The Evaluation of Lyophilized Polymer Matrices for Administering Recombinant Human Bone Morphogenetic Protein-2

Abstract

Novel unitary devices, prepared by lyophilization of viscous solutions of sodium carboxymethylcellulose (CMC) and methylcellulose (MC), were evaluated as sustained-release delivery systems for recombinant human bone morphogenetic protein-2 (rhBMP-2). In vitro characterization of the unitary devices, which contained rhBMP-2-loaded poly (d,l lactide-co-glycolide) (PLGA) bioerodible particles (BEPs), was conducted over a 2-month period. Determinations included buffer uptake, mass and molecular weight loss and rhBMP-2 release from the unitary devices. CMC devices imbibed approximately 16 times their weight of buffer, while with MC, equilibrium uptake was approximately 6 times the dry weight of the devices. Overall mass loss percentages were approximately 55 and 35%, respectively, for CMC and MC devices. rhBMP-2 release from the devices was essentially a triphasic process: an initial phase during which "free" protein (rhBMP-2 present on the surface and within the pores of the PLGA BEPs) was released, a lag period during which no release was discerned, and then release of "bound" rhBMP-2 (protein adsorbed to the BEPs). The release of bound protein correlated with the mass loss of the polymer which began after 3 weeks. Release from the unitary devices was lower than that from the BEPs alone, due to a retardation effect of the gelled CMC/MC polymers. In rabbits in which full-thickness cranial bone defects were created, the implants were well tolerated and induced significant new bone growth during an 8-week evaluation period. The CMC devices appear to have induced bone earlier (at 2 weeks), but this did not affect eventual 8-week results. CMC devices without rhBMP-2 appeared to provide some bone conduction, in contrast to the blank MC devices.

Effect of a freeze-dried CMC/PLGA microsphere matrix of rhBMP-2 on bone healing

“…Such studies have been elusive partly because of a lack of sterile implantable devices that were capable of controlled release. Lyophilized matrices of MC and CMC, containing PLGA microspheres loaded with rhBMP-2, have been suggested and partially tested as 1 such implant type [16][17][18][19][20][21][22][23][24][25][26]. That work was unable to show statistically significant increases in new bone growth because of the presence of rhBMP-2.…”

“…PLGA microsphere delivery systems for rhBMP-2 have been previously reported [16,[24][25][26]. In a study of various carriers for rhBMP-2 microspheres, Rodgers et al [26] found that methylcellulose elicited more fibrosis than did carboxymethylcellulose (CMC) and that CMC alone (ie, with no added rhBMP-2 microspheres) showed a mild promotion of bone growth.…”

“…Many systems have been developed to localize growth factors [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Several controlled-release formulations have been approved (eg, Leutinizing hormone releasing hormone) agonists, tetanus toxoid, human growth hormone [1][2][3]).…”

“…Availability via recombinant DNA technology, cloning, protein 2 expression, and purification science [5][6][7][8][9][10][11] has allowed intensive research efforts toward the use of rhBMP-2 in bone restoration and repair [12][13][14][15][16][17][18][19][20][21]. The protein's osteoinductive property of causing mesenchymal differentiation into chondrocytes, with subsequent calcification of the cartilaginous matrix, can be enhanced by prolonging its p resence at the site of healing [ 22].…”

Sustained‐release microcapsules of a bone formation stimulant, TAK‐778, for local injection into a fracture site

“…Furthermore, most water –soluble substances are easily released from the carriers 10. Indeed, 40% of BMP in the PLGA particles was released within 3 days after administration 11. Low‐molecular‐weight compounds can overcome these obstacles.…”