are concerned. However, the cell viability and bacterial survival data suggest some possibly negative aspects of this fluid formation.