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

Abstract

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.

Figure 1

Scanning electron micrographs demonstrating topography of PTFE materials. (a) Nonporous PTFE (np-PTFE), and ePTFE materials with average intranodal distances of (b) 1.2 µm (1.2-ePTFE), (c) 3.0 µm (3.0-ePTFE), and (d) 4.4 µm (4.4-ePTFE). Distance measurements outlined in Table II are indicated in (d), internodal distance indicated between black arrows (measured at 1000×), intranodal distance between white arrows (measured at 1000×), and interfiber distance at point of black and white arrow head (measured at 3000×). Magnification 1000×, scale bar = 10 µm.

Figure 2

Dermal areas from mice containing PTFE materials implanted subcutaneously for 4 weeks were removed, processed for histology and stained with hematoxylin and eosin. In each panel, the designation material indicates (a) np-PTFE, (b) 1.2-ePTFE, (c) 3.0-ePTFE and (d) 4.4-ePTFE. The 4.4-ePTFE provided pores sufficient in size for some cellular invasion (examples designated with arrows). Scale bar = 10 µm.

Figure 3

Capsule thickness surrounding PTFE materials implanted subcutaneously for 4 weeks in mice that were removed, processed for histology, and stained with Masson’s trichrome. Average ± sem collected from 5 implants of np-PTFE and 4 implants of 4.4-ePTFE, * denotes p<0.01 in comparison with np-PTFE.

Figure 4

MC/MO production of IL-1β in response to TCPS, np-PTFE and a series of porous ePTFE materials expressed as IL-1β concentration for total cell number per well. Average ± sem, n = 4 donors; * denotes p<0.001 in comparison with np-PTFE.