Teemu Tirri

In vitro evaluation of poly(ε-caprolactone-co-dl-lactide)/ bioactive glass composites

In vitro bioactivity of composites of poly(e-caprolactone-co-DL-lactide) P(CL/DL-LA) containing different amounts (40, 60 and 70 wt%) of bioactive glass, S53P4, was evaluated. Two ranges of granule size of bioactive glass (<45 μm and 90–315 μm) were blended with P(CL/DL-LA) copolymer in a batch mixer. The composites were characterised by dynamic mechanical thermal analysis. The molecular weight and the melting temperature of the copolymer matrix were adjusted to enable the application of the composite material by injection below 50°C. Formation of Ca-P deposition on the surface of the composites after dissolution in simulated body fluid at 37°C was recorded by scanning electron microscopy. Degradation of the composite material was measured by water absorption and changes in the average molecular weights as a function of the dissolution time. In vitro bioactivity was found to be dependent on the weight fraction and granule size range of the bioactive glass used. The presence of the bioactive filler also accelerated the degradation compared with the neat polymer sample.

In vitro Ca-P precipitation on biodegradable thermoplastic composite of poly(ε-caprolactone-co-dl-lactide) and bioactive glass (S53P4)

Bioactive properties of composites containing poly(epsilon-caprolactone-co-DL-lactide) with molar ratio 96/4 and bioactive glass (BAG), S53P4, were tested in vitro. The glass content in the tested materials was 40, 60 or 70 wt%, and two granule size ranges (<45 and 90-315 microm) were used. The composites were analysed for their apatite-forming ability. This was determined as a function of time by the dissolution pattern of Si and Ca ions and structural changes on the specimen surfaces. Composite specimens were immersed in simulated body fluid at 37 degrees C for up to 6 months. The changes in Si and Ca concentrations of the immersion medium were determined with UV-Vis and atomic absorption spectrophotometry. The calcium phosphate precipitation and apatite formation were evaluated by scanning electron microscopy (SEM) and infra-red spectroscopy (IR) using the attenuated total reflectance (ATR) system. The SEM and SEM-EDX analysis of the depositions formed on the composite surfaces was in line with the changes in ion concentrations. The clearest results with IR were seen in the material containing 60 wt% small glass particles. The results indicate that composites containing over 40 wt% BAG granules are bioactive, and that a higher BAG surface area/volume ratio favors the apatite formation in vitro.

Peri-implant tissue response to TiO2 surface modified implants.

OBJECTIVES The objective of this study was to evaluate peri-implant soft tissue attachment and alveolar bone height on nanoporous TiO(2) thin film on commercial titanium dental implants compared with unmodified standard implants. MATERIAL AND METHODS In six adult beagle dogs, the mandibular premolars P2-P4 were extracted bilaterally. Sol-gel-derived nanoporous TiO(2) thin film was produced on smooth coronal part of standard ITI Straumann implants (4.1 mm x 8.0 mm) by dip coating method. After 3 months healing period of the extraction sockets modified (n=24) and unmodified (n=11) control implants were placed bilaterally. The animals were killed after 8 weeks and the samples were retrieved and processed for histologic/histomorfometric and TEM/SEM evaluations. RESULTS Histological examination showed mild or absent inflammatory reaction in peri-implant connective tissues around the surface modified implants. Further, junctional epithelium (JE)/connective tissue (CT) appeared to be in immediate contact with the experimental implants. Of the experimental implants, 22% were judged to be detached from the implant surface while 45% of the untreated control implants were detached. Dense plaques of hemidesmosomes were found in TEM evaluation of the JE cell membrane facing the surface-treated implants. In the histomorfometric analysis, the distance between the implant margin and alveolar bone crest was significantly shorter in surface-treated implants than in the control implants (P<0.02). CONCLUSION Nanoporous sol-gel-derived TiO(2) thin film on ITI Straumann dental implants improved soft tissue attachment in vivo.

Fate of Bone Marrow-Derived Stromal Cells after Intraperitoneal Infusion or Implantation into Femoral Bone Defects in the Host Animal

The fate of intraperitoneally injected or implanted male rat bone marrow-derived stromal cells inside female sibling host animals was traced using Y-chromosome-sensitive PCR. When injected intraperitoneally, Y-chromosome-positive cells were found in all studied organs: heart muscle, lung, thymus, liver, spleen, kidney, skin, and femoral bone marrow with a few exceptions regardless of whether they had gone through osteogenic differentiation or not. In the implant experiments, expanded donor cells were seeded on poly(lactide-co-glycolide) scaffolds and grown under three different conditions (no additives, in osteogenic media for one or two weeks) prior to implantation into corticomedullar femoral defects. Although the impact of osteogenic in vitro cell differentiation on cell migration was more obvious in the implantation experiments than in the intraperitoneal experiments, the donor cells stay alive when injected intraperitoneally or grown in an implant and migrate inside the host. However, when the implants contained bioactive glass, no signs of Y-chromosomal DNA were observed in all studied organs including the implants indicating that the cells had been eliminated.

Nanoporous TiO(2) Thin Film on Titanium Oral Implants for Enhanced Human Soft Tissue Adhesion: A Light and Electron Microscopy Study

BACKGROUND Previous experimental studies have demonstrated direct soft tissue attachment for nanoporous titanium dioxide (TiO(2) ) thin film on implants, while implants without TiO(2) thin film have not shown this capability. PURPOSE The aims were to evaluate and compare TiO(2) surface-modified experimental microimplants with unmodified microimplants with respect to tissue interaction of the human oral mucosa evaluated by light microscopy on ground sections and semithin sections and transmission electron microscopy on ultrathin sections, and to characterize the inflammatory response and the level of the marginal bone resorption. MATERIALS AND METHODS The study was a single-center, randomized, comparative, clinical investigation with intrasubject comparison of implants with and without TiO(2) thin film in 15 patients. RESULTS Two comparator microimplants showed mild erythema and expulsion of fluids. The surrounding tissues around all test implants were clinically healthy. The oral mucosa in contact with the abutment part of the microimplant was 72% for the test implants and 48% for the comparator implants, a statistically significant difference (p =.0268). No statistically significant difference was found in other histological variables. The marginal bone loss in 14 weeks was 0.5 mm for the stable test (n = 11) and 1.7 mm for the stable comparator implants (n = 9; p = .0248). CONCLUSIONS The nanoporous TiO(2) surface modification has potential clinical benefits because of increased adherence of soft tissue and possible reduced bone resorption.

Ectopic bone formation in and soft-tissue response to P(CL/DLLA)/bioactive glass composite scaffolds.

OBJECTIVES To characterize biological response to subcutaneously implanted macroporous poly(ε-caprolactone/D,L-lactide)-based scaffolds, and to evaluate the effect of bioactive glass (BAG) filler and osteogenic cells to the tissue response and ectopic bone formation. MATERIAL AND METHODS In the first part of this study, six different scaffold types were screened in a rat subcutaneous implantation model. The polymer scaffolds with 70/30 caprolactone/lactide ratio and corresponding composites with < 45 μm BAG filler size were chosen for the further ectopic bone formation assay. The scaffolds were loaded with differentiating bone marrow stromal cells and implanted subcutaneously in syngeneic rats. RESULTS With plain scaffolds, only mild foreign body reaction with no signs of gross inflammation was observed after 4 weeks of implantation. Furthermore, the scaffolds were fully invaded by well-vascularized soft connective tissue. Overall, all the tested scaffold types showed an appropriate host response. With cell-seeded scaffolds, several loci of immature mineralizing tissue and small amounts of mature bone were observed after 4 weeks. The incidence of mature bone formation was two and four in polymer scaffolds and composites, respectively (n = 8). After twelve weeks, mature bone was observed in only one polymer scaffold but in seven composites (n = 8). Excluding bone formation, the host response was considered similar to that with cell-free scaffolds. CONCLUSIONS Plain scaffolds supported the ingrowth of well-vascularized fibroconnective tissue. Furthermore, cell seeded composites with BAG filler showed enhanced ectopic bone formation in comparison with corresponding neat polymer scaffolds.

A Review of Two Animal Studies Dealing with Biological Responses to Glass-Fibre-Reinforced Composite Implants in Critical Size Calvarial Bone Defects in Rabbits

In these studies, E-glass-fibre-reinforced composite (FRC) implants with photopolymerisable resin systems and bioactive glass granules (BAG) were evaluated as a reconstructive material in the critical size bone defects made to rabbits’ calvarial bones. In the first study, a new experimental resin system, DD1/MMA/BDDMA, was used to impregnate the doubleveil FRC-implants, while in the second study, a commercial resin system composed of BisGMA/MMA/PMMA was used in impregnation. These double-veil FRC-implants were coated with bioactive glass granules (BAG, 315-500 0m). In the second study, an experimental FRC consisting of two laminates of woven fibres, was also tested as an implant material. These implants were filled with BAG-granules and pure fused quartz fibers (Quartzel wool). In the first study, implantation time was 4 or 12 weeks, while in the second study, it was 12 weeks for both the implant types. Results: In the first study, the healing of the defects had started in the form of new bone growth from the defect margins, as well as small islands of woven bone in the middle of the defect, at 4 weeks postoperatively. Ingrowth of dense connective tissue into the pores of the implant was widely seen. At 12 weeks postoperatively, more bony islands were seen as compared to the animals studied at 4 weeks. Part of the newly formed bone had an appearance of lamellar structure. The porous structures of the implant were deeply filled with fibroconnective tissue. Ingrowth of maturing bone to the implant structures was occasionally seen. The inflammatory reaction was moderate, and was mostly found inside the upper part of the implant. In the second study, inflammatory reactions caused by both types of the FRC implants were very slight. Small amount of new bone had started to grow from the defect margins in doulble-veil implanted defects. No ingrowth of connective tissues or new bone formation was seen inside these implants. Instead, both the connective tissues and newly formed, mineralizing bone were seen inside the experimental double-laminate implants. SiO2-fibres seemed to cause moderate inflammatory reaction inside the implants, while BAG granules did not. In both the study groups, the brain tissue was oedemic, but no obvious serious damage was found. Conclusions: The structural properties of the FRC-implants had an influence on the healing process of the bone defect. BAG, as a constituent of the FRCimplants, enhanced the bone formation process. After some modifications to the properties of the FRC, this type of implant has possibilities to become one material alternative in clinical bone defect reconstruction at the craniofacial area in the future.

Enhanced osteogenicity of bioactive composites with biomimetic treatment.

Purpose. This study aimed to explore if initiation of biomimetic apatite nucleation can be used to enhance osteoblast response to biodegradable tissue regeneration composite membranes. Materials and Methods. Bioactive thermoplastic composites consisting of poly(ε-caprolactone/DL-lactide) and bioactive glass (BAG) were prepared at different stages of biomimetic calcium phosphate deposition by immersion in simulated body fluid (SBF). The modulation of the BAG dissolution and the osteogenic response of rat mesenchymal stem cells (MSCs) were analyzed. Results. SBF treatment resulted in a gradual calcium phosphate deposition on the composites and decreased BAG reactivity in the subsequent cell cultures. Untreated composites and composites covered by thick calcium phosphate layer (14 days in SBF) expedited MSC mineralization in comparison to neat polymers without BAG, whereas other osteogenic markers—alkaline phosphatase activity, bone sialoprotein, and osteocalcin expression—were initially decreased. In contrast, surfaces with only small calcium phosphate aggregates (five days in SBF) had similar early response than neat polymers but still demonstrated enhanced mineralization. Conclusion. A short biomimetic treatment enhances osteoblast response to bioactive composite membranes.

Long-Term Tissue Reactions of Three Biomaterials in Craniofacial Surgery

Successful craniofacial reconstruction needs both a well-known and a reliable reconstruction material. However, there is often a lack of long-term knowledge of the tissue reactions and healing process in the human body. In this study, frontal sinus obliterations with bovine bone natural hydroxyapatite derivative (BHA), synthetic bioactive glass S53P4 (BAG) and hydroxyapatite cement (HAC) were investigated with clinical, histologic, scanning electron microscopic (SEM) and energy dispersive x-ray analysis (EDXA) 27, 12 and 3 years postoperatively. The aim was to determine the long-term clinical biocompatibility of the used materials. Histologic studies revealed bone formation with BHA particles and lamellar bone with BAG granule remnants in close contact to the new bone formation. In HAC reconstruction there was scattered fibroconnective tissue growth without new bone formation in the surface of HAC implantation. Neither foreign body reaction nor any abnormal findings were seen. SEM studies revealed a CaP layer on the surface of BAG granule remnants. In EDXA studies, composition profiles showed Ca-, P- and Si- rich layers on the BAG granule surface. No differences were found in CaO and P2O5 levels between BHA granules and HAC implantation and the surrounding bone. All investigated biomaterials were well tolerated in long-term applications.

Glass Fibre Reinforced Porous Bone Cement Implanted in Rat Tibia or Femur: Histological and Histomorphometric Analysis

Acrylic bone cements are used to fix joint replacements to bone. Typically, these cements are fabricated combining a polymer powder and a monomer liquid component together, of which the monomer phase autopolymerizes within 10 – 15 min after mixing the components. The main substance in powder is poly(methylmethacrylate) or related copolymers, and in liquid, methylmethacrylate monomer or related monomer. Shortcomings of the bone cements include among others the dense polymer structure of cement that does not allow bone ingrowth into cement. In this study, the biological behavior of porous bone cement was investigated in vivo. The porous structure was in situ created using pore-generating filler (20 wt%), i.e. an experimental biodegradable polyamide of naturally occuring trans-4-hydroxy-L-proline, which was incorporated in non-degradable acrylic bone cement. According to the histological evaluation of the modified bone cement, signs of bone ingrowth to the cement were noticed.