Bacterial cellulose as a potential meniscus

Bacterial cellulose as a potential meniscus

JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE SHORT COMMUNICATION J Tissue Eng Regen Med 2007; 1: 406–408. Published online in Wiley InterScience (w.interscience.wiley.com) DOI: 10.1002/term.51

Bacterial cellulose as a potential meniscus implant

1Biopolymer Technology, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden 2Molecular Biotechnology, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden 3Department of Orthopaedic and Regenerative Medicine, Sahlgrenska University Hospital, Gothenburg, Sweden

Abstract

Traumatic or degenerative meniscal lesions are a frequent problem. The meniscus cannot regenerate after resection. These lesions often progress and lead to osteoarthritis. Collagen meniscal implants have been used in clinical practice to regenerate meniscal tissue after partial meniscectomy. The mechanical properties of bacterial cellulose (BC) gel were compared with a collagen material and the pig meniscus. BC was grown statically in corn steep liquid medium, as described elsewhere. Pig meniscus was harvested from pigs. The collagen implant was packed in sterile conditions until use. The different materials were evaluated under tensile and compression load, using an Instron 5542 with a 500 N load cell. The feasibility for implantation was explored using a pig model. The Young’s modulus of bacterial cellulose was measured to be 1 MPa, 100 times less for the collagen material, 0.01 MPa in tensile load. The Young’s modulus of bacterial cellulose and meniscus are similar in magnitude under a compression load of 2 kPa and with five times better mechanical properties than the collagen material. At higher compression strain, however, the pig meniscus is clearly stronger. These differences are clearly due to a more ordered and arranged structure of the collagen fibrils in the meniscus. The combination of the facts that BC is inexpensive, can be produced in a meniscus shape, and promotes cell migration makes it an attractive material for consideration as a meniscus implant. Copyright 2007 John Wiley & Sons, Ltd.

Keywords bacterial cellulose; biomaterial; meniscus; biomechanics

1. Introduction

Traumatic or degenerative meniscal lesions are a frequent problem. Total and partial meniscectomy may elicit degenerative changes in the affected joint. These lesions often progress and lead to osteoarthritis. Allogeneic meniscal transplantation is performed in some centres to treat symptomatic middle-aged patients after extended or total mensicectomy. Collagen meniscal implants have been used in clinical practice to regenerate meniscal tissue after partial meniscectomy (Tienen et al., 2004). Reports

*Correspondence to: Paul Gatenholm, Biopolymer Technology, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-41296 Gothenburg, Sweden. E- mail: Paul.Gatenholm@chalmers.se after 6 years of follow-up have shown promising results (Zaffagnini et al., 2007). The aim of this study was to evaluate the feasibility of bacterial cellulose as a meniscal implant.

The mechanical properties of bacterial cellulose (BC) gel were compared with a collagen material and pig meniscus. BC was grown statically in corn steep liquid medium, as described elsewhere (AufderHeide 2004), giving a gel of 3–15 m in thickness. Pig meniscus was harvested from pigs (34 kg), kept in PBS buffer, quenched in liquid nitrogen and kept frozen until measurement, as reported by Sweigart and Athanasiou (2001). The collagen implant (Tissue Fleece; Baxter AG, Germany) was packed in sterile conditions until use. The different materials were evaluated under tensile and compression load, using an Instron 5542 with a 500 N load cell.

Copyright 2007 John Wiley & Sons, Ltd.

Bacterial cellulose as a potential meniscus implant 407

The crosshead speed was set to 0.25 m/s. The Young’s modulus was determined from the linear region of the stress–strain curve at very small deformation; in this case 0–4% compression strain and 0–15% tensile strain. Circular discs of each material were used for the compression test, bacterial cellulose with a diameter of 10 m and thickness of 15 m, and menisci and collagen material with a diameter of 7.95 m and thickness of 3 m. In tensile load, strips of each material were prepared, bacterial cellulose with a width of 18 m and thickness of 3 m and collagen with a width of 18 m and thickness of 4 m.

Bacterial cellulose was moulded into a half-moon shape with dimensions similar to those of a meniscus (Figure 1). The wedge character of the meniscus was created by introducing a silicone support in the middle of the fermentation vessel, which was successively lowered during production, tilting the cellulose network on the surface. The feasibility for implantation was explored using a pig model. Shortly after resection of the lateral meniscus, the cellulose implant was transplanted and secured with sutures (PDS 6.0; Ethicon) to the remaining capsular tissue. The stability after flexion and extension of the knee was evaluated subjectively.

The Young’s modulus of bacterial cellulose was measuredtobe1 MPa,100timesless forthecollagen material, 0.01 MPa in tensile load. This can be compared with the human meniscus, which has a radial elastic modulus of 3.74–16.21MPa (AufderHeide and Athanasiou, 2004). These differences are clearly due to a more ordered and arranged structure of the collagen fibrils in the meniscus. The microfibrils in bacterial cellulose are arranged randomly and are moulded in the collagen material into a porous material, as shown by the scanning electron microscopy (SEM) images in Figure 2. Fibre volume is smaller in bacterial cellulose (1%) compared to the collagen fibrils in the native meniscus (30%). This is another reasonable explanation for the difference in compression stress.

The Young’s modulus of bacterial cellulose and meniscus are similar in magnitude under a compression

Figure 1. Pig meniscus (left) and bacterial cellulose (right)

Figure 2. Compression stress–strain curve of pig meniscus (ž), bacterial cellulose ( ) and collagen ( ). The SEM images show the morphology of each material: (top) pig meniscus with ordered collagen fibrils (bar = 10 µm); middle, bacterial cellulose (bar = 1 µm) with cellulose microfibrils randomly distributed; bottom, collagen fabricated in porous fashion (bar = 100 µm). Original magnifications: ×10, ×10 0 and ×100, respectively load of 2 kPa. At higher compression strain, however, the pig meniscus is clearly stronger. The Young’s modulus of the collagen material is more than three times lower, 0.43 MPa (Table 1).

Bacterial cellulose has a Young’s modulus in compression load similar to that of pig meniscus and better mechanical properties than the collagen material. The combination of the facts that the material is inexpensive, can be produced in a meniscus shape, and promotes cell migration makes it an attractive material for consideration as a meniscus implant (Backdahl et al., 2006). We have seen in the surgical context that this implant demonstrated good implantation properties regarding handling and fixation. We aim to induce bone formation by introducing calcium phosphate to enhance the fixation to the bone at the anterior and posterior horn of the implant. Furthermore, could the fibre direction be manipulated in the radial direction in order to improve the compression strength. Finally, could the porosity in the outer third of the bacterial cellulose implant be modified.

Table 1. Young’s modulus and compression modulus of pig meniscus, bacterial cellulose and collagen (n = 3) at 4%, 10% and 20% compression

Material

Young’s modulus (kPa) at 0–4% strain

Compression modulus (kPa) at 10% strain

Compression modulus (kPa) at 20% strain

408 A. Bodin et al.

References

AufderHeide AC, Athanasiou KA. 2004; Mechanical stimulation toward tissue engineering of the knee meniscus. Ann Biomed Eng 32(8): 1161–1174.

Backdahl H, Helenius G, et al. 2006; Mechanical properties of bacterial cellulose and interactions with smooth muscle cells. Biomaterials 27(9): 2141–2149.

Matsuoka M, Tsuchida T, et al. 1996; A synthetic medium for bacterial cellulose production by Acetobacter xylinum subsp. sucrofermentans. Biosci Biotechnol Biochem 60(4): 575–579.

Sweigart MA, Athanasiou KA. 2001; Toward tissue engineering of the knee meniscus. Tissue Eng 7(2): 1–129.

Tienen TG, Verdonschot N, et al. 2004; Prosthetic replacement of the medial meniscus in cadaveric knees: does the prosthesis mimic the functional behavior of the native meniscus? Am J Sports Med 32(5): 1182–18.

Zaffagnini S, Giordano G, et al. 2007; Arthroscopic collagen meniscus implant results at 6–8 years follow-up. Knee Surg Sports Traumatol Arthrosc 15(2): 175–183.

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