Microtopography and soft tissue response

Fucoidan/collagen composite coating on magnesium alloy for better corrosion resistance and pro-endothelialization potential

Magnesium alloy stents (MAS) have broad application prospects in the treatment of cardiovascular diseases. However, poor corrosion resistance and biocompatibility greatly limit the clinical application of MAS. In this work, the coating consisting of MgF2 layer, polydopamine layer, fucoidan and collagen IV was constructed on Mg-Zn-Y-Nd (ZE21B) alloy to improve its corrosion resistance and pro-endothelialization potential. The fucoidan and collagen IV in the coating could obviously enhance the hemocompatibility and pro-endothelialization potential respectively. Compared with bare ZE21B alloy, the fucoidan/collagen composite coating modified ZE21B alloy possessed lower corrosion current density and better corrosion resistance. Moreover, the modified ZE21B alloy exhibited relatively low hemolysis rate, fibrinogen adsorption and platelet adhesion in the blood experiments, suggesting the improved hemocompatibility. Furthermore, the modified ZE21B alloy favorably supported the adhesion and proliferation of vascular endothelial cells (ECs) and effectively regulated the phenotype of smooth muscle cells (SMCs), thus improving the pro-endothelialization potential of vascular stent materials. The fucoidan/collagen composite coating can significantly improve the corrosion resistance and pro-endothelialization potential of ZE21B alloy, showing great potential in the development of degradable MAS.

A composite membrane with microtopographical morphology to regulate cellular behavior for improved tissue regeneration

Tissue engineering scaffolds with specific surface topographical morphologies can regulate cellular behaviors and promote tissue repair. In this study, poly lactic(co-glycolic acid) (PLGA)/wool keratin composite guided tissue regeneration (GTR) membranes with three types of microtopographies (three groups each of pits, grooves and columns, thus nine groups in total) were prepared. Then, the effects of the nine groups of membranes on cell adhesion, proliferation and osteogenic differentiation were examined. The nine different membranes had clear, regular and uniform surface topographical morphologies. The 2 µm pit-structured membrane had the best effect on promoting the proliferation of bone marrow mesenchymal stem cells (BMSCs) and periodontal ligament stem cells (PDLSCs), while the 10 µm groove-structured membrane was the best for inducing osteogenic differentiation of BMSCs and PDLSCs. Then, we investigated the ectopic osteogenic, guided bone tissue regeneration and guided periodontal tissue regeneration effects of the 10 µm groove-structured membrane combined with cells or cell sheets. The 10 µm groove-structured membrane/cell complex had good compatibility and certain ectopic osteogenic effects, and the 10 µm groove-structured membrane/cell sheet complex promoted better bone repair and regeneration and periodontal tissue regeneration. Thus, the 10 µm groove-structured membrane shows potential to treat bone defects and periodontal disease. STATEMENT OF SIGNIFICANCE: PLGA/wool keratin composite GTR membranes with microcolumn, micropit and microgroove topographical morphologies were prepared by dry etching technology and the solvent casting method. The composite GTR membranes had different effects on cell behavior. The 2 µm pit-structured membrane had the best effect on promoting the proliferation of rabbit BMSCs and PDLSCs and the 10 µm groove-structured membrane was the best for inducing the osteogenic differentiation of BMSCs and PDLSCs. The combined application of a 10 µm groove-structured membrane and PDLSC sheet can promote better bone repair and regeneration as well as periodontal tissue regeneration. Our findings may have significant potential for guiding the design of future GTR membranes with topographical morphologies and clinical applications of the groove-structured membrane/cell sheet complex.

Emerging modulators for osteogenic differentiation: a combination of chemical and topographical cues for bone microenvironment engineering

Bone presents an intrinsic ability for self-regeneration and repair, however critical defects and large fractures require invasive and time-consuming clinical interventions. As an alternative to current therapy, bone tissue engineering (BTE) has primarily aimed to recreate the bone microenvironment by delivering key biomolecules and/or by modification of scaffolds to guide cell fate towards the osteogenic lineage or other phenotypes that may benefit the bone regeneration mechanism. Considering that bone cells communicate, in their native microenvironment, through biochemical and physical signals, most strategies fail when considering only chemical, geometrical or mechanical cues. This is not representative of the physiological conditions, where the cells are simultaneously in contact and stimulated by several cues. Therefore, this review explores the synergistic effect of biochemical/physical cues in regulating cellular events, namely cell adhesion, proliferation, osteogenic differentiation, and mineralization, highlighting the importance of the combined modifications for the development of innovative bone regenerative therapies.

Additive Manufacturing of Multi-Scale Porous Soft Tissue Implants That Encourage Vascularization and Tissue Ingrowth

Medical devices, such as silicone-based prostheses designed for soft tissue implantation, often induce a suboptimal foreign-body response which results in a hardened avascular fibrotic capsule around the device, often leading to patient discomfort or implant failure. Here, it is proposed that additive manufacturing techniques can be used to deposit durable coatings with multiscale porosity on soft tissue implant surfaces to promote optimal tissue integration. Specifically, the "liquid rope coil effect", is exploited via direct ink writing, to create a controlled macro open-pore architecture, including over highly curved surfaces, while adapting atomizing spray deposition of a silicone ink to create a microporous texture. The potential to tailor the degree of tissue integration and vascularization using these fabrication techniques is demonstrated through subdermal and submuscular implantation studies in rodent and porcine models respectively, illustrating the implant coating's potential applications in both traditional soft tissue prosthetics and active drug-eluting devices.

Surface Modification of Aliphatic Polyester to Enhance Biocompatibility

Aliphatic polyester is a kind of biodegradable implantable polymers, which shows promise as scaffolds in tissue engineering, drug carrier, medical device, and so on. To further improve its biocompatibility and cell affinity, many techniques have been used to modify the surface of the polyester. In the present paper, the key factors of influencing biocompatibility of aliphatic polyester were illuminated, and the different surface modification methods such as physical, chemical, and plasma processing methods were also demonstrated. The advantages and disadvantages of each method were also discussed with the hope that this review can serve as a resource for selection of surface modification of aliphatic products.

Negating Tissue Contracture Improves Volume Maintenance and Longevity of In Vivo Engineered Tissues

BACKGROUND

Engineering large, complex tissues in vivo requires robust vascularization to optimize survival, growth, and function. Previously, the authors used a "chamber" model that promotes intense angiogenesis in vivo as a platform for functional three-dimensional muscle and renal engineering. A silicone membrane used to define the structure and to contain the constructs is successful in the short term. However, over time, generated tissues contract and decrease in size in a manner similar to capsular contracture seen around many commonly used surgical implants. The authors hypothesized that modification of the chamber structure or internal surface would promote tissue adherence and maintain construct volume.

METHODS

Three chamber configurations were tested against volume maintenance. Previously studied, smooth silicone surfaces were compared to chambers modified for improved tissue adherence, with multiple transmembrane perforations or lined with a commercially available textured surface. Tissues were allowed to mature long term in a rat model, before analysis.

RESULTS

On explantation, average tissue masses were 49, 102, and 122 mg; average volumes were 74, 158 and 176 μl; and average cross-sectional areas were 1.6, 6.7, and 8.7 mm for the smooth, perforated, and textured groups, respectively. Both perforated and textured designs demonstrated significantly greater measures than the smooth-surfaced constructs in all respects.

CONCLUSIONS

By modifying the design of chambers supporting vascularized, three-dimensional, in vivo tissue engineering constructs, generated tissue mass, volume, and area can be maintained over a long time course. Successful progress in the scale-up of construct size should follow, leading to improved potential for development of increasingly complex engineered tissues.

Sol-gel method to fabricate CaP scaffolds by robocasting for tissue engineering

Highly porous calcium phosphate (CaP) scaffolds for bone-tissue engineering were fabricated by combining a robocasting process with a sol-gel synthesis that mixed Calcium Nitrate Tetrahydrate and Triethyl Phosphite precursors in an aqueous medium. The resulting gels were used to print scaffolds by robocasting without the use of binder to increase the viscosity of the paste. X-ray diffraction analysis confirmed that the process yielded hydroxyapatite and β-tricalcium phosphate biphasic composite powders. Thus, the scaffold composition after crystallization of the amorphous structure could be easily modified by varying the initial Ca/P ratio during synthesis. The compressive strengths of the scaffolds are ~6 MPa, which is in the range of human cancellous bone (2-12 MPa). These highly porous scaffolds (~73 vol% porosity) are composed of macro-pores of ~260 μm in size; such porosity is expected to enable bone ingrowth into the scaffold for bone repair applications. The chemistry, porosity, and surface topography of such scaffolds can also be modified by the process parameters to favor bone formation. The studied sol-gel process can be used to coat these scaffolds by dip-coating, which induces a significant enhancement of mechanical properties. This can adjust scaffold properties such as composition and surface morphology, which consequently may improve their performances.

Control of cell nucleus shapes via micropillar patterns

We herein report a material technique to control the shapes of cell nuclei by the design of the microtopography of substrates to which the cells adhere. Poly(D,L-lactide-co-glycolide) (PLGA) micropillars or micropits of a series of height or depth were fabricated, and some surprising self deformation of the nuclei of bone marrow stromal cells (BMSCs) was found in the case of micropillars with a sufficient height. Despite severe nucleus deformation, BMSCs kept the ability of proliferation and differentiation. We further demonstrated that the shapes of cell nuclei could be regulated by the appropriate micropillar patterns. Besides circular and elliptoid shapes, some unusual nucleus shapes of BMSCs have been achieved, such as square, cross, dumbbell, and asymmetric sphere-protrusion.

Does drainage hole size influence adhesion on ventricular catheters?

PURPOSE

Ventricular catheter drainage holes of shunt systems used to treat hydrocephalus obstruct with tissue commonly comprising monocytes/macrophages, astrocytes, and giant cells. Despite high rates of obstruction, very few studies have manipulated drainage hole orientation, number, position, or diameter. By altering the hole diameter but maintaining a constant hole surface area, we manipulated shear stress through the holes, which we hypothesized would change the degree of macrophage and astrocyte attachment.

METHODS

First, a hole fabrication method was chosen from two fabrication techniques including punched holes in catheter tubing and constructed holes using nanofabrication techniques.

RESULTS

Punched holes were chosen to vary hole size from 282 to 975 μm because (1) samples were geometrically similar to commercially available ventricular catheters without significant microscopic differences in roughness values and (2) total macrophage and astrocyte adhesion on the punched holes was not significantly different from adhesion on the commercially available catheters. Overall adhesion from least to most adherent appeared to follow 975 < 754 ≈ 500 < 282-μm hole diameter for macrophages and 975 < 500 < 754 < 282 for astrocytes with an obvious dependency on catheter orientation with respect to the horizontal; a dependency to the proximity of the hole to the catheter tip was not observed.

CONCLUSION

This study suggests that macrophage and astrocyte adhesion generally decreases with increasing hole diameter under flow conditions and underscores the necessity for future work to examine how hole diameter impacts inflammatory-based shunt obstruction.

Hybrid coaxial electrospun nanofibrous scaffolds with limited immunological response created for tissue engineering

Electrospinning using synthetic and natural polymers is a promising technique for the fabrication of scaffolds for tissue engineering. Numerous synthetic polymers are available to maximize durability and mechanical properties (polyurethane) versus degradability and cell adhesion (polycaprolactone). In this study, we explored the feasibility of creating scaffolds made of bicomponent nanofibers from both polymers using a coaxial electrospinning system. We used a core of poly(urethane) and a sheath of a mixture of poly(ε-caprolactone) and gelatin, all dissolved in 1,1,1,3,3,3-hexafluror-2-propanol. These nanofibrous scaffolds were then evaluated to confirm their core-sheath nature and characterize their morphology and mechanical properties under static and dynamic conditions. Furthermore, the antigenicity of the scaffolds was studied to confirm that there is no significant foreign body response to the scaffold itself that would preclude its use in vivo. The results show the advantages of combining both natural and synethic polymers to create a coaxial scaffold capable of withstanding dynamic culture conditions and encourage cellular migration to the interior of the scaffold for tissue-engineering applications. Also, the results show that there is no significant immunoreactivity in vivo to the components of the scaffolds.

The difference of fibroblast behavior on titanium substrata with different surface characteristics

Connective tissue, one of the main components of peri-implant soft tissue, is key to the formation of the peri-implant mucosal seal and helping to prevent epithelial ingrowth. Rough surfaces (Rs), machined surfaces (Ms) or microgrooved surface (MG) are used in the neck area of commercially available titanium implants. In this paper, we aimed to evaluate the influence of surface topography of titanium substratum on connective tissue fibroblasts to gain a better understanding of this effect. Fibroblasts were cultured on titanium plates with Rs, Ms and MG. Adhesion cell number at day 3 was compared and protein distribution of both F-actin and vinculin was determined to observe cellular structure and adhesion. Cell adhesion strength was compared on each surface. At day 3, the number of fibroblasts attached on each substratum was in the order of MG ≈ Ms > Rs. Fibroblasts strongly expressed vinculin in the peripheral area on Ms and MG, and showed strong F-actin architecture. Decreased expression of vinculin and weaker continuity of F-actin were observed on Rs. Fibroblasts on MG were aligned along the grooves, with a significantly higher cell density, whereas cells on Ms and Rs had no clear orientation. The cell adhesion strength was significantly lower on Rs, and no significant difference was seen between MG and Ms. Both MG and Ms showed greater adhesion cell numbers and adhesion strength of fibroblasts when compared with Rs at day 3. The cell density on MG was greater than those on other substrata.

Biomechanics of the sensor-tissue interface-effects of motion, pressure, and design on sensor performance and the foreign body response-part I: theoretical framework

The importance of biomechanics in glucose sensor function has been largely overlooked. This article is the first part of a two-part review in which we look beyond commonly recognized chemical biocompatibility to explore the biomechanics of the sensor-tissue interface as an important aspect of continuous glucose sensor biocompatibility. Part I provides a theoretical framework to describe how biomechanical factors such as motion and pressure (typically micromotion and micropressure) give rise to interfacial stresses, which affect tissue physiology around a sensor and, in turn, impact sensor performance. Three main contributors to sensor motion and pressure are explored: applied forces, sensor design, and subject/patient considerations. We describe how acute forces can temporarily impact sensor signal and how chronic forces can alter the foreign body response and inflammation around an implanted sensor, and thus impact sensor performance. The importance of sensor design (e.g., size, shape, modulus, texture) and specific implant location on the tissue response are also explored. In Part II: Examples and Application (a sister publication), examples from the literature are reviewed, and the application of biomechanical concepts to sensor design are described. We believe that adding biomechanical strategies to the arsenal of material compositions, surface modifications, drug elution, and other chemical strategies will lead to improvements in sensor biocompatibility and performance.

Sandblasted-acid-etched titanium surface influences in vitro the biological behavior of SaOS-2 human osteoblast-like cells

Osseointegrated dental implants have been successfully used over the past several years, allowing functional replacement of missing teeth. Surface properties of titanium dental implants influence bone cell response. Implant topography appears to modulate cell growth and differentiation of osteoblasts thus affecting the bone healing process. Optimal roughness and superficial morphology are still controversial and need to be clearly defined. In the present study we evaluated in vitro the biological behavior of SaOS-2 cells, a human osteoblast-like cell line, cultured on two different titanium surfaces, smooth and sandblasted-acid-etched, by investigating cell morphology, adhesion, proliferation, expression of some bone differentiation markers and extracellular matrix components. Results showed that the surface topography may influence in vitro the phenotypical expression of human osteoblast-like cells. In particular the tested sandblasted-acid-etched titanium surface induced a significantly increased Co I deposition and α2-β1 receptor expression as compared to the relatively smooth surface, promoting a probable tendency of SaOS-2 cells to shift toward a mature osteoblastic phenotype. It is therefore likely that specific surface properties of sandblasted-acid-etched titanium implants may modulate the biological behavior of osteoblasts during bone tissue healing.

Fabrication and cell affinity of biomimetic structured PLGA/articular cartilage ECM composite scaffold

An ideal scaffold for cartilage tissue engineering should be biomimetic in not only mechanical property and biochemical composition, but also the morphological structure. In this research, we fabricated a composite scaffold with oriented structure to mimic cartilage physiological morphology, where natural nanofibrous articular cartilage extracellular matrix (ACECM) was used to mimic the biochemical composition, and synthetic PLGA was used to enhance the mechanical strength of ACECM. The composite scaffold has well oriented structure and more than 89% of porosity as well as about 107 μm of average pore diameter. The composite scaffold was compared with ACECM and PLGA scaffolds. Cell proliferation test showed that the number of MSCs in ACECM and composite scaffolds was noticeably bigger than that in PLGA scaffold, which was coincident with results of SEM observation and cell viability staining. The water absorption of ACECM and composite scaffolds were 22.1 and 10.2 times respectively, which was much higher than that of PLGA scaffolds (3.8 times). The compressive modulus of composite scaffold in hydrous status was 1.03 MPa, which was near 10 times higher than that of hydrous ACECM scaffold. The aforementioned results suggested that the composite scaffold has the potential for application in cartilage tissue engineering.

Biomaterial topography alters healing in vivo and monocyte/macrophage activation in vitro

The effect of biomaterial topography on healing in vivo and monocyte/macrophage stimulation in vitro was assessed. A series of expanded polytetrafluoroethylene (ePTFE) materials were characterized by increasing average intranodal distance of 1.2 μm (1.2-ePTFE), 3.0 μm (3.0-ePTFE), and 4.4 μm (4.4-ePTFE), but presented consistent surface chemistry with nonporous PTFE (np-PTFE). Subcutaneous implantation of 4.4-ePTFE into mice resulted in a statistically thinner capsule that appeared less organized and less dense than the np-PTFE response. In vitro, isolated monocytes/macrophages cultured on np-PTFE produced low levels of interleukin 1-beta (IL-1β), 1.2-ePTFE and 3.0-ePTFE stimulated intermediate levels, and 4.4-ePTFE stimulated a 15-fold increase over np-PTFE. Analysis of cDNA microarrays demonstrated that additional proinflammatory cytokines and chemokines, including IL-1β, interleukin 6, tumor necrosis factor alpha, monocyte chemotactic protein 1, and macrophage inflammatory protein 1-beta, were expressed at higher levels by monocytes/macrophages cultured on 4.4-ePTFE at 4 and 24 h, respectively. Expression ratios for several genes were quantified by RT-PCR and were consistent with those from the cDNA array results. These results demonstrate the effect of biomaterial topography on early proinflammatory cytokine production and gene transcription by monocytes/macrophages in vitro and decreased fibrous capsule thickness in vivo.

PHBV microspheres--PLGA matrix composite scaffold for bone tissue engineering

Polymer scaffolds, particularly in the form of microspheres, have been employed to support cells growth and deliver drugs or growth factors in tissue engineering. In this study, we have established a scaffold by embedding poly (beta-hydroxybutyrate-co-beta-hydroxyvalerate) (PHBV) microspheres into poly (L-lactic-co-glycolic acid) (PLGA) matrix, according to their different solubility in acetone, with the aim of repairing bone defects. PLGA/PHBV scaffolds had good pore parameters, for example, the porosity of PLGA/30% PHBV scaffold can reach to 81.273 +/- 2.192%. Besides, the pore size distribution of the model was evaluated and the results revealed that the pore size mainly distributed between 50 mum and 200 mum. With increasing the amount of PHBV microspheres, the compressive strength of the PLGA/PHBV scaffold enhanced. The morphology of the hybrid scaffold was rougher than that of pure PLGA scaffold, which had no significant effect on the cell behavior. The in vitro evaluation suggested that the model is suitable as a scaffold for engineering bone tissue, and has the potential for further applications in drug delivery system.

Porous silicon as a potential electrode material in a nerve repair setting: Tissue reactions

We compared porous silicon (pSi) with smooth Si as chip-implant surfaces in a nerve regeneration setting. Silicon chips can be used for recording neural activity and are potential nerve interface devices. A silicon chip with one smooth and one porous side inserted into a tube was used to bridge a 5 mm defect in rat sciatic nerve. Six or 12 weeks later, new nerve structures surrounded by a perineurium-like capsule had formed on each side of the chip. The number of regenerated nerve fibers did not differ on either side of the chip as shown by immunostaining for neurofilaments. However, the capsule that had formed in contact with the chip was significantly thinner on the porous side than on the smooth side. Cellular protrusions had formed on the pSi side and the regenerated nerve tissue was found to attach firmly to this surface, while the tissue was hardly attached to the smooth silicon surface. We conclude that a pSi surface, due to its large surface area, diminished inflammatory response and firm adhesion to the tissue, should be a good material for the development of new implantable electronic nerve devices.

Adhesion formation of primary human osteoblasts and the functional response of mesenchymal stem cells to 330nm deep microgrooves

The surface microtexture of an orthopaedic device can regulate cellular adhesion, a process fundamental in the initiation of osteoinduction and osteogenesis. Advances in fabrication techniques have evolved to include the field of surface modification; in particular, nanotechnology has allowed for the development of experimental nanoscale substrates for investigation into cell nanofeature interactions. Here primary human osteoblasts (HOBs) were cultured on ordered nanoscale groove/ridge arrays fabricated by photolithography. Grooves were 330nm deep and either 10, 25 or 100microm in width. Adhesion subtypes in HOBs were quantified by immunofluorescent microscopy and cell-substrate interactions were investigated via immunocytochemistry with scanning electron microscopy. To further investigate the effects of these substrates on cellular function, 1.7K gene microarray analysis was used to establish gene regulation profiles of mesenchymal stem cells cultured on these nanotopographies. Nanotopographies significantly affected the formation of focal complexes (FXs), focal adhesions (FAs) and supermature adhesions (SMAs). Planar control substrates induced widespread adhesion formation; 100microm wide groove/ridge arrays did not significantly affect adhesion formation yet induced upregulation of genes involved in skeletal development and increased osteospecific function; 25microm wide groove/ridge arrays were associated with a reduction in SMA and an increase in FX formation; and 10microm wide groove/ridge arrays significantly reduced osteoblast adhesion and induced an interplay of up- and downregulation of gene expression. This study indicates that groove/ridge topographies are important modulators of both cellular adhesion and osteospecific function and, critically, that groove/ridge width is important in determining cellular response.

A review of the management of implanted medical devices for diabetes: trends and directions

The management of diabetes is progressing rapidly from the use of traditional finger sticks for glucose monitoring and multiple daily injections of insulin to more user-friendly devices and approaches. These advances hold the promise of freeing persons with diabetes from the need for continued daily compliance, thereby improving their quality of life and improving control of their underlying diabetes. An underlying theme to solutions based on percutaneous or fully implanted devices is that the useful lifetime of such devices is often limited by the body's foreign body response. This review briefly outlines general factors associated with point-in-time needle stick approaches to the growing use of short-term percutaneous implants (< or =7 days) to the challenges of more extended devices, both technical and regulatory, faced by developers of these devices.

Generation of an artificial skin construct containing a non-degradable fiber mesh: a potential transcutaneous interface

Generation of a stable interface between soft tissues and biomaterials could improve the function of transcutaneous prostheses, primarily by minimizing chronic infections. We hypothesized that inclusion of non-biodegradable biomaterials in an artificial skin substrate would improve integration of the neodermis. In the present study, we compared the biocompatibility of an experimental substrate, consisting of collagen and glycosylaminoglycans, with commercially available artificial skin of similar composition. By utilizing a mouse excisional wound model, we found that the source of collagen (bovine tendon versus hide), extent of injury and wound contraction were critical determinants of inflammation and neodermis formation. Reducing the extent of injury to underlying muscle reduced inflammation and improved remodeling; the improved conditions allowed the detection of a pro-inflammatory effect of hide-derived collagen. To eliminate the complication of wound contraction, subsequent grafts were performed in guinea pigs and showed that inclusion of carbon fibers or non-degradable sutures resulted in increased foreign body response (FBR) and altered remodeling. On the other hand, inclusion of a polyester multi-stranded mesh induced a mild FBR and allowed normal neodermis formation. Taken together, our observations suggest that non-degradable biomaterials can be embedded in an artificial skin construct without compromising its ability to induce neodermis formation.

Biocompatibility issues with modern implants in bone - a review for clinical orthopedics

Skeletal defects may result from traumatic, infectious, congenital or neoplastic processes and are considered to be a challenge for reconstructive surgery. Although the autologous bone graft is still the “gold standard”, there is continuing demand for bone substitutes because of associated disadvantages, such as limited supply and potential donor side morbidity [1]. This is not only true for indications in orthopedic and craniomaxillofacial surgeries, but also in repairing endodontic defects and in dental implantology.

Before clinical use all new bone substitute materials have to be validated for their osseoconductive and - depending on the composition of the material also –inductive ability, as well as for their long-term biocompatibility in bone. Serving this purpose various bone healing models to test osteocompatibility and inflammatory potential of a novel material on one hand and, on the other hand, non-healing osseous defects to assess the healing potential of a bone substitute material have been developed. Sometimes the use of more than one implantation site can be helpful to provide a wide range of information about a new material [2].

Important markers for biocompatibility and inflammatory responses are the cell types appearing after the implantation of foreign material. There, especially the role of foreign body giant cells (FBGC) is discussed controversial in the pertinent literature, such that it is not clear whether their presence marks an incompatibility of the biomaterial, or whether it belongs to a normal degradation behavior of modern, resorbable biomaterials.

This publication is highlighting the different views currently existing about the function of FBGC that appear in response to biomaterials at the implantation sites. A short overview of the general classes of biomaterials, where FBGC may appear as cellular response, is added for clarity, but may not be complete.

Surface patterning: tool to modulate stem cell differentiation in an adipose system

There are several issues that need to be better understood before breast tissue-engineering becomes viable clinically. One of the key issues is the interaction between cells and the microtopography of the implant surface. The aim of this study was to evaluate the efficacy of D1 cells, multipotent mouse bone marrow stromal precursors, in differentiating to fat and to characterize their metabolic activity (lactic acid released and glucose consumed) and lipid production when cultured on patterned poly-L-lactide (PLLA) films. It was determined that, with appropriate stimulation, the D1 cells displayed morphological characteristics of adipocytes and produced lipid. The results show that the patterned surfaces did affect the rate of lipid production. Polynomial models were proposed to predict the metabolic activity of the cells over a period of time.

Poly(butyl methacrylate-co-methacrylic acid) tissue engineering scaffold with pro-angiogenic potential in vivo

A poly(butyl methacrylate-co-methacrylic acid) (BMA-MAA) scaffold was fabricated by an in situ polymerization solvent casting/particulate leaching technique. It displayed high porosity (85-90%), pore interconnectivity, and a pore size range of 100-650 microm. Compression testing of the scaffolds demonstrated a dependence of the compressive stiffness on several fabrication variables including the ratio of monomer to salt used during the polymerization, the degree of salt fusion, and the choice of alternative comonomers to BMA. Subcutaneous implantation of BMA-MAA scaffolds in mice revealed an increased level of histological angiogenesis in tissue invading the pores of the scaffold compared to a BMA control, consistent with the prediction that methacrylic acid (MAA) containing copolymer beads are angiogenic in a wound healing context. At postoperative day 21, the capillary density in the BMA-MAA scaffolds was 56 +/- 13/mm(2) as compared to 32 +/- 8/mm(2) for the BMA scaffolds. With further investigation, it is expected that this biomaterial capable of eliciting an angiogenic response will have widespread application in tissue engineering.

Effects of sterilization on implant mechanical property and biocompatibility

This article concisely reviews the effects of sterilization on the mechanical properties and surface chemistries of implantable biomaterials. This article also summarizes the biological effects of the sterilization-related changes in the implant. Because there are so many different types of implant materials currently in use (including metals, polymers, and diverse biological materials), the response of tissue to these different materials varies dramatically. This review further discusses the effects of sterilization on in vivo and in vitro tissue response specifically to implantable metals and polyethylene, with the possibility of future biocompatibility testing of the implants sterilized with supercritical phase carbon dioxide sterilization.

Adhesion and proliferation of OCT-1 osteoblast-like cells on micro- and nano-scale topography structured poly(l-lactide)

The impact of the surface topography of polylactone-type polymer on cell adhesion was to be concerned because the micro-scale texture of a surface can provide a significant effect on the adhesion behavior of cells on the surface. Especially for the application of tissue engineering scaffold, the pore size could have an influence on cell in-growth and subsequent proliferation. Micro-fabrication technology was used to generate specific topography to investigate the relationship between the cells and surface. In this study the pits-patterned surfaces of polystyrene (PS) film with diameters 2.2 and 0.45 microm were prepared by phase-separation, and the corresponding scale islands-patterned PLLA surface was prepared by a molding technique using the pits-patterned PS as a template. The adhesion and proliferation behavior of OCT-1 osteoblast-like cells morphology on the pits- and islands-patterned surface were characterized by SEM observation, cell attachment efficiency measurement and MTT assay. The results showed that the cell adhesion could be enhanced on PLLA and PS surface with nano-scale and micro-scale roughness compared to the smooth surfaces of the PLLA and PS. The OCT-1 osteoblast-like cells could grow along the surface with two different size islands of PLLA and grow inside the micro-scale pits of the PS. However, the proliferation of cells on the micro- and nano-scale patterned surface has not been enhanced compared with the controlled smooth surface.

Electrospun nano- to microfiber fabrics made of biodegradable copolyesters: structural characteristics, mechanical properties and cell adhesion potential

Nano- to micro-structured biodegradable poly(L-lactide-co-epsilon-caprolactone) (PLCL) fabrics were prepared by electrospinning. Electrospun microfiber fabrics with different compositions of PLCL (mol% in feed; 70/30, 50/50, and 30/70), poly(L-lactide) (PLL) and poly(epsilon-caprolactone) (PCL) were obtained using methylene chloride (MC) as a solvent. The PLL microfiber exhibited a nanoscale-pore structure with a pore diameter of approximately 200-800 nm at the surface and subsurface regions, whereas such a surface structure was hardly observed in other polymers containing CL. The microfiber fabric made of PLCL 50/50 was elastomeric. Nanoscale-fiber fabrics with PLCL 50/50 (approx. 0.3 or 1.2 microm in diameter) were electrospun using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a solvent. Mercury porosimetry showed that the decrease in the fiber diameter of the fabric decreased porosity, but increased fiber density and mechanical strength. Human umbilical vein endothelial cells (HUVECs) were adhered well and proliferated on the small-diameter-fiber fabrics (0.3 and 1.2 microm in diameter), both of which are dense fabrics, whereas markedly reduced cell adhesion, restricted cell spreading and no signs of proliferation were observed on the large-diameter-fiber fabric (7.0 microm in diameter). The potential biomedical application of electrospun PLCL 50/50 was discussed.

The response of healing corneal epithelium to grooved polymer surfaces

Corneal epithelial wounds heal rapidly by the inwards growth of tissue with a contracting wound front. A synthetic polymer lens to correct refractive error (an implantable contact lens) could be incorporated into the cornea using this wound healing process. Topographical cues on the polymer surface may facilitate epithelial tissue migration over the anterior device surface. Here, silicone discs with a defined surface geometry of parallel grooves (groove and ridge widths of 1, 2, 5 and 10 microm; groove depths of 1 and 5 microm) were implanted into corneas and maintained in organ culture. The nature and rate of epithelial tissue migration over the test surfaces was monitored for 8 days and evaluated using microscopy and histology. Irrespective of the pitch, deep groove geometries directed tissue migration laterally along the grooves but this prevented contraction of the wound front and retarded migration rates. No guidance occurred on any of the shallow groove geometries but these allowed inwards radial migration with a contracting wound front and supported migration rates equivalent to a flat surface. None of the geometries tested promoted tissue migration above a flat polymer surface and data suggested that parallel grooves may not be optimal for this application.

Effects of the chemical structure and the surface properties of polymeric biomaterials on their biocompatibility

Polymeric biomaterials have extensively been used in medicinal applications. However, factors that determine their biocompatibility are still not very clear. This article reviews various effects of the chemical structure and the surface properties of polymeric biomaterials on their biocompatibility, including protein adsorption, cell adhesion, cytotoxicity, blood compatibility, and tissue compatibility. Understanding these aspects of biocompatibility is important to the improvement of the biocompatibility of existing polymers and the design of new biocompatible polymers.

Model porous surfaces for systematic studies of material-cell interactions

A model system for studying cell-surface interactions, based on microfabricated cell culture substrates, has been developed and is described here. Porous surfaces consisting of interconnecting channels with openings of subcellular dimensions are generated on flat, single crystal, silicon substrates. Channel size (width, depth), distribution, and surface coating can be varied independently and used for systematic investigation of how topographical, chemical, and elastic surface properties influence cell or tissue biological responses. Model porous surfaces have been produced by using two different microfabrication methods. Submicron-sized channels with very high depth-to-width aspect ratios (up to 30) have been made by using electron beam lithography and anisotropic reactive ion etching into single-crystal silicon. Another method uses thick-resist photolithography, which can be used to produce channels wider than 1 microm and with depth-to-width aspect ratios below 20 in an epoxy polymer. Preliminary cell culture tests show that fibroblasts bridge 0.8- to 1.8-microm-wide channels with very few exceptions (i.e., a continuous space below the cell-surface interface is created). It has also been shown that variation of channel periodicity significantly affects fibroblast morphology and attachment density. With this model system, it is possible to load the channels with bioactive substances intended to interact with cells at or near the surface in a time-dependent manner.

Pore size in implanted polypropylene filters is critical for tissue organization

Widely different implant materials induce surprisingly similar tissue reactions in vivo in contrast to their in vitro responses. Increasing attention has recently been given to the surface texture of the material. When both the material composition and the surface topography are varied, the surface topography seems to be the predominant factor for the induced tissue response. The present study addresses differences in the tissue response to commercially available Millipore mesh filters of polypropylene with pore sizes of 0.6, 10.0 or 30.0 microm. The Millipore filters with adjacent tissue were directly sectioned in a cryostat and evaluated via an immunofluorescence technique with double and triple staining, allowing simultaneous analysis of different antigens in tissue sections. These results show that macrophages, total cells, necrotic cells, nitric oxygen distribution, early angiogenesis, and capsule thickness were influenced by the surface structure. Implants with pore sizes of 0.6 microm, where entrance of inflammatory cells was inhibited, induce the most pronounced foreign body capsule formation. The 10- and 30-microm filters, in contrast, had large amounts of macrophages inside the filter structure, although very few inflammatory cells were found outside the filters. The inflammatory cells within the filters appeared not to influence the foreign body capsule induction. The critical factor for the formation of a foreign body capsule seems to be the localization of implant-close macrophages. Whether this is due to differences in cell activation or in signal transduction to collagen-synthesizing fibroblasts remains an open question.

Application of magnetic resonance microscopy to tissue engineering: a polylactide model

Absorbable polymers are unique materials that find application as temporary scaffolds in tissue engineering. They are often extremely sensitive to histological processing and, for this reason, studying fragile, tissue-engineered constructs before implantation can be quite difficult. This research investigates the use of noninvasive imaging using magnetic resonance microscopy (MRM) as a tool to enhance the assessment of these cellular constructs. A series of cellular, polylactide constructs was developed and analyzed using a battery of tests, including MRM. Distribution of rat aortic smooth muscle cells within the scaffolds was compared as one example of a tissue engineering MRM application. Cells were loaded in varying amounts using static and dynamic methods. It was found that the cellular component was readily identified and the polymer microstructure readily assessed. Specifically, the MRM results showed a heterogeneous distribution of cells due to static loading and a homogenous distribution associated with dynamic loading, results that were not visible through biochemical tests, scanning electron microscopy, or histological evaluation independently. MRM also allowed differentiation between different levels of cellular loading. The current state of MRM is such that it is extremely useful in the refinement of polymer processing and cell seeding methods. This method has the potential, with technological advances, to be of future use in the characterization of cell-polymer interactions.

The effect of bone anchoring and micro-grooves on the soft tissue reaction to implants

Here we aimed to compare the tissue reaction to smooth and micro-grooved implants, at different implantation sites. We hypothesised that subperiosteally less mobility is to be expected between an implant and the surrounding tissue, which can lead to a more subdued tissue response. In addition, we hypothesised that a similar effect can be reached when substrata are equipped with micro-grooves. Poly-L-lactic acid smooth or micro-grooved surfaces (width 2 or 10 microm, depth 1 microm) were implanted subperiosteally on the frontal bone of the skull, or subcutaneously in the flanks of goats for 2, 4 and 12 weeks. After sacrifice, implants and surrounding tissue were histologically processed. Light microscopical and histomorphometrical evaluation of the histomorphometrical analyses, capsule thickness, capsule quality and implant-tissue interface was performed. In addition, we stained for alpha-smooth muscle actin. collagen and CD-68 expression. All implants were surrounded by a fibrous capsule. Capsules around subperiosteal implants were more matured than around subcutaneous implants. In time, capsule thickness significantly decreased around subperiosteal implants, but increased around subcutaneous implants. Also, nowhere differences were found in the presence of collagen or alpha-smooth muscle actin. The interfacial cells around all implants frequently showed staining for the monocyte-macrophage marker CD-68. We concluded that in this model, decreased mobility of an implant relative to the surrounding tissue did positively influence the peri-implant tissue response, but the applied surface topography did not.

Soft-tissue response to silicone and poly-L-lactic acid implants with a periodic or random surface micropattern

Tissue reaction to biomaterials is dependent on properties such as surface topography. The aim of this study was to evaluate the tissue reaction around implants with different surface topographies. We made coin-shaped silicone and poly-L-lactic acid (PLLA) implants with double-sided parallel microgrooves (depth 1.0 microm; width 10.0 microm) and random roughness on a micrometer scale. The control implants were smooth. These implants were inserted into subcutaneous pockets created on the flanks of goats. After 1, 3, or 12 weeks, the goats were sacrificed and the implants retrieved and histologically processed. Light microscopic evaluation revealed the formation of fibrous tissue capsules around all implant materials. The PLLA did not visibly degrade during the study period. Histomorphometric analyses were performed on capsule thickness, capsule quality, and on the implant-tissue interface quality. Compared with the silicone implants, the capsules around the PLLA implants showed significantly better capsule quality. Compared to the smooth implants, the capsules around the microgrooved implants were thicker, but the capsules around the roughened implants were thinner. However, randomly roughened implant surfaces generally elicited a stronger and more prolonged inflammatory reaction compared to smooth and microgrooved implant surfaces. We conclude that the application of microgrooves or random surface roughness to polymer implants apparently does not have beneficial effects on peri-implant tissue healing.

Tissue response to single-polymer fibers of varying diameters: evaluation of fibrous encapsulation and macrophage density

An in vivo study was conducted to assess the sensitivity of fibrous capsule thickness and macrophage density to polymer fiber diameter. Single polypropylene fibers of diameters ranging from 2.1 to 26.7 microm were implanted in the subcutaneous dorsum of Sprague-Dawley rats. Results at 5 weeks demonstrated reduced fibrous capsule thickness for small fibers. Capsule thickness was 0.6 (+/-1.8) microm, 11.7 (+/-12.0) microm, 20.3 (+/-11.6) microm, and 25.5 (+/-10.0) microm for fibers in the ranges of 2.1 to 5.9, 6.5 to 10.6, 11.1 to 15.8, and 16.7 to 26.7 microm, respectively. Fibers very near to blood vessels had smaller capsules than did those with local vasculature further away. The macrophage density in tissue with fiber diameters 2.1 to 5.9 microm (23.03 +/- 8.67%) was comparable to that of unoperated contralateral control skin (18.72+/-10.06%). For fibers with diameters in the ranges of 6.5 to 10.6, 11.1 to 15.8, and 16.7 to 26.7 microm, macrophage densities were 33.90+/-13.08%, 34.40+/-15.77%, and 41.68+/-13.98%, respectively, all of which were significantly larger (p<0.002) than that for the control. The reduced fibrous capsule thickness and macrophage density for small fibers (<6 microm) compared with large fibers could be due to the reduced cell-material contact surface area or to a curvature threshold effect that triggers cell signaling. A next step will be to extend the analysis to meshes to evaluate fiber-spacing effects on small-fiber biomaterials.