Tissue-implant Interface Research Articles

Dependence of macrophage superoxide release on the pulse amplitude of an applied pressure regime: a potential factor at the soft tissue-implant interface

Failure of soft tissue implants has been largely attributed to the influence of biomaterial surface properties on the foreign body response, but some implant complications, e.g. macrophage accumulation and necrosis, are still not effectively addressed with surface treatments to minimize deleterious biomaterial effects. We explored an alternative explanation for implant failure, linking biocompatibility with implant micromotion-induced pressure fluctuations at the tissue-biomaterial interface. For this purpose, we used a custom in vitro system to characterize the effects of pressure fluctuations on the activity of macrophages, the predominant cells at a healing implant site. Initially, we quantified superoxide production by HL60-derived macrophage-like cells under several different pressure regimes with means of 5-40 mmHg, amplitudes of 0-15 mmHg and frequencies of 0-1.5 Hz. All pressure regimes tested elicited significantly (p < 0.05) reduced superoxide production by macrophage-like cells relative to parallel controls. Notably, pressure-sensitive reductions in superoxide release correlated (r(2) = 0.74; p < 0.01) only with pulse pressures. Based on the connection between superoxide production and cell viability, we also explored the influence of cyclic pressure on macrophage numbers and death. Compared to controls, adherent macrophage-like cells exposed to 7.5/2.5 mmHg cyclic pressures for 6 h exhibited significantly (p < 0.01) reduced cell numbers, independent of cell death. A similar effect was observed for cells treated with 10 U/ml superoxide dismutase. Collectively, our results suggest that pressure pulses are a putative regulator of macrophage adhesion via a superoxide-related effect. Pressure fluctuations, e.g. due to implant micromotion, may, therefore, potentially modulate macrophage-dependent wound healing.

Electrochemical removal of metallic implants from Technovit 9100 New embedded hard and soft tissues prior to histological sectioning

Solid metallic implants in soft or hard tissues are serious challenges for histological processing. However, metallic implants are more frequently used in e.g. cardiovascular or orthopaedic therapies. Before clinical use, these devices need to be tested thoroughly in a biological environment and histological analysis of their biocompatibility is a major requirement. To allow the histological analysis of metallic implants in tissues especially in calcified hard tissues, we describe a method for embedding these tissues in the resin Technovit 9100 New and removing the metallic implants by electrochemical dissolution. With the combination of these two processes, we are able to achieve 5μm thick sections from soft or hard tissues with a superior preservation of tissue architecture and especially the implant-tissue interface. These sections can be stained by classical stainings, immunohistochemical and enzymehistochemical as well as DNA-based staining methods.

In Vivo and In Vitro Studies of Epithelial Cell Behavior around Titanium Implants with Machined and Rough Surfaces

The surface roughness of a dental implant affects the epithelial wound healing process and may significantly enhance implant prognosis. We explored the influence of surface roughness on peri-implant epithelium (PIE) sealing and down-growth by comparing machine-surfaced (Ms) and rough-surfaced (Rs) implants. (1) Maxillary first molars were extracted from rats and replaced with Ms or Rs implants. (2) We also compared changes in the morphology of cultured rat oral epithelial cells (OECs) grown on Ms or Rs titanium (Ti) plates. (1) After 4 weeks, the PIE around Ms and Rs implants showed a similar structure to junctional epithelium (JE). At 16 weeks, Rs implants appeared to form a weak epithelial seal at the tissue-implant interface and exhibited markedly less PIE down-growth than Ms implants but was deeper than that observed in natural teeth. (2) We observed less expression of adhesion proteins in OECs cultured on Rs plates than in cells grown on Ms plates. Additionally, cell adherence, migration, and proliferation on Rs plates were lower, whereas apoptosis was reduced on Ms plates. Ms implants are a better choice for integration with an epithelial wound healing process.

Magnetoelastic vibrational biomaterials for real-time monitoring and modulation of the host response

Magnetoelastic (ME) biomaterials are ferromagnetic materials that physically deform when exposed to a magnetic field. This work describes the real-time control and monitoring capabilities of ME biomaterials in wound healing. Studies were conducted to demonstrate the capacity of the materials to monitor changes in protein adsorption and matrix stiffness. In vitro experiments demonstrated that ME biomaterials can monitor cell adhesion and growth in real-time, and a long-term in vivo study demonstrated their ability to monitor the host response (wound healing) to an implant and control local cell density and collagen matrix production at the soft tissue-implant interface. This approach represents a potentially self-aware and post-deployment activated biomaterial coating as a means to monitor an implant surface and provide an adjuvant therapy for implant fibrosis.

Osseointegration: An Update

Osseointegration, defined as a direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant, is critical for implant stability, and is considered a prerequisite for implant loading and long-term clinical success of end osseous dental implants. The implant-tissue interface is an extremely dynamic region of interaction. This complex interaction involves not only biomaterial and biocompatibility issues but also alteration of mechanical environment. The processes of osseointegration involve an initial interlocking between alveolar bone and the implant body, and later, biological fixation through continuous bone apposition and remodeling toward the implant. The process itself is quite complex and there are many factors that influence the formation and maintenance of bone at the implant surface. The aim of this present review is to analysis the current understanding of clinical assessments and factors that determine the success & failure of osseointegrated dental implants.

In situ optical coherence tomography of percutaneous implant-tissue interfaces in a murine model

Novel surface coatings of percutaneous implants need to be tested in biocompatibility studies. The use of animal models for testing usually involves numerous lethal biopsies for the analysis of the implant-tissue interface. In this study, optical coherence tomography (OCT) was used to monitor the reaction of the skin to a percutaneous implant in an animal model of hairless but immunocompetent mice. In vivo optical biopsies with OCT were taken at days 7 and 21 after implantation and post mortem on the day of noticeable inflammation. A Fourier-domain OCT was programmed for spoke pattern scanning schemes centered at the implant midpoint to reduce motion artifacts during in vivo imaging. Image segmentation allowed the automatic detection and morphometric analysis of the skin contour and the subcutaneous implant anchor. On the basis of the segmentation, the overall refractive index of the tissue within one OCT data set was estimated as a free parameter of a fitting algorithm, which corrects for the curved distortion of the planar implant base in the OCT images. OCT in combination with the spoke scanning scheme and image processing provided time-resolved three-dimensional optical biopsies around the implants to assess tissue morphology.

Determination of the Dynamics of Healing at the Tissue-Implant Interface by Means of Microcomputed Tomography and Functional Apparent Moduli

It is currently a challenge to determine the biomechanical properties of the hard tissue-dental implant interface. Recent advances in intraoral imaging and tomographic methods, such as microcomputed tomography (micro-CT), provide three-dimensional details, offering significant potential to evaluate the bone-implant interface, but yield limited information regarding osseointegration because of physical scattering effects emanating from metallic implant surfaces. In the present study, it was hypothesized that functional apparent moduli (FAM), generated from functional incorporation of the peri-implant structure, would eliminate the radiographic artifact-affected layer and serve as a feasible means to evaluate the biomechanical dynamics of tissue-implant integration in vivo. Cylindric titanium mini-implants were placed in osteotomies and osteotomies with defects in rodent maxillae. The layers affected by radiographic artifacts were identified, and the pattern of tissue-implant integration was evaluated from histology and micro-CT images over a 21-day observation period. Analyses of structural information, FAM, and the relationship between FAM and interfacial stiffness (IS) were done before and after eliminating artifacts. Physical artifacts were present within a zone of about 100 to 150 Μm around the implant in both experimental defect situations (osteotomy alone and osteotomy + defect). All correlations were evaluated before and after eliminating the artifact-affected layers, most notably during the maturation period of osseointegration. A strong correlation existed between functional bone apparent modulus and IS within 300 Μm at the osteotomy defects (r > 0.9) and functional composite tissue apparent modulus in the osteotomy defects (r > 0.75). Micro-CT imaging and FAM were of value in measuring the temporal process of tissue-implant integration in vivo. This approach will be useful to complement imaging technologies for longitudinal monitoring of osseointegration.

Poly(Vinyl Alcohol)/Poly(Acrylic Acid) Hydrogel in a dc Electric Field: Swelling, Shape Change, and Actuation Characteristics.

Poly(vinyl alcohol) (PVA)/Poly(acrylic acid) (PAA) hydrogel can be utilized as a biomimetic actuator and coating material for tissue-implant interface, when employing an electrical stimulus. The swelling, shape change, and actuation characteristics of PVA/PAA hydrogel in a range of dc electrical fields were determined to find the optimal electric field for the hydrogel application as biomimetic actuator and coating materials. The hydrogel samples were prepared by dissolving PVA and PAA in deionized water at 4 wt% and mixed together at 1:1 ratio. Two custom made experimental setups were fabricated; one used for the measurement of swelling ratio of the hydrogels; and the other used for the shape changes or actuation characteristics of the hydrogels. Swelling experiments show increased swelling ratios of the hydrogel due to 10 V, 20 V, and 30 V electric fields. The rate of increment of the swelling ratio of hydrogel samples under 10V was higher compare to those samples under 20 V and 30 V. The width and height changes of rectangular shapes and maximum deflection along the length of hydrogel sample due to a range of electric fields (0-30V) were measured using an optical microscope. Incremental shape change up to a specific threshold value (around 10V) was observed due to electric stimulus. Electrostatic actuation pressure of hydrogel samples under 10V was higher compare to those samples under 20 V and 30 V. These results suggested that optimal performance of PVA/PAA hydrogel can be achieved around 10V.

Preparation and characterization of stainless steel 316L/HA biocomposite

The austenitic stainless steel 316L is the most used metallic biomaterials in orthopedics applications, especially in the manufacture of articulated prostheses and as structural elements in fracture fixation, since it has high mechanical strength. However, because it is biologically inactive, it does not form chemical bond with bone tissue, it is fixed only by morphology. The development of biocomposites of stainless steel with a bioactive material, such as hydroxyapatite - HA, is presented as an alternative to improve the response in the tissue-implant interface. However significant reductions in mechanical properties of the biocomposite can occur. Different compositions of the biocomposite stainless steel 316L/HA (5, 20 and 50 wt. (%) HA) were prepared by mechanical alloying. After milling the powders for 10 hours, the different compositions of the biocomposite were compacted isostatically and sintered at 1200 ºC for 2 hours. The mechanical properties of the biocomposites were analyzed by compression tests. The powders and the sintered composites were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Titanium alloys (AoN) and their involvement in osseointegration.

Background:Osseointegration is essential for a long-term successful and inflammation-free dental implant. Such a result depends on osteoblastic cells growth and differentiation at the tissue-implant interface. The aim of this study was to compare two different AoN titanium layers (GR4 and GR5) to investigate which one had a greater osteoconductive power using human osteoblasts (HOb) culture at two different time-points.Materials and Methods:The expression levels of some bone-related (ALPL, COL1A1, COL3A1, SPP1, RUNX2, and SPARC) were analyzed using real time reverse transcription-polymerase chain reaction (real time RT-PCR).Results:Real-time RT-PCR data showed that after 3 days of treatment with TiA4GR, the genes up-regulated were COL3A1, ALPL, SPP1, and RUNX2. Moreover, no difference in gene expression was noticed 4 days later. On the other hand, the genes that overexpressed after 3 days of treatment with AoN5GR were ALPL, SPP1, and RUNX2. In both cases, the expression of COL1A1 and SPARC was negatively regulated.Conclusion:Our data showed that both titanium surfaces led to osteoblasts recruitment, maturation, and differentiation, thus promoting osseointegration at the tissue-implant interface.

Influence of Titanium Surface Topography on Peri-Implant Soft Tissue Integration

At the neck area of dental implant surface, machined surface (Ms) has been employed to avoid surface contamination. Recently, implants which have roughened surface texture (Rs) at their neck are also available. However, from the viewpoint of soft tissue integration, it remains to be elucidated whether or not surface topography affects the soft tissue attachment around implants. The aim of the present study was to clarify the influence of surface topography on peri-implant soft tissue integration. First, surface roughness of both surfaces was measured. Second, protein adsorption capability on both surfaces was examined. Then, as the rat implant model, titanium implants with each surface were inserted into the maxillae. Horseradish peroxidase (HRP) tracer was applied 4 weeks post implantation to the gingival sulci of implants or natural teeth (NT) to investigate the sealing capability of periodontal/peri-implant soft tissue. Collagen density was also observed by fluorescent staining. As a result, surface roughness (Sa) of Ms and Rs was 0.16 µm and 0.25 µm, respectively. Protein adsorption capability on both surface showed no significant differences. In the NT group of the rat implant model, presence of HRP was restricted only in the coronal portion of epithelium. In both implant groups, in contrast, more invasion of HRP was observed in the soft tissue around implants. Especially in the Ms group, more HRP was observed in the deeper area compared with Rs group. Stronger expression of collagen was observed around Rs compared to Ms at the connective tissue-implant interface. It could be speculated that, with dense collagen, Rs implants showed stronger soft tissue integration compared with Ms implants, but the integration is not as strong as NT’s.

Lubricin and smooth muscle α-actin-containing myofibroblasts in the pseudomembranes around loose hip and knee prostheses

The objective was to evaluate the presence and distribution of the lubricating and anti-adhesion glycoprotein lubricin and cells containing the contractile isoform smooth muscle α-actin (SMA) in pseudomembranes around loose hip prostheses. Periprosthetic tissue was obtained at revision arthroplasty of eight aseptic, loose hip implants, and for comparison three loose knee prostheses. Immunohistochemical analysis was performed in 3 zones: zone 1, within 300μm of the edge of the implant–tissue interface; zone 2, between zones 1 and 3; zone 3, within 300μm of the resected/trimmed edge. The presence of lubricin was extensive in all samples: (1) as a discrete layer at the implant–tissue interface; (2) within the extracellular matrix (ECM); (3) intracellularly. There was significantly more high grade (>50%) lubricin surface staining at the implant–tissue interface compared with the resected edge. While there was also a significant effect of location of high grade ECM lubricin staining, there was no significant effect of implant type (i.e. hip versus knee). All but two hip pseudomembrane samples showed the presence of many SMA-containing cells. There was a significant effect of location on the number of SMA-expressing cells, but not of implant type. These findings might explain why the management of loose prosthesis is so challenging.

Artificial Muscle for Reanimation of the Paralyzed Face

Current management of permanent facial paralysis centers on nerve grafting and muscle transfer; however, limitations of those procedures call for other options. To determine the durability and biocompatibility of implanted artificial muscle in a gerbil model and the degree of inflammation and fibrosis at the host tissue-artificial muscle interface. Electroactive polymer artificial muscle (EPAM) devices engineered in medical-grade silicone were implanted subcutaneously in 13 gerbils. The implanted units were stimulated with 1 kV at 1 Hz, 24 h/d via a function generator. Electrical signal input/output was recorded up to 40 days after implantation. The animals were euthanized between 23 and 65 days after implantation, and the host tissue-implant interface was evaluated histologically. The animals tolerated implantation of the EPAM devices well, with no perioperative deaths. The muscle devices created motion for a mean of 30.3 days (range, 19-40 days), with a mean of 2.6 × 106 cycles (range, 1.6 × 106 to 3.5 × 106 cycles). Histologic examination of the explanted devices revealed the development of a minimal fibrous capsule surrounding the implants, with no evidence of bacterial infection or inflammatory infiltrate. No evidence of device compromise, corrosion, or silicone breakdown was noted. Artificial muscle implanted in this short-term animal model was safe and functional in this preliminary study. We believe that EPAM devices will be a safe and viable option for restoration of facial motions in patients with irreversible facial paralysis.

Lubricin in human breast tissue expander capsules

Capsular contraction is the most common complication of breast reconstruction surgery. While presence of the contractile protein alpha smooth muscle actin (α-SMA) is considered among the causes of capsular contraction, the exact etiology and pathophysiology is not fully understood. The objective of this study was to investigate the possible role of lubricin in capsular formation and contraction by determining the presence and distribution of the lubricating protein lubricin in human breast tissue expander capsules. Related aims were to evaluate select histopathologic features of the capsules, and the percentage of cells expressing α-SMA, which reflects the myofibroblast phenotype. Capsules from tissue expanders were obtained from eight patients. Lubricin, at the tissue-implant interface, in the extracellular matrix, and in cells, and α-SMA-containing cells were evaluated immunohistochemically. The notable finding was that lubricin was identified in all tissue expander capsules: as a discrete layer at the tissue-implant interface, extracellular, and intracellular. There was a greater amount of lubricin in the extracellular matrix in the intimal-subintimal zone when compared with the tissue away from the implant. Varying degrees of synovial metaplasia were seen at the tissue-implant interface. α-SMA-containing cells were also seen in all but one patient. The findings might help us better understand factors involved in capsule formation.

Early‐stage osseointegration capability of a submicrofeatured titanium surface created by microroughening and anodic oxidation

The role of nanoscale/submicron morphological features in the process of osseointegration is largely unknown. This study reports the creation of a unique submicrofeatured titanium surface by a combination of anodic oxidation and sandblasting and determines how the addition of this submicrofeature to a microroughened surface affects the early-stage process of osseointegration. Nonmicroroughened implants were prepared by machining Ti-6Al-4V alloy in a cylindrical form (1mm diameter and 2mm long). Microroughened implants were prepared by sandblasting machined implants, while submicrofeatured implants were created by anodic oxidation of the sandblasted implants. Implants were placed into rat femurs and subjected to biomechanical, interfacial, and histological analyses at 1 and 2weeks post-implantation (n=6). The submicrotopography was characterized by 50-300nm nodules and pits in addition to other submicron-level irregularities formed entirely within the sandblast-created microstructures. The biomechanical strength of osseointegration increased continuously from week 1 to 2 for the submicrofeatured implants but not for the microroughened implants. A significant increase in bone-implant contact and bone volume, as well as a reduction in soft tissue intervention, were commonly found for the microroughened surface and the submicrofeatured surface compared with the nonmicroroughened surface. However, there were no differences in these parameters between the microroughened surface and the submicrofeatured surface. An extensive area of bone tissue at the submicrofeatured implant interface was retained intact after biomechanical shear testing, while the microroughened implant-tissue interface showed a gap along the entire axis of the implant, leading to clear separation of the tissue during the shear procedure. This study demonstrates that a submicrofeatured titanium surface created by a combination of sandblasting and anodic oxidation enhances the strength of early-stage osseointegration, primarily because of the increased resistance of peri-implant bone tissue against external force rather than modulation of bone morphogenesis.

Changes in soft tissues around immediate full‐arch rehabilitations: a prospective study

Nowadays, aesthetic appearance is receiving more and more attention from clinicians and patients. Therefore, it is of paramount importance for the surgeon to maintain or to improve the quality and the stability of the soft tissue-implant interface. The scientific literature supports the idea that the immediate placement and provisionalization of endosseus implants and abutments can indeed offer additional clinical control over the peri-implant tissue architecture. On this basis, this prospective study aims to evaluate the changes in soft tissues around immediately loaded dental implants in full-arch rehabilitations, over a period of 3 months. Fifteen subjects were treated for immediate full-arch rehabilitations. Following implant placement, provisional rehabilitations made of bisphenol-A-glycidyldimethacrylate (BIS-GMA) and resin were placed. All records were made using a periodontal probe. The facial soft-tissue level was measured evaluating the distance between the soft-tissue margin and the incisal edge of the crown. Moreover, papilla levels were measured at the mesial and distal sites from a reference line connecting the occlusal edge of the crowns. The average value at the mesial site was -0.035 mm (±1, median 0 mm), while at the midfacial site, it was 0 mm (±0.76, median 0 mm) and at the distal site, -0.05 mm (±0.92, median 0 mm). The plaque score index showed a reduction during the follow-up period. Our data indicate that no differences at the midfacial point were detectable over the observation period. This is in agreement with several studies; it is plausible that these results are linked to a correct position of the implant in the alveolar socket. Moreover, comparing our results with what has been reported by other authors, it is surprising that while other studies highlight that papilla loss at the mesial and distal aspect is an expected consequence of immediate implant restorations, our data do not show any changes. The explanation of these results remains unclear. Further studies are needed to support our data and to clarify what mechanisms are involved in the maintenance of soft tissue.

Role of surface topography of titanium endosseous implants for improved osseointegration

Osseointegration is the basis of successful endosseous implantology. The process itself is complex, and many factors influence the formation and maintenance of bone at the implant surface. Studies have shown that implant-tissue interface can be influenced by different methods of surface treatment that affect the biologic response to the implant. Methods of surface treatment include alteration of the microstructure and physicochemical parameters of the implant surface.

Decreasing Bacterial Colonization of External Fixation Pins Through Nitric Oxide Release Coatings

Bacterial infection of the pin tract represents the most common complication associated with external fixation. This study was designed to evaluate the antibacterial activity of nitric oxide (NO)-releasing xerogel films applied to commercially pure titanium pins in a rat model. Pins were coated with xerogel solution through a dip-coating procedure. Half of the xerogel-coated implant pins were modified into NO donors and served as the NO-releasing group, whereas the remaining pins were left unmodified to serve as non-NO-releasing xerogel-coated controls. Acid-etched pins served as uncoated controls. Animal selection was randomized and every rat had one pin from each of the three groups randomly allocated to the third, fourth, or fifth tail vertebrae. Quantification of bacterial infection was performed 48 days postoperatively and the tissue-implant interface was inspected for clinical signs of infection on Days 14 and 28 postimplantation. Pin tract bacterial colony counts of the NO-releasing group (170,000 ± 181,000) were significantly lower than both the xerogel-coated group (677,000 ± 675,000) and the control group (1,181,000 ± 2,717,000) 48 days postoperatively (P < 0.05). No significant difference in colony counts was observed between the xerogel-coated group and the control group. The NO-releasing group also had significantly fewer clinical signs of infection than both the coated and the control groups on postoperative Day 28 (P < 0.05). The application of NO-releasing xerogel coatings can inhibit bacterial colonization of external fixation pins both during the initial postsurgical period and up to 48 days postimplantation.

Evaluations of epithelial sealing and peri‐implant epithelial down‐growth around “step‐type” implants

Implant designs that can stimulate and integrate with an epithelial wound-healing process may significantly enhance the efficacy of dental implants. Here, we evaluated the potential of "step-type" implant systems to improve the sealing between the peri-implant epithelium (PIE) and the implant surface, and investigated the effect of implant structure on PIE down-growth. Right maxillary first molars were extirpated from rats and implanted with either a straight-type or a step-type implant varying in step height and/or width (N(s): 0.8 mm height, 0.1 mm width; W(s): 0.8 mm height, 0.2 mm width; H(s): 0.4 mm height, 0.1 mm width). Maxillae were harvested at various time points over 16 weeks to evaluate laminin-5 distribution as an indicator of wound healing and PIE formation, horse-radish peroxidase (HRP) penetration as a measurement of epithelial sealing, and PIE down-growth formation. In all implant models, the PIE formed from the oral sulcular epithelium and spread apically along the implant surface. In the W(s) group, HRP penetration was detected only in the coronal region of the PIE at 4 weeks, whereas in the straight-type, it was observed in the apical region and the connective tissue. At 16 weeks, the W(s) implants exhibited markedly less PIE down-growth than the Con, N(s) or H(s) implants, and were equivalent to that observed in natural teeth. The step-type implant system may have the potential for improving epithelial sealing at the tissue-implant interface, as well as reducing apical PIE down-growth, thus enhancing dental implant efficacy.

Ex Vivo Examination of the Biocompatibility of Biodegradable Magnesium via Microdialysis in the Isolated Perfused Bovine Udder Model

Being biodegradable, magnesium is considered a promising future implant material but very little is known about the biocompatibility for the tissues in direct contact with it. In this study, the degradation of pure magnesium implants in the skin of an isolated bovine udder was examined over a period of five hours. Microdialysis technique was used in order to investigate the reactions at the interface of implant and tissue. Pure titanium implants served as control. Degradation behavior and biocompatibility were evaluated via extracellular magnesium ion concentration and PGE2 and TNF alpha served as indicators of inflammation. Concentrations of 5.5 mmol/l Mg2+ were detected at the beginning, which decreased to a plateau of about 3.5 mmol/l after approximately two and a half hours. PGE2 and TNF alpha concentrations indicated no major inflammatory tissue response to the degradation. These results give an idea of the ion burden at the implantation site of degrading magnesium and suggest good biocompatibility even at the tissue-implant interface.