Osteointegration of biomimetic apatite coating applied onto dense and porous metal implants in femurs of goats.

Biomimetic calcium phosphate (Ca-P) coatings were applied onto dense titanium alloy (Ti6Al4V) and porous tantalum (Ta) cylinders by immersion into simulated body fluid at 37 degrees C and then at 50 degrees C for 24 h. As a result, a homogeneous bone-like carbonated apatitic (BCA) coating, 30 microm thick was deposited on the entire surface of the dense and porous implants. Noncoated and BCA-coated implants were press-fit implanted in the femoral diaphysis of 14 adult female goats. Bone contact was measured after implantation for 6, 12, and 24 weeks, and investigated by histology and backscattered electron microscopy (BSEM). After 6 weeks, bone contact of the BCA-coated Ti6Al4V implants was about 50%. After 12 and 24 weeks, bone contact was lower in comparison with the 6-week implantations at, respectively 24 and 39%. Regarding the BCA-coated porous Ta implants, bone contacts were 17, 30, and 18% after 6, 12, and 24 weeks, respectively. However, bone contact was always found significantly higher for BCA-coated dense Ti6Al4V and porous Ta cylinders than the corresponding noncoated implants. The results of this study show that the BCA coating enhances the bone integration as compared to the noncoated implants.

In vitro and in vivo degradation of biomimetic octacalcium phosphate and carbonate apatite coatings on titanium implants.

Calcium phosphate (Ca-P) coatings have been applied onto titanium alloys prosthesis to combine the srength of metals with the bioactivity of Ca-P. It has been clearly shown in many publications that Ca-P coating accelerates bone formation around the implant. However, longevity of the Ca-P coating for an optimal bone apposition onto the prosthesis remains controversial. Biomimetic bone-like carbonate apatite (BCA) and Octacalcium Phosphate (OCP) coatings were deposited on Ti6Al4V samples to evaluate their in vitro and in vivo dissolution properties. The coated plates were soaked in alpha-MEM for 1, 2, and 4 weeks, and they were analyzed by Back Scattering Electron Microscopy (BSEM) and by Fourier Transform Infra Red spectroscopy (FTIR). Identical coated plates were implanted subcutaneously in Wistar rats for similar periods. BSEM, FTIR, and histomorphometry were performed on the explants. In vitro and in vivo, a carbonate apatite (CA) formed onto OCP and BCA coatings via a dissolution-precipitation process. In vitro, both coatings dissolved overtime, whereas in vivo BCA calcified and OCP partially dissolved after 1 week. Thereafter, OCP remained stable. This different in vivo behavior can be attributed to (1) different organic compounds that might prevent or enhance Ca-P dissolution, (2) a greater reactivity of OCP due to its large open structure, or (3) different thermodynamic stability between OCP and BCA phases. These structural and compositional differences promote either the progressive loss or calcification of the Ca-P coating and might lead to different osseointegration of coated implants.

Critical size defect in the goat's os ilium. A model to evaluate bone grafts and substitutes.

Bone defects and their treatment are a well known problem in orthopaedic surgery. A critical size defect is a suitable model to study bone replacement materials. This study describes a critical size defect in the goal and the evaluation of three bone fillers (particulate autograft, particulate allograft, and a polyethylene oxide/polybutylene terephthalate copolymer) in this defect. The goat allows for implantation of large implants and has a metabolic rate more comparable with that of humans than small animals. The critical size defect, located in the goat's iliac wing, is easily reproducible and allows qualitative and quantitative evaluation of bone grafts and bone graft substitutes. After 3 months of healing, the unfilled defects showed 13.5% bone in the defect, the autografted defects 36.3%, and the allografted 18.5%. The copolymer gave only 1.5% bone in the defect; this is in contrast to previous reports. The described model allows for the evaluation of bone graft substitutes before introduction into clinical practice.

A comparative study of flexible (Polyactive) versus rigid (hydroxylapatite) permucosal dental implants. II. Histological aspects.

Of the many materials that are applied in dental implantology, most have a high Young's modulus. In the concept of osseointegration, which is generally preferred, chewing forces are therefore directly transmitted from rigid implant materials to the relatively flexible surrounding bone. Polyactive is an elastomeric polyethylene-oxide polybutylene-terephthalate (PEO:PBT) copolymer, with a low modulus of elasticity, that exhibits bone-bonding characteristics. Previous finite-element analysis emphasized the benefit of the application of flexible implant materials. To assess the validity of this finite element model, one dense and two porous types of flexible Polyactive permucosal dental implants and one rigid hydroxylapatite (HA) implant were clinically tested in a beagle dog study and were compared during 30 weeks of loading. In an earlier report, it was concluded that dense Polyactive implants function clinically adequately and resemble the mobility of natural teeth. In the current study, the amount of bone contact was quantitatively assessed. Polyactive implants showed a statistically significantly higher bone contact, as compared to the HA implants, probably due to a significant water uptake and a subsequent increase in the volume of the denser Polyactive. Morphological analysis, based on back-scatter electron microscopy and light microscopy, revealed little remodelling activity of the bone surrounding the Polyactive implants. Few remodelling lacunae were seen and de novo bone formation was rarely observed. At some locations, a continuity between calcification zones with the polymer surface and the surrounding interfacial bone was observed, indicating the occurrence of bone-bonding. Also, the bone surrounding the HA implants showed little remodelling activity, although large resorption lacunae were observed, in which HA particles were present. Based on the observations of this study, flexible bone bonding implants might be more capable of transferring stresses to the surrounding bone and are therefore promising alternatives to "routine' rigid implants.

Long-term analysis of peritoneal plasminogen activator activity and adhesion formation after surgical trauma in the rat model.

OBJECTIVE: Recent literature has shown that a common pathway in postsurgical adhesion formation is a transient reduction in local plasminogen activator activity, shortly after peritoneal trauma. This deficit in fibrinolysis permits deposited fibrin to become organized into fibrous, permanent adhesions. Although adhesion formation is a process that continues beyond the first postoperative days, long-term analysis of this theory has not been performed. DESIGN: A standardized peritoneal adhesion model in the rat. MAIN OUTCOME MEASURE(S): Long-term analysis of the peritoneal fibrinolytic activity (extraction technique) was related to the extent of postsurgical adhesion formation, up to 1 year postoperatively. RESULT(S): Total and tissue plasminogen activator activity were significantly increased at days 3 and 8, and 1 month postoperatively. A mean adhesion percentage of 75% per peritoneal defect was found to persist throughout all evaluation times, which was directly related to the increase of fibrinolysis. CONCLUSION(S): In contrast to the classical concept that adhesion formation is related to a reduction in fibrinolysis, an impressive increase of the fibrinolysis was found to be associated with the persistence of adhesions.

Polyactive as a bone-filler in a beagle dog model.

Calcification is a crucial step in the bone-bonding mechanism of PEO/PBT hydrogel copolymers (Polyactive, a new generation of bone-fillers. A beagle dog study was conducted to determine whether the preoperative presence of a calcium phosphate layer (precalcification) on a PEO/PBT 80/20 copolymer would further increase the bone-bonding rate. Standard bone cavities were filled with either precalcified or nonprecalcified porous cylindric PEO/PBT 80/20 implants, or hydroxyapatite granules held together with PEO/PBT 70/30, or were left unfilled. A significantly higher percentage of mineralized component was present in the cavities filled with the precalcified PEO/PBT 80/20 copolymer than in the control defects. As a result of swelling by fluid-uptake, the press-fit inserted copolymer implants showed a significant reduction in pore size, thus preventing optimal bone ingrowth. Both precalcification of the copolymer and underfilling of the defect, to create space for the copolymer to increase in diameter, stimulate postoperative calcification and bone ingrowth in PEO/PBT 80/20 copolymers.

Quantitative analysis of the inflammatory reaction surrounding sutures commonly used in operative procedures and the relation to postsurgical adhesion formation.

Inflammatory reaction as well as the extent of postsurgical adhesion formation are described as varying according to suture material or diameter used. Whether the inflammatory reaction influences the formation of adhesions or is a mere consequence of surgical trauma itself or of type and amount of foreign body material used has never been elucidated entirely. In this study a quantitative analysis of both variables was therefore performed, according to previously described techniques, and correlated within 120 peritoneal defects of a standard side wall-uterine horn adhesion model in the rat. Three different suture characteristics, material (Prolene, Vicryl, Catgut), diameter (USP gauges 3/0, 5/0, 6/0) and knot configuration (2 = 2, S x S x S x S x S) were analysed for this purpose. Both the inflammatory reaction and the adhesion percentage showed significant differences within and in between suture characteristics, but no significant correlation between the two variables was found after statistical analysis. The conclusion is made that, when evaluated after 14 d, the extent of postsurgical adhesion formation is not related to the inflammatory reaction.

Observations of the bone activity adjacent to unloaded dental implants coated with Polyactive or HA.

In addition to bone-bonding biomaterials such as calcium phosphate ceramics and Bioglass/glass ceramics, an elastomeric poly(ethylene oxide) poly(butylene terephthalate) (PEO/PBT) segmented block co-polymer (Polyactive) was recently introduced. In contrast to ceramic biomaterials, Polyactive is a flexible material. In a previous three-dimensional finite element analysis study, it was stated that application of a flexible Polyactive coating simulates the function of the periodontal ligament. The topic of this investigation was to compare the bone-bonding capacity of Polyactive-coated titanium implants with hydroxylapatite (HA) coated implants. The implants were inserted bilaterally in the edentulous part of the mandibular bone of 12 goats. After 3 weeks, the implants were in close contact with the cortical bone, but no cortical bone reaction or remodelling was observed. After 9 weeks, an extensive bone reaction was seen around the HA and Polyactive-coated implants and contact was frequently encountered between newly formed bone and the implants. Within the surface of the Polyactive coating, a considerable amount of calcification was present. After 25 weeks, cortical remodelling was still apparent. A striking finding was the apparent association between osteon formation and calcification within the surface of the Polyactive layer. Back-scatter analysis of the non-decalcified Polyactive bone interface showed the presence of a calcium phosphate layer in the implant material that apparently formed a continuity with the mineral matrix of bone, suggesting bone-bonding. In general, it was observed that the bone reactions to HA and Polyactive were comparable. A swelling of the coating, just beneath the cortical layer (champagne-cork effect) was often seen.(ABSTRACT TRUNCATED AT 250 WORDS)

A semiquantitative rat model for intraperitoneal postoperative adhesion formation.

A reproducible and semiquantitative rat model for the evaluation of therapeutic modalities used for the prevention of postoperative adhesion formation is designed within three experiments. In all experiments, a standard peritoneal defect was excised, sutured and adhesion formation was evaluated after 2 weeks according to the extent. Variation in extent of adhesions and type of tissue involved depended on the experimental design. While neither cecum nor colon descendens participated in the adhesions after a clamping trauma, the uterine horn was found to participate in almost all cases, especially when sutured proximally and distally to the peritoneal defect. The peritoneal defect/uterine horn model proved to be valid and reproducible and allowed a semiquantitative scoring. Additionally, the amount of blood loss as graded did not influence the presented rat adhesion model.