Soft tissue reaction to microgrooved poly-L-lactic acid implants loaded with transforming growth factor beta(3)

The inflammatory cell influx and cytokines changes during transition from acute inflammation to fibrous repair around implanted materials

The inflammatory and fibrous responses in a subcutaneous rat model were evaluated around degradable polyurethane urea (PUUR; Artelon), with titanium and tissue culture polystyrene (PS) discs having different surface chemical properties but similar surface topography. Cytokines, viability, cellular response, differentiation of cells and fibrous capsule formation and vascularization was investigated after 1, 7 and 21 days of implantation. The exudates retrieved from the pockets were analysed with respect to the total cell numbers, the proportions of cell types, the differentiation of monocytes/macrophages (ED1, ED2), the DNA content and the viability (LD, Trypan blue). Tumour necrosis factor alpha ((h)TNF-alpha) and interleukin-10 ((h)IL-10) were quantified by ELISA. The number of blood vessels, blood vessel luminal area, blood vessel distribution and the fibrous capsule thickness were analysed. The highest number of cells in the exudates around all implants was detected during the early phase of healing (1-7 days). The proportion of ED2-positive cells in the exudates increased from 2-8% at 1 day to 43-56% at 21 days. The levels of TNF-alpha were low with a decrease at 7 days. After 21 days high amounts of IL-10 in the exudates were detected, in particular around PUUR. This study shows that the transition from inflammation to repair (1-21 days) around PUUR, Ti and PS materials was characterized by a decrease in inflammatory cell influx, an increasing proportion of ED2-expressing macrophages, a biphasic TNF-alpha secretion, an increase of IL-10 and a fibrous capsule formation similar to all materials tested.

Connective-tissue responses to defined biomaterial surfaces. I. Growth of rat fibroblast and bone marrow cell colonies on microgrooved substrates

Surface microgeometry plays a role in tissue-implant surface interactions, but our understanding of its effects is incomplete. Substrate microgrooves strongly influence cells in vitro, as evidenced by contact guidance and cell alignment. We studied "dot" colonies of primary fibroblasts and bone marrow cells that were grown on titanium-coated, microgrooved polystyrene surfaces that we designed and produced. Rat tendon fibroblast and rat bone marrow colony growth and migration varied (p < 0.01) by microgroove dimension and slightly by cell type. We observed profoundly altered morphologies, reduced growth rates, and directional growth in colonies grown on microgrooved substrates, when compared with colonies grown on flat, control surfaces (p < 0.01). The cells in our colonies grown on microgrooved surfaces were well aligned and elongated in the direction parallel to the grooves and colonies. Our "dot" colony is an easily reproduced, easily measured and artificial explant model of tissue-implant interactions that better approximates in vivo implant responses than culturing isolated cells on biomaterials. Our results correlate well with in vivo studies of titanium dioxide-coated polystyrene, titanium, and titanium alloy implants with controlled microgeometries. Microgrooves and other surface features appear to directionally or spatially organize cells and matrix molecules in ways that contribute to improved stabilization and osseointegration of implants.

In vitro and in vivo effects of deoxyribonucleic acid-based coatings funtionalized with vascular endothelial growth factor

Vascularization is important in wound healing and essential for tissue ingrowth into porous tissue-engineering matrices. Furthermore, peri-implant tissue vascularization is known to be important for the functionality of subcutaneously implanted biosensors (e.g., glucose sensors). As a first exploration of the use of deoxyribonucleic acid (DNA)-based coatings for the optimization of biosensor functionality, this study focused on the effect of DNA-based coatings functionalized with vascular endothelial growth factor (VEGF) on in vitro endothelial cell behavior and vascularization of the peri-implant tissue in vivo. To that end, DNA-based coatings consisting of poly-D-lysine and DNA were functionalized with different amounts of VEGF (25 and 250 ng) and compared to non-coated controls and non-functionalized DNA-based coatings. The results demonstrated the superiority of VEGF-functionalized DNA-based coatings in increasing endothelial cell proliferation and migration in vitro over non-coated controls and non-functionalized DNA-based coatings. In vivo, a significant increase in vascularization of the peri-implant area was observed for VEGF-functionalized DNA-based coatings. Because no dosage-dependent effects were observed, future experiments should focus on optimizing VEGF concentration for this purpose. Additionally, the administration of VEGF in combination with other (pro-angiogenic) factors should be considered.

Stereological methods to assess tissue response for tissue-engineered scaffolds

The stereological approach can provide an objective unbiased assessment of structural change in biological systems. In this review, we elucidate the basic principles of stereology and their implementation in the analysis of tissue response to tissue-engineering scaffolds. A brief outline of tissue response parameters that can be estimated using stereological approach is included. The focus is on frequently quantified parameters in tissue response, such as host tissue infiltration, inflammatory cell numbers, angiogenesis, fibrous tissue thickness, areas of calcification, and/or necrosis, among others. Special consideration is given to sampling techniques and how these techniques can influence the reliability of the obtained results as well as minimizing potential sources of bias. These basic principles are illustrated with practical examples, where measurements are performed and estimations calculated using conventional stereological techniques. As the next generation of biomaterials continue to be developed, it is essential that researchers develop a rigorous and unbiased method of performance quantification.

AnIn Vivo Study of the Host Response to Starch-Based Polymers and Composites Subcutaneously Implanted in Rats

Implant failure is one of the major concerns in the biomaterials field. Several factors have been related to the fail but in general these biomaterials do not exhibit comparable physical, chemical or biological properties to natural tissues and ultimately, these devices can lead to chronic inflammation and foreign-body reactions. Starch-based biodegradable materials and composites have shown promising properties for a wide range of biomedical applications as well as a reduced capacity to elicit a strong reaction from immune system cells in vitro. In this work, blends of corn starch with ethylene vinyl alcohol (SEVA-C), cellulose acetate (SCA) and polycaprolactone (SPCL), as well as hydroxyapatite (HA) reinforced starch-based composites, were investigated in vivo. The aim of the work was to assess the host response evoked for starch-based biomaterials, identifying the presence of key cell types. The tissues surrounding the implant were harvested together with the material and processed histologically for evaluation using immunohistochemistry. At implant retrieval there was no cellular exudate around the implants and no macroscopic signs of an inflammatory reaction in any of the animals. The histological analysis of the sectioned interface tissue after immunohistochemical staining using ED1, ED2, CD54, MHC class II and alpha/beta antibodies showed positively stained cells for all antibodies, except for alpha/beta for all the implantation periods, where it was different for the various polymers and for the period of implantation. SPCL and SCA composites were the materials that stimulated the greatest cellular tissue responses, but generally biodegradable starch-based materials did not induce a severe reaction for the studied implantation times, which contrasts with other types of degradable polymeric biomaterials.

Transforming growth factor-beta3-loaded microtextured membranes for skin regeneration in dermal wounds

Adverse effects of wound healing, such as excessive scar tissue formation, wound contraction, or nonhealing wounds represent a major clinical issue in today's healthcare. Transforming growth factor (TGF)-beta3 has specifically been implicated in wound healing. Our hypothesis was that local administration of TGF-beta3 to excisional dermal wounds would diminish wound contraction and scar formation. Microtextured wound covers, containing different concentrations of TGF-beta3, were placed onto full-thickness excisional skin wounds in guinea pigs. Tattooed reference marks were used to quantify wound contraction. Sixty-four male guinea pigs in four study groups (5 ng TGF-beta3, 50 ng TGF-beta3, no growth factor, sham wound) were followed for up to 6 weeks. We analyzed 19 different parameters of wound healing. Results showed that, in some instances, the 50-ng TGF-beta3 group gave less contraction, whereas the 5-ng TGF-beta3 group gave more contraction. These differences confirm that TGF-beta3 has an optimum working concentration, and suggest this concentration to be closer to 50 ng than to 5 ng TGF-beta3. However, only very few significant differences occurred, and thus we conclude that the clinical relevance of our findings is negligible. Earlier studies, reporting clinically improved wound healing by TGF-beta3, could therefore not be confirmed by this study.

The effect of seprafilm and interceed on capsule formation around silicone discs in a rat model

The insertion of a foreign substance, such as a breast implant into mammalian soft tissues, evokes a wound healing response that culminates in a dense connective-tissue envelope or capsule surrounding the implant. Several biodegradable products, such as Seprafilm (carboxymethylcellulose and hyaluronic acid) and Interceed (oxidized regenerated cellulose), have been demonstrated to inhibit adhesions in abdominal and gynecologic surgery. The ability of these cellulose compounds to inhibit capsule formation was addressed in this investigation. Twenty-eight rats were implanted intermuscularly with either plain silicone discs (10 animals), discs wrapped in Seprafilm (10 animals), or discs covered with Interceed (8 animals). Additional control animals (6 animals) consisted of two that had sham operations, two animals implanted with Seprafilm only, and two more implanted with Interceed only. Animals were sacrificed in pairs at varying time intervals after implantation (2, 4, 8, 12, and 16 wk), and the tissues around the silicone discs were analyzed with light microscopy. Control animals were sacrificed at 8 wk. Both Interceed and Seprafilm slowed the formation of a capsule around the implanted silicone discs as both products were degraded. Evidence of residual material, presumably Seprafilm and Interceed, was seen intracellularly in animals 3 to 4 mo, respectively, after implantation. However, neither material prevented the eventual formation of a fibrous capsule around the silicone discs. The results of this study suggest that encapsulating foreign substances with these types of biodegradable materials will not significantly hinder capsule formation. A more direct attack on the wound healing mechanism may provide a definitive solution for capsule problems with implanted materials.