In vivo osteocompatibility of lotus-type porous nickel-free stainless steel in rats

The bone response to lotus-type porous nickel-free stainless steels implants was investigated using Sprague-Dawley rats. The implants were inserted in the femora and tibiae of rats (n = 60) and bone formation inside the pores of the implants was followed up to 12 weeks. Bone ingrowth in transverse histological sections was calculated using an image analysis program. Shear strength of the bone–implant interface was evaluated by the push-out test. Histological examination showed that bone grew into apparent direct contact with the implant surface and into the pores, which sizes were between 70–650 μm. At 12 weeks, maximum compressive shear strengths of 24 ± 1 MPa were obtained; these values are substantially higher than the typical shear strength achieved by porous-coated materials. These results clearly indicate that lotus-type porous structure allowed bone cells and tissue to invade the implant throughout superficial porous spaces, which resulted in an efficient biological fixation responsible for the mechanical stability at the implantation site.     

Direct visualization and quantification of bone growth into porous titanium implants using micro computed tomography

The utility of porous metals for the integration of orthopaedic implants with host bone has been well established. Quantification of the tissue response to cementless implants is laborious and time consuming process requiring tissue processing, embedding, sectioning, polishing, imaging and image analysis. Micro-computed tomography (μCT) is a promising three dimensional (3D) imaging technique to quantify the tissue response to porous metals. However, the suitability and effectiveness of μCT for the quantification of bone ingrowth remains unknown. The purpose of this study was to evaluate and compare bone growth within porous titanium implants using both μCT and traditional hard-tissue histology techniques. Cylindrical implants were implanted in the distal femora and proximal tibiae of a rabbit. After 6 weeks, bone ingrowth was quantified and compared by μCT, light microscopy and backscattered electron microscopy. Quantification of bone volume and implant porosity as determined by μCT compared well with data obtained by traditional histology techniques. Analysis of the 3D dataset showed that bone was present in the pores connected with openings larger 9.4 μm. For pore openings greater than 28.2 μm, the size of the interconnection had little impact on the bone density within the porosity for the titanium foams.     

Bone substitute biomedical material of multi-(amino acid) copolymer: in vitro degradation and biocompatibility

Degradable polymers with good mechanical strength as bone repair biomaterials have been paid more attention in biomedical application. In this study, a multi-(amino acid) copolymer consisting of 6-aminocaproic acid and five natural amino acids was prepared by a reaction of acid-catalyzed condensation. The results revealed that the copolymer could be slowly degradable in Tris-HCl solution, and lost its initial weight of 31.9 wt% after immersion for 12 weeks, and the changes of pH value of Tris-HCl solution were in range from 6.9 to 7.4 during soaking. The compressive strength of the copolymer decreased from 107 to 68 MPa after immersion for 12 weeks. The proliferation and differentiation of MG-63 cells on the copolymer significantly increased with time, and the cells with normal phenotype extended and spread well on the copolymer surfaces. When the copolymer was implanted in muscle and bone defects of femoral cortex of dogs for 12 weeks, the histological evaluation confirmed that the copolymer exhibited excellent biocompatibility and more effective osteogenesis in vivo. When implanted into cortical bone defects of dogs, the copolymer could be combined directly with the natural bone without fibrous capsule tissue between implants and host bone. The results indicated that the multi-(amino acid) copolymer with sufficient strength, good biocompatibility and osteoconductivity had clinical potential for load-bearing bone repair or substitution.     

Filling of bone defects with porous hydroxyapatite reinforced with polylactide or polyglycolide fibres

Hydroxyapatite has intrinsically poor mechanical resistance for loading bone replacements and its clinical applications are mainly limited to use as a filling device. In the present study, hydroxyapatite blocks were reinforced with resorbable polyglycolide (PGA) or polylactide (PDLLA) fibres so that most of the implant pores remained open assuming intimate contact with the host bone. The reinforced blocks, 2×3×4 mm in size (Interpore 200), were implanted into the proximal and diaphyseal tibiae of rabbits in order to study the tissue and bone ingrowth into the implants. The samples were studied by histological, histomorphometrical, microradiological, and oxytetracycline fluorescence analyses. The results suggested that PGA or PDLLA fibre reinforcement does not hinder bony ingrowth into the hydroxyapatite implant. Maximal bone ingrowth was observed at 6 weeks but thereafter the amount of ingrowth remained constant up to the end of the 24-week follow-up period. Modest foreign body type reactions around the fibres were histologically seen and there was no difference between the two types fibres in relation to the bone ingrowth. With implants used in this study the bone ingrowth as measured with histomorphometry was 12.9±1.4% in the cancellous implantation and 17.1±1.5% in the cortical implantation. It seems that fibre reinforcement does not hinder bone ingrowth into the coralline hydroxyapatite implants and supports their further development as bone graft substitute in high loading conditions.     

Bone ingrowth behaviour of hydroxyapatite-coated,polyethylene-intruded and uncoated,sandblasted pure titanium implants in an infected implantation site: an experimental study in miniature pigs

We studied the dynamics of bone tissue ingrowth into the pores of hydroxyapatite-coated (plasma-spraying technique) and uncoated wire meshes of pure Ti in an infected implantation site. Samples of the test materials were implanted into the femora of 15 adult Göttingen minipigs. Just before implantation they were contaminated with Staphylococcus aureus. The pigs were killed after 4, 8, 12 or 24 weeks. Undecalcified ground sections of bone tissue were prepared and stained with toluidine blue for comparative histological evaluation. The hydroxyapatite-coated implants already demonstrated advanced new bone formation after 4 weeks. By 12 weeks most of the implant pores were filled with newly formed bone although all samples showed macro- as well as microscopic signs of persistent infection. Comparable reactions of the uncoated implants could be observed only after 24 weeks. Signs of degradation of the hydroxyapatite coating were seen in contact with soft tissue. This was more extensive in the infected than in the uninfected site. The results and possible clinical consequences are discussed.     

Enhanced osteointegration of orthopaedic implant gradient coating composed of bioactive glass and nanohydroxyapatite

We conducted histologic and histomorphometric studies to evaluate the osteointegration of gradient coatings composed of bioactive glass and nanohydroxyapatite (BG–nHA) on titanium-alloy orthopaedic implants and surrounding bone tissue in vivo. Titanium-alloy implants with a gradient coating (gradient coating group), uncoated implants (uncoated group), and implants with a conventional hydroxyapatite (HA) coating (HA coating group) were randomly implanted in bilateral femoral condyles of 36 male New Zealand rabbits. The bone–implant contact at 12 and 24 weeks and the new bone volume in the notch created for observing bone ingrowth at 4, 12, and 24 weeks were found greater in the gradient coating group than those in both the uncoated group and the HA coating group (p < 0.05). Fluorescence micrographs showed active osteogenesis in the gradient coating group at 4 weeks after implantation. These findings indicated that BG–nHA gradient coatings could enhance the osteointegration of orthopaedic implant.     

Long term results after implantation of tissue engineered cartilage for the treatment of osteochondral lesions in a minipig model

In present study we determined the long term in vivo integration and histological modeling of an in vitro engineered cartilage construct. Tissue engineered autologous cartilagenous tissue was cultured on calcium phosphate cylinders and implanted into osteochondral defects into the femoral condyles in minipigs. Radiological follow-up was performed at 2, 8, 26 and 52 weeks, condyles were harvested 26 and 52 weeks post-implantation. Thickness of cultivated tissue (1.10 ± 0.55 mm) was comparable to in situ cartilage and cells produced in vitro cartilage specific proteins. In vivo, 26 and 52 weeks post-implantation defects were resurfaced with hyaline-like tissue, the implants were well integrated with no gap at the interface between the engineered neocartilage and the adjacent articular cartilage. Synthesis of type II collagen was detected 26 and 52 weeks after implantation. The modified ICRS score increased from 26 to 52 weeks. Histomorphometric evaluation revealed a decrease in cellularity in tissue engineered cartilage from 2.2-fold of native cartilage after 26 weeks to 1.5-fold after 52 weeks. In conclusion, these findings demonstrate the integration and maturation of tissue engineered cartilage pellets attached on a bone substitute carrier implanted in osteochondral defects over a long time. J. P. Petersen, P. Ueblacker, C. Goepfert have contributed equally to this study.     

Clinical evaluation of β-TCP in the treatment of lacunar bone defects: A prospective,randomized controlled study

The aim of this study was to investigate the potential wide application of beta tricalcium phosphate (β-TCP) only for bone defects as compared to allograft. 95 patients with a solitary bone cyst were randomly assigned to the treatment. A new radiographic scoring system was employed to calculate the biodegradation of bone graft and to evaluate the influence of multiple factors. At an average of 28.43 months after surgery, a radiographic semi-quantitative analysis revealed that the degradation rates of β-TCP and the allograft were comparable (p > 0.05). Age, complication, packing methods and granule diameters have a significant influence on β-TCP degradation. The loose packing method and 3–5 mm granule size should be employed in clinical practice. A histological analysis of biopsy showed that β-TCP supported the growth of fibrous tissue, vascular tissue, as well as bone tissue into the implants. The results proved that single β-TCP is an advantageous alternative to allografts for lacunar bone defect repair and would well guide the design and clinical application of the β-TCP.     

Effect of surface structure on biomechanical properties and osseointegration

The purpose of this study is to improve the bone-bonding ability between titanium implants and living bone through the control of geometric design and chemical compositions of an implant surface. We compared the tissue healing response and resulting implant stability for three surface designs by characterizing the histological and mechanical properties of the healing tissue around smooth-surfaced Ti–6Al–4V (SS), CP-Ti plasma-spray-coated (PSC), alkali- and heat-treated (AHT) implants. The implants were transversely inserted into a dog thighbone and evaluated at 4, 8, and 12 weeks. Histological examination indicated that initial matrix mineralization leading to osseointegration occurred more rapidly with the AHT implant. During the 4, 8, and 12 week healing periods, new bone on the surface of AHT implant showed denser growth than that on the SS and PSC implants. The more extensive tissue integration and more rapid matrix mineralization with the AHT implant were reflected in the mechanical test data, which demonstrated superior attachment strength and interfacial stiffness for the AHT implant after healing for 4, 8 and 12 weeks of healing because of the mechanical interlocking in the micrometer sized rough surface and the large bonding area between bone and implant caused by the nanosized porous surface structure. Histological and mechanical data demonstrate that with the appropriate surface design selection, bone bone-bonding ability can be improved and can induce acceleration of the healing response, thereby improving the potential for implant osseointegration.     

Tissue response to hafnium

The aim of the present experimental study was to evaluate the tissue response to hafnium (Hf) a reactive metal closely related to titanium (Ti) and zirconium (Zr). Hf has not been previously evaluated as implant material in a biologic environment. In a first experiment, 21 machined Hf non-threaded implants (test) and 21 similar Ti implants (control) were inserted in the abdominal wall of 21 rats. Animals were sacrificed after 8 days (6 rats), 6 (7 rats) and 12 weeks (8 rats). In a second experiment, 18 rabbits received 18 Hf and 18 Ti threaded implants in their tibiae, one implant in each tibia. The rabbits were sacrificed after 6, 12 and 24 weeks (6 animals/time interval). The bulk metal of the abdominal wall implants, embedded together with the surrounding tissue, was electrolytically dissolved and semithin (1 m) sections of the intact tissue–implant interface were evaluated by light microscopy (morphometry). Bone-implant contact and bone area within threads were evaluated in ground sections. In soft tissues, a fluid space containing predominantly monocytes/macrophages surrounded the abdominal implants at 8 days. At 6 and 12 weeks, a fibrous capsule, consisting of layers of macrophages and fibroblasts, surrounded the implants. Macrophages, including multinuclear giant cells, always formed the innermost layer in contact with the implant surface. No quantitative or qualitative difference in the tissue organization was detected between Ti and Hf implants. In rabbits, 6 weeks after insertion, the proximal two threads located within the cortical bone were filled with bone in contact with Hf and Ti. The distal threads contained bone marrow. After 12 and 24 weeks, mature bone was present in the proximal 3–4 implant threads. No statistically significant difference was found between Hf and Ti implants at any time periods. It is concluded that Hf is an interesting metal for biomedical applications in bone and soft tissue. © 2001 Kluwer Academic Publishers     

A new titanium fiber mesh-cuffed peritoneal dialysis catheter: An experimental animal study

CAPD catheters are associated with infectious complications. To solve this problem, we developed a new catheter. In our design, sintered titanium fiber mesh material replaced the Dacron cuffs, as used in standard Tenckhoff catheters. The purpose of the current study was to compare the tissue response to new titanium-cuffed vs. Dacron-cuffed catheters. Experimental and standard Tenckhoff catheters were inserted intraperiotoneally in 12 goats, using a so-called two-stage surgical technique. In the first surgical session, the catheters were implanted. However, the percutaneous part of the catheter was buried subcutaneous. After 3-5 weeks, the percutaneous part of the catheter was exteriorized. After 14 weeks of implantation, all implants with surrounding tissue were retrieved and prepared for histological evaluation. Subsequently, we quantified: the characteristics of the fibrous tissue capsule surrounding the cuffs, the tissue inside the cuff porosity, and the epidermal downgrowth. Histologic and histomorphometric evaluation showed that titanium mesh evoked a lesser inflammatory response inside the cuff porosity compared with Dacron cuffs. Besides, the fibrous tissue capsule surrounding the titanium cuffs was significantly thinner. Supported by the obtained results, we conclude that the use of titanium fiber mesh has a great potential for application in percutaneous devices.     

Biomechanical assessment of bone ingrowth in porous hydroxyapatite

Porous hydroxyapatite (Endobon®) specimens were implanted into the femoral condyle of New Zealand White rabbits for up to 6 months. After sacrifice, specimens were sectioned for histology and mechanical testing, where the extent of reinforcement by bony ingrowth was assessed by compression testing and fixation was assessed by push-out testing. From histological observations, it was established that the majority of bone ingrowth occurred between 10 day and 5 weeks after implantation and proceeded predominantly from the deep end of the trephined defect, with some integration from the circumferential sides. At 3 months, the implants were fully integrated, exhibiting bony ingrowth, vascularization and bone marrow stroma within the internal macropores. After 5 weeks, the mean ultimate compressive strength of retrieved implants (6.9 MPa) was found to be greater than that of the original implant (2.2 MPa), and by 3 months the fully integrated implants attained a compressive strength of approximately 20 MPa. Push-out testing demonstrated that after 5 weeks in vivo, the interfacial shear strength reached 3.2 MPa, increasing to 7.3 MPa at 3 and 6 months.     

Tissue reaction against a self-setting calcium phosphate cement set in bone or outside the organism

Calcium phosphate cements are able to set in situ when injected into bone tissue. We evaluated the tissue reaction occurring when a DCPD-based calcium phosphate cement was either set within the bone or implanted when already set. The samples were implanted in rabbit condyles and examined histologically after 8 and 16 weeks. The relative bone surface, the fibrous capsule around the implants and the implant section surface were measured. Solid material seemed to be better tolerated than paste implants. More bone was found at the solid implant contact whatever the implantation time and the solid material degraded much less rapidly. In conclusion, the physico-chemical modification of the biological environment occurring during setting increases the foreign body reaction against the material.     

Nanoscale characterization of bone–implant interface and biomechanical modulation of bone ingrowth

Bone–implant interface is characterized by an array of cells and macromolecules. This study investigated the nanomechancial properties of bone–implant interface using atomic force microscopy in vitro, and the mechanical modulation of implant bone ingrowth in vivo using bone histomorphometry. Upon harvest of screw-type titanium implants placed in vivo in the rabbit maxilla and proximal femur for 4 weeks, nanoindentation was performed in the bone–implant interface at 60-μm intervals radially from the implant surface. The average Young's Moduli (E) of the maxillary bone–implant interface was 1.13 ± 0.27 MPa, lacking significant differences at all intervals. In contrast, an increasing gradient of E was observed radially from the femur bone–implant interface: 0.87 ± 0.25 MPa to 2.24 ± 0.69 MPa, representing significant differences among several 60-μm intervals. In a separate experiment, bone healing was allowed for 6 weeks for proximal femur implants. The right femoral implant received axial cyclic loading at 200 mN and 1 Hz for 10 min/d over 12 days, whereas the left femoral implant served as control. Cyclic loading induced significantly higher bone volume, osteoblast numbers per endocortical bone surface, mineral apposition rate, and bone formation rate than controls. These data demonstrate nanoscale and microscale characterizations of bone–implant interface, and mechanical modulation of bone ingrowth surrounding titanium implants.     

Effect of porous NiTi alloy on bone formation: A comparative investigation with bulk NiTi alloy for 15 weeks in vivo

The purpose of this study is to investigate the effect of porous NiTi alloy on bone formation with a bulk NiTi alloy as a contrast. The porous NiTi alloy prepared by element powder sintering under Ar protection has a porosity of 45% and a mean pore size of 130 μm, and the pores are highly interconnected. The porous and bulk NiTi alloys were bilaterally implanted into the femurs of rabbits for 15 weeks. The bone-implant interface and bone ingrowth were evaluated by undecalcified histological examination under light and fluorescent microscope as well as environmental scanning electron microscope (ESEM). The results show: osteoblasts are very active with fast proliferation and no adverse tissue reaction occurs for the porous NiTi alloy after 15 weeks implantation; porous NiTi alloy has better osteoconductivity and osteointegration than the bulk one; the osteoblasts can ingrow the pores of porous NiTi implant, and direct bone-implant interface can be observed by fluorescent light microscope.     

Mechanical and histological evaluations of cobalt-chromium alloy and hydroxyapatite plasma-sprayed coatings in bone

This study evaluated the mechanical and histological behavior of cobalt-chromium (CoCr) alloy and hydroxyapatite (HA) plasma-sprayed coatings in canine cortical bone after 6 and 12 weeks of implantation, using CoCr alloy as the substrate. the substrate was bond-coated with microtextured CoCr alloy coating to ensure adherence between the substrate and top coats. A macrotextured CoCr alloy top coat with surface roughness R _a=34.25±5.50 m was produced to create suitable pores ranging from 25 m to 200 m for bone ingrowth. For HA top coat, a relatively smooth surface (R _a=15.14±3.21 m) was prepared for bone apposition. Shear testing of bone/implant interfaces showed that the CoCr alloy top coat exhibited significantly lower (p<0.01) mean shear strength than the HA top coat at each time interval. The maximum shear strength was 10.88±0.38 MPa for HA-coated implants 12 weeks post-implantation. After histological evaluations, substantial differences in the extent of new bone formation and the types of implant/bone contact were found between two kinds of implants. Direct bone-to-HA coating contact was consistently observed, while a layer of fibrous tissue intervening at the bone-CoCr alloy coating interface was found. Occasionally, partial dissolution of HA coating was seen after 12 weeks of implantation. The results of this study suggested that plasma-sprayed macrotextured CoCr coatings may not be an effective alternative for biological fixation.     

The effect of bone ingrowth depth on the tensile and shear strength of the implant–bone e-beam produced interface

New technologies, such as selective electron beam melting, allow to create complex interface structures to enhance bone ingrowth in cementless implants. The efficacy of such structures can be tested in animal experiments. Although animal studies provide insight into the biological response of new structures, it remains unclear how ingrowth depth is related to interface strength. Theoretically, there could be a threshold of ingrowth, above which the interface strength does not further increase. To test the relationship between depth and strength we performed a finite element study on micro models with simulated uncoated and hydroxyapatite (HA) coated surfaces. We examined whether complete ingrowth is necessary to obtain a maximal interface strength. An increase in bone ingrowth depth did not always enhance the bone–implant interface strength. For the uncoated specimens a plateau was reached at 1,500 μm of ingrowth depth. For the specimens with a simulated HA coating, a bone ingrowth depth of 500 μm already yielded a substantial interface strength, and deeper ingrowth did not enhance the interface strength considerably. These findings may assist in optimizing interface morphology (its depth) and in judging the effect of bone ingrowth depth on interface strength.     

Evaluation of bone response to titanium-coated polymethyl methacrylate resin (PMMA) implants by X-ray tomography

High-resolution three-dimensional data about the bone response to oral implants can be obtained by using microfocus computer tomography. However, a disadvantage is that metallic implants cause streaking artifacts due to scattering of X-rays, which prevents an accurate evaluation of the interfacial bone-to-implant contact. It has been suggested that the use of thin titanium coatings deposited on polymeric implants can offer an alternative option for analyzing bone contact using micro-CT imaging. Consequently, the aim of the current study was to investigate bone behavior to titanium-coated polymethylmethacrylate (PMMA) implants by micro-CT and histological evaluation. For the experiment titanium-coated PMMA implants were used. The implants had a machined threaded appearance and were provided with a 400–500 nm thick titanium coating. The implants were inserted in the right or left tibia of 10 goats. After an implantation period of 12 weeks the implants were retrieved and prepared for micro-computer tomography (μCT), light microscopy, and X-ray microanalysis. The micro-CT showed that the screw-threads and typical implant configuration were well maintained through the installation procedure. Overall, histological responses showed that the titanium-coated implants were well tolerated and caused no atypical tissue response. In addition, the bone was seen in direct contact with the titanium-coated layer. The X-ray microanalysis results confirmed the light microscopical data. In conclusion, the obtained results proof the final use of titanium-coated PMMA implants for evaluation of the bone-implant response using μCT. However, this study also confirms that for a proper analysis of the bone-implant interface the additional use of microscopical techniques is still required.     

Response to polyetherimide based composite materials implanted in muscle and in bone

The in-vivo response to a composite material obtained with polyetherimide (PEI) reinforced with carbon/glass fibers was investigated by histological methods by implanting cylinders in muscle and in bone of the New Zealand White rabbit. A common metallic alloy, widely used in orthopaedic surgery, was used as control (Stellite). The aim of the study was to analyze the biological response towards the surface of the material. Composite implants and metallic implants did not induce adverse or inflammatory reactions. The morphological picture produced was similar, in muscle and in bone, for both materials. In muscle, cylinders were confined by an extremely thin fibrous layer and the overall appearance of the muscular tissue was normal. In bone, cylinders were confined by a nearly annular rim of newly formed bone. From these data it is possible to derive that the response to PEI-based composite material is comparable with the response to metallic substrate and, then, the material can be suitable for clinical application. ©1999 Kluwer Academic Publishers     

Does sodium fluoride in bone cement affect implant fixation Part II: Evaluation of the effect of sodium fluoride additions to acrylic bone cement and the fixation of titanium implants in ovariectomized rabbits

Bone integration of threaded implants made of cured polymethylmethacrylate containing sodium fluoride or commercially pure (c.p.) titanium were studied in normal and estrogen deficient New Zealand white rabbits. Nine had been ovariectomized through laparoscopy and nine served as controls. Four weeks after the ovariectomy two threaded implants made of cured bone cement with or without sodium fluoride addition were inserted in each tibia. One threaded commercially pure titanium implant was inserted in each patello–femoral joint flush to the cartilage. Six weeks after implant insertion measurement of the peak removal torque necessary to loosen the implants and light microscopical histomorphometrical investigations of tissue integration were performed. In the ovariectomized rabbits addition of sodium fluoride to the cement resulted in increased area of bone in the threads (p=0.04), but no corresponding effect could be noted in the controls. The removal torque was lower in the ovariectomized rabbits compared to the non-ovariectomized when comparing implant with sodium fluoride addition (p=0.02). The bone tissue response and the removal torque of the titanium implants were not influenced by ovariectomy in these rabbits. ©2002 Kluwer Academic Publisher