Evaluation of the Biocompatibility of Poly (ortho ester), Copolymer of ε-caprolactone/D,L-lactide and the Composite of Copolymer of ε-caprolactone/D,L-lactide and Tricalciumphosphate as Bone Filling Material

The purpose of this series of studies was to evaluate the biocompatibility of poly (ortho) ester (POE), copolymer of ε-caprolactone and D,L-lactide [P (ε-CL/DL-LA)] and the composite of P(ε-CL/DL-LA) and tricalciumphosphate (TCP) as bone filling material in bone defects. Tissue reactions and resorption times of two solid POE-implants (POE 140 and POE 46) with different methods of sterilization (gamma- and ethylene oxide sterilization), P(ε-CL/DL-LA)(40/60 w/w) in paste form and 50/50 w/w composite of 40/60 w/w P(ε-CL/DL-LA) and TCP and 27/73 w/w composite of 60/40 w/w P(ε-CL/DL-LA) and TCP were examined in experimental animals. The follow-up times were from one week to 52 weeks. The bone samples were evaluated histologically and the soft tissue samples histologically, immunohistochemically and electronmicroscopically. The results showed that the resorption time of gamma sterilized POE 140 was eight weeks and ethylene oxide sterilized POE 140 13 weeks in bone. The resorption time of POE 46 was more than 24 weeks. The gamma sterilized rods started to erode from the surface faster than ethylene oxide sterilized rods for both POEs. Inflammation in bone was from slight to moderate with POE 140 and moderate with POE 46. No highly fluorescent layer of tenascin or fibronectin was found in the soft tissue. Bone healing at the sites of implantation was slower than at control sites with the copolymer in small bone defects. The resorption time for the copolymer was over one year. Inflammation in bone was mostly moderate. Bone healing at the sites of implantation was also slower than at the control sites with the composite in small and large mandibular bone defects. Bone formation had ceased at both sites by the end of follow-up in large mandibular bone defects. The ultrastructure of the connective tissue was normal during the period of observation. It can be concluded that the method of sterilization influenced the resorption time of both POEs. Gamma sterilized POE 140 could have been suitable material for filling small bone defects, whereas the degradation times of solid EO-sterilized POE 140 and POE 46 were too slow to be considered as bone filling material. Solid material is difficult to contour, which can be considered as a disadvantage. The composites were excellent to handle, but the degradation time of the polymer and the composites were too slow. Therefore, the copolymer and the composite can not be recommended as bone filling material.

Studies on diamond-like carbon and novel diamond-like carbon polymer hybrid coatings deposited with filtered pulsed arc discharge method

The main obstacle for the application of high quality diamond-like carbon (DLC) coatings has been the lack of adhesion to the substrate as the coating thickness is increased. The aim of this study was to improve the filtered pulsed arc discharge (FPAD) method. With this method it is possible to achieve high DLC coating thicknesses necessary for practical applications. The energy of the carbon ions was measured with an optoelectronic time-of-flight method. An in situ cathode polishing system used for stabilizing the process yield and the carbon ion energies is presented. Simultaneously the quality of the coatings can be controlled. To optimise the quality of the deposition process a simple, fast and inexpensive method using silicon wafers as test substrates was developed. This method was used for evaluating the suitability of a simplified arc-discharge set-up for the deposition of the adhesion layer of DLC coatings. A whole new group of materials discovered by our research group, the diamond-like carbon polymer hybrid (DLC-p-h) coatings, is also presented. The parent polymers used in these novel coatings were polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE). The energy of the plasma ions was found to increase when the anode-cathode distance and the arc voltage were increased. A constant deposition rate for continuous coating runs was obtained with an in situ cathode polishing system. The novel DLC-p-h coatings were found to be water and oil repellent and harder than any polymers. The lowest sliding angle ever measured from a solid surface, 0.15 ± 0.03°, was measured on a DLC-PDMS-h coating. In the FPAD system carbon ions can be accelerated to high energies (≈ 1 keV) necessary for the optimal adhesion (the substrate is broken in the adhesion and quality test) of ultra thick (up to 200 µm) DLC coatings by increasing the anode-cathode distance and using high voltages (up to 4 kV). An excellent adhesion can also be obtained with the simplified arc-discharge device. To maintain high process yield (5µm/h over a surface area of 150 cm2) and to stabilize the carbon ion energies and the high quality (sp3 fraction up to 85%) of the resulting coating, an in situ cathode polishing system must be used. DLC-PDMS-h coating is the superior candidate coating material for anti-soiling applications where also hardness is required.