Preliminary Results on Heparin-Modified Double-Layered PCL and PLA-Based Scaffolds for Tissue Engineering of Small Blood Vessels.

Low-diameter blood vessels are challenging to replace with more traditional synthetic vascular grafts. Therefore, the obvious choice is to try to regenerate small veins and arteries through tissue-engineering approaches. However, the layered structure of native vessels and blood compatibility issues make this a very challenging task. The aim of this study is to create double-layered tubular scaffolds with enhanced anticoagulant properties for the tissue engineering of small blood vessels. The scaffolds were made of a polycaprolactone-based porous outer layer and a polylactide-based electrospun inner layer modified with heparin. The combination of thermally induced phase separation and electrospinning resulted in asymmetric scaffolds with improved mechanical properties. The release assay confirmed that heparin is released from the scaffolds. Additionally, anticoagulant activity was shown through APTT (activated partial thromboplastin time) assay. Interestingly, the endothelial cell culture test revealed that after 14 days of culture, HAECs (human aortic endothelial cell lines) tended to organize in chain-like structures, typical for early stages of vascular formation. In the longer culture, HAEC viability was higher for the heparin-modified scaffolds. The proposed scaffold design and composition have great potential for application in tissue engineering of small blood vessels.

Biodegradable intramedullary nails reinforced with carbon and alginate fibers: In vitro and in vivo biocompatibility.

BACKGROUND: Commonly, intramedullary nails are made of nondegradable materials, and hence they need to be removed once the bone fracture is healed. We propose a novel composite material consisting of poly-L-lactide matrix modified with carbon and alginate fibers to be used for biodegradable intramedullary fixation. The aim of this study was to make in vitro and in vivo biocompatibility assessments. METHODS: In the in vitro conditions, biocompatibility of biomaterials was compared using normal human osteoblasts. After 3 and 7 days, cytotoxicity, viability and proliferation tests were performed, as well as cell morphology and adhesion observations. In the in vivo experiments, Californian rabbits (approx. 9 months old) were used. The composite nails and controls (Kirschner wires) were used for fixation of distal femoral osteotomy. The evaluation was made on the basis of clinical observations, radiographs taken after 2, 4, 6 and 8 weeks post implantation, and macroscopic and histological observations. RESULTS: Cell tests indicated that both modifiers had a positive influence on cell viability. Biodegradable composite nails led to bony union when used for fixation of distal diaphysis osteotomy in rabbits. Histological analysis showed that the initial focal necrosis should be fully compensated for by the osteoblast proliferation and trabeculae formation. CONCLUSIONS: Both in vitro and in vivo tests confirmed biocompatibility and potential applicability of novel biodegradable intramedullary nails modified with long carbon and alginate fibers for osteosynthesis of bone epiphysis.

Polylactide- and polycaprolactone-based substrates enhance angiogenic potential of human umbilical cord-derived mesenchymal stem cells in vitro - implications for cardiovascular repair.

Recent approaches in tissue regeneration focus on combining innovative achievements of stem cell biology and biomaterial sciences to develop novel therapeutic strategies for patients. Growing recent evidence indicates that mesenchymal stem cells harvested from human umbilical cord Wharton's jelly (hUC-MSCs) are a new valuable source of cells for autologous as well as allogeneic therapies in humans. hUC-MSCs are multipotent, highly proliferating cells with prominent immunoregulatory activity. In this study, we evaluated the impact of widely used FDA approved poly(α-esters) including polylactide (PLA) and polycaprolactone (PCL) on selected biological properties of hUC-MSCs in vitro. We found that both polymers can be used as non-toxic substrates for ex vivo propagation of hUC-MSCs as shown by no major impact on cell proliferation or viability. Moreover, PCL significantly enhanced the migratory capacity of hUC-MSCs. Importantly, genetic analysis indicated that both polymers promoted the angiogenic differentiation potential of hUC-MSCs with no additional chemical stimulation. These results indicate that PLA and PCL enhance selected biological properties of hUC-MSCs essential for their regenerative capacity including migratory and proangiogenic potential, which are required for effective vascular repair in vivo. Thus, PLA and PCL-based scaffolds combined with hUC-MSCs may be potentially employed as future novel grafts in tissue regeneration such as blood vessel reconstruction.

Influence of the intramedullary nail preparation method on nail's mechanical properties and degradation rate.

When it comes to the treatment of long bone fractures, scientists are still investigating new materials for intramedullary nails and different manufacturing methods. Some of the most promising materials used in the field are resorbable polymers and their composites, especially since there is a wide range of potential manufacturing and processing methods. The aim of this work was to select the best manufacturing method and technological parameters to obtain multiphase, and multifunctional, biodegradable intramedullary nails. All composites were based on a poly(l-lactide) matrix. Either magnesium alloy wires or carbon and alginate fibres were introduced in order to reinforce the nails. The polylactide matrix was also modified with tricalcium phosphate and gentamicin sulfate. The composite nails were manufactured using three different methods: forming from solution, injection moulding and hot pressing. The effect of each method of manufacturing on mechanical properties and degradation rate of the nails was evaluated. The study showed that injection moulding provides higher uniformity and homogeneity of the particle-modified polylactide matrix, whereas hot pressing favours applying higher volume fractions of fibres and their better impregnation with the polymer matrix. Thus, it was concluded that the fabrication method should be individually selected dependently on the nail's desired phase composition.

Gentamicin release from biodegradable poly-l-lactide based composites for novel intramedullary nails.

One of the major problems in orthopedic surgery is infection associated with implantation. The treatment is a very difficult and long-term process. A solution to this issue can be the use of implants which additionally constitute an antibiotic carrier preventing the development of an infection. Prototypes of biodegradable intramedullary nails made of three different composites with a poly(L-lactide) matrix were designed. The nails served as gentamicin sulfate (GS) carrier - an antibiotic commonly used in the treatment of osteomyelitis. The matrix was reinforced with carbon fibers (CF), alginate fibers (Alg) and magnesium alloy wires (Mg), as well as modified with bioactive particles of tricalcium phosphate (TCP) in various systems. In this way, novel, multi-phase and multifunctional degradable intramedullary nails were obtained. The tests demonstrated strong dependence between the type of the modifying phase introduced into the composite, and the rate of drug release. Introduction of gentamicin into the nail structure strengthened and prolonged antibacterial activity of the nails.

Gradient composite materials for artificial intervertebral discs.

Composites with the gradient of Young's modulus constitute a new group of biomimetic materials which affect the proper distribution of stresses between the implant and the bone. The aim of this article was to examine the mechanical properties of gradient materials based on carbon fibre-polysulfone composite, and to compare them to the properties of a natural intervertebral disc. Gradient properties were provided by different orientation or volume fraction of carbon fibres in particular layers of composites. The results obtained during in vitro tests displayed a good durability of the gradient materials put under long-term static load. However, the configuration based on a change in the volume fraction of the fibres seems more advantageous than the one based on a change of the fibres' orientation. The materials under study were designed to replace the intervertebral disc. The effect of Young's modulus of the material layers on the stress distribution between the tissue and the implant was analyzed and the biomimetic character of the gradient composites was stated. Unlike gradient materials, the pure polysulfone and the non-gradient composite resulted in the stress concentration in the region of nucleus pulposus, which is highly disadvantageous and does not occur in the stress distribution of natural intervertebral discs.

Magnesium alloy wires as reinforcement in composite intramedullary nails.

A promising group of biomaterials assigned for the production of intramedullary nails are composites with a polylactide (PLA) matrix, reinforced with wires made of magnesium alloys and carbon fibres. The paper describes the effect of the composition of magnesium alloy wires, their number and orientation in the composite, as well as their connection with differently directed long carbon fibres, on the mechanical properties and the degradation rate of the obtained intramedullary nails. Among the tested implant prototypes, the best mechanical characteristics and a gradual and uniform course of magnesium alloy wires were exhibited by the PLA+CF1D+MgI composite nails (with a unidirectional orientation of carbon fibres and an axially oriented single Mg alloy wire). The strength of these nails became gradually decreased with the incubation time, which should allow for a gradual loading of the bone. In the case of the PLA with only magnesium alloy wires (without carbon fibres), the increase of the number of wires, on the one hand, stimulates the improvement of the nails' strength, yet on the other hand, a higher content of magnesium alloys in the PLA matrix affects the nails' faster resorption.

The evaluation of the possibilities of using PLGA co-polymer and its composites with carbon fibers or hydroxyapatite in the bone tissue regeneration process - in vitro and in vivo examinations.

Synthetic polymers belonging to the aliphatic polyester group have become highly promising biomaterials for reconstructive medicine. The purpose of the present work is a biological evaluation of lactide-glycolide co-polymer (PLGA) and its composites with carbon fibers (PLGA+CF) or hydroxyapatite (PLGA+HA). The cytotoxicity of the evaluated materials towards hFOB 1.19 human osteoblast-like cells was assessed. Moreover, during the one-year contact of the assessed materials with living osseous tissue, the progress of bone formation was analyzed and the accompanying process of the materials' degradation was evaluated. The materials under evaluation proved to be biocompatible.

The influence of carbon fibres on the resorption time and mechanical properties of the lactide-glycolide co-polymer.

In this study the influence of short carbon fibres (CF) on mechanical properties and degradation time of the lactide-glycolide co-polymer (PGLA) and on the mechanism of bone ingrowth into the implants was determined. Mechanical properties and push-out tests were measured. The pH of solutions and the implants' weights were tested after incubation in Ringer fluid. Analysis was based upon FT-IR and SEM with EDS studies. Pathological examinations were also performed. The in vitro examination revealed that carbon fibres accelerated polymer degradation process and increased the mechanical strength of polymer. In the case of PGLA + CF under in vivo conditions, initially, the superficial polymer degradation with new tissue in-growth was observed. Next, the degradation process included also the inner part of the implant, while the bone began to grow on exposed carbon fibres. In the case of pure PGLA the growth of soft tissue can be observed at the bone-implant interface and in the implant area. Our research indicates that PGLA + CF composite can be used in bone surgery as a short-term multifunctional load-bearing implant, which initially provides a mechanical support. During the time of controlled resorption of PGLA, carbon fibres act as a scaffold for the bone growth.