In vivo testing of crosslinked polyethers. II. Weight loss, IR analysis, and swelling behavior after implantation

As reported in Part I (In vivo testing of crosslinked polyethers. I. Tissue reactions and biodegradation, J. Biomed. Mater. Res., this issue, pp. 307-320), microscopical evaluation after implantation of crosslinked (co)polyethers in rats showed differences in the rate of biodegradation, depending on the presence of tertiary hydrogen atoms in the main chain and the hydrophilicity of the polyether system. In this article (Part II) the biostability will be discussed in terms of weight loss, the swelling behavior, and changes in the chemical structure of the crosslinked polyethers after implantation. The biostability increased in the order poly(POx) < poly(THF-co-OX) < poly(THF) for the relatively hydrophobic polyethers. This confirmed our hypothesis that the absence of tertiary hydrogen atoms would improve the biostability. On the other hand, signs of biodegradation were observed for all polyether system studied. Infrared surface analysis showed that biodegradation was triggered by oxidative attack on the polymeric chain, leading to the formation of carboxylic ester and acid groups. It also was found that in the THF-based (co)polyethers, α-methylene groups were more sensitive than β-methylene groups. For a hydrophilic poly(THF)/PEO blend, an increase in surface PEO content was found, which might be due to preferential degradation of the PEO domains

Forced oscillation assessment of respiratory mechanics in ventilated patients

The forced oscillation technique (FOT) is a method for non-invasively assessing respiratory mechanics that is applicable both in paralysed and non-paralysed patients. As the FOT requires a minimal modification of the conventional ventilation setting and does not interfere with the ventilation protocol, the technique is potentially useful to monitor patient mechanics during invasive and noninvasive ventilation. FOT allows the assessment of the respiratory system linearity by measuring resistance and reactance at different lung volumes or end-expiratory pressures. Moreover, FOT allows the physician to track the changes in patient mechanics along the ventilation cycle. Applying FOT at different frequencies may allow the physician to interpret patient mechanics in terms of models with pathophysiological interest. The current methodological and technical experience make possible the implementation of portable and compact computerised FOT systems specifically addressed to its application in the mechanical ventilation setting

Myoblast seeding in a collagen matrix evaluated in vitro

Collagens may be used as biomaterials for soft tissue reconstruction, e.g., the abdominal wall. We previously developed a biocompatible dermal sheep collagen (DSC), which in an abdominal wall reconstruction model showed controlled biodegradation and functioned as a matrix for ingrowth of fibroblasts but not of muscle. It was hypothesized that regeneration of muscle via DSC may be possible by seeding of muscle cells. Using a syringe, mouse C2C12 myoblasts were seeded in DSC disks and incubated in methylcellulose-based growth medium, changed at 24 h into differentiation medium. An estimated 85% of the cells were well distributed, especially in the top half of the DSC disks. Some 15% of the cells ended up on top. At 4 h, all cells showed a spherical morphology, sometimes with clear adhesion plaques. At 24 h, cells on the top started to form a ''capsule'' with well-spread cells. Underneath the capsule, of the remaining 85% of the cells, approximately 30% showed adhesion and spreading on/in between collagen bundles. At day 3 after the addition of differentiation medium, the spread cells showed first indications of myotube formation. At day 7, myotube formation had proceeded, while extracellular matrix, i.e., collagen and elastin, had been deposited. This study shows that myoblast seeding into DSC is feasible, resulting in a reasonable cell distribution and survival of 45% of the cells. The surviving cells are able to differentiate into myotubes and form an extracellular matrix. (C) 1996 John Wiley & Sons, Inc

Regeneration of full‐thickness wounds using collagen split grafts

Collagen-based skin substitutes are among the most promising materials to improve regeneration of full-thickness wounds. However, additional meshed grafts or cultured epidermal grafts are still required to create epidermal regeneration. To avoid this, we substituted collagen-based split grafts, i.e., grafts with a separated top and bottom layer, in a rat full-thickness wound model and compared regeneration with nontreated, open control wounds. We hypothesized that epidermal regeneration would occur in the split in between the two layers, with the top layer functioning as a clot/scab and the bottom layer as a dermal substitute. Two types of dermal sheep collagen (DSC) split grafts were tested: one with a top layer of noncrosslinked DSC (NDSC) and bottom layer of hexamethylenediisocyanate crosslinked DSC (HDSC), further called N/HDSC; and the second with both a top and bottom layer of HDSC (H/HDSC). With the N/HDSC split graft NDSC did not function as a sponge for formed exudate and as a consequence the split was no longer available to facilitate epidermal regeneration. In contrast, with the H/HDSC graft the split facilitated proliferation and differentiation of the epidermal cells in the proper way. With this graft, clot formation was restricted to the top layer, which was rejected after 8 weeks, while the bottom layer functioned during gradual degradation as a temporary matrix for the formation of autologous dermal tissue. H/HDSC strongly inhibited infiltration of myofibroblasts, resulting in a 30% wound contraction, while a 100% contraction was found with the open control wound. The results show that H/HDSC split-grafts function conforms to the hypothesis in regeneration of large, full-thickness wounds without further addition of seeded cells or use of meshed autografts. (C) 1995 John Wiley & Sons, Inc

CYTOTOXICITY TESTING OF WOUND DRESSINGS USING METHYLCELLULOSE CELL-CULTURE

Wound dressings may induce cytotoxic effects. In this study, we check several, mostly commercially available, wound dressings for cytotoxicity. We used our previously described, newly developed and highly sensitive 7 d methylcellulose cell culture with fibroblasts as the test system. Cytotoxicity is assessed by monitoring cell growth inhibition, supported by cell morphological evaluation using light and transmission electron microscopy. We tested conventional wound dressings, polyurethane-based films, composites, hydrocolloids and a collagen-based dressing. It was shown that only 5 out of 16 wound dressings did not induce cytotoxic effects. All 5 hydrocolloids were found to inhibit cell growth (> 70%), while cells had strongly deviant morphologies. The remaining wound dressings showed medium cytotoxic effects, with cell growth inhibition, which varied from low (+/- 15%), medium-low (+/- 25%) to medium-high (+/- 50%). Measurable cytotoxic effects of dressings detected in vitro are likely to interfere with wound healing when applied in vivo. The results are discussed in view of the clinical uses with contaminated wounds, impaired epithelialization or hypergranulation