PubMed · 14232234
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D M FREEMAN. 1965. FACING REPLACEMENT.. https://pubmed.ncbi.nlm.nih.gov/14232234/
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The local tissue response of the biomaterial is the most important criteria for determination of its biocompatibility. In the present study, full and semi-interpenetrating polymer networks (IPN) based on polyacrylic acid (AAc) and gelatin (Ge) crosslinked with 0.5 mol % N,N'-methylene bisacrylamide (BAm) and 4% glutaraldehyde (GA), respectively, were evaluated for tissue response in rats. IPNs with varying ratios of AAc and Ge were implanted subcutaneously in rats. Gentamicin sulfate (GS)-loaded IPN samples were also studied to evaluate the possible therapeutic use of these polymers. The site of implantation was biopsied and processed for light microscopy (LM) with image analysis for assessment of tissue reaction at 2-, 6-, and 12-week intervals. The tissue reaction was evaluated as a function of composition and time. The degree of neutrophil, lymphocyte and macrophage infiltration, fibrosis, granuloma formation, integration with extracellular matrix, vascular proliferation, and damage of adjacent structures were assessed. Polymers with >66% crosslinked Ge (Gx) showed persistence of acute inflammatory reaction till 3 months, with marked tissue injury and fibrosis. On the other hand, high crosslinked AAc (Ax) content showed chronic inflammatory reaction with high macrophage infiltration. Macrophages took active part in phagocytosis, degradation, and removal of polymers without granuloma formation or significant giant cell reaction. The IPNs with acrylic acid and gelatin in the ratio of 1:1 showed least tissue reaction and thus appeared to be most biocompatible. The majority of the polymers showed integration with extracellular matrix and growth of capillaries in and around the polymer. The heamogram, liver and renal function tests, and histology of vital organs were all normal. GS loading showed no additional local or systemic reaction suggesting the potential usefulness of the hydrogels as carrier for drugs such as GS.
Polymeric micelles are emerging as attractive drug delivery systems. Hydrophobic drugs including photosensitizers for photodynamic therapy can be covalently bound or physically entrapped in the core of the micelles and thus be systemically delivered to, for example, tumors using passive or active targeting strategies. Polymers used for photosensitizer encapsulation include pluronics, poly(ethylene glycol) (PEG)-lipid conjugates, and pH-sensitive poly(N-isopropylacrylamide) based micelles or polyion complex (PIC) micelles. This paper reviews the results obtained so far, including drug loading, biodistribution studies, and therapeutic efficiency. The pH-sensitive micelles appear to be promising candidates for photosensitizer delivery.
Carbomer (C) and procaine (P) were selected respectively as models of polyelectrolyte (PE) and basic drug (B) of low stability in aqueous solution. The purpose of this investigation was to test if a (C-P) aqueous system provides a microenvironment in which P is less exposed to hydroxyl ion catalyzed degradation, its main degradation pathway over a wide pH range. It was determined that in (C-P) a high fraction of P was present in the form of ion pairs [RCOO-PH+] with the carboxylate groups of C. The [RCOO-PH+] fraction was above 97% for compositions containing higher than 50 mol% of P. The chemical stability of C-P was assayed at two selected pHs (7.5 and 8.5) in comparison with conventional reference solutions (RS) without C. Procaine in (C-P) was 4.2 and 6.2 times more stable than in its respective RS at the two conditions assayed. The stabilizing factor was calculated as the ratio of the rate constants k(obs)(RS)/k(obs)(C-P).Since C-B systems exhibit negative electrokinetic potential that attracts positive ions such as (H+) and repels negative ones such as (OH(-)), the stabilizing effect would be associated with the higher acidity of (C-P) environment, in which PH+ molecules attached to the PE should also have lower kinetic energy than those in the bulk medium.