Improvement and characterization of the adhesion of electrospun PLDLA nanofibers on PLDLA-based 3D object substrates for orthopedic application.

Intensive research has demonstrated the clear biological potential of electrospun nanofibers for tissue regeneration and repair. However, nanofibers alone have limited mechanical properties. In this study we took poly(L-lactide-co-D-lactide) (PLDLA)-based 3D objects, one existing medical device (interference screws) and one medical device model (discs) as examples to form composites through coating their surface with electrospun PLDLA nanofibers. We specifically investigated the effects of electrospinning parameters on the improvement of adhesion of the electrospun nanofibers to the PLDLA-based substrates. To reveal the adhesion mechanisms, a novel peel test protocol was developed for the characterization of the adhesion and delamination phenomenon of the nanofibers deposited to substrates. The effect of incubation of the composites under physiological conditions on the adhesion of the nanofibers has also been studied. It was revealed that reduction of the working distance to 10 cm resulted in deposition of residual solvent during electrospinning of nanofibers onto the substrate, causing fiber-fiber bonding. Delamination of this coating occurred between the whole nanofiber layer and substrate, at low stress. Fibers deposited at 15 cm working distance were of smaller diameter and no residual solvent was observed during deposition. Delamination occurred between nanofiber layers, which peeled off under greater stress. This study represents a novel method for the alteration of nanofiber adhesion to substrates, and quantification of the change in the adhesion state, which has potential applications to develop better medical devices for orthopedic tissue repair and regeneration.

Potential use of craniosynostotic osteoprogenitors and bioactive scaffolds for bone engineering.

The cranial bone has a very limited regenerative capability. Patients with craniosynostosis (the premature fusion of cranial sutures, leading to skull abnormalities) often require extensive craniofacial reconstruction and repeated surgery. The possibility of grafting autologous osteoprogenitor cells seeded on bioabsorbable matrices is of great potential for inducing regeneration of craniofacial structure and protecting the brain from external insult. To this purpose we have studied the behaviour of normal and craniosynostotic mouse osteoblast cell lines, and of human primary osteoprogenitors from craniosynostotic patients. We have monitored their ability to grow and differentiate on plastic and on a scaffold composed of bioactive glass and bioabsorbable polymer by live fluorescent labelling and expression of bone differentiation markers. Cells from syndromic patients display a behaviour very similar to that observed in the stable mouse cell line we generated by introducing the human FGFR2-C278F, a mutation found in certain craniosynostosis, into MC3T3 osteblastic cells, indicating that the mutated cell line is a valuable model for studying the cellular response of human craniosynostotic osteoblasts. Both normal and mutated calvarial osteoprogenitors can attach to the bioactive scaffold, although mutated cells display adhesion defects when cultured on plastic. Furthermore, analysis of bone differentiation markers in human osteoblasts shows that the composite mesh, unlike PLGA(80) plates, supports bone differentiation. The ability of the mesh to support homing and differentiation in both normal and mutant osteoprogenitors is important, in view of further developing autologous biohybrids to repair cranial bone deficits also in craniosynostotic patients undergoing extensive reconstructive surgery.

Innovation in multifunctional bioabsorbable osteoconductive drug-releasing hard tissue fixation devices.

We review in this paper the work performed by our group to develop multifunctional bioabsorbable ciprofloxacin releasing bone implants. Poly lactide-co-glycolide (PLGA 80/20 and polylactide (P(L/DL)LA 70/30) were used. Ciprofloxacin (CF) and bioactive glass (BaG) 13-93 were added. The mixture was then extruded and self-reinforced. CF release, mechanical strength, and the effect on S. epidermidis attachment and biofilm formation were evaluated. In rabbits, tissue reactions were assessed. Pull out strength was evaluated in cadaver bones. CF was released over 44 weeks (P(L/DL)LA) and 23-26 weeks (PLGA). Initial shear strength of the CF screws was 152 MPa (P(L/DL)LA) and 172 MPa (PLGA). Strength was retained for 12 weeks (P(L/DL)LA) and 9 weeks (PLGA). Histologically, CF releasing implants did not show much difference from control plain PLGA screws except for increased giant cells. CF miniscrews had lower pullout strength than the controls, but CF tacks had better values than controls. BaG led to a drop in pullout strength properties. Bacterial growth, attachment and biofilm formation on CF implants was significantly reduced when compared to controls. Accordingly, bioabsorbable multifunctional implants with appropriate CF release, mechanical, and biocompatibility properties are possible to develop and are considered appropriate to apply clinically.

In vitro mechanical and drug release properties of bioabsorbable ciprofloxacin containing and neat self-reinforced P(L/DL)LA 70/30 fixation screws.

Osteomyelitis is inflammation of the bone caused by a pathogenic organism. Both its acute and chronic forms are difficult to heal. Antibiotics are still the basic treatment for osteomyelitis. Bioabsorbable ciprofloxacin containing bone fixation screws based on self-reinforced (SR) copolylactide P(L/DL)LA 70/30 have been developed for local treatment of bone infections. These screws gradually released ciprofloxacin during the in vitro bulk degradation of the matrix polymer and at the same time have sufficient mechanical strength. All the loaded ciprofloxacin was released from the gamma sterilized screws during 44 in vitro weeks and the concentration of the released drug per day remained between 0.06 and 8.7 microg/ml after the start-up burst peak.

The fixation properties of carbon fiber-reinforced liquid crystalline polymer implant in bone: an experimental study in rabbits.

A novel composite material with ultra-high strength and a low elastic modulus called carbon fiber-reinforced liquid crystalline polymer (LCP/CF) has been developed. We studied the fixation properties of an intramedullary LCP/CF rod in rabbit bone. The medullary canals of both femora were reamed with a drill 3.2 mm in diameter starting from the trochanteric fossa in eleven New Zealand White rabbits weighing on average 4.8 kg. A smooth LCP/CF rod 3.2 mm in diameter and 50 mm in length was introduced into the medullary canal of both femora. The follow-up intervals were 0, 6, 12, and 52 weeks. The upper part of the harvested femora was cut into two pieces, each 25 mm in length. A mechanical push-out test was performed within 48 h to determine bone-implant interface attachment strength in the proximal (cancellous) and distal (cortical) locations. The mean push-out strength values at 0, 6, 12, and 52 weeks were 61, 250, 382, and 612 KPa in the cancellous location and 0, 32, 41, and 68 KPa in the cortical location, respectively. The strength of the bone/implant interface appeared to be quite low, similar to other uncoated or nonporous implants, but it was found to increase with time.