Improved methods for acrylic-free implants in nonhuman primates for neuroscience research.

Traditionally, head fixation devices and recording cylinders have been implanted in nonhuman primates (NHP) using dental acrylic despite several shortcomings associated with acrylic. The use of more biocompatible materials such as titanium and PEEK is becoming more prevalent in NHP research. We describe a cost-effective set of procedures that maximizes the integration of headposts and recording cylinders with the animal's tissues while reducing surgery time. Nine rhesus monkeys were implanted with titanium headposts, and one of these was also implanted with a recording chamber. In each case, a three-dimensional printed replica of the skull was created based on computerized tomography scans. The titanium feet of the headposts were shaped, and the skull thickness was measured preoperatively, reducing surgery time by up to 70%. The recording cylinder was manufactured to conform tightly to the skull, which was fastened to the skull with four screws and remained watertight for 8.5 mo. We quantified the amount of regression of the skin edge at the headpost. We found a large degree of variability in the timing and extent of skin regression that could not be explained by any single recorded factor. However, there was not a single case of bone exposure; although skin retracted from the titanium, skin also remained adhered to the skull adjacent to those regions. The headposts remained fully functional and free of complications for the experimental life of each animal, several of which are still participating in experiments more than 4 yr after implant.NEW & NOTEWORTHY Cranial implants are often necessary for performing neurophysiology research with nonhuman primates. We present methods for using three-dimensional printed monkey skulls to form and fabricate acrylic-free implants preoperatively to decrease surgery times and the risk of complications and increase the functional life of the implant. We focused on reducing costs, creating a feasible timeline, and ensuring compatibility with existing laboratory systems. We discuss the importance of using more biocompatible materials and enhancing osseointegration.

[The experimental assessment of high-density ultrahigh molecular weight polyethylene for the prosthetic treatment of auditory ossicles].

The objective of the present study was the comparative assessment of the influence of titanium and high-density ultrahigh molecular weight polyethylene (HDMPE) on the selected biochemical and immunological properties of blood and morphological features of the middle ear tissues in experimental animals. A total of 35 rabbits used were allocated to 3 groups. Groups 1 and 2 included 15 animals each. They were involved in three series of experiments (5 animals per series lasting 15, 60, and 90 days). Group 3 was comprised of 5 animals. Prosthetic treatment of auditory ossicles was performed using implants from modified high-density ultrahigh molecular weight polyethylene (group 1) and titanium implants (group 2). Control animals (group 3) remained intact. There were no significant difference between total bilirubin, AsAT, glucose, creatinine, and total protein levels in blood plasma at different time-points after surgery. HDMPE turned out to have no appreciable effect on immunological characteristics and morphological features of the soft tissues lining tympanic bulla. It is concluded that HDMPE may serve as a material for the fabrication of prostheses of the auditory ossicle chain.

Histological assessment of titanium and polypropylene fiber mesh implantation with and without fibrin tissue glue.

Polypropylene (PP) and titanium (Ti) meshes are well-known surgical implants that provoke a relative low foreign body reaction. Firm stabilization of the implant is important to prevent migration and subsequent failure of the operation. Fibrin tissue glues are commercially available adhesives and are widely accepted and applied in the medical field for hemorrhage, surgical bleeding, support of wound healing, wound and tissue gluing, sealing, and closure but also as antiadhesive agent in certain applications. The objective of this study was to evaluate the additional histological effect of fibrin glue application combined with two different types of meshes. Six pieces of mesh of each were subcutaneously implanted for 3, 6, and 12 weeks, with and without fibrin glue. After excision, processing, and staining, light microscopic analysis was performed on the sections, using subjective histological description and histomorphometry. Capsule quality, capsule thickness, interstitial quality, and total score were evaluated. To compare the samples with glue and without glue, analysis of variance (ANOVA) tests were carried out. No complications were observed. In general, the glue remnants remained visible at 3 and 6 weeks of implantation, accompanied by an inflammatory reaction and macrophage activity. At 12 weeks, all samples showed good tissue integration without evidence of glue. Evidently, the samples with glue demonstrated a prolonged inflammatory response and were surrounded by fibrous tissue capsules that were significantly thicker compared with the samples without glue (p < 0.05).

Intra-thoracic fibrous tissue induction by polylactic acid and epsilon-caprolactone copolymer cubes, with or without slow release of basic fibroblast growth factor.

OBJECTIVE: We investigated whether implantation of polylactic acid and epsilon-caprolactone copolymer (PLAC) cubes with or without basic fibroblast growth factor (b-FGF) released slowly from gelatin microspheres was able to induce fibrous tissue in the dead space remaining after pneumonectomy in the thoracic cavity. METHODS: Left pneumonectomy was performed in Japanese white rabbits. In the control group (n=6), the left thoracic cavity was closed without any treatment. In the FGF group (n=6), gelatin microspheres that released 100 microg of b-FGF were implanted into the left thoracic cavity. In the PLAC group (n=6), PLAC cubes were implanted into the left thoracic cavity. In the PLAC/FGF group (n=6), both PLAC cubes and gelatin microspheres releasing 100 microg of b-FGF were implanted into the left thoracic cavity. RESULTS: In the control and FGF groups, herniation of the heart, mediastinal shift, and overinflation of the right lung were observed. No granular tissue formation was observed. In the PLAC and PLAC/FGF groups, a dense area of newly formed soft tissue was observed, and only a mild mediastinal shift was observed during the 3-month follow-up period. Pathological examination revealed induction of fibrous and granular tissue in the left thoracic cavity. The foreign-body reaction induced by PLAC was very mild. CONCLUSIONS: Implantation of PLAC cubes with or without gelatin microspheres releasing 100 microg of b-FGF is able to induce fibrous tissue in the post-pneumonectomy dead space.

How to image cell adhesion on soft polymers?

Here, we present a method to investigate cell adhesion on soft, non-conducting polymers that are implant candidate materials. Neuronal cells were grown on two elastomers (polydimethylsiloxane (PDMS) and Ecoflex®) and prepared for electron microscopy. The samples were treated with osmium tetroxide (OsO4) and uranylacetate (UrAc). Best results can be achieved when the polymers were coated with a thin iridium layer before the cell culture. This was done to emphasize the usage of soft polymers as supports for implant electrodes. A good contrast and the adhesion of the cells on soft polymers could be visualized.

In vivo biocompatibility of bacterial cellulose.

The biocompatibility of a scaffold for tissue engineered constructs is essential for the outcome. Bacterial cellulose (BC) consists of completely pure cellulose nanofibrils synthesized by Acetobacter xylinum. BC has high mechanical strength and can be shaped into three-dimensional structures. Cellulose-based materials induce negligible foreign body and inflammatory responses and are considered as biocompatible. The in vivo biocompatibility of BC has never been evaluated systematically. Thus, in the development of tissue engineered constructs with a BC scaffold, it is necessary to evaluate the in vivo biocompatibility. BC was implanted subcutaneously in rats for 1, 4, and 12 weeks. The implants were evaluated in aspects of chronic inflammation, foreign body responses, cell ingrowth, and angiogenesis, using histology, immunohistochemistry, and electron microscopy. There were no macroscopic signs of inflammation around the implants. There were no microscopic signs of inflammation either (i.e., a high number of small cells around the implants or the blood vessels). No fibrotic capsule or giant cells were present. Fibroblasts infiltrated BC, which was well integrated into the host tissue, and did not elicit any chronic inflammatory reactions. The biocompatibility of BC is good and the material has potential to be used as a scaffold in tissue engineering.

Collagen deposition around polypropylene tapes implanted in the rectus fascia of female rats.

OBJECTIVE: Implantation of the mesh induces a foreign-body reaction followed by the development of connective tissue that may alter tape property. The aim of our study was to evaluate the deposition of collagen in the vicinity of monofilament tension-free vaginal tape (TVT; Ethicon Inc., Johnson & Johnson) and multifilament intravaginal slingplasty (IVS; Tyco Healthcare) polypropylene tapes implanted in female rats. METHODS: The samples of the meshes (10 mg each) were implanted in the rectus fascia of 14 Wistar female rats and removed after 42 days. Collagen was extracted with 0.5 M acetic acid and subsequently with pepsin (1 mg/ml in 0.5 M acetic acid). Collagen concentration was measured using Sircol Collagen Assay (Biocolor Ltd.) and normalised for milligrams of tape weight. For histological examination, tape samples were stained with haematoxylin and eosin or with silver for type III collagen. RESULTS: The total amount of collagen extracted did not differ significantly between TVT and IVS samples. For both tapes, extraction with acetic acid yielded a higher amount of collagen (about 70%) than extraction with pepsin. On histological examination, less densely packed bundles of collagen fibres and a slightly more intense inflammatory reaction were observed with TVT compared with IVS mesh. CONCLUSION: The total amount of collagen deposited around the polypropylene mesh implanted in female rats was similar for TVT and IVS meshes, but differences were noted in the arrangement of the collagen fibres and the intensity of the inflammatory reaction.

Finite element modeling of multi-level cervical spinal segments (C3-C6) and biomechanical analysis of an elastomer-type prosthetic disc.

A three-dimensional finite element (FE) model for the multi-level lower cervical spinal segment C3-C6 has been developed using computed tomography (CT) data, and applied to study of the effects of the fusion and the artificial disc prosthesis on the biomechanical behavior of the lower cervical spine. The NURBS computer adided dedsig (CAD) data used in this study for modeling the vertebrae facilitate adding surface patch layouts for seamless attachment of the soft tissues, such as intervertebral discs onto the vertebrae. A FE model was completed by generating mesh out of this geometry. Its accuracy was validated by comparing with previously published experimental and numerical results for the flexion-extension, axial rotation, and lateral bending moments. An implantation of an elastomer-type disc prosthesis or fused graft between C4-C5 vertebrae was considered in the FE model by modifying the intact disc. It is shown that the fusion reduced the mobility at its level by about 50-70% for the considered loading cases. It is numerically demonstrated that an elastomer with Young's modulus of 5.9 MPa for the artificial disc prosthesis well restores the biomechanical behavior of the intact spine.

Zirconia to Ti-6Al-4V braze joint for implantable biomedical device.

A strong, hermetic, reliable, and biocompatible ceramic-to-metal seal is essential for many implantable medical devices. Yttria-stabilized tetragonal zirconia polycrystals (Y-TZPs) and a titanium alloy Ti-6Al-4V were selected as the ceramic and metal components of the seal because both materials have excellent mechanical properties and favorable biocompatibility. A brazing method using titanium nickel (TiNi)-clad braze filler material is presented to bond the components together forming a seal. Laboratory tests show that the ceramic-to-metal seal is hermetic, strong, and resistant to electrochemical corrosion. Twenty-eight microstimulators utilizing the ceramic-to-metal seals were implanted in seven sheep to stimulate the hypoglossal nerve. When the tissue was evaluated by gross inspection at necropsy and examined histologically by a pathologist, there were no signs of local hemorrhage, infection, or hypoglossal nerve tissue damage.

In vitro and in vivo biocompatibility evaluation of a polyalkylimide hydrogel for soft tissue augmentation.

Injectable fillers are commonly used in Plastic and Reconstructive Surgery to correct serious and slight aesthetic defects due to their low invasiveness and an easy implant technique procedure. Synthetic hydrogels are proposed as filler materials for their similarity with soft tissue and to avoid many disadvantages of naturally derived materials such as short persistence, allergenicity, and immunogenicity. Our studies are focused on the biocompatibility evaluation of a polyacrylic hydrogel containing alkylimide-amide groups and pyrogen free water (96%) (Bio-Alcamid by means of the in vitro cytotoxicity and mutagenicity assays and the in vivo skin irritation, sensitization test, and subcutaneous implant. All tests conducted on Bio-Alcamid showed no toxicity. It is a substance easy to inject and remove; it does not migrate, and its safety allows it to be a suitable filler for the correction of slight and also very serious aesthetic defects.

Histological studies of monofilament and multifilament polypropylene mesh implants demonstrate equivalent penetration of macrophages between fibrils.

The tissue reaction to implanted monofilamentous and multifilamentous polypropylene mesh was compared in samples removed at operation from the perivaginal area of a 58 year old patient. The fibrils of both were surrounded by collagenous connective tissue, collagen types I and III, and proteoglycans. Smaller, less compacted bundles were seen in the vicinity of the monofilamentous mesh than around the multifilamentous mesh, and in addition, a greater number of inflammatory cells and larger multinucleate giant cells were seen apposed to the monofilamentous mesh. Following this, eight rats were implanted with multifilamentous synthetic polypropylene tape and examined at two, four, six and eight weeks after surgery. Macrophages and multinucleated giant cells were seen in the immediate vicinity of the fibrils, while fibrovascular connective tissue surrounded the implantation site. These observations do not support the prevailing hypotheses that macrophages cannot penetrate between the fibrils of multifilament tape. They do suggest that differences in tensile strength may be present in the artificial neoligaments created by the two tapes.

Effects of the polypropylene mesh implanted through inguinotomy in the spermatic funiculus, epididium and testis of dogs.

PURPOSE: To investigate the effects of polypropylene mesh, implanted by inguinotomy, in the spermatic funiculus, epididium and testis of dogs. METHODS: Eighteen dogs were considered (12-23 Kg), separated in three groups. Group A (n=7): left side (with mesh) versus right side (without mesh); Group B (n=7): left side (without mesh) versus right side (with mesh) and Group C (n=4): without any surgical manipulation (control group). After being observed for 60 days, the animals were subjected to bilateral removal of the spermatic funiculus, epididium and testis that were submitted to histological analysis. During the re-operation, a macroscopic evaluation was performed. RESULTS: On the mesh side, we noted 100% of mesh adherence to the posterior wall of the inguinal canal, as well as the adherence of the spermatic funiculus to the mesh. A congestion of the pampiniform plexus was noted in three animals. Chronic inflammation reaction and foreign body reaction in the spermatic funiculus was observed in 100% of the animals. On the side that did not carry a mesh, chronic inflammatory reaction was observed in 71% of the animals. All the animals presented chronic inflammatory reaction in the deferent duct in the mesh side and in eleven animals in the side without the mesh. These alterations were not found in Group C. There was a considerable statistical reduction in the average difference of the diameter of the lumen of the deferent duct in the mesh side. In the epididium and testis, macro and microscopic alterations were not significant, although one animal presented a marked reduction of spermatogenesis on the mesh side. CONCLUSION: The polypropylene mesh, when in contact with the spermatic funiculus of dogs, causes a more intense chronic inflammatory reaction and a significant reduction in the diameter of the lumen of the deferent duct.

Functional evaluation of an artificial anal sphincter using shape memory alloys.

This article describes an implantable artificial anal sphincter using shape memory alloys and its in vivo assessment in porcine models. The new design was developed as a low invasive prosthesis with a simple structure to solve the problem of severe fecal incontinence in patients with hypoplastic sphincters or without anal sphincters and especially for ostomates. The artificial anal sphincter consists of two shape memory alloy (SMA) plates as the main functional parts to perform two basic functions when the SMA artificial sphincter is fitted around intestines (i.e., an occlusion at body temperature and an opening function on heating). Our previous assessments with short-term animal experiments revealed promising properties with the occlusion function of the device, although some complications, such as overpressure induced ischemia, heat burn, and infections, remained. This article addresses the concerns related to the practical use of the device, the power supplement to drive the actuator, and overheating protection of the device inside bodies. Results of chronic animal experiments of up to 4 weeks suggested great potential for the improved device.

Preliminary study of a genetically engineered spinal cord implant on urinary bladder after experimental spinal cord injury in rats.

The objective of this study was to determine the effect of neurotrophin-secreting Schwann cell implants on the urinary bladder after spinal cord contusion. One hour after severe spinal cord contusion at the T8 to T11 level, carbon filaments containing nonsecreting Schwann cells, brain-derived neurotrophic factor (BDNF)-secreting Schwann cells, neurotrophin-3 (NT-3)-secreting Schwann cells, or Schwann cells secreting both BDNF and NT-3 were implanted into the spinal cord. Untreated spinal cord injured (SCI) rats and noncontused rats (C) were also studied. Two months after spinal cord injury, cystometry was performed and the bladders were studied using light microscopy. SCI rats had significantly increased bladder mass, thickness, and smooth muscle mass compared to C rats. Bladder capacity of SCI rats and rats with spinal cord implants were both significantly greater than that of C rats. This preliminary study suggests that neurotrophin-secreting Schwann cell implants may lead to improved bladder structure after spinal cord injury.

[Tissue reaction to polypropylene mono-or multi-filament tapes used in surgical techniques of stress urinary incontinence treatment]. / Reakcja tkankowa wokól wszczepionych fragmentów tasmy polipropylenowej: mono-i multifilamentowej stosowanych w leczeniu wysilkowego nietrzymania moczu u kobiet.

OBJECTIVES: The "gold standard" in surgical treatment of stress urinary incontinence (SUI) is sling operation with polypropylene tape appliance under the mid urethra. There are two types of polypropylene tape which are the most popular nowadays. These two tapes are differently knitted so they have different biomechanical features. The TVT tape is monofilament, rarely knitted and highly elastic but the IVS mesh is multifilament, densly knitted and has only little possibility to stretch. The aim of our study was to assess the tissue reaction to the mono-(TVT) and multifilament (IVS) tapes. MATERIAL AND METHODS: The 10 mm x 10 mm pieces of TVT and IVS tapes were implanted inlay the fascia of musculus abdominis rectus of 14 rat females (2 groups of 7 animals). The tapes with the margin of surrounding fascia were taken off after 6 weeks of healing. All samples were fixed in 10% Formaldehyde in phosphate buffered saline and embedded in paraffin. Four micron tissue sections were stained with hematoxylin and eosin, the reticulin silver impregnation stain according to Gomori (for collagen type III) and periodic acid Schiff and alcian blue (for proteoglycan). RESULTS: In all sections filaments visible as elipsoids were surrounded by resorptive granulation with large multinucleated giant cells like around "foreign body". The diameter of monofilaments was about 150 microns. The connective tissue in the vicinity of mesh was rich of inflammatory cells like histiocytes, lymphocytes, a few polymorphonuclear leucocytes as well as adipocytes and fibroblasts. The large multinucleated giant cells adjacent to monofilaments were relatively bigger than these cells around multifilaments. Moreover, this granulation tissue has a lot of new blood vessels and collagenous fibrous tissue. The multifilaments were about 40 microns in diameter. The inflammatory granulation infiltrated aggregates of multifilaments. This tissue had only few inflammatory cells in comparison to tissue around monofilaments. The large multinucleated giant cells apposed to the mesh were small and collagen created thicker, more compacted bundles. CONCLUSION: The multifilament polypropylene tape induces weaker inflammatory tissue reaction than monofilament mesh. The thicker and more compacted collagen bundles are created around multifilaments so the natural tensile strength of the surrounding tissue is probably higher.

Evaluation of bioabsorbable multiamino acid copolymer/α-tri-calcium phosphate interbody fusion cages in a goat model.

STUDY DESIGN: A study of cervical interbody fusion using polyamino acid-based bioabsorbable fusion cages in a goat model. OBJECTIVE: To compare interbody fusion of a bioabsorbable multiamino acid copolymer/α-tri-calcium phosphate (MAACP/α-TCP) fusion cage with an autologous tricortical iliac-crest bone graft and a titanium cage. SUMMARY OF BACKGROUND DATA: Polyamino acid is widely used as a carrier for drug delivery. To our knowledge, no study investigates interbody fusion cage made of polyamino acid. METHODS: A total of 15 sheep underwent C3/C4 discectomy and fusion. The following stabilization techniques were used: group A, autologous tricortical iliac crest bone graft (n = 5); group B, MAACP/α-TCP cage filled with autologous cancellous bone graft (n = 5); group C, titanium cage filled with autologous cancellous bone graft (n = 5). Radiographic scans to determine disc space height were performed before and after surgery and after 4, 8, and 12 weeks, respectively. After 12 weeks, the C3/C4 motion segment was isolated and sectioned to create a 5-mm thick parasagittal section from which lateral radiographs were obtained. All the radiographs were encoded and reviewed in a blinded fashion to evaluate interbody fusion within the cage devices according to a three-point radiographic score. Biomechanical testing was performed in flexion, extension, axial rotation, and lateral bending to determine range of motion (ROM). Histomorphological and histomorphometrical analyses were performed to evaluate fusion and foreign-body reactions associated with the bioabsorbable cages. RESULTS: Radiographic results showed that the disc space height (DSH) in MAACP/α-TCP cage group was better than that of bone graft group and the best radiographic score was found in MAACP/α-TCP cage group. Biomechanical test showed that no significant difference was found in ROM between MAACP/α-TCP cage group and titanium cage group whereas the value of ROM in bone graft group was the largest. Histologic evaluation showed a higher intervertebral bone volume/total volume ratio and a better interbody fusion in the MAACP/α-TCP cage group than in the other two groups. Two MAACP/α-TCP cages showed microcracks and the other three cages had maintained their original geometry. All MAACP/α-TCP cages showed excellent biocompatibility. CONCLUSION: After 12 weeks, there was no significant difference between the MAACP/α-TCP cage and the titanium cage in distractive properties and biomechanical properties. Compared with titanium cages, MAACP/α-TCP cages showed an advanced interbody fusion. Although MAACP/α-TCP cages developed cracks after only 12 weeks, they showed significantly better distractive properties, biomechanical properties, and an advanced interbody fusion than the tricortical iliac crest bone graft. Improvement should be made to insure the strength of MAACP/α-TCP cage last at least 6 month after implantion.

Degradation of and angiogenesis around multiblock copolymers containing poly(p-dioxanone)- and poly(epsilon-caprolactone)-segments subcutaneously implanted in the rat neck.

The degradation behavior and the effect on angiogenesis of multiblock copolymers based on poly(p-dioxanone)- and poly(epsilon-caprolactone)-segments (PDC) were studied in vivo. PDC is a multifunctional biomaterial combining degradability and shape-memory capabilities. The "in vivo" degradation of PDC is characterized by a fragmentation occurring at the material tissue interface. This observation is consistent with the enzyme supported degradation behaviour, which was determined "in vitro". PDC revealed to induce the formation of blood micro-vessels nearby in the periimplantary tissues. Both might explain the good PDC integration into tissues in terms of a strong connection between the implant and the periimplantary tissue. Micro blood-vessels might be involved in the clearance of the small particles, which appear in the periimplantary tissue when PDC degrades.

Small peptide (P-15) bone substitute efficacy in a rabbit cancellous bone model.

P-15 is a synthetic 15-amino acid residue identical to the cell binding domain of type I collagen. P-15 can be adsorbed onto anorganic bovine bone mineral (ABM) and will enhance cell attachment and subsequent cell activation. Although ABM/P-15 has been studied as a bone graft substitute in the oral cavity, its use in orthopedic models has been limited. Thus, this study investigated the efficacy of ABM/P-15 treatment in a rabbit model of long bone cancellous healing. Defects were created in the distal femurs and proximal medial tibiae of rabbits and were filled with either ABMP/P-15 suspended in hydrogel, ABM alone suspended in hydrogel, hydrogel carrier alone, or no graft material. Rabbits were sacrificed at 1, 2, 4, or 8 weeks postsurgery, and the femurs and tibiae were harvested. Histomorphometric analyses indicated that defects treated with ABM/P-15 had significantly larger areas of new bone formation than the other three treatments at 2 and 8 weeks postsurgery. ABM/P-15 treated defects also had significantly more bone growth than defects left empty or filled with ABM alone at 4 weeks postsurgery. Furthermore, histological examination did not reveal acute inflammatory infiltrate cells in any of the treatment conditions. These results are consistent with the findings of ABM/P-15 use in human oral-maxillofacial studies and in large animal spine fusion models.

The influence of Young's modulus of loaded implants on bone remodeling: an experimental and numerical study in the goat knee.

The aim of this study was to examine the influence of the Young's modulus of the implant material on the bone remodeling in a loaded condition. A combined animal experimental and computational study was set up. The animal experimental group comprised of 16 Saanen goats, each receiving one titanium implant (Young's modulus 110 GPa) and one high-density polyethylene (HDPE) implant (Young's modulus 1 GPa) in the left femoral condyle. Both types of implants received a titanium coating of 100 nm thickness. The implants protruded in the knee joint space and were directly weight bearing. The first group of eight goats was sacrificed after 6 weeks of loading and the second group of eight goats after 6 months of loading. The 16 femoral condyles with the 32 implants were prepared for microfocus computed tomography (micro-CT) scanning and histological sectioning. Three-dimensional trabecular bone parameters were calculated on the micro-CT images for the zones neck, middle, and apex of the implant. The percent of bone contact with the implant was measured on longitudinal histological sections. An axisymmetric finite element (FE) model was created to compare peri-implant bone strains and relative motion between a titanium and a HDPE implant for the experimental loading condition, and to assess the influence of different bone-implant interface (contact) conditions. From the statistical analysis of the 3D bone parameters, the difference between the titanium and HDPE implants was not significantly different (p > 0.05) between the zones (neck, middle, and apex) for both groups of goats. The implants could be considered in their entirety. After 6 weeks of loading, the PE implant presented lower connectivity and smaller marrow spaces in the circular region of 0-500 microm. In the region 500-1500 microm more bone volume was present for the PE implant. After 6 months, the PE implants showed more bone volume and thicker trabeculae than the titanium implants for the entire length of the implant. This effect was already present in the smallest region of interest, 0-500 microm. After 6 months more fibrous encapsulation was found around titanium implants. FE results demonstrated a substantial influence of the interface conditions on peri-implant strains and relative motion. For interface conditions that were representative for the early postoperative situation (involving press-fit and friction), differences in peri-implant bone strain distributions between titanium and HDPE could be related to the experimentally observed differences in amounts of bone and fibrous encapsulation. In contrast, differences in relative motion did not seem to play a role. Both the experimental and computational results suggest that implant stiffness can affect the peri-implant tissue response, which may be related to differences in peri-implant strains.

In vivo evaluation of injectable thermosensitive polymer with time-dependent LCST.

The focus of this study was to examine the biocompatibility, time-dependent LCST, and bioerodable properties of a copolymer system composed of NIPAAm, dimethyl-gamma-butyrolactone (DMBL), and acrylic acid (AAc). Sprague Dawley rats were subcutaneously injected with 25 wt % solutions of poly(NIPAAm-co-DMBL-co-AAc). At predetermined times, animals were sacrificed and polymer implants were recovered for characterization via 1H-NMR. In addition, polymer-contacting tissue sections were harvested and processed for histology. The biocompatibility of the implants was assessed by counting the number of fibroblasts and leukocytes present at the tissue-implant interface. The LCST data obtained from the in vivo implants was shown to agree with that of in vitro findings. Implant mass was shown to decrease after 4 days, indicating accelerated diffusion rates with increased implant swelling, hydrolytic degradation was confirmed with 1H-NMR measurements. The cellular presence at the copolymer implant-tissue interface was shown to return to that of normal tissue 30 days postimplantation, which suggests a normal wound healing response.