B. Chehroudi

The effects of the surface topography of micromachined titanium substrata on cell behavior in vitro and in vivo.

Surface properties, including topography and chemistry, are of prime importance in establishing the response of tissues to biomaterials. Microfabrication techniques have enabled the production of precisely controlled surface topographies that have been used as substrata for cells in culture and on devices implanted in vivo. This article reviews aspects of cell behavior involved in tissue response to implants with an emphasis on the effects of topography. Microfabricated grooved surfaces produce orientation and directed locomotion of epithelial cells in vitro and can inhibit epithelial downgrowth on implants. The effects depend on the groove dimensions and they are modified by epithelial cell-cell interactions. Fibroblasts similarly exhibit contact guidance on grooved surfaces, but fibroblast shape in vitro differs markedly from that found in vivo. Surface topography is important in establishing tissue organization adjacent to implants, with smooth surfaces generally being associated with fibrous tissue encapsulation. Grooved topographies appear to have promise in reducing encapsulation in the short term, but additional studies employing three-dimensional reconstruction and diverse topographies are needed to understand better the process of connective-tissue organization adjacent to implants. Microfabricated surfaces can increase the frequency of mineralized bone-like tissue nodules adjacent to subcutaneously implanted surfaces in rats. Orientation of these nodules with grooves occurs both in culture and on implants. Detailed comparisons of cell behavior on micromachined substrata in vitro and in vivo are difficult because of the number and complexity of factors, such as population density and micromotion, that can differ between these conditions.

The effects of micromachined surfaces on formation of bonelike tissue on subcutaneous implants as assessed by radiography and computer image processing.

Surface topography varies widely among commercially available orthopedic and dental implants. While it is generally accepted that the surface topography of an implant influences the formation of bone and affects its performance, few systematic studies have dealt with this important feature. Quantification of the mineralized tissue at the implant interface has typically been attempted using histologic methods or conventional radiographic procedures. However, histologic methods are often technically demanding and time consuming, whereas conventional radiographic procedures lack resolution and sensitivity to identify small areas of mineralization. The objective of this study was to study systematically the effects of micromachined surfaces on bone formation by applying digital radiographic techniques to identify and quantify mineralized tissue. Titanium-coated epoxy replicas of 19 different micromachined grooved or pitted surfaces that ranged between 30 and 120 microns deep, as well as smooth control surfaces, were implanted percutaneously and fixed to the parietal bone of rats. After 8 weeks the implants and attached tissue were removed and processed for light and electron microscopy. A total of 316 implant surfaces were processed, radiographed using conventional and digital techniques, and sectioned for histologic observations. The area of the bonelike tissue and its density were calculated using National Institutes of Health Image software. Mineralization was frequently noted at the interface of some types of micromachined surface but rarely on smooth surfaces. The presence of bone in histologic sections and areas identified as bone through digital radiography and image processing correlated strongly. The frequency of bonelike foci formation decreased as the depth of the grooves increased. In contrast, mineralization occurred more frequently as the depth of the pit increased. In addition, bonelike foci were oriented along the long axis of the grooves. It is thus feasible that the bonelike tissue is shaped, directed, or engineered to a predetermined configuration which is dictated by the surface topography. This study indicated that surface topography influences the frequency as well as the amount of bone deposited adjacent to implants, and mineralized product can be guided by the surface topography. Moreover, digital radiography and image processing can be used reliably to identify and quantify mineralized tissue at the implant interface.

Subcutaneous microfabricated surfaces inhibit epithelial recession and promote long-term survival of percutaneous implants

The long-term success of percutaneous devices is compromised by problems such as infection, mechanical avulsion and epithelial downgrowth. The objective of this study was to test the effects of microfabricated surfaces on tissue integration and long-term survival of percutaneous implants, using a modified implant design and a two-stage surgical method. Hexagonal titanium-coated epoxy implants were constructed with separate subcutaneous and percutaneous components, so that the effects of surface topography on connective tissue could be separated from the effects on epithelium. Subcutaneous components with 30-microm-deep micromachined grooves, 120-microm-deep tapered pits, or smooth control surfaces were secured to the calvarial bone of rats by a titanium pin. After 8 weeks, a percutaneous smooth-surfaced component was secured to the subcutaneous component. Dental impression materials were used to make models of the components and adjacent tissues at weekly intervals and tissue recession around the implants was measured. Some implants were removed at intervals up to 24 weeks and processed for histology. Connective-tissue ingrowth and mineralized tissue were noticed on the micromachined surfaces, whereas a thick capsule and epithelial downgrowth were observed on smooth control surfaces. On all implants, recession occurred most rapidly in the first 3 weeks, but was significantly reduced relative to the smooth controls only on implants with micromachined grooved subcutaneous surfaces (p<0.05). In addition, the time before failure was significantly (p<0.05) longer for implants with grooved subcutaneous surfaces than implants with smooth and pitted subcutaneous surfaces. This study indicated that an impression technique could be used to monitor tissue recession on percutaneous devices, and that micromachined grooved surfaces located subcutaneously improved the performance and longevity of percutaneous devices by promoting tissue integration.

An in vitro study of plasticized poly(lactic-co-glycolic acid) films as possible guided tissue regeneration membranes: material properties and drug release kinetics.

Guided tissue regeneration (GTR), in periodontal therapy, involves the placement of a barrier membrane, to ensure the detached root surface becomes repopulated with periodontal ligament cells capable of regenerating this attachment. GTR procedures exhibit large variability in surgical outcome as a consequence of poor membrane performance. The objective of this study was to evaluate the suitability of plasticized poly(lactic-co-glycolic acid) (PLGA) as a material for GTR membranes. The material was also investigated as a localized controlled release system for the antibiotic, anti-inflammatory agent tetracycline. Films made from PLGA (85:15), plasticized with either 10% w/v methoxypoly(ethyleneglycol) (MePEG) or a diblock copolymer [poly(D,L-lactic acid)-block-methoxypoly(ethyleneglycol)] were loaded with tetracycline base (or hydrochloride salt) and cast by solvent evaporation. Drug release was measured using high performance liquid chromatography (HPLC). The time-course of elasticity changes and swelling were determined using a stress-strain apparatus or gravimetric/dimensional determinations, respectively. Cells extracted from periodontal ligament cell explants were used to evaluate the effect of material and drug loading on cell morphology. Tetracycline·HCl released more rapidly than tetracycline from PLGA films. The addition of either MePEG or diblock caused a concentration dependent increase in release rates for both drugs. Release profiles ranged from a small initial burst phase followed by slow sustained release to almost full drug release after 1 day. After incubation in PBS, the films stiffened and swelled within 30 min. Periodontal ligament cell morphology was not affected by the inclusion of tetracycline. Plasticized PLGA films displayed desired features for possible use as GTR membranes.

Bone formation on rough, but not polished, subcutaneously implanted Ti surfaces is preceded by macrophage accumulation†

Implanted rough surfaces have long been associated with the accumulation of macrophages and other cells of the monocytic lineage such as foreign body giant cells and osteoclasts. As cells of the moncytic lineage are part of the immune system, the response of this cell family to biomaterials has attracted wide concern. This study compared events at the interface of implant surface topographies with varied roughness in a rat subcutaneous model. Titanium-coated epoxy replicas of machined, etched, blasted, titanium-plasma-sprayed (TPS), sandblasted-and-etched (SLA), micromachined, and polished surfaces were implanted for up to 11 weeks, and processed for light or electron microscopy or immunohistochemistry for ED1, a marker for recruited macrophages. Initially, healing appeared similar among all surfaces, the frequency of mineralization followed the order of SLA, micromachined, TPS, machined, etched, blasted, and polished surfaces. On the SLA surface macrophages, as identified by both ultrastructural morphology and immunohistochemistry were the predominant cell type at 1 week and persisted until mineralization occurred as early as 2 weeks. On smoother surfaces collagenous matrix predominated at 2 weeks and subsequently increased with time. There, thus, appears to be two routes to bone-like tissue formation on Ti implants in this rat subcutaneous model; macrophage-mediated and macrophage-independent dense collagenous-matrix-associated.

Controlled Release of Alendronate from Polymeric Films

Bisphosphonate drugs alter the balance of bone resorption and formation, leading to a net increase in bone density. Therefore, these drugs are commonly used to treat osteoporosis or as an adjunct to cancer chemotherapy. Local delivery of bisphosphonates, such as alendronate, from polymeric films has the potential to improve efficacy and decrease side-effects common to oral bisphosphonate therapy. Alendronate was effectively encapsulated in film formulations composed of poly(lactic-co-glycolic acid) (PLGA) blended with poly(DL-lactic acid)-block-methoxy poly(ethylene glycol) (diblock co-polymer) and the films were characterized for elasticity, swelling, thermal and drug-release properties. Increasing the proportion of diblock co-polymer in the formulation decreased the glass transition temperature of PLGA, allowing for improved handling via increases in film elasticity. Immersion in aqueous media caused a rapid stiffening and swelling of the films. The inclusion of diblock co-polymer increased the rate of drug release from the films over a 3-week period. Drug-loaded polymeric films containing 0.25% alendronate increased osteoblast viability after 4 days compared to polymer alone. After 5 weeks, there was a significant increase in alkaline phosphatase activity and calcium nodule formation in osteoblasts grown on films containing 1.25% alendronate in 5% diblock co-polymer in PLGA.

Discrimination of Tooth Layers and Dental Restorative Materials Using Cutting Sounds

Dental restoration begins with removing carries and affected tissues with air-turbine rotary cutting handpieces, and later restoring the lost tissues with appropriate restorative materials to retain the functionality. Most restoration materials eventually fail as they age and need to be replaced. One of the difficulties in replacing failing restorations is discerning the boundary of restorative materials, which causes inadvertent removal of healthy tooth layers. Developing an objective and sensor-based method is a promising approach to monitor dental restorative operations and to prevent excessive tooth losses. This paper has analyzed cutting sounds of an air-turbine handpiece to discriminate between tooth layers and two commonly used restorative materials, amalgam and composite. Support vector machines were employed for classification, and the averaged short-time Fourier transform coefficients were selected as the features. The classifier performance was evaluated from different aspects such as the number of features, feature scaling methods, classification schemes, and utilized kernels. The total classification accuracies were 89% and 92% for cases included composite and amalgam materials, respectively. The obtained results indicated the feasibility and effectiveness of the proposed method.

Tooth materials monitoring scheme for dental operations using cutting sounds

This paper introduces a monitoring scheme for discerning the boundary of the tooth in dental operations. In this scheme, tooth structures and dental fillings were discriminated based on their cutting sounds. Support vector machines were employed for classification; and averaged short time Fourier transform coefficients were selected as the features. The results confirmed capability and feasibility of the proposed scheme.