Engineering the tissue which encapsulates subcutaneous implants. III. Effective tissue response times

Abstract

The results of two previous studies have shown that implant porosity can be used to increase both the measured diffusion coefficients and the vascularity within the tissue encapsulating long-term subcutaneous implants. This study investigates the hypothesis that the analyte concentrations within the tissue surrounding porous implants will respond more quickly to changes in plasma levels than does the densely packed, avascular fibrous capsule surrounding nonporous implants. The average concentration of lissamine-rhodamine was measured in tissue within 100 microm of the following implants at four different times following injection of the tracer: PVA-skin, PVA-5, PVA-60, PVA-700 (polyvinyl alcohol nonporous, 5 microm, 60 microm, and 700 microm mean pore sizes, respectively) and PTFE-0.5 and PTFE-5 (polytetrafluoroethylene 0.5 microm and 5 microm mean pore sizes, respectively). The results were compared to those of unimplanted subcutaneous tissue (SQ). In addition, the data were analyzed with a simple two-compartment model in which a tissue response time constant (taup) was extracted. As in the case of vascular density, the cellular dimension of the PVA-60 pore sizes produced surrounding tissue with the optimum response times to changes in plasma concentrations. The concentrations of rhodamine within the tissue surrounding the PVA-60 implant were the highest at all time points and responded to the change in plasma rhodamine concentration approximately three times more quickly (taup = 764 s) than the fibrous tissue encapsulating the nonporous PVA-skin (taup = 2058 s) and more than twice as quickly as SQ (taup = 1627 s). The overall mass transfer rate between plasma and the tissue surrounding the different implants calculated from the permeability and density of vessels from the previous study correlated very well (r2 = 0.7, p < .02, slope of 0.98) with the reciprocal of the tissue response time constant (taup).

Induction of angiogenesis in tissue-engineered scaffolds designed for bone repair: A combined gene therapy–cell transplantation approach

“…The primary function of vasculature is to facilitate the transport of nutrients and oxygen to cells invading from the host tissue and cells transplanted in the scaffolds. Accordingly, insufficient neovascularization is demonstrated to result in the formation of fibrous capsule surrounding implants and prevention of biochemical transport into their interior (5,6). Despite its critical role, blood vessel invasion from the host tissue is limited to a depth of several hundred micrometers from the surface of the implant (7,8).…”

In VitroFluid Dynamics of the Ahmed Glaucoma Valve Modified with Expanded Polytetrafluoroethylene

“…11,16 Previous work has well established that a fibrous capsule impedes mass transport of fluid to and from implanted devices. [17][18][19] Though the preponderance of groups report no relative improvement in IOP control when using antimetabolites during GDD implantation, [20][21][22][23][24] another study employed both postoperative and extended duration (mean 7.3-7.4 min) intraoperative antimetabolite usage in conjunction with GDD implantation. This group demonstrated improved long-term IOP control rates, possibly through retardation of fibrotic capsule formation.…”

“…Certain materials with defined porous microstructure are known to induce a vascular encapsulation response when implanted. 18,19,26 Combining these materials with a GDD to promote formation of a disorganized, highly vascular tissue adjacent to the implant instead of the usual dense capsule may be a novel way to improve long-term IOP control. Expanded ePTFE is one such material that alters foreign body tissue response when implanted.…”

Blood Glucose Self-Monitoring with a Long-Term Subconjunctival Glucose Sensor

“…Several attempts to overcome FBR are discussed in the literature, e.g., specially designed surface architectures and biocompatible or drug-eluting surface coatings. [28][29][30][31][32][33][34][35] This article provides in vivo data from a clinical trial of the EyeSense subconjunctival glucose monitoring system (SGMS) with a biocompatible surface coating, designed to minimize protein-surface interaction, to prolong the duration of action of the system.…”