Correction to: Tissue Eng Regen Med (2021) 18(6):1009–1020 https://doi.org/10.1007/s13770-021-00378-5

The original article contains errors in Abstract, Introduction, Materials and Methods, Results, Discussion, References, and Trial registration just above the References section. Especially, the citation number on the 8th line of the 3rd paragraph in the introduction section is incorrectly marked as 9. Because the reference to be citated was marked as No. 22, and the references should be numbered in the order of citation, we corrected reference 22 as 11 and reordered the reference numbers. Lastly, the legend of the supplementary figures is presented which was missing in the original version.

Abstract section

The paragraph of Results (word correction): Six weeks after repair, the PR and PNR groups showed less adipose cells, less CD68-stained cells, and more parallel tendon collagen fibers than the SR group.

Introduction section

The third paragraph (citation number correction): Several studies have sought to biologically enhance tendon-to-bone healing and reduce fatty degeneration, in efforts to lower the failure rate of rotator cuff repair [3, 6, 9, 10, 11].

The third paragraph (citation number correction): Healing was assessed both histologically and biologically after repair of chronic rotator cuff tears in a rabbit model [11].

The third paragraph (citation number correction): Conversely, some studies have reported that after arthroscopic rotator cuff repair, PRP treatment did not improve tendon healing or functional recovery [12–14].

The fourth paragraph (citation number correction): Similarly, polydeoxyribonucleotide (PDRN) is a tissue regeneration activator that is composed of a mixture of nucleotides and activates adenosine A2A receptors, stimulating vascular endothelial growth factor (VEGF)expression and the activity of fibroblasts [15, 16].

The fourth paragraph (word correction): The drug is obtained by a classified extraction process to purify the substance from nuclei and ensures a very high percentage of polydeoxyribonucleotides.

The fourth paragraph (citation number correction): It is likely that PDRN is cleaved by active cell membrane enzymes, providing a source of purine and pyrimidine deoxyribonucleosides and deoxyribonucleotides that can increase the proliferation and activity of cells in different tissues [17].

The fourth paragraph (citation number correction): Previous studies have shown that PDRN improves wound healing especially in diabetic rat and mouse models [9, 15, 16].

The fourth paragraph (citation number correction): There are several preclinical studies regarding rotator cuff tear and PDRN [18–20].

The fourth paragraph (citation number correction): They undergo enzymatic cleavage and progressively release both water molecules and smaller oligonucleotides that retain moisturizing and viscoelastic properties, thereby maintaining the effect over a long time period [21, 22].

Materials and Methods section

The second paragraph (citation number correction): For biomechanical testing, a priori power analysis revealed that a minimum of 8 rats per group was necessary to detect a significant difference in peak load to failure (mean difference: 10.0 N, standard deviation: 5.5 N) with a power of 0.8 and an alpha of 0.05, assuming a 25% drop-out rate [1, 3, 11].

The fifth paragraph (citation number correction): We graded each of these parameters semiquantitatively using 4 stages (present with < 25% proportion [grade 0], 25%–50% proportion [grade 1], 50%–75% proportion [grade 2], and > 75% proportion [grade 3]) [11].

Results section

The second paragraph (addition of supplemental data): The overall results of histological and IHC evaluation at 6 weeks were similar to those at 3 weeks with a greater improvement (Supplementary Fig. 1A–F, Supplementary Fig. 1 legend).

Discussion section

The first paragraph (word correction): Six weeks after repair, the PR and PNR groups showed less adipose cells, less CD68-stained cells, and more parallel tendon collagen fibers than the SR group.

The third paragraph (citation number correction): Various biological methods have been used to enhance tendon healing and reduce fatty degeneration, such as local administration of PRP, stem cells, and growth factors [3, 20, 31, 32].

The third paragraph (citation number correction): Chung et al. [11] showed that tendon-to-bone healing was enhanced after local administration of autologous PRP, as assessed both histologically and biomechanically in a rabbit model of chronic rotator cuff tears.

The third paragraph (citation number correction): On the other hand, several clinical studies have shown that PRP does not aid in rotator cuff healing [12–14].

The fourth paragraph (citation number correction): PDRN is a tissue regeneration activator that is composed of a mixture of nucleotides and activates adenosine receptors of fibroblasts to stimulate VEGF expression and fibroblast activity, in turn enhancing collagen fiber synthesis [9, 15, 16].

The fifth paragraph (citation number correction): Several studies have shown that PDRN and PN stimulate wound healing and tissue regeneration [9, 15, 16, 34, 35].

The fifth paragraph (citation number correction): Altavilla et al. [15]. used an immunostaining method to study the effect of PDRN on wound healing in a diabetic mouse model.

The fifth paragraph (citation number correction): In addition, Kwon et al. [18–20]. performed three animal studies using rabbit cuff tear model. They showed PDRN combined with UCB-MSC or microcurrent was effective.

The sixth paragraph (citation number correction): As PDRN and PN both stimulate growth factor production [9, 16, 35], such measurements would have been useful, and are required in future studies.

The sixth paragraph (citation number correction): Second, in humans, chronic rotator cuff tears develop slowly over a long period of time, and are influenced by various factors [17].

Just above the reference section (word correction): Design registration Rat muscle fixation device (KR Design Registration 30–0854878).

References section

The reference numbers were reordered as the below.

11. Chung SW, Song BW, Kim YH, Park KU, Oh JH. Effect of platelet-rich plasma and porcine dermal collagen graft augmentation for rotator cuff healing in a rabbit model. Am J Sports Med. 2013;41:2909–18.

12. Charousset C, Zaoui A, Bellaïche L, Piterman M. Does autologous leukocyte-platelet-rich plasma improve tendon healing in arthroscopic repair of large or massive rotator cuff tears? Arthroscopy. 2014;30:428–35.

13. Malavolta EA, Gracitelli ME, Ferreira Neto AA, Assunção JH, Bordalo-Rodrigues M, de Camargo OP. Platelet-rich plasma in rotator cuff repair: a prospective randomized study. Am J Sports Med. 2014;42:2446–54.

14. Wang A, McCann P, Colliver J, Koh E, Ackland T, Joss B, et al. Do postoperative platelet-rich plasma injections accelerate early tendon healing and functional recovery after arthroscopic supraspinatus repair? A randomized controlled trial. Am J Sports Med. 2015;43:1430–7.

15. Altavilla D, Squadrito F, Polito F, Irrera N, Calò M, Lo Cascio P, et al. Activation of adenosine A2A receptors restores the altered cell-cycle machinery during impaired wound healing in genetically diabetic mice. Surgery. 2011;149:253–61.

16. Galeano M, Bitto A, Altavilla D, Minutoli L, Polito F, Calò M, et al. Polydeoxyribonucleotide stimulates angiogenesis and wound healing in the genetically diabetic mouse. Wound Repair Regen. 2008;16:208–17.

17. Squadrito F, Bitto A, Altavilla D, Arcoraci V, De Caridi G, De Feo ME, et al. The effect of PDRN, an adenosine receptor A2A agonist, on the healing of chronic diabetic foot ulcers: results of a clinical trial. J Clin Endocrinol Metab. 2014;99:E746-53.

18. Kwon DR, Park GY, Lee SC. Treatment of full-thickness rotator cuff tendon tear using umbilical cord blood-derived mesenchymal stem cell and polydeoxyribonucleotides in a rabbit model. Stem Cells Int. 2018;2018:7146384.

19. Kwon DR, Park GY, Moon YS, Lee SC. Therapeutic effects of umbilical cord blood-derived mesenchymal stem cells combined with polydeoxyribonucleotides on full-thickness rotator cuff tendon tear in a rabbit model. Cell Transplant. 2018;27:1613–22.

20. Kwon DR, Moon YS. Synergistic regenerative effects of polydeoxyribonucleotide and microcurrent on full-thickness rotator cuff healing in a rabbit model. Ann Phys Rehabil Med. 2020;63:474–82.

21. Giarratana LS, Marelli BM, Crapanzano C, De Martinis SE, Gala L, Ferraro M, et al. A randomized double-blind clinical trial on the treatment of knee osteoarthritis: the efficacy of polynucleotides compared to standard hyaluronian viscosupplementation. Knee. 2014;21:661–8.

22. Vanelli R, Costa P, Rossi SM, Benazzo F. Efficacy of intra-articular polynucleotides in the treatment of knee osteoarthritis: a randomized, double-blind clinical trial. Knee Surg Sports Traumatol Arthrosc. 2010;18:901–7.

Supplementary Fig. 1 legend

The histological and immunohistochemical findings. 1–4: 3 weeks, 5–8: 6 weeks. A grading for adipocytes on H&E stain of M-T region (x200). Black arrows are adipocytes. PR and PNR groups show less adipocytes than SR groups. PNR group shows the lowest portion of adipocytes. B CD68-stained cells on M-T region (x400). Black arrows are CD68-stained cells. PR and PNR groups show less CD68-stained cells than SR group. PNR group shows the lowest number of CD68-stained cells. C CD168-stained cells on M-T region (x400). Black arrows are CD168-stained cells. At 3 weeks, PR groups shows the largest number of CD168-stained cells and SR shows the smallest one. At 6 weeks, three groups show similar number of CD168 stained cells. D Vascularity and Cellularity on H&E stain of M-T region (x200). Black arrows are vessels. Three groups show similar vascularity and cellularity. E Collagen fiber continuity and parallel orientation on Masson’s trichrome stain (x100) of T-B junction. PR and PNR group show more continuous and parallelly oriented collagen fiber that SR group. From 3 to 6 weeks, tendon regeneration progressed in three group, it is more marked in PR and PNR groups. F CSA on H&E stain of M-T region (x400). PR groups shows the largest CSA and SR groups the smallest one. From 3 to 6 weeks, CSA increased gradually in three groups. M-T: musculotendinous, T-B: tendon to bone, SR: Saline + Repair, PR: PDRN + Repair, PNR: PN + Repair, CSA: cross-sectional area of muscle fiber.