Mechanical characterisation of unidirectional and cross-directional multilayered urinary bladder matrix (UBM) scaffolds

Abstract

Multilayered biological scaffolds derived from mammalian extracellular matrix (ECM) have shown promising long-term clinical results when reconstructing damaged tissues and organs. Despite their established clinical applicability, experimental studies that describe the effects of alternate manufacturing protocols on an ECM's mechanical properties are lacking. In the present study the mechanical properties of multilayered ‘unidirectional’ porcine urinary bladder matrix (UBM) scaffolds were determined in favour of its longitudinal and circumferential axes. The scaffold's unidirectional mechanical properties were then compared with ‘cross-directional’ UBM scaffolds. The results showed significant variations when alternate manufacturing protocols for multilayered UBM were applied. Unidirectional longitudinal UBM remained the strongest biomaterial on a consistent basis. Its failure strength occurred at 4.79 ± 0.85 MPa compared to 3.36 ± 0.53 MPa for unidirectional circumferential and 2.91 ± 1.05 MPa for cross-directional UBM respectively (p < 0.0001). Distensibility was greatest in unidirectional circumferential UBM with failure extension occurring at 14.77 ± 1.66 mm. In comparison, failure extension occurred at 12.88 ± 0.94 mm and 13.04 ± 4.35 mm for unidirectional longitudinal and cross-directional UBM respectively (p = 0.0024). The present study demonstrates that predefined manufacturing protocols for UBM should be considered when reconstructing anatomical structures with specific mechanical requirements.

Introduction

Tissue-engineered biological scaffolds derived from mammalian extracellular matrix (ECM) have shown promising long-term clinical results when reconstructing damaged tissues and organs. Their potential for true clinical applicability is reflected by their gradual yet effective progression from animal studies into human clinical trials over the last 2 decades [1]. To date, ECMs have been successfully applied to cardiovascular, genitourinary, musculoskeletal, respiratory and gastrointestinal systems for reconstructive purposes in over 2 million human patients [2], [3].

Typically, ECMs are prepared from porcine organs as porcine mammalian models are easily sourced and possess similar physiological parameters to humans [4]. Initially, the porcine organ is manually harvested post mortem and subjected to thorough preparation techniques prior to surgical implantation. Urinary bladder matrix (UBM) is an ECM derived from the porcine bladder. Its preparation steps include manual manipulation of the harvested bladder tissue, chemical decellularisation, lyophilisation and sterilisation [5]. Although these processing steps are necessary for constructing a biocompatible tissue-engineered biomaterial, an overriding clinical concern is damage to the scaffold's mechanical properties and ultrastructure during the invasive preparation process [6], [7]. Specific collagenous arrangements are frequently disrupted when ECMs are exposed to chemical reagents leading to significant decreases in mechanical strength. Intuitively, reductions in the mechanical strength of UBM affect its durability, reliability and clinical applicability [8].

It is widely accepted that decreases in the mechanical properties of UBM are preventable by ‘plying’ sheets of single-ply UBM on top of one another to form ‘multilayered UBM’ with four-ply multilayered urinary bladder matrix demonstrating sufficient mechanical strength to support its use in hernia repairs [9], orthopaedic surgery [10] and in repairing defective bladder segments [11]. Intuitively, there are two potential plying combinations for four-ply UBM during its preparation process as illustrated in Fig. 1; ‘unidirectional’ and ‘cross-directional’. Although both plying combinations have been applied clinically, the effect of both preparation techniques on the ECM's mechanical properties has not previously been compared in preclinical settings. Therefore, the present study aimed to evaluate and compare the mechanical properties for multilayered unidirectional and cross-directional porcine urinary bladder matrix scaffolds.